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  • Chemical recycling of poly(lactic acid) by water-ethanol solutions
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-17
    Fabiola Iñiguez-Franco, Rafael Auras, Kirk Dolan, Susan Selke, Daniel Holmes, Maria Rubino, Herlinda Soto-Valdez
    更新日期:2018-01-17
  • A propane burner test for passive fire protection (PFP) formulations containing added halloysite, carbon nanotubes and graphene
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-17
    A.G. Gibson, W.N.B. Wan-Jusoh, G. Kotsikos

    Passive fire protection materials (PFP) have been characterised quantitatively using a constant heat flux propane burner test, with the PFP attached to a steel substrate. The burner test was able to produce a large, constant heat flux, to simulate a severe fire condition. The heat transferred through the PFP was calculated from the temperature rise of the steel. A simplified model is discussed, to account for different combinations of substrate thickness, PFP thickness, heat flux and exposure time. It was found that, despite the complex processes of resin decomposition and intumescence, heat transmission could be modelled, to a reasonable approximation, by treating the PFP as a material with single point values of apparent thermal diffusivity and conductivity. This leads to an equation that can be used to characterise PFPs and indeed to specify their required thickness. The burner test was employed to interpret the effects of adding small quantities of three nano-materials: halloysite nanotubes (HNT), multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNP), to a standard PFP formulation. It was found that HNT addition resulted in a significant performance improvement, whereas the other nano-materials did not produce an improvement.

    更新日期:2018-01-17
  • Effect of carbon black distribution on the properties of polyethylene pipes part 1: Degradation of post yield mechanical properties and fracture surface analyses
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-11
    Suleyman Deveci, Nisha Antony, Birkan Eryigit

    In this study, we investigated the effect of carbon black distribution on the degradation of mechanical properties of high-density polyethylene in the form of plastic pipes used in water distribution networks. Polyethylene pipes with similar carbon black concentrations but different carbon black distributions were produced with industrial scale compounding and extrusion equipment. Tensile specimens were directly prepared from extruded pipe samples and elongated to fracture at different strain rates. Carbon black distributions of bulk samples and fracture surfaces were investigated using stereo and scanning electron microscopy (SEM). It was found that the carbon black distributions, fracture surfaces and fracture modes were significantly different in these pipes. Although the yield properties were similar, the post-yield properties of samples were significantly different, dramatically decreasing with the increasing inhomogeneity of carbon black distribution. Pipes with a certain level of heterogeneity in the carbon black distribution showed ductile and brittle fractures in the same fracture plane, whereas homogenous black and natural polyethylene (without carbon black) showed ductile fractures only.

    更新日期:2018-01-12
  • Coupled aging effects in nanofiber-reinforced siloxane foams
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-11
    Andrea Labouriau, Tom Robison, Drew Geller, Carl Cady, Adam Pacheco, Jamie Stull, Joseph H. Dumont

    This study investigates the combined effects of ionizing radiation and thermal treatments on the aging of siloxane foams containing small amounts of carbon nanofibers. Our siloxane foams were exposed to accelerated aging conditions for more than two years, resulting in very low dose rates. In addition, foams were aged under compressive load to evaluate the strength of the porous microstructure. Samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), Mössbauer, mass spectroscopy, electron paramagnetic resonance spectroscopy (EPR), solvent swelling, imaging techniques, uniaxial compressive load testing and tear testing. No significant changes in thermal stability or chemistry of the accelerated aged foam were observed, although gas evolution was detected. Changes in crystallization levels at low temperatures, microstructure, and mechanical properties were observed for foams with and without carbon nanofibers. In particular, foams aged under compressive load showed irreversible deformation of the porous microstructure. This study demonstrates that aging effects were enhanced when thermal and radiolysis were coupled together and that the addition of carbon nanofibers did not improve aging effects.

    更新日期:2018-01-11
  • Crystallization kinetics of polylactide: Reactive plasticization and reprocessing effects
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-09
    Berit Brüster, Antonio Montesinos, Pauline Reumaux, Ricardo A. Pérez-Camargo, Agurtzane Mugica, Manuela Zubitur, Alejandro J. Müller, Philippe Dubois, Frédéric Addiego

    This work focused on the determination of crystallization kinetics of neat polylactide (PLA) and a plasticized grade of PLA obtained by reactive extrusion (pPLA), as a function of thermomechanical recycling. In particular, the materials were submitted to repeated extrusion and injection procedures to simulate recycling. Prior reprocessing, spherulitic growth rate determined by polarized light optical microscopy indicated that pPLA crystallized into much smaller spherulites as compared to PLA. This finding was explained by a lower nucleation energy barrier promoted by the plasticization of pPLA. Isothermal overall crystallization kinetics were determined by differential scanning calorimetry measurements. It was found that pPLA crystallized much faster than neat PLA due to the plasticization effect. With increasing the number of processing cycles up to 5, PLA crystallization rate gradually increased, while at the same time that of pPLA remained constant. This result was explained by more important degradation mechanisms in PLA as compared to pPLA that enhanced chain mobility, as shown by molecular weight measurements. Moreover, pPLA had a very high initial chain mobility that is maintained regardless of the number of processing cycles. However, the final crystallinity degree was lower in reprocessed pPLAs, as grafting and cross-linking reactions produced during reactive extrusion interrupt crystallizable linear crystallizable sequences and reduced the amount of crystals formed.

