Miscibility and flexibility of poly(lactic acid) blends with octadecenylsuccinic anhydride Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-14 Trong-Ming Don, Ting-Shu Li, Wei-Chi Lai
Poly(lactic acid) (PLA) is the most used biodegradable polymer derived from renewable resources. However, PLA is a brittle plastic with low resistance to fracture. In this study, we tried to increase flexibility and hydrophobicity by melt-blending it with octadecenylsuccinic anhydride (ODSA) which was synthesized by reaction of octadecene and maleic anhydride. After mixing, thermal and mechanical properties of the PLA/ODSA blends (100/5, 100/10, 100/15) were measured. The results showed that at low contents of ODSA, the PLA was miscible with ODSA, and the PLA/ODSA blends had higher hydrophobicity than the neat PLA. The water contact angle of the PLA/ODSA (100/15) reached a value of 95.9°. Moreover, The addition of ODSA decreased the glass transition temperature and crystallization temperature, producing most α′ crystals during crystallization and therefore resulting in the observed exotherm in DSC curves owing to the α′-to-α crystal transformation. Most importantly, the flexibility was improved as the elongation at break increased from 3.1% for the PLA to 15.1% for the PLA/ODSA blend (100/10), in which stress-whitening was observed during tensile testing. The biodegradability of the PLA/ODSA blends was tested using proteinase K, and the results showed the addition of ODSA did not affect the enzymatic degradability of the PLA.
IR spectroscopic quantification of small molecule transport and desorption phenomena in polymers Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-13 Erik Linde, Mathew C. Celina
Bioresorbable pH- and temperature-responsive injectable hydrogels-incorporating electrosprayed particles for the sustained release of insulin Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-13 Dang Tri Nguyen, V.H. Giang Phan, Doo Sung Lee, Thavasyappan Thambi, Dai Phu Huynh
In situ-forming injectable hydrogels are attractive delivery vehicles not only for the controlled delivery of drugs and proteins but also for the controlled the delivery of nanometer sized particles. In this study, pH- and temperature-responsive pentablock copolymers were synthesized by the conjugation reaction between carboxylic groups of oligo (serine) and alcohol groups of temperature-responsive triblock copolymers, poly (ε-caprolactone)-b-poly (ethylene glycol)-b-poly (ε-caprolactone). Owing to their pH- and temperature-responsive property, the pentablock copolymers were found to be soluble at high pH, and transformed to viscoelastic gel at the physiological condition (pH 7.4, 37 °C). Furthermore, the free-flowing pentablock copolymer sols form a stable hydrogel depot on the back of Sprague-Dawley rats. The hydrogel depot was found to be degradable in a controlled manner and bioresorbable after one month. Insulin-incorporated nanosized chitosan particles were prepared via the electrospraying method and mixed with the pentablock copolymer solution to control the release of insulin. At high pH, the negatively charged pentablock copolymers and insulin-incorporated chitosan particles form an ionic complex through electrostatic interaction. Interestingly, in physiological conditions, the complex formed a viscoelastic gel and controlled the release of insulin in a spatiotemporal-controlled manner for over one month with remarkable inhibition of first-burst of insulin. These results demonstrated that modular design of injectable smart hydrogels with chitosan particles showing great prospect to control the delivery of insulin.
Temperature and LET effects on radiation-induced modifications in non-perfect polyethylenes Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-13 K. Furtak-Wrona, M. Cornaton, D. Durand, V. Dauvois, J.-L. Roujou, S. Esnouf, M. Ferry
Regarding the nuclear safety, the potential accumulation of explosive gases during storage, transport and final disposal of Intermediate Level Long Lived Wastes (IL-LLW) has to be well understood and precisely evaluated. In this paper, we have investigated the Linear Energy Transfer (LET) effect that takes into account the different emitters present in the packages, but also the temperature impact in transport safety cases. We have focused our study on polyethylene, as this polymer presents one of the highest hydrogen radiation chemical yield (G0(H2)), and because of the explosive and inflammable nature of this gas. Chemical defects included in the polymer in the form of carbonyl (C=O) and vinyl (C=C) groups were explored. Depending on the atmosphere of irradiation, they are the main defects formed in polyethylene under irradiation and they are known to be effective energy and radical scavengers. Characterization of the chemical structure of pristine materials has been done. Hydrogen radiation chemical yields were quantified after polymers irradiation. Additionally, the carbon monoxide release was measured for polyethylenes with C=O moieties. Whatever the type of double bonds present in the polymer and whatever the irradiation conditions, hydrogen emission decreases compared to neat materials. Double bonds are effective scavenging groups to which energy is transferred regardless the irradiation nature. Underlying phenomena are explained in this work.
Controlling the size of spherulite and the degradation of poly(butylene succinate-co-adipate) by solvent and gel preparation temperature Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-13 Hana Yamazaki, Saya Kamitabira, Tomoki Maeda, Atsushi Hotta
The size of spherulites observed in the poly(butylene succinate-co-adipate) (PBSA) gel was found to be effectively controlled by the careful selection of the types of solvent and the gel preparation temperature. Additionally, the degradation behavior of the PBSA dried-gels with different sizes of spherulites was studied. By using different solvents, such as toluene (TOL), o-dichlorobenzene (o-DCB), and cyclohexanone (CHN), the diameter of the spherulites could be changed from 16.7 μm to 186.2 μm, while the gel preparation temperature was kept constant at 28 °C. The gel preparation temperature was then changed from −50 °C to 28 °C using CHN, and it was found that the diameter of the spherulites changed from 25.2 μm to 186.2 μm. Regarding the degradation behavior, the PBSA dried-gel with relatively smaller spherulites (∼20 μm in diameter) exhibited higher weight loss of over 80% at the immersion time of 6 days, while the PBSA dried-gels with relatively larger spherulites (∼186 μm in diameter) presented lower weight loss of below 30% at the immersion time of 6 days. It was therefore concluded that the degradation rate became lower with the increase in the size of spherulites.
Sulfur fertilizer based on inverse vulcanization process with soybean oil Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-12 Stella F. Valle, Amanda S. Giroto, Rodrigo Klaic, Gelton G.F. Guimarães, Caue Ribeiro
Biobased 1,5-pentanediol derived aliphatic-aromatic copolyesters: Synthesis and thermo-mechanical properties of poly(pentylene succinate-co-terephthalate)s and poly(pentylene adipate-co-terephthalate)s Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-12 Jing Lu, Zhisong Li, Lizhong Zhou, Linbo Wu, Bo-Geng Li
1,5-Pentanediol (PeDO) is a biobased but less studied diol monomer for polyester synthesis. As one of a series of studies on PeDO-derived polyesters, two aliphatic-aromatic copolyesters, poly(pentylene succinate-co-terephthalate) (PPeST) and poly(pentylene adipate-co-terephthalate) (PPeAT), were synthesized through melt copolycondensation of biobased PeDO, SA (or AA) and TPA. The chemical structure was characterized by 1H NMR, and the thermo-mechanical properties were assessed by DSC, WAXD, TGA and tensile test. The 1H NMR results demonstrated random structure and controllable copolymer composition. PPeATs showed two-stage thermal decomposition as the PeA units were clearly less stable than the PeT units at high temperature. In comparison, PPeSTs exhibited better thermal stability which was improved with increasing PeT unit content. Due to the difference in thermal stability, high intrinsic viscosity (0.78–1.4 dL/g) was facilely reached in synthesizing PPeSTs with melt copolycondensation, but medium intrinsic viscosity (0.58–0.66 dL/g) for PPeATs. Both kinds of copolyesters showed isodimorphism behavior and composition-dependent weak crystallizability. The PeT-rich copolyesters like PPeST85 and PPeAT85 showed reasonably good tensile properties because of higher crystallizability and stronger chain interaction.
Degradation of full aromatic polyamide NF membrane by sulfuric acid and hydrogen halides: Change of the surface/permeability properties Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-10 Byung-Moon Jun, Hyung Kae Lee, You-In Park, Young-Nam Kwon
We investigated the effects of both sulfuric acid (pH 0 to 2) and hydrogen halides (pH 0) on the physical, chemical, and performance properties of full aromatic nanofiltration (NF) polyamide (PA) NE90 membrane. Surface characterizations of the degraded membranes were conducted by Scanning Electron Microscopy (SEM), Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), goniometer, and zeta potential analyzer. No noticeable changes were observed in the surface properties of the membrane exposed to sulfuric acid; however, the permeable characteristics were changed due to the distortion of hydrogen bonding from additionally generated proton bridge for O-protonation and the formation of tetrahedral structure for N-protonation. On the other hand, the membrane's physico-chemical properties were much affected by hydrogen halides compared with sulfuric acid. Amide peaks N-H bending at 1541 cm−1 and C=O stretching at 1663 cm−1 in ATR-FTIR were reduced because of the reaction of the PA with halogens produced by oxidation of hydrogen halides. Molecular halogen gases (Cl2, Br2, I2) generated in the reaction bottle were also analyzed by GC/MS during exposure of the membrane to various types of acids. The increment in halogenation on PA was in the order HCI, HBr, and HI, and it was the same as the order of temporary dipole moment from the effect of molecular size. Water flux after exposure to hydrogen halides was severely decreased due to broken hydrogen bonding by halogenation. Investigation of sulfuric acid and hydrogen halides on the change of the physico-chemical characteristics in the NE90 can be utilized when full aromatic NF membrane is applied to treat/recycle several industrial processes, which include sulfuric acid or hydrogen halides.
