Polymer Degradation and Stability (v.94, #7)

Calendar (I-II).

Investigating the role of metal oxidation state on the degradation behaviour of LDPE by P.K. Roy; P. Surekha; R. Raman; C. Rajagopal (1033-1039).
Transition metal stearates have been reported to act as effective pro-oxidants for polyethylene, even at trace concentrations. This study is an attempt to investigate the effect of the oxidation state of a metal on its pro-oxidant nature. Three metal stearates, namely manganese, iron and cobalt, in their common oxidation states (+2 and +3), were synthesized and their effect on the photo-oxidative and thermo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. Films of 70 ± 5 μ were prepared by film blowing technique, exposed to xenon arc weatherometer and air oven at 70 °C for extended time periods. The chemical and physical changes induced by this exposure were followed by monitoring the changes in mechanical properties (tensile strength and elongation at break), carbonyl index (CI), molecular weight (viscometry), MFI, density, and thermal properties. The results were analysed to explain the structural and chemical modifications taking place in the polymeric matrix as a result of aging. The studies reveal that the oxidation state of the metal did not affect its ability to initiate and accelerate degradation. The thermo-oxidative degradation in the presence of metal stearate was found to follow the order: cobalt > manganese > iron. However, iron stearate was capable of initiating photo-oxidative degradation to the same extent as cobalt and manganese, in the concentration range investigated. The results indicate that iron is primarily an effective photo-oxidant, while cobalt and manganese can act both as photo-oxidant as well as thermo-oxidant.
Keywords: Degradation; Pro-oxidant; Polyethylene; Weathering;

Thermal degradation of star-shaped poly(ɛ-caprolactone) by Wenyuan Xie; Zhihua Gan (1040-1046).
Thermal degradation of a serials of star-shaped poly(ɛ-caprolactone) (PCL) with well-defined arm numbers and arm length was investigated. The weight loss of star-shaped PCL during heating process showed a two-stage character, and its dependence on molecular weight and multi-armed structure was well discussed. It was found that the thermal stability could be improved not only by increasing molecular weight but also by increasing arm numbers when the molecular weight is in a certain range. Based on the analyses of pyrolytic products by 1H NMR and TGA–FTIR, two mechanisms of thermal degradation for the random cleavage of ester bonds of PCL chains were proposed. Ester bonds were pyrolyzed into alkene and carboxyl functional groups in mechanism I while they were pyrolyzed into ketene and hydroxyl functional groups in mechanism II. The effects of multi-armed structure of star-shaped PCL on the cleavage of ester bonds of PCL chains were discussed in terms of the limitation of central “core” on mobility of each PCL arm. Combined the results of viscosity analysis with thermal analysis, it could be concluded that both thermal stability and processability of PCL materials can be improved by controlling the multi-armed structures.
Keywords: Thermal degradation; Star-shaped poly(ɛ-caprolactone); Multi-armed structure; Molecular weight; Pyrolytic products;

Hydrothermal catalytic oxidation was an effective method in the dechlorination and oxidation of waste poly(vinylidene chloride) (PVC) on Pd/AC catalyst. The PVC was decomposed by hydrothermal catalytic oxidation in the system of NaOH at appropriate temperature in our experiments. The degree of dechlorination and oxidation increased with increasing concentration of H2O2, reaching up to 90% and 50% under the condition of 180 °C and 0.5 MPa pressure. The main products were Cl and CO2, and the rest comprises a range of water-soluble organic acids, which were nontoxic and can be treated by biological purification. Therefore, the hydrothermal catalytic oxidation had significant potential in application for treatment of chlorinated waste plastics.
Keywords: Hydrothermal catalytic oxidation; Dechlorination; Skeletal carbon chain oxidation; PVC; Pd/AC catalyst;

Soluble and heat-resistant s-triazine-containing poly(aryl ether)s have been prepared for their potent utilities as high-temperature membranes and composite matrix materials. They have been synthesized by the nucleophilic displacement polymerization of 2,4-bis(4-fluorophenyl)-6-phenyl-1,3,5-triazine (BFPT) with each of resorcinol (RS), 4,4′-dihydroxydiphenyl sulfone (DS), and bisphenol-like 4-(4-hydroxylphenyl)(2H)-phthalazin-1-one (HP). The presence of meta-ether linkages, sulfone groups or phthalazinone moieties in the polymer chain results in an improvement in the solubility of s-triazine-containing poly(aryl ether)s in common organic solvents (e.g., N,N′-dimethylacetamide, N-methyl-2-pyrrolidinone). The new polymers are amorphous and exhibit excellent thermal stability. The apparent activation energy values (E a) as determined by using Kissinger method are respectively 268.1, 245.9 and 215.1 kJ/mol under N2 flow in dynamic heating conditions, for the first degradation stage of RS-PE, DS-PE and HP-PE, which are in well agreement with those values (272.6, 249.9 and 239.1 kJ/mol) determined by using Flynn–Wall–Ozawa method. The thermal stability classification among the polymers is made on the basis of the E a values, and it follows the decreasing order: RS-PE > DS-PE > HP-PE. The properties of these polymers have been also compared with those of corresponding poly(aryl ether)s.
Keywords: s-Triazine; Poly(aryl ether)s; Heat-resistant; Activation energy; Thermodynamics;

