Polymer Degradation and Stability (v.133, #C)
High mechanical strength and stability of alginate hydrogel induced by neodymium ions coordination by Shunli Liu; Mengmeng Kang; Imtiaz Hussain; Kewen Li; Fang Yao; Guodong Fu (1-7).
An alginate-based, stable and high mechanical strength hydrogel was fabricated by trivalent ions coordination in the presence of neodymium Ions. The chemical components and morphology of the hydrogel were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The effects of pH values on the swelling properties of hydrogels were investigated as it reveals that the pH values have an obvious effect on the swelling ratio. The as-prepared hydrogel exhibited high compressive strength and stability, which is much higher than that of the alginate hydrogel formed by Ca2+ ionic cross-linked. Moreover, the Nd(III)-Alg hydrogel also exhibited the properties of fluorescence. The easy and fast fabrication, outstanding mechanical and stable properties indicated the hydrogel as a promising material that can be used in cartilage tissue.
Keywords: Alginate; Hydrogel; Stability; Lanthanide ions; Coordination;
Synergistic effect of chitosan-based flame retardant and modified clay on the flammability properties of LLDPE by Mohamed Hassan; Mohamed Nour; Yasser Abdelmonem; Ghada Makhlouf; Aksam Abdelkhalik (8-15).
The synergistic effect of melamine salt of chitosan phosphate (MCHP) and organic modified montmorillonite (OMMT) on the thermal stability and flammability properties of linear low density polyethylene (LLDPE) was studied. MCHP was synthesized by reaction of chitosan phosphate with melamine. OMMT was formed by the reaction of cetyl trimethyl ammonium bromide (CTAB) with sodium montmorillonite. The structures of MCHP and OMMT were characterized by FTIR and 1H NMR. The thermogravimetric analysis of various LLDPE composites showed that the addition of OMMT to MCHP effectively improved the thermal stability of LLDPE and increased the char residues. The flammability properties of LLDPE composites demonstrated that addition of 1 wt% OMMT to 30 wt% MCHP promoted achieving V-0 rating in UL-94 test. Moreover, it participated remarkably in decreasing the peak of heat release rate (pHRR), total heat release (THR), CO and CO2 emissions, and fire growth index (FGI). This indicated that addition of OMMT/MCHP reduced the fire risks of LLDPE. The digital photographs and SEM images of char formed after cone calorimeter test showed that addition of 1 wt% OMMT with MCHP promoted the formation of coherent and compact char layer.
Keywords: Synergistic effect; Chitosan; OMMT; Intumescent; Flammability; LLDPE;
Improving crosslinking of stabilized polyacrylonitrile fibers and mechanical properties of carbon fibers by irradiating with γ-ray by Weizhe Zhao; Yonggen Lu; Jing Wang; Qiang Chen; Liangxiao Zhou; Junqi Jiang; Li Chen (16-26).
Polyacrylonitrile (PAN) fibers were stabilized continuously through a series of temperature zones, and the stabilized PAN fibers (SFs) taken out from different zones were irradiated with γ-ray, finally, some of the irradiated SFs were carbonized continuously. Structure changes of the SFs and mechanical properties of the derived carbon fibers were investigated. It is found that γ-ray not only could destroy the nitrile crosslinking bonds and form nitrile groups again in slight SFs, but could make more crosslinked structure including ether crosslinking and carbon-carbon crosslinking in slight and deep SFs, which improved thermal stability of the SFs and tensile strength of the carbon fibers. The irradiation also induced cyclization in short sequence in slight SFs, however, such a cyclization structure didn't significantly improve thermal stability.
Keywords: Stabilized PAN fibers; γray; Crosslinking mechanism; Thermal stability; High carbon yield;
An innovative approach to construct photodegradation curves for TiO2 incorporated latex coatings via probing localized degradation by Yongyan Pang; Pengke Huang; Lihua Zhang (27-35).
The main objective of this study was to establish a new approach to construct local photodegradation curves for TiO2 incorporated latex coatings via innovatively probing polymer photodegradation in the vicinity of nanoparticle agglomerates using laser scanning confocal microscope (LSCM) under a wet and a dry conditions. First, nanoparticle dispersion in surface/subsurface of latex coatings was investigated with LSCM. Second, 2D LSCM images were used to show how nanoparticles were gradually revealed with UV exposure. Third, 3D and ortho LSCM images were applied to illustrate how polymer surface was gradually decreased and how the polymer/nanoparticle interface regions were gradually degraded. The ortho images were also used to calculate the relative vertical height change in polymer matrix and in interface regions referred to the front of nanoparticle agglomerates. Finally, local photodegradation curves in the polymer matrix and in the interface regions were obtained under the wet and dry conditions by plotting the relative changes in height as a function of the UV exposure time. By comparison of the local photodegradation curves in different stages, at different locations and under different exposure conditions, it was found that under UV radiation, after the exposure of nanoparticles onto polymer surface, the photocatalytic effect of nanoparticles could significantly affect the photodegradation of the interface of filled coatings, which would result in severely inhomogeneous photodegradation, especially under the wet condition.
Keywords: Photodegradation; Titanium dioxide; Laser scanning confocal microscope; Latex coating; Local photodegradation curve;
The degree of acetylation affects the microbial degradability of mannans by Ran Bi; Jennie Berglund; Francisco Vilaplana; Lauren S. McKee; Gunnar Henriksson (36-46).
Hemicelluloses as major components of plant cell walls are acetylated to different extents. The biological functions of acetylation are not completely understood but suggested that one reason is to decrease the microbial degradability of cell walls. Model seed galactomannan and glucomannan, which are structurally similar to an abundant class of wood hemicelluloses, were acetylated to various degrees and used as sole carbon source on agar plates for microbial growth. When soil samples were inoculated on the plates, significantly fewer strains grew on the agar plates with highly acetylated mannans than with slightly acetylated or non-acetylated mannans. One filamentous fungus isolated and identified as a Penicillium species was shown to grow faster and stronger on non-acetylated than on highly acetylated mannan. The data therefore support the hypothesis that a high degree of acetylation (DSac) can decrease the microbial degradability of hemicelluloses. Possible mechanisms and the technological significance of this are discussed.
Keywords: Wood biodegradation; Acetylation; Hemicellulose; Mannan; Microorganism; Biodegradability;
Sustainable fire retardancy of textiles using bio-macromolecules by Santanu Basak; S. Wazed Ali (47-64).
The field of the flame retardant finishing of polymeric textile substrates is facing numerous challenges for the living beings because of the toxicity, carcinogenicity and effluent generation issues related to the finishing agent used for developing this novel property. Therefore, to this end, a lot of innovative researches have been performed and reported by the researchers to meet those critical issues. In the same line, very recently, different bio-macromolecules also have come into the domain of the fire retardant finishing. The latest research findings on the fire retardancy of polymeric substances using different bio-macromolecules (protein, plant, starch, chitosan based) are critically summarized in this review. The mechanisms behind the thermal stability of the materials are also highlighted in detail. Besides, the article provides a brief knowledge on the thermal degradation, structural composition of both the bio-macromolecules and the polymeric substrate. The degradation mechanism of bio-macromolecule treated polymeric substrates is also presented. In addition, the composition summarizes the comparison on the effect of different bio-macromolecules imparted to textiles. Advantages and current challenges of using these novel bio-macromolecules in the area of fire retardancy of materials have also been discussed.
Keywords: Cellulose; Bio-macromolecule; Thermal degradation; Char morphology; Flame retardant;
Evaluation of the co-pyrolysis of lignin with plastic polymers by TG-FTIR and Py-GC/MS by Wei Jin; Dekui Shen; Qian Liu; Rui Xiao (65-74).