Temperature dependence of structural alteration by ultraviolet irradiation in acrylic-urethane coatings studied by positron annihilation spectroscopy and solvent swelling behavior Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-08 Takato Ishida, Ryoma Kitagaki, Shogo Yamane, Hideaki Hagihara
The structural alteration of acrylic-urethane coatings, induced by photo-aging, and its temperature dependence, was investigated using positron annihilation lifetime spectroscopy and solvent swelling experiments. The results revealed a slight structural alteration due to photo-aging at 20 °C. On the other hand, a significant structural alteration occurred due to photo-aging at 60 °C, which resulted in a decrease in the pore size and total pore volume. To study the mechanism of such morphological changes, infrared spectra were measured before and after aging the samples. The results revealed the breakage of the urethane crosslink points and the generation of various photo-products including peroxide species that can form hydrogen bonds. This indicates the foundation of new physical and chemical crosslinks (different from the initial urethane linkage). Based on the chemical modifications, probable mechanisms of the internal morphological changes are proposed. Moreover, the changes are mainly due to an enhancement in the chain-mobility, due to the destruction of the polymer network and an increase in the inter-chain interactions. The results of this study reveal that significant internal structural alterations can occur after sufficient damage to the initial network structure. The proposed explanation is reasonable in relation to the temperature dependence of photo-induced structural alterations, and with respect to the molecular mobility and reaction ratio of photo-oxidation.
Recycling of aramid fiber using subcritical and supercritical water Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-08 Idzumi Okajima, Hayato Okamoto, Takeshi Sako
Poly(p-phenylene terephthalamide) (Kevlar®) fibers, with good chemical and mechanical strengths, were hydrolyzed into their constituent p-phenylenediamine and terephthalic acid monomers using supercritical water, subcritical water, and subcritical water with sodium hydroxide. The two monomers recovered from the Kevlar® fibers were purified using simple extraction and precipitation methods, and the purity of each monomer exceeded 99%. Treatment with subcritical water and sodium hydroxide for 6 h completely decomposed the Kevlar® fibers, with yields of approximately 95% for each monomer obtained at 250 °C, 4 MPa, and an initial molar ratio of sodium hydroxide to the Kevlar® unit of five. On the other hand, treatment with subcritical and supercritical water resulted in lower decomposition efficiencies and monomer yields. In addition, the kinetics of Kevlar®-fiber hydrolysis was examined assuming a cylindrical-surface reaction model, and temporal changes in the decomposition efficiencies of Kevlar® fibers were found to be reproduced well using this model.
Synthesis and characterization of a phosphorous/nitrogen based sol-gel coating as a novel halogen- and formaldehyde-free flame retardant finishing for cotton fabric Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-07 Angela Castellano, Claudio Colleoni, Giuseppina Iacono, Alessio Mezzi, Maria Rosaria Plutino, Giulio Malucelli, Giuseppe Rosace
A novel formaldehyde- and halogen-free coating, containing phosphorus, nitrogen and silicon, was synthesized with a promising approach to enhance flame retardancy of cotton fabric. To this aim, a new sol-gel precursor, comprising in the same molecule P, N and Si, namely (3-Glycidyloxypropyl triethoxysilane modified N-(phosphonomethyl) iminodiacetic acid (PGPTES), was co-hydrolysed and co-condensated with tetraethylorthosilicate (TEOS), as silane linker, and used for producing a self-extinguishing cotton fabric coating. The structure of PGPTES was characterized by 1H/13C/31P nuclear magnetic resonance and the obtained coating was investigated by FT-Infrared Spectroscopy and Scanning Electron Microscopy. The thermal properties of the treated fabric were studied by Thermogravimetric Analyses and Cone Calorimetry Tests. The obtained results show that the synthetized coating is able to catalyse the dehydration and char formation of cellulose based polymer at a lower temperature, thanks to the thermal decomposition of phosphate giving rise to acidic intermediates, able to further react with cellulose-based fabric, hence improving the flame retardant properties of the latter.
Three-dimensional cross-linking structures in ceramifiable EVA composites for improving self-supporting property and ceramifiable properties at high temperature Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-06 Dong Zhao, Menglu Xia, Yucai Shen, Tingwei Wang
Ceramifiable EVA composite with three dimensional cross-linking structures was prepared by bis (tert-butylperoxy) diisopropyl benzene (BIPB) as cross-linking agent, and silicate glass frits (SGF) and ammonium polyphosphate (APP) were utilized as additives. By using FTIR, DSC and measurement of gel content, the formation of cross-linking structures was studied. Rheometer and TGA were used to characterize the rheological properties and thermal stability of the composite. The effect of cross-linking structures on the self-supporting property and the ceramifiable properties of the composite was investigated. The apparent porosity of the ceramic residues was examined. XRD and SEM were used for the phase composition and morphology of the ceramic residues analysis respectively. Results suggested that the cross-linking reaction occurred in the EVA matrix and the SGF and APP have no effect on the cross-linking reaction. The formation of cross-linking structures improved the rheological properties and thermal stability of the composite, resulting in the improvement on self-supporting and ceramifiable properties. Further, we demonstrated that cross-linking structures as “skeletal structures” could support its own weight before inorganic crystalline phases appeared, which provided a necessary prerequisite for its excellent self-supporting property in the range of 0–1000 °C. In addition, it has been proved that the apparent porosity was decreased and the compactness of ceramic residues was enhanced after the cross-linking structures were formed.
Microfibers of microporous carbon obtained from the pyrolysis of electrospun β-cyclodextrin/pyromellitic dianhydride nanosponges Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-05 Claudio Cecone, Marco Zanetti, Anastasia Anceschi, Fabrizio Caldera, Francesco Trotta, Pierangiola Bracco
Novel activated carbon materials are being constantly developed and applied in many research and industrial applications. The choice of the precursor represents a key step, to achieve satisfying resulting features in terms of surface development, structural features, carbon contents, and amount of ash. In this work, a novel carbon product has been obtained starting from an electrospun β-cyclodextrin/pyromellitic dianhydride linked nanosponge. After the pyrolysis, the polymeric mat resulted in carbon material still displaying fibrous morphology, characterized by a diameters distribution of 1.3 ± 0.5 μm. A peculiar granular microstructure was observed via FESEM, a 692 m2/g surface area and a 5–12 Å pore size distribution, with pore volume of 0.14 cm3/g, resulted via BET characterization, while −32.8 ± 0.7 mV resulted after ζ potential analysis. These results confirmed β-cyclodextrin/PMDA-linked electrospun nanosponges as a suitable precursor for a novel carbon material preparation.
Determination of limit values of 1H spin-spin relaxation time to assess lifetime of thermally aged acrylonitrile butadiene rubber Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-05 Kaori Numata, Hideto Kurokawa, Sokei Sekine, Yasumoto Nakazawa, Atsushi Asano
We propose a method to determine the limit value of 1H spin–spin relaxation time (T2) for assessing the lifetime of thermally aged acrylonitrile butadiene rubber (NBR) parts. So far, it has been difficult to determine the limit values of T2 without performing other experiments such as mechanical property measurements and air tightness tests. We exposed two types of NBR diaphragm sheets to air at 100 °C for up to 7540 h and 6000 h, respectively. After that, we tested their air-tightness and we measured T2 of the virgin and aged diaphragms. To evaluate the temperature dependence of T2, T2 measurements were performed at 20, 40, and 60 °C. Additionally, we observed the 13C Nuclear Magnetic Resonance (NMR) spectra, toluene swelling ratio, acetone soluble fraction, and glass transition temperature for only one type of the diaphragm sheets. The diaphragm aged for 7540 h had lost sealability, and all the results indicated that this was caused by the degradation of NBR. The 13C NMR spectra clearly revealed that the degradation of NBR proceeded in three stages: self-cross-linking reactions in the initial stage, concurrent reactions of cross-linking and molecular chain scission in the second stage, and an increased number of reactions of cross-linking and molecular chain scission in the final stage. The results of the T2 measurements showed that T2 is useful not only to evaluate the complicated degradation behavior quantitatively, but also to determine the different limit values of T2 itself corresponding to large and small safety margins. Finally, we demonstrated that the temperature dependence of T2 is an effective parameter for quantitatively predicting the ultimate lifetime at each aging temperature with no safety margin for various thermally aged NBR rubber sheets.
A novel bio-based flame retardant for polypropylene from phytic acid Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-05 Yu-Yang Gao, Cong Deng, Yuan-Yuan Du, Sheng-Chao Huang, Yu-Zhong Wang
Phytic acid mainly exists in seeds, roots and stems of plants, which has a potential value in flame-retarding polymers due to the high content of phosphorus. In this work, a novel bio-based phytic acid salt PHYPI was prepared through a salt formation reaction between phytic acid and piperazine. The structure of the bio-based PHYPI was verified using 1H NMR spectrascoppy. When PHYPI was used to fabricate flame-retardant polypropylene (PP), it showed high efficiency in combustion tests. The limiting oxygen index (LOI) value for PP containing 18.0 wt% PHYPI is 25.0%, showing a 38.9% increase compared to 18.0% for PP containing no additive. Moreover, it passed the UL-94 V-0 rating in the vertical burning test, superior to the no rating for pure PP. Obviously, the flame-retarding efficiency of PHYPI is higher than that of typical traditional intumescent flame retardant containing ammonium polyphosphate or pentaerythritol. Cone calorimeter test revealed that the heat release and smoke production of PP were efficiently restrained by the presence of PHYPI. The peak of heat release rate (PHRR), total heat release (THR), and the peak of smoke release rate (PSPR) for PP containing 20 wt% PHYPI were decreased by 65.6%, 13.5%, and 32.8%, respectively, compared to the same values for PP alone. Fourier transform infrared spectroscopy (FTIR) was used to investigate the changes which accompanied the thermal degradation of the polymer containing PHYPI. Changes in the infrared spectra for the polymer undergoing degradation indicate that structures containing C=C and P-N-C were formed as a consequence of the presence of PHYPI. These transformations enhanced char formation to provide condensed phase protective action. At the same time, non-combustion volatile gases such as water and carbon dioxide may be released to dilute the fuel load in the gas phase. All evidences illustrate that PHYPI is an effective flame retardant for PP.
