Polymer Degradation and Stability (v.89, #1)

Investigation of wood wettability changes during heat treatment on the basis of chemical analysis by Mohammed Hakkou; Mathieu Pétrissans; André Zoulalian; Philippe Gérardin (1-5).
Contact angles, measured by Wilelhmy technique, during beech heat treatment by mild pyrolysis under inert atmosphere, indicated a significant increase of wood hydrophobicity for a temperature between 130 and 160 °C. This behaviour, generally reported for higher temperatures, has been investigated in terms of chemical modifications and molecular organization of wood biopolymers to understand the reasons of these hydrophobic properties. Different experiments indicate that degradation reactions and extractives generation are not the origin of these properties. 13C MAS NMR and FTIR analysis suggest that wettability modification during heat treatment could be explained by a modification of conformational arrangement of wood biopolymers due to loss of residual water or more probably to plasticisation of lignin.
Keywords: Chemical composition; Contact angle; Heat treatment; Wettability; Wood;

The ultrasonic degradation of polystyrene (PS) and ethylene–propylene diene monomer (EPDM) melts was conducted in a specially designed reactor. A degradation model of polymer melts was proposed to explain the ultrasonic degradation, and degradation of polymer melts is treated as a mechanochemical process. Ultrasonic degradation kinetics obeys the equations: M t = M ∞ + A ⅇ − k t or [ η ] t = [ η ] ∞ + ( [ η ] 0 − [ η ] ∞ ) ⅇ − k t . The experimental results show that the molecular weight or intrinsic viscosity of polymer melts decreased with ultrasonic irradiation time and approached a limiting value, below which no further degradation took place. Different from ultrasonic degradation of polymer solutions, the scission of chains in polymer melts is random in the initial stage, and then non-random. FTIR spectra of samples ultrasonically treated and untreated confirmed that the initial product of ultrasonic degradation in polymer melts is a macroradical. The effects of ultrasonic intensity and reaction temperature on degradation of PS and EPDM melts were also investigated. The significant results showed that the degradation rate, the limiting value and degradation extent are correlated greatly with the experimental conditions.
Keywords: Ultrasound; Degradation; Polystyrene; Ethylene–propylene diene monomer; Melt;

Poly(3-dodecylthiophene) (p3ddt) was prepared by oxidative polymerisation, doped with iodine, and characterised by surface resistivity, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), to study its stability and structural changes upon repeated doping and de-doping. The surface resistivity of p3ddt was greatly affected by the thermal de-doping temperature; at lower de-doping temperatures (<200 °C), its conductivity gradually recovered with doping time; it would partially or completely lose conductivity above the de-doping temperature at 200 °C. Both the pristine and doped p3ddt decomposed at around 350 °C; the iodine uptake ability decreased while re-doping with the increase in heating temperature. XPS results revealed that doping and heating was accompanied by oxidation with the participation of oxygen. These structural distortions and chemical transformations may contribute to the increase in surface resistivity upon heating.
Keywords: Poly(3-dodecylthiophene); Doping and de-doping; Conductive polymer; Stability;

Sequential poly(ester amide)s derived from glycolic acid, 1,6-hexanediamine and dicarboxylic acids with an even number of methylene groups have been synthesized by two different methods. Molecular weights are higher when a new thermal polycondensation reaction based on the formation of metal halide salts is employed. The thermal properties of the series of new polymers have been studied by differential scanning calorimetry. In all cases, a melting point in the 115–150 °C range has been measured, which tends to the melting point of polyethylene as the methylene content increases. Thermogravimetric analysis indicates that this series of polymers is stable through fusion, and consequently these new poly(ester amide)s can be easily processed from the melt.Hydrolytic and enzymatic degradation studies, where weight losses, intrinsic viscosity changes, NMR spectra and calorimetric data of degraded samples were evaluated, have also been undertaken. The polymers seem interesting because of their application as new biodegradable materials.
Keywords: Poly(ester amide)s; Differential scanning calorimetry; Degradability; Glycolic acid;