    更新日期:2018-01-10
  • The anaerobic biodegradation of poly(lactic) acid textiles in photosynthetic microbial fuel cells: Self-sustained bioelectricity generation
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-09
    Xiang Qi, Yi Bo, Yiwei Ren, Xingzu Wang

    Poly(lactic) acid (PLA) is a promising material due to the complete biodegradability and environmental-friendly characteristics, but it is difficult to decompose by traditional anaerobic composting. Photosynthetic microbial fuel cells (MFC) are envisaged as a potential bioenergy harvesting techniques in recent years. In this work, the anaerobic biodegradation of PLA textiles for bioelectricity generation was explored in a dual chamber MFC devices using the hybrid anoxygenic photosynthetic bacteria (APB). The result showed that the surface of PLA textiles appeared the widespread damage by SEM micrographs observation, and the corresponding weight loss was 26.67%. The analysis of FT-IR suggested that the breakage process was a biochemical action due to the function of depolymerase. Meanwhile, a stable current density generation of 4.4 ± 0.2 mA/cm2 (500 Ω external resistor) at PLA textiles concentration of 1 g/L was obtained under the shortage of other carbon sources. However, the microbial community structure was obvious difference before and after the test. Moreover, the exploration will provide more potential information for self-sustained bioelectricity generation of MFC.

    更新日期:2018-01-09
  • Transparent and soluble polyimide films from 1,4:3,6-dianhydro-D-mannitol based dianhydride and diamines containing aromatic and semiaromatic units: Preparation, characterization, thermal and mechanical properties
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-09
    Zhiming Mi, Zhixiao Liu, Jianan Yao, Chunbo Wang, Changjiang Zhou, Daming Wang, Xiaogang Zhao, Hongwei Zhou, Yumin Zhang, Chunhai Chen

    To develop colorless and soluble polyimide films, a novel dianhydride containing 1,4:3,6-dianhydro-D-mannitol unit, 2,5-bis(3,4-dicarboxyphenoxy)-1,4:3,6-dianhydromannitol dianhydride (IMDA) was synthesized. And two series of polyimides were prepared via a two-step thermal imidization, PI−(1−4) were obtained from IMDA and four kinds of aromatic diamines while PI−(5−7) from IMDA and three kinds of semiaromatic diamines. All the polyimides were readily soluble in common polar solvents and could afford flexible, tough and colorless films with transparency up to 89% at 450 nm. Especially, polyimides simultaneously containing 1,4:3,6-dianhydrohexitol units in diamine and dianhydride exhibited comparable optical and soluble performance with the alicyclic fluorinated ones. Meanwhile, it was certified that 1,4:3,6-dianhydrohexitol fragment in dianhydride was more determinant in solubility and transmittance of polyimides than that in diamine. An overall investigation of these polyimides on thermal, mechnical, morphological, soluble, optical and dielectric properties was presented, and their structure-property relationships were discussed in detail.

    更新日期:2018-01-09
  • Effect of ZnO particle sizes on thermal aging behavior of natural rubber vulcanizates
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-08
    Yong Hwan Lee, Misuk Cho, Jae-Do Nam, Youngkwan Lee

    The effects of ZnO particle size on crosslinking and thermal aging behavior of natural rubber (NR) were investigated. NR vulcanizates filled with nano ZnO allowed higher crosslink density, lower polysulfide crosslink, and stronger mechanical properties than those filled with micro ZnO. After thermal aging, NR filled with nano ZnO exhibited much more stable chemical and mechanical properties. The high crosslink density as well as the formation of more stable mono- and di-sulfidic crosslinks was attributed to the good dispersion and high surface area of the nano ZnO.

    更新日期:2018-01-09
  • Key role of magnesium hydroxide surface treatment in the flame retardancy of glass fiber reinforced polyamide 6
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-08
    M. Casetta, G. Michaux, B. Ohl, S. Duquesne, S. Bourbigot

    In this paper, the fire retardant properties of two magnesium dihydroxide (MDH) were compared into glass fiber reinforced polyamide 6 (PA6 GF). The difference between the additives lies in the presence of a vinylsilane treatment at the surface of one of the two MDH (H5A grade) whereas the other is a non-treated MDH (H5 grade). The investigations showed that better fire properties were obtained with PA6 GF/H5A formulation compared to the PA6 GF/H5 one. More precisely, a higher UL-94 rating, a higher glow wire ignition temperature (GWIT) and a higher time to ignition (TTi) at the mass loss calorimeter (MLC) were obtained. To understand the differences between H5 and H5A in terms of fire performances, the mechanisms of degradation of the two fire retarded (FR) formulations was investigated, analyzing both the gas phase and the condensed phase. A significant part of the study was also devoted to the characterization of the ceramic protective layer formed thanks to the use of MDH. The analysis of the gas phase revealed that the degradation products of the two FR formulations were similar. Moreover, as shown by the condensed phase analysis, no chemical reaction occurs between PA6 and H5 or H5A, proving that the MDH surface treatment was not involved in chemical reactions during the processing of the formulation or its degradation. On the contrary, the main differences between the two formulations concern the properties of protective layer formed during the degradation. It was shown that the silane treatment and the MgO formed during MDH dehydration lead to the formation of a cohesive structure between the glass fibers when the material degrades, resulting in a highly insulating and resistant protective layer.

