Polymer Degradation and Stability (v.93, #12)

Calendar (I-II).

2-(6-oxido-6H-dibenz(c,e)(1,2)oxaphosphorin-6-yl)-1,4-naphthalenediol (DOPONQ) was prepared by the addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with 1,4-naphthoquinone. The phosphorus-containing diol (DOPONQ) was used as a reactive flame retardant by an advancement reaction with the diglycidyl ether of bisphenol-A epoxy (DGEBA) resin at various stoichiometric ratios. DOPONQ-containing advanced epoxy was separately cured with various dicyanate esters to form flame-retardant epoxy/cyanate ester systems. The effect of the phosphorus content and dicyanate ester structure on the curing characteristic, glass transition temperature, dimensional stability, thermal stability, flame retardancy, and dielectric property was studied and compared with that of the control advanced bisphenol-A epoxy system. The DOPONQ-containing epoxy/cyanate ester systems exhibited higher glass transition temperatures as well as better thermal dimensional and thermal degradation stabilities. The flame retardancy of the phosphorus-containing epoxy/dicyanate ester system increased with the phosphorus content, and a UL-94 V-0 rating could be achieved with a phosphorus content as low as 2.1%.
Keywords: Dicyanate ester; Flame retardancy; Phosphorus-containing epoxy resin; Thermal property;

A kinetic study of the decross-linking of cross-linked polyethylene in supercritical methanol by Hong-shik Lee; Ju Hyeong Jeong; Hang-Kyu Cho; Chong Min Koo; Soon Man Hong; Hwayong Kim; Youn-Woo Lee (2084-2088).
The recycling of cross-linked polyethylene (XLPE) by a decross-linking reaction in supercritical methanol was studied using a batch reactor. XLPEs with initial gel contents of 45, 55 and 65% were employed and subjected to reaction temperatures between 320 and 360 °C. Complete decross-linking of XLPE was achieved in 10 min in supercritical methanol at 360 °C and 15 MPa. For the first time, chemical kinetics for the decross-linking reaction is proposed based on the gel concentration, and applicable to the reactor design. With respect to the gel concentration, the first-order reaction model agreed well with the experimental results. The evaluated kinetic constant was 0.0867 ± 0.0082 cm3/mg min at 350 °C, and the activation energy was 578 ± 25 kJ/mol.
Keywords: Cross-linked polyethylene; Supercritical methanol; Decross-linking; Kinetics; Recycling;

The synthesis, characterization, and degradability of the novel aliphatic polyester bearing pendant N-isopropylamide functional group are reported for the first time. 2-(N-Isopropyl-2-carbamoylethyl)cyclohexanone (CCH) was first synthesized by the Michael reaction of N-isopropylacrylamide with cyclohexanone and was subsequently converted into 6-(N-isopropyl-2-carbamoylethyl)-ɛ-caprolactone (CCL) by the Baeyer-Villiger oxidation reaction using 3-chloroperoxybenzoic acid (mCPBA) as the oxidant. Finally, the novel functionalized poly(ɛ-caprolactone) bearing the pendant N-isopropylamide functional groups, poly(6-(N-isopropyl-2-carbamoylethyl)-ɛ-caprolactone-co-ɛ-caprolactone)s (poly(CCL-co-CL)), were carried out successfully by bulk ring-opening polymerization of CCL and ɛ-CL initiated by Sn(Oct)2. Poly(CCL-co-CL) were characterized by 1H NMR, 13C NMR, SEC and DSC. The copolymer containing 9.1 mol% CCL formed flexible films and was used to study its degradability. A phosphate buffer (pH = 7.4) with temperature 37 °C was adopted to proceed the degrading study all through. Compared with poly(ɛ-caprolactone), the hydrolytic degradation of poly(CCL-co-CL) was much faster, which is confirmed by the weight loss and change of intrinsic viscosity.
Keywords: Biodegradation; Ring-opening polymerization; PCL; Pendant N-isopropylamide functional groups;

