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  • Biodegradation of linear and branched nonisocyanate condensation polyurethanes based on 2-hydroxy-naphthalene-6-sulfonic acid and phenol sulfonic acid
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-16
    A. Białkowska, M. Bakar, O. Marchut-Mikołajczyk

    The present work investigates the biodegradation of nonisocyanate condensation polyurethanes (NIPU) by aerobic bacterial strains (Achromobacter xylosoxidans G21). The study was conducted on linear and branched polyurethanes prepared from oligoetherol, urea, phenolsulfonic acid, 2-hydroxynaphthalene-6-sulfonic acid and various amounts of formaldehyde. The tensile strength, pH, emulsification and protein concentration were determined during the biodegradation of the prepared polymers. FTIR and DSC were employed for the structure characterization of the tested samples and SEM for the morphology analysis. It was confirmed that the regularity of the structure and the increasing degree of cross-linking of the polymer led to the increase in resistance to bacteria. Based on the elemental analysis, DSC and FTIR, it was found that urea, urethane and sulfonic groups which formed the crystalline regions were subjected to biodegradation. SEM micrographs have shown the disappearance of ordered hard domains. Besides the pronounced biodegradation resistance, synthesized NIPU exhibited acceptable performance properties (tensile strength and strain at break before and after biodegradation). The tensile strength of branched polyurethanes increased with the increasing amount of formaldehyde due to an increased degree of crosslinking.

    更新日期:2018-11-16
  • Preparation and properties of biobased autocatalytic polyols and their polyurethane foams
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-16
    Shuping Huo, Can Jin, Guifeng Liu, Jian Chen, Guomin Wu, Zhenwu Kong

    In the present work, we developed a green and more efficient method to prepare biobased polyurethane (PU) foams under catalyst-free condition. Firstly, novel organosilicon grafting cardanol-based autocatalytic polyols (SCAPs) with low viscosity were synthesized through the ring opening of cardanol glycidyl ether (CGE) and the hydrosilation of unsaturated alkyl chain with heptamethyltrisiloxane (HMTS). Subsequently, PU foams were synthesized by SCAPS in absence of catalyst. The structure and properties of the PU foams were evaluated and discussed. In addition, the thermal degradation mechanism of PU foams was investigated by using a thermogravimetric analysis instrument coupled with fourier transform infrared and mass spectrometer (TG-FTIR-MS). The results showed that the PU foams had high compression strength and thermo-stability.

    更新日期:2018-11-16
  • Enzyme- and cell-mediated degradation of poly(ethylene carbonate) by surface erosion
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-16
    Adam Bohr, Kaveh Memarzadeh, Necati Harmankaya, Moritz Beck-Broichsitter

    Poly(ethylene carbonate) (PEC) is a biodegradable polymer with attractive properties for controlled drug delivery applications. However, the mechanisms by which the polymer is degraded and the control hereof are not yet completely understood. Here, we investigated the degradation behavior of PEC films in vitro in the presence of distinct enzymes, cells, bacteria and tissue homogenates.PEC was degraded by a surface erosion process (constant molecular weight with an almost linear mass loss during incubation). Of the enzymes tested, only cholesterol esterase from porcine pancreas and lipase from Thermomyces lanuginosus caused significant polymer erosion. Enzymatic degradation was arrested by the addition of a protease inhibitor cocktail. Furthermore, PEC films, which were exposed to the macrophage cell lines RAW 264.7 and J774.1 showed a rapid degradation profile. The polymer erosion process triggered by phagocytes was dose-dependently diminished in the presence of vitamin C. When PEC films were incubated with pancreas homogenate no measurable degradation by mass was detected. However, scanning electron microscopy analysis showed signs of erosion on the surface of the polymer samples.Overall, this study identified specific enzymes, cells and organ homogenates, which degraded PEC in vitro and thus, should be involved in the clinical picture to facilitate an on-demand drug release at the diseased site of action. Application of enzyme inhibitors and antioxidants further highlighted the relevant role of radicals during macrophage-triggered degradation of PEC.

    更新日期:2018-11-16
  • Model of aliphatic polyesters hydrolysis comprising water and oligomers diffusion
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-16
    P.I. Borovikov, A.P. Sviridov, E.N. Antonov, A.G. Dunaev, L.I. Krotova, T.H. Fatkhudinov, V.K. Popov

    The work is dedicated to the development of mathematical models of hydrolysis of aliphatic polyesters in aqueous media under conditions of water and oligomers diffusion. Water molecule is considered as a reagent in hydrolysis reactions, oxidation reactions and influence of the autocatalytic channel are taken into account. The analysis of the spatiotemporal distribution of molecular weight of the polymer depending on the hydrolysis reaction rate constants, the diffusion coefficients of water and short oligomers has been carried out. In case of large water diffusion coefficients, the heterogeneous channel of polymer hydrolysis is actually described by the equation of pseudo-first order, as in most modern models, and occurs predominantly in the volume (V-type). With the decreasing water diffusion coefficient, the participation of water as a reagent becomes very important. The resorption of the polymer occurs mainly near the surface (S-type). The comparison/verification of the developed computer model has been carried out basing on experimental data for molecular weight dynamic of monolithic polylactoglycolide samples (75:25) of different thicknesses in phosphate-buffer saline. The choice of kinetics parameters of hydrolysis reactions and diffusion coefficients of water and oligomers has been justified by fitting of experimental and model data.

    更新日期:2018-11-16
  • Reduction of poly(hydroxybutyrate-co-hydroxyvalerate) secondary crystallisation through blending with saccharides
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-16
    Mike J. Jenkins, Annabel V.L. Fitzgerald, Catherine A. Kelly

    A significant problem associated with the use of polyhydroxybutyrate and its copolymers in food packaging is their high initial crystallinity coupled with an ability to undergo secondary crystallisation over time which results in progressive embrittlement. This paper details work undertaken to hinder the secondary crystallisation process through the blending of poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-co-HV) with mono-, di- and tri-saccharides. Following blending, the melt viscosity and melting point were observed to decrease with increasing saccharide concentration. The incorporation of saccharides into PHB-co-HV did not completely prevent the secondary crystallisation process, however, the rate of change in the Young's modulus and ultimate tensile stress were significantly reduced. The percentage change in the mechanical properties of these blends was found to be directly related to the size of the saccharide which was deemed to be as a result of greater steric hindrance and an increasing number of hydroxyl groups available for interaction with PHB-co-HV. This, along with the reduction in melt viscosity and melting point, makes the addition of mono, di and tri saccharides worthwhile for improving the processability and prolonging the effective life time of products made from PHB-co-HV.

    更新日期:2018-11-16
  • Biodegradation of poly(3-hydroxybutyrate)-derived polymers with different 4-hydroxybutyrate fractions by a novel depolymerase from Paecilomyces sp. 1407
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-16
    Fan Li, Ziqi Guo, Na Wang, Hongmei Xia, Dongbo Liu, Shan Chen

    A poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)]-degrading strain was isolated and identified as Paecilomyces sp. A novel P(3HB-co-4HB) depolymerase with a molecular weight of 55 kDa was purified by column chromatography from the culture supernatant of the strain. The purified depolymerase showed optimum activity at pH 6.0 and 30 °C, and it was stabilized at pH 4.0–7.0 and below 40 °C. The depolymerase degraded poly(3-hydroxybutyrate) (PHB), poly(hydroxybutyrate-co-hydroxyvalerate), and several short-chain-length esters other than P(3HB-co-4HB) but showed no remarkable activity on poly(ε-caprolactone) and poly(L-lactic acid). The main enzymatic products comprised hydroxybutyrate monomers, including 3HB and 4HB. The enzymatic erosion rate on the films increased markedly with increasing fraction of 4HB units. Enzymatic hydrolysis processes of PHB and P(3HB-co-4HB) were systematically analyzed in three aspects: enzyme adsorption, single-polymer-chain dissociation, and chemical linkage breakdown. Results indicate that 4HB insertion caused no effect on the degradation of solid-phase PHB-derived material at the molecular chain level but affected enzyme adsorption and crystallinity of the materials. Hindering single-chain stripping by crystallinity dominantly affects the degradation behavior of the polymer.

    更新日期:2018-11-16
  • Effect of metal oxides on the thermal degradation of polychloroprene and chlorosulfonated polyethylene
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-15
    Bidur Rijal, Florian Klipfel, Isabelle Dez, Jean Colin, Philippe Bazin, Franck Arethuse, Emmanuel Tellier, Loïc Le Pluart

    Polychloroprene (PCP) and chlorosulfonated polyethylene (CSM) rubbers undergo a multiple step degradation pathway involving a common dehydrochlorination step which causes HCl release from the macromolecules as evidenced by thermogravimetric analyses associated with operando FTIR analyses. Dehydrochlorination is detected at lower temperatures for CSM than for PCP. It is preceded by non-simultaneous and very distinctive desulfonation reaction at even lower temperatures as shown by chemical analyses of the evolved phase during a thermal treatment. Incorporation of Bi2O3, La2O3 and WO3 as potential fillers for lead-free radioprotective materials leads to diverse effect on the thermal stability of these rubbers. Whereas transition metal oxides do not affect the degradation mechanisms, bismuth oxide strongly promotes the dehydrochlorination reaction leading to a decrease of the rubbers thermal stability which is detrimental to the potential processability and recyclability of these materials.

