Polymer Degradation and Stability (v.95, #2)

Calendar (I).

Atmospheric and soil degradation of aliphatic–aromatic polyester films by Thitisilp Kijchavengkul; Rafael Auras; Maria Rubino; Edgar Alvarado; José Roberto Camacho Montero; Jorge Mario Rosales (99-107).
The degradation of an aliphatic–aromatic biodegradable polyester film was studied under conditions of solar exposure and soil burial in a tropical area. Film samples were evaluated for changes over 40 weeks by visual examination, scanning electronic microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, mechanical properties, molecular weight, gel content, and thermal properties. Photodegradation played a major role in the atmospheric degradation of the film, causing it to lose integrity and mechanical properties after week 8 due to main chain scission and crosslinking. SEM micrographs and FTIR spectra indicated that photodegradation started at the exposed side of the film and propagated through the polymer matrix after week 8. FTIR spectra also indicated that subsequent photooxidation processes took place. The reduction of molecular weight of the soil burial samples was much slower than that of the non-crosslinked portion of solar exposed film samples. The reduction of number average molecular weight of the non-crosslinked solar exposed samples followed a first order reaction, whereas the soil burial samples show a surface erosion biodegradation behavior. The relationship among total solar radiation, gel content and number average molecular weight indicated that an accumulated total solar radiation of 800 MJ/m2, reached in approximately 7 weeks at the exposure site, is required for PBAT mulch film integrity loss.
Keywords: Aliphatic–aromatic polyester; PBAT; Photodegradation; Biodegradation; Mulch films;

Investigation of the flammability of different textile fabrics using micro-scale combustion calorimetry by Charles Q. Yang; Qingliang He; Richard E. Lyon; Yuan Hu (108-115).
Evaluating and analyzing the performance of flame retardant (FR) textiles are a critical part of research and development of new FR textiles products by the industry. The testing methods currently used in the industry have significant limitations. Most analytical and testing techniques are not able to measure heat release rate (HRR), the single most important parameter in evaluating the fire hazard of materials. It is difficult to measure HRR of textile fabrics using cone calorimetry because textile fabrics are dimensionally thin samples. The recently developed micro-scale combustion calorimetry (MCC) is able to measure the following flammability parameters for textile using milligram sample sizes: heat release capacity, HRR, temperature at peak heat release rate (PHRR), total heat release and char yield. In this research, we applied MCC to evaluate the flammability of different textile fabrics including cotton, rayon, cellulose acetate, silk, nylon, polyester, polypropylene, acrylic fibers, Nomex and Kevlar. We also studied the cotton fabrics treated with different flame retardants. We found that MCC is able to differentiate small differences in flammability of textile materials treated with flame retardants. We were also be able to calculate the limiting oxygen index (LOI) using the thermal combustion properties of various textile samples measured by the MCC. The calculated LOI data have yielded good agreement with experimental LOI results. Thus, we conclude that MCC is an effective new analytical technique for measuring textile flammability and has great potentials in the research and development of new flame retardants for textiles.
Keywords: Micro-scale combustion calorimetry; Flame retardant finishing; Heat release rate; Textile flammability;

Processing of poly(lactic acid): Characterization of chemical structure, thermal stability and mechanical properties by F. Carrasco; P. Pagès; J. Gámez-Pérez; O.O. Santana; M.L. Maspoch (116-125).
The processing of poly(lactic acid) (injection and extrusion/injection) as well as annealing of processed materials were studied in order to analyze the variation of its chemical structure, thermal degradation and mechanical properties. Processing of PLA was responsible for a decrease in molecular weight, as determined by GPC, due to chain scission. The degree of crystallinity was evaluated by means of differential scanning calorimetry and X-ray diffraction. It was found that mechanical processing led to the quasi disappearance of crystal structure whereas it was recovered after annealing. These findings were qualitatively corroborated by means of FTIR. By analyzing 1H NMR and 13C NMR chemical shifts and peak areas, it was possible to affirm that the chemical composition of PLA did not change after processing, but the proportion of methyl groups increased, thus indicating the presence of a different molecular environment. The thermal stability of the various materials was established by calculating various characteristic temperatures from thermograms as well as conversion and conversion derivative curves. Finally, the mechanical behaviour was determined by means of tensile testing (Young modulus, yield strength and elongation at break).
Keywords: Poly(lactic acid); Injection; Extrusion; Crystallinity; Degradation; Tensile testing;