Pyrolysis and combustion of polymer mixtures: Exploring additivity of the heat release rate Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-02 A. Yu Snegirev, M. Koraiem Handawy, V.V. Stepanov, V.A. Talalov
The microscale combustion calorimetry study of polymer mixture pyrolysis is presented. Binary mixtures of HDPE with a number of massively produced polymers (LDPE, PET, PS, PP, PC, PVC, PMMA), binary PC-PS and PMMA-PVC mixtures, and the ternary mixture composed of HDPE, PC, and PS are considered. The extent of interaction between the mixture components in pyrolysis is assessed by comparing the shapes of the measured temperature dependencies of the heat release rate in volatile oxidation with those for the curves obtained by the mass-weighted summation of the individual contributions of the pure polymers constituting the mixture. The strongest interaction is observed in HDPE-PET, HDPE-PS, HDPE-PS-PC, and in PMMA-PVC mixtures. A destabilizing interaction occurs in mixtures containing polyethylene and polystyrene, while the presence of polyvinylchloride has a stabilizing effect. In the binary mixtures, no clear correlation of the dependence of the conversion-averaged apparent activation energy (obtained by the iso-conversional method of Friedman) on the component proportion has been observed. In HDPE-PET mixture, in which the temperatures of peak pyrolysis rates are separated, the dependence of the apparent activation energy on conversion is interpreted in terms of the dependencies derived for pyrolysis of the individual components. Except for PMMA-PVC mixtures, in all binary mixtures considered in this work the heat of volatile combustion and the char yield were found to be additive quantities and varied almost linearly with the variation of the component mass fractions. Dissimilar to that, the PMMA-PVC mixtures produced a higher amount of charring residue and a lower heat of combustion of volatiles compared to the component-based predictions assuming additivity.
Addition of carbon nanotubes to electrospun polyacrylonitrile as a way to obtain carbon nanofibers with desired properties Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-01 Aleksandra Benko, Marek Nocuń, Marta Gajewska, Marta Błażewicz
Usage of CNTs as matrix modifiers during fabrication of CNFs from the electrospun polymer precursor is an interesting approach to obtain composite materials with a new set of properties. However, the progress in this field is hindered by the lack of consistency of the CNTs used in the studies and sometimes insufficient materials characterization. In this study, two types of CNTs were at first characterized to reveal their chemical composition and morphology (by TEM and XPS) and then used as matrix additives in the process of electrospinning. The outcome product was evaluated for morphology (SEM), chemical composition (XPS, FTIR), course of thermal transition (STA-FTIR) and level of structural arrangement (TEM combined with SAED) to answer the question how do CNTs interact with polymer matrix and how it impacts the process of thermal transition and properties of the as-received carbon nanofibers. Highly oxidized and short CNTs were found to increase the structural arrangement, catalyzing the thermal transition, while thin and long CNTs, with low amount of oxygen, entrap the nitrogen atoms, yielding nitrogen-doped CNFs that might be suggested as high-performance oxygen reduction reaction catalysts.
High-performance poly(benzoxazole/benzimidazole) bio-based plastics with ultra-low dielectric constant from 3-amino-4-hydroxybenzoic acid Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-02-01 Aniruddha Nag, Mohammad Asif Ali, Makoto Watanabe, Maninder Singh, Kittima Amornwachirabodee, Shunsuke Kato, Tetsu Mitsumata, Kenji Takada, Tatsuo Kaneko
High-performance bio-based plastics can make a major contribution to environmental sustainability. A series of high-performance poly(2,5-benzoxazole-co-2,5-benzimidazole)s (PBO-co-PBI) bio-based plastic films, were developed using the aromatic biomolecule 3-amino-4-hydroxybenzoic acid and the commercial product 3,4-diaminobenzoic acid. The partially bio-based PBO-co-PBI films exhibit higher thermal and mechanical performance than conventional bio-based polymers such as polyamide 11 or poly(lactic acid). The robust PBO-co-PBI films exhibit lower dielectric constants (εr) than conventional high-performance aromatic polymers, attaining the value comparable to those of polyethylene or polypropylene.
Intumescent ethylene-vinyl acetate copolymer: Reaction to fire and mechanistic aspects Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-31 Serge Bourbigot, Johan Sarazin, Fabienne Samyn, Maude Jimenez
Reductants for polyperoxides to accelerate degradation at elevated temperatures Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-29 Eriko Sato, Michihiro Yuri, Akikazu Matsumoto, Hideo Horibe
The alternating copolymer of a conjugated diene monomer and oxygen, i.e., polyperoxide, is a main-chain degradable polymer and undergoes radical chain degradation by heating. During the degradation process, oxygen-centered radicals are formed and thus side reactions such as hydrogen abstraction from the polymer by the oxygen-centered radicals and subsequent coupling, which prevent the degradation, sometimes take place. In this study, in order to promote the degradation of polyperoxides only at elevated temperatures while maintaining their stability at ambient temperature, appropriate organic reductants, which do not significantly react with the polyperoxides at 30 °C but react at 100 °C, were explored. N,N-Dimethylaniline, which is a conventional reductant for redox initiation systems, initiated the redox degradation of cyclopentadiene-based polyperoxides even at 30 °C due to the very high nucleophilicity. The introduction of an electron donating group at the para position, i.e., 4-dimethylaminoacetophenone, 4-dimethylaminobenzaldehyde, and 4-dimethylaminobenzonitrile, successfully maintained the stability of the polyperoxide at 30 °C and accelerated the degradation at 100 °C due to the reduced nucleophilicity. Similar results were obtained by using 1-acetyl-2-phenylhydrazine and 1-phenyl-3-pyrazolidone (PhP) as a reductant, and PhP resulted in the most significant acceleration effect at 100 °C. The activation energy for the overall degradation of the polyperoxide in the presence of PhP was much lower than that of the polyperoxide in the absence of a reductant. In the case of sorbic ester-based polyperoxides, their stabilities at 30 °C were not maintained in the presence of the reductants and the stability was improved by increasing the 2,5 structure regarding the diene moiety in the main-chain.
Study of various diameter and functionality of TEMPO-oxidized cellulose nanofibers on paraquat adsorptions Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-29 Chih-Feng Huang, Cheng-Wei Tu, Rong-Ho Lee, Cheng-Han Yang, Wei-Chen Hung, Kun-Yi Andrew Lin
Hydrolytic stability of aliphatic poly(carbonate-urea-urethane)s: Influence of hydrocarbon chain length in soft segment Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-28 Magdalena Mazurek-Budzyńska, Marc Behl, Muhammad Y. Razzaq, Ulrich Nöchel, Gabriel Rokicki, Andreas Lendlein
Poly(carbonate-urethane)s (PCUs) exhibit improved resistance to hydrolytic degradation and in vivo stress cracking compared to poly(ester-urethane)s and their degradation leads to lower inflammation of the surrounding tissues. Therefore, PCUs are promising implant materials and are considered for devices such as the artificial heart or spine implants. In this work, the hydrolytic stability of different poly(carbonate-urethane–urea)s (PCUUs) was studied under variation of the length of hydrocarbon chain (6, 9, 10 and 12 methylene units) between the carbonate linkages in the precursors. PCUUs were synthesized from isophorone diisocyanate and oligo(alkylene carbonate) diols using the moisture-cure method. The changes of sample weight, thermal and mechanical properties, morphology, as well as the degradation products after immersion in a buffer solution (PBS, pH = 7.4) for up to 10 weeks at 37 °C were monitored and analyzed. In addition, mechanical properties after 20 weeks (in PBS, 37 °C) were investigated. The gel content was determined based on swelling experiments in chloroform. Based on the DSC analysis, slight increases of melting transitions of PCUUs were observed, which were attributed to structure reorganization related to annealing at 37 °C rather than to the degradation of the PCUU. Tensile strength after 20 weeks of all investigated samples remained in the range of 29–39 MPa, whereas the elongation at break εm decreased only slightly and remained in the range between 670 and 800%. Based on the characterization of degradation products after up to 10 weeks of immersion it was assessed that oligomers are mainly consisting of hard segments containing urea linkages, which could be assigned to hindered-urea dissociation mechanism. The investigations confirmed good resistance of PCUUs to hydrolysis. Only minor changes in the crystallinity, as well as thermal and mechanical properties were observed and depended on hydrocarbon chain length in soft segment of PCUUs.
The influences of 3,4-dihydroxybenzaldehyde on the microstructure and stability of collagen fibrils Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-28 Lian Duan, Hongzhao Xiang, Xiao Yang, Lindong Liu, Zhenhua Tian, Huilin Tian, Jiao Li
3,4-dihydroxybenzaldehyde (DB), a derivative of catechol, were applied to improve the physicochemical properties of collagen fibrils, prepared via the self-assembly of collagen molecules. The aldehyde group of DB interacted with ε-amino group of collagen, and then the catechol group of DB was oxidized and self-polymerized, resulting in the formation of cross-links among collagen. The results of spectral experiment showed that the triple helix structure of collagen were integrated and the Tyr residues of collagen might react after cross-linking. Collagen fibrils became dark brown and the yellowness (Δb*) ascended from 0 to 3.24 when the [CHO]/[NH2] ratio rose from 0:1 to 40:1. Due to the effects of DB, the adjacent collagen fibrils agglomerated without particular orientation and the pore size of collagen fibril network decreased. The thermal stability of collagen fibrils had been improved about 15 °C while the elastic modulus obviously increased from 19 to 834 Pa after cross-linking. Moreover, the presence of DB also caused the dramatically enhancement in the enzymatic resistance of collagen fibrils while the biocompatibility of collagen fibrils was still desirable. These promising data suggested biomedical materials based on collagen fibrils with requisite properties can be obtained via adjusting the dose of DB.