    更新日期:2018-11-15
  • Plasticizer incorporated, novel eco-friendly bio-polymer based solid bio-membrane for electrochemical clean energy applications
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-15
    P. Perumal, P. Christopher Selvin, S. Selvasekarapandian, P. Sivaraj, K.P. Abhilash, V. Moniha, R. Manjula Devi

    High-molecular-weight, carbohydrate based Solid Biopolymer Electrolyte (SBE) pectin-lithium perchlorate [C6H10O7:LiClO4 = 60:40 M mass percentage (m.m.%)] with ethylene carbonate (EC) as plasticizer has been prepared by simple solution casting technique. Addition of EC results in enhanced electrochemical window from 3.39 V to 3.55 V. The flexibility of the SBE is also improved which leads to attain an enriched ionic conductivity of 3.89 × 10−4 Scm−1 in the sample with optimum salt and plasticizer composition. The eco-friendly membrane with highest conductivity contributes good cycling properties and possesses higher value of cationic transference number when compared with other electrolyte samples. A lithium ion conducting battery constructed using the highly conducting polymer membrane sample is used to light up the red LED, display an Open Circuit Voltage (OCV) of 1.65 V.

    更新日期:2018-11-15
  • The effect of gamma-irradiation on morphology and properties of melt-spun poly (lactic acid)/cellulose fibers
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-15
    Tassadit Aouat, Mustapha Kaci, José-Marie Lopez-Cuesta, Eric Devaux, Mohamed Mahlous

    The effect of gamma irradiation on both morphology and properties of neat poly(lactic acid) (PLA), PLA/microcrystalline cellulose (MCC) and PLA/cellulose nanowhiskers (CNW) fibers loaded at 1 wt% filler content was investigated in presence of PLA-grafted maleic anhydride (PLA-g-MA) used as the compatibilizer. Multifilament yarns were prepared by a melt-spinning process and subjected to gamma irradiation at various doses from 5 to 30 kGy keeping the dose rate at 1.92 kGy/h under ambient conditions. Chemical structure, morphology and property changes induced by gamma irradiation on the samples were evaluated by several techniques considering the filler aspect ratio effect. The results showed a dose-related increase in the scission index (SI) of the irradiated samples whatever the filler size, while thermal and tensile properties significantly decreased. However, the incorporation of cellulosic fillers in PLA fibers, in particular MCC, was found to hinder the radiolytic degradation process of the irradiated samples.

    更新日期:2018-11-15
  • The photo-stability of acrylic tri-block copolymer blends for the consolidation of cultural heritage
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-14
    Chelsey A. Del Grosso, Johannes A. Poulis, E. René de la Rie

    A variety of adhesives are used for the conservation of paintings. These materials include natural adhesives such as animal glues, waxes, and gums which may chemically degrade over time resulting in unwanted discoloration and mechanical failure. Synthetic adhesives have been introduced to address these concerns. However, most consolidating adhesives have not been specifically formulated and tested to meet the high demands of conservation, ultimately resulting in undesirable physical and mechanical properties. Additionally, some synthetic adhesives are less stable and may cross-link making it difficult to remove years after application. This paper investigates the photo-stability of commercially available tri-block acrylic copolymers (PMMA-PnBA-PMMA) to assess their potential long-term serviceability as consolidants for flaking paint. These copolymers were combined with synthetic low molecular weight resins to reduce viscosity of the adhesive and provide tack. The polymer blends underwent accelerated aging under simulated indoor conditions. Blends were analysed for degradation using Fourier-transform infrared spectroscopy and size exclusion chromatography. Upon irradiation, acrylic copolymers (PMMA-PnBA-PMMA) undergo shifts to higher and lower molecular weight, suggesting that degradation occurs by polymer cross-linking and chain scission. Furthermore, the acrylic copolymer degradation rate was influenced by the type of low molecular weight resin. However, with the addition of a hindered amine light stabilizer these blends exhibited minimal changes in molecular weight. Lastly, the peel strength of the blends were investigated and shown to have comparable peel strength to a popular commercial material, Paraloid™ B-72, often used in consolidation thus showing their promise for use within cultural heritage.

    更新日期:2018-11-14
  • Tough and biodegradable thermosets derived by blending of renewable resource based hyperbranched epoxy and hyperbranched polyester
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-13
    Aditi Saikia, Deepshikha Hazarika, Niranjan Karak

    Renewable resource derived polymers are the most widely explored polymers from the past two decades because of their non-toxicity and environment-friendly nature. Therefore, in the present study blends from two different bio-based polymers with the special architecture, viz. hyperbranched epoxy and hyperbranched polyester were prepared by mechanical mixing at different weight ratios. The prepared blends were characterized by Fourier transform infrared spectroscopy and X-ray diffraction technique. The thermosets of these blends showed good tensile strength (14.9 MPa), elongation at break (274%), impact resistance (21.3 kJ/m2), scratch resistance (up to 6.5 kg) and thermal (Onset temperature: 224 °C) properties indicating improvements in flexibility and thermostability up to an appreciable extent. The blends also showed good biodegradability when exposed to gram positive and gram negative bacterial stains.

    更新日期:2018-11-13
  • Morphological structure, impact toughness, thermal property and kinetic analysis on the cold crystallization of poly (lactic acid) bio-composites toughened by precipitated barium sulfate
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-11
    Ji-nian Yang, Yu-xuan Xu, Shi-bin Nie, Guo-jun Cheng, Yu-lun Tao, Jin-bo Zhu

    The bio-composites of poly (lactic acid) (PLA) involving a varied mass fraction of precipitated barium sulfate (BaSO4) were prepared via melt-compounding and subsequent injection molding. The morphologies, impact toughness and thermal properties of the composites were investigated carefully, and the toughening mechanism was emphasized by a combination of BaSO4 content and the crystallization ability. Results showed that an adequate amount of BaSO4 could disperse homogeneously in PLA matrix with well-bonded interfaces. The impact toughness was increased significantly by 52.7% due to added inorganic particles as well as the increased actual crystallinity of the composites. The added BaSO4 let the cold crystallization occur earlier (shifting to low temperature) while suppressing the cold crystallinity of PLA phase. Such inhibition effects derived from the increased inorganic filler were then further explored and confirmed by the kinetic analysis on the cold crystallization under non-isothermal conditions. Indeed, the added BaSO4 increased the crystallization half-time and crystallization parameter of F(T) based on Mo equation. Moreover, the activation energy on cold crystallization was strengthened along with the increasing BaSO4. It seemed that there is little change in the reaction order of PLA/BaSO4 bio-composites, following the unique reaction thermal decomposition, whereas the activation energies were decreased steadily based on Carrasco method.

    更新日期:2018-11-12
  • The crystallinity and thermal degradation behaviour of polyamide 6/Oil Based Mud Fillers (PA6/OBMFs) nanocomposites
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-10
    Shohel Siddique, Lorraine Kwoffie, Kofi Addae-Afoakwa, Kyari Yates, James Njuguna

    The crystallinity and thermal degradation behaviours of Polyamide 6/Oil Based Mud Fillers (PA6/OBMFs) nanocomposites have been investigated using DSC and TGA. TGA indicates the onset decomposition temperature of D1/2 (half-decomposition) is 16 °C higher for PA6 with 10.0 wt% of OBMFs than that of PA6, whereas the lowest onset decomposition temperature difference among the nanocomposites and neat PA6 is 8 °C for PA6 with 7.5 wt% of OBMFs. However PA6 with 5.0 wt % OBMFs nanocomposite has taken the longest time (1 min 36 s more than neat PA6) to reach D1/2. It can be deduced in this study that PA6 with 5.0 wt % OBMFs nanocomposite provided the maximum heat resistant property whereas PA6 with 7.5 wt % OBMFs nanocomposite showed the maximum heat absorbance property among different nanocomposites and PA6 with 10.0 wt % exhibited the maximum thermal stability. There is a sigmoidal curve generated based on the TIF and wt% filler content value which shows three significant points at intersections of 50% TIF line which are highlighted as exfoliation (4.2 wt%), intercalation (6.8 wt%) and agglomeration (9.0 wt%) points. These TIF values explained the investigated heat resistant, heat capacity and thermal stability properties of PA6/OBMFs nanocomposites illustrating the ratio of TIF and MAF is the key measure which can be considered as an effective approach to identify the nanomorphology of PA6/OBMFs nanocomposites.

    更新日期:2018-11-10
  • Hydrolytic degradation of branched PLA produced by reactive extrusion
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-09
    Heather Simmons, Marianna Kontopoulou

    Reactive extrusion using dicumyl peroxide (DCP) and a tri-functional coagent, triallyl trimesate (TAM) is implemented to introduce long-chain branching (LCB) in poly(lactic acid) (PLA). The effects of this modification on the long-term hydrolysis of PLA are assessed by monitoring the mass, molar mass distributions, and thermal properties of specimens exposed to hydrolytic degradation at a temperature of 60 °C. A slow initial rate of mass loss coupled with an immediate and rapid loss in molar mass are characteristic of a bulk erosion mechanism. Significant loss is observed in all molar mass averages within the first 20 days. In LCB PLA the most drastic decrease was observed in the z-average molar mass, Mz, as a result of the cleavage of the LCB segments from the polymer chain. Degradation induced crystallinity is observed in all formulations, attributed to the combined influence of annealing and the plasticizing effect of water. Although the hydrolysis profile was altered, reactive modification does not affect negatively the degradability of LCB PLA over a 12-week period, suggesting that these modified PLAs can be used in commodity applications that require degradable polymers.

