A new insight into morphological, thermal, and mechanical properties of melt-processed polylactide/poly(εε-caprolactone) blends Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-25 Orebotse Joseph Botlhoko, James Ramontja, Suprakas Sinha Ray
Low molecular weight hindered amine light stabilizers (HALS) intercalated MgAl-Layered double hydroxides: Preparation and anti-aging performance in polypropylene nanocomposites Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-25 Qian Zhang, Fabrice Leroux, Pinggui Tang, Dianqing Li, Yongjun Feng
A low molecular weight hindered amine light stabilizer (HALS), contains 2, 2, 6, 6-tetramethyl piperidine functional group has been successfully prepared and intercalated into the interlayer region of Mg-Al layered double hydroxides (LDH) via a co-precipitation method to produce HALS-LDH. Furthermore, a series of HALS-LDH/PP nanocomposites were fabricated by dispersing HALS-LDH in poly(propylene) (PP) in a solvent casting route. Through the accelerated aging test method, the morphological properties, the thermal-oxidative degradation and photo-oxidative degradation behavior of HALS-LDH/PP composites were carefully investigated. The results show that the thermal stability of HALS in HALS-LDH was improved compared to that of HALS free of LDH dispersed into PP, and there is no negative effect on the crystallization behavior of PP after the addition of HALS-LDH. Besides, the HALS-LDH significantly enhances synergistically the thermal- and photo-stability of PP compared when LDH platelets CO3-LDH or HALS are used separately. Under the experimental conditions, a mass loading of HALS-LDH optimized as 4 wt % in respect to PP was found to exhibit an excellent anti-aging performance for potential applications.
Fire-resistant natural fibre-reinforced composites from flame retarded textiles Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-24 W. Pornwannachai, J.R. Ebdon, B.K. Kandola
Thermoplastic composites were prepared by melt pressing fabrics from commingled natural (flax) –thermoplastic (polypropylene (PP) and poly lactic acid (PLA)) polymeric fibres. Fabrics were treated with a number of commercial flame retardants (FRs) used for textiles prior to composite preparation. Their flammabilities and mechanical performances have been evaluated in terms of FR types effective on each fibre type. The fire performances of the composite laminates evaluated using UL-94 showed that flax/PP control and all flame retarded composite samples failed the UL-94 test, except for one treated with organophosphonate FR. On the other hand all flame retarded flax/PLA samples achieved V0 rating. Cone calorimetric results obtained at 35 kW/m2 also showed that all FRs significantly reduced the flammability of the composites and that their efficiencies were more pronounced in flax/PLA than in flax/PP composites. The mechanical performances of composites evaluated in tensile, flexural and impact modes indicated that all flame retardants reduced the mechanical properties of the composites, with the extent of reduction dependent on the pH of the flame retardant solution used. The reduction in mechanical properties was more severe in flax/PLA composites than in flax/PP composites.
Improving fire safety of epoxy filled with graphene hybrid incorporated with zeolitic imidazolate framework/layered double hydroxide Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-23 Wenzong Xu, Xiaoling Wang, Yucheng Liu, Wu Li, Rui Chen
In this work, a novel graphene (RGO) hybrid added with Zeolitic Imidazolate Framework/Layered Double Hydroxide (ZIF/LDH) was prepared to obtain a synergistic system (RGO-LDH/ZIF-67). Subsequently, RGO-LDH/ZIF-67 was mixed into epoxy resin (EP) by physical blending for the purpose of improving its fire safety. Based on a series of tests and analyses, it was found that RGO-LDH/ZIF-67 was beneficial to reducing the heat release of EP during its burning process. The peak heat release rate (PHRR) and total heat release (THR) of the composite with 2 wt% RGO-LDH/ZIF-67 were reduced to 464 kW m−2 and 37.9 MJ m−2, respectively. Simultaneously, the smoke production in its flame and flameless combustion were also reduced significantly. According to the char analysis of different composites, the main mechanism is discussed. This work provided a new type of modified RGO for improving the fire safety of EP.
Facile synthesis of a novel hyperbranched poly(urethane-phosphine oxide) as an effective modifier for epoxy resin Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-22 Chao Ma, Shuilai Qiu, Junling Wang, Haibo Sheng, Yi Zhang, Weizhao Hu, Yuan Hu
Diffusion-limited oxidation of polyamide: Three stages of fracture behavior Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-22 Xin-Feng Wei, Kai J. Kallio, Stefan Bruder, Martin Bellander, Hans-Henning Kausch, Ulf W. Gedde, Mikael S. Hedenqvist
Simultaneous improvement of mechanical and fire retardant properties of synthesised biodegradable guar gum-g-poly(butyl acrylate)/montmorillonite nanocomposite Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-22 Dharmendra K. Jena, Prafulla K. Sahoo
A novel multicomponent biopolymer based nanocomposite was synthesised via graft copolymerization of butyl acrylate (BA) onto guar gum (GG) and montmorillonite (MMT) by using ammonium persulfate (APS) as a free radical initiator, in the presence of N,N′-methylene bisacrylamide (MBA) as a crosslinking agent. BA had been grafted onto GG chains and the participation of -OH groups of MMT in polymerization reaction was confirmed by FTIR spectra. XRD and TEM observations revealed that MMT was exfoliated and uniformly dispersed in guar gum-g-poly (butyl acrylate) (GG-g-PBA) matrix. The resultant nanocomposite showed remarkably improved thermal stability and mechanical properties. In addition, the excellent fire retardancy of nanocomposite results from the formation of compact and continuous char which not only hinders the migration of volatile decomposition products out of polymer matrix but also provides barrier for heat transfer evaluated by limiting oxygen index (LOI) and cone calorimetry test. The biodegradation of nanocomposite has been carried out for better commercialization and environmental concern.
Biodegradable PHBH/PVA blend nanofibers: Fabrication, characterization, in vitro degradation, and in vitro biocompatibility Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-21 Rina Afiani Rebia, Sélène Rozet, Yasushi Tamada, Toshihisa Tanaka
Enhancing the biodegradation rate of Poly(Lactic acid) films and PLA bio-nanocomposites in simulated composting through bioaugmentation Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-18 E. Castro-Aguirre, R. Auras, S. Selke, M. Rubino, T. Marsh
Poly(hexamethylene 2,5-furandicarboxylate) copolyesters containing phosphorus: Synthesis, crystallization behavior, thermal, mechanical and flame retardant properties Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-16 Guoqiang Wang, Min Jiang, Qiang Zhang, Rui Wang, Xiaoling Qu, Guangyuan Zhou
A series of phosphorus-containing poly (hexamethylene 2,5-furandicarboxylate)s (PHFCs) were synthesized from available biobased 2,5-furandicarboxylic acid (FDCA), 1,6-hexanediol (HDO), and 2-carboxyethyl (phenyl)phosphinic acid (CEPPA). Microstructure, molecular weight and its distribution, crystallization behavior, thermal, mechanical and flame retardant properties were characterized. Moreover, the effects of composition on various properties were investigated systematically. All PHFCs exhibited the excellent thermal stability. Glass transition temperature of PHFC slightly decreased with the increasing of CEPPA. Furthermore, nano-TiO2 not only improved the molten drops phenomenon, but also increased the crystallization rate. The limiting oxygen index of PHFC with 10 mol% CEPPA and 1 wt% TiO2 was 26% and UL94V-0 rating was obtained.
Hydrolytic degradation of D-mannitol-based polyurethanes Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-09 Lucía Romero-Azogil, Elena Benito, Antxon Martínez de Ilarduya, M.Gracia García-Martín, Juan A. Galbis
The capacity of redox D-mannitol-based polyurethanes to modulate the glutathione response under physiological conditions, as well as their effectiveness for sustained and site-specific drug release in the gastrointestinal tract (GIT), have been demonstrated in previous studies. Based on those promising results, our attention has now been drawn towards hydrolytic degradation processes at 37 °C and different pH values, from acidic to basic conditions, as in the GIT. For that, two sets of branched and linear D-mannitol-based polyurethanes containing disulfide bonds have been synthesized, which has been possible depending on the starting D-mannitol-derived monomer. Thus 3,4-O-isopropylidene-D-mannitol, having two secondary hydroxyl groups in addition to the two primary hydroxyl groups, afforded polyurethanes with a certain degree of branching. In contrast, 2,4:3,5-di-O-isopropylidene-D-mannitol and 2,3:4,5-di-O-isopropylidene-D-mannitol, lacking secondary hydroxyl groups, led to linear polyurethanes. Removal of the O-isopropylidene protecting groups resulted in more-hydrophilic materials. As in glutathione-mediated degradation, the branched polyurethanes presented enhanced degradation under physiological conditions, proportional to the content of D-mannitol, whereas linear polyurethanes were degraded slowly, and pH 8 and 10 were required.
A non-destructive method for crack quantification in photovoltaic backsheets under accelerated and real-world exposures Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-08 Addison G. Klinke, Abdulkerim Gok, Silas I. Ifeanyi, Laura S. Bruckman
The long-term durability of photovoltaic modules is paramount for the continued growth of the industry. Polymer backsheets are of particular concern since they provide electrical insulation and an environmental barrier. In this study, 23 freestanding, multilayer backsheets with nine unique material combinations underwent four different weathering exposures under accelerated and real-world conditions. Besides changes in color and gloss, the induced degradation included parallel or mudflat cracks on 11 backsheets, sometimes in combination with delamination or blistering. Similar degradation has been observed in previous studies and is concerning since cracks compromise the mechanical integrity and electrical safety of backsheets. Quantitative parameters are desirable to reliably classify categories of cracks and supply unbiased features for statistical analysis in predictive lifetime models. We developed an analysis technique that utilizes surface profilometry data to quantify the depth, width, area, spacing, and number of cracks. Parameters are automatically extracted from the raw data by an algorithm running on a high performance distributed computing cluster. Our algorithm excelled at characterizing parallel cracks with minimal de-adhesion, and only an estimated 4% of crack detections were false positives. The addition of humidity and temperature variation formed up to three times as many cracks on a photodose basis compared to dry, constant temperature exposures. Cracks in real-world and accelerated exposures propagated to similar depths with equivalent photodoses; however, the number of cracks formed in accelerated exposures was far greater on a photodose basis. Of samples that cracked, the best performing backsheet configuration was polyvinyl fluoride/poly (ethylene-terepthalate)/polyethylene (PVF/PET/PE) while the least durable was PET/PET/ethylene-vinyl acetate. None of the six PVF/PET/PVF backsheets cracked in any of the exposures.