Role of intermediate species in the formation of an energetic ion latent track in PADC: A review Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-28 Michel Fromm, Satoshi Kodaira, Tamon Kusumoto, Rémi Barillon, Tomoya Yamauchi
This review paper intends at identifying the early processes arising during the formation of a latent ion track in Poly Allyl Diglycol Carbonate (PADC). We briefly summarize the physical and chemical processes specific to the description of the interaction of ionizing radiation with matter. Then we gather published information in relation to PADC response regarding energy absorption and further transient species formation. Emphasis is given to the chemistry of radicals. Due to a lack of available data in relation with clearly identified unpaired electron carriers in PADC, we use data stemming from surrogate molecules. Based on such data we suggest mechanisms for the decomposition of PADC during the early times of ion track formation. The α-sites of ether functional groups in PADC appear undoubtedly as critical targets which during further decomposition behave as the most probable origin of Carbon dioxide release. All suggested mechanisms are multi-step processes. Combining different concepts and data in relation with the dynamics of transient species formed in the ion track of a polymer material, we propose that the effective track radius may be described as the radial extension of reactive species formed rather than the maximum distance at which δ-rays escape out of ion's trajectory. Lastly, generalization of the different processes collected allows two major pathways to be proposed for describing the fate of damaged ether moieties in PADC. This way, evidence is given for a higher sensitivity of ether functional groups compared to ester carbonate ones. The latter generally being destroyed as a consequence of prior damaging of the ether group.
Valencene as a naturally occurring sesquiterpene monomer for radical copolymerization with maleimide to induce concurrent 1:1 and 1:2 propagation Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-25 Hiroaki Hashimoto, Hisaaki Takeshima, Tomonari Nagai, Mineto Uchiyama, Kotaro Satoh, Masami Kamigaito
Valencene, a naturally occurring sesquiterpene that can be obtained from various citrus fruits, was copolymerized as an unconjugated 1,1-disubstituted bulky vinyl monomer by radical copolymerization with conjugated monomers possessing electron-withdrawing substituents, such as maleimides, acrylates, methacrylates, acrylonitrile, and methacrylonitrile, in toluene and PhC(CF3)2OH. The fluorinated alcohol increased the copolymerizability, as in the radical copolymerization of other unconjugated non-polar olefins with those electron-acceptor comonomers. In particular, the copolymerization of valencene and N-phenylmaleimide in PhC(CF3)2OH proceeded via concurrently occurring 1:1 and 1:2 propagation, in which the monomer reactivity ratio of maleimide and valencene to the maleimide radical with the penultimate valencene unit was close to 1 according to a kinetic analysis of the copolymerization based on the penultimate model. Therefore, the copolymerizability of valencene was higher than that of limonene, which is a similar unconjugated 1,1-disubstituted vinyl monomer with a smaller cyclohexenyl substituent that undergoes selective 1:2 radical copolymerization with maleimide derivatives under the same conditions. Reversible addition-fragmentation chain transfer RAFT copolymerization using a trithiocarbonate resulted in copolymers with controlled molecular weights and chain-end groups. The biobased copolymers of valencene and N-phenylmaleimide showed relatively high glass transition temperatures (Tg) of approximately 220–240 °C and relatively high thermal stability with 5% decomposition temperatures (Td5) of approximately 330–340 °C due to their rigid main-chain structures.
Synergistic effect of comonomers on the thermal oxidative stabilization of polyacrylonitrile copolymers for carbon materials Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-25 Dong Won Cho, Sung Chul Hong
Thermal oxidative stabilization (TOS) behaviors of polyacrylonitrile (PAN) (co)polymers with different comonomers, such as itaconic acid (IA), methacrylic acid (MA), methyl methacrylate (MMA), vinyl acetate (VA), and VA/IA mixture, were investigated through Fourier transform infrared spectroscopy analysis to quantitatively determine the role of the comonomers. Poly(acrylonitrile-co-MMA) exhibited slow progress of TOS, indicating general radical mediated TOS processes. Facilitated stabilization behaviors of poly(acrylonitrile-co-IA) (PAIA) and poly(acrylonitrile-co-MA) (PAMA) were observed, indicating additional ionic initiating activity of the comonomer carboxylic units. Poly(acrylonitrile-co-VA) exhibited a certain induction period, followed by an accelerated TOS in the later stage, indicating effective in situ generation of acetic acid through the degradation of vinyl acetate units during the TOS. Interestingly, the PAN-based terpolymer containing both VA and IA exhibited not only the most efficient but also the fastest progress of cyclization among the (co)polymers. The results demonstrated a synergistic combination of VA and IA in terms of TOS characteristics, likely stemming from the cascade initiation activity of the carboxylic acid groups from IA and VA. The results suggested the importance of the type and combination of comonomers as a crucial factor to control the TOS processes, providing technical information to design an optimum precursor for better carbon materials.
Thermal, mechanical and physical properties of chain extended recycled polyamide 6 via reactive extrusion: Effect of chain extender types Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-24 Selin Celebi Ozmen, Guralp Ozkoc, Ersin Serhatli
Chain extenders having different structures such as: alternating copolymer of ethylene and maleic anhydride (EMA), multi-functional epoxy-based oligomeric chain extender (EPO), polyester wax with reactive caprolactam groups (CW) and dimeric 2,4-toluene diisocyanate (DTDI), were melt compounded with recycled polyamide6 (rPA6) in various amounts via a twin screw extruder. DTDI, which is generally used for polyurethane applications, was used as a chain extender for rPA6 for the first time. In order to evaluate the effects of chain extender's structural differences on the chain extension behavior of the resulting materials, differential scanning calorimetry (DSC) measurements, heat deflection temperature (HDT) measurements, vicat softening temperature (VST) measurements, relative viscosity measurements and mechanical tests including tensile and impact tests were performed. The results showed that mechanical properties were improved by all chain extenders, however the highest improvement was achieved with EMA. The addition of EMA increased relative viscosity by 41%, HDT 12.4%, elongation at break by 6.3 times and impact strength by 26%. DTDI showed 22% increase in relative viscosity, 10% increase in HDT, 23% increase in impact strength and it also increased elongation at break by 6.1 times, making it a very good chain extender candidate for rPA6.
Ammonium polyphosphate modified with β-cyclodextrin crosslinking rigid polyurethane foam: Enhancing thermal stability and suppressing flame spread Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-24 Qimin Li, Jingyu Wang, Lamei Chen, Hui Shi, Jianwei Hao
Ammonium polyphosphate modified with β-Cyclodextrin (β-CD) as intumescent flame retardants was prepared and then incorporated in rigid polyurethane foam (RPUF) to improve thermal stability and flame retardancy. Scanning electron microscope (SEM), Transmission electron microscope (TEM), Fourier-transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) were used to characterize the modified APP (β-APP). The results showed that the surface of β-APP was covered of β-CD and the dispersibility of β-APP in substrate was improved apparently. In addition, the influence of β-APP on the cell structure, crosslink density, thermal stability and flame retardancy of RPUF were investigated. The results showed that β-APP was able to promote cellular distribution of RPUF into smaller and homogeneous. The results of dynamic thermomechanical analysis (DMA) and thermogravimetric analysis (TGA) indicated that the glass transition temperature (Tg) and crosslink density of β-APP/RPUF increased obviously, and the thermal stability of β-APP/RPUF was better than other FR-RPUFs. During combustion, flame spreading speed of 25wt%β-APP/RPUF reduced by 67.3% relative to pure RPUF and extinguish time decreased to 2.1s with the most complete inner char and the most dense outside char. In addtion, peak heat release rate (PHRR) of the sample decreased by 43.8% compared to pure RPUF. Therefore β-APP exhibited a prominent charring property and flame-retardant effect in condensed phase for RPUF.
Effects of thermo-oxidative aging on structure and low temperature impact performance of rotationally molded products Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-22 Lanlan Chen, Xiaojie Sun, Yueqing Ren, Wenbin Liang, Ke Wang
In this work, the effects of thermo-oxidative aging on the microstructure and impact properties of polyethylene during the rotational molding process were studied. FTIR and Raman analysis showed that the degradation of polyethylene was responsible for the low-temperature impact strength (LT-IS) and the brittle fracture behavior of samples those subjected to prolonged heating time during rotational molding process. The DSC and polarizing microscope analysis showed that the degradation process was delayed by the addition of antioxidants. Through use and optimization of antioxidants, the thermo-oxidative aging of polyethylene can be modulated, a broader processing window can be achieved, and the products may exhibit better mechanical properties with a wider heating time range.
Separation of waste polyester/cotton blended fabrics by phosphotungstic acid and preparation of terephthalic acid Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-22 Chen Ling, Shi Sheng, Wensheng Hou, Zhifeng Yan
In order to recycle the waste polyester/cotton blended fabrics (WBFs), an environmentally friendly process was designed for separating WBFs with phosphotungstic acid (H3PW12O40, HPW). Polyester and microcrystalline cellulose (MCC) were obtained after the process and the polyester was further degraded into terephthalic acid (TPA) by neutral hydrolysis. The effects of separation conditions were investigated, and the optimum conditions were determined as follows: HPW concentration of 3.47 mmol/L, a solid/liquid ratio of 1:20, reaction temperature of 140 °C, and reaction time of 6 h. Under the optimum conditions, the yields of polyester and MCC were 99.77% and 85.12%, respectively. HPW could be extracted and recycled easily with diethyl ether without affecting the yields of polyester and MCC. In addition, the separated polyester, MCC and prepared TPA were characterized. The results showed that the crystallinity of polyester decreased, and the cotton was hydrolyzed to MCC after the separation treatment. TPA was prepared with a high purity of 99.92%, and exhibited high crystallinity, favorable thermal stability, and small particle size.