    更新日期:2018-01-09
  • Highly efficient flame-retardant glass-fiber-reinforced polyamide 6T system based on a novel DOPO-based derivative: Flame retardancy, thermal decomposition, and pyrolysis behavior
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-08
    Weijiang Huang, Wentao He, Lijuan Long, Wei Yan, Min He, Shuhao Qin, Jie Yu

    A novel bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative (PN-DOPO) was used to fabricate a flame-retardant glass fiber-reinforced polyamide 6T (GFPA6T). The effects of PN-DOPO on the flame retardancy, thermal decomposition, and pyrolysis behavior of GFPA6T was systematically investigated, compared to neat GFPA6T and its composite flames retarded by aluminium diethylphosphinate (OP1230). The flame retardancy, thermal stabilities, and burning behaviors of the composites were evaluated by vertical burning test (UL-94), limiting oxygen index (LOI), thermogravimetric analysis (TGA), and cone calorimeter test. Moreover, the flame-retardant mechanism was analyzed by pyrolysis-gas chromatograph/mass spectrometer (Py-GC/MS), Fourier transform infrared coupled with the thermogravimetric analyzer (TG-FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Results reveal that the modified GFPA6T, with the addition of 15 wt% PN-DOPO, achieves a V-0 rating and LOI value of 28.9%, whereas introducing OP1230 at levels up to 17.5 wt% can achieve a V-0 rating and LOI value of 40.1%. The superior flame retardancy for GFPA6T/PN-DOPO system can be attributed to two factors as follows: the release of pyrolytic gases containing phosphorus-based aromatic structures and nonflammable gases at the early stage, thereby playing an important role in the gas phase, and the formation of char layer consisting of phosphorus-containing char layer and polyaromatic structures in the condensed phase. In comparison, diethyl-phosphorus oxides and their derivatives are detected in the gas phase for GFPA6T/OP1230 samples, and the residues consist of aluminum phosphorus oxides, polyphosphates, and a slight amount of charred polymer.

    更新日期:2018-01-09
  • Control of the secondary crystallisation process in poly(hydroxybutyrate-co-hydroxyvalerate) through the incorporation of poly(ethylene glycol)
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-05
    Catherine A. Kelly, Annabel V.L. Fitzgerald, Mike J. Jenkins

    Poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-co-HV) is a sustainable and biodegradable polymer, but as a potential packaging material, it suffers from a narrow processing window and embrittlement over time due to secondary crystallisation. This study aims to extend previous research by exploring the effect of the addition of poly(ethylene glycol) (PEG), in a range of molecular weights and compositions, on the rate of embrittlement. On blending, it was apparent that there was a reduction in both the melting point (of up to 7 °C) and the melt viscosity. Furthermore, there was a reduction in both the modulus and tensile strength indicating that PEG acts as an effective plasticiser in PHB-co-HV. In terms of the secondary crystallisation process, the addition of PEG could not prevent the process from occurring, only hinder it. PEG 600 in relatively high concentrations was found to be the most effective in this regard with a 53% reduction in the change in Young's modulus compared to pure PHB-co-HV. This observation, together with the melting point reduction which extends the processing window for PHB-co-HV, makes PEG a worthwhile additive to an otherwise fundamentally brittle polymer.

    更新日期:2018-01-05
  • Exterior and under glass natural weathering of hemp fibers reinforced polypropylene biocomposites: Impact on mechanical, chemical, microstructural and visual aspect properties
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-04
    Célia Badji, Joana Beigbeder, Hélène Garay, Anne Bergeret, Jean-Charles Bénézet, Valérie Desauziers

    This work aims to investigate exterior and under glass weathering representing decking and car interior end uses of hemp fibers reinforced polypropylene (PP) biocomposites. For this reason, mechanical flexural tests were firstly performed. Then, the evolution of the PP matrix microstructure was determined through Differential Scanning Calorimetry (DSC). The chemical composition was studied by infrared spectroscopy to understand the photo- and thermo-chemical mechanisms. CIELab system-based colorimetric measurements were carried out to determine the evolution of the chromaticity and lightness. Through a new approach, gloss was obtained by determining the type of reflection of materials as either specular or diffuse, and the surface aspect was characterized by rugosimetry. The influence of the rate of hemp fibers (from 0 to 30 wt%) was studied. Results showed that biocomposites were generally more sensitive than neat PP whatever the weathering conditions. However, each type of weathering assessment allowed understanding the contribution of each degradation factor. Indeed, rainfall or UV-A rays induced an increase in the vinyl concentration and the formation of cracks on the surface whereas the carbonyl functional groups rate was not influenced by the type of weathering. The high temperatures under windshield glass favored a chemicrystallization and biocomposites yellowing at the first period of exposition whereas outdoor exposure induced red color loss.

    更新日期:2018-01-04
  • Correlation between artificial and natural weathering of hemp fibers reinforced polypropylene biocomposites
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-04
    Célia Badji, Joana Beigbeder, Hélène Garay, Anne Bergeret, Jean-Charles Bénézet, Valérie Desauziers

    The degradation behaviors of hemp fibers reinforced PP biocomposites under outdoor and artificial weathering were compared to establish a correlation. For this purpose, several measurements were performed throughout the expositions. Mechanical performance was tested by three-point bending test. Microstructure and chemical composition changes were also assessed. Otherwise, visual aspect and topography were determined. The artificial weathering effectively accelerated the degradation mechanisms. Oxidation pathways and surface aspect alteration of both polymer and biocomposites occurred faster. However, whereas biocomposites were mainly subjected to outdoor conditions due to high sensitivity of hemp fibers, neat PP was globally mostly affected by laboratory chamber conditions. Its oxidation rate largely outstripped reinforced materials ones. Principal Component Analysis was used for verifying the differences of variables correlations profiles between artificial and exterior ageing dataset in order to compare the degradation mechanisms. Through the statistical analysis, some attempts were made to find equivalence between artificial and outdoor weathering times thanks to properties degradation rate similarities.