Innovating routes for the reused of PP-flax and PP-glass non woven composites: A comparative study Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-05 Alain Bourmaud, Marina Fazzini, Nicolas Renouard, Karim Behlouli, Pierre Ouagne
The significant industrial development of non-woven biocomposites requires the implementation of environmentally and economically coherent end-of-life recycling solutions. In this study, we studied the recycling of a non-woven poly-(propylene)-flax composite by injection but also by thermo compression. For comparison, a material with the same architecture but reinforced by glass fibres was studied. Both recycling methods showed strong specificities. Injection recycling leads to efficiently homogenised microstructures of the parts but also to drastically reduced lengths of the fibres, up to 10 times lower than with compression moulding. This method globally promotes high failure strengths while compression moulding, by preserving the length of the fibrous reinforcements, guarantees higher stiffness. This work also highlights the impacts of the length and division of the fibre elements on the microstructure of the injected parts; thus, after a series of compression recycling cycles, injected parts exhibit an important skin-core effect larger than after initial injection recycling cycles, whether in terms of orientation or local fibre volume fraction. As a consequence, after a series of recycling by compression, a new injection cycle has for effect to improve the tensile mechanical performances. For example, the strength and modulus of PP-flax composites are increased by 103% and 75%, respectively. These results highlight the technical feasibility and relevance of implementing these two recycling methods, depending on the volumes or equipment available and the final properties to promote, as they enable the production of new high-performance parts.
Assessment of pro-oxidant activity of natural phenolic compounds in bio-polyesters Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-05 Nadka Tzankova Dintcheva, Marilena Baiamonte, Marilena Spera
In this work, natural phenolic compounds, such as Vanillic Acid (VA), Ferulic Acid (FA) and Thymol (Th), at very high concentrations, have been considered as pro-oxidant agents for Polylactic acid (PLA). Specifically, thin films of neat PLA and PLA-based systems containing 2 and 3 wt% of VA, FA and Th have been produced and subjected to accelerated degradation in different environmental conditions. Preliminary characterizations, through rheological, mechanical, optical and morphological analysis, of the formulated PLA-based systems show that the VA and FA, even less the Th, are able to exert a plasticizing action during the processing and subsequently, the PLA crystallinity and rigidity slightly decrease, while, the PLA ductility increase and its optical performance and morphology remain almost unchanged. To assess the pro-oxidant activity of the considered natural phenolic compounds, thin films of PLA and PLA-based systems containing VA, FA and Th have been subjected to accelerated degradation in different environmental conditions: (i) water-medium hydrolysis, (ii) photo-oxidation upon UVB exposure and (iii) thermo-oxidation upon thermal treatment in oven. All obtained results pointing out that the considered natural compounds, at these high concentrations, exert a clear pro-oxidant activity in PLA during the water-medium hydrolysis and the photo- and thermo-oxidative degradation. Moreover, the VA, FA and Th can be considered as suitable pro-degradant additives for PLA, also in order to control the bio-polyester degradation times.
Inhibition mechanism of the radical inhibitors to alkaline degradation of anion exchange membranes Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-04 Niya Ye, Yixin Xu, Dengji Zhang, Jingshuai Yang, Ronghuan He
We employed four radical inhibitors to investigate their influences on the degradation of poly (4-vinylbenzyl chloride-styrene) based anion exchange membranes (AEMs) in alkaline solutions. It is found that the presence of the radical inhibitors could effectively restrain the nucleophilic attack of hydroxide ions to the AEMs according to the conductivity measurements, especially the one p-ethyl phenol (PEP), which could significantly protect the AEMs against the attack. More evidences including water uptake, swelling ratio as well as FT-IR analysis further proved this phenomenon by comparison those properties of the membranes before and after the stability test in 8 M KOH at 80 °C for 24 h. According to the 1H NMR spectra, the quaternary ammonium groups of the AEMs were mainly degraded into tertiary amines in the hot alkaline solutions; while in the presence of PEP, this degradation was restrained and the quaternary ammonium groups maintained by reaction with PEP. Fenton test results further indicated that high oxidative stability of the AEMs benefited from the presence of a small amount of PEP, which could reduce the generation of the oxidants. Thus an inhibition reaction mechanism of the radical inhibitors preventing the AEMs from alkaline degradation is proposed.
A recyclability study of bagasse fiber reinforced polypropylene composites Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-04 Manish Kumar Lila, Arpit Singhal, Sukhwant Singh Banwait, Inderdeep Singh
Natural fiber reinforced composites are gaining attention nowadays due to their low cost, biodegradable characteristics, lower density and comparable mechanical properties with synthetic fibers reinforced composites. As the recyclable properties of these composites are still not fully explored and this could be the reason that these are not much used in domestic and other applications to their full potential. In the current experimental investigation, the effects of mechanical recycling on the properties of bagasse fiber reinforced polypropylene composites have been studied. Tensile properties, crystallinity and aspect ratio exhibits an increase, while flexural properties decrease with each recycling step. No significant change in thermal behavior has been detected even after 5 cycles but a slight increase in the hardness has been observed. SEM images confirmed the change in aspect ratio due to crushing of fibers as well as fiber fracture became more dominant after each recycling step.
Wide range control in the elastic properties of PDMS polymer by ion beam (H+) irradiation Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-03 Robert Huszank, Attila Bonyár, Judit Kámán, Enikő Furu
The effects of ion irradiation on the elastic and surface properties, nanostructure and the chemical changes of the widely used polydimethylsiloxane (PDMS) polymer were investigated as a function of the ion fluence, induced by high-energy ionizing radiation (2.0 MeV proton beam). The polymer was irradiated with different fluences of protons and then the chemical changes, the elastic modulus and surface roughness were investigated by infrared spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM). The FT-IR measurements showed very significant chemical changes in the material upon proton irradiation, such as detachment of methyl side groups first, then the starting of the main chain scissions, until the major silicatization of the PDMS by the formation of an inorganic silica like final product (SiOx). The AFM force curves were obtained by performing contact-mode point-spectroscopy. Their evaluation showed, that the surface elastic properties of PDMS can be controlled in the range of 240 MPa to 49 GPa (Young's modulus) with ion fluencies between 1.68 × 1013 ions/cm2 to 1.25 × 1016 ions/cm2, respectively. Compared to the 3–4 MPa of the reference material this indicates a more than four orders of magnitude increase in the elastic modulus of the material. The accompanying changes in the nanostructure of the polymer were characterized with AFM topography measurements and are also discussed in detail.
Hydroxyl accessibility and dimensional changes of Scots pine sapwood affected by alterations in the cell wall ultrastructure during heat-treatment Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-03 Michael Altgen, Wim Willems, Reza Hosseinpourpia, Lauri Rautkari
There is a complex link between the water sorption behavior and the presence of accessible hydroxyl groups in the wood cell wall, which can be altered by heat-treatment (HT). This study analyses the effect of changes in the cell wall ultrastructure caused by two HT techniques on the hydroxyl accessibility, water vapor sorption and dimensional changes of Scots pine (Pinus sylvestris L.) sapwood. HT of wood in pressurized hot water at 120–170 °C was applied to cause the preferential bond cleavage, whereas HT of wood in oven-dry state in superheated steam at 180–240 °C was performed to create additional covalent cross-links within the cell wall matrix. Removal of cell wall polymers by HT and water leaching reduced the oven-dry dimensions of wood and enhanced the cellulose aggregation during drying. Cellulose aggregation restricted the cell wall shrinkage in circumferential direction, resulting in inhomogeneous shrinkage of the cell wall with only little changes in lumen volume by HT. Cellulose aggregation also reduced the water-saturated dimensions, but a decrease in swelling was only achieved when additional cross-links were formed by HT in dry state. Additional cross-links in the cell wall matrix also resulted in an additional reduction in water sorption at 25 °C and 93% RH. However, this was not caused by a further reduction in the hydroxyl accessibility. Instead, cross-linking was shown to reduce the amount of accessible OH groups that are simultaneously active in sorption, which was explained based on the concept of sorption of water dimers at hydroxyl group pairs at high RH levels.
High-performance flame retardant epoxy resin based on a bi-group molecule containing phosphaphenanthrene and borate groups Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-30 Shuo Tang, Lijun Qian, Yong Qiu, Yuping Dong
A flame retardant named ODOPB-Borate constructed by phosphaphenanthrene (DOPO) and borate groups was synthesized via esterification reaction between boric acid and 10-(2,5-dihydroxyphenyl)-10-H-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB). The molecular structure of ODOPB-Borate was characterized and verified. To research the group synergistic effect of phosphaphenanthrene and borate groups, ODOPB-Borate was incorporated into epoxy resin, diglycidyl ether of bisphenol-A (DGEBA), cured by 4,4-diamino-diphenyl sulfone (DDS). ODOPB-Borate increased the LOI and particularly improved the UL94 classification of epoxy resin thermosets, and also reduced the heat release of epoxy thermosets. Further, the decrease of total mass loss value of thermoset containing ODOPB-Borate revealed that ODOPB-Borate facilitated the EP composites to form more residue. The analyzed pyrolysis route of ODOPB-Borate revealed that ODOPB part mainly exerted quenching effect in gas phase and the borate part mostly remained in condensed phase and promoted charring effect and smoke suppressing effect. The synergistic effect from phosphaphenanthrene and borate groups endowed epoxy resins with flame retardancy. Moreover, ODOPB-Borate also increased the glass transition temperature and impact strength of epoxy resin.