Lignin extracted from black liquor was co-pyrolyzed with three kinds of plastic polymers (low density polyethylene (LDPE); polycarbonate (PC); polystyrene (PS)), in order to investigate the effect of plastic polymers on the distribution of pyrolysis products (especially monomeric aromatic compounds). TG-FTIR and Py-GC/MS were employed to understand the thermal behavior and identify the typical products from the pyrolysis of individual samples and their mixtures (mass ratio for the mixture: 1:1). For TG-FTIR analysis, the thermal decomposition behavior of lignin-PC mixture exhibits notable difference between the experimental and estimated results over that of lignin-PS mixture and lignin-LDPE mixture. The apparent activation energy for the main conversion zone of co-pyrolysis of lignin with PC (73.08 kJ/mol) is lowest among those of the lignin-plastic mixtures (180.17 kJ/mol for lignin with LDPE and 179.91 kJ/mol for lignin with PS mixtures), suggesting the strongest interaction between lignin and PC. The H2O produced by the decomposition of lignin at low temperature may promote the hydrolytic reaction of PC and the release of CO2. The production of several aromatic compounds assigned to lignin pyrolysis was suppressed by the addition of PC or LDPE, while the formation of monomer aromatic hydrocarbons was notably promoted during the co-pyrolysis of lignin with PS.
Keywords: Lignin; Plastic polymers; Co-pyrolysis; Mechanism; Aromatic compounds;
Biodegradable soy protein films with controllable water solubility and enhanced mechanical properties via graft polymerization by Yi Zhao; Helan Xu; Bingnan Mu; Lan Xu; Yiqi Yang (75-84).
Graft polymerization of acrylic acid endowed soy protein films with good tensile properties and water solubility without sacrificing biodegradability. In this research, soy protein was grafted with acrylic acid and cast into biodegradable films as substitutes of non-biodegradable Poly(vinyl alcohol) (PVA) films. The grafted soy protein films had 318%, 114%, 60% and 9% higher tensile strength, elongation, dissolving rate and transmittance, compared to ungrafted ones, respectively. Acrylic acid grafting provided soy protein films with biodegradability, flexibility, and adhesion to yarns substantially higher than PVA, while water solubility and abrasion resistance similar to PVA, leading to high potential applications of the grafted soy proteins in the fields of water soluble packaging films and slashing to substitute PVA.
Keywords: Soy protein; Poly(vinyl alcohol); Water soluble film; Biodegradation; Graft polymerization; Acrylic acid;
Effect of nano zinc oxide as UV stabilizer on the weathering performance of wood-polyethylene composite by Davood Rasouli; Nadka Tzankova Dintcheva; Mehdi Faezipour; Francesco Paolo La Mantia; Mohammad Reza Mastri Farahani; Mehdi Tajvidi (85-91).
In this study, the effect of using nano-sized zinc oxide (ZnO) particles on the enhancement if the degradation resistance of wood-high density polyethylene (HDPE) composite was investigated through artificial weathering. Samples with different amounts of ZnO mixing ratio (0, 1, 2, and 4 wt%) were manufactured using an internal mixer followed by compression molding. The prepared samples were then exposed to the artificial weathering process in a QUV weatherometer. The weathering behavior of samples was characterized using tensile strength, contact angle analysis, colorimetry, ATR-FTIR spectroscopy and FE-SEM. The results indicated that the amount of surfaces crack, tensile strength loss and contact angle changes decreased as a function of ZnO addition, while lightness changes were not affected. Analysis of the functional groups at the composite surface by ATR-FTIR showed that the incorporation of nano-sized ZnO particles in the composite formulation changed the degradation mechanism of composite to photocatalytic reactions, leading to the production of high levels of zinc carboxylate in the structure of weathered composite.
Keywords: Wood-HDPE composite; Weathering; Nano-zinc oxide; UV absorbent;
Thermo-oxidative stabilization of poly(lactic acid) with antioxidant intercalated layered double hydroxides by Lucía Pérez Amaro; Francesca Cicogna; Elisa Passaglia; Elisabetta Morici; Werner Oberhauser; Sahar Al-Malaika; Nadka Tzankova Dintcheva; Serena Coiai (92-100).
Two antioxidant modified layered double hydroxides (AO-LDHs) were successfully prepared by the intercalation of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (IrganoxCOOH) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) in the layered structure of LDH. It was found that by anchoring the phenolic moieties to the LDH layers the antioxidant power is retained in the case of Trolox, and even amplified in the case of IrganoxCOOH. A small amount of the two AO-LDHs was incorporated into poly(lactic acid), PLA, by solution mixing and melt extrusion. The thermo-oxidative stability of the composites was compared with that of the neat PLA and PLA containing free AOs. SEC analysis indicates that, after a controlled period of ageing, both the AO-LDHs protect the PLA from chain scission. The oxidation induction time (OIT, DSC) at 230 °C shows also the beneficial effects of the presence of the functional filler in the polymer matrix. Further, results from a preliminary migration test suggest that the AO species have a low tendency to migrate away from the AO-LDHs embedded in the polymer matrix thus keeping the AO protected inside the nanofiller layers thereby remaining active for a longer time.
Keywords: Antioxidants; Layered double hydroxides (LDHs); Poly(lactic acid); Thermo-oxidative degradation;
Study on the photodegradation of nanocomposites based on polypropylene and TiO2 nanotubes by Paula A. Zapata; Andrés Zenteno; Nicolás Amigó; Franco M. Rabagliati; Francisco Sepúlveda; Fernando Catalina; Teresa Corrales (101-107).
Composites of polypropylene (PP) were synthesized by the melting process in the presence of titanium dioxide nanotubes (TiO2-Ntbs). Nanotubes were used either as synthesized or organically modified with hexadecyltrimethoxysilane (Mod-TiO2-Ntbs). The photoageing of the neat PP and PP-TiO2-Ntbs was studied during 10 days. The nanotubes incorporated into the PP promoted and accelerated its photodegradation due to reactive species generated during irradiation. PP-Mod-TiO2-Ntbs composites with 8% of modified nanotubes produced the highest degradation according to chemiluminescence analysis (CL), carbonyl index (CI), degree of crystallinity (%χ), and thermogravimetric analysis (TGA). Furthermore, SEM analysis after photoageing the polymers presented several cavities of ca. 5 μm.
Keywords: Polypropylene; Nanocomposites; TiO2 nanotubes; Photoaged polypropylene;
Biotemplate-SnO2 particles intercalated PANI matrix: Enhanced photo catalytic activity for degradation of MB and RY-15 dye by M. Karpuraranjith; S. Thambidurai (108-118).
New biotemplate material with SnO2 particles intercalated to polyaniline (PANI) matrix was synthesized via two step methods. Biotemplate (CS)―SnO2 particles were prepared by chemical precipitation method and effectively assembled on PANI matrix by in-situ chemical oxidative polymerization method. The amine, imine and hydroxyl functional groups of chitosan-SnO2 intercalated PANI was characterized by FTIR spectroscopy. The nanocomposites of fibrous structures collapsed with sphere like structure analyzed from HR-SEM with EDAX. TEM analysis reveals that existence of the formed nanocomposites with size ∼8.46–11.34 nm and the surface area of BSP-0.75 nanocomposites were observed as ∼147.13 m2/g using BET analysis. Thermal stability of biotemplate based SnO2 intercalated PANI was higher than that of CS-PANI composite. The results demonstrate that biotemplate-SnO2 intercalated PANI matrix has better reinforced effect compared to other three components. Therefore, Biotemplate based SnO2 particles intercalated to PANI matrix act as an efficient photo catalyst for the degradation of methylene blue and reactive yellow 15 dye under direct sunlight irradiation.