Solid phase microextraction to concentrate volatile products from thermal degradation of polymers by Janaina H. Bortoluzzi; Eduardo A. Pinheiro; Eduardo Carasek; Valdir Soldi (33-37).
Solid phase microextraction (SPME) was used to analyse the products evolved in the thermal degradation of polypropylene (PP) which was used as a model polymer. The degradation was performed under nitrogen at 470 °C using polydimethylsiloxane and carboxen/polydimethylsiloxane as the fibres for the product pre-concentration. The evolved degradation products were identified by infrared spectroscopy (FTIR) and gas chromatography/mass spectroscopy (GC/MS). More than 30 evolved products associated with alkenes (61.0%), alkanes (33.0%) and alkadienes (4.3%), were identified. In agreement with the literature, evolved products such as 2,4-dimethyl-1-heptene, n-pentane, 2-pentene, propylene, 2-methyl-1-pentene, 2,4,6-trimethyl-1-nonene, etc., were detected from the polypropylene thermal degradation. The results suggest that the SPME technology offers important factors such as, rapid analysis and great efficiency in the pre-concentration of evolved products from the thermal degradation of polymers.
Keywords: Solid phase microextraction; Volatile products; Thermal degradation; Polymers;

Analysis of chlorine distribution in the pyrolysis products of poly(vinylidene chloride) mixed with polyethylene, polypropylene or polystyrene by Thallada Bhaskar; Maki Tanabe; Akinori Muto; Yusaku Sakata; Chiung-Fang Liu; Ming-Der Chen; Chih C. Chao (38-42).
The analysis of chlorine distribution in the pyrolysis products of poly(vinylidene chloride) PVDC mixed with polyethylene (PE), polypropylene (PP) or polystyrene (PS) were investigated [PE/PVDC, PP/PVDC, PS/PVDC and 3P/PVDC, where 3P is equal mixture of PE, PP and PS] and reported for the first time. The interaction of degradation products from individual (PE, PP and PS) and mixed (3P) plastics with the PVDC degradation products was investigated and compared with poly(vinyl chloride), PVC. The formation of chlorinated hydrocarbons in the liquid products were in the order of PS/PVDC > 3P/PVDC > PP/PVDC > PE/PVDC. Surprisingly, the quantities of chlorinated hydrocarbons were less compared with the pyrolysis liquid products of PVC mixed plastics even though the chlorine content in PVDC is higher than in PVC. The structurally similar chlorinated hydrocarbons were observed from PVDC or PVC with PE, PP, and PS liquid products. Thermogravimetric analysis results suggest that the decomposition temperature of PVDC is lower than PVC and major portion of chlorine (from PVDC) left the degradation reactor before the degradation of PP, PE, and PS.
Keywords: Poly(vinylidene chloride); PVDC; Poly(vinyl chloride); PVC; Pyrolysis; Waste plastics;

The effect of aluminum countercations on the thermal behavior of Nafion®-117 membrane was studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and accelerating rate calorimetry (ARC®). Aluminum countercations exchanged into a Nafion®-117 membrane were found to adversely affect the thermal properties of the membrane. The aluminum cations may give rise to a catalytic decomposition of the perfluoroalkylether (PFAE) side chains of the Nafion®. This result, together with some previously reported data, indicate that not just the size of the countercations, but the properties of the countercations themselves can also have a very strong effect on ionomer properties.
Keywords: Nafion®; Aluminum; Ionomer; Membrane; Thermal behavior;

The number of degradable polyethylene films on the market is increasing. These degradable films show different degradation behaviour depending on the pro-oxidant system incorporated in them. The degradation of the films gives rise to complex collections of degradation products. The key question in this work was to classify the types of pro-oxidant systems in degradable polyethylene films and the state of degradation of the films. The classification was performed with chromatographic fingerprints of carboxylic acids, the most abundant type of degradation product. The acids were extracted from films oxidised at 80 °C and were thereafter methylated and analysed by GC–MS. Classification and prediction models were obtained by Multivariate Data Analysis. The diacids were grouped according to both the type of pro-oxidant system and the state of degradation. This showed that both the type of pro-oxidant system and the state of degradation are predictable from the diacid fingerprints. The monoacids were shown to be useful for classifying materials from their initial compositions of stearates but not for predicting the degradation state. The goal was also to see how changes in activation energies for hydroperoxides, noticed earlier with chemiluminescence, were reflected in the degradation mechanisms. The observed increase in chemiluminescence peak temperature of the polyoctylene-containing film was related to the initial degradation of the polyoctylene.
Keywords: Classification; Prediction; Chromatographic fingerprinting; Degradation mechanisms; Pro-oxidant systems; Chemiluminescence;