Facile synthesis and characterization of activated star-shaped itaconic acid based thermosetting resins Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-01 Arash Jahandideh, Nima Esmaeili, Kasiviswanathan Muthukumarappan
Novel star-shaped thermosetting resins were synthesized by condensation-reaction of itaconic acid and glycerol, followed by treatment of the oligomers, by methanol and allyl alcohol. Employing 1H and 13C NMR and FT-IR, the chemical structures of the resins were studied. The thermomechanical properties were evaluated by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). Viscometry and thermogravimetric analyses (TGA) were also employed to study the rheological and thermal properties of samples. The viscosity of the methanol-treated resin was 4.2 Pa s at 25 °C, which dropped to 0.25 Pa s at 70 °C. The allyl alcohol-treated resin showed a lower viscosity (1.8 Pa s at room temperature, and 0.14 Pa s at 70 °C). A substantially higher glass temperature (Tg) was recorded for methanol-treated resin (150 °C) compared to that of the allyl alcohol-treated resin (93 °C). Compared to the allyl alcohol-treated resin, very good mechanical properties for the methanol-treated resin was achieved, in terms of storage modulus, (61% higher G′). Excellent environmental profile (i.e. high biobased contents and biodegradability), inexpensive raw materials, along with promising rheological and thermomechanical properties are advantages of these novel resins, which make the resins comparable with, and superior in some aspects, to other thermosetting systems.
Thermal decomposition of phosphonate-containing methacrylate-based copolymers Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-05-01 Eike Thomas Röchow, Liane Häußler, Andreas Korwitz, Doris Pospiech
The synthesis of novel phosphonate-containing copolymers with methyl methacrylate (MMA) is reported. As phosphonate comonomers ethyl-2-[4-(dihydroxyphosphoryl)-2-oxabutyl]acrylate (EDHPOBA), with free phosphonic acid group, and the respective methyl ester ethyl-2-[4-(dimethoxyphosphoryl)-2-oxabutyl]acrylate (EDMPOBA) are employed. The impact of the phosphonate-containing comonomers on the thermal decomposition of P(MMA) copolymers is discussed using data obtained from thermogravimetric analysis (TGA). P(MMA) decomposes completely under nitrogen leading to a negligible residue, while the decomposition of copolymers containing the phosphonate comonomer EDHPOBA yields a significant residue (up to 32 wt.%) indicating a significant alteration of the decomposition mechanism. TGA/FTIR experiments are performed to determine the volatile decomposition products of the copolymers. It is demonstrated that incorporation of the phosphonic acid-containing monomer in P(MMA) suppresses the depolymerization of P(MMA) Alternative pyrolysis reactions take place and MMA is not detected in the gas phase. The decomposition proceeds essentially in four steps: transesterification between acrylate ester groups and phosphonic acid, anhydride formation, decarboxylation, McLafferty rearrangement and cyclization (char forming). It is found that this reaction sequence cannot occur in copolymers with the ester EDMPOBA comonomer, thus resulting in a less favored influence on the decomposition mechanism. Microscale combustion calorimetric measurements prove that incorporation of the phosphonate monomers drastically reduces the total heat release and heat release capacity.
Crystallizability of substituted Poly(lactic acid)s: Effects of alkyl side-chain structure Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-30 Hironori Marubayashi, Ryo Mizukami, Yuji Hamada, Shuichi Nojima
The side-chain-substituted poly (lactic acid)s (SPLAs) having C3–C4 alkyl side chains (Pr, iPr, n-Bu, iBu, and s-Bu for propyl, isopropyl, n-butyl, isobutyl, and sec-butyl groups, respectively) were synthesized from l-amino acids, and their crystallizability was systematically investigated (unknown for Pr, n-Bu, and s-Bu but already known for iPr and iBu). s-Bu was found to be a crystalline polymer like iPr, whereas Pr and n-Bu had little or no crystallizability like iBu. The crystal structure, melting behavior, and crystallization rate of s-Bu were examined in detail. The crystal structure and crystallinity (ca. 60%) of s-Bu were not affected at all by the crystallization temperature and casting solvent. The melting temperature and spherulite growth rate of s-Bu were compared with those of iPr and referenced data of SPLA with methyl side chains (Me) [i.e., poly (l-lactic acid)] and that with ethyl side chains (Et) [i.e., poly (L-2-hydroxybutanoic acid)]. The magnitude relation among melting temperatures of SPLAs would be iPr > s-Bu > Me > Et, and that among spherulite growth rates iPr > Me ≈ s-Bu > Et.
Biobased multiblock copolymers: Synthesis, properties and shape memory behavior of poly(hexamethylene 2,5-furandicarboxylate)-b-poly(ethylene glycol) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-27 Guoqiang Wang, Min Jiang, Qiang Zhang, Rui Wang, Xiaoling Qu, Guangyuan Zhou
A series of novel multiblock copolymers poly(hexamethylene 2,5-furandicarboxylate)-b-poly(ethylene glycol) (PHFEGs) were synthesized from available biobased 2,5-furandicarboxylic acid (FDCA), 1,6-hexanediol (HD), and poly(ethylene glycol) (PEG) by a two-step melt polycondensation method. A systematic investigation of microstructure, molecular weight and its distribution, crystallization behavior, thermal stability of PHFEGs was performed using 1H NMR, GPC, DSC, and TGA, respectively. Moreover, effects of composition on mechanical and shape memory properties of PHFEGs were investigated systematically. Results showed that the weight percentage of PEG in PHFEGs was consistent with that in feed. DSC data showed most PHFEGs were double-crystalline block copolymers. All PHFEGs exhibited the excellent thermal stability. In summary, compared with PHF, the addition of PEG toughened PHF to the extent and endowed the double-crystalline block copolymers with excellent shape-memory ability, suggesting PHFEGs with excellent shape-memory properties have great potential in application.
Role of phenol and phosphite antioxidant combinations in the thermal stabilisation of metallocene LLDPE (mLLDPE): Optimisation and performance and influence of metal stearates on multiple extrusions Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-26 Norman S. Allen, Michele Edge, Christopher M. Liauw, Eric Hoang
This study progresses our earlier studies and takes the performance characteristics of a 1:1 Irganox 1010: Irgafos 168 combination at 1000 ppm each through multiple extrusion processes in a metallocene LLDPE (mLLDPE) investigating for the first time the role of a broad range of calcium and zinc stearates based on animal vs vegetable origins of the stearine function. In this case performance was assessed using Melt Flow Rate (MFR) coupled with HPLC to determine not only the additive depletions after processing but also the rate of production of the phosphite to phosphonate. Comparative control studies were also undertaken on the single use of the separate antioxidants. Both stearates influenced the activity of the antioxidants in particular their consumption. A greater consumption after the third and fifth extrusion was observed with metal stearates produced from the vegetable stearine. Moreover, zinc stearates seemed to provide a greater detrimental effect than calcium stearates. Hydroperoxide analysis on the stearates confirmed the animal stearine to contain higher levels of peroxides which may contribute toward the higher activity. The optimisation of the thermal stabilisation of the metallocene polyethylene (mLLDPE) has also been investigated in this study. Several conditions of stability were determined for the determination of the optimal antioxidant (phenol:phosphite) ratio. The main parameter was high melt stability for a maximum processing stability of the final package via DSC analysis (OIT) coupled with assessments of embrittlement time (oven ageing) and yellowness index. Long-term stability against thermo-oxidation was considered coupled with a consideration of their hydrolytic stability as a complicating factor. In this work the (phenol/phosphite) antioxidant formulations with two different phenolic antioxidants (Irganox 1010, Irganox 1076) and six different phosphite antioxidants (Irgafos 168, Irgafos P-EPQ, Adekastab PEP-8, Adekastab PEP-36, Adekastab PEP-24G, Adekastab HP-10) were assessed at different levels taking into account the various criteria for optimal performance providing hitherto useful information than many prior studies on 1:1% ratios i.e. how much phosphite is required for optimal activity. A question often posed in the field with the results concluding an interesting unified optimum ratio of 4:1 (for most antioxidants studied) taking into account all the critical parameters.
Diffusion and hydrolysis effects during water aging on an epoxy-anhydride system Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-24 Guillermina Capiel, Julieta Uicich, Diana Fasce, Pablo E. Montemartini
Hydrothermal aging of an epoxy-anhydride network has been studied by means of gravimetric analysis, Fourier transform infrared spectroscopy (FTIR) and modulated differential scanning calorimetry (MDSC). The long-term aging results revealed a fourth stage mechanism in which an initial short diffusional period is followed by the hydrolysis of the ester groups. Degraded materials showed two values of glass transition temperature suggesting a heterogeneous process. Hydrolysis undergoes in preferential sites due to the catalytic effect of the carboxyl acids formed during the chemical degradation. Domains with low crosslinking density and high mobility are formed. At long degradation time, samples presented a unique glass transition temperature around 50 °C. The lixiviation of low molecular weight species formed by the hydrolytic scissions was confirmed by FTIR and pH variations.