    更新日期:2018-01-04
  • Identification of antioxidants in polymeric insulating materials by terahertz absorption spectroscopy
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-18
    Takuya Kozai, Takuya Kaneko, Naoshi Hirai, Yoshimichi Ohki

    For the purpose of using organic polymeric materials for electrical insulation, various additives such as antioxidants are added to prevent degradation or oxidative decomposition of the polymers. Therefore, it is desirable that we can identify antioxidants added in polymers by instrument analyses. In this research, terahertz absorption spectroscopy was conducted for nine kinds of antioxidants. The spectroscopy was also conducted for sheets of low-density polyethylene, to which each antioxidant had been added with different contents. As a result, it has become clear that each antioxidant has its own specific spectrum. In addition, for most antioxidants, the absorption intensity is proportional to the content of antioxidant added in LDPE. However, several absorption peaks change their spectral shapes when the antioxidant is in LDPE.

    更新日期:2017-12-18
  • Weathering resistance of PMMA/SiO2/ZrO2 hybrid coatings for sandstone conservation
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-16
    Laura Bergamonti, Federica Bondioli, Ilaria Alfieri, Silvia Alinovi, Andrea Lorenzi, Giovanni Predieri, Pier Paolo Lottici

    Accelerated weathering of polymethylmethacrylate (PMMA) and of hybrid PMMA/SiO2/ZrO2 films was monitored by spectroscopic, thermal and colorimetric measurements. The hybrid polymers were obtained by sol-gel process adding tetraethylorthosilicate (TEOS) and zirconyl chloride (ZrOCl2*8H2O) to a solution of PMMA. Photo ageing tests on polymeric films under artificial sunlight irradiation in a climatic chamber suggest that the addition of the inorganic fillers slows down the chemical degradation of PMMA. The polymers were deposited on two different sandstones from Tuscany (Italy): Pietra Dorata and Pietra Serena. Capillary water absorption, contact angle and color measurements show that the hybrid-PMMA coatings retain the water repellency of the sandstone and do not introduce noticeable changes of the aesthetic appearance. Accelerated weathering of the treated sandstone confirms that the SiO2/ZrO2 inorganic filler delays the chromatic changes of the polymer. The hybrid coating may then be proposed for application in the field of outdoor conservation of sandstones, used as building material in ancient and modern architectures.

    更新日期:2017-12-18
  • Plasma induced degradation and surface electronic structure modification of Poly(3-hexylthiophene) films
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-14
    Marinos Tountas, Dimitra G. Georgiadou, Angelos Zeniou, Kostas Seintis, Anastasia Soultati, Ermioni Polydorou, Spyros Gardelis, Antonios M. Douvas, Thanassis Speliotis, Dimitris Tsikritzis, Stella Kennou, Mihalis Fakis, Evangelos Gogolides, Dimitris Tsoukalas, Panagiotis Argitis, Maria Vasilopoulou

    Plasma treatment is an environmentally friendly solution for modifying or nanostructuring the surface of several materials including photoactive polymers. The detailed characterization of the effect of plasma treatment on chemical and optoelectronic properties of photoactive polymers is, therefore, of specific interest. Herein, the effect of the exposure of poly(3-hexylthiophene) (P3HT) thin films to plasma created in three different gases (oxygen, argon and hydrogen) was studied. A range of spectroscopic techniques, such as x-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy in conjunction with UV–vis absorption, Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopies, are employed to quantify the extent of chemical modification occurring in each particular case. It is shown that oxygen plasma treatment leads to the disruption of the π-conjugation via the direct oxidation of the sulfur atom of the thiophene ring while the aliphatic side chain remains nearly unaffected. An oxidation mechanism is proposed according to which the sulfur atom of the thiophene ring is oxidized into sulfoxides and sulfones, which subsequently degraded into sulfonic esters or sulfonic acids in a relatively small degree. For argon and hydrogen plasma treatments some oxidation products are detected only at the polymer surface. In all cases the polymer surface Fermi level is shifted closer to the highest occupied molecular orbital (HOMO) energy after plasma treatment indicating p-type doping arising from surface oxidation.

    更新日期:2017-12-15
  • Biodegradation rate of biodegradable plastics at molecular level
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-13
    Selene Chinaglia, Maurizio Tosin, Francesco Degli-Innocenti