The necessity for inspection and assessment of glued laminated timber structures in service has raised interest in the evaluation of the glue lines. Glue line spectra were analysed and are discussed in detail with respect to spectral contributions from the adhesive, the hardener, the wood lamella below the adhesive, the curing temperature as well as ageing-related spectral changes. The combination of near infrared (NIR) spectroscopy and principal component analysis (PCA) allowed distinguishing between aged and non-aged samples and different copper azole preservative treatment levels of phenol-resorcinol-formaldehyde (PRF) glue lines. NIR-based partial least squares (PLS) regression modelling was performed for the glue line shear strength and for the curing temperature. These findings show that NIR spectroscopy is a fast and useful technique to evaluate the degradation on the PRF glue lines of untreated and copper azole treated laminated timber.
Keywords: Wood; Delamination; Near infrared (NIR) spectroscopy; Partial least squares regression; Copper azole; Phenol-resorcinol-formaldehyde (PRF) glue lines;

Polyurethane–zinc borate composites with high oxidative stability and flame retardancy by Basar Yıldız; M. Özgür Seydibeyoğlu; F. Seniha Güner (1072-1075).
Novel polyurethane zinc borate composites were prepared with the main aim to increase the flame retardancy of the polyurethane. It was discovered that the zinc borate had very significant effects on the oxidative stability of the neat polymer which was first observed by oxygen induction time tests and supported with actual weathering chamber tests. The oxidative stability of zinc borate-filled polyurethane was compared with the polyurethane stabilized with a commercial light stabilizer, Tinuvin B75 from Ciba SC. The performance of zinc borate-filled polyurethane was much better, as shown by oxygen induction time and weathering chamber tests. Additionally the flame retardancy was measured and significant flame retardancy was achieved. Mechanical tests, thermogravimetric analysis and scanning electron microscope studies were performed to characterize the products.
Keywords: Polyurethane; Zinc borate; Oxidative stability; Flame retardancy;

The thermal properties of composite materials composed of polylactide (PLA) and green coconut fiber (GCF) were evaluated. Blends containing maleic anhydride-grafted PLA (PLA-g-MA/GCF) exhibited noticeably superior thermal properties due to greater compatibility between the two components. The dispersion of GCF in the PLA-g-MA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules, between the carboxyl groups of PLA-g-MA and the hydroxyl groups in GCF. In addition, the PLA-g-MA/GCF blend was more easily processed due to a lower melt viscosity. Each composite was subject to biodegradation tests in a Burkholderia cepacia BCRC 14253 compost. The bacterium completely degraded both the PLA and the PLA-g-MA/GCF composite films. Morphological observations indicated severe disruption of the film structure after 9–12 days of incubation. The PLA-g-MA/GCF (10 wt%) films were not only more biodegradable than those made of PLA, but also exhibited lower molecular weight and intrinsic viscosity, implying a strong connection between these characteristics and biodegradability.
Keywords: Blend; Polylactide; Biodegradation; Coconut;

Effects of temperature on the weathering lifetime of coated polycarbonate by James E. Pickett; Jonathan R. Sargent; Holly A. Blaydes; Nicole Babbie (1085-1091).
The lifetime of polycarbonate (PC) coated with silicone hardcoats containing UV absorber is shorter at elevated temperatures. The activation energy (E a) for delamination was found to be 18 ± 2 kJ/mol (4.3 ± 0.5 kcal/mol) at the 95% confidence level in this study. This E a is the consequence of the sensitivity of the substrate and the UV absorber to temperature. The E a for PC photodegradation was previously found to be 17–21 kJ/mol (4–5 kcal/mol). The E a for loss of absorbance in the second-generation silicone hardcoat was found to be 28.5 ± 5.4 kJ/mol (6.8 ± 1.3 kcal/mol) at the 95% confidence level. Results are consistent with experimental findings when these activation energies are used in published predictive models. Since the E a for coating delamination depends on the E a of UV absorber loss, coating systems different from the one in this study will need to be investigated separately.
Keywords: Coatings; Polycarbonate; Activation energy; Lifetime prediction; UV absorber;