Keywords: Biotemplate-tin oxide; PANI; Nanocomposite; Thermal stability; High surface area; Dye degradation;
Glycolysis of high resilience flexible polyurethane foams containing polyurethane dispersion polyol by D. Simón; A. de Lucas; J.F. Rodríguez; A.M. Borreguero (119-130).
In the last years, high resilience polyurethane foams (HR foams) production has experienced an intensive growth as a consequence of their wide application field, causing an important increment of the generated waste. HR foams containing PU dispersions polyols are the last tendency in the HR foam industry, due to the improvement of the flame retardant properties and the emissions reduction of volatile compounds in comparison to the traditional graft polymeric HR polyols. In this work the extension of the glycolysis process to the recycling of this kind of foams has been carried out. Diethylene glycol (DEG), glycerol 99% PS and crude glycerol, coming from the biodiesel production, have been assayed as glycolysis agents. All of these glycolysis agents provided a split phase product with an upper phase mainly constituted by a traditional HR polyol and a bottom phase consisting of the excess of glycolysis agent and several reaction byproducts. However, the polyol content in the final product has been greater with the employment of glycerol. Moreover, flexible and rigid foams have been synthesized by using the recycled polyols or the glycolysis bottom phase, respectively. This way, it is achieved a global and sustainable recycling process for the valorization of two waste substances: the HR PU foam and the crude glycerol.
Keywords: Polyurethane; High resilience; Glycolysis; Dispersion polyol; Crude glycerol;
Accelerated hydrothermal aging of cycloaliphatic epoxy/graphene nanoparticle composites by J.M. Tomasi; I.D. Helman; W.A. Pisani; D.R. Klimek-McDonald; S. Chinkanjanarot; I. Miskioglu; J.A. King; G.M. Odegard (131-135).
Cycloaliphatic epoxy (CE) resin systems are of primary interest in applications that require improved resistance to harsh conditions relative to other epoxy systems. Because other epoxy systems have demonstrated improved resistance to hydrothermal aging with the addition of carbon-based nanoparticle reinforcement, it is expected that the hydrothermal resistance of CE resins will likewise be improved with incorporation of nanoparticles. Therefore, the objective of this study is to determine the influence of graphene nanoparticles (GNP) on the hydrothermal aging resistance of CE resins. CE specimens are fabricated with varying levels of GNP and exposed to elevated temperatures and moisture levels for varying amounts of time up to 400 h. The results from flexure and dynamical-mechanical testing indicate that the addition of GNP provides modest improvements in the stiffness and glass transition temperature for all aging levels, while the strength is improved for aging times below 400 h.
Keywords: Nanocomposites; Degradation; Hygrothermal; Weathering;
A novel liquid Ca/Zn thermal stabilizer synthesized from tung-maleic anhydride and its effects on thermal stability and mechanical properties of PVC by Mei Wang; Jianling Xia; Jianchun Jiang; Shouhai Li; Kun Huang; Wei Mao; Mei Li (136-143).
A novel liquid Ca/Zn thermal stabilizer was synthesized from tung-maleic anhydride (TMA) as feedstock and evaluated for its stabilizing effects on poly (vinyl chloride) (PVC). First, N-(3-amino-benzoic acid) tung-maleamic acid (ABTMA) was prepared from the ammonolysis of TMA and para-aminobenzoic acid (PABA). Then its complex calcium salt (ABTMA-Ca) and zinc salt (ABTMA-Zn) were synthesized through a one-step method, and investigated by Fourier transform infrared spectroscopy and elemental analysis. ABTMA-Ca and ABTMA-Zn were separately treated with diethylene glycol monobutyl ether at 120 °C for 3 h to form liquid ABTMA-Ca (LABTMA-Ca) and liquid ABTMA-Zn (LABTMA-Zn). The effects of LABTMA-Ca/LABTMA-Zn, CaSt2/ZnSt2 and C36DA-Ca/C36DA-Zn on thermal stability of PVC were studied through Congo Red test, discoloration tests and dynamic thermal stability analysis. The LABTMA-Ca/LABTMA-Zn thermal stabilizer exhibit excellent long-term stability. Analysis of tensile and dynamic mechanical properties shows PVC samples stabilized with LABTMA-Ca/LABTMA-Zn and the other two Ca/Zn systems all display comparable strength, modulus and glass transition. A common stabilizing mechanism of LABTMA-Ca/LABTMA-Zn system and its radical mechanism were presented, respectively.
Keywords: Poly(vinyl chloride); Tung-maleic anhydride; Para-aminobenzoic acid; Calcium-zinc stabilizers; Liquid thermal stabilizers;
Influence of down shifting particles on the photochemical behaviour of EVA copolymers by Anthony Perthué; Philippe Boutinaud; Sandrine Therias; Jean-Luc Gardette (144-151).
The influence of SrAl2O4: Eu2+, Dy3+ particles (10–30% w/w) on the oxidation of ethylene-vinyl acetate copolymer (EVA) (18 wt% of vinyl acetate) exposed to UV-light irradiation was studied. EVA is sensitive to UV light at wavelengths above 300 nm, as described in the literature. Light-induced oxidation results in the formation of carboxylic acids, and the infrared absorbance of the CO band at 1716 cm−1 was consequently used to follow the oxidation of the EVA polymer. Linear increases were observed in response to increases in the exposure time, and the rate of the photo oxidation of the host matrix EVA was higher for the composite. SrAl2O4: Eu2+, Dy3+ particles strongly absorb in a domain extending up to 455 nm. The absorption of the particles is sufficiently high to compete with the absorption by EVA. As a result, an inner filter effect was expected, but this effect was not observed. Moreover, experiments have been performed as “side experiment” in order to understand the relationship between the oxidation rate and the absorbed light intensity. Samples with different thicknesses ranging from 50 to 160 μm were irradiated. The oxidation rate varied linearly with the amount of absorbed light. The rates of the oxidation of EVA in the neat material and in the composite were compared for irradiations under monochromatic light at 365 nm. The obtained result showed that the rates were similar, although EVA absorbed less in the composite than in the neat material. This result could be attributed to the potential photocatalytic capacity of SrAl2O4: Eu2+, Dy3+ or the diffusion of light by the particles, which increased the optical pathway.
Keywords: Photodegradation; Luminescence; Encapsulating layers; EVA;
Degradable tannic acid/polyethyleneimine polyplex particles with highly antioxidant and antimicrobial effects by Nurettin Sahiner; Selin Sagbas; Mehtap Sahiner; Sahin Demirci (152-161).
Tannic acid/Polyethylene imine (TA/PEI) polyplex particles in spherical form were synthesized via the electrostatic interaction between the TA molecules' phenolic groups and PEI positively charged ammonium groups. The size of polyplex particles was observed to be between 500 nm and 5 μm via SEM images. It was found that the TA/PEI polyplex particles showed thermal durability of 4.8 wt% residue in comparison to both components, TA or PEI, at 900 °C. Hydrolytic degradation of TA/PEI polyplex particles at different pHs e.g., pH 1.5 similar to stomach conditions, pH 7.4 similar to physiologic conditions, and pH 9 similar to intestinal conditions were investigated by UV–Vis spectroscopy by measuring degraded TA amount at 37.5 °C over two days and 65%, 31%, and 52% weight losses were found, respectively. FC, TEAC, and DPPH tests were used to determine the antioxidant properties of TA/PEI polyplex particles. The antimicrobial properties of TA/PEI polyplex particles were determined using micro-dilution and disc diffusion methods against gram-negative Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 10145, gram-positive Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633 bacteria strains, and Candida albicans ATCC 10231 yeast strain. MIC values of TA/PEI polyplex particles were found to change between 0.025 and 0.1 mg/mL concentration depending on the type of microorganism and indicate that the polyplex particles possess strong antimicrobial activity.