    Plastics are solid materials where biodegradation happens on the surface. Only the surface is affected by biodegradation while the inner part should not be readily available for biodegradation. Thus, at a laboratory level, the biodegradation rate is expected to be a function of the surface area of the tested sample. The higher the surface area, the higher the biodegradation rate, all other environmental conditions being equal. In order to further explore the role of particle size on biodegradability, plastic pellets of polybutylene sebacate were milled and sieved into different particle sizes, thus obtaining four samples, pellets included, with different specific surface areas (33, 89, 193, and 824 cm2g-1). The surface areas were assessed through direct measurement (pellets) or a theoretical estimation followed by an image analysis. The different samples were tested for biodegradation in soil for 138 days. The rates calculated with a linear regression in the first part of the biodegradation process were related to the respective total available surface area. The data are well described by a linear regression of the double reciprocal plot (the Lineweaver-Burk approach used in enzymatic kinetics) that enables the estimation of the theoretical maximum biodegradation rate (kmax = 97 mg Cpolymer day−1). The kmax can be considered as an estimation of the biodegradation rate at molecular level, when the available surface area is not limiting biodegradation. An additional hypothesis is that the same polymer tested in soils with different microbial loads would display different kmax. The Michaelis constant (Km), i.e. the surface area at which the reaction rate k is half the maximum rate, is 1122 cm2. It is remarkable to notice that if polybutylene sebacate could be tested in a nanopolymeric form, it could very likely satisfy the Organization for Economic Co-operation and Development (OECD) criteria of “ready biodegradability” for chemicals (e.g. 60% biodegradation in a 10-day window within a 28-day test). This is the first time that the biodegradation kinetics of a solid polymer have been estimated by using the Michaelis-Menten approach.

    更新日期:2017-12-14
  • Application of ammonia pretreatment to enable enzymatic hydrolysis of hardwood biomass
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-12
    Kiyoshi Sakuragi, Kiyohiko Igarashi, Masahiro Samejima

    Ammonia pretreatment greatly improves enzymatic hydrolysis of grass biomass, but is reported to be ineffective for hardwood biomass. Here, we examined the effectiveness of ammonia pretreatment of biomass from six hardwood species with different contents of xylan and lignin. Ammonia pretreatment greatly improved enzymatic hydrolysis of polysaccharides in birch and willow, but was less effective for acacia, eucalyptus, and poplar. The effectiveness of ammonia pretreatment increased with xylan content but decreased with lignin content of the hardwood species. By adding a recombinant xylanase to the commercial enzyme digestion cocktail, the yield of enzymatic hydrolysis of ammonia-pretreated birch biomass was improved to a similar level to that obtained with grass biomass. Our results indicate that enzymatic hydrolysis of biomass from hardwood species having a relatively high xylan/lignin ratio can be achieved with a xylanase-enriched enzyme cocktail after ammonia pretreatment.

    更新日期:2017-12-14
  • Methanolysis of microbial polyester poly(3-hydroxybutyrate) catalyzed by Brønsted-Lewis acidic ionic liquids as a new method towards sustainable development
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-11
    Xiuyan Song, Fusheng Liu, Hui Wang, Chan Wang, Shitao Yu, Shiwei Liu

    Chemical recycling of bio-based polymer poly(3-hydroxybutyrate) (PHB) by methanolysis was discussed in detail from the perspective of biological refining. The results of methanolysis transformed PHB into ester monomer successfully by using some ionic liquids. PHB was depolymerized into methyl 3-hydroxybutyrare (M3HB) at lower degradation temperatures in the presence of Brønsted-Lewis acidic ionic liquid 1-(3-sulfonic acid)-propyl-3-methylimidazole ferric chloride ([MIMPS]FeCl4 as catalyst. Obtained M3HB from this reaction can be used in many areas, which is consistent with the principles of sustainable development. Then, the influences of reaction parameters on PHB methanolysis were investigated and the optimum conditions were obtained. Under the optimum conditions, the conversion of PHB and yield of M3HB was 98.5% and 87.4%, respectively. This catalyst could be recycled up to 6 times with no apparent decrease in catalytic activity. At the same time, the methanolysis mechanism of PHB is proposed through the experiments. In addition, kinetic study indicated that this reaction was pseudo-first-order reaction with activation energy of 24.74 kJ/mol.

    更新日期:2017-12-14
  • Effect of styrene butadiene rubber on the light pyrolysis of the natural rubber
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-06
    Pan Song, Xiaoyu Wu, Shifeng Wang

    The use of styrene butadiene rubber (SBR) in tire rubber presents a challenge for the recycling of tire rubber because of its complex degradation behavior compared with that of natural rubber (NR). The effect of the composition of SBR on the degradation of NR was observed by light pyrolysis at variable times at 300 °C. The morphology, sol-gel evolution of the NR/SBR blends and the degradation mechanism was investigated. In addition, the structural evolution of the sol and gel fractions were measured by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results indicated that the mechanism of degradation between SBR and NR differed significantly at 300 °C. The broken molecular chains present in SBR recombined with themselves or those of NR to form a new crosslinked network. The results also showed that the ratio of NR/SBR in the sol and gel fractions remains almost constant and unrelated to the original ratio of the NR/SBR blends. Following an increase in SBR content, the sol fraction of different NR/SBR blends mainly consisted of the small molecular chains of NR, whereas the gel fraction mostly constituted re-crosslinked SBR molecular chains.