Stabiliser diffusion in long-term pressure tested polypropylene pipes analysed by IR microscopy by Guru Geertz; Robert Brüll; Jürgen Wieser; Raquel Maria; Mirko Wenzel; Kurt Engelsing; Jürgen Wüst; Martin Bastian; Michael Rudschuck (1092-1102).
Pipes of random polypropylene was (PP-R) were hydrostatic pressure tested and the distribution of the primary stabiliser, Irganox 1010, was measured in the radial direction over the pipe wall by Infrared (IR) microscopy. Parabolic concentration profiles of the stabiliser develop during testing indicating a loss of stabiliser, at both the inner and outer pipe walls. Raising the temperature of the water bath leads to a uniformly accelerated loss of stabiliser. An increase of the hoop stress accelerates the stabiliser migration at the inner pipe wall.The concentrations of Irganox 1010 averaged over the pipe wall as determined by IR microscopy were in excellent agreement with those obtained from High Performance Liquid Chromatography and Oxidation Induction Time (OIT) analysis. Diffusion constants were calculated from the stabiliser concentration profiles based on the Fickian equations using appropriate initial and boundary conditions. A literature value is compared to these experimental results. The developed IR technique allows monitoring the stabiliser migration faster and more reproducibly than the conventional approach by manual abrasion of layers and measurement of the OIT. Additionally, this brings a tremendous improvement with regard to spatial resolution. As a result the impact of hoop stress and extrusion rate on the migration of stabiliser in PP-R pipes can be shown for the first time.
Keywords: Hydrostatic pressure test; Diffusion of antioxidants; IR; Pipes; Poly(propylene), PP; Ageing;

A novel waterborne polyurethane/flower-like ZnO nanowhiskers (WPU/f-ZnO) composite with different f-ZnO content (0–4.0 wt%) was synthesized by an in-situ copolymerization process. The f-ZnO consisting of uniform nanorods was prepared via a simple hydrothermal method. In order to disperse and incorporate f-ZnO into WPU matrix, f-ZnO was modified with γ-aminopropyltriethoxysilane. Morphology of f-ZnO in WPU matrix was characterized by scanning electron microscope. The properties of WPU/f-ZnO composites such as mechanical strength, thermal stability as well as water swelling were strongly influenced by the f-ZnO contents. It was demonstrated that appropriate amount of f-ZnO with good dispersion in the WPU matrix significantly improved the performance of the composites. The mechanical property was enhanced with an increase of f-ZnO content up to the optimum content (1 wt%) and then declined. Incorporation of f-ZnO enhanced the water resistance of the composites remarkably. It was amazing to observe that the thermal degradation temperatures of the composites initially decreased significantly and then leveled off with content increase of f-ZnO, which was different from the results of other WPU composite systems reported. Antibacterial activity of WPU/f-ZnO composite films against Escherichia coli and Staphylococcus aureus was also tested. The results revealed that the antibacterial activity enhanced with the increasing f-ZnO content, and the best antibacterial activity was obtained at the loading level of 4.0 wt% f-ZnO.
Keywords: Waterborne polyurethane; Nanocomposites; ZnO nanowhiskers; Thermal decomposition; Antibacterial activity;

Copolymer nanocomposites were prepared by suspension copolymerization of bis[2-(methacryloyloxy)ethyl] phosphate and methyl methacrylate, together with bis(2-ethylhexyl) phosphate layered double hydroxide and a montmorillonite, Cloisite 93A. X-ray diffraction and transmission electron microscopy were used to characterize the morphology of nanocomposites and the dispersion of additives in the polymer. The thermal stability of the nanocomposites has been assessed by thermogravimetric analysis and cone calorimetry has been used to study the fire properties. Bis[2-(methacryloyloxy)ethyl] phosphate not only copolymerized with MMA, but also aids in the dispersion of additives in PMMA. The copolymer nanocomposites have better dispersion and higher degradation temperature and more char mass than the corresponding PMMA nanocomposites. The largest peak reduction in the heat release rate of the copolymer nanocomposites are 52 and 65% for LDH and MMT additives, respectively.
Keywords: Nanocomposites; Layered double hydroxides; PMMA; Fire retardancy;