    更新日期:2018-11-09
  • Synergistic effect of (3-Aminopropyl)Trimethoxysilane treated ZnO and corundum nanoparticles under UV-irradiation on UV-cutoff and IR-absorption spectra of acrylic polyurethane based nanocomposite coating
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-09
    Mhd Abd Cader Mhd Haniffa, Yern Chee Ching, Cheng Hock Chuah, Kuan Yong Ching, Liou Nai-Shang

    ZnO and corundum (α–Al2O3) nanoparticles were successfully synthesized by aqueous precipitation and sintering techniques respectively. ZnO nanoparticles were effectively coated with (3-aminopropyl)trimethoxysilane (APTMS) by polycondensation method to prevent the photocatalytic activity of ZnO during a UV-weathering study. X-ray diffractogram and FTIR were used to confirm the crystalline structure of as prepared nanoparticles, blue shift of the AlO bond and the formation of a secondary amine via polycondensation of APTMS over ZnO surface. The prepared APTMS-ZnO, corundum and commercially available surface modified hydrophobic SiO2 (M − SiO2) nanoparticles were used to prepare the acrylic polyurethane (AP: Poly-Macrynal® SM 510 N coating resign) bases nanocomposite coating on a polyurethane substrate. Individual and mixed nanoparticles were dispersed into acrylic polyurethane to prepare the coating layer on polyurethane film substrate separately. IR-active and UV–visible regions of the FTIR and UV–Vis spectroscopies were used to investigate the synergistic effect of the nanoparticles on a selected range of the radiative spectrum, especially the UV-resistant and IR-absorption properties of the coated films with and without exposure of UV-irradiations. Polyurethane substrate coated with APTMS-ZnO (2 wt%) based acrylic polyurethane-based nanocomposite coating (APUC) layer containing 2 wt% corundum (D50) and 6 wt% M − SiO2 (F50) exhibited 98.77% and 97.60% of UV-resistant property respectively. These results indicate that the visible light transparency and transmittance ability reduced significantly after 500 h of UV-irradiation exposure. Both of the activity and deformation have great impact on the IR-absorption property of the APUC.

    更新日期:2018-11-09
  • Effects of chemical composition on the in vitro degradation of micelles prepared from poly(D,L-lactide-co-glycolide)-poly(ethylene glycol) block copolymers
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-09
    Feng Su, Chenglong Li, Rongye Li, Peng Yun, Yuandou Wang, Laishun Xi, Yangsheng Chen, Suming Li

    In this work, a series of poly(D,L-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) diblock copolymers with relatively short PLGA blocks were synthesized by ring-opening polymerization of D,L-lactide and glycolide in the presence of monomethoxy PEG with Mn of 2000. Spherical micelles were obtained by self-assembly of copolymers using direct dissolution method. The degradation of the micelles was investigated under in vitro conditions at 37 °C. The effects of chemical composition on micelle degradation were evaluated from NMR, GPC, DLS and TEM measurements. The molar mass of copolymers constantly decreases during degradation in all cases. The copolymers with longer hydrophobic PLGA blocks exhibit larger molar mass decrease rate since only the PLGA block is degradable. Meanwhile, the molar mass distribution remains almost unchanged, in agreement with random chain cleavage. NMR spectra show that the final degradation products are lactic acid and glycolic acid. A pH decrease is also detected during degradation. The size of the micelle depends on the chemical composition of copolymers. Micelle size is smaller for copolymers with longer hydrophobic PLGA blocks because of more compact core structure. With the hydrolysis of the PLGA blocks, the structure of micelles becomes looser, and the micelle size exhibits a sharp increase after a lag time. At the later stage of degradation, the size of micelles decreases as they become unstable and could collapse. The micelle structure could be clearly distinguished after 45 days degradation for copolymers with longer PLGA blocks, whereas those with shorter PLGA blocks lost the structural integrity. It is also noteworthy that the LA/GA ratio has little effect on the degradation of PLGA-PEG copolymer micelles, which may be related to the amorphous structure of PLGA block and the relatively short block length. These findings should be helpful for the conception of drug delivery systems based on PLGA-PEG micelles.

    更新日期:2018-11-09
  • Effects of heat treatment on the chemical compositions and thermal decomposition kinetics of Japanese cedar and beech wood
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-08
    Yi-Chi Chien, Teng-Chun Yang, Ke-Chang Hung, Cheng-Chun Li, Jin-Wei Xu, Jyh-Horng Wu

    This study investigated variations in the chemical compositions and thermal decomposition kinetics of Japanese cedar and beech wood during heat treatment. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra revealed that various reactions, such as hemicellulose deacetylation, condensation reactions causing lignin cross-linking, and reductions in cellulose amorphous regions, were carried out during the heat treatment process. In addition, combinations of FTIR spectra and principal component analysis (PCA) succeeded in discriminating the major changes in functional groups of wood at various heat treatment temperatures. On the other hand, the decrease in the storage modulus of wood was more rapid in the presence of oxygen than in an oxygen-free atmosphere during heat treatment. Accordingly, the activation energies of thermal decomposition using Arrhenius model for Japanese cedar and beech were 120.6 and 141.3 kJ/mol under air, respectively, while these values were 124.8 and 150.0 kJ/mol under nitrogen, respectively.

    更新日期:2018-11-08
  • A comparative study on in vitro degradation behavior of PLLA-based copolymer monofilaments
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-07
    Daokun Shi, Yahong Kang, Guoyi Zhang, Chenguang Gao, Wei Lu, Caihong Yang, Hua Zou, Hongyan Jiang

    Three kinds of high molecular weight polymers were synthesized by ring-opening polymerization with various monomer feeding ratios (named as PLLA, PLCL 95/5 and PLGC 80/15/5, respectively). Then oriented monofilament was produced through melt-extrusion and tensile orientation based on each kind of polymer. In vitro degradation properties of the monofilaments were studied over a range of degradation time from 1 to 21 days at 60 °C by using SEM, GPC, DSC, XRD and tensile test. Degradation results showed that the mass loss, Tg and morphology integrity of the PLLA monofilament basically remained unchanged, and partial degradation in amorphous region emerged with slight increase of crystallinity. For the PLCL 95/5 monofilament, the crystallinity was increased and the monofilament was fractured at 14 days accompanying with obvious decrease of the mass and Tm, indicating that most part of the amorphous region was degraded. Apparently, the PLGC 80/15/5 monofilament showed the fastest degradation rate with considerable mass loss and decrease of Tg. The amorphous region was degraded sharply in the early stage due to its good water absorbability and lower structural regularity, and the initially-formed crystalline region was degraded slowly later evidenced from the change of crystallinity and it was fractured at 3 days. The accelerated effects calculated according to the first-order kinetic model demonstrated that the PLCL 95/5 monofilament was degraded 2.5 times faster than pure PLLA and the PLGC 80/15/5 monofilament was degraded 7.5 times faster than PLLA. These were nearly consistent with those based on [η] (2.5 and 6.9 times respectively). The comparative study of in vitro degradation behavior of PLLA-based copolymer monofilaments would provide useful information for controlling the monomer composition of PLLA-based materials with specific degradation requirements.

    更新日期:2018-11-07
  • Consolidation of degraded polyurethane foams by mean of polysiloxane mixtures: Polycondensation study and application treatment
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-02
    Céline Daher, Isabelle Fabre-Francke, Nathalie Balcar, Gilles Barabant, Sophie Cantin, Odile Fichet, Hervé Chéradame, Bertrand Lavédrine, Agnès Lattuati Derieux

    Polyurethane (PUR) ester foams are found in 20th century museum collections in a variety of artworks and objects. Unfortunately PUR ester foams are prone to degradation, and present – among other plastic materials – important conservation issues. They are very sensitive to moisture, and their hydrolysis leads to several degradation processes such as yellowing and embrittlement, drastically changing the artwork aspect and materiality. Few researches were conducted on the consolidation of PUR ester foams. In this paper, a curative treatment that should limit the hydrolysis of the degraded PUR foams, and that mechanically consolidate the foams’ structure is presented. This work focuses on the innovative use of alkoxysilanes mixtures and on their application modes on foam samples. Different binary mixtures of OTMS (n-octyltriethoxysilane, hydrophobic and trifunctional) and AMDES (3-aminopropylmethyldiethoxysilane, hydrophilic and bifunctional) in various proportions were tested. The kinetic evolution of their polycondensation using spectral decomposition of FTIR spectra revealed that OTMS does not react with atmospheric water vapor and that the presence of an amine (AMDES) is required to initiate its polycondensation. This result justifies the use of a mixture of both siloxanes. The different treatments were then applied on artificially degraded PUR ester foams using concentration of 2.5% and 10% of alkoxysilanes in HMDS (hexamethyldisiloxane, solvent). The treatment was applied by pouring the solution over the samples and resulted in a homogeneous impregnation of the foams, whereas vaporization modes were unsuccessful regarding the penetration of the treatment in the foam cells. The hydrophilicity of the treatments was characterized using water contact angle measurements and it appears that at least 25% of hydrophobic OTMS in the mixture is needed to decrease the wettability of the samples, in order to avoid further hydrolysis. The reinforcement properties were studied using mechanical tests, and resulted in a need of a solution of 10% (in HMDS) for an acceptable reinforcement. Finally, colorimetric measurements showed that the visual aspect of the degraded samples was improved with the treatment.

    更新日期:2018-11-05
  • A novel star-shaped, cardanol-based bio-prepolymer: Synthesis, UV curing characteristics and properties of cured films
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-02
    Jun-Jie Li, Jian Sun, Yong-Xin Xie, Chen Zhao, Hong-Xia Ma, Cheng-Mei Liu

    Starting from renewable Cardanol, a novel inherently fire-retardant UV curable bio-based prepolymer (AEHCPP) with phosphazene core and six Cardanol arms are prepared in this report. The chemical structure of all newly prepared intermediates compounds and AEHCPP are well-characterized using nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). UV-curable mixture consisting of AEHCPP and different diluents were formulated and their photopolymerization dynamics were investigated on Photo-calorimetry (photo-DSC). The thermal properties of crosslinked coatings were estimated using thermal analysis technology. Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) results show that glass transition temperatures of all cured films are above room temperature (>30 °C), the 5% weight loss temperature in nitrogen is higher than 266 °C. The fire-retardant properties are estimated by TGA and all calculated Limiting Oxygen Index (LOI) values are over 24, implying the excellent fire-resistance of cured films.