    更新日期:2017-12-14
  • The effect of de- and re-polymerization during heat-treatment on the mechanical behavior of Scots pine sapwood under quasi-static load
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-06
    Michael Altgen, Tuuli Uimonen, Lauri Rautkari

    Loss in strength and ductility is a major drawback for the heat-treatment of solid wood. Previous studies focused mainly on the de-polymerization of cell wall constituents as a cause and the importance of the preferential removal of hemicelluloses. This study tested the hypothesis that the mechanical behavior of wood is additionally affected by re-polymerization reactions within the cell wall matrix during heat-treatment. This was achieved by comparing changes in chemical composition, FT-IR spectra, and mechanical properties of Scots pine sapwood that was heat-treated in either dry state in superheated steam or in wet state using pressurized hot water. Although preferential de-polymerization of hemicelluloses was evident for both heat-treatment techniques, the analysis of the chemical composition and FT-IR spectroscopy indicated additional re-polymerization reactions within the cell wall matrix of dry heat-treated wood. The consequent formation of covalent bonds and cross-links increased the resistance against compression loads and hindered inelastic deformation during bending. This resulted in an additional reduction in bending strength and strain energy density of dry compared to wet heat-treated wood. Re-polymerization reactions during heat-treatments of wood in dry state were suggested as the main cause for the brittle failure under bending loads, while the effect of hemicellulose-removal on brittleness was much smaller than stated previously.

    更新日期:2017-12-14
  • Fire retardant sol-gel coated polyurethane foam: Mechanism of action
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05
    S. Bellayer, M. Jimenez, B. Prieur, B. Dewailly, A. Ramgobin, J. Sarazin, B. Revel, G. Tricot, S. Bourbigot

    This paper investigates the flame retardant (FR) mechanism of action of a flexible PU foam, flame retarded with a sol-gel coating made of a mixture of tetraethoxysilane (TEOS), methyl triethoxysilane (MTES), 3-amino propyl triethoxysilane (APTES) and diethyl phosphite (DEP) in an ethanol/water solution. To build a mechanism of action, the coating as well as the residues obtained after fire testing were analyzed using solid state nuclear magnetic resonance (NMR), rheology, thermogravimetric analyses coupled with infrared detection (TGA-FTIR), microcalorimetry of combustion (MCC), smoke box and Pyrolysis Gas chromatography coupled with mass spectrometry (Py-GCMS). The coating shows an intumescent behavior upon burning exhibiting significant expansion and bubbling. The expansion occurs in two steps: a first step around 190 °C, related to the release of ethanol, and a second one around 380 °C, related to the release of non-degraded DEP, ammonia and propylene during degradation of the PU matrix. The flame retardant effect occurs (i) in the condensed phase by intumescence, which yields a thermal insulating layer made of a SiO2 and Si-O-P network mixed with orthophosphate at the surface of the PU foam, but also (ii) in the gas phase by the release of non-degraded DEP, which acts as free radical scavenger. The coating allows the protection of the underlying PU foam during burning as well as the reduction of the amount of smoke released.

    更新日期:2017-12-14
  • Multi detection in Size-Exclusion Chromatography of electron beam irradiated Ethylene Norbornene Copolymers
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05
    Hala Barakat, Wowro Sonia Rosine Lago, Caroline Aymes-Chodur, Ange Privat Ahoussou, Najet Yagoubi

    Ethylene Norbornene Copolymers (ENCs) belong to the Cyclic Olefin Copolymers (COC) family and are used in numerous industrial fields. The goal of this paper is to compare the behavior under electron beam radiation of three grades of ENCs. Several radiation doses have been tested: 25 kGy to simulate sterilization dose and higher doses (75 and 150 kGy) to emphasize the electron beam effect on polymer ageing. By using Triple Detection (Refractometer/Laser Scattering/Viscometer) Size-Exclusion Chromatography, we wanted to study more accurately the evolution of ENCs under radiation than the previous studies available. Thanks to Triple detection, molecular weights were calculated without being dependent of calibration standards, branching was evidenced as the major effect of electron beams on those materials over a dose of 25 kGy, and long chain branching and branching chains frequencies were also calculated. This study focuses on the effect of additive concentration and norbornene (NB) content and a trend has merged: for a same NB content, the higher the phenolic antioxidant concentration, the less crosslinked was the copolymer with the dose. By increasing NB content, radiation effects were minimized.

    更新日期:2017-12-14
  • Intercalation of phosphotungstic acid into layered double hydroxides by reconstruction method and its application in intumescent flame retardant poly (lactic acid) composites
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05
    Sheng Zhang, Yongxin Yan, Wenjia Wang, Xiaoyu Gu, Hongfei Li, Jianhua Li, Jun Sun

    Phosphotungstic acid is a typical kind of superior catalysts, and it is hardly to intercalate into the layered double hydroxides (LDH) by ion-exchange process because of its low negative charge. In this work, a phosphotungstic acid intercalated MgAl-LDH (PWA-LDH) was prepared by reconstruction method, and it was then introduced into poly (lactic acid) (PLA) resin in association with intumescent flame retardant (IFR) by melt blending to prepare a flame-retardant biodegradable PLA composite. The effects of PWA-LDH on the flame retardancy of PLA composites were characterized by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. The results showed that the composite sample containing 18.0 wt% IFR and 2.0 wt% PWA-LDH achieved the maximal LOI value of 48.3%, passed the UL-94 V-0 rating, and significantly decreased the peak heat release rate from 306.3 kW/m2 of neat PLA to 40.1 kW/m2. Thermogravimetric analysis showed that both the thermal stability and the char formation were enhanced. The char morphology observation revealed that PWA-LDH was beneficial to form dense and compact char layers. It was demonstrated that there existed a synergistic effect between IFR and PWA-LDH in promoting the char formation and enhancing the fire resistance.