Photo-induced degradation of cellulose by J. Malešič; J. Kolar; M. Strlič; D. Kočar; D. Fromageot; J. Lemaire; O. Haillant (64-69).
Irradiation by light is considered to be one of the primary sources of damage exerted upon cellulosic substrates at ambient conditions. Yet, contrary to studies on thermal ageing of cellulose, only limited attention is devoted to light induced degradation of paper.This research demonstrates that extensive oxidative degradation of cellulose, accompanied by formation of hydroxyl radicals, occurs during exposure to light with λ  > 340 nm. As demonstrated by size exclusion chromatography, degradation is not random. No high-molecular weight fraction appears in the irradiated sample, meaning that cross-linking is not a dominant process. This justifies the use of viscometry for light-irradiated cellulosic materials. Studies show that the rate of degradation, carbonyl formation and brightness decrease may be reduced by addition of magnesium carbonate.
Keywords: Cellulose; Photo-ageing; Degradation; Oxidation; Size exclusion chromatography; Viscometry; Carbonyl groups; Brightness; Deacidification;

Expandable graphite/polyamide-6 nanocomposites by Fawn M. Uhl; Qiang Yao; Hiroyoshi Nakajima; E. Manias; Charles A. Wilkie (70-84).
Polyamide-6 (PA-6)/graphite nanocomposites were prepared by melt blending, using a variety of graphites, including virgin graphite, expandable graphites and expanded graphite. The resulting nanocomposites were characterized by X-ray diffraction, thermogravimetric analysis, cone calorimetry, and tensile mechanical analysis. Nanocomposite formation does occur, as denoted by the nanometre dispersion of graphite layers in the polymer matrix, and the dispersion depends on the graphite treatment. The material properties of the resulting composites are improved relative to the virgin/unfilled polymer; in particular, there is an enhancement of the thermal stability without any significant deterioration of the mechanical properties.
Keywords: Expandable graphite; Polyamide-6; Nanocomposites;

Fire retardancy of vinyl ester nanocomposites: Synergy with phosphorus-based fire retardants by Grace Chigwada; Panchatapa Jash; David D. Jiang; Charles A. Wilkie (85-100).
Vinyl ester (PVE) nanocomposites were prepared using both clay and polyhedral oligosilsesquioxanes (POSS) as the nano-dimensional material. From cone calorimetric data, it was shown that both POSS and clay affect the flammability of the nanocomposites to the same extent. To improve on the flame retardancy, the nanocomposites were combined with phosphorous-containing fire retardants (FRs) and the result compared to the benchmark halogen-containing system. The use of the cone calorimeter to investigate the fire properties of these nanocomposites showed a great reduction in peak heat release rate (PHRR) in the presence of phosphate and slight improvements in average mass loss rate (AMLR) while thermogravimetric analysis showed improvement in char yield in the presence of phosphate. Several different organically modified clays were used and they affected the flammability to different extents. The time that the resin and clay were mixed and the atmosphere in which the reaction was carried out do not have an effect on the flammability and thermal stability of the nanocomposites. The effect of curing temperature on the clay dispersion and flammability was also investigated.
Keywords: Vinyl esters; Nanocomposites; Fire retardancy; Thermal stability;