    更新日期:2018-11-05
  • A preliminary study on the physicochemical properties of pigmented Sty/nBA/MMA emulsion films: The effect of thermal ageing
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-03
    T. Fardi, E. Kampasakali, Z. Terzopoulou, V. Pintus, E. Pavlidou, M. Schreiner, D. Bikiaris, G. Kyriacou

    The effect of temperature and humidity on the physicochemical and mechanical properties of pigmented Sty/nBA/MMA emulsion polymers containing synthetic organic pigments was studied. Thin films of artist's commercial paints from Liquitex (U.S.A.) and Rembrandt (NL) containing Azo yellow (PY3), diketopyrrolopyrrole red (PR264), phthalocyanine blue (PB15) and phthalocyanine green (PG7) were naturally dried and subjected to moderate artificial ageing at 60 °C and 55% RH and artificial soiling, to simulate thermally aged paints exposed to heat, humidity and dirt deposition. The changes in the paints' surface morphology were studied by Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS), Fourier Transform Infrared Spectroscopy in ATR mode (FTIR-ATR) and Differential Scanning Calorimetry (DSC) were used for their physicochemical characterization. In addition, mechanical testing was performed to investigate variations of the tensile properties. The study allowed the detection of deterioration patterns and defects, which include micro wrinkling and roughening of the surface due to the exposure of the inorganic fillers. Additionally, the extent of soil particles' penetration was observed to be dependent on the type and the mobility of the surfactant during and post artificial ageing. Physicochemical changes include increase of the polymer's Tg and decrease of the overall paint's physical and mechanical stability. Certain observations regarding the interaction of the components within the paint and the resultant resistance to thermal and mechanical stresses are discussed.

    更新日期:2018-11-05
  • A predictive model for polyethylene cable insulation degradation in combined thermal and radiation environments
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-03
    Anna Vykydalová, Tibor Dubaj, Zuzana Cibulková, Gabriela Mizerová, Michal Zavadil

    Reliable prediction of material service lifetime is important for ensuring safe operation in safety-critical systems such as nuclear facilities. Materials in these environments degrade due to several simultaneous effects, most important stressors are heat and radiation. In this work, samples of medium density polyethylene cable insulation were subjected to thermal (110 °C) and γ-radiation stress (500 Gy h−1); a combined thermal and radiation test (85 °C and 4.5 Gy h−1) was also performed. Stability of cable insulation was studied by differential scanning calorimetry and isoconversional kinetic analysis employing a non-Arrhenian temperature function was carried out. From the dependence of residual stability on the degradation dose a predictive model for the cable service life was developed based on the thermal and radiation stress tests; the model validity was verified using the combined stress test results. The model assumes a first-order exponential decay of the residual stability with degradation dose. It allows to predict the degree of insulation damage in wide range of environmental conditions as both temperature and radiation dose effects are considered and radiation dose rate effect is also taken into account.

    更新日期:2018-11-05
  • Cutinases catalyze polyacrylate hydrolysis and prevent their aggregation
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-31
    Ruoyu Hong, Lingqia Su, Jing Wu

    During the recycling of waste paper, the accumulation of polyacrylates present in the waste paper causes the formation of tacky substances known as stickies. Deposition of these stickies on the machinery decreases the quality of the recycled paper and increases the usage of circulating water. Enzymes that hydrolyze these polyacrylates can minimize or eliminate the deposition of stickies. In initial experiments, the abilities of the cutinases from Humicola insolens, Fusarium solani and Thermobifida fusca to hydrolyze poly (methyl acrylate) (PMA) and poly (ethyl acrylate) (PEA) within a macroporous resin were compared. Then, to simulate the environment encountered during paper recycling, PMA and PEA dispersions were used as substrates. The decrease in turbidity was measured at a concentration of 0.5 mg mL−1. When used at pH 8.0 and 30–50 °C, T. fusca cutinase limited the turbidity decrease to about 1.0% and favored the hydrolysis of PEA over PMA. F. solani and H. insolens cutinases performed best at pH 8.5 and temperatures of 35 and 50 °C, respectively. At a polyacrylate concentration of 0.1 mg mL−1, the optimal temperatures of these cutinases decreased. The optimal T. fusca cutinase dosage was lower than those of F. solani and H. insolens cutinases.

    更新日期:2018-11-02
  • Assessment of localization and degradation of ZnO nano-particles in the PLA/PCL biocompatible blend through a comprehensive rheological characterization
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-11-01
    Yeganeh Ahmadzadeh, Amir Babaei, Alireza Goudarzi

    The aim of this work was to investigate the effect of addition of various amounts of zinc oxide (ZnO) nanoparticles on the polylactide/polycaprolactone (PLA/PCL) blend prepared by melt mixing method. The morphological, rheological and degradation of prepared nanocomposites were studied. The morphology was characterized as dispersed PCL droplets into the PLA matrix, and according to Young's equation, zinc oxide nanoparticles (ZnO-NPs) was anticipated to preferentially locate in the matrix phase. The results of ATR-FTIR and the hydrolytic degradation tests demonstrated that, addition of ZnO-NPs introduced an accelerated degradation on the PLA/PCL blends. Subsequently, comprehensive linear viscoelastic evaluations were carried out to support these results and also give a deeper insight on the possible influences associated with the ZnO-NPs incorporation. Rheological results showed that with increasing nanoparticles, the elastic modulus and the complex viscosity decreased, which it was correlated to the degradation and chain scission of polymeric chains induced by ZnO-NPs.

    更新日期:2018-11-02
  • Significantly reduced pre-oxidation period of PAN fibers by continuous electron beam irradiation: Optimization by monitoring radical variation
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-30
    Wenli Zhang, Mouhua Wang, Wenfa Zhang, Weihua Liu, Chenguang Yang, Rongfang Shen, Guozhong Wu
    更新日期:2018-10-31
  • Extrusion of wood fibre reinforced poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) biocomposites: Statistical analysis of the effect of processing conditions on mechanical performance
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-31
    Luigi-Jules Vandi, Clement Matthew Chan, Alan Werker, Des Richardson, Bronwyn Laycock, Steven Pratt

    Wood fibre reinforced polyhydroxyalkanoate (PHA) composites have attracted significant interest as promising new sustainable biocomposites. However, their manufacture can be challenging due to PHA's relatively low thermal stability and melt viscosity. There is currently a lack of understanding of the effect of extrusion processing parameters on the molecular weight of the PHA matrix and, ultimately, on the mechanical properties of the composites. In this study, we show that commercially-relevant mechanical properties of a wood-poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) composite can be achieved through extrusion processing, even at temperatures as high as 190 °C, by adjusting screw speed and feeding rate, and consequently the induced shear rate and residence time. Moreover, the mechanical properties of 40 wt% wood-PHBV were found to be superior to properties previously reported in the literature. Relative to neat PHBV, a 73% increase in modulus and 80% retention of tensile strength was achieved. A Taguchi approach to experimental design was adopted to systematically investigate the effect of extrusion parameters (temperature profile, screw speed, feeding rate, and fibre mixing) on the processing of neat PHBV biopolymer and wood-PHBV composites with wood contents of 10, 20, 30, and 40 wt%. Evaluation of the mechanical performance was conducted through testing of tensile strength, tensile modulus and strain at maximum load. Changes in molecular weight were analysed via gel permeation chromatography (GPC). For both neat PHBV and wood-PHBV composites, molecular weight Mw was found to decrease under high shear stress and long residence time from 550-650 kDa to 350–550 kDa. However, Mw reductions were not enough to result in a decrease of mechanical performance. This discovery is significant for industrial-scale production as it shows that the processing window for wood-PHBV composites is not as narrow as expected, because thermal degradation can be limited by optimising a combination of processing parameters.

    更新日期:2018-10-31
  • Wear-induced mechanical degradation of plastics by low-energy wet-grinding
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-31
    Kartik Ravishankar, Praneeth Srivanth Ramesh, Balaji Sadhasivam, Dhamodharan Raghavachari

    Mechanical degradation of polymers reported so far, utilize cutting, impact or attrition for size reduction, which is very different from the low-magnitude forces experienced by the polymers during their service life. In this work, we have studied the effect of such low-magnitude forces, on the polymeric articles, using a low-energy rolling compression-type wet-grinder. The rolling compression action produces shear and compression on the polymer article, leading to abrasion and resulting in the formation of crazes, micro-cracks and chip-offs, akin to the wearing. Measurements using Raman spectroscopy showed that the shear forces, generated upon grinding, produced strains on the polymer backbone, which upon sufficient build-up, results in chain scission at the points of physical entanglement. These homolytic chain scissions produced "mechano"radicals, which were confirmed by radical-scavenging using DPPH. The ensuing reduction in the molecular weight was further analyzed using GPC, light scattering and viscometry. Surprisingly, XRD measurements showed strain-induced crystallization as well. In order to theoretically validate the studies, a probabilistic model, explaining the "complex" response of the molecular weight distribution and the PDI upon mechanical degradation, has also been presented. Crosslink density function was incorporated to explain the preferential chain scission of the high molecular weight species, leading to a gradual reduction in the average molar mass.