A reactive phosphorus-containing polyol incorporated into flexible polyurethane foam: Self-extinguishing behavior and mechanism Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-23 Wen-Hui Rao, Zong-Min Zhu, Shui-Xiu Wang, Ting Wang, Yi Tan, Wang Liao, Hai-Bo Zhao, Yu-Zhong Wang
A novel liquid phosphorus-containing polyol named as PDEO was prepared via reactions between ethylene glycol and phenylphosphonic dichloride. PDEO reacts with the -NCO-terminated prepolymers and forms urethane linkages in the chain extension reaction step, thus, it was used to prepare inherently flame-retardant flexible polyurethane foams (FPUFs). The structure and properties of flame-retardant FPUF were characterized by scanning electron microscopy (SEM), tensile measurements, limiting oxygen index (LOI), vertical burning tests, cone calorimeter tests and thermogravimetric analysis (TGA). The vertical burning test demonstrated that fire extinguished instantly after the withdrawn of the pilot flame, while the PDEO loading was only 10 php. In addition, the persistent flame retardancy of PDEO in FPUFs was proved by thermal ageing test. The corresponding flame-retardant mechanism of PDEO-containing FPUFs was investigated by pyrolysis gas chromatography mass spectrometry (Py-GC/MS), X-ray photoelectron spectroscopy (XPS), SEM and FTIR, and the results indicated a gaseous phase dominated flame-retardant mechanism of PDEO.
Getting a better insight into the chemistry of decomposition of complex flame retarded formulation: New insights using solid state NMR Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-23 N. Hansupo, G. Tricot, S. Bellayer, P. Roussel, F. Samyn, S. Duquesne, M. Jimenez, M. Hollman, P. Catala, S. Bourbigot
This paper aims at developing an innovative approach to characterize the char residue of an intumescent coating obtained after a UL1709 furnace test. The intumescent formulation is based on an epoxy resin and contains numerous additives including zinc borate, ammonium polyphosphate and silicate fibers. The purpose is to characterize the numerous reactions that can occur upon burning using crossed methods including Electron Probe Micro-Analysis (EPMA), X-ray diffraction (XRD) and 1D/2D solid state Nuclear Magnetic Resonance (NMR). In particular, it emphasizes the potential of the advanced NMR technique namely two-dimensional Dipolar Heteronuclear Multiple Quantum Correlation (2D D-HMQC) NMR. As a result, EPMA evidenced that B/P and B/Si are located in the same domain suggesting the formation of boron-phosphorus and/or boron-silicone containing compounds on the sample surface. H3BO3 was identified by XRD as a main crystalline specie, additional species (e.g. SiO2, Zn4O(BO2)6) were also identified. The borate, silicate and phosphate chemical species were then characterized using 1D NMR but no definitive assignments could be given. To specify those assignments, 2D D-HMQC NMR was performed and the formation of amorphous borophosphates and borosilicates was evidenced emphasizing the chemical reactivity between the ingredients of the formulation. It was suggested that these species allow reinforcing the char and improving the fire protective properties of the coatings. This work highlights the particular interest of advanced NMR technique, which provides unique information on the characterization of intumescent char.
Synergistic effects of synthetic phosphonium sulfonates with expandable graphite on flame retardancy for EVA rubber blends Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-22 Shijie Hou, Yong Jian Zhang, Pingkai Jiang
Synergistic effects of synthetic phosphonium sulfonates (PhSs) bearing different groups with expandable graphite (EG) on flame retardancy properties in poly(ethylene-co-vinyl acetate) (EVA) rubber blends have been studied by limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), and thermogravimetric analysis (TGA). The EVA/EG/PhS composites revealed excellent flame retardancies. Upon adding 2.5 wt% of PhSs and 20 wt% of EG to EVA matrix, V-0 rating can be achieved. The heat release rate (HRR) and the total heat release (THR) of EVA/PhS-2(2.5 wt%)/EG(20 wt%) and EVA/PhS-4(2.5 wt%)/EG(20 wt%) blends decreased remarkably based on CCT. In addition, the thermal stabilities and mechanical properties of EVA/EG/PhS composites did not deteriorate comparing with those of EVA/EG composites.
Effects of ZnO quantum dots on the photostability of acrylate photopolymers used as recording materials Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-22 Georgia G. Goourey, Pascal Wong-Wah-Chung, Lavinia Balan, Yaël Israëli
ZnO quantum dots, QDs (5 nm diameter) by their photogenerated charge carriers clearly influence the degradation of the acrylate host matrix, under conditions simulating solar light. As a result, QDs undergo a partial quenching of their fluorescence. To rationalize this influence, the investigation requires understanding the photochemical behavior of the acrylate photopolymer (carrier of ester and ether groups) in the absence of nanofiller. The matrix undergoes simultaneously a post-polymerization and photooxidative degradation. Infrared analysis and headspace gas chromatography coupled with mass spectrometry reveal that the main volatile organic compounds result from the oxidation of the ether groups, supposed to be the primary sites of degradation. The nanofiller increases the rate of degradation. Also, the concentration of the volatile organic compounds is all the more important as the doping percentage increases. However, the photostability of ZnO/polymer material strongly depends on the size of the nanoparticles. Whereas ZnO QDs display a photocatalytic effect, nanoparticles with a bigger size (10–30 nm) exhibit an unexpected UV-screening effect.
Stability, mechanism and unique “zinc burning” inhibition synergistic effect of zinc dehydroacetate as thermal stabilizer for poly(vinyl chloride) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-20 Bozhen Wu, Yating Wang, Si Chen, Muyan Wang, Meng Ma, Yanqin Shi, Xu Wang
A novel kind of poly(vinyl chloride) (PVC) thermal stabilizer, zinc dehydroacetate (ZnL2), was designed and synthesized using zinc acetate and dehydroacetic acid (DA) as raw materials, which had a unique "zinc burning" inhibition synergistic effect with calcium stearate (CaSt2) that was 8 times greater than that of the CaSt2/ZnSt2 combination reference stabilizer. The structure and stability of ZnL2 were confirmed by Fourier-transform infrared, elemental analysis, and thermogravimetric analysis. The stability distinction of ZnL2 and ZnSt2, and the stable effect of the two systems after being combined with CaSt2, were investigated by the Congo red test, solution acidity test, and discoloration test. The results showed that in the Congo red test the stability time of ZnL2 was 8.9 min, which was 1.3 times that of ZnSt2, and the stability time of ZnL2/CaSt2 was 13 min, which was 1.4 times that of a traditional Ca/Zn stabilizer. Furthermore, the stability time of ZnL2 was 36 min in the solution acidity test, which was 2 times higher than that of ZnSt2, and the stability time was increased to 196 min after combining it with CaSt2, which was 8 times greater than that of the Ca/Zn stabilizer. Moreover, the dehydrochlorination rate of PVC stabilized with ZnL2 was slower than with other stabilizers. The system with ZnL2/CaSt2 could effectively delay “zinc burning” because of the excellent synergistic effect in the thermal aging test, with a stability time as long as 140 min. At the same time, the mechanism of PVC stabilization by ZnL2 was studied in two simple experiments, and the stabilization mechanism of ZnL2 in PVC degradation was speculated on.
Polyethylene glycol-albumin/fibrin interpenetrating polymer networks with adaptable enzymatic degradation for tissue engineering applications Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-18 Marie Deneufchâtel, Véronique Larreta-Garde, Odile Fichet
A new series of polyethylene glycol-albumin/Fibrin interpenetrating polymer networks (PEG-BSA/Fb IPNs) combining a fibrin gel with a co-network of polyethylene glycol and serum albumin has been developed in order to study the enzymatic degradation of such architectures combining protein and synthetic polymer partners. BSA provides biodegradability thank to its many segments cleavable by enzymes while PEG ensures material resistance (shape preservation, mechanical moduli, …). Previous the degradation study of these easily manipulable PEG-BSA/Fb IPNs, it was shown that each partner (fibrin, PEG and BSA) contributes to the elastic modulus value which is only possible in an IPN architecture where the different polymer partners form a continuous phase in the whole material. The homogeneous protein distribution in the materials was also confirmed by confocal microscopy. Then, their biodegradability was studied by combining three complementary characterizations: on the one hand, absorbance of the hydrolytic enzyme solution in which they were immersed to quantify the proportion of protein fragment extracted and, on the other hand, viscoelastic moduli of the hydrogels after immersion in the same enzyme to evaluate their mechanical resistance, and finally, MEB imaging to check the hydrolysis homogeneity. The proteolytic enzyme degrades quickly IPNs containing less than 3 wt% PEG while other IPNs remain resistant to proteolysis over long periods, although their viscoelastic properties are reduced by 70% and morphology at the microscopic level changed in a few hours. The degradation rate of these materials is thus easily tunable by composition adjustment.
A comparative study of three-dimensional printing directions: The degradation and toxicological profile of a PLA/PHA blend Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-17 Jennifer Gonzalez-Ausejo, Joanna Rydz, Marta Musioł, Wanda Sikorska, Michał Sobota, Jakub Włodarczyk, Grażyna Adamus, Henryk Janeczek, Iwona Kwiecień, Anna Hercog, Brian Johnston, Habib R. Khan, Vinodh Kannappan, Keith R. Jones, Mark R. Morris, Gouzhan Jiang, Iza Radecka, Marek Kowalczuk
The use of biobased plastics is of great importance for many applications. Blending thermoplastic polylactide (PLA) with polyhydroxyalkanoate (PHA) enables the formulation of a more mechanically powerful material and this enables tailored biodegradation properties. In this study we demonstrate the 3D printing of a PLA/PHA blend as a potential candidate for biocompatible material applications. The filament for 3D printing consisted of PHA, which contains predominantly 3-hydroxybutyrate units and a small amount of 3-hydroxyvalerate units, as revealed by multistage mass spectrometry (ESI-MSn). This research found that the properties of 3D printed species before and during abiotic degradation are dependent on printing orientation. Furthermore, the 3D printed specimens exhibited good biocompatibility with HEK293 cells, indicating real promise as biological scaffolds for tissue engineering applications.