Polymerisation and degradation of an aromatic amine-based naphthoxazine by Tamer Uyar; Zeynep Koyuncu; Hatsuo Ishida; Jale Hacaloglu (2096-2103).
Pyrolysis mass spectrometry (MS) analysis of aromatic amine-based naphthoxazine monomer (15-Na) and Poly15-Na has been carried out. Evaporation and degradation of the monomer are detected during the curing process while the polymerisation proceeded. The polymerisation and degradation mechanisms are proposed for 15-Na and Poly15-Na, respectively. The proposed polymerisation mechanism for naphthoxazine monomer was through the aniline units either by coupling of the radicals generated by cleavage of the side rings or by substitution to the benzene ring of aniline. It has been determined that polymerisation followed opposing paths yielding some thermally less stable linkages through which thermally crosslinked polynaphthoxazine (Poly15-Na) suffers from low thermal stability. It has been shown that pyrolysis MS is a very useful technique to investigate the polymerisation and degradation mechanisms and degradation products of these materials.
Keywords: Naphthoxazine; Polynaphthoxazine; Polybenzoxazine; Polymerisation mechanism; Degradation; Pyrolysis mass spectroscopy;

Thermogravimetric and wide angle X-ray diffraction analysis of thermoplastic elastomers from nylon copolymer and EPDM rubber by Cibi Komalan; Kochimoolayil Elias George; Konnanilkunnathal Thomas Varughese; Viju Susan Mathew; Sabu Thomas (2104-2112).
Nylon copolymer (PA6, 66) and ethylene propylene diene (EPDM) blends with and without compatibilizer were prepared by melt mixing using Brabender Plasticorder. The thermal stability of nylon copolymer (PA6, 66)/ethylene propylene diene rubber (EPDM) blends was studied using thermogravimetric analysis (TGA). The morphology of the blends was investigated using scanning electron microscopy (SEM). In this work, the effects of blend ratio and compatibilisation on thermal stability and crystallinity were investigated. The incorporation of EPDM rubber was found to improve the thermal stability of nylon copolymer. The kinetic parameters of the degradation process were also studied. A good correlation was observed between the thermal properties and phase morphology of the blends. By applying Coats and Redfern method, the activation energies of various blends were derived from the Thermogravimetric curves. The compatibilization of the blends using EPM-g-MA has increased the degradation temperature and decreased the weight loss. EPM-g-MA is an effective compatibilizer as it increases the decomposition temperature and thermal stability of the blends. Crystallinity of various systems has been studied using wide angle X-ray scattering (WAXS). The addition of EPDM decreases the crystallinity of the blend systems.
Keywords: Nylon copolymer; EPDM; Thermal behaviour; Crystallinity;

It has been shown that heating polypropylene powder under a nitrogen atmosphere leads to the significant prolongation of the oxidation induction time measured by chemiluminescence in oxygen at 130 and 140 °C. While heating in nitrogen from 0 to 4 h at 140 °C leads to the linear increase of oxidation induction time, the maximum chemiluminescence intensity I stat increases with the time of sample annealing until 2 h; then it starts to decay. The different and sometime unknown thermal history of the sample may thus explain the scatter of induction times of oxidation observed with different PPs whether they be pure or stabilised. Maximum chemiluminescence intensity plotted vs. concentration of oxygen in the surrounding atmosphere at 130 and 140 °C also increases linearly; however, this does not correspond with very small reduction of oxidation induction time. The four-parametric “master equations” used in our earlier papers were applied to fit the chemiluminescence runs both in oxygen and in nitrogen. The equation operates with the rate constants of hydroperoxide decomposition and oxidation spreading but at the same time, it takes into account the possible effect of oxidation products on decomposition of hydroperoxides.
Keywords: Chemiluminescence; Polypropylene; Oxidation; Annealing; Oxygen concentration;

Effect of annealing on hydrophobic stability of plasma deposited fluoropolymer coatings by Arun Kumar Gnanappa; Cian O'Murchu; Orla Slattery; Frank Peters; Balázs Aszalós-Kiss; Syed A.M. Tofail (2119-2126).
Fluorinated amorphous carbon (a-C:F) films e.g. plasma polymerised perfluorocyclobutane have long attracted much consideration due to their low surface energy, hydrophobicity, low refractive index, good electrical and thermal insulation and good thermal stability. Although a-C:F films have many advantages, hydrophobic stability over time in air and water remains a major concern. In this study, the effects of weathering conditions on the hydrophobicity of fluorocarbon films prepared from perfluorocyclobutane precursors were examined using water contact angle measurements. It was found that the high initial hydrophobicity of as-deposited films degrades rapidly in humid conditions. The stability of hydrophobicity can be significantly improved when a suitable treatment such as annealing is employed. The mechanism of weathering was explained with the help of a number of morphological and chemical characterisation techniques such as Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). In particular, XPS results demonstrated that a reduction in the overall amount of –CF3 radical, oxygenation of surface fluorides and the formation of an overlayer all influence the degradation of fluorocarbon in aquatic environment.
Keywords: Plasma polymer; Fluorocarbon coatings; Hydrolytic stability; Degradation; Weathering; Aging;