    更新日期:2018-10-31
  • Degradation of poly(5-hydroxy-trimethylene carbonate) in aqueous environments
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-31
    Fei Chen, Ronghui Qi, Locke Davenport Huyer, Brian G. Amsden

    Poly(5-hydroxy-trimethylene carbonate) (PHTMC) was synthesized through ring-opening polymerization of 5-benzyloxy trimethylene carbonate followed by debenzylation. The water solubility of the resulting homopolymer was measured as a function of its molecular weight, and its degradation in acidic (pH 2.0), and basic (pH 12.0) solutions of deionized water, as well as in phosphate buffered saline (PBS, pH 7.4) assessed. PHTMC exhibited notable hydrophilicity, even at molecular weights as high as 49 kDa. The pendant hydroxyl functional groups also allowed PHTMC to degrade rapidly (<1 h) under basic conditions via an intramolecular cyclization process along the polymer backbone. The ultimate degradation products were the biologically benign glycerol and carbon dioxide.

    更新日期:2018-10-31
  • Biodegradable plastic designed to improve the soil quality and microbiological activity
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-28
    Amanda Aleixo Moreira, Suzana Mali, Fabio Yamashita, Ana Paula Bilck, Maria Tereza de Paula, Aline Merci, André Luiz Martinez de Oliveira

    Biodegradable plastic composites were produced from mixtures of polyvinyl alcohol (PVA) and starch, which were mixed with different natural fillers [sugarcane bagasse (SB), oat hulls (OH) or silkworm exuvia (SE)] and nutrients to stimulate the biodegrading microbiota. The physicochemical and biodegradability characteristics of the produced materials were studied, in addition to their influence over the microbiota involved in biodegradation. The SB-composite showed reduced solubility in water, a lower water absorption capacity and a slower mineralization rate when buried in a commercial substrate for seedlings production, as compared with those of the OH- and SE-composites. Scanning electron micrographs demonstrated the increased colonization of materials by the biodegrading microbiota over time, which were predominated by filamentous fungi in OH- and SE-composites, while the SB-composite was predominantly colonized by bacteria. A Fourier transform-infrared spectroscopy (FT-IR) analysis of the biodegraded materials highlighted the chemical differences in the protein and carbohydrate content between formulations, corroborating the activity of different microbial groups on their mineralization. Regardless of its composition, the mineralization rate of the materials was positively correlated with the microbial biomass carbon (C mic) and basal respiration (RB) of the substrate. However, the correlation between the mineralization rate and the metabolic quotient of the substrate (qCO2) was negative for the OH- and SE-composites, while the SB-composite showed no significant correlation among these variables. The differences observed in the formulations indicated that biodegradable plastics can be designed for a given goal by selecting the most appropriate formulation.

    更新日期:2018-10-30
  • Correlation between the chemical structure and enzymatic hydrolysis of Poly(butylene succinate), Poly(butylene adipate), and Poly(butylene suberate)
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-29
    Zhenhui Bai, Ke Shi, Tingting Su, Zhanyong Wang

    Poly(butylene succinate) (PBS), poly(butylene adipate) (PBA), and poly(butylene suberate) (PBSub) were synthesized and enzymatic hydrolysis was performed in the presence of cutinase. The residues degraded at different times were characterized with respect to their molecular, thermal, crystalline, and chemical structures. The results showed that the degradation behavior of the three polyesters highly depends on their CH2/CO ratio, morphology, and thermal characteristics. The three polyesters were nearly degraded after 24 h, and the degradation rates was in the order of PBSub > PBA > PBS. Gel permeation chromatography and end-group analysis confirmed that the mechanism of enzymatic hydrolysis changed from endo-type to exo-type. The analyses of differential scanning calorimetry, powder X-ray diffraction, and Fourier transform infrared spectroscopy indicated that the cutinase could simultaneously degrade the crystalline and amorphous regions of polyester films.

    更新日期:2018-10-30
  • Thermal stability of bacteriocin nisin in polylactide-based films
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-26
    Pavlina Holcapkova, Anna Hurajova, Pavel Bazant, Martina Pummerova, Vladimir Sedlarik

    This work investigates the thermal stability of bacteriocin nisin in polylactide (PLA) and polylactide/polyethylene glycol (PLA/PEG) blends at temperatures of 90 °C–180 °C. The samples were prepared by solvent cast technique and characterized according to their mechanical and thermal properties. Research on the thermal stability of nisin in the PLA and PLA/PEG systems was carried out by exposing the given films to various temperatures (90 °C, 120 °C, 160 °C, and 180 °C) for a duration of up to 48 h. Assessment of the antibacterial activity of the samples was carried out by the agar diffusion method against Micrococcus luteus, while structural analysis involved the use of high-performance liquid chromatography with mass detection. Structural changes in the polymer matrix were evaluated by gel permeation chromatography and scanning electron microscopy. The results showed that nisin retained almost 70% of its antimicrobial activity in the PLA matrix, even after treatment at 160 °C for 15 min. The presence of PEG significantly enhanced the degradation of nisin above 120 °C.

    更新日期:2018-10-27
  • Application of an in vitro plant ecotoxicity test to unused biodegradable mulches
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-26
    H. Serrano-Ruíz, L. Martín-Closas, A.M. Pelacho

    Biodegradable plastics have emerged as an encouraging alternative to reduce the production of plastic waste, especially for agricultural mulches. However degradation of these plastics in the field may involve the release of products from the mulch into the soil, before and during the in-soil biodegradation. The present work aims to assess the potential effects on two agricultural plant species (Lactuca sativa L.–lettuce-, and Lycopersicon esculentum Mill. -tomato) of extracts from biodegradable (BDMs: Mater-Bi, Bioplast-SP4 and SP-6, BioFilm, BioFlex, Ecovio, Mirel, Paper) and polyethylene mulch films. A previously designed highly sensitive in vitro ecotoxicity test was used. Some of the extracts from the biodegradable plastics had effects on plant development. Germination was reduced by Bioplast films treatments, both in lettuce (B-SP4) and in tomato (B-SP4 and SP-6). In lettuce, root development was notably reduced by all treatments except for Paper and Polyethylene. Plant aerial growth was also limited with Bioplast and BioFlex, but enhanced with Paper extracts. At a whole, tomato plants showed higher sensitivity than lettuce in the test. Tomato aerial plant and root growth were reduced by all treatments with the exception of BioFlex and polyethylene. For both plant species, inhibitory effects on development were associated to proline increases, a physiological marker for some plant stresses. It can be concluded that the contact of unused biodegradable films with a water solution may result in changes in plant development that depends on the nature of the biodegradable film. The in vitro used test revealed to be a highly sensitive tool for ecotoxicity studies. These results are to contribute to design safe materials for agricultural applications.

    更新日期:2018-10-27
  • Single and hybrid electromagnetic absorbing coatings on polyacrylonitrile precursor to motivate the microwave pre-oxidation
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-25
    Tienah H.H. Elagib, Elwathig A.M. Hassan, Cheng Fan, Keqing Han, Muhuo Yu

    Nano silicon carbide was used separately and as an auxiliary absorber for the modification of the PAN precursor fibers to upgrade their microwave absorbability in order to undergo the subsequent pre-oxidization by using microwave. Surface coatings were successfully applied to the PAN precursor and the coated fibers were pre-oxidized over the microwave furnace for 60 min. To study the effect of the coatings on the pre-oxidized fibers, a series of characterizations were carried out. FTIR analysis results showed clear changes in the basic chemical structure of pre-oxidized fiber, which approved the occurrence of the cyclization and crosslinking reactions. Furthermore, the cyclization was confirmed by the thermal analysis results. According to the listed oxygen values, it can be suggested that the pre-oxidized fibers can resist the high temperatures in the following stage (carbonization). In addition, the crystalline analysis revealed a reduction in crystallinity, while the mechanical analysis demonstrated a reduction in tensile strength and elongation at break of pre-oxidized fibers.

    更新日期:2018-10-26
  • Polylactide-based self-reinforced composites biodegradation: Individual and combined influence of temperature, water and compost
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-25
    O. Gil-Castell, J.D. Badia, S. Ingles-Mascaros, R. Teruel-Juanes, A. Serra, A. Ribes-Greus

    Self-reinforced polymer composites (SRCs) are proposed as a suitable alternative for composite development, based in the combination of a polymeric matrix and a polymeric fibre made of the same polymer. SRCs based in polylactide (PLA) could be fully biodegradable and presumably their valorisation routes could be assimilated to those for neat PLA. In this sense, the aim of this study was to develop new self-reinforced PLA-based composites and ascertain their biodegradability. Self-reinforced PLA-based composites were suitably obtained through a thermo-compression procedure and their biodegradability corroborated under standard conditions (ISO 20200). Moreover, a deep study of the effect of the different factors involved in the biodegradation of PLA-based self-reinforced composites such as the temperature, water and compost medium was considered relevant to delimitate the long-term properties and valorisation routes for these materials. For this purpose, the macroscopic and microscopic appearance as well as the thermo-oxidative stability, the thermal properties and the molar mass were evaluated. Although degradation was perceived due to the effect of temperature, the synergistic combination of water and temperature ‒and compost‒ was found to play a key role in the biodegradation of these materials. Overall, these SRCs can be considered promising candidates, since their end-of-life management options can be guaranteed under standardised composting conditions.

    更新日期:2018-10-26
  • In vivo studies of novel scaffolds with tannic acid addition
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-25
    Beata Kaczmarek, Alina Sionkowska, I. Otrocka-Domagała, I. Polkowska

    Scaffolds based on chitosan, collagen, and hyaluronic acid supplemented with nano-hydroxyapatite and tannic acid were obtained by using the freeze-drying method. Biocompatibility was studied by the in vivo implantation into proximal tibial bones of rabbits. The bones were drilled and the biomaterial was introduced by filling the pre-drilled space. The histological studies were carried out three months after the implantation. The results showed low stability of the scaffolds based on chitosan, collagen, and hyaluronic acid supplemented with hydroxyapatite and tannic acid. The histological images showed the cetia and calcification centers. Moreover, the presence of thin-walled vessels filled with blood was noticed. Macrophages were observed in the area surrounding the implanted materials. The tissue response to the material implantation confirms that the tissue regeneration was initiated. The results showed satisfactory tissue response to the implanted scaffolds.