    更新日期:2017-12-14
  • Long term stabilization of pe by the controlled release of a natural antioxidant from halloysite nanotubes
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05
    József Hári, Márk Sárközi, Enikő Földes, Béla Pukánszky

    A natural antioxidant, quercetin, was adsorbed on the surface of halloysite nanotubes in various amounts to prepare a controlled release device. The combined additive was added to polyethylene providing antioxidant levels of 250, 500, 750 and 1000 ppm. All polymer samples contained 1000 ppm Sandostab PEPQ phosphonite secondary antioxidant as well. The stabilizing efficiency of quercetin was determined in processing experiments and by accelerated ageing. Quercetin proved to be a very efficient stabilizer of polyethylene. The use of the halloysite nanotube support resulted in more homogeneous dispersion and facilitated the dissolution of the compound in the polymer. Because of the high energy of halloysite surface, the stabilizer adhered to it very strongly and did not dissolve in polyethylene below a critical concentration. The melt stabilization efficiency of quercetin did not decrease in the presence of the halloysite support. The efficiency of long term stabilization decreased somewhat, but halloysite nanotubes pretreated with the stabilizer possessed a controlled release function, ageing was slower in their presence than with separately dispersed components or in the absence of the halloysite.

    更新日期:2017-12-14
  • Influence of oxidation on the dynamics in amorphous ethylene-propylene-diene-monomer copolymer: A molecular dynamics simulation
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05
    Weiwang Wang, Yasuhiro Tanaka, Tatsuo Takada, Shinya Iwata, Hiroaki Uehara, Shengtao Li

    This work is dedicated to the mechanism underlying the influence of the oxidation on the dynamic and static characteristics of ethylene-propylene-diene monomer (EPDM) copolymer. A molecular dynamics simulation was employed to provide an insight into the effects of oxidation on the micro and macroscopic properties, such as the density and self-diffusion, free volume, glass transition, and chain transition dynamics. The carbonyl product, the chain scission, and the crosslinking in the EPDM were considered. Self-coefficients and radial distribution function were analyzed to achieve the diffusion and the structure of the systems using a 10 ns produce run at an equilibrium (298 K). The temperature dependence of glass transition and the autocorrelation function for internal torsional rotation have been discussed for understanding the chain dynamics and flexibility after aging, such as the relaxation time and the activation energy. It turns out that the introduction of more carbonyl groups suppresses the internal rotation and the conformational transition of the chains, resulting in the decrease of diffusion and less flexibility due to the strong polar interaction. A system associated with short chains after chain scission possesses a low activation energy, indicating a more flexibility of the chains. Furthermore, the crosslinked structure contributes to the weak chain transition of EPDM (higher Tg) and the high modulus (harden). The different molecular dynamics could be derived from the interaction energy and the structures, such as polar and nonbonded interaction. Some aspects of the details of chain rotation are discussed in this paper.

    更新日期:2017-12-14
  • Multi-scale and multi-technical analysis of the thermal degradation of Poly(Ether imide)
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05
    Emilie Courvoisier, Yoann Bicaba, et Xavier Colin

    The thermal degradation of PEI has been studied in wide ranges of temperature (between 180 and 250 °C) and oxygen partial pressure (between 0.21 and 50 bars). On one hand, the chemical ageing mechanisms have been analysed and elucidated by FTIR spectrophotometry and by differential calorimetry (DSC) on sufficiently thin PEI films (between 10 and 60 μm thickness) to be totally free of the effects of oxygen diffusion. As expected, and by analogy with other aromatic polymers of similar chemical structure, oxidation occurs preferentially on the methyl groups of the isopropylidene unit of the bisphenol A part, thus causing the disappearance of their characteristic IR absorption band at 2970 cm−1 and the growth of a new IR absorption band at 3350 cm−1, attributed to alcohols. In addition, oxidation leads successively to a relative predominance of chain scissions and crosslinking, resulting in a non-monotonic change of Tg. On the other hand, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on polished cross-sections of PEI plates of 3 mm thickness. The diffusion control of oxidation leads to the development of profiles of Young's modulus within the sample thickness, which correlate perfectly with the changes in chemical structure determined by FTIR spectrophotometry. However, the increase in Young's modulus in the superficial oxidized layer is not the direct consequence of oxidation but of a physical ageing.

    更新日期:2017-12-14
  • Thermal and mechanical properties of graphene oxide nanocomposite hydrogel based on poly (acrylic acid) grafted onto amylose
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05
    Mohammad Taghi Taghizadeh, Reza Abdollahi, Samira Savani

    In the present study, a nanocomposite hydrogel was synthesized based on poly (acrylic acid) grafted onto amylose (PAA-g-amylose) which was containing different loadings of graphene oxide (GO) nanosheets. The structural properties of optimized sample were characterized by X-ray analysis (XRD) and Fourier transform infrared spectroscopy (FTIR). The thermal and mechanical behaviors of synthesized hydrogel were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. XRD and scanning electron microscopy study demonstrates the formation of highly exfoliated GO layers and its homogenous dispersion throughout the polymer matrix with 3 and 5wt% GO. However, the intercalated structure is predominant with 5wt% GO. The homogenous and the strong interaction of the GO layers and the PAA-g-amylose hydrogel matrix induced the significant improvement in thermal and mechanical properties of the nanocomposite hydrogel. The tensile strength and elastic modulus of the nanocomposite hydrogel increased by 124% and 26%, respectively with 3wt% GO loading. The thermal stability improved by 67 °C and Tg shifted higher temperature by 53 °C at 5wt% GO loading, compared to the pristine hydrogel matrix.