Photochemical stability of poly(vinyl pyrrolidone) in the presence of collagen by Alina Sionkowska; Justyna Kozlowska; Anna Planecka; Joanna Skopinska-Wisniewska (2127-2132).
The photochemical stability of poly(vinyl pyrrolidone) (PVP) in the presence of 1%, 3% and 5% of collagen has been studied by UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TG) and derivative thermogravimetry (DTG). Surface properties have been studied by contact angle measurements. PVP samples and samples containing 1%, 3% and 5% of collagen were irradiated with UV light of wavelength λ  = 254 nm in air for up to 24 h. The amount of gel created during UV irradiation was estimated.PVP in the presence of 1%, 3% and 5% of collagen is less stable both thermally and photochemically. Collagen enhances photochemical processes leading to crosslinking of PVP. The contact angle measurements and values of surface free energy showed that the wettability of PVP films was changed by the addition of collagen and by UV irradiation. The increase of polarity of samples indicates an efficient photooxidation on the surface upon UV irradiation.
Keywords: Poly(vinyl pyrrolidone); Collagen; Polymer blends; UV irradiation;

Effect of silica content on thermal stability of fumed silica/epoxy composites by J. Tarrío-Saavedra; J. López-Beceiro; S. Naya; R. Artiaga (2133-2137).
Composites of a fumed silica industrial residue and an epoxy resin were prepared and their thermal stability and thermal degradation behaviour were studied by TGA in air. Classical thermal stability parameters, based on the initial decomposition temperature (IDT), temperature of maximum rate of mass loss (T max) and integral procedure decomposition temperature (IPDT) were calculated before and after subtraction of the filler mass from the TGA curves. Without filler mass subtraction, the thermal stability of the epoxy resin seems to be improved and the mass loss rate was reduced by the addition of fumed silica. Nevertheless, after subtraction of the filler mass, the thermal degradation behaviour of the resin was only slightly affected by the silica content. A possible negative effect of the silica content on the cure was also found.
Keywords: TGA; Filler effect; Thermal stability; Filler subtraction; Fumed silica; Epoxy;

A detailed study of photodegradation of wood surfaces by xenon light source and a UV laser has been carried out. Silver birch, rubberwood, Scots pine and chir pine wood veneers were irradiated with a xenon light source or a 244 nm argon ion laser. The changes in chemical structure of wood surfaces were monitored by UV resonance Raman (UVRR), photoacoustic Fourier transform infrared (FTIR-PAS) and UV–vis reflectance spectroscopies. The depth profile of xenon lamp irradiated wood surfaces was carried out by measuring FTIR-PAS spectra at different moving mirror velocities. The UVRR and FTIR-PAS spectra of irradiated wood surfaces showed degradation of aromatic structure in lignin combined with strong formation of carbonyl structures. The FTIR-PAS spectra measured from xenon irradiated wood surfaces indicate that hardwood lignin degrades at a faster rate than softwood lignin. The UVRR spectra of xenon irradiated wood show a significant decrease in the intensities of aromatic structures at 1602 cm−1. This is accompanied by a significant band broadening and notable shift towards longer wavenumbers, which has been attributed to the formation of o- and p-quinone structures as degradation products. The formation of quinone structures was also supported by the generation of a broad absorption band between 350 and 600 nm in UV–vis reflectance spectra of irradiated wood surfaces. There was a significant broadening in the region of 1500–1000 cm−1 in UVRR spectra due to the formation of unsaturated structures as a result of lignin degradation. The UVRR spectra of laser irradiated wood showed similar behaviour i.e., overall broadening and a rapid reduction in the intensity of lignin aromatic structure. The rate of degradation by laser was very high. However, the extent of band broadening was higher in xenon irradiated wood indicating the generation of several different types of structures as compared to laser irradiation, which produces only particular type of structures. UVRR spectra of laser irradiated Whatman paper showed significant photodegradation of cellulose by UV laser. The UV degradation rate of lignin was much higher than cellulose.
Keywords: Cellulose; Fourier transform infrared spectra; Lignin; Photodegradation; Raman spectroscopy; Wood;