Physical and chemical effects of biodiesel storage on high-density polyethylene: Evidence of co-oxidation Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-19 Maren Erdmann, Martin Böhning, Ute Niebergall
Collagen matrices containing poly(vinyl alcohol) microcapsules with retinyl palmitate – Structure, stability, mechanical and swelling properties Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-17 Justyna Kozlowska, Anna Kaczmarkiewicz
The aim of this study was to obtain and investigate new materials for cosmetic or dermatological applications. Microcapsules typically have a particle size from 1 to 1000 μm in diameter and they consist of an inner core containing an active agent, covered by a layer of polymer. Encapsulation technology have been used for improving the long-term stability of active substances and enhancing and prolonging the effectiveness of active ingredients. Microcapsules were obtained by coacervation/cross-linking method. The core was made of retinyl palmitate and was coated with poly(vinyl alcohol). In the next step, different quantities of microcapsules were incorporated into polymer matrices, which were prepared from collagen isolated from fish scales of Esox lucius in our laboratory. Polymer matrices were cross-linked with EDC/NHS (1-ethyl-3(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide) mixture. The Scanning Electron Microscopy confirmed the porous structure of the obtained materials with the presence of microcapsules. The highest values of Young's modulus were observed for the collagen matrices with incorporated larger amount of PVA microcapsules. All the matrices had high swelling properties. Based on the analysis, it was found that collagen matrices with incorporated retinyl palmitate-loaded PVA microcapsules are a promising material for the cosmetic or pharmaceutical industry.
Impact of hydrolytic degradation on mechanical properties of PET - Towards an understanding of microplastics formation Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-17 Mael Arhant, Maelenn Le Gall, Pierre-Yves Le Gac, Peter Davies
Ocean pollution by microplastics, i.e. small pieces of plastic of less than 5 mm, is one of the major concerns for the future of our planet. Secondary microplastics formation is due to fragmentation of macroplastic waste. This fragmentation can be attributed to environmental loadings such as waves, winds and tides, coupled with a change in mechanical properties of polymers induced by UV and seawater ageing. This study aims to characterize and understand changes in the mechanical behaviour of Polyethylene Terephthalate (PET) induced by hydrolysis, especially for high degradation levels. Thin films (200 microns) of PET were aged in water at temperatures from 110 °C to 80 °C for up to 150 days. Embrittlement occurs with chain scission during hydrolysis when molar mass of the polymer falls below 17 kg/mol. When the polymer is brittle, i.e. for high levels of degradation, the stress at break decreases linearly with the molar mass, and can be described by a simple mathematical expression.
EG-based coatings for flame retardance of shape stabilized phase change materials Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-17 Ling Xu, Xuan Liu, Zhenhua An, Rui Yang
Shape stabilized phase change material (SSPCM) is a promising thermal storage material used in energy-saving buildings, and much attention has been paid on its flame retardant property. In this paper, surface coating strategy was used to improve the flame retardance of SSPCMs (paraffin/polymer matrix/OMMT = 60/40/20). Three coatings, including acrylic resin/expandable graphite (EG), alkyd resin/EG and epoxy resin/EG, were surface coated on SSPCMs. Their flame retardant effects were evaluated by horizontal burning test, limiting oxygen index (LOI) determination, vertical burning test and cone calorimeter test. The results showed that all surface coated SSPCMs exhibited excellent flame retardance when the EG content exceeded a certain level. The horizontal burning times were increased largely; the UL-94 V0 level was achieved; and the LOI values were increased from 17.4 vol.% to over 30 vol.%. Moreover, the peak heat release rates (PHRRs) were decreased by 62–84%, and the heat release processes extended remarkably with reduced total smoke productions. The flame retardant mechanism of the surface coating strategy was investigated by in-situ Fourier transfer infrared spectrometry (FTIR) and thermogravimetric analysis (TGA). It was found that the coatings could hinder the escape of gaseous paraffin at low temperatures. Once exposed to fire or at high temperatures, the formed thick porous char layers helped to delay paraffin evaporation, trap generated combustibles and block the spread of oxygen and heat into the matrix.
Investigation of Poly(ethersulfone)/Polyvinylpyrrolidone ultrafiltration membrane degradation by contact with sodium hypochlorite through FTIR mapping and two-dimensional correlation spectroscopy Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-16 J. Chokki, G. Darracq, P. Poelt, J. Baron, H. Gallard, M. Joyeux, B. Teychené
It is well recognized that chlorine is responsible for aging of membrane materials. The goal of this study is to investigate the modifications of a commercial PES/PVP hollow fiber membrane exposed to hypochlorite solution at pH 7.5 by continuous filtration. Thanks to ATR-FTIR 2D Correlation Spectroscopy (2DCoS) analysis it was confirmed that PVP is oxidized into succinimide compound. 2DCoS analysis revealed the sequence order of PES/PVP membrane degradation: PVP oxidation is followed by the modifications of C-H cyclic structures and finally the formation of succinimide compounds. ATR-FTIR-microscopy mapping unveiled that PVP was mainly situated at the inner surface of hollow fibers exhibiting initially a 67 μm thickness layer. PVP layer disappearance was not homogenous versus the exposure dose suggesting the topochemical character of the PVP-chlorine reaction. Results demonstrate that advanced material characterization are key methodologies to understand membrane aging mechanisms.
Recycling a carbon fibre reinforced polymer with a supercritical acetone/water solvent mixture: Comprehensive analysis of reaction kinetics Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-16 Matthew J. Keith, Luis A. Román-Ramírez, Gary Leeke, Andrew Ingram
The decomposition of a carbon fibre reinforced epoxy resin with an acetone/water solvent supplied in the ratio of 80:20 v/v has been investigated using a non-stirred batch reactor. Temperatures and pressures in the range of 300–380 °C and 16–30 MPa were studied over a reaction time of up to 150 min using an initial reactor loading of 30 gresin Lsolvent−1. The minimum conditions necessary for effective fibre recovery were identified as 320 °C and 20 MPa. After processing for 120 min at this temperature and pressure, up to 95 wt.% of the resin was stripped from the fibre surface and the original weave architecture was retained. Increasing the reactor loading to 90 gresin Lsolvent−1 demonstrates no significant effect on the extent of resin decomposition. This, combined with imaging using X-ray computer tomography, suggests that the solvent is always in excess and that the mass transfer of the solvent into the composite and degradation products away from the surface is fast. A first order reaction rate equation based on the Arrhenius expression and a reaction-rate limited shrinking core model (SCM) have both been successfully fitted to the experimental data. From this, the parameters activation energy and frequency factor have been calculated to be 222.3 kJ mol−1 and 7.64 × 1017 min−1 respectively for the Arrhenius model and 164.3 kJ mol−1 and 1.29 × 1012 min−1 for the SCM. The results presented in this work demonstrate that either approach can be used to predict the resin decomposition to within ±5% which is similar to the margin of experimental error.
Novel controllable degradation behavior and biocompatibility of segmented poly–ε–caprolactone in rats Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-15 Jean-Dean Yang, Yi-Ting Shu, Hsi-Wei Jia
Bioresorbable polymers have multiple clinical applications; however, the reaction methods required for their synthesis generally require harsh reaction conditions and long reaction times. This study uses a new conceptual molecular control method that links poly–ε–caprolactone (PCL) diols of differing molar mass with an aliphatic diisocyanate as a coupling agent for polymerization to develop a new type of segmented polycaprolactone (SM-PCL) material. Relative to the polymerization of typical high molecular weight polyester materials, this polymerization process only requires ordinary pressure and low temperature to yield product with sufficiently high molecular weight. The results of in vitro cytotoxicity and in vivo implantation assays show that the newly synthesized SM-PCL exhibits excellent biocompatibility. In addition, in vivo degradation analyses demonstrate that the porous SM-A material was nearly completely degraded at 6 months after implantation in rat tissue (P < 0.01), whereas porous PCL homopolymer was only degraded to 53.25% of the initial molecular weight even after 12 months. The study indicated that the degradation rates of porous and solid thin film SM-PCL were higher than those of PCL homopolymer and that its degradation behavior could be controlled. Moreover, the material did not result in significant adverse pathological reactions and has good tissue compatibility. For clinical application, this material may therefore be suitable as a carrier for controlled drug release or as an artificial material for soft tissue repair.
Wetting/drying cyclic effects on mechanical and physicochemical properties of quasi-isotopic flax/epoxy composites Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-14 Fabrice Kossi Sodoke, Lotfi Toubal, Luc Laperrière
The aim of this work is to investigate the effects of wet/dry aging cycles on flax/epoxy composite properties for long-term structural applications. The mechanical performance of flax/epoxy exposed to wet/dry cycles during 104 days was evaluated. The physicochemical changes induced by wet/dry cycles were also studied. Unaged and cyclic aged samples were characterized by tensile test, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The tensile test results showed good aging performance of this composite. FTIR chemical investigation revealed the disappearance of the characteristic peaks of the cyanoethylation treatment at the fiber/matrix interface during cyclic aging. TGA data showed an improvement in thermal properties of the composite after the hydrolysis of cyanoethyl group, as well as the increase of the crystallinity index, as measured from XRD during cyclic wet/dry aging. This explains the limitation of mechanical degradation of this composite despite the severe wetting-drying cycles aging conditions. The results also show the positive effects of the cyanoethylation fiber treatment on the long-term durability of flax/epoxy composite.