Polypropylene (PP) was pyrolysed over various catalysts using a laboratory fluidised-bed reactor operating isothermally at ambient pressure. The yield of volatile hydrocarbons for zeolite catalysts (HZSM-5 > HUSY ≈ HMOR) was higher than that for non-zeolite catalysts (SAHA ≈ MCM-41). Product distributions with HZSM-5 contained more olefinic materials with about 60 wt% in the range of C3–C5. However, both HMOR and HUSY produced more paraffin streams with large amounts of isobutane (i-C4) and both catalysts were deactivated during the course of the degradation. SAHA and MCM-41 showed the lowest conversion and generated an olefin-rich product with a rise to the broadest carbon range of C3–C7. Experiments carried out with various catalysts gave good yields of volatile hydrocarbons with differing selectivity in the final products dependent on reaction conditions. The selectivity could be further influenced by changes in reactor conditions; in particular, olefins and iso-olefins were produced by low temperatures and short contact times. It is demonstrated that under appropriate reaction conditions suitable catalysts can have the ability to control both the product yield and product distribution from polymer degradation, potentially leading to a cheaper process with more valuable products.
Keywords: Pyrolysis; Polypropylene; Fluidised-bed reactor; Catalysts; Degradation; Selectivity;

This paper presents the results of a series of experimental investigations conducted to assess the influence of ethanol exposure at different concentrations on the mechanical properties of a plasticized PVC membrane. Exposure to pure ethanol resulted in a reduction in flexibility, or embrittlement, and the transformation of the PVC membrane from a flexible material capable of undergoing large strain hyperelastic behaviour to a stiffer material with pronounced yield behaviour. Results of X-ray fluorescence measurements indicate the loss of the plasticizer from the PVC membrane as a contributing factor for the alteration in the mechanical properties of the PVC membrane. The experiments also indicate a slower rate of plasticizer leaching during exposure to lower concentrations of ethanol. Exposure of the PVC membranes to 80% and 50% concentrations of ethanol and pure water has a reduced influence on the loss of large strain deformability of the PVC membrane, even after more than one year of exposure. The PVC membranes exposed to a mixture of ethanol and pure water in equal volume proportions indicate that, after longer period, the PVC membranes became softer and exhibit greater deformation under the same external load. This phenomenon can be attributed to the swelling of the PVC membrane.
Keywords: Plasticized PVC; Uniaxial testing; Chemical exposure; Strain-rate effects; Embrittlement; Geosynthetic liners;

A study on the electrical conductivity decay of polypyrrole coated wool textiles by Alessio Varesano; Lorenzo Dall'Acqua; Claudio Tonin (125-132).
Loose wool fibres were coated with electrically conducting doped polypyrrole (PPy) by in situ chemical oxidative synthesis from an aqueous solution of pyrrole. PPy coated wool fibres were spun and knitted using conventional industrial machinery. Electrical and thermal properties of the fabrics were studied using simulated ageing tests, with the aim of evaluating the performances decay during the processing stages and the final use of the products. Fastness tests were performed according to established international standards. The coating evenness and degradation were investigated by Light Microscopy (LM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) Microanalysis and Infrared Spectroscopy (FT-IR).The results show that fabrics made of PPy coated wool fibres have an acceptable conductivity decay with respect to most of the stress that textile products are usually subjected to; low fastness was found only to washing, probably due to alkali dedoping of conducting PPy coating, although an excellent resistance to organic solvents allows conventional dry cleaning treatments.
Keywords: Polypyrrole; Wool; Polymer coating; Conductivity; Stability to use;

An experimental study on different polyesters (PET, PBT, PEN, PEA, PCT-co-ET) subjected to γ-irradiation up to 1 MGy was carried out through viscometry, thermal analysis and positron annihilation lifetime spectroscopy. Chain scission induced by irradiation prevails for doses up to 100 kGy; it is influenced by the length of the aliphatic chain as well as by the presence of the aromatic ring. Crosslinking dominates for doses between 100 and 300 kGy, while the oxidative degradation mechanism, present at the highest doses, increases its importance with the amorphous fraction of the polymer. Free volume structure is not modified by irradiation.
Keywords: Polyesters; Irradiation effects; Viscometry; Oxygen; Positron annihilation lifetime spectroscopy;