Chemical structures assigned for the low molecular weight fractions from degradation of poly(styrene sulfides) by Lijing Xue; Denka G. Hristova-Bogaerds; Jesper G. van Berkel; Guy Verbist; Piet J. Lemstra (126-131).
A non-destructive analysis is performed of thermally unstable sulfur–styrene reaction products, combining preparative size exclusion chromatography (P-SEC), ultraviolet–visible (UV–vis) and nuclear magnetic resonance (NMR). The crystallizing compounds are identified as be 2,4-diphenylthiophanes with short sulfur bridge (x ∼ 2) contrary to earlier suggestions which were based on destructive analysis. A new cyclic structure (styrene polysulfide x = 1 up to 8) was assigned to the amorphous species containing a single styrene repeating unit. Comparison with the amorphous fractions suggests that the rigid ring of styrene repeating units in adjacent sequences is the characteristic feature for the crystallisability. The melting and crystallization behaviour of this crystalline component was observed, by optical microscopy (OM) and differential scanning calorimetry (DSC), to be step-wise as well as broad, due to the variation in the length of the sulfur bridge.
Keywords: Styrene polysulfide; Thermal stability; Non-destructive technique; 2,4-Diphenylthiophanes; Sulfur bridge; “Stepwise” melting;

Different chelating agents such as poly(ethylene glycol), propylene glycol monooctadecanoate and palm oil were used for modification of the surface-treated montmorillonite (MMT). The work also included the development of a technique for mixing chelating agents with MMTs using different methods and different proportions of MMT/chelating agent/ethanol. Evaluation of the result of mixing was performed by thermogravimetric analysis, X-ray diffraction and high-resolution scanning electron microscopy (HR-SEM). The results showed that the chelating agents used were intercalated in MMT, increasing the interlayer spacing. The OMMT was used in the manufacture of composites with rigid PVC using a microcompounder. The master batch concept turned out to be promising in terms of dispersion and delamination of clay, as observed in HR-SEM photographs. However, despite good dispersion and exfoliation of MMT, poor compatibility between clay platelets and PVC matrix remains to be solved to enable full exploitation of its engineering potential. Despite this drawback, good thermal stability and mechanical properties have already been achieved.
Keywords: Polymer nanocomposite; Montmorillonite; PVC; Thermal stability; Dispersion; Compatibility;

Microbial degradation of poly(butylene succinate) by Fusarium solani in soil environments by Michiharu Abe; Koji Kobayashi; Naoya Honma; Kiyohiko Nakasaki (138-143).
The use of mulch made of biodegradable plastic in agriculture is expected to help solve the problem of the enormous amount of plastic waste emission, and to save the labor of removing the mulch after harvesting crops. In this study, we isolated a microorganism possessing the ability to degrade one of the promising biodegradable plastics, poly(butylene succinate) (PBS), and investigated the degradation characteristics of the microorganism in soil environments. Fungal strain WF-6, belonging to Fusarium solani, that had not been reported could be isolated from farmland as the PBS-degrading microorganism. Strain WF-6 degraded 2.8 percent of the PBS in a 14-day experimental run in a sterile soil environment, as determined by measuring CO2 evolution. Furthermore, we ascertained that the degradability of strain WF-6 was enhanced by co-culturing with the newly isolated bacterial strain Stenotrophomonas maltophilia YB-6, which itself does not show PBS-degrading activity. We then investigated the effects of cell density of the indigenous microorganisms in the soil environments on the degradability of the co-culture of strains WF-6 and YB-6 by inoculating these strains into non-sterilized and partially sterilized soils, which contained 108, 106, and 103 CFU/g-dry solid of soil of indigenous microorganisms. The degradability strongly depended on the cell density level of the indigenous microorganisms and was remarkably diminished when the cell concentration level was the highest, 108 CFU/g-dry solid. Quantitative PCR analysis revealed that the growth of strains WF-6 and YB-6 was inhibited in the non-sterile soil environment with the highest cell density level of the indigenous microorganisms.
Keywords: Biodegradable plastic; Poly(butylene succinate); Microbial degradation; Cumulative emission of carbon; Fusarium solani; Stenotrophomonas maltophilia;

Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin by Baljinder K. Kandola; Bhaskar Biswas; Dennis Price; A. Richard Horrocks (144-152).
A thermoplastic toughener, polyether sulphone (PES) and a number of different types of flame retardants were blended in different ratios with a commercial epoxy resin triglycidyl-p-aminophenol (TGAP) and 4,4-diamino diphenyl sulphone (DDS) a curing agent. The effect of type and levels of flame retardants (FR) and the toughening agent on the curing, thermal decomposition and char oxidation behaviour of the epoxy resin was studied by the simultaneous differential thermal analysis and thermogravimetric techniques. It was observed that the toughener slightly increases the curing temperature (by up to 20 °C) but had minimal effect on the decomposition temperature of the resin. Flame retardants, however affected all stages depending upon the type of flame retardant used. The curing peak for samples containing tougher and flame retardants although slightly changed depending upon the type of FR, was not more than ± 20 °C compared to that of samples containing toughener only. All flame retardants lowered the decomposition temperature of the epoxy resin. Phosphorus- and nitrogen-containing flame retardants reduced the char oxidation leading to more residual char, whereas halogen- containing flame retardants had less effect on this stage.
Keywords: Epoxy resin; Flame retardancy; Toughener; Curing; DTA–TGA;

Low-energy electrons and X-ray irradiation effects on plasma-polymerized allylamine bioactive coatings for stents by Sylvain Massey; Enrico Gallino; Pierre Cloutier; Michaël Tatoulian; Léon Sanche; Diego Mantovani; Denis Roy (153-163).
Radiation used in biomedical applications causes chemical changes to biomedical materials. This work is an ex situ simulation of the influence of low-energy electron (LEE) impact and X-ray irradiation on the chemical properties of plasma-polymerized allylamine (PPA) bioactive and biocompatible stent coatings. Preliminary X-ray photoelectron spectroscopy (XPS) results show that PPA coatings oxidize in contact with ambient air by the detection of C–O and C=O bonds which are typical of polymer oxidation. Chemical changes after LEE and X-ray irradiation are mainly a loss of oxygen, assuming a surface deoxidizing and not a complete destruction of the surface. XPS survey analyses show that the amine groups remain stable during irradiation. LEE impact measurements by TOF mass spectrometry show that the main ionic losses are H ions. It appears that CN groups are stable under irradiation and we observe a loss of hydrogen and oxygen as the main chemical modifications. In conclusion, these results suggest that PPA coatings are stable under biomedical radiation, and they can therefore be used for bioactive and biocompatible stent coatings.
Keywords: Allylamine; Plasma coating; Low-energy electron impact; X-ray irradiation; X-ray photoelectron spectroscopy;

The high-temperature α relaxation in gamma irradiated isotactic polypropylene (iPP) was studied over the temperature (298–406 K), frequency (103–106 Hz) and absorbed dose (0–700 kGy) ranges by means of dielectric spectroscopy. The multiple α relaxation was resolved from the β relaxation by curve fitting and its parameters were determined. Its position, intensity and activation energy were found to be strongly dependent on the changes in the structural and morphological parameters attributed to the exposure of the samples to radiation. Wide angle X-ray diffraction (WAXD) was used to investigate radiation-induced changes in the crystalline structure and degree of crystallinity, since this relaxation is connected with the crystal phase. Infrared (IR) spectroscopy and gel measurements were used to determine the changes in the oxidative degradation and the degree of network formation, respectively; the polar (carbonyl and/or hydroperoxide) groups that were introduced by irradiation were considered as tracer groups. Conclusions derived according to different methods were compared. The results reveal uncommon α relaxation behaviour with gamma radiation and confirm the multiple nature of this process, together with high dielectric and/or relaxation sensitivity of iPP to the radiation-induced changes.
Keywords: Polypropylene; Relaxation; Gamma radiation; Dielectric spectroscopy; Polar groups;