Keywords: Polyplex particle; Tannic acid; Polyethylene imine; Antimicrobial/antioxidant; Biocompatible composites; Microgel/nanogel polyplex;
Synthesis of a novel bridged-cyclotriphosphazene flame retardant and its application in epoxy resin by Bin Zhao; Wen-Jun Liang; Jun-Sheng Wang; Fei Li; Ya-Qing Liu (162-173).
A novel flame retardant, named bisphenol-A bridged penta(anilino)cyclotriphosphazene (BPA-BPP), was successfully synthesized. Its chemical structure was characterized by Fourier transform infrared (FTIR), 1H NMR and 31P NMR. Then, different amounts of BPA-BPP were mixed with diglycidyl ether of bisphenol-A (DGEBA) to fabricate flame retardant epoxy resin (EP). Nonisothermal differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were used to study the curing kinetics and thermal degradation behaviors of flame retardant EPs. The results of limiting oxygen index (LOI), vertical burning tests (UL-94) suggested that BPA-BPP exhibited good flame-retarded efficiency on the EP loaded with low phosphorus content. Compared with the neat EP, the LOI value of EP/9%BPA-BPP increased from 21.0 vol% to 28.7 vol%. Furthermore, the peak of heat release rate (PHRR), total heat release (THR), total smoke production (TSP) of the same sample, obtained from cone calorimetry, were declined obviously, suggesting excellent flame retardancy and smoke inhibition. The morphology and chemical structures of the char layers were analyzed by SEM, Raman and FTIR. The Py-GC/MS was used to investigate the pyrolysis behavior and flame-retardant mechanism of BPA-BPP. In the process of heating, aniline, diphenylamine and NH3 were released from BPA-BPP in gaseous phase, and phosphorus-rich carbonaceous chars were left in condensed phase. BPA-BPP could promote EP to form intumencent protective char layers, enhancing flame retardancy of EP effectively.
Keywords: Flame-retardant; Epoxy resin; Phosphazene; Thermal degradation; Cone calorimeter;
A renewable and compostable polymer for reducing consumption of non-degradable plastics by Bahareh Bahramian; Ali Fathi; Fariba Dehghani (174-181).
Poly(propylene carbonate) (PPC) is a biodegradable and partially renewable polymer that is synthesized from CO2. PPC is a suitable alternative to non-degradable polymers and a possible option for effectively recycling CO2. In this study, the properties of PPC are compared with other commercial polymers. It is demonstrated that while the mechanical properties of PPC are comparable to non-degradable polyethylene, its permeability to oxygen and water vapor are remarkably lower. PPC degradation in compost soil is nearly 9% within six months that is comparable with biodegradable polymers such as Eco-Flex. Meanwhile, PPC is chemically stable when exposed to a broad range of simulated media such as low or high pH as negligible mass loss and molecular weight deductions are detected after six months exposure to these media. Therefore, PPC is deemed to be an ideal polymer for food packaging and many other applications such as biomedical devices. The application of PPC can significantly reduce the disposal of non-degradable polymers in landfills and minimize the reliance on fossil fuel based polymers.
Keywords: Poly(propylene carbonate); Biodegradable polymer; Compostable; Packaging;
Lipase-mediated degradation of poly-ε-caprolactone in toluene: Behavior and its action mechanism by Muhammad Haziq Aris; Mohamad Suffian Mohamad Annuar; Tau Chuan Ling (182-191).
Lipase-catalyzed hydrolysis of poly(ɛ-caprolactone) (PCL) in toulene was investigated. PCL with number-average molecular weight (M n) 10,000 g mol−1 was hydrolyzed using immobilized Candida antarctica lipase B (CALB). The increase in PCL concentration led to a decrease in degradation rate. Enhanced rate was observed when reaction temperature was increased from 30 to 50 °C. Enzymatic chain scission of PCL yielded cyclic dicaprolactone, tricaprolactone, tetracaprolactone and oligomers with M n less than ∼1000 g mol−1. Catalytic formation of cyclic lactones via back-biting mechanism in low water content environment was attributed to CALB. Its hydrolysis of PCL displayed consecutive random- and chain-end scission with time from detailed thermal, molecular weight and structural analyses. Apparent activation energy, E a for hydrolysis was 45 kJ mol−1 i.e. half of that reverse reaction. Dicaprolactone and oligomers from hydrolysis readily re-polymerized to produce mid-range polymer with M n 1400 g mol−1 after 36 h in the same reaction medium.
Keywords: Poly(ɛ-caprolactone); Lipase; Enzymatic degradation; Organic solvent; Cyclic lactones; Scission mechanism;
Melt stabilization of polyethylene with dihydromyricetin, a natural antioxidant by B. Kirschweng; K. Bencze; M. Sárközi; B. Hégely; Gy. Samu; J. Hári; D. Tátraaljai; E. Földes; M. Kállay; B. Pukánszky (192-200).
Experiments have been carried out to compare the stabilization effect of two flavonoid type natural antioxidants, dihydromyricetin (DHM) and quercetin (Q) in polyethylene (PE). Additive concentrations changed between 0 and 500 ppm in several steps and 1000 ppm Sandostab PEPQ phosphorus containing secondary stabilizer was also added to each compound. Both antioxidants are very efficient stabilizers for PE, sufficient melt stability was achieved already at 50 ppm DHM content. At small concentrations dihydromyricetin proved to be more efficient melt stabilizer and it protected the secondary antioxidant better than quercetin. In spite of its better efficiency in melt stabilization, polymers containing DHM had the same residual stability as those prepared with quercetin. Accordingly, the larger efficiency does not result from the larger number of active phenolic hydroxyls in the molecule, but from interactions with the phosphorous secondary stabilizer that is stronger or at least different for DHM than quercetin. In spite that DHM is a white powder, it gave the polymer a brownish color which became deeper with increasing number of extrusions and additive content. Nevertheless, both natural antioxidants can be used efficiently for the stabilization of polymers in applications in which color is of secondary importance.
Keywords: Polyethylene; Processing stabilization; Long chain branching; Natural antioxidants; Dihydromyricetin; Solubility; Color;
Antioxidative behavior of a novel samarium complex in styrene-butadiene rubber/silica composites by Yongkun Zou; Yangkun Sun; Yunlong Zhang; Jingwei He; Zhenghai Tang; Lixin Zhu; Yuanfang Luo; Fang Liu (201-210).
The focus of this study was on the thermo-oxidative aging resistance of a new rare earth complex, samarium lysine dithiocarbamate (Sm-LDC), in the styrene-butadiene rubber (SBR)/silica composites. The anti-aging behavior of SBR/silica composites with Sm-LDC, as well as several common commercial antioxidants, was systematically investigated by oxidation induction time (OIT), mechanical testing, crosslink density determination, Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), and thermo-gravimetric analysis (TGA). The results demonstrated that Sm-LDC significantly improve the thermo-oxidative stability of SBR/silica composites and protect the composites against the thermo-oxidative aging more effectively than the widely used antioxidant 4010NA and antioxidant MB in rubber industry. It could be attributed to the synergistic effect between dithiocarboxyl groups and samarium ions in Sm-LDC, which can high-efficiently decompose the hydroperoxide and scavenge the oxy radicals, respectively. Besides, the results of whiteness and yellowness index (Y.I.) analysis indicated that Sm-LDC can hardly cause discoloration to the SBR/silica composites and is better than the recognized light-colored antioxidant MB in the aspect of color. This research might open up new opportunities for preparing highly thermo-oxidative aging-resistant rubber composites without color contamination.