    更新日期:2018-10-25
  • Assessment of polyethylene degradation after aging through anaerobic digestion and composting
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-22
    A. Alassali, H. Moon, C. Picuno, R.S.A. Meyer, K. Kuchta

    Impurities in bio-waste enter biogas and compost facilities during bio-waste treatment. The plastic fraction is usually separated and sent for incineration. This study is aimed at evaluating the quality of low density polyethylene after being exposed to anaerobic digestion, composting or both processes sequentially, in order to assess for the optimum post-processing of these plastic fractions, eventually undergoing recycling processes. The alteration in the polymer's quality was first analyzed by non-destructive optical methods, including FTIR, NIR, SEM and EDX. These tests were followed by thermal and mechanical properties' assessment. The surface of the specimens showed signs of degradation, yet the extent of the changes was microscopic. The FTIR and NIR spectra showed higher intensities for C-H bonds in treated samples, which might be an indication of shorter polymer's chain length and/or higher chain scissoring. FTIR showed weak transmission spectral changes at regions representing C-O and O-H bonds for anaerobically digested and sequentially anaerobically digested and composted samples, indicating the existence of oxidized products, which was confirmed by the EDX analysis, where slightly higher oxygen content on the surface of specimens underwent the anaerobic digestion process was observed. However, NIR spectra did not show conforming spectra. It was accordingly concluded that the oxidized products are contaminants (residues on the specimens' surfaces), which was as well confirmed by the DSC analysis. The thermal analysis indicated a decrease in the polymer's crystallinity after being treated, where the decrease effect was the highest by anaerobic digestion, however, the mechanical properties (including tensile strength, elastic modulus and strain at break) pointed out minor quality alteration in treated samples, especially for samples underwent both processes successively. Based on the provided assessment, the general properties of LDPE plastic specimens are acceptable to be recycled, even after undergoing accelerated aging conditions, such as anaerobic digestion and composting. Further analyses are needed to evaluate plastics with additives as well as bags and films.

    更新日期:2018-10-22
  • Thermal degradation of poly(alkyl methacrylate) synthesized via ATRP using 2,2,2-tribromoethanol as initiator
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-18
    Ana Paula Rodrigues Camilo, Paula de Almeida, Cesar Liberato Petzhold, Maria Isabel Felisberti

    Poly(alkyl methacrylate)s (alkyl = methyl, ethyl, n-butyl and n-hexyl) synthesized by Atom Transfer Radical Polymerization (ATRP) using 2,2,2 tribromoethanol as initiator present a first mass loss below 200 °C in thermogravimetric experiments. In order to investigate the possible mechanism of this degradation step, the polymers were subjected to thermal treatment at 150 °C under argon atmosphere. The volatiles were analyzed by gas chromatography coupled to mass spectrometry, while the thermally treated polymers were analyzed by thermogravimetry, 1H and 13C nuclear magnetic resonance and size exclusion chromatography. The main mechanism of the first step of degradation is HBr elimination from initiator fragments attached to the chain ends, resulting in vinylidene, lactone and aldehyde terminal groups of the polymer chains. Moreover, volatiles produced by the chain-end elimination were mainly alkyl bromides, alkyl alcohols, alkyl methacrylates and products successive to HBr elimination and polymer chain scission. The amount of monomer release at 150 °C varied with the alkyl group in the range of 3–17 wt %; however, polymer chain configuration, molar mass and dispersity did not significantly change. Polymer chains free of the ATRP initiator were thermally stable at least up to 250 °C.

    更新日期:2018-10-19
  • Designing reliable silicone elastomers for high-temperature applications
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-12
    Elisa Ogliani, Liyun Yu, Piotr Mazurek, Anne L. Skov
    更新日期:2018-10-14
  • Biobased flame retardants from tartaric acid and derivatives
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-12
    Bob A. Howell, Wenxiao Sun

    Biobased flame retardants represent attractive alternatives to traditional organohalogen compounds which are persistent in the environment, tend to bioaccumulate and may pose risks to human health. Tartaric acid is generated annually in great abundance as a by-product of wine making. It is nontoxic and widely used as a food ingredient. It is tetrafunctional which provides broad opportunity for conversion to a wide spectrum of useful materials. It has been used as a base for the generation of a variety of new compounds that display good flame retardancy in DGEBA (diglycidyl ether of bis-phenol A) epoxy. These range from simple phosphinate and phosphonate esters to oligomeric materials containing bromine, in both saturated and unsaturated units, or bromine and phosphorus.

    更新日期:2018-10-14
  • Influence of network structure on the degradation of poly(ether)amine-cured epoxy resins by inorganic acid
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-11
    Jonathon D. Tanks, Masatoshi Kubouchi, Yoshihiko Arao

    In this paper, we investigate the case of bisphenol-type epoxy crosslinked with poly(ether)amine, immersed in sulfuric acid at elevated temperature. The results show that very high equilibrium mass-change (up to 40%) is observed, and that amine protonation is largely responsible for this behavior. When the acid solution concentration is 5mass% or higher, alcohol dehydration and aromatic ether cleavage reactions occur by excess acid (after amine protonation). A mechanistic degradation model is proposed, which requires no empirical parameters and accounts for polymer network structure differences. The model is supported by calculating the theoretical crosslink density using gravimetric data of penetrated acid at equilibrium.

    更新日期:2018-10-12
  • Pyrolysis mechanism of Poly(lactic acid) for giving lactide under the catalysis of tin
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-09
    Lidong Feng, Songyang Feng, Xinchao Bian, Gao Li, Xuesi Chen

    In order to obtain the mechanisms of the pyrolysis reaction that poly (lactic acid) (PLA) gives lactide in the presence of Sn, the four types of low molecular weight PLAs (L-PLA) with different end-groups were prepared, including HO-L-PLA-COOH, R-L-PLA-OH, R-L-PLA-COOH, and R-L-PLA-R, and depolymerized by thermogravimetry at different heating rates. As for the pyrolysis reactions of the L-PLAs, their activation energy (Ea) were estimated by the several isoconversional model-free methods and their kinetic models were also explored by the Malek method. The random degradation behavior of L-PLAs was determined by the plots of ln { − ln [ 1 − ( 1 − w ) 0.5 ] } vs. 1/T for experimental data from TG for L-PLAs and model reactions. The experimental results showed that the Ea values and the possible kinetic models for the pyrolysis reactions of the L-PLAs were different due to the different end-groups and thereof the mechanisms for the pyrolysis reactions of PLA that give lactide were proposed under the catalysis of Sn. The pyrolysis reactions of R-L-PLA-OH and R-L-PLA-R trend to be controlled by a single kinetic model. The pyrolysis reactions of HO-L-PLA-COOH and R-L-PLA-COOH are more complex and controlled by not less than two kinetic processes. The pyrolysis reaction of PLA selectively produces lactide through the unzipping and intramolecular transesterification reactions, including the backbiting reaction caused by the Sn-carboxylate and Sn-alkoxide chain ends, which are directly formed from the hydroxyl and carboxyl end-groups of PLA, and the lactide selective elimination at the random position of the polymeric backbone.

    更新日期:2018-10-10
  • 更新日期:2018-10-10
  • Chain extension of poly (butylene adipate-co-terephthalate) and its microcellular foaming behaviors
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-09
    Jingsi Song, Jianguo Mi, Hongfu Zhou, Xiangdong Wang, Yuxia Zhang

    A facile chain extension and solid-phase batch foaming method was proposed to prepare microcellular poly (butylene adipate-co-terephthalate) (PBAT) foams in the presence of supercritical CO2. Branching structure and micro cross-linking structure were generated in modified PBAT with styrene-acrylonitrile-glycidyl methacrylate terpolymer (SAG) as chain extender, which was confirmed by Fourier transform infrared spectra, gel permeation chromatography and gel fraction measurements. The intrinsic viscosity and branching degree of modified PBAT increased as well as their viscoelasticity was improved respectively, with the SAG content increasing. The crystallization temperature and crystallinity of various PBAT samples increased and then decreased slightly due to the heterogeneous nucleation effect of branching points and the generation of cross-linking structure. An interesting complex cellular structure was observed in modified PBAT foams with the SAG content of 1 and 3 wt%, owing to the different rheological properties in branching molecular chain regions and linear molecular chain regions.

    更新日期:2018-10-09
  • Bio-inspired engineering of boron nitride with iron-derived nanocatalyst toward enhanced fire retardancy of epoxy resin
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-09
    Zhi Li, Sara Isabel Montero Lira, Lu Zhang, Daniel Fernández Expósito, Vignesh Babu Heeralal, De-Yi Wang

    Aiming at improving fire retardancy of epoxy resin (EP), the thermal-exfoliated boron nitride nanosheets (BN) underwent the bio-inspired polydopamine (PDA) nano-coating and in-situ interfacial growth of iron-derived nanocatalyst (Fe) to prepare nanohybrid (BN@PDA@Fe). The design complied with principles: 1) PDA promoted the dispersion of BN in EP matrix and offered active sites for functionalization 2) bio-stabilized iron-derived nanoparticles catalyzed the polyaromatic reaction towards higher quality. Resultantly, 6 wt% BN@PDA@Fe increased limiting oxygen index (LOI) of EP by 10.0% and suppressed fire spread in UL-94 test. The peak heat release rate (pHRR) was reduced by 38.9% with notably suppressed CO and smoke production. Ignition time, as a key aspect of fire safety, was effectively delayed due to enhanced thermal conductivity of BN-based EP nanocomposites. The optimization of char structure due to the interfacial charring accounted for the improved fire retardancy. In perspective, the bio-inspired engineering of BN offered a viable approach to improving fire safety of polymers.