Photo-antioxidant abilities of 2-hydroxybenzoyl compounds by Yoshiyuki Dobashi; Jun-ichi Kondou; Yasukazu Ohkatsu (140-144).
Plastics are indispensable for our comfortable life. But, they are easily degraded by autoxidation, especially under the action of UV light, due to their organic character. Therefore, additives preventing the photo-oxidation are needed. 2-Hydroxybenzophenones are widely used as ultraviolet absorbers (UVA), and their effect is discussed in many papers. However, there are few papers, in which the effect of substituents on the benzene nucleus and/or the 2-hydroxybenzoyl group on the photo-antioxidant ability is directly examined. This study focuses on clarifying such substituent effect. As a result, it has been made clear that the photo-antioxidant ability is better improved by introducing a substituent into p-position than m-position of the 2-hydroxyl group. In addition, it was found that the photo-antioxidant ability is enhanced by enlarging the conjugation system of the group bonded to the 2-hydroxybenzoyl carbonyl group. The substituent effect activity of (2-hydroxybenzoyl)-benzene is also discussed.
Keywords: UVA; 2-Hydroxybenzophenone; 2′-Hydroxyacetophenone; 2-Hydroxybenzoyl; Substituent effect;

The evolution of gas during the catalytic pyrolysis of three commercial ethylene–vinyl acetate copolymers in the presence of mesoporous MCM-41 has been studied by TGA/FTIR. The results have been compared with those corresponding to the thermal pyrolysis carried out under the same experimental conditions, and showed that the formation of alkenes and aromatics and shorter and/or more branched hydrocarbons is favoured in the presence of the catalyst.
Keywords: Catalytic pyrolysis; EVA copolymers; TGA; FTIR; MCM-41;

The non-oxidative thermal degradation of poly(di-n-alkyl itaconates). I. Analysis of the thermolysis volatiles by Ivanka G. Popović; Lynne Katsikas; Jovan S. Veličković (153-164).
The volatiles arising from the thermal degradation of poly(di-n-alkyl itaconates) with ester substituents ranging from methyl to n-octyl were analysed. The corresponding monomer was found to be the major degradation product. A significant amount of itaconic acid in the volatiles was also found in the case of poly(diethyl itaconate). A detailed mechanism of the thermal degradation of the studied polymers is given.
Keywords: Thermal degradation; Polyitaconates; Volatiles; Mechanism;

The non-oxidative thermal degradation of poly(di-n-alkyl itaconates). II. Analysis of the polymer residue by Ivanka G. Popović; Lynne Katsikas; Jovan S. Veličković (165-174).
The residues remaining after the thermal degradation of poly(di-n-alkyl itaconates) with ester substituents ranging from methyl to n-octyl were studied. It was found that the thermal stability of the polymers decreased with increasing size of the alkyl group. Depolymerisation was the main degradation pathway with the depolymerisation zip length being very small and independent of the alkyl substituent. The number of bonds broken per monomer unit, s/P 0, increased with increasing temperature and time of degradation, as well as with increasing size of the alkyl substituent. The threshold temperature of degradation of each polymer was calculated from the values of s/P 0. At lower degradation temperatures and times branching occurs in PDBI and PDHI and crosslinking in PDOI.
Keywords: Thermal degradation; Polyitaconates; Residue; Stability;

The heterogeneous oxidation model is adapted to polyethylene melts at low temperature. It takes into account that decomposition of associated hydroperoxides in the low temperature range is no longer fast in comparison with their formation through successive oxidation of the same elementary volumes. Consideration of both formation and decomposition of associated hydroperoxides leads to a mathematical model accounting for the experimental results. Accumulation of associated hydroperoxides as well as alcohol formation in the low temperature range are explained. The rate of decomposition that is deduced from data fitting is comparable to the published rate for low molecular mass associated hydroperoxides. Different aspects of heterogeneous oxidation kinetics are discussed.
Keywords: Polyethylene; Thermal oxidation; Processing; Oxidation products; Hydroperoxides; Alcohols; Mechanisms; Heterogeneous kinetics;