The analysis of the chromatographic pattern of virgin, reprocessed, thermo-oxidised, and recycled high-impact polystyrene (HIPS) proves to be a suitable and sensitive tool to assess the degree of degradation of HIPS during its first life and subsequent recycling. Different low molecular weight compounds, such as residues of polymerisation, degradation products, and additives have been identified and relatively quantified in HIPS, using microwave-assisted extraction and further analysis by gas chromatography–mass spectrometry (GC–MS). The release of residues of polymerisation has been proven to occur during reprocessing, thermo-oxidation, and in recycled samples, which may show the emissions of volatile and semi-volatile organic compounds during the life cycle of HIPS. A wide range of oxidised degradation products are formed during reprocessing and thermo-oxidation; these products can be identified as oxidised fragments of polystyrene (PS), oxidised fragments from polybutadiene (PB) phase, and oxidised fragments from the grafting points between the PS and PB phase. Real recycled HIPS samples may also contain contaminations and fragments from additives included in their original formulations; the presence of brominated fragments from flame retardants in electronic waste is here observed.
Keywords: Chromatographic pattern; High-impact polystyrene (HIPS); Degradation; Thermo-oxidation; Processing; Volatile organic compounds (VOCs);

There is a growing keen interest aimed at recycling post-consumer poly(ethylene terephthalate), PET, wastes for both environmental and economic reasons. In this study ethanolamine (EA) has been investigated for aminolytic degradation of PET waste in the presence of dibutyl tin oxide (DBTO) as a catalyst. The process proceeds at 190 °C and under atmospheric pressure. The yield of white precipitate was subject to spectroscopic measurements (FT-IR, NMR, XRD and MS), to thermal analyses (DSC, DTA and TG) and to chemical testing (elemental analysis and solubility characterization).Based on the data reached from various examinations, the product formed is identified as bis(2-hydroxyethylene) terephthalamide (BHETA) which could be consider a source for differing polyurethanes. These kinds of materials have potential for many applications such as adhesives and coatings.
Keywords: PET waste; Ethanolamine; Dibutyl tin oxide; Spectroscopic measurement; Thermal analysis;

Enzyme-mediated biodegradation of heat treated commercial polyethylene by Staphylococcal species by Sumana Chatterjee; Bappaditya Roy; Dipa Roy; Rajat Banerjee (195-200).
Extruded low-density polyethylene (LDPE) films commonly available in the market as 20-micron thick carrier bags were autoclaved, overlaid on nutrient agar plates and inoculated with BP/SU1 strain of Staphylococcus epidermis. The nutrient agar plate showed growth of the organism within two to three days. The polymer film supporting the growth of the organism showed pore formation as recorded by SEM analysis. The growth of BP/SU1 is supported by the presence of shredded LDPE as its only carbon source in inorganic salt minimal nutrient medium. The organism survives even after three months of inoculation and this is accompanied by gradual breakdown of the size of the shredded plastic as seen by light scattering. The cell-free supernatant of the organism, grown with the help of shredded plastic shows the presence of the over expressed proteins with approximate molecular weight of about 55 kDa and 35 kDa, through SDS-PAGE analysis.
Keywords: LDPE; Staphylococcus epidermis; BP/SU1; Biodegradation; SEM; FT-IR;

Effect of different coupling agents on the browning of cellulose–polypropylene composites during melt processing by M.U. de la Orden; C. González Sánchez; M. González Quesada; J. Martínez Urreaga (201-206).
The effects of two coupling agents on the discoloration of cellulose/polypropylene composites during melt processing have been investigated. Composites of polypropylene, coupling agent and bleached eucalyptus Kraft pulp were produced by compounding in a twin-screw extruder. The coupling agents were maleic anhydride-grafted polypropylene (MAPP) and polyethylenimine (PEI). The discoloration was measured using standard colorimetry and the discoloration was investigated using diffuse reflectance (FTIR and UV–Visible) spectroscopy. Both MAPP and PEI increase the browning, but the two mechanisms are clearly different. PEI reacts with carbonyl compounds produced in the cellulose degradation to form new chromophores; however, no specific discoloration processes were detected in composites made with MAPP. In this case, the detrimental effect on the discolouration was related to the increased frictional degradation.
Keywords: Coupling agent; Cellulose; Composite; Polypropylene; Discoloration;