Keywords: Samarium complex; Thermo-oxidative aging; Antioxidant; Styrene-butadiene rubber (SBR);
Improvement of the atomic oxygen resistance of carbon fiber-reinforced cyanate ester composites modified by POSS-graphene-TiO2 by Dequn Peng; Wei Qin; Xiaohong Wu (211-218).
Atomic oxygen (AO) in low Earth orbit (LEO) causes severe damages to the polymer materials used for the construction of spacecraft. To improve the AO resistance of cyanate ester (CE) which is ubiquitous in the space-structures, novel composites prepared by incorporating POSS, graphene and TiO2 (POSS-Graphene-TiO2, PGT) into CE matrix through a solution mixing method. The mass loss ratio of the resulting PGT/CE composites was significantly decreased in comparison to the pristine CE, which is due to the less surface damages. Chemical composition analysis shows that a surface passivation layer is formed on the PGT/CE composites upon exposure to the AO. Carbon fiber-reinforced PGT/CE composites (i.e., T700/PGT/CE) were fabricated. Compared with the T700/CE composite, the interlayer shear strength of the T700/PGT/CE composite was increased by 43% after the AO exposure. Our findings indicate that the PGT fillers contribute the improved AO resistance of the prepared carbon fiber/PGT/CE composites.
Keywords: Cyanate ester; POSS; Composites; Degradation; Atomic oxygen;
Thermal-oxidative aging behavior of nitrile-butadiene rubber/functional LDHs composites by Xianru He; Tianxiang Li; Zhengren Shi; Xin Wang; Fei Xue; Zihong Wu; Qian Chen (219-226).
NBR-based layered double hydroxide (LDH) composites were prepared using a sodium p-styrenesulfonate hydrate (SSS) modified LDH (LDH-SSS) filler through ion exchange. The modified filler, LDH-SSS, was investigated by XRD, FTIR and TGA-DTGA, showing its layered structure was successfully obtained, as compared with the unmodified LDH-NO3. Mechanical tests of the NBR composites showed that their thermal-oxidative aging was improved, specifically by LDH-SSS. ATR-FTIR was used to study for the aging mechanism of composites. The morphology of the composites revealed by SEM and XRD shows a stronger interaction between NBR and the LDH particles with the presence of SSS. The chemical structure and the thermal properties of the composites revealed by various techniques showed an exfoliation phenomenon of the LDH-SSS, and NBR can be branched with LDH-SSS in the aging process of the composites.
Keywords: Acrylonitrile butadiene rubber (NBR); Layered double hydroxides; Sodium p-styrenesulfonate hydrate (SSS); Thermal-oxidative aging properties;
Kinetics of the pyrolysis process of terpene acrylate homopolymers by Marta Worzakowska; Enelio Torres-Garcia (227-233).
The kinetics of the pyrolysis process along with the thermal behavior and evolution of gaseous decomposition products of differently structured, highly solvent and chemically resistant terpene acrylate homopolymers in inert atmosphere, poly(geranyl acrylate) and poly(citronellyl acrylate), were studied by means of the TG/DSC/FTIR-coupled method. In this work, two kinds of model-free-kinetic algorithms, differential Friedman and integral Kissinger–Akahira–Sunose (KAS) methods were combined to obtain the energetic profile in continuous mode as a function of the transformation degree (α). The obtained results were discussed in terms of energetic demand at each degradation stage through the dependence of E(α) on α, and its relationship with the global reaction rate (dα/dt).
Keywords: Terpene acrylate homopolymers; Thermal stability; TG-FTIR; Kinetics;
Tailoring of the thermal, mechanical and dielectric properties of the polypropylene foams using gamma-irradiation by Miroslav Mrlík; Mariam Al Ali Al Maadeed (234-242).
This study investigate the influence of gamma-irradiation (GI) doses from 0 up to 50 kGy on the polypropylene (PP) foams, mainly the impact on their structural and physical properties. It was found that structural properties were not significantly changed and the cellular structure of the PP foams sustain the same, while the thermal properties were significantly enhanced with increasing GI doses, due to the present cross-linking created within the irradiation. The cross-linking was confirmed also by the swelling measurements. The dielectric properties shows the three time increase of capacitance with increasing GI doses, due to the additional charges created in the foam voids by GI. Investigated mechanical properties in case of tensile tests as well as dynamical mechanical analysis proved, that enhanced behaviour was observed only in case of samples with irradiated by low doses, 1 kGy and 5 kGy, respectively, while the higher doses significantly decrease these ones, due to the present scission confirmed by FTIR and other investigations. Finally, it was found the competition between the cross-linking of the PP foam and present scission due to the applied GI and therefore the physical properties can be easily tailored.Display Omitted
Keywords: PP foams; Gamma irradiation; Structural properties; Thermal properties; Mechanical properties; Dielectric properties;
Effect of ammonia treatment on enzymatic hydrolysis and cell wall components of Erianthus by Daichi Yamashita; Satoshi Kimura; Masahiro Samejima; Masahisa Wada (243-248).
Powdered samples of Erianthus were treated with anhydrous ammonia at 50–140 °C. The crystal structure of cellulose in the sample changed to cellulose IIII, and its crystallite size increased with increasing temperature. Lignin content decreased with increasing temperature, while most reducing sugars, including glucose, were maintained at nearly 80%. Enzymatic hydrolysis of the ammonia-treated samples was carried out at 37 °C using a mixture of cellulase and β-glucosidase in solution. The samples treated at a higher temperature showed better enzymatic degradability. Furthermore, transverse sections of Erianthus stem were also treated with ammonia, and cell wall components and their distributions were detected with microscopic observation. By using fluorescence microscopy, it was also found that lignin content decreased with increased temperature. The immuno-labeling of pectin and β-1,3-1,4-glucan showed a change to a water-soluble form and complete removal by the ammonia treatment. However, xylan had substantial resistance to ammonia treatment.
Keywords: Erianthus; Ammonia treatment; Enzymatic hydrolysis; Cellulose; Cell wall components; Immunofluorescence labeling;
A comparison study of the degradative effects and safety implications of UVC and 405 nm germicidal light sources for endoscope storage by Daniel Irving; Dimitrios A. Lamprou; Michelle Maclean; Scott J. MacGregor; John G. Anderson; M. Helen Grant (249-254).
Storage of flexible endoscopes under germicidal ultraviolet (UVC) light has been associated with degradation of device material leading to failure and increased risk to patients. 405 nm germicidal light presents a possible alternative, potentially providing effective bacterial inactivation without material damage. Samples of endoscope material were exposed to UVC and 405 nm germicidal light sources and a broad spectrum light source control. Material properties were monitored using FTIR, AFM, contact angle and confocal microscopy. Significant changes were observed with samples exposed to the UVC source, with variations in FTIR spectra indicative of side chain scission, a decrease in contact angle from 82.6° to 61.4°, an increase in average surface roughness from 2.34 nm to 68.7 nm and visible cracking of the surface. In contrast samples exposed to the 405 nm light source showed little to no changes, with any variations being comparable to those seen on samples exposed to the broad spectrum control. Bacterial adhesion tests on samples showed an 86.8% increase in Pseudomonas aeruginosa adhesion on UVC exposed samples and no significant increase in adhesion with samples exposed to the other light sources. 405 nm germicidal light therefore potentially represents a safer alternative to UVC light for use in flexible endoscope storage.