About thermo-oxidative ageing at moderate temperature of conventionally vulcanized natural rubber Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-14 François Grasland, Laurent Chazeau, Jean-Marc Chenal, Regis schach
This article is dedicated to the understanding of the mechanisms involved in the evolution of the structure of a “conventionally” vulcanized rubber during thermo-oxidative (TO) aging. Based on swelling measurements, WAXS and DSC, a scenario of these mechanisms is proposed. Our results show that the crosslinking reactions are far from being complete at the end of the vulcanization process. During TO aging carried out at a moderate temperature 77 °C (350 K), the creation of long bridges first takes place via the consumption of residual sulfur; this mechanism is mainly responsible of the increase in the density of elastically active chains. The presence of residual antioxidants inhibits in the early stages of aging the chemical reactions involving oxygen. For longer aging time (here 7 days), these reactions can then occur and create "unidentified" bridges whose formation may also involves sulfur grafted onto the polymer chains. Finally, all these cross-linking reactions seem to enhance the heterogeneity of the spatial distribution of the crosslinks - already existing in the initial material - and to create highly crosslinked domains.
Characterizing the weathering induced degradation of Poly(ethylene-terephthalate) using PARAFAC modeling of fluorescence spectra Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-11 Devin A. Gordon, Zhonghao Zhan, Laura S. Bruckman
Poly(ethylene-terephthalate) (PET) film is widely used in photovoltaic module backsheets, for its dielectric breakdown strength, and in applications requiring high optical clarity. PET degrades under exposure to ultraviolet (UV) irradiance, heat, and moisture, which leads to loss of optical clarity and performance properties. To study the weathering driven degradation of PET films, three grades of PET, including unstabilized and stabilized grades, were exposed to three types of accelerated weathering exposure. Fluorescence excitation-emission matrix (EEM) spectra were collected after predetermined exposure intervals. Parallel factor analysis (PARAFAC) was applied to the resulting spectra to decompose the fluorescence data into individual fluorophore components and monitor their relative concentrations over time. EEM-PARAFAC was used to identify and distinguish between the formation of monohydroxy-terephthalate and dihydroxy-terephthalate units in PET over time under the UV-light bearing accelerated exposures. The relative concentrations of these fluorophores were found to increase, while the relative concentration of the PARAFAC component assigned to PET was found to generally decrease. ATR-FTIR was used to support findings from EEM-PARAFAC. Results were also used to assess the impact of additives (UV stabilizer and TiO2) on degradation.
Interaction of Poly(dimethylsiloxane) and octamethylcyclotetrasiloxane with aluminum oxides comprising different acid-base properties Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-09 Artur Kochanke, Christoph Üffing, Andreas Hartwig
Interactions between polymer matrices and inorganic mineral surfaces are especially relevant in polymer-filler composites and in adhesion science. Knowledge about underlying mechanisms at the interphase is a prerequisite for understanding functionality and aging. Therefore, interactions of poly(dimethylsiloxanes) (PDMS) and octamethylcyclotetrasiloxane (D4) with aluminum oxides comprising different acid-base properties were studied. For this purpose, thin layers of siloxanes were applied on aluminum oxides and analyzed by Raman spectroscopy and thermogravimetric analysis. It was observed that aluminum oxides are able to react with PDMS and D4 by heterolytic bond cleavage of SiO bonds, either by reactions with physisorbed water under catalysis of aluminum oxide or by direct reaction of the surface with siloxanes. Both reaction paths can yield SiOAl bonds and thus chemisorption which lead to strong interactions between siloxanes and aluminum oxides. However, the shown reaction paths concomitantly act as aging mechanisms leading to degradation of polymer.
Microbial composition and polymer hydrolytic activity of Japanese washed-rind cheeses Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-09 Yohko Tachibana, Kohei Kageyama, Miwa Suzuki, Hitomi Koshigumo, Hiroyuki Takeno, Yuya Tachibana, Ken-ichi Kasuya
Since the use of biodegradable polymers for food packaging is becoming popular, it is important to investigate the biodegradable-polymer-hydrolyzing potential of microorganisms in fermented foods. Here, we focused on 4 Japanese washed-rind cheeses. Metagenomic analyses revealed that microbiota in the 4 Japanese washed-rind cheeses was composed of bacteria classified into 515 operational taxonomic units (OTUs) and fungi classified into 74 OTUs. Remarkably, a considerable number of marine bacteria were identified in 3 of 4 cheeses. Further, we isolated a poly(3-hydroxybutyrate) (P(3HB))-degrading bacterium, designated as strain MC1, from one of the cheeses—Muchuri. The strain was a gram-negative, rod-shaped bacterium. It grew well and formed a large clear zone on P(3HB)-containing medium at a temperature range of 30–37 °C, while it did not degrade P(3HB) at 4 °C. The phenotypic properties and phylogenetic inference indicated that strain MC1 is related to Alcanivorax dieselolei B-5T, which is a marine inhabitant. Our study demonstrated that MC1 degrades P(3HB) and that components in cheese promote the degradation of P(3HB) while nutrient-rich conditions suppress it. This suggests that packaging material made of P(3HB) for cheeses could be used under low temperatures and nutrient-rich conditions.
Comics’ VOC-abulary: Study of the ageing of comic books in archival bags through VOCs profiling Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-09 Jacopo La Nasa, Marco Mattonai, Francesca Modugno, Ilaria Degano, Erika Ribechini
In the last years, the price of several collectible comic books reached the record value of millions of dollars. Since the value of collectible comic books is strictly related to their state of preservation, specialized rating agencies certificate their quality and condition, and for the same reason comics books are commonly encapsulated in sealed containers or bags for preservation and protection. Nonetheless, recent studies regarding micro-climate frames for the exhibition or storage of artworks as paintings suggest that the storage of any composite object made of organic materials in a sealed environment could lead to the presence of a significant concentration of volatile organic compounds (VOCs) in the enclosed micro-climate, that can be related to unexpected degradation pathways, or to an increase in the ageing rate of materials. In this study, we characterized the volatile organic compounds (VOCs) emitted by comic books stored in archival bags for the first time in the literature. In particular, we analyzed the VOCs emitted by comic books printed in the last six years by the same publisher. We applied solid phase micro extraction (SPME) to characterize the VOCs profile inside archival bags containing comic books by gas chromatography/mass spectrometry (GC/MS). The semi-quantitative data obtained on more than 60 individual VOCs were elaborated by principal component analysis (PCA) allowing us to highlight a variation in the profiles of the emissions of the series of comics books printed from 2012 to 2018 and stored in sealed archival bags immediately after the purchase. Select ion flow tube mass spectrometry (SIFT-MS) was also used to obtain quantitative results in real time, as an alternative to the SPME sampling step. This study represents the first reported application of SIFT-MS in heritage science. The study contributed to identify VOC profiles and molecular markers that can be used to study the emission of comic books in sealed bags, and can ultimately be correlated to the degradation processes of the materials used in their production.
Accelerated laboratory weathering of polypropylene composites filled with synthetic silicon-based compounds Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-07 Arkadiusz Niemczyk, Katarzyna Dziubek, Marek Grzymek, Krystyna Czaja
Non-functionalized and n-alkyl functionalized polyhedral oligomeric silsesquioxanes (POSS), siloxane-silsesquioxane resins and the sol-gel silicas were for the first time examined as possible UV-stabilizers and/or antioxidants in polypropylene (PP). The obtained composites were subjected to the accelerated laboratory weathering tests. The influence of the weathering conditions on the structure and properties of the PP materials was evaluated on the basis of the results from Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) studies. It was found that weathering resistance of the PP materials was strongly depended on the kind of the silicon-based filler used. Functionalized silsesquioxanes and siloxane-silsesquioxane resins improved weathering resistance of the PP materials, most probably because of its uniform dispersion in polymer, and thus, they could be considered as antioxidant additives. The changes in structural characteristics influenced thermal properties of the PP composites. It was revealed that the addition of the n-alkyl functionalized POSS and siloxane-silsesquioxane resins caused less significant changes in the melting and crystallization behavior of PP materials.
Self-healing of biobased furan polymers: Recovery of high mechanical strength by mild heating Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-08 Naoko Yoshie, Shoma Yoshida, Koji Matsuoka
Bio-based self-healing polymers exhibiting recovery of high mechanical strength by mild heating are developed. A series of bio-based network polymers was prepared from furan copolymers, poly(2,5-furandimethylene succinate-co-propylene succinate)s, through the reversible Diels-Alder reaction with bismaleimide. By changing the comonomer composition of the copolymer and the amount of bismaleimide added to the copolymer, the network polymers with various glass transition temperature, Tg, covering from −19 to 37 °C were obtained. Healing test of these network polymers at r.t. and 50 °C revealed a clear relationship between healing ability and Tg: healing required a healing temperature Th > Tg+15 °C. Furthermore, the network polymers with r.t < Tg < 50 °C expressed recovery of quite high tensile strength of 11–18 MPa at 50 °C. This result indicates that setting Tg slightly above r.t. and Th above Tg+15 °C shoud be a good strategy to obtain a good balance between mild healing conditions and recovery of high mechanical strength.
Synthesis and properties of curdlan branched and linear mixed ester derivatives Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-08 Wenjia Zhai, Tadahisa Iwata
Curdlan (CD) is a high-molecular-weight bacterial exopolysaccharide with linear β-(1 → 3)-glycosidic linkages. In a previous report, we showed that CD branched esters, namely, CD isobutyrate (CDiBu) and CD pivalate (CDPi), had very high melting temperatures (Tm = ca. 340 °C) that were similar to their thermal degradation temperatures (Td), which prevented their thermal processing [J Polym Res 2017; 25:181]. To solve this problem, a series of CD branched and linear mixed esters, CD isobutyrate heptanoate (CDiBuHep) and CD pivalate heptanoate (CDPiHep), were synthesized and characterized. No significant difference in Td was observed between CD homoesters and mixed esters. Tm values were observed for CDiBuHeps, but not for CDPiHeps, indicating that CDiBuHeps and CDPiHeps were crystalline and amorphous polymers, respectively. Tm values of CDiBuHeps were controlled from 280 °C to 72 °C by adjusting the degree of substitution ratios of branched and linear carboxylic acids. These Tm values were lower than the Td, suggesting that thermal processing was applicable to these mixed esters. All films of mixed esters were colorless and highly transparent, and their mechanical properties ranged from rigid to soft and rubbery states depending on the ratio of the linear ester group.