Porous nano-hydroxyapatite/polycaprolactone (nHA/PCL) scaffolds with different composition ratios of nHA/PCL were fabricated via a melt-molding/porogen leaching technique. All scaffolds were characterized before and after degradation in vitro for six months. The original scaffolds had high porosity at around 70% and showed decreasing compressive modulus (from 24.48 to 2.69 MPa for hydrated scaffolds) with the introduction of nHA. It was noted that the scaffolds could retain relatively stable architecture and mechanical properties for at least six months, although some slight changes happened with the nHA/PCL scaffolds in the mass, the nHA content, the PCL molecular weight and the crystallinity. Moreover, during the 7 days culture of bone marrow stromal cells (BMSCs) on scaffolds, the cell adhesion and proliferation of BMSCs were presented well on both the surface and the cross-section of the scaffolds. All of these results suggested the nHA/PCL scaffolds to be promising in bone tissue engineering.
Keywords: Porous scaffold; Polycaprolactone; Nano-hydroxyapatite; Degradation; Bone tissue engineering;

We have studied the potential degradation of poly(lactic acid)-based fabrics treated with commercial softeners and stored under two sets of conditions for one year. Initial wet-processing caused a fall in molecular weight of about 28%, irrespective of after-treatment. Storage at 40 °C and 80% RH produced further degradation which, with few exceptions, was aggravated by the presence of softeners. Ultimately, all samples degraded beyond the point of commercial usefulness. No clear distinction could be made between the effects of softeners having differing compositions. In contrast, fabrics stored under milder conditions of 23 °C and 50% RH showed no significant time-dependent polymer degradation, irrespective of the treatment applied. There were slight changes in tensile properties and some evidence of physical structural effects having occurred, which we attribute to physical aging. However, we do not believe these to be so serious as to call into question the long-term viability of PLA-based textile products.
Keywords: PLA; Polylactic acid; Stability; Softener; Storage;

Lignin and starch as potential inductors for biodegradation of films based on poly(vinyl alcohol) and protein hydrolysate by Markéta Julinová; Jan Kupec; Pavol Alexy; Jaromír Hoffmann; Vladimír Sedlařík; Tomáš Vojtek; Jitka Chromčáková; Peter Bugaj (225-233).
The objective of this work was to study the biodegradation of blow-moulded films of poly(vinyl alcohol) (PVA)/protein hydrolysate (PH) which contain biodegradation inductors of the starch (S) and lignin (LI) types. These increase the biodegradation rate of PVA while preserving or improving the technical and usage properties of blends. The aim of the work was to reach the maximum breakdown rate so that rapid disintegration of PVA could take place at a wastewater treatment plant. The biological material chosen was activated sludge from a municipal wastewater treatment plant. Preparation of the blends required that a plasticiser be used, in this case glycerol (G). This allowed for successful processing but prolonged the lag phase of PVA breakdown as well as reducing its final biodegradation percentage. The influence of G, in this respect, was not affected by incorporating PH. S and LI reduced the influence of the plasticiser but caused a breakdown rate comparable to PVA itself. Contrarily, after adapting biomass to PVA, applying G produced a PVA breakdown rate three times greater, albeit with a lag phase prolonged fivefold. However, due to the duration of breakdown (the period above the retention time of wastewater during activation), this effect was not positive. The addition of PH to the blends mentioned did not exhibit any clear favourable influence. Adding S  resulted in a shorter lag phase, in addition to which the degradation rate increased by approximately 1.5 times. Combining LI and S distinctly accelerated the degradation of a blend, although a disadvantage of doing so is an incomplete breakdown of the substrate, which lowers the final biodegradation percentage. Therefore, an eventual compromise was arrived at, this being a blend of PVA/G PH S. Its breakdown time is half that of pure PVA, and the films produced, from a mechanical standpoint, are more convenient.
Keywords: Poly(vinyl alcohol); Lignin; Protein hydrolysate; Starch; Biodegradation; Activated sludge;