Keywords: UVC; 405 nm light; Photodegradation; Bacterial adhesion; Endoscope material; Decontamination;
Water diffusion and swelling stresses in highly crosslinked epoxy matrices by Andrea Toscano; Giuseppe Pitarresi; Michele Scafidi; Maria Di Filippo; Giuseppe Spadaro; Sabina Alessi (255-263).
The present work investigates the swelling induced stresses arising in two epoxy systems during water uptake. The analysed systems are two epoxy resin based on DGEBA monomer and DGEBF monomer respectively, both fully cured by DDS amine. The systems achieve different cross-link density degrees, and are characterised by high glass transition temperatures ranging between 200 and 230 °C. Both epoxies have been conditioned in deionized water baths at two different temperatures (50 °C and 80 °C). A desorption process at room temperature in a dry airborne environment was performed after saturation. Dynamic Mechanical Thermal Analysis, carried out at the various stages of hydrothermal conditioning, has allowed to characterise the modifications occurring in the network structures during aging. Photoelastic Stress Analysis is adopted to monitor the evolution of stresses on rectangular beam samples during absorption and desorption of water. Correlation of water uptake, dynamic mechanical behaviour and transitory stress fields, has allowed to make some assumptions about the influence of the epoxy network on the swelling behaviour.
Keywords: Epoxy resin; Hydrothermal aging; Swelling; Dynamic Mechanical Thermal Analysis; Photoelastic Stress Analysis;
Semi-continuous flow recycling method for carbon fibre reinforced thermoset polymers by near- and supercritical solvolysis by Lucile Henry; Anna Schneller; Janosch Doerfler; Wolfgang M. Mueller; Cyril Aymonier; Siegfried Horn (264-274).
Keywords: Recycling; Carbon fibres; Polymer matrix composite; Near- and supercritical fluids; Solvolysis;
Atomic oxygen erosion behaviors of PBO fibers and their composite: Microstructure, surface chemistry and physical properties by Lei Chen; Caifeng Wang; Zijian Wu; Guangshun Wu; Yudong Huang (275-282).
Poly(p-phenylene benzobisoxazole) (PBO) fibers are ideal candidates for cables in tether application and reinforcements in advanced composites. Upon exposure to atomic oxygen (AO) in low earth orbit (LEO), PBO fibers are severely eroded. In this study, the AO erosion behaviors of PBO fibers and their composite were investigated in simulated AO environment, based on the evaluation of microstructure, surface chemistry, thermal stability and mechanical properties. Surface morphologies and crystalline structure confirmed that PBO fibers were significantly eroded after AO irradiation. X-ray photoelectron spectroscopy (XPS) showed that the relative content of C―C decreases with the increase of AO irradiation time, suggesting a chain scission of PBO fibers. After 8 h AO exposure, the tensile strength of PBO fibers was decreased by 31.6%, and the onset decomposition temperature was reduced by 30.8 °C. Monofilament pull-out tests showed that the interfacial shear strength (IFSS) of PBO/epoxy composite was as low as 61.3% that of pristine composite due to the interface damage caused by AO penetration.
Keywords: PBO fiber; Atomic oxygen; Erosion; Tensile strength; Interface;
Synthesis, characterization and thermal, hydrolytic and oxidative degradation study of biobased (BisFuranic-Pyridinic) copolyesters by A. Bougarech; M. Abid; S. Abid; E. Fleury (283-292).
Polymers from renewable resources are of high interest since it could be possible to valorize the biomass and in parallel to tune their macromolecular structures in relation with their properties. Here novel bisfuranic-pyridinic copolyesters, namely poly (ethylene furoate-co-ethylene pyridinate) (PEBF-co-PEPy) were prepared by applying a two-stage melt polycondensation method at high temperature, in a presence of titanium derivatives as catalyst. Molecular weights of resulting copolyesters are in the range 24000–45200 g mol−1 and their chemical microstructures statistical as shown by NMR. These furano-pyridinic copolyesters are amorphous with Tg ranging from 62 to 67 °C and their thermal and hydrolysis stabilities are influenced by presence of the pyridinic dyads Py-ED-Py. Finally the oxidative degradation in H2O2/CoCl2 cannot be effective because of the chelating properties of pyridinic moieties.
Keywords: Polycondensation; Bio-based polymer; Furanic; Pyridinic; Hydrolytic degradation;
Effects of electron beam irradiation on thermal and mechanical properties of poly(lactic acid) films by Mohammed Mansouri; Abdelkader Berrayah; Christophe Beyens; Christine Rosenauer; Charafeddine Jama; Ulrich Maschke (293-302).
The purpose of this study is to examine the effect of electron-beam (EB) radiation on biodegradable polylactic acid (PLA), and to understand radiation-induced degradation mechanisms. PLA films were irradiated between 0 and 120 kGy and physical properties were characterized by means of GPC, DSC, DMA and tensile drawing. It was shown that degradation of PLA under EB leads to a random chain scission responsible for a reduction of the molar mass. These molar mass changes affect glass transition temperature T g , degree of crystallinity, and mechanical properties. It was found that T g , stress and strain at break decrease with increasing irradiation dose, whereas the degree of crystallinity increases up to 45 kGy then decreases. Cross-linking G x and chain scission G s values of PLA revealed that chain scission reactions at lower dose predominate over cross-linking. DMA results exhibit an exothermal re-crystallization for neat and irradiated samples, which disappears with increasing heating rate. These results were confirmed by DSC measurements. Ductile-brittle transition was determined as function of EB-dose and crosshead speed. A change of physico-chemical and mechanical properties was evidenced during application of a dose of 45 kGy.
Keywords: Polylactic acid; Electron beam; Degradation; Mechanical properties;
Effect of thermal treatment on properties of ramie fibers by Jian-Min Yuan; Yan-Rong Feng; Li-Ping He (303-311).
The properties of ramie fibers treated by thermal treatments at 200 °C under nitrogen and air atmospheres, including thermal stability, crystalline properties, chemical structure, longitudinal thermal deformation behavior and surface performance, were studied. When the ramie samples had been treated, both the lateral order indices (LOI) and infrared (IR) crystallinity ratios were increased, whereas the crystallinity indices of X-ray diffraction analysis were decreased. The absorbed water had a great impact on the properties of the treated ramie samples, promoting the LOI and the crystallite sizes and reducing IR crystallinity ratios, crystallite d-spacings and crystallinity indices. Oxidation in thermal treatments led to the decrease of crystallite sizes and crystallinity indices. The longitudinal thermal deformation behavior of ramie fibers were further measured by thermo mechanical analyzer. The results showed that 2 treated samples with moisture absorption were of thermal expansion properties, the one without moisture absorption and treated under dried air exhibited thermal shrinkage in the temperature range below 100 °C and thermal expansion above 100 °C, while the one without moisture absorption and treated under dried nitrogen displayed thermal shrinkage in the whole temperature range. These different behaviors were attributed to the diversity of chemical structure and crystalline structure in fiber samples resulted from the absorbed water, oxidative decomposition and thermal degradation. The fracture morphology of ramie fibers/epoxy resin composites was observed by scanning electron microscopy, which disclosed that the compatibility between fibers and resin matrix was enhanced through thermal treatments, and the failure tips of fiber samples without moisture absorption are coarser and looser than those with moisture absorption because of the influence of absorbed water on cellulose structure. It can be seen that the atmospheres of thermal treatments and moisture absorption are the main factors to affect the properties of the treated ramie fibers.
Keywords: Ramie fibers; Thermal treatment; Thermal stability; Moisture absorption; Longitudinal thermal deformation; Crystallinity;
Synthesis and characterization of MMP degradable and maleimide cross-linked PEG hydrogels for tissue engineering scaffolds by Jingjing Yu; Feng Chen; Xichi Wang; Nianguo Dong; Cuifen Lu; Guichun Yang; Zuxing Chen (312-320).