Improving flame retardancy of linear low-density polyethylene/nylon 6 blends via controlling localization of clay and intumescent flame-retardant Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-16 Chang Lu, Xi-ping Gao, Da-hu Yao, Cheng-lin Cao, Yu-jing Luo
Four processing methods were employed to control the localization of intumescent flame-retardant (IFR) and clay in linear low-density polyethylene/nylon 6 (LLDPE/PA6) blends and the effect of IFR and clay localization in blends on flame retardancy was investigated. The results obtained from the LOI and UL-94 tests showed that the flame retardancy in the blends with clay localization in the LLDPE phase was better than that of the blends with clay localization in the PA6 phase. Cone calorimeter test results demonstrated that IFR localization in the PA6 phase caused lower peak heat release rate (PHHR) than in the LLDPE phase. The combined effect resulted in the best flame retardancy exhibited in the blends with localization of IFR in the PA6 phase and clay in the LLDPE phase in comparison with the blends with other localization of IFR and clay. Scanning electron microscopy showed that clay localization in the LLDPE phase and IFR localization in the PA6 phase promoted the formation of an integrated and highly expansive char layer. It is believed the results of the study provide the references for optimizing the flame retardancy of polymer blends.
Fire resistant polyphenols based on chemical modification of bio-derived tannic acid Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-14 Zhiyu Xia, Weeradech Kiratitanavit, Patrick Facendola, Sammaiah Thota, Shiran Yu, Jayant Kumar, Ravi Mosurkal, Ramaswamy Nagarajan
Utilization of renewable materials for the development of safer and nontoxic flame retardants has been of interest from environmental safety and sustainability perspective. Tannic acid (TA) is an abundantly available bio-based polyphenol that exhibits good intumescence and char forming characteristics upon being subjected to heat. Intumescence and char formation are important prerequisites for certain types of effective flame retardant (FR) additives. However, the potential for utilizing TA as an FR has been limited by its poor thermal stability. A single step chemical modification process that overcomes the limitations of TA while allowing the utilization of its beneficial properties is reported here. TA was crosslinked using interfacial polycondensation with terephthaloyl chloride to yield tannic acid terephthalate (TAT). The complex structure of TAT necessitated the synthesis of several model compounds based on methyl gallate (MG) to facilitate the complete structural characterization of TAT using FTIR and 1H NMR. TAT is thermally stable up to 230 °C (less than 3% weight loss) and shows 30% higher char yield and extremely low heat release capacity (<80 J/g-K) as compared to that for TA. Detailed thermal degradation studies combined with gas phase spectroscopy using thermogravimetric analysis - Fourier-transform infrared spectroscopy (TGA-FTIR) and pyrolysis - gas chromatography - mass spectrometry (Py-GC-MS) provide an understanding of the degradation process. Crosslinked phenolic species enhance char formation in the condensed phase and allow for utilization of these compounds as flame retardant coatings for polymers such as Nylon 6,6. TAT coating on Nylon 6,6 fabric significantly impedes flame propagation in the fabric, resulting in quick self-extinguishing behavior and reduced char length in vertical flame tests. Morphological characterization, thermo-oxidation studies and microscale combustion calorimetry (MCC) (at high heating rates) of TAT-coated fabric reveal the beneficial effects of char formation and its direct impact on flame retardancy.
Thermooxidative degradation of crosslinked EVA/EPDM copolymers: Impact of Aluminium TriHydrate (ATH) filler incorporation Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-13 Juliette Colombani, Ahmedou Sidi, Jean-François Larché, Christine Taviot-Gueho, Agnès Rivaton
This study focuses on the thermal oxidation of model composites of insulating materials based on a cross-linked mixture of EVA (Ethylene Vinyl Acetate) and EPDM (Ethylene Propylene Diene Monomer) highly loaded (60 wt %) with ATH (Aluminium TriHydrate) filler. A thorough analysis of the material is performed, focusing not only on the polymer but also on the ATH filler. This preliminary study is essential firstly to determine the possible influence of a large amount micrometric filler incorporation on the structure of crosslinked EVA/EPDM materials, and secondly on the thermooxidative degradation mechanisms at different levels and scales (chemical structure, microstructure and architecture, degradation profile, functional properties …). The structure of both the polymer and the filler are modified during the processing step of the composite. It is shown that the reactivity of the ATH fillers leads to the probable intercalation of some segments of the polymer into the interlayer space of the ATH, and to a much less dense polymer network in the composite compared to the unfilled material. Then, the role of the added ATH filler on the thermooxidative degradation and on the resistance of the composite to ageing is studied. After thermooxidative ageing, there is only a very limited accelerator effect of ATH on the oxidation rate of the polymer within the composite compared to the unfilled material, but significant difference between materials with or without ATH filler in terms of oxidation profile or insulating properties. Nevertheless, a noticeable effect on the mechanical properties is highlighted: the mechanical properties of the unfilled materials are retained all through the oxidation process while these properties reduce drastically in the case of filled composites. The significant loss of mechanical properties occurring in the filled composites can be explained by the combination of three factors: only 40 wt % of polymer in the composite, a low density polymer network within the composite, and de-cohesion process between the ATH filler and the polymer matrix upon thermooxidative degradation.
Fire retardant action of zinc phosphinate and polyamide 11 blend containing lignin as a carbon source Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-13 Neeraj Mandlekar, Giulio Malucelli, Aurelie Cayla, Francois Rault, Stephane Giraud, Fabien Salaün, Jinping Guan
This study investigates the thermal decomposition and fire behavior of zinc phosphinate (ZnP) in combination with low sulphonate content alkali lignin (LS) in a polyamide 11 (PA11) matrix. The influence of ZnP with LS on PA11 was assessed by using thermogravimetric analysis coupled with FTIR spectroscopy (TG-FTIR). Such decomposition products as hydrocarbons, amide and carbonyl units, phenolic and phosphinate compounds control the decomposition. The chemical structure of the condensed phase was evaluated by FTIR measurements carried out on the residues. The fire behavior was investigated using UL 94 vertical flame spread tests and cone calorimetry tests. In the ternary blends, the addition of LS promotes char formation as assessed by TG analyses; furthermore, ZnP contributes to flame inhibition mainly by radical trapping and partially by dilution of fuel, due to phosphinate ions and a small amount of phosphinic acid released in the gas phase. Besides, phosphate compounds are formed in the condensed phase. The combination of LS and ZnP enhanced flame-retardant properties due to the formation of a stable char layer with barrier features.
Stabilization of recombinant spider silk in thermo-oxidative degradation: High-throughput screening for antioxidants Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-12 Anh T.N. Dao, Jun'ichi Shimokata, Kengo Takeuchi, Koyuru Nakayama, Toshiaki Taniike
Recombinant spider silk has arisen as one of the most promising nature-derived building blocks owing to its extraordinary mechanical properties, while its instability against thermo-oxidative degradation becomes a major drawback toward industrial applications. Here, we have firstly implemented a high-throughput screening of antioxidants on the stabilization of recombinant spider silk at an elevated temperature. The usage of high-throughput chemiluminescence imaging has allowed us to screen antioxidants with a wide spectrum of molecular structures and quickly provided two good candidates to stabilize recombinant spider silk powder through an impregnation process: E310 and BHT. An accelerated aging has further proven that these antioxidants suppressed the thermo-oxidation of recombinant spider silk through scavenging the formed radical species and slowed down the formation of carbonyl groups as oxidation products. In addition, we have employed a solution mixing process to further improve the stabilization efficacy of the antioxidants and this method also extended our selection on effective antioxidants, including vitamin E, AO-30, AO-40, HP-10, and especially Irganox 1098. These screening results provide guidelines of selecting or even developing potential antioxidants for stabilizing protein materials.
Effect of gallic acid and umbelliferone on thermal, mechanical, antioxidant and antimicrobial properties of poly (vinyl alcohol-co-ethylene) films Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-12 F. Luzi, D. Puglia, F. Dominici, E. Fortunati, G. Giovanale, G.M. Balestra, L. Torre
Poly(vinyl alcohol-co-ethylene) (EVOH) ﬁlms containing two different active ingredients (AIs), gallic acid (GA) and umbelliferone (UMB) at 5 wt. % and 15 wt. %, were successfully produced by solvent casting and extrusion. The effects of process techniques, AIs presence, typology and content on optical, morphological, thermal and mechanical properties of EVOH based films have been investigated. In addition, moisture content, migration and radical scavenging activity, antimicrobial and antifungal studies were performed, with the aim of evaluating the effect of AIs on structural and functional properties of realized food packaging systems. Results from colorimetric and transparency investigation underlined that the presence of AIs in EVOH copolymer induced important alterations, whereas migration to food simulant data restricted the use of produced films in contact with fatty foods. On the other hand, the use of AIs clearly induced positive antioxidant response, inhibitions of bacterial and antifungal growth, confirming the possibility of practically using these materials in the food packaging sector.
Comparative study of the photochemical stability of HDPE/Ag composites Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-12 Ifigenia Grigoriadou, Eleni Pavlidou, Kostas M. Paraskevopoulos, Zoe Terzopoulou, Dimitrios N. Bikiaris
In the present study, HDPE composites containing different concentrations of silver (Ag) nanoparticles (0.5%, 1%, 2%, 3%, and 5 wt%) were prepared by melt mixing on a Haake-Buchler Reomixer. Composites in the form of thin films were exposed to UV irradiation at 280 nm at constant temperature (25 °C) and relative humidity (50%) for several hours. The samples were characterized for their photochemical stability with several methods. From FTIR spectroscopy it was found that new chemical compounds were formed during UV exposure containing carbonyl, vinyl, and hydroxyl/hydroxyperoxide groups. According to the spectra, the nanoparticles act as inhibitors to the photo-oxidation mechanism of the polymer matrix. Moreover, as the loading of nanoparticles increased, better protection was achieved. Further study of the samples was performed using tensile strength tests, showing that neat HDPE was affected significantly by UV irradiation, while its composites with Ag were affected in a lower extend. The greater the loading of the nanoparticles in the polymer matrix, the more they reduce the mobility of the molecules, thus inhibiting the chain scission of HDPE. Degree of crystallinity was also affected from UV exposure time and the addition of nanoparticles. Finally, the mechanism of thermal degradation of HDPE and its composite with 1 wt% Ag before and after UV exposure was studied by Pyrolysis-gas chromatography–mass spectroscopy (Py-GC/MS).