Cross-infection in thermo-oxidation of polymers Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-08 Xuan Liu, Rui Yang
In practical applications, a polymer is usually used together with others, where the aging behavior will become more complex than the polymer used individually. The interactions between adjacent polymers during aging are the cross-infection effects. In this study, the cross-infection between unstabilized polypropylene (PP) and seven typical polymers during thermo-oxidation was investigated by using chemiluminescence (CL) and Fourier transform infrared spectroscopy (FTIR). The changes of peak times by CL and functional groups by FTIR were chosen as the indicators. Thermo-oxidation of most of the seven polymers was accelerated by unstabilized PP, and different polymers had different susceptibility. In return, the acceleration of the typical polymers on unstabilized PP could also be observed. Cross-infection was thus demonstrated a common phenomenon in thermo-oxidation of various kinds of polymers. Inappropriate polymer combinations used together might cause mutual accelerated deterioration. These results were of great significance to industrial applications.
Promoting cell growth on porous PLA microspheres through simple degradation methods Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-04 Xudong Shi, Liguo Cui, Hai Sun, Ni Jiang, Liping Heng, Xiuli Zhuang, Zhihua Gan, Xuesi Chen
Poly(lactic acid) (PLA) microspheres are widely used in the field of tissue engineering. However, cell adhesion and proliferation on PLA microspheres is limited due to the lack of hydrophilicity and cell recognition sites on microspheres surface. Current methods used to modify PLA microspheres are either complicated or expensive. Aminolysis and hydrolysis are two simple and economical degradation methods. However, up to now, there are few studies using aminolysis or hydrolysis to directly modify PLA microspheres and alter the cell growth behaviour on microspheres. In this study, aminolysis and hydrolysis were used to modify the surface of porous PLA microspheres. After the surface modification, PLA microspheres showed a finely porous structure. Cell culture experiments showed that the modification successfully made the surface of porous PLA microspheres more favourable for cell binding and growth. The increases of porosity, polar groups, hydrophilicity and roughness on microspheres surface were good to cell attachment and proliferation. This study shows that the aminolysis and hydrolysis are simple and effective methods to modify porous PLA microspheres for promoting cell grow on them.
Synthesis and characterization of two new biobased poly(pentylene 2,5-furandicarboxylate-co-caprolactone) and poly(hexamethylene 2,5-furandicarboxylate-co-caprolactone) copolyesters with enhanced enzymatic hydrolysis properties Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-04 Nejib Kasmi, Mohamed Wahbi, Lazaros Papadopoulos, Zoi Terzopoulou, Nathanaël Guigo, Nicolas Sbirrazzuoli, George Z. Papageorgiou, Dimitrios N. Bikiaris
Herein, two fully renewable copolyester series, namely poly(pentylene 2,5-furandicarboxylate-co-caprolactone) (PPeCFs) and poly(hexamethylene 2,5-furandicarboxylate-co-caprolactone) (PHeCFs) have been successfully synthesized combined ε-caprolactone (CL) with poly(pentylene 2,5-furandicarboxylate) (PPeF) and poly(hexamethylene 2,5-furan dicarboxylate) (PHeF) with different molar ratios. These materials, with a CL content ranging from 10 to 50 mol%, were synthesized for first time using stannous octoate as catalyst through ring opening polymerization (ROP). Their chemical structures and molar composition were evaluated by 1H NMR, 13C NMR and FTIR spectroscopies, while their thermal properties were investigated in detail using Fast Scanning Calorimetry (FSC), Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA). The obtained results in combination with Wide-Angle-X-ray diffractometry (WAXD) showed that copolymerization of CL with PHeF and PPeF led to semi-crystalline and partially amorphous copolyesters respectively, providing the basis for significant thermal properties enhancement with respect to polycaprolactone (PCL) homopolymer, and therefore a much wider range of melting points (Tm) and glass transition temperatures (Tg) was obtained. TGA of the new copolymers showed excellent thermal stability, exceeding 310 °C and 360 °C for PHeCFs and PPeCFs respectively, while their decomposition mechanism was evaluated by pyrolysis-gas chromatography-mass spectroscopy analysis (Py-GC/MS). Almost all copolyesters and mainly these with 40 and 50 mol% of CL content showed enhanced enzymatic hydrolysis.
PLGA–PEG terpolymers as a carriers of bioactive agents, influence of PEG blocks content on degradation and release of herbicides into soil Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-05 Piotr Rychter, Kamila Lewicka, Małgorzata Pastusiak, Marian Domański, Piotr Dobrzyński
Nowadays, researchers in the field of agrochemicals are trying to find effective methods to limit the excessive usage of pesticides and protect the environment. One of the most popular and promising techniques is the immobilization of pesticides using environment-friendly polymers. In the conducted research, it was demonstrated that the family of lactide/glycolide copolymers are unsuitable for this purpose due to very slow degradation in the soil. We examined influence of relatively small content of PEG blocks in newly synthesized poly(L-lactide-co-glycolide)-poly(ethylene glycol)–poly(L-lactide-co-glycolide) (PLGA–PEG–PLGA) on the degradation in soil, in activated sludge and usefulness of this terpolymers as a biodegraded carrier for the controlled release of two commonly used herbicides (Metazachlor and Pendimethalin). Presence of even small amount of PEG block in the terpolymer chain increases slightly the hydrophilicity of the polymeric chain, thereby increasing its susceptibility to hydrolytic and unexpectedly strongly to enzymatic degradation in soil environment. The amorphism of used as a carriers PLGA-PEG-PLGA terpolymers and the lack of the phenomenon of increasing the degree of crystallinity during degradation allow to achieve uniform progress of degradation, and thus is obtained a relatively constantly release of tested herbicides. In this way, it is possible to determine the optimal profile of degradation of polymer in soil and proper rate of diffusion and leaching of active agents which allows the release of herbicides in optimal and effective doses within 3–4 months of its application.
An investigation of the thermal and (bio)degradability of PBS copolyesters based on isosorbide Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2019-01-02 Jiefei Qi, Jing Wu, Jingying Chen, Huaping Wang
As an essential biodegradable polyester species, poly(butylene succinate) (PBS) is restricted for wider applications due to its low thermal/mechanical properties and unsatisfactory (bio)degradability. Current practice of introducing either stiff or flexible building blocks into PBS main chains remains challenging to achieve a synergistic enhancement of the thermal and (bio)degradability of this material. We herewith report a series of PBS copolyesters based on the carbohydrate-derived isosorbide (1,4:3,6-dianhydro-D-glucidol, IS) (PBIS) by utilizing its unique intrinsic characters of being rigid and hydrophilic. The target copolyesters were constructed with a broad scope of IS content (0–100 mol%) and with random microstructures. The Mn values and the intrinsic viscosities of these polyesters are in the scopes of 7300–38,700 g mol−1 and 0.33–0.82 dL g−1, respectively. The results shown in this work clearly demonstrated that the presence of IS enhances the Tg values almost linearly and simultaneously promotes (neutral, acidic) hydrolytic and enzymatic degradations (with porcine pancreas) of the copolyesters. PBIS copolyester containing 20 mol% IS displays comparable hydrolytic and enzymatic degradation rates with those of PBSA (20 mol% adipic acid), but a substantially 23 °C higher Tg value. Detailed characterization of the molecular structures, micro-sequential structures, molecular weights and polydipersities, thermal properties, hydrophilicities and (bio)degradability are provided. The (bio)degradation and degradation mechanism study of these copolyesters are reported for the first time.
The stability and degradation of PECVD fluoropolymer nanofilms Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-29 James Bowen, David Cheneler
Fluoropolymer films are frequently used in microfabrication and for producing hydrophobic and low-k dielectric layers in various applications. As the reliability of functional coatings is becoming a more pressing issue in industry, it is necessary to determine the physical stability and degradation properties of this important class of films. To this end, a study has been undertaken to ascertain the aging characteristics of fluoropolymer films under various environmental conditions that such a film may experience during its use. In particular, fluorocarbon films formed by plasma-enhanced chemical vapour deposition (PECVD) using octafluorocyclobutane, or c-C4F8, as a precursor gas have been exposed to abrasive wear, elevated temperatures, ultraviolet radiation, as well as oxygen plasma and SF6 plasma, the latter being commonly used in conjunction with these films in ion etching processes. The results show that sub-micron thick fluoropolymer films exhibit a significant amount of elastic recovery during nanoscratch tests, minimising the impact of wear. The films exhibit stability when exposed to 365 nm UV light in air, but not 254 nm light in air, which generated significant decreases in thickness. Exposure to temperatures up to 175 °C did not generate loss of material, whereas temperatures higher than 175 °C did. Etching rates upon exposure to oxygen and SF6 plasmas were also measured.
Energy migration effect on the formation mechanism of different unsaturations in ethylene/styrene random copolymers Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-23 M. Ferry, J.M. Ramillon, T. Been, P.J. Lutz, Y. Ngono-Ravache, E. Balanzat
To evaluate the influence of specific parameters, i.e. energy sink concentration and excitons and/or radical migration, on the mechanisms underlying the formation of double bonds in aliphatic polymers, materials with energy sinks in the chain were synthesized. By following the radiation-induced modifications in ethylene/styrene random copolymers, as a function of the styrene content and of the irradiation temperature, we were able to understand the formation mechanisms of trans-vinylenes, trans-trans-dienes, allyl radicals and vinyls. The irradiation temperature allows the discrimination between energy transfers (at 11 K and at room temperature, RT) and of radical migration (at RT). Irradiations were performed using swift heavy ions, and we could show that track overlapping has also an influence on the studied chemical group concentrations. For instance, trans-vinylenes are influenced by excitation transfer and radical migration: their formation decreases in presence of styrene aromatic rings, whatever the dose range and the irradiation temperature. On the opposite, vinyls are formed only at high ionizing density and are not influenced by excitation transfer; however, their concentration is influenced by radical migration.