A series of poly(ethylene glycol) (PEG) hydrogels were successfully prepared via Michael-type addition between 4-arm PEG-maleimide (PEG-4MAL) and MMP degradable peptide. The gelation time was significantly short (∼10 min) in a low concentration of TEA (4 mM). Thermogravimetric analysis indicated the thermal stabilities of hydrogels. SEM images confirmed a porous structure and the pore size increased with the increase of the PEG chain length. Rheological measurements indicated that all the hydrogels exhibited the characteristics of elastomer and the cross-linking density had a correlation to the polymer weight percentage. After immersing in 0.9% sodium chloride injection, PEG hydrogels exhibited a good water absorption capacity, and their swelling ratio were directly related to the amount of cross-linking. Biological activities of the hydrogels were evaluated by in vitro enzymatic degradation and in vitro cell compatibility on mesenchymal stem cells (MSCs) and the results showed that the hydrogels were biocompatible and could be degraded by exogenously delivered MMPs or cell-secreted MMPs. Thus, PEG hydrogels exhibited the potential for tissue engineering scaffolds.
Keywords: PEG hydrogels; MMP degradable; Maleimide; Michael-type addition;
Structure and improved thermal stability of phenolic resin containing silicon and boron elements by Shan Li; Fenghua Chen; Boxing Zhang; Zhenhua Luo; Hao Li; Tong Zhao (321-329).
Phenolic resin modified with silicon and boron (SNBA) was prepared by a simple two-step method: silane was firstly grafted onto phenolic resin, with silicon modified phenolic resin (SN) obtained; and then boric acid was introduced into SN. Boric acid, acting as a curing agent, catalyzed the self-polymerization of the silane in SN, and induced phase separation in the cured SNBA systems. Thermal stability was evaluated by thermogravimetric analysis (TGA). In air, the maximum decomposition rate (Dmax) decreased about 2%/min and the residual weight at 900 °C (R900) increased 16.7% after the introduction of boron and silicon. Oxyacetylene flame ablation also confirmed the improved ablative properties of the hybrids. The flame retardancy was studied by cone calorimeter. The total heat release (THR), the total smoke produce (TSP) and the rate of mass loss (RML) were decreased after the modification. The structure of the oxidized resin was characterized to study the mechanism of the improved thermal stability and flame retardancy. The oxide compounds of silicon and boron were formed during high temperature oxidation, which consumed some oxygen and hindered the permeation of heat and oxygen, protecting the matrix from thermal oxidation.
Keywords: Phenolic; Boron; Silicon; Structure; Thermal stability;
Corrigendum to “Kinetic analysis for thermal cracking of HDPE: A new isoconversional approach” [Polymer Degrad. Stab. 129 (2016) 306–318] by Sahar Khedri; Siamak Elyasi (330-338).
Converting waste plastic into marketable hydrocarbons is a promising way to protect the environment and earn financial gain. While several kinetic studies have examined the cracking of waste plastic, they are often oversimplified or inappropriate for designing an industrial reactor. This work proves the necessity of using isoconversional methods by using Differential Scanning Calorimetry (DSC). DSC verified that cracking of waste plastic involves the production of several intermediates, indicating that the kinetics is more complex and requires further studies. Several isoconversional methods such as Friedman, Ozawa, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and model-free were applied to estimate the apparent activation energy and frequency factor of thermal cracking of high-density polyethylene (HDPE) using non-isothermal and isothermal Thermogravimetric Analysis (TGA). The determined kinetic parameters from each method were evaluated against the experimental data. In order to overcome the failures and shortages engaged with the employed methods, a new isothermal isoconversional model was proposed and good matching results were observed.
Keywords: Thermal cracking; Kinetic parameters; HDPE; Isothermal TGAs; Non-isothermal TGAs; Isoconversional methods;
Effect of different mechanical recycling processes on the hydrolytic degradation of poly(l-lactic acid) by F.R. Beltrán; V. Lorenzo; M.U. de la Orden; J. Martínez-Urreaga (339-348).
The growing production of poly(lactic acid) (PLA) has increased the interest for the mechanical recycling of this polymer. The main objective of this work is to study the effect of different mechanical recycling processes on the hydrolytic degradation of PLA. A commercial grade of PLA was subjected to two different recycling processes, one of them comprising an accelerated thermal and photochemical aging and a second melt compounding and compression molding step, and other including a demanding washing step after the accelerated aging process. The accelerated aging and, especially, the washing step had a significant effect on degradation during recycling. Samples of virgin and recycled plastic immersed in a phosphate buffered solution at 37 or 58 °C were removed at selected times and then characterized by gravimetric analysis, IR and UV spectroscopy, thermal analysis, x-ray diffraction and microhardness and viscosity measurements. The water absorption process, at both temperatures, can be modeled using a Fickian model only when the immersion times were short. The different recycling processes caused an increase of the diffusion coefficient of PLA at 37 °C, while at 58 °C the differences were smaller. DSC results pointed out that mechanical recycling promotes a slight crystallization of PLA at 37 °C that explains the increasing of the hardness during the hydrolysis.
Keywords: Poly(lactic acid); Mechanical recycling; Water absorption; Hydrolytic degradation;
Corrigendum to “Kinetic analysis for thermal cracking of HDPE: A new isoconversional approach” Polymer Degradation and Stability 2016; 129: 306–318 by Sahar Khedri; Siamak Elyasi (349).
Gas-phase flame-retardant effects of a bi-group compound based on phosphaphenanthrene and triazine-trione groups in epoxy resin by Shuo Tang; Lijun Qian; Xinxin Liu; Yuping Dong (350-357).
A flame retardant TAD constructed by phosphaphenanthrene and triazine-trione groups was synthesized via addition reaction between triallyl isocyanurate (TAIC) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Then, the molecular structure and thermal stability of TAD were characterized. To research its flame-retardant behaviors, TAD was incorporated into epoxy resin, diglycidyl ether of bisphenol-A, cured by 4,4′-diamino-diphenyl sulfone (DDS). TAD obviously increased the LOI values and UL94 rating of epoxy resin thermosets. TAD also reduced the values including peak of heat release rate (pk-HRR), total heat release (THR), average effective heat of combustion (av-EHC), average CO2 yield and total mass loss (TML), and increased average CO yields of epoxy thermosets. Further, the different decrease ratio of av-EHC and TML from thermoset containing TAD reveals that TAD exerted more gas-phase flame-retardant effect than condensed-phase effect. The opinion also was testified by the TAD/EP residues with loosen morphology from the cone calorimeter test. The analyzed pyrolysis route of TAD reveals that phosphaphenanthrene group mainly exerted quenching effect and the triazine-trione group exerted gas dilution effect. The excellent flame-retardant performance of TAD is resulted by the group synergistic effect from the two typical flame-retardant groups: phosphaphenanthrene and triazine-trione.
Keywords: Flame retardant; Triazine-trione; DOPO; Epoxy; Synergistic effect;
Synthesis of a novel flame retardant containing phosphorus, nitrogen and boron and its application in flame-retardant epoxy resin by Shuang Yang; Qiaoxin Zhang; Yefa Hu (358-366).