Kinetics, evolving thermal properties, and surface ignition of carbon fiber reinforced epoxy composite during laser-induced decomposition Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-11 Nicholas C. Herr, Ashley E. Gonzales, Glen P. Perram
The decomposition kinetics, heats of reaction, evolving thermal conductivity and emissivity, and surface ignition conditions of carbon fiber reinforced polymer (CFRP) composites during laser-induced polymer matrix decomposition were investigated. Woven carbon fiber-epoxy panels of different thicknesses were irradiated with a 1.07-μm, 2-kW ytterbium fiber laser at irradiances of 5–525 W/cm2. The changing front and backside surface temperatures were measured using a mid-wave infrared camera, adjusted using measured emissivity of irradiated and un-irradiated CFRP samples. The evolving temperature maps were fit to a 3D, explicit, finite difference, thermal model to estimate Arrhenius kinetic rate parameters, heats of reaction, and thermal conductivity during a two-step epoxy decomposition reaction and a single stage char oxidation reaction. The kinetics is not strongly dependent on heating rates of 20–700 °C/sec and parameters determined at lower laser powers extrapolate well to higher powers. Surface ignition occurs at critical surface temperatures of 1198 ± 50 °C.
Novel biocompatible PBS-based random copolymers containing PEG-like sequences for biomedical applications: From drug delivery to tissue engineering Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-10 Martina Fabbri, Giulia Guidotti, Michelina Soccio, Nadia Lotti, Marco Govoni, Emanuele Giordano, Massimo Gazzano, Rita Gamberini, Bianca Rimini, Andrea Munari
A series of random poly(butylene succinate)-based copolymers, (poly(butylene/triethylene succinate) (P(BSmTESn)), containing ether-oxygen atoms were successfully synthesized by melt polycondensation of succinic acid and 1,4-butanediol in the presence of triethylene glycol (TEG) (TEG content up to 40 mol%). The copolymers were characterized from the molecular, thermal, structural and mechanical point of view. Hydrolytic degradation studies were performed under physiological conditions. The biocompatibility of the samples under investigation through indirect and direct biocompatibility studies was investigated by using embryonic rat cardiac H9c2 cells. To evaluate the potential of these polymers also for controlled drug delivery systems, the diffusion profile of Dexamethasone, an anti-inflammatory drug, through nanoparticles prepared by oil-in-water miniemulsion process was investigated. Results showed that solid-state properties could be tailored nicely by simply varying copolymer composition. Crystallinity degree and hydrophobicity significantly decreased with the increase of triethylene succinate co-unit (TES) mol%. Moreover, hydrolytic degradation of PBS, depending on polymer crystallinity degree and hydrophilicity, was remarkably improved: the copolymer containing 40 mol% of triethylene succinate co-unit after 200 days lost over 22% of its initial weight. The newly developed biomaterials showed lack of cell cytotoxicity. Among them, PBS and the copolymers containing up to 20 mol% of TES co-units sustained a better cell adhesion and proliferation. In addition, such copolymers induced muscle phenotype commitment in H9c2 cells cultured onboard. Lastly, the release profile of Dexamethasone obeyed to a first order kinetic law, the copolymer richest in TES co-unit content showing the highest encapsulation capability and the fastest drug release kinetics. Anyway, PBS and the copolymers containing up to 20 mol% of TES co-unis sustained a better cell adhesion and proliferation, with the copolymers characterized by a myosin heavy chain expression, which appeared to be up to twofold increased on respect to the one of PBS homopolymer.
Effect of the addition of polyester-grafted-cellulose nanocrystals on the shape memory properties of biodegradable PLA/PCL nanocomposites Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-10 Valentina Sessini, Iván Navarro-Baena, Marina P. Arrieta, Franco Dominici, Daniel Lopez, Luigi Torre, José M. Kenny, Philippe Dubois, Jean-Marie Raquez, Laura Peponi
In this work the thermally-activated shape memory response of biodegradable nanocomposites based on PLA/PCL blend reinforced with different type of cellulose nanocrystals has been reported, and compared with those of the neat matrix, at the same transition temperature of 55 °C and at the same different deformations, 50%, 100% and 150%. In particular, cellulose nanocrystals have been synthesized and then functionalized by “grafting from” reaction by ring opening polymerization of both PLLA and PCL using the OH groups onto the cellulose nanocrystals surface as initiators for the reaction. The morphology, thermal and mechanical analysis have been performed in order to obtain the parameters for the thermo-mechanical shape memory cycles. Moreover, the addition of the CNC-based nanofillers on the compatibility of PLA-PCL blends in 70:30 proportion has been evaluated. All the biodegradable nanocomposite formulations showed excellent shape memory response, similar to those of the neat matrix, with strain recovery ratio and strain fixity ratio higher than 80% and 90%, respectively. This fact indicates that in this case, the shape memory response of the nanocomposites is mainly controlled by the response of the neat blend and they are slightly influenced by the increase of compatibility between the components of the blend. In addition, all nanocomposite films were fully disintegrated under composting conditions confirming their biodegradable nature, obtaining that the presence of CNC-based nanofillers speeds up the disintegration rate of the nanocomposites in comparison with the pure matrix.
Study on the dehydrofluorination of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) copolymer Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-10 Donghan Li, Mingyi Liao
This study evaluates the dehydrofluorination of fluoroelastomer (poly(VDF-co-HFP) copolymer) which was dissolved by organic solvent and reacted with different concentrations of KOH and different amount of phase transfer catalyst (PTC) at 20–60 °C.The structures, sequence types and contents of double bonds of samples were analyzed and investigated by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy(ATR-FTIR), 1H nuclear magnetic resonance (NMR), 19F NMR spectroscopy and chemical titration method. The results revealed that dehydrofluorination of the studied fluoroelastromers could be carried out at room temperature in alkaline environments, wherein the temperature and alkali concentration were the great factors. And the dehydrofluorination of poly(VDF-co-HFP) copolymer conformed mainly to Zaitsev's rule and partially to Hofmann's rule. The double bonds (–C=C–) would generate in five positions of molecular chains and contents could be controlled. With increase of alkali concentration or reaction temperature, there would be dehydrofluorination accompanied with oxidation reaction whereby some –C=C– converted to hydroxyl groups. Finally, the mechanism of reaction was also deduced.
Synthesis and crystallization of new fully renewable resources-based copolyesters: Poly(1,4-cyclohexanedimethanol-co-isosorbide 2,5-furandicarboxylate) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-10 Nejib Kasmi, Mustapha Majdoub, George Z. Papageorgiou, Dimitrios N. Bikiaris
In this paper, a series of fully biobased poly(1,4-cyclohexanedimethanol-co-isosorbide 2,5-furandicarboxylate)s (PCIsFs) copolyesters have been synthesized from dimethyl-2,5-furandicarboxylate (DMFD), isosorbide (IS) and 1,4-cyclohexanedimethanol (CHDM) by melt polycondensation. The structure of prepared polymers was characterized by 1H-NMR and FTIR spectroscopies. Differential scanning calorimetry (DSC) results indicated that the crystallizability and melting temperature (Tm) of PCIsFs can be controlled with the increasing content of isosorbide furanoate units into the copolyesters structure, whereas their glass transition temperatures (Tg) showed a beneficial increase ranging from 76.8 °C to 103.5 °C. Wide-Angle X-ray Diffractometry (WAXD) patterns revealed that a small portion of isosorbide units are inserted into the crystals of PCHDMF, resulting in increase of the interplanar distances and crystal defects. A banded spherulitic morphology was observed, while coarsening of spherulites and increase in band distance occurred with increasing isosorbide content. Thermogravimetric analysis (TGA) results showed an excellent thermal stability up to 360 °C for all copolymers.
Degradation under composting conditions of lysine-modified polyurethane based on PCL obtained by lipase biocatalysis Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-10 Marina P. Arrieta, Karla A. Barrera Rivera, Castor Salgado, Antonio Martínez Richa, Daniel López, Laura Peponi
Enzymatic polymerization has a large potential as an environmentally friendly synthetic process. Lipase is a renewable catalyst with high catalytic activity from which it is possible to develop a versatile method for the production of sustainable polyurethanes. In this work oligomeric PCL-diol was synthesized using biocatalysis with immobilized Yarrowia lipolytica lipase (YLL) and diethyleneglycol as initiator. Then, two different linear polyurethanes were prepared. One was obtained directly from the previous synthesized PCL-diol and hexamethylene diisocyanate, named PU, and the other one has been obtained by incorporating l-lysine amino acid as end group (lys-PU). PU and lys-PU disintegration under composting conditions was evaluated. The influence of the presence of l-lysine on the disintegration performance of PU was studied by evaluating the disintegration degree, monitoring the weight loss. Structural and morphological changes were followed by Fourier transformed infrared spectroscopy (FTIR) and by scanning electron microscopy (SEM).