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.
Keywords: Polyaniline; Conducting polymer; Infrared spectroscopy; Raman spectroscopy; Thin films; Thermal degradation;

The curing of mixtures of bis(m-aminophenyl)methylphosphine oxide based benzoxazine and glycidylether or benzoxazine of Bisphenol A has been studied. In all samples the molar ratio of benzoxazine monomers or the benzoxazine–epoxy system was varied to achieve different phosphorus content. The phosphorus-containing polybenzoxazines have been characterized by dynamic mechanical and thermogravimetric analysis. Limiting oxygen index values indicate good flame retardant properties.
Keywords: Flame retardant; Benzoxazine; Epoxy; Heteroatom-containing polymers;

Synergism between flame retardant and modified layered silicate on thermal stability and fire behaviour of polyurethane nanocomposite foams by M. Modesti; A. Lorenzetti; S. Besco; D. Hrelja; S. Semenzato; R. Bertani; R.A. Michelin (2166-2171).
Synergy in flame retardancy of polyurethane foams between phosphorus-based flame retardant (aluminium phosphinate) and layered silicates has been investigated. We used pristine montmorillonite as well as ammonium modified clay (commercially available) and diphosphonium modified clay, which were synthesised by the intercalation of the quaternary diphosphonium salt according to a procedure reported here. The morphology of the foams was characterised through X-ray diffraction (XRD), while thermal properties were characterised by oxygen index test, cone calorimeter and thermogravimetric analysis (TGA). The morphological characterisation showed that pristine and diphosphonium modified clays are almost slightly intercalated, while ammonium modified one is very well dispersed. The results of thermal characterisation showed that in the presence of phosphinate enhancements of oxygen index, fire behaviour, measured by cone calorimeter, and thermal stability have been achieved. Phosphinate is therefore an efficient flame retardant for polyurethane foams and its flame retardancy action takes place in both condensed and gas phases. Pristine and ammonium modified layered silicate bring some enhancements of thermal stability while having no important effect in decreasing peak heat release rate (PHRR) and total heat evolved (THE) when used in conjunction with phosphinate; their main advantage is related to the enhancement of compactness of the char layer formed. Diphosphonium clay is instead effective in further improving the fire behaviour of the foams because of the flame retardancy action of phosphonium: both PHRR and THE were decreased. The analysis of cone calorimeter data showed that clays act through physical effect constituting a barrier at the surface which is effective in preventing or slowing the diffusion of volatiles and oxygen, while phosphinate and phosphonium are more effective owing to their combined action in both condensed and gas phases.
Keywords: Polyurethane; Nanocomposite; Synergy; Phosphorus; Fire;

In vitro hydrolytic degradation of poly(ɛ-caprolactone) grafted dextran fibers and films by Madhab Prasad Bajgai; Kawn-Woo Kim; Daman Chandra Parajuli; Yeon Chun Yoo; Wan Doo Kim; Myung-Seob Khil; Hak Yong Kim (2172-2179).
We studied the hydrolytic degradation of poly(ɛ-caprolactone) grafted dextran (PGD) fibers and films (matrices) prepared by electrospinning and solvent evaporation methods, respectively. In vitro degradation and erosion experiments were carried out in phosphate buffered saline (pH 7.4 ± 0.1) at 37 ± 1 °C for 150 days. Changes in molecular weights and morphologies of the PGD matrices were monitored as a function of degradation time. The extent of degradation was measured by physical weight loss, scanning electron microscopic (SEM) observations, Fourier transform-infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). During the progress of hydrolysis, GPC chromatograms appeared bi modal for fibers and bi and trimodal for the films. The crystallization temperature (T c) and heat of fusion were significantly increased in both matrices; this indicated preferential hydrolytic degradation in amorphous regions followed by cleavage-induced crystallization. The biodegradation rates were faster for the films (28%) than fibers (23%). After 150 days of degradation, the pH was steady at 5.8 ± 0.3 for fibers and 6.1 ± 0.3 for films. The faster degradation of the films could be probably due to autocatalysis in the interior of the films and the degraded oligomers are hard to diffuse out into the surrounding solution due to its compact physical geometry. Thus, our preliminary results about the degradation of matrices suggested that PGD nanofibers could be excellent matrices in tissue engineering over the films.
Keywords: Autocatalysis; Hydrolytic degradation; Nanofibers; Scaffolds; Tissue engineering;