    更新日期:2018-10-09
  • Processing, thermo-mechanical characterization and gas permeability of thermoplastic starch/poly(butylene trans-1,4-cyclohexanedicarboxylate) blends
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-05
    Laura Genovese, Franco Dominici, Matteo Gigli, Ilaria Armentano, Nadia Lotti, Elena Fortunati, Valentina Siracusa, Luigi Torre, Andrea Munari

    In this contribution, binary blends of thermoplastic starch (TPS) and poly(butylene trans-1,4-cyclohexanedicarboxylate) (PBCE) have been prepared by melt extrusion. The effect of different amounts of PBCE and the presence of citric acid as compatibilizer have been studied with respect to the blend behavior. In particular, morphological and thermal studies allowed for the determination of the compatibility between the blend components, and of their characteristic thermal transitions and thermal stability. Envisioning potential packaging applications, surface wettability, moisture absorption and migration of food simulant have been investigated. In addition, mechanical properties and gas permeability have been evaluated after conditioning the films in dry and humid environment.

    更新日期:2018-10-06
  • Synergistic crosslink of double bond and nitrile group of nitrile rubber in H2S environment
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-05
    Chuanbo Cong, Qingkun Liu, Jia Li, Xiaoyu Meng, Qiong Zhou

    This study investigated the corrosion test of nitrile-butadiene rubber (NBR) in H2S. Butadiene rubber (BR) and hydrogenated nitrile-butadiene rubber (HNBR) were used to simulate the structural units of 1,4-polybutadiene and polyacrylonitrile in NBR. The characterizations of infrared spectra, CHNS elemental analysis, and XPS may indicate that when double bonds and nitrile groups coexist, NBR has the highest reactivity with H2S and crosslinks of monosulfur and disulfide appear inside the rubber. However, the reactivity of BR and HNBR was reduced and no crosslinking was produced when both were isolated. Therefore, double bonds and nitrile groups have a synergistic effect in the H2S environment.

    更新日期:2018-10-05
  • Degradation and related changes in supermolecular structure of poly(caprolactone) in vivo conditions
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-01
    P. Sajkiewicz, M.K. Heljak, A. Gradys, E. Choińska, S. Rumiński, T. Jaroszewicz, I. Bissenik, W. Święszkowski

    The degradation in vivo and its effect on the supermolecular structure of poly(caprolactone) was examined. Poly(caprolactone) (PCL) samples were prepared in the form of porous scaffolds implanted into rat calvarial defects. The degradation was investigated by means of gel permeation chromatography, wide angle X-ray scattering (WAXS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The study showed that the observed decrease of PCL crystallinity during degradation is accompanied by reduction of crystal size and/or perfection. The observed phenomenon could be explained by the presence of the high content of the low mobile fraction of investigated polymer, consisting not only almost 50% of crystal fraction but also most probably relatively high fraction of s.c. rigid amorphous fraction (RAF). Considering the type of structure characterized by the dominance of low mobile fraction, it is expected that the degradation will mainly concern these fractions, which in turn will lead to a decrease in the degree of crystallinity as well as crystal size and/or perfection.

    更新日期:2018-10-02
  • Synthesis and application of a benzoxazine-type phosphorus-containing monomer on epoxy/benzoxazine copolymer: Thermal stability and compatibility with liquid oxygen
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-02
    Cong Peng, Chang Gao, Yuhuan Yuan, Zhanjun Wu, Dayu zhou

    Alkene-terminated monofunctional benzoxazine monomer (A-BA) was synthesized using allylamine, phenol and paraformaldehyde. Subsequently, the phosphorous-containing benzoxazine monomer (PBA) was obtained through the addition reaction between 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and A-BA in toluene. Finally, epoxy/benzoxazine copolymer with chemically-bonded DOPO was prepared using the synthesized PBA as hardener of DGEBA. DMA results showed that polymer with the chemically-bonded DOPO possessed higher modulus and crosslink density than that with physical-blended DOPO. Thermal gravimetric analysis (TGA) showed that the epoxy/benzoxazine copolymer possessed much better thermal stability around 500 °C and the DOPO-containing epoxy/benzoxazine copolymer showed promoted behavior compared to the neat one. The char residue of the epoxy/benzoxazine copolymer revealed dense surface layer and unbroken original dimension which was in accordance with the TGA results and the phosphorous-rich cover was observed. The liquid oxygen (LOX) compatibility of the copolymers was evaluated through mechanical impact in accordance with ASTM D2512-95 which showed that the LOX compatibility of the epoxy/benzoxazine copolymers were better than the epoxy/amine ones and the epoxy/benzoxazine copolymer including PBA exhibited promoted stability in the impact test. The surface elemental composition of the specimen before and after mechanical impact was investigated by X-ray photoelectron spectroscopy (XPS) and increased oxidation state of phosphorus was observed which explained the mechanism of phosphorus on promoting the LOX compatibility of the copolymer.

    更新日期:2018-10-02
  • Discoloration of poly(vinyl acetate) (PVAc) gluelines in wood assemblies
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-10-02
    Fabio Chiozza, Ilaria Santoni, Benedetto Pizzo

    The bondline chromatic alteration of poly(vinyl acetate) (PVAc) in wood assemblies has an appreciable impact on the aesthetic characteristic of these products (mostly important for panels used in furniture). While the origin of this phenomenon has been explained for the cases of pure polymers and wood substrates alone, present work investigates about the origin of discoloration for the case of bondlines prepared with selected wood species (cherry and maple) and two commercial PVAc dispersions, one containing and one not containing aluminum ions. Assemblies were exposed to temperature and UV light. The comparison (carried out through GC-MS analysis) among the compounds extracted by these species before and after exposure allowed identifying specific flavonoids that were used as model-compounds to replicate the discoloration process in laboratory. Thus, using spectrophotometric measurements and TLC analysis it is shown that discoloration is related to the presence of aluminum in the dispersion, whose interaction with flavonoids in wood generates different forms of complexes that can be modified upon irradiation and emitting in the visible range. Although the specific involved compounds are species-related, it can be suggested that the identified mechanism at the basis of discoloration in PVAc-wood bondlines has general validity.

    更新日期:2018-10-02
  • Characterization of the secondary structure of degummed Bombyx mori silk in modern and historical samples
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-27
    Diego Badillo-Sanchez, David Chelazzi, Rodorico Giorgi, Alessandra Cincinelli, Piero Baglioni

    Understanding the degradation mechanisms of silk is essential for improving preventive conservation measures, and developing consolidation materials to restore the degraded fibers. Here, modern and historical silk samples were analyzed with an inclusive set of analytical techniques, in order to investigate the changes in the protein secondary structure that occurred upon natural aging or manufacturing processes. FTIR 2D Imaging-Chemical mapping allowed the non-invasive characterization of the structure, and the obtained information was supported by Optical microscopy (OM), Scanning electron microscopy (SEM) and thermal analysis (Thermogravimetry, TGA, and Differential Scanning Calorimetry, DSC). Based on the acquired data, a different degradation stage was proposed for each historical sample, highlighting a heterogeneous conservation status.

    更新日期:2018-09-28
  • 更新日期:2018-09-27
  • Impact of thermal oxidation of polymers on features of fluorescent probes
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-26
    Géraldine Rapp, Eric-Aimé Poutougnigni, Jean-Luc Gardette, Pierre-Olivier Bussiere, Sandrine Therias

    The aim of this work was to evaluate the potential of 2-dimethylamino-6-propionylnaphthalene (denoted Prodan®) as a sensitive fluorophore for monitoring the oxidation of polymers at low extent of oxidation within the “induction period” and for characterizing the chemical modification of polymers induced by thermal oxidation. The fluorophore was introduced into polyethylene films (85 microns thick) by soaking in a methanolic solution before and after thermal oxidation carried out for various durations. The emission features of this fluorescent probe are known to be strongly dependent on the polarity of the medium. Changes in polarity due to the formation of oxidized products provoked a notable shift of the wavelength at the maximum of fluorescence, which was correlated to the extent of the oxidation measured by infrared spectroscopy. Moreover, the emission intensity of the probe was observed to dramatically increase with the amount of oxidation products. It was observed that there was a good correlation between the wavelength at the emission maximum, the amount of fluorophore absorbed, and the oxidation extent. Interestingly, the modification of the fluorophore features was detected within the induction period when no oxidation product could be detected by infrared spectroscopy. The probe fluorescence was then used as a sensitive and easy method to monitor the chemical modification of the polymer at the early stages of oxidation.