Effect of gamma radiation on dilute aqueous solutions and thin films of N-succinyl chitosan by Chutima Vanichvattanadecha; Pitt Supaphol; Naotsugu Nagasawa; Masao Tamada; Seiichi Tokura; Tetuya Furuike; Hiroshi Tamura; Ratana Rujiravanit (234-244).
N-Succinyl chitosan (N-SC) products with various degrees of substitution were synthesized by a direct reaction between chitosan and succinic anhydride. The susceptibility of the as-synthesized polymers to degradation upon their exposure to γ-ray radiation was investigated. The results were compared with the as-received chitosan. The size exclusion chromatographic results showed that chitosan and N-SC products in their dilute aqueous solution state were more subservient to degradation by γ-ray radiation than in their solid film state, despite the much less exposure to the radiation (i.e., 5–30 kGy for the solutions versus 20–100 kGy for the films). Increasing the radiation dose resulted in the rather monotonous decrease in the molecular weights of the polymers. Structural analyses of the irradiated polymers by Fourier-transformed infrared spectroscopy (FT-IR) and UV–visible spectrophotometry indicated the increase in the amount of carbonyl groups with the radiation dose. The formation of the carbonyl groups suggested that the radiolysis of chitosan and N-SC products occurred at the glycosidic linkages. In addition, FT-IR, elemental analysis and proton nuclear magnetic resonance spectroscopy (1H NMR) results suggested that γ-ray radiation affected both the N-acetyl and N-substituted groups on the polymer chains.
Keywords: Chitosan; Substituted chitosan; N-Succinyl chitosan; Degradation; Radiolysis; Gamma radiation;

The 2-(2-(5,5-dimethyl-1,3,2-dioxaphosphinyl-2-ylamino)ethy-amino)-N,N,N-triethyl-2-oxoethanaminium chloride (compound c ) containing phosphorus–nitrogen structure was synthesized and characterized. A novel intumescent flame retardant, namely montmorillonite (MMT) by modified with compound c ( c -MMT), was prepared by ion exchanging of the nanometer Na+-montmorillonite (Na-MMT) with compound c . Both FTIR and X-ray diffraction (XRD) indicated that compound c had intercalated with Na-MMT and exfoliated c -MMT/PU nanocomposites have obtained by in-situ polymerization. TEM results further support the formation of the exfoliated nanocomposites. The thermal stability and flammability of c -MMT/PU composites were investigated by thermogravimetric analysis (TGA) and cone calorimeter test respectively. The results showed that the addition of flame retardant c -MMT enhanced the thermal stability and flame retardancy of PU significantly. SEM results indicated that c -MMT can achieve better dispersion in the chars after combustion and the compact and dense intumescent char is formed for c -MMT/PU composites after combustion. It is found that the char structure plays an important role for c -MMT in PU resin. The thermal stability and flame retardancy of PU resin were also significantly improved by an addition of c -MMT in PU resin.
Keywords: Montmorillonite; Flame retardant; Phosphorus–nitrogen structure; Nanocomposite; Polyurethane;

The effect of sterilization methods on the thermo-gelation properties of xyloglucan hydrogels by Amanda K. Andriola Silva Brun-Graeppi; Cyrille Richard; Michel Bessodes; Daniel Scherman; Tetsuharu Narita; Guylaine Ducouret; Otto-Wilhelm Merten (254-259).
In this study, the influence of different sterilization methods on the thermo-gelation and structural properties of xyloglucan hydrogels was investigated. Xyloglucan samples were treated by either 70% ethanol, 70% isopropanol, γ-irradiation (10 kGy) at room temperature, γ-irradiation (10 kGy) in dry ice or autoclaving. These samples were tested for sterility by incubation with sterile Lysogeny Broth (LB) at room temperature, 30 °C and 37 °C for 30 days. According to the results obtained, xyloglucan hydrogels were only effectively sterilized by autoclaving or by γ-irradiation either at room temperature or in dry ice. These samples were analyzed by rheology measurements and dynamic and static light scattering analysis. Gamma-irradiation at room temperature markedly changed the polymer structure, preventing thermo-gelation. Only autoclaving and γ-irradiation in dry ice preserved the rheological properties of the polymer. The sol–gel transition as a function of the temperature was similar for these samples and the control sample.
Keywords: Sterilization; Thermo-gelation; Xyloglucan; Degradation;