Oxidative and non-oxidative degradation of a TDI-based polyurethane foam: Volatile product and condensed phase characterisation by FTIR and solid state 13C NMR spectroscopy Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-24 D. Allan, J. Daly, J.J. Liggat
The oxidative and non-oxidative degradation behaviour of a flexible polyurethane foam, synthesised from toluene diisocyanate and a polyether polyol, is reported. Both toluene diisocyanate and diaminotoluene were identified as major products under non-oxidative conditions, which indicates that the urethane linkages are degrading by two competing degradation mechanisms. Degradation of the urethane linkage by a depolymerisation reaction to yield toluene diisocyanate and polyol is proposed to occur initially. In addition, the atmospheric pressure conditions favour the degradation of the urethane linkages via a six-membered ring transition state reaction to form diaminotoluene, carbon dioxide and alkene terminated polyol chains. Solid-state 13C NMR spectroscopy and elemental analysis of the residues indicates that at temperatures above 300 °C ring fusion of the aromatic components within the foam occurs, and this leads to a nitrogen-containing carbonaceous char which has a complex aromatic structure. It is proposed that under the confined conditions of the degradation the aromatic nitrogen-containing species, such as toluene diisocyanate and diaminotoluene, undergo secondary reactions and ring fusion to yield a complex char structure. Under oxidative conditions, degradation, including ring fusion, occurs at a lower temperature than under non-oxidative conditions. Neither toluene diisocyanate nor diaminotoluene were observed as major degradation products. The polyol is observed to undergo thermo-oxidative degradation at much lower temperatures than purely thermal degradation. As a consequence, the depolymerisation reaction via the six-membered ring transition state is limited in extent and diaminotoluene is not evolved. The absence of toluene diisocyanate is proposed to be a result of this species undergoing oxidative degradation reactions which lead to it being incorporated into the char.
Enhanced PET processing with organophosphorus additive: Flame retardant products with added-value for recycling Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-24 Ali Gooneie, Pietro Simonetti, Khalifah A. Salmeia, Sabyasachi Gaan, Rudolf Hufenus, Manfred P. Heuberger
At elevated temperatures, polyethylene terephthalate (PET) is known to undergo a cascade of interconnected chemical reactions, in particular oxidative crosslinking, which can lead to severe limitations in processability, product properties, and recyclability. To control such undesired reactions, a newly synthesized phosphorus-based additive with promising flame retardant properties (T. Stelzig et al. Dopo-Based Hybrid Flame Retardants. EP2921498 (A1), 2015), by the chemical name 6-((1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octan-4-yl)methoxy)dibenzo[c,e][1,2]oxaphosphinine 6-oxide (DOPO-PEPA, or simply DP), was added to PET in different concentrations. To assess the miscibility of DP and PET at the nanoscale, a multiscale simulation scheme was developed by combining molecular dynamics and dissipative particle dynamics. DP showed a prominent inter-chain lubrication effect in PET in extrusion experiments. To replicate the heating cycles during repeated recycling, the thermal stability of PET melts was assessed on extended timescales using rheological measurements. Time-resolved frequency sweep experiments were conducted with or without the novel DP additive, under air and nitrogen atmospheres. By combining various chemical analysis techniques, a chemical stabilizing mechanism could be proposed that describes how the DP molecule intervenes with the degenerative chemical reactions of PET chains in the melt processing phase. The proposed mechanism outlines trace-release from DP involving the formation of phosphorus radicals including DOPO•, PEPA•, and PO•. Such radicals scavenge the oxygen radicals from air and can thus protect the linearity of PET chains. The results underline the synergistic effects of DP on the processing of high performance PET. Together with flame retardancy of the original product, the environmental-friendly DP chemically-protects and lubricates PET during subsequent recycling of the waste.
Specific oligomer recovery behavior from cured unsaturated polyester by superheated steam degradation Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-24 Chi Hoong Chan, Minato Wakisaka, Haruo Nishida
To examine the specific oligomer recovery behavior from cured unsaturated polyester resin (cUPR), super-heated steam (SHS) was employed as a reactant. The cUPR was treated by SHS in a temperature range of 300–350 °C and solubilized, resulting in recovery of solvent extracted residues (SE-SDRs). From size-exclusion chromatography analysis, an interesting finding was that the molecular weight (MW) value of SE-SDR, increased gradually with degradation time. This specific recovery behavior was analyzed by FT-IR and 1H NMR spectroscopies. Based on the analytical results, a proposed SHS degradation mechanism was that first orthophthalate and glycol ester groups were degraded and removed as short length fragments, after which cleavage of styrene unit crosslinkers induced collapse of the 3-D network structure with the resulting solubilizing cUPR as SE-SDR. This mechanism can explain the specific oligomer recovery behavior whereby an increase in MW of SE-SDR occurred with SHS-degradation time. Obtained styrene-fumarate copolymer having Mn 2550 and Mw 9480 was recovered in a maximum 57 wt% yield after SHS treatment at 325 °C for 180 min.
Toughness enhancement of poly(lactic acid) through hybridisation with epoxide-functionalised silane via reactive extrusion Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-22 Jae Choon Lee, Myeon-Cheon Choi, Dong-Hee Choi, Chang-Sik Ha
Poly(lactic acid) (PLA) was hybridised with epoxide-functionalised silane (GTMS) through reactive extrusion. The GTMS was grafted successfully to PLA via a ring-opening reaction with the nucleophilic end groups of PLA. For hybridisation, PLA was extruded with various amounts of GTMS between 0 and 2.0 ph at 200 °C. The PLA hybrids were characterised by Fourier transform infrared spectroscopy and scanning electron microscopy. Their properties were examined by tensile testing, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and rheological characterisation. The glass transition temperature of the hybrids decreased to 52.7 °C compared to that of PLA (60.1 °C). The toughness was enhanced significantly by approximately 380% with only a 0.5 phr loading of GTMS. The hydrolytic degradation was also delayed by the hybridised GTMS in the PLA matrix. In conclusion, hybridisation by GTMS influenced the thermal, mechanical and degradable properties of the PLA hybrids substantially.
Thermal behaviour and fungi resistance of composites based on wood and natural and synthetic epoxy resins cured with maleopimaric acid Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-21 Liliana Rosu, Fanica Mustata, Cristian–Dragos Varganici, Dan Rosu, Teodora Rusu, Irina Rosca
Wood/epoxy resin composites based on diglycidyl ether of bisphenol A (DGEBA)/epoxidized oil (EO)/Diels–Alder adducts of resin acids with maleic anhydride (RAMA) in acetone (80%) were obtained by impregnation. Epoxidation was carried out in the presence of hydrogen peroxide (H2O2), acetic acid (AAc), sulfuric acid (H2SO4) as catalyst and cyclohexane (CHx) as solvent at a molar ratio of 0.5/1.5/1 (AAc/hydrogen peroxide/ethylene unsaturation). The kinetic parameters (activation energy and pre–exponential factor) of the DGEBA/EO/RAMA curing reaction and thermal characterization of the crosslinked compounds and wood epoxy composites (WECs) were obtained using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Based on the chemical structure of the evolved gases resulted during thermal decomposition of the crosslinked polymers and WECs, identified with FT–IR, a probable mechanism of thermal degradation was proposed. Resistance to three fungi was also tested.
A study on the stereochemistry of direct conversion of polyamides to hydroxyesters using monomeric secondary chiral amines as a model compound Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-19 Akio Kamimura, Kosuke Ikeda, Yugo Akinari, Hiroshi Matsumoto, Kouji Kaiso
Stereochemistry of direct conversion of polyamides to hydroxyesters was investigated using model compounds. Optically active secondary-alkyl amines underwent the conversion to corresponding secondary alcohols in moderate yields by treatment with supercritical methanol in the presence of glycolic acid. The reaction progressed through almost completely stereochemical inversion to give secondary alcohols in high yields. Thus, the substitution reaction of the amino group to hydroxyl group progresses through SN2 type transition state accompanying with stereoinversion.
Efficient enzymatic degradation of poly (ɛ-caprolactone) by an engineered bifunctional lipase-cutinase Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-12-17 Min Liu, Tianrui Zhang, Liangkun Long, Rui Zhang, Shaojun Ding
Lipases and cutinases belong to esterase family and can be used as biocatalysts for poly (ɛ-caprolactone) (PCL) degradation and recycling. A number of synthetic fusion enzymes with two or more catalytic domains were reported to be superior to the parental enzymes or their mixture for many biotechnological applications but rarely for the polyester biodegradation. To develop a more efficient biocatalyst for poly (ɛ-caprolactone) (PCL) degradation and recycling, a bifunctional lipase-cutinase (Lip-Cut) constructed by end-to-end fusion was successfully overexpressed in Pichia pastoris with 0.9% of methanol induction at pH 6.0 and temperature 27 °C. Lip-Cut displayed more efficient poly (ɛ-caprolactone) degradation capability, and the weight loss of PCL film by Lip-Cut at 6 h was 13.3, 11.8 and 5.7 times higher than that by Lip, Cut and Lip/Cut mixture, respectively. GC-MS analysis of the degraded products of PCL revealed that the mainly degraded product was 6-hydroxyhexanoic acid and small ratio of ɛ-caprolactone. Our results demonstrated that the proper construction of bifunctional lipase-cutinase could enhance the synergistic action of two moieties due to the complementary properties of both enzymes in substrate specificity and hydrolysis pattern. The method provided an effective approach to engineer more efficient biocatalyst for bio-application in degradation and recycling of PCL.
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