Impact of the formulation of biosourced phenolic foams on their fire properties Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-09 C. Delgado-Sánchez, J. Sarazin, F.J. Santiago-Medina, V. Fierro, A. Pizzi, S. Bourbigot, A. Celzard
The fire retardance properties of rigid, biosourced phenolic foams derived from tannins, which are novel, environment-friendly thermal insulators, are essential before the latter can be applied to the building sector. In this work, tannin-based foams prepared from new formulations and using different foaming methods were investigated by thermo-gravimetric analysis (TGA), cone calorimetry, and pyrolysis combustion flow calorimeter (PCFC). It was found that the flammability strongly depends on the formulation, so that tannin foams perform very differently depending on the presence of surfactant and plasticiser and, more importantly, on their initial water content. Moreover, a good correlation was observed between TGA and PCFC results. Nevertheless, due to their highly resistant phenolic, crosslinked, polymer network, all materials released a quite low amount of hydrocarbon fuel during thermal decomposition, leading to low heat release rates and high ignition times, and thus providing very good fire retardance properties. Based on the above, the foam presenting the highest fire retardance was identified, confirming our conclusions about the role of the ingredients in the formulation.
Effects of chain-extending stabilizer on bioplastic poly(lactic acid)/polyamide blends compatibilized by reactive extrusion Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-07 JeongIn Gug, Margaret J. Sobkowicz, James Soule, Bin Tan
The immiscible bio-plastic blend of poly(lactic acid) (PLA) and polyamide11 (PA11 or Nylon11) was compatibilized, using a catalyzed the ester-amide interchange chemical reaction during reactive extrusion. The effects of screw configuration on mixing and reaction optimization were explored. It was found that effective mixing and minimized degradation were achieved when kneading elements were installed only near the die end of the extruder rather than near the beginning of the melt section. However, significant degradation of PLA could not be avoided during processing, which led to a decrease in mechanical strength of blend. To prevent the molecular weight reduction, tris(nonylphenyl) phosphite (TNPP) stabilizer was introduced to improve the thermal stability of PLA matrix. Improvement to both tensile strength and elongation were achieved in the resulting PLA/PA11/TsOH/TNPP blend.
Photo-degradation of electrospun composite mats based on poly(D,l-lactide) submicron fibers and zinc oxide nanoparticles Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-07 Heriberto Rodríguez-Tobías, Graciela Morales, Hortensia Maldonado-Textle, Daniel Grande
Electrospun polymeric mats constitute promising materials in the environmental area as filtering media. However, mats are typically subjected to UV irradiation throughout their use; therefore, investigation related to additives useful for mitigating their photo-degradation is necessary. In this regard, this paper addresses the long-term photo-degradation study of submicron poly (D,l-lactide) (PLA) fibers with embedded or sprayed ZnO nanoparticles which were engineered by means of electro-hydrodynamic techniques, namely electrospinning or electrospinning/electrospraying tandem processes. An extensive physico-chemical characterization of the corresponding PLA/ZnO composite fibers was performed before and after artificial UV agingby ATR-FTIR, SEC, and SEM. It was demonstrated that the ZnO concentration and the electro-hydrodynamic technique utilized had a significant effect on the UV shielding related to the nanoparticles distribution/dispersion achieved. Furthermore, a morphological development as a function of UV aging time was proposed, thus suggesting an optimal life cycle of the PLA/ZnO composite fibers, which could be extremely useful for future applications as UV-activated filtering media.
Behaviour of aeronautical polymer composite to flame: A comparative study of thermoset- and thermoplastic-based laminate Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-06 E. Schuhler, A. Coppalle, B. Vieille, J. Yon, Y. Carpier
The influence of the fire exposure on the degradation mechanism of thin carbon/epoxy and carbon/polyphenylene sulphide (PPS) laminates has been investigated using a propane burner. The burner used in this work is able to provide a controlled and repeatable heating condition, with the test condition of 106 kW/m2 representative of a severe fire condition. Mass loss and temperature measurements made during the fire aggression coupled with post-fire microscopic analysis aim at providing a better understanding of the physical and mechanical changes on laminates depending on matrix nature and different fire-exposure times. For a high heat flux, a 300s fire exposure is more detrimental for the carbon/epoxy sample (22% mass loss) than for the carbon/PPS (6% mass loss) although ATG results show a similar char yield of around 75% under nitrogen for both materials. Observation and analysis of microscopic images after different fire-exposure times fire suggest that the thermal behaviour of the 2 mm thin laminates is driven by the formation of major delamination and macroscopic pores forming a thermal barrier as the analysis of the images indicates a void content 2 to 5 times higher for the carbon/PPS sample than for the carbon/epoxy specimens. On the one hand, the degradation of the thermoplastic PPS matrix into a viscous product seems to trap pyrolysis gases into macroscopic gaseous cells. These porosities provide an efficient thermal barrier protecting the back surface from the flame high thermal flux. On the other hand the degradation of the thermosetting epoxy matrix forms a dry network of carbon fibres and porous char.
Impact of curing time on ageing and degradation of phenol-urea-formaldehyde binder Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-04 D.V. Okhrimenko, A.B. Thomsen, M. Ceccato, D.B. Johansson, D. Lybye, K. Bechgaard, S. Tougaard, S.L.S. Stipp
Phenol-urea-formaldehyde (PUF) resin is one of the most important thermosetting polymers. It is widely used in many industrial and construction applications as an organic coating and adhesive. For example, in production of mineral wool for insulation, PUF is used together with the coupling agent (3-aminopropylsilane, APS) and serves as a binder for attaching mineral fibers to each other and to create the necessary mechanical integrity and shape of the final product. However, during ageing under high humidity (95%) and temperature (70 °C), hydrolysis can degrade PUF, decreasing product quality. A better understanding of the chemical processes caused by hydrolysis would promote development of more stable PUF binders. We investigated the composition and stability changes during ageing of cured PUF powder binder and mineral wool fibers where PUF binds the fibers together. We aged the samples in hot water (80 °C) or in a controlled climate chamber (70 °C; 91% RH) and analyzed them using X-ray photoelectron spectroscopy (XPS), element analysis and thermogravimetric (TG) analysis. We investigated the composition of species released from PUF during hydrolysis by electrospray ionization (ESI) of the aqueous solutions. The results show that the extent of PUF curing and the presence of APS as the coupling agent have an important impact on its stability. XPS revealed that poorly cured PUF contains a high fraction of NH CH2 O CH2 NH bonds which are easily hydrolyzed, while longer curing results mostly in more stable methylene bridges, NH CH2 NH . We also observed evidence for urea NH CO bond decomposition by ESI analysis. Mineral wool fiber ageing studies showed that PUF rearranges on the fiber surface and detaches from it, together with the APS coupling agent. This improved understanding of the effects of ageing provides clues for designing a more robust binder, leading to increased quality and stability of mineral wool insulation.
Isolation and role of polylactic acid-degrading bacteria on degrading enzymes productions and PLA biodegradability at mesophilic conditions Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-04-03 Tiparporn Bubpachat, Narongrit Sombatsompop, Benjaphorn Prapagdee
Enumeration and isolation of polylactic acid (PLA)-degrading bacteria from soils and wastewater sludge were performed on emulsified PLA agar. Two isolates of potent PLA-degrading bacteria, designated as CH1 and WS3, were selected and identified as Stenotrophomonas pavanii and Pseudomonas geniculata, respectively. PLA was presented as a substrate to stimulate production of protease and PLA-degrading enzyme by S. pavanii CH1 and P. geniculata WS3. The optimal pH values for both protease and PLA-degrading enzyme production by S. pavanii CH1 and P. geniculata WS3 were 7.5 and 8.0, respectively. The optimal gelatin concentrations for stimulating protease production in S. pavanii CH1 and P. geniculata WS3 were 0.3% (w/v), while those for PLA-degrading enzyme production in S. pavanii CH1 and P. geniculata WS3 were 0.1 and 0.3% (w/v), respectively. In addition, P. geniculata WS3 had a higher percentage of PLA film-weight loss than that of S. pavanii CH1, corresponding with reduced molecular weight of PLA. A significant increase of lactic acid content in culture broth was directly correlated with the increasing percentage of PLA film-weight loss. Our results clearly demonstrated that P. geniculata WS3, a novel isolated bacterium, has played a substantial role in PLA biodegradation by producing PLA-degrading enzyme and adhering on PLA surface.
Rheological properties, oxidative and thermal stability, and potential application of biopolyols prepared via two-step process from crude glycerol Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-28 Aleksander Hejna, Paulina Kosmela, Marek Klein, Kamila Gosz, Krzysztof Formela, Józef Haponiuk, Łukasz Piszczyk
In this work, previously synthesized biopolyols were analyzed in terms of their rheological and thermal properties, very important from the technological point of view. For better evaluation of performed synthesis, the influence of its time and temperature on the properties of biopolyols was determined. In the end, obtained materials were used to prepare rigid polyurethane-polyisocyanurate (PUR-PIR) foams, to evaluate their potential application in polymer technology. Presented results fully justified conducting of synthesis in two steps. Biopolyols obtained after second step of synthesis were characterized by two times lower viscosity than polyglycerols resulting from first step. Moreover, their thermal and oxidative stability was noticeably higher and enabled their effective incorporation into manufacturing of PUR-PIR foams. Spectroscopic and microscopic analysis confirmed that foams were successfully obtained from polyglycerols and biopolyols, however, there were noticeable differences in the mechanical performance of prepared materials. Partial substitution of petrochemical polyol with polyglycerol resulted in the decrease of compressive strength, comparing to reference sample, while incorporation of biopolyols noticeable enhanced that parameter.