Structure, morphology, thermal stability and carbonization mechanism studies of electrospun PA6/Fe-OMT nanocomposite fibers by Yibing Cai; Fenglin Huang; Qufu Wei; Lei Song; Yuan Hu; Yun Ye; Yang Xu; Weidong Gao (2180-2185).
In the present work, Fe-montmorillonite (Fe-MMT) was synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The polyamide 6 (PA6)/organic-modified Fe-montmorillonite (Fe-OMT) nanocomposite fibers were prepared by a facile compounding and electrospinning. The catalyzing carbonization studies of the Fe-OMT based on PA6 nanocomposite fibers were performed. It was found from High-resolution electron microscopic (HREM) observations that the silicate clay layers were well dispersed within the nanocomposite fibers and was oriented along the fiber axis. The Scanning electron microscopic (SEM) images indicated that the nanofibers were randomly distributed to form the fibrous web and the Fe-OMT additives decreased the diameters of nanocomposite fibers. The Thermogravimetric analyses (TGA) revealed that the loading of the Fe-OMT led to the crosslinking of the PA6, promoted the charred residue yield and catalytic graphitization effect. The structure and morphology of the purified charred residue, characterized by XRD, HREM, Selected area electron diffraction (SAED) and Laser Raman spectroscopic (LR), approved further the presence of graphite sheets. The possible catalyzing carbonization mechanisms included: (1) catalyzing effect of the Fe3+, which promoted the crosslinking of polymer, (2) Hofmann degradation of the Fe-OMT, whose degraded products had also positive role in promoting crosslinking reactions, (3) gas barrier properties of the nano-dispersed silicate clay layers stopped or reduced the releases of the pyrolytic products, which was dehydrogenated and aromatized to form graphite.
Keywords: Electrospinning; Nanocomposite fibers; Fe-OMT; Thermal stability; Carbonization mechanism;

Preparation and flammability of a novel intumescent flame-retardant poly(ethylene-co-vinyl acetate) system by De-Yi Wang; Xiao-Xia Cai; Ming-Hai Qu; Yun Liu; Jun-Sheng Wang; Yu-Zhong Wang (2186-2192).
A phosphorus-containing flame retardant, 4-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorinan-2-yloxymethyl)-2,6,7-trioxa-1-phospha-bicyclo[2.2.2]octane-1-oxide (MOPO), was synthesized successfully and characterized. The flame retardancy and thermal behavior of a new intumescent flame-retardant (IFR) system for EVA, which was made of MOPO and ammonium polyphosphate (APP), were investigated by limiting oxygen index (LOI) test, vertical burning test (UL-94), cone calorimeter, and thermogravimetric analysis (TGA). An LOI value of 28.4 and UL-94 V-0 rating can be achieved when the total loading of MOPO and APP was 30 wt.%. The results from cone calorimeter indicate that both the heat release rate (HRR) and the total heat release (THR) of IFR-EVA decreased significantly compared with those of neat EVA. TG curves showed that the amount of residues increased significantly when intumescent additives were added; it also could be found that the LOI values increased with the increase in char residues. Meanwhile, morphology of the residues obtained from burning IFR-EVA in LOI test was studied through the SEM observations and rich compact char layers could explain the excellent flame retardance.
Keywords: Flame retardance; Intumescence; Cone calorimeter; Poly(ethylene-co-vinyl acetate);

The important polymer stabilizer, 1,2-bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyl)hydrazine, which serves a dual role as a metal deactivator and antioxidant, is shown to have crystal polymorphism. Although the published melting range is 225–232 °C, which is well above the processing temperature of many polymers in which it is used, existence of a second polymorph that transforms below 205 °C is demonstrated. This α polymorph, which is thermodynamically stable at room temperature, is thermodynamically un-favored at temperatures above about 176 °C. It is shown that under some conditions the α polymorph can endothermically pass directly into the melt state at temperatures below 205 °C, while under other conditions it undergoes a direct endothermic solid–solid transition to the higher melting β polymorph.The results highlight the potential importance of polymorphs for controlling polymer additive behavior and elucidate important phenomena relevant to dispersion of this additive in polymer compounds.
Keywords: Antioxidant crystal polymorphism; Metal deactivator; Melt dispersion; Hydrazine; Hydrazide; Phase transition;