A novel halogen-free flame retardant (DTB) containing phosphorus, nitrogen and boron was successfully synthesized. The chemical structure of DTB was characterized by Fourier transform infrared spectroscopy (FTIR), 1H and 31P nuclear magnetic resonance (NMR). DTB was then blended with diglycidyl ether of bisphenol-A (DGEBA) to prepare flame-retardant epoxy resins. Thermal properties, flame retardancy and combustion behavior of the cured EP thermosets were investigated by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL94 vertical burning test and cone calorimeter test. The results indicated that DTB significantly improved the flame retardancy as well as smoke inhibition performance of EP/DTB thermosets. Compared with the neat EP thermoset, the LOI of EP/DTB-3 thermoset was increased to 35.6% and the sample reached UL94 V-0 rating; the average of heat release rate (av-HRR), total heat release (THR) and total smoke production (TSP) of EP/DTB-3 thermoset were decreased by 33.3%, 33.0% and 35.5%, respectively. TGA results indicated that the char yields of EP/DTB thermosets were increased by 45.1–72.8% compared with that of the neat EP thermoset. The FTIR, SEM-EDX and Py-GC/MS results indicated that DTB contributed to form intumescent and glassy char layers and decomposed to generate free radicals with quenching effect. DTB was effective radical trapper as well as efficient charring agent for epoxy resin and exerted flame-retardant effect in gaseous and condensed phases simultaneously.
Keywords: Epoxy resin; Flame retardant; DOPO; Nitrogen; Boron;
Surface studies of UV-irradiated poly(vinyl chloride)/poly(methyl methacrylate) blends by Jolanta Kowalonek (367-377).
Surface properties of poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA) and their blends have been studied using FTIR-ATR spectroscopy, AFM and contact angle measurements. It was found that the surfaces of PVC/PMMA blends were enriched in PMMA, the lower surface free energy component. The results also revealed the existence of weak interactions between the blend components resulting in partial miscibility of system observed for the blends containing below 40% of PMMA.UV-irradiation made the sample surfaces more polar and rough owing to photochemical processes such as oxidation, degradation, dehydrochlorination, depolymerization or etching. The oxidation was more efficient for PVC compared to PMMA. In the case of PVC/PMMA blends, the efficiency of oxidation reactions increased with increasing PVC content and this process was approximately the average of the changes in the pure polymers. The photooxidation reactions were accompanied by degradation reactions leading to formation of low molecular weight oxidized products.AFM studies of UV-irradiated sample surfaces revealed cone-like and globular objects which were easily removed from the surfaces after washing the samples. These objects were made of low molecular weight oxidized material and/or methyl methacrylate. Only neat PMMA surface behaved contrary to all samples. It seemed that irradiation did not yield any changes in surface morphology of PMMA but washed surface of this polymer revealed presence of cone-like structures. It suggests that the mechanism of photooxidative degradation of pure PMMA and PMMA in the blends was different. Probably the presence of chlorine radicals from PVC modifies the route of PMMA photochemical processes in PVC/PMMA blends.
Keywords: Polymer blends; PVC; PMMA; UV-irradiation; Surface free energy; AFM;
Hybridization of α-zirconium phosphate with hexachlorocyclotriphosphazene and its application in the flame retardant poly(vinyl alcohol) composites by Lingfeng Xu; Caihong Lei; Ruijie Xu; Xiaoqing Zhang; Feng Zhang (378-388).
A planar-like inorganic α-zirconium phosphate (α-ZrP) particles were modified by a kind of cyclophosphazene derivative via three-step hybridization method, first modified by melamine (MA), then combined with hexachlorocyclotriphosphazene (HCCP) through nucleophilic substitution and further integrated with excessive MA. Thus, a hybrid flame retardant (HAC) was successfully synthesized. The composites based on poly(vinyl alcohol) (PVA) and HAC were prepared by solution blending. The thermal, mechanical properties and flame retardancy of the composites were studied. It was found that HAC showed a catalytic effect in the initial decomposition stage and promoted the formation of char at high temperatures. When the content of HAC was 15 wt%, the limiting oxygen index (LOI) reached 28.4% and classified V-0 rating, whereas with the same content of fire retardant, for PVA/α-ZrP and PVA/product of MA with HCCP composites (one kind of intumescent flame retardant IFR), the LOI values were only 24.7% and 27.1%, respectively. The combination of IFR and α-ZrP could remarkably improve the yield and graphitization of char residues, make the char more stable, compact and continuous, inhibiting underlying PVA from contacting heat and oxygen. Moreover, the mechanical properties could be reinforced and toughened with certain content of HAC.
Keywords: Hybridization; α-zirconium phosphate; Hexachlorocyclotriphosphazene; Flame retardancy; Synergistic effect; Poly(vinyl alcohol);
Reprocessing of UV-weathered wood flour reinforced polypropylene composites: Study of a natural outdoor exposure by L. Soccalingame; D. Perrin; J.-C. Bénézet; A. Bergeret (389-398).
This work aims to determine and understand the influence of a one-year natural UV weathering on the reprocessing of a wood-plastic composite (WPC), i.e. a wood flour reinforced polypropylene (PP) composites. Two wood flour contents (10% w/w and 30% w/w) were studied in comparison to neat PP. Injected samples of were submitted to a long-term natural outdoor exposure followed by one complete reprocessing cycle (grinding then injection). The visual aspect evolution of the surface was followed by optical microscopy. In order to understand the material physical degradation, the mechanical behaviour was measured thanks to tensile and Charpy impact tests. The assessment of the microstructural evolution was performed by differential scanning calorimetry (crystallinity ratio), rheological tests (viscosity), size exclusion chromatography tests (average molecular weights) and infrared spectroscopy analysis (chemical structure). A “regeneration” phenomenon was highlighted as mechanical properties are recovered after reprocessing. This is due to the mixing and the dilution of the degraded chains into the material as no recombination or crosslinking mechanism was detected. A comparison with an artificial UV weathering performed on the same samples and exposed in a previous study was finally investigated.
Keywords: Polypropylene; Wood flour; Biocomposites; Reprocessing; Natural UV weathering; Microstructure; Mechanical properties; Degradation;
Preparation and characterization of zinc-mannitol complexes as PVC thermal stabilizers with high efficiency by Lizhi Zhu; Yijian Wu; Baoqing Shentu; Zhixue Weng (399-403).
A series of zinc oxide-mannitol complexes (Zn-Ma complexes) with different zinc contents were prepared, and the composition of Zn-Ma complexes was determined by atomic absorption spectroscopy and elemental analysis. The components of Zn-Ma complexes were separated by Soxhlet extraction and characterized by FT-IR. Dependence of the reaction extent on time at different temperature was investigated in order to optimize the preparation technology. The thermal stability of poly (vinyl chloride) (PVC) with Zn-Ma complexes was investigated by Congo red tests. The results showed that Zn-Ma complexes could significantly improve the thermal stability of PVC. The thermal stabilization mechanism and synergism effect of Zn-Ma complexes were also discussed.
Keywords: PVC; Thermal stabilizer; Zinc-mannitol complexes; Preparation; Characterization;
Modelling the non Fickian water absorption in polyamide 6 by Mael Arhant; Pierre-Yves Le Gac; Maelenn Le Gall; Christian Burtin; Christophe Briançon; Peter Davies (404-412).
This paper investigates the water absorption of polyamide 6. The high amount of absorbed water in the polymer and the large resulting decrease in the glass transition temperature (Tg) leads to a non Fickian water diffusion when samples are immersed, which is a significant difficulty when trying to model the water profile in thick specimens. The aim of this study is to be able to model this particular behaviour based on physical considerations. First, it is shown that the non Fickian water diffusion is caused by an increase in the diffusivity during water absorption. Two cases are then identified; one below Tg where the diffusivity is described using an Arrhenius law and one above Tg based on the free volume theory. Then, these two laws are implemented in a specific model that is able to describe the non Fickian water diffusion over a wide range of temperatures.
Keywords: Water absorption; Free volume; Polyamide 6; Sea water; Modelling;