Growth associated degradation of aliphatic-aromatic copolyesters by Cryptococcus sp. MTCC 5455 Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-27 Mayilvahanan Aarthy, Puhazhendi Puhazhselvan, Ramchary Aparna, George Sebastian Antony, Marichetti Kuppuswami Gowthaman, Niraikulam Ayyadurai, Kazuo Masaki, Toshiaki Nakajima-Kambe, Numbi Ramudu Kamini
Halloysite nanotubes and thymol as photo protectors of biobased polyamide 11 Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-27 Giuliana Gorrasi, Valeria Bugatti, Martina Ussia, Raniero Mendichi, Daniela Zampino, Concetto Puglisi, Sabrina Carola Carroccio
The formulation of cost-effectiveness sustainable materials is extensively growing and becoming an attractive approach for both industrial and academic fields. In this context, the bio-based aliphatic polyamide 11 (PA11) has acquired significant interest as environmentally friendly thermoplastic option. In addition, its formulation with selected natural antioxidant and/or reinforced compounds through green processing methods, might improve physical and mechanical properties without sacrificing the intrinsic bio-based nature of the matrix. In this work, we have investigated and compared the photo-oxidative degradation processes occurring on PA11 composites based on thymol and halloysite nanotubes prepared by using ball-milling method. In particular, halloysite nanotubes were used as green nano-container of a natural antioxidant molecule, and reinforced nano-filler as well. Molecular and structural information of photo-exposed samples were obtained by using size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Thermal and mechanical properties were also tested as well as thymol release. Data collected confirmed that PA11 filled with HNTs-Thymol nano-hybrid showed superior durability performance if compared to both pure PA11 and PA11 blend realized by simply adding thymol and HNTs to polymer matrix. Furthermore, we found that HNTs and thymol combined in the nano-hydrid form exhibited an active and synergic role to achieve a major photo stabilization of PA11 biocomposite, without sacrificing its mechanical properties.
Synthesis and application of synergistic azo-boron-BPA / polydopamine as efficient flame retardant for poly(lactic acid) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-26 Benjamin Tawiah, Bin Yu, Wai Yi Cheung, Shuk Ying Chan, Wei Yang, Bin Fei
PLA (Polylactic acid) as a bioplastic polymer has limited applications in areas that require high fire safety due to its inherent flammability and dripping when exposed to flames. In this paper, azo-boron-BPA (AZ-A) and polydopamine (PDA) were synthesized, characterized and incorporated into PLA using the solvent approach and hot compression molding. Nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR) and Raman spectra showed that AZ-A and PDA were successfully synthesized. The flame retardant (FR) properties of synergistic AZ-A/PDA were investigated by vertical burning test, limiting oxygen index (LOI), cone calorimeter and thermogravimetric analysis (TGA). TGA analysis showed that synergistic AZ-A/PDA was generally more efficient in reducing the degradation rate of PLA and gave appreciably much higher char residue compared to the individual FR components. The synergistic AZ-A/PDA achieved V-0 rating with LOI value of 23.7% at 10 wt% loading in the ratio 1:1 whereas the individual FR components could only give a V-2 rating. The AZ-A/PDA synergy also resulted in an obvious reduction in PHRR (up to 19%) with increased residue (up to 17.7%). This research work will contribute to and expand the frontiers of knowledge in flame retardant azo boron compounds and their synergies for PLA.
Reactive compatibilization and melt compounding with nanosilicates of post-consumer flexible plastic packagings Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-26 E. Garofalo, L. Di Maio, P. Scarfato, F. Di Gregorio, L. Incarnato
Flexible plastic packagings are rapidly gaining market share since they offer significant functional benefits. However, they also pose a challenge from a recycling perspective. In fact, due to the presence of different polymeric fractions and to contamination by organic substances and out-of-target materials, such as paper and metals, the mechanical properties of the recycled material are relatively poor. Addition of nanoparticles to plastic waste can offer the combinations of improved properties and processing, and reduce operational cost. Moreover, in recent studies it was demonstrated that they can also act as blend compatibilizers. The aim of this study is the upgrading of Fil-s (acronym for film-small), a fraction of mixed plastic waste stream obtained by the separation and mechanical recycling of post-consumer packaging films of small size. Physical, chemical and rheological characterization evidenced that Fil-s stream is mainly composed of polyethylene and a smaller fraction of polypropylene. With the purpose to improve the performances of Fil-s, lamellar and acicular organoclays were melt compounded with the recycled material in a twin-screw extruder. Moreover, in order to enhance the compatibility between the polyolefin components and the nanofiller dispersion in the mixed polymer matrix, the functionalization of Fil-s with maleic anhydride (MAH) was realized by reactive extrusion. Morphological, thermal, rheological and mechanical properties of the functionalized materials and the nanocomposite systems were extensively discussed. The positive effect of the MAH-grafting on the compatibilization between the two polyolefin components of Fil-s was pointed out and an interesting improvement in ductility of Fil-s was obtained. The further addition of the nanoclays also significantly increased the stiffness of the systems.
Towards understanding the breakdown and mechanisms of glass fiber reinforced polyester composites in sub-critical water using some of the most employed and efficient additives from literature Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-26 Hülya U. Sokoli, Morten E. Simonsen, Erik G. Søgaard
This study describes the hydrolysis of glass fiber reinforced unsaturated polyester (UP) composites using some of the most employed and efficient additives from the literature. This includes the use of KOH, a mix of KOH/phenol and reference experiments without additives. Sub-critical water in a temperature range of 200–325 °C and a constant pressure of 300 bar were chosen as process parameters to cover a wide temperature range. It was possible to explain the mechanisms producing the majority of the different reaction products identified by GC-MS. The monomer phthalic anhydride was only recovered in the experiments without additives and was most stable at 200–250 °C. The increase or decrease in the production of monomers and other reaction products at different temperatures with and without additives has been clarified by the GC-MS investigations, which introduces new possibilities for tailoring the production of monomers and various chemical compounds via hydrolysis of polymer composites.
Layer-by-layer assembly of efficient flame retardant coatings based on high aspect ratio graphene oxide and chitosan capable of preventing ignition of PU foam Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-19 Lorenza Maddalena, Federico Carosio, Julio Gomez, Guido Saracco, Alberto Fina
The layer-by-layer (LbL) technique is adopted for the construction of multilayers encompassing chitosan and graphene oxide (GO) platelets capable of improving the flame retardant properties open cell PU foams. The LbL assembly follows a linear growth regime as evaluated by infrared spectroscopy and yields a multilayer structure where GO platelets are embedded within a chitosan continuous matrix. 3 and 6 bi-layers (BL) can efficiently coat the complex 3D structure of the foam and substantially improve its flame retardant properties. 3BL only add 10% to the original mass and can suppress the melt dripping during flammability and reduce both the peak of heat release rate by 54% and the total smoke released by 59% in forced combustion tests. Unprecedented among other LbL assemblies employed for FR purposes, the deposition 6BL is capable of slowing down the release of combustible volatile to the limits of non-ignitability thus preventing ignition in half of the specimens during cone calorimetry tests. This has been ascribed to the formation of a protective coating where the thermally stable char produced by chitosan serves as a continuous matrix embedding GO platelets, which control volatile release while mechanically sustaining the PU foam structure.
Flame retardant efficiency of KH-550 modified urea-formaldehyde resin cooperating with ammonium polyphosphate on polypropylene Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-19 Ying Ren, Dandan Yuan, Wenmin Li, Xufu Cai
This paper surveys the char forming effect of urea-formaldehyde resin (UF) and the flame retardancy of UF cooperating with ammonium polyphosphate (APP) for polypropylene (PP). UF was firstly synthesized and then modified by a silane coupling agent 3-aminopropyltriethoxysilane (KH-550). UF and KH-550 modified urea-formaldehyde resin (M-UF) were characterized by field-emission scanning electron microscope (FE-SEM), energy-dispersive analysis (EDS), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Compared with UF, M-UF had better thermal stability and higher mass of residue char. Afterwards the intumescent flame retardants (IFRs), consisting of UF + APP and M-UF + APP respectively, were introduced into PP. The flame retardant efficiency of PP composites was investigated by limiting oxygen index (LOI), UL-94 vertical burning, and micro combustion calorimetry (MCC). The possible decomposition mechanisms were investigated by TGA, FT-IR and EDS. When the addition of PP, APP and UF was 70, 24 and 6 wt%, the LOI value reached 23.5 and UL-94 test could not pass. However, when the loading of PP, APP and M-UF was 70, 20 and 10 wt%, the LOI value reached 29.5 and UL-94 test was V-0. The residual char layers of some PP composites were analyzed by Laser Raman spectroscopy (LRS) and FE-SEM. The LRS and FE-SEM presented that the char layer of 20%APP+10%M-UF/PP was more compact and had higher strength than 20%APP+10%UF/PP. Furthermore, tensile tests showed that M-UF/APP could improve break strength and toughness for PP compared with the same ratio of UF/APP. To sum up, M-UF + APP/PP have better flame retardant efficiency and tensile properties compared with UF + APP/PP.
Influence of tannin containing coatings on weathering resistance of wood: Water based transparent and opaque coatings Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-03-16 Eylem D. Tomak, Ferhat Arican, Oktay Gonultas, Ebru D. Sam
The aim of this study was to improve weathering resistance of Scots pine wood by treating the surfaces with water based transparent and opaque wood coatings containing valex, mimosa and pine tannins. Samples coated with tannin containing coatings with various concentrations were exposed to artificial weathering for 1512 h. Color, gloss, surface roughness and macroscopic changes were evaluated periodically during the test, and the results of coated samples were compared with controls. Visible surface degradations such as erosion, cracks and checks occurred on control samples while no crack formations were recorded for coated samples. Color measurement data showed that high concentration levels were needed for the least color change on the surfaces however concentration increase of tannins in the transparent coating affected surface gloss and roughness of samples negatively. The most promising tannin types in transparent coatings against the surface degradations were determined as valex and pine tannins. Opaque coating alone was found to be resistant against weathering factors, and the measurements clearly showed that there is no need to corporate any UV absorbers to this coating.
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