    更新日期:2017-12-14
  • 更新日期:2017-12-14
  • 更新日期:2017-12-14
  • PEG-based nanocomposite hydrogel: Thermo-responsive sol-gel transition and degradation behavior controlled by the LA/GA ratio of PLGA-PEG-PLGA
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-02
    Midori Kitagawa, Tomoki Maeda, Atsushi Hotta

    The sol-gel transition behavior and the degradation behavior of the nanocomposites consisting of laponite clay nanoparticles and poly(D, L-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(D,L-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers (laponite/PLGA-PEG-PLGA nanocomposites) were studied changing the LA/GA ratios of the PLGA blocks in the PLGA-PEG-PLGA. The thermo-responsive sol-gel transition at the physiological temperature (25–37 °C) was observed using the PLGA-PEG-PLGA with a high PEG/PLGA ratio of ∼0.8 regardless of the LA/GA ratios (LA/GA: 1.1, 4.0, and 8.8). The decomposition rates of the laponite/PLGA-PEG-PLGA nanocomposites at 37 °C were regulated by adjusting the LA/GA ratios (LA/GA: 1.1, 4.0, and 8.8). Specifically, ∼45% of the weight loss was observed after 10 days of the decomposition for the laponite/PLGA-PEG-PLGA nanocomposites with the LA/GA ratio of 1.1, while ∼30% of the weight loss was observed after 10 days of the decomposition for the laponite/PLGA-PEG-PLGA nanocomposites with the LA/GA ratios of 4.0 and 8.8.

    更新日期:2017-12-14
  • Synthesis and flame retardant efficacy of hexakis(3-(triethoxysilyl)propyloxy)cyclotriphosphazene/silica coatings for cotton fabrics
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-02
    Michał Dutkiewicz, Marcin Przybylak, Rafał Januszewski, Hieronim Maciejewski

    The development of novel flame retardants for cotton textiles that form a stable layer on the textile fiber is of high economical and practical relevance. Hexakis(3-(triethoxysilyl)propyloxy) cyclotriphosphazene has been synthesized in this work as a novel flame retardant capable of bonding to cotton fiber surface. This is the first report on the application of hydrosilylation to synthesis of triethoxysilyl cyclophosphazene derivative. The flame retardant properties of treated cotton textiles were assessed by measuring heat release rate on a pyrolysis-combustion flow microcalorimeter and determining the limiting oxygen index, whereas the thermal stability was studied by thermogravimetry. The modified fabrics were characterized by SEM-EDS analysis and surface morphology. The influence of the preparation methodology of the coating on the flame retardant performance and thermal stability are discussed.

    更新日期:2017-12-14
  • Mechanical recycling: Compatibilization of mixed thermoplastic wastes
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-11-06
    Joachim Maris, Sylvie Bourdon, Jean-Michel Brossard, Laurent Cauret, Laurent Fontaine, Véronique Montembault

    Plastics have numerous properties that render them superior to other materials in many applications. Since the past 50 years, the use of plastics has dramatically increased in our daily lives. However, household refuse and industrial disposal of plastic materials is a major environmental concern. Because of legal requirements, which have been enforced to protect the environment, there is a pressing need to develop methods to recycle plastic waste. Mechanical recycling has emerged as the most economical, as well as the most energetic and ecologically efficient option. After introducing the mechanical recycling concept, this review will focus on the strategies that have been used for compatibilization of blends of mixed thermoplastic waste.

    更新日期:2017-12-14
  • Thermogravimetric evaluation of novel antimicrobial phthalimido aromatic 1,3,4-oxadiazole derivatives as stabilizers for rigid PVC
    Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-09-23
    Nadia A. Mohamed

    A series of novel N-aryl phthalimides containing the aromatic 1,3,4-oxadiazole system has been synthesized starting from their corresponding precursors phthalimido aromatic hydrazide derivatives via a thermally induced cyclodehydration reaction. The synthesized derivatives' structures were elucidated on the basis of elemental analyses, FTIR, 1H-NMR, and mass spectroscopy. They were screened for antibacterial activity against Bacillis subtilis and Streptococcus pneumoniae as Gram-positive bacteria and against E. coli as Gram-negative bacteria and for antifungal activity against Aspergillus fumigatus, Geotricum candidum and Syncephalastrum racemosum fungi by agar well diffusion method. They showed good antimicrobial activity as judged by their high inhibition zone diameter and low minimum inhibition concentration. They are more potent against Gram-positive bacteria than against Gram-negative bacteria. Some of the prepared derivatives displayed comparable or even better antibacterial and antifungal activities than the reference bactericides or fungicides. These derivatives were evaluated as thermal stabilizers for rigid PVC using thermogravimetric analysis under a nitrogen atmosphere. They exhibited improved heat stabilizing effects relative to dibasic lead carbonate (DBLC), cadmium-barium-zinc (Cd-Ba-Zn) stearate complex and di-n-octyltin bis (isooctylmercaptoacetate) (n-octyltin mercaptide, n-OTM) reference thermal stabilizers as shown by their higher initial decomposition temperature and higher residual weight percent at particular temperatures. Their stabilizing efficiency is also illustrated by lower rates both of discoloration as well as degree of chain scission of the polymer during degradation. The stabilizing efficiency increased with the introduction of electron donating substituent groups in the aromatic ring of 1,3,4-oxadiazole part of these derivatives.

    更新日期:2017-12-08
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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