Commercial polystyrene (PS) has been studied as a modifier for commercial poly(vinyl chloride) (PVC) when it was submitted to gamma irradiation. PVC/PS blends were prepared with 100/0, 95/05 and 90/10 compositions. Results for gamma-irradiated (60Co) blends are reported and changes in viscosity-average molar mass (M v) were analyzed. The study showed that the addition of PS into PVC decreased by 73% (95/05) and 79% (90/10) the number of scissions/100 eV in the dose range of 25–100 kGy. Viscosity analyses by the Pan et al. criterion and analyses of FT-IR spectra in the C–Cl vibration region showed negligible intermolecular interactions between the components of PVC/PS blends. However when the films of blends were irradiated to 50 kGy, certain intermolecular interactions were observed by the viscosity method. The addition of PS to PVC and the main scission effect induced by gamma irradiation decreased crosslink density of blends causing changes in the elongation of break and Young's modulus.
Keywords: PVC/PS blend; Radiolytic stabilization; Miscibility; Mechanical property;

Previous studies focused on the behaviour of different samples of vacuum gas oil (VGO), polyethylene (PE) and vacuum gas oil–polyethylene blends (VGO–PE) in thermal and catalytic pyrolysis, showed that the pyrolysis of the blends goes through two decomposition steps, where the first is related to the elimination of the VGO fraction, and the second to the pyrolysis of PE. Moreover, the presence of catalyst mainly affects the PE decomposition. In this work, the evolution of the composition of the gases evolved in the thermal and catalytic pyrolysis decomposition of VGO, PE and VGO–PE blend with temperature (or time) has been studied by GC/MS. The results agree with the previous studies and allow the behaviour of such systems to be better understood, yielding valuable information for designing processes of plastic recycling by mixing with VGO and the mixture being treated in a unit similar to the industrial fluid catalytic cracking unit.
Keywords: Catalytic pyrolysis; Dynamic pyrolysis; GC/MS; VGO; PE; VGO–PE blends;

Studies on erosion of silicone rubber exposed to partial arc discharges by Kenichi Haji; Yong Zhu; Masahisa Otsubo; Tatsuya Sakoda (2214-2221).
The effect of electrolyte conductivity on the partial arc discharge development between two electrolyte electrodes on a silicone rubber sheet surface was investigated. Tests were executed by placing the salt-waterlogged glass-filter paper on a silicone rubber sheet to simulate a polluted electrolyte layer, and partial arc discharges with a constant current value of 10 mA were observed. It was found that the formation of an arc channel and a temperature distribution on the sample surface varied with the electrolyte conductivity. In addition, the relation between the electrolyte conductivity and the weight loss due to the heat erosion of specimens was also investigated by a 3D morphological observation and a simulated calculation. The partial arc discharge did significantly not influence on the sample surface erosion under serious polluted conditions. In contrast, the severest erosion appeared under the light pollution with comparatively lower conductivity of the electrolyte electrodes.
Keywords: Polymer insulator; Erosion; Silicone rubber; Partial arc discharge; Electric field;

A novel phosphate acrylate monomer (TGMAP) has been synthesized by allowing phosphoric acid to react with glycidyl methacrylate. Its structure was characterized by Fourier transformed infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance spectroscopy (1H NMR). The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR). The char yield was 36.3% at 600 °C. TG data indicate that the material undergoes degradation in three characteristic temperature stages, which can be attributed to the decomposition of the phosphate, thermal pyrolysis of aliphatic chains, and degradation of an unstable structure in char, respectively. The volatilized products formed on thermal degradation of TGMAP indicated that the volatilized products are CO, CO2, carboxylic acid, acid anhydride, water, alkane, and aromatic compounds according to the temperature of onset formation.
Keywords: UV curing; Phosphate; Flame retardant; Thermal degradation;

Constitutive modeling of radiation effects on the permanent set in a silicone elastomer by A. Maiti; R.H. Gee; T. Weisgraber; S. Chinn; R.S. Maxwell (2226-2229).
When a networked polymeric composite under high stress is subjected to irradiation, the resulting chemical changes like chain scissioning and crosslink formation can lead to permanent set and altered elastic modulus. Using a commercial silicone elastomer as a specific example we show that a simple 2-stage Tobolsky model in conjunction with Fricker's stress transfer function can quantitatively reproduce all experimental data as a function of radiation dosage and the static strain at which radiation is turned on, including permanent set, stress–strain response, and net crosslink density.
Keywords: Radiation effects; Constitutive model; Siloxanes; Permanent set;