    更新日期:2018-09-26
  • Early-stage photodegradation of aromatic poly(urethane-urea) elastomers
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-26
    Tianlong Zhang, Fengwei Xie, Julius Motuzas, Peter Bryant, Valsala Kurusingal, John M. Colwell, Bronwyn Laycock
    更新日期:2018-09-26
  • Boron particles acting as antioxidants for fluorosilicone rubber due to their radical scavenging activity
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-22
    Anna Zheng, Yongkang Huang, Yang You, Jian Hu, Dafu Wei, Xiang Xu, Yong Guan

    The heat resistance enhancement of fluorosilicone rubber (FSR) can make it more suitable for cutting-edge applications and extreme conditions. This paper focused on the antioxidant properties of boron particles for FSR and the corresponding mechanism. The thermal stability of FSR and FSR/boron composites was characterized by thermal gravimetric analysis (TGA), isothermal degradation and thermal-oxidative ageing. The results showed that boron significantly improved the thermal stability of FSR. In particular, the FSR/boron (100/10) composite retained 95% of its weight after isothermal degradation at 350 °C for 12 h, while the FSR lost 55% of its weight within the initial 1 h. The antioxidant mechanism of boron was further investigated by chemiluminescence (CL), electron paramagnetic resonance (EPR) and vulcanization curves. It was shown that boron has powerful radical scavenging activity (RSA) and inhibited the oxidation scission of the side groups. Moreover, boron revealed no RSA towards the tert-butoxy radical, ensuring the good vulcanization of the FSR/boron composites.

    更新日期:2018-09-25
  • Degradation of waste polycarbonate via hydrolytic strategy to recover monomer (bisphenol A) catalyzed by DBU-based ionic liquids under metal- and solvent-free conditions
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-22
    Mengshuai Liu, Jiao Guo, Yongqiang Gu, Jun Gao, Fusheng Liu

    The application of ionic liquids in chemical recycling of waste polycarbonate (PC) via the simple hydrolytic strategy has shown great potential. Herein, a series of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) based ILs were facilely synthesized and characterized, and could efficiently catalyze the hydrolysis of PC in the absence of transition metal and solvent. The catalyst structures and reaction conditions were optimized, and 100% PC conversion with 97% bisphenol A (BPA) yield could be obtained under the conditions of n(H2O)/n(PC) = 3:1, n(Cat.)/n(PC) = 0.1:1, 140 °C for 3.0 h. Based on the experimental results and in-situ FT-IR analysis of the PC residues and BPA product, a feasible molecular activation and catalytic pathway for [HDBU][LAc] catalyzed hydrolysis of PC was proposed.

    更新日期:2018-09-25
  • Accelerated aging of polyethylene pipe grades in aqueous chlorine dioxide at constant concentration
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-24
    M. Bredács, A. Frank, A. Bastero, A.Stolarz, G. Pinter

    The impact of disinfected water on the degradation of polyethylene (PE) was investigated with immersion tests of two PE pipe materials in 10 and 5 ppm chlorine dioxide (ClO2) medium at 60 °C. Aging experiments in 1 ppm ClO2 at 60, 50 and 40 °C were also carried out to study the effect of different aging temperatures. During conditioning, the pH was kept at 6.8. A specific exposure device with continuous concentration control and adjustment has been applied in order to generate reliable and reproducible aging conditions. Sample characterization applying scanning electron microscopy (SEM), tensile test, dynamic oxidation tests as well as FTIR-spectroscopy indicated accelerated antioxidant consumption and polymer degradation. Material aging at 50 °C and above was found to be much faster than at 40 °C applying 1 ppm ClO2 concentration. An optimized testing condition for fast material characterization in case of 1 mm thick specimens was found to be a concentration of 1 ppm ClO2 at 50 °C. The simultaneously increasing material embrittlement and the consumption of active antioxidant molecules imply an apparent unselective reaction of ClO2 with the polymer and the stabilizers molecules. Moreover, the radical nature and the high reactivity of ClO2 led to the formation of carbon-chlorine species, which are assumed to originate from degraded antioxidant molecules.

    更新日期:2018-09-25
  • Use of ion-assisted sputtering technique for producing photocatalytic titanium dioxide thin films: Influence of thermal treatments on structural and activity properties based on the decomposition of stearic acid
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-21
    V. Vishnyakov, P.J. Kelly, J. Humblot, R.J. Kriek, N.S. Allen, N. Mahdjoub

    Titanium dioxide thin films were deposited by the reactive ion-assisted sputtering method from titanium targets at various partial pressures and deposition parameters. The films were deposited onto substrates at temperatures ranging from room-temperature conditions to 722 K. A selection of thin films was post-deposited annealed at temperatures up to 972 K for 10 min and characterized by micro-Raman spectroscopy and scanning electron microscopy (SEM) and subsequently analysed to assess their photocatalytic activity. Micro-Raman characterization revealed that the as-deposited films had either predominant amorphous, rutile-like structures, anatase-like structures or anatase-rutile mixed structures. The thin films deposited with a high substrate temperature and with energy assistance from the ion source tended to be amorphous, while films deposited on a hot substrate without ion energy assistance tended to have a mixed crystalline phase. On subsequent annealing the amorphous films changed to a rutile structure at temperatures above 672 K, while mixed anatase-rutile films changed to predominant rutile structures only after thermal treatments above 872 K. Thus, this study has revealed an astonishing persistence of the anatase-rutile mixed phase at very high temperatures and showed the possible existence of a key transition temperature at 672 K, where it was possible to see a transformation from amorphous or mixed phase to a rutile or dominant rutile mixed phase. Photocatalytic tests were undertaken by using a novel method consisting of observing the degradation of a film of stearic acid by the thin films under artificial UV radiation. Of the films investigated those with anatase-rutile mixed phases showed the greatest photoactivity. This work was essential in the understanding of the correlation between growth deposition conditions, phase transitions and photocatalytic activity. This set of experiments demonstrated that titania made under a highly oxidizing atmosphere, with no temperature applied on the substrate during fabrication and using an ion sputtering method, is a useful and valuable novel method for creating active TiO2 thin films.

    更新日期:2018-09-22
  • Quantitative analysis of changes in antioxidant in crosslinked polyethylene (XLPE) cable insulation material exposed to heat and gamma radiation
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-19
    Shuaishuai Liu, Stephen W. Veysey, Leonard S. Fifield, Nicola Bowler

    Quantitative analysis of the antioxidant poly(1,2-dihydro-2,2,4-trimethylquinoline) (pTMQ) was conducted on pristine, thermally-aged, and gamma radiation-aged commercial cross-linked polyethylene-(XLPE-)based cable insulation material aged at temperatures 60, 90, and 115 °C, with gamma radiation exposure dose rates of 0, 120, 300, and 540 Gy/h for 15 days. The quantification of antioxidant was performed using pyrolysis gas chromatography-mass spectrometry (Py-GCMS). Oxidation induction time (OIT) was measured using differential scanning calorimetry (DSC) and correlation was made between the quantified depletion of antioxidant and measured OIT. It was observed that, in the case of isothermal aging, the quantity of antioxidant and OIT decreased with increasing gamma radiation dose. In the case of samples exposed to the same gamma radiation dose, the quantity of antioxidant and OIT were observed to decrease with increasing aging temperature. Depletion in the quantity of antioxidant relative to that in the pristine material ranged from 7 to 93% for differently aged samples. The measured decline in OIT ranged from 0 to 80%. Change in the quantity of antioxidant in the material was observed to follow the same trend as the change in OIT when the samples were aged under various conditions, with a correlation coefficient of 0.82. The observations are explained in terms of the reaction between the antioxidant and free radicals created during exposure of the samples to thermal and gamma radiation.

    更新日期:2018-09-20
  • Nondestructive evaluation of sintering and degradation for rotational molded polyethylene
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-18
    F.P.C. Gomes, M.R. Thompson

    Developments in new sensor technologies and data processing are helping to increase the number of applications of nondestructive characterization methods. In this study, two major physiochemical phenomena affecting product quality of rotationally molded polyethylene parts, namely sintering and degradation, were evaluated using both traditional characterization techniques and a newer alternative ultrasonic-based method. Oven temperature and heating cycle time were controlled to produce six different process conditions for rotomolding. Increasing peak internal air temperature (PIAT) inside the mold produced a reduction in surface voids (pitting) and increased the impact strength for produced parts, which can be related to greater densification during sintering. Contrary to these characterizations denoting improved part quality, degradation was detected for PIAT above 220 °C by an increase in surface carbonyl groups by Fourier-transform infrared spectroscopy (FT-IR) and an increase in zero-shear viscosity, both relatable to thermo-oxidative free radical reactions. The newly proposed monitoring technique applying propagating ultrasonic guided waves showed that its data-rich spectral features based on harmonic frequencies were positively correlated to the same sintering and degradation properties observed above. Coupled with multivariate statistical analysis, the nondestructive ultrasonic technique shows great promise for combining multiple analyses in a single sensor technology, making it well suited to the implementation of advanced manufacturing methodologies in polymer processing practices.

    更新日期:2018-09-19
  • The effect of thermal treatment on the decomposition of phthalonitrile polymer and phthalonitrile-polyhedral oligomeric silsesquioxane (POSS) copolymer
    Polym. Degrad. Stabil. (IF 3.193) Pub Date : 2018-09-18
    Xiaodan Li, Yuanjun Sun, Dongxing Zhang, Nan Zhu, Lei Jing

    Phthalonitrile polymer and phthalonitrile-polyhedral oligomeric silsesquioxane (POSS) copolymer were sintered at 500 °C, 600 °C, or 800 °C. The samples before and after sintering were evaluated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) coupled to FT-IR (TG-FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results suggest that phthalonitrile-polyhedral oligomeric silsesquioxane copolymers have better thermal stability than phthalonitrile polymers. After sintering at 800 °C, the phthalonitrile polymers decomposed completely while the phthalonitrile-polyhedral oligomeric silsesquioxane copolymers retain their original structure. The presence of the rigid POSS structure in the copolymer may limit the thermal movement of polymer chains at higher temperatures, thereby increasing the intermolecular forces between polymer chains. Moreover, POSS generates spatial steric hindrance, further restraining movement of chains and hindering degradation of labile groups; the overall effect is to improve the thermal stability of the composite under higher temperatures.

    更新日期:2018-09-19
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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