Pyrolytic hydrolysis of polycarbonate in the presence of earth-alkali oxides and hydroxides by Guido Grause; Katsuya Sugawara; Tadaaki Mizoguchi; Toshiaki Yoshioka (1119-1124).
The rise in the use of polycarbonate (PC) calls for the development of after-use treatments. In this work, we describe a process for obtaining bisphenol A (BPA), phenol and isopropenyl phenol (IPP) from PC by hydrolysis at temperatures between 300 and 500 °C. The experiments were carried out in a steam atmosphere in the presence of MgO, CaO, Mg(OH)2 or Ca(OH)2 as catalysts, respectively. The results were compared with the hydrolysis of PC in the absence of any catalysts. All of these catalysts accelerated the hydrolysis of PC drastically, with MgO and Mg(OH)2 being more effective than their Ca counterparts. The differences between oxides and hydroxides were negligible indicating the same mechanism for both, oxides and hydroxides. BPA was the main product at 300 °C, with a yield of 78% obtained in the presence of MgO. At 500 °C, BPA was mainly degraded to phenol and isopropenyl phenol (IPP). It can be shown that a combined process involving PC hydrolysis at 300 °C and BPA fission at 500 °C leads to high yields of phenol and IPP and the drastic decrease of residue.
Keywords: Polycarbonate; Bisphenol-A; Phenols; Flash-hydrolysis; Feedstock recycling; Monomer recovery;

Thermal decomposition and burning behavior of cellulose treated with ethyl ester phosphoramidates: Effect of alkyl substituent on nitrogen atom by Sabyasachi Gaan; Patrick Rupper; Viktoriya Salimova; Manfred Heuberger; Stefan Rabe; Frédéric Vogel (1125-1134).
This research explores the structural effect of phosphoramidates as flame retardants (FRs) for cotton cellulose. Flame retardant (FR) and thermal decomposition actions of phosphate such as triethyl phosphate (TEP), primary phosphoramidate such as diethyl phosphoramidate (DEPA) and secondary phosphoramidates such as phosphoramidic acid, N(2-hydroxy ethyl) diethylester (PAHEDE), diethyl ethyl phosphoramidate (DEEP) and diethyl 2-methoxyethylphosphoramidate (DEMEP) on cotton cellulose were investigated. Limiting oxygen index (LOI) of treated cotton cellulose showed that all phosphoramidates exhibited better flame retardant properties as compared to TEP. Secondary phosphoramidate PAHEDE had better flame retardant properties as compared to DEMEP and DEEP which indicate that flame retardancy of secondary phosphoramidates is structure related. Test performed on pyrolysis combustion flow calorimeter (PCFC) for treated cellulose showed higher reduction in heat of combustion for efficient FRs (PAHEDE, DEPA). Evolved gas analysis using thermogravimetric analyzer–Fourier transform infrared spectroscopy (TGA–FTIR) and thermogravimetric analyzer–mass spectrometer (TGA–MS) of treated cellulose showed that phosphoramidates could catalyze the dehydration and char formation of cellulose at a lower temperature. The enhanced flame retardant action of phosphoramidate may be due to the catalytic thermal decomposition of the phosphoramidate structure to produce acidic intermediates which could react with cellulose to alter its thermal decomposition.
Keywords: Flame retardant; Phosphoramidates; TGA–FTIR; PCFC; Cellulose; Thermal degradation; TGA–MS;

Polymeric methylene diphenyl diisocyanate (PMDI) was added as chain extender to a blend of recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) with compatibilizer of maleic anhydride-grafted poly(styrene–ethylene/butadiene–styrene) (SEBS-g-MA). Hydroxyl end groups of PET can react with both isocyanate groups of PMDI and maleic anhydride groups of SEBS-g-MA, which are competing reactions during reactive extrusion. The compatibility and properties of the blends with various contents of PMDI were systemically evaluated and investigated. WAXD results and SEM observations indicated that chain extension inhibits the reaction between PET and SEBS-g-MA. As the PMDI content increased, the morphology of dispersed phase changed from droplet dispersion to rodlike shape and then to an irregular structure. The DSC results showed that the crystallinity of PET decreased in the presence of PMDI, and the glass transition temperature (T g) of PET increased with addition of 0–0.7 w% PMDI. The impact strength of the blend with 1.1 w% PMDI increased by 120% with respect to the blend without PMDI, accompanied by only an 8% tensile strength decrease. It was demonstrated that the chain extension of PET with PMDI in R-PET/LLDPE/SEBS-g-MA blends not only decreased the compatibilization effect of SEBS-g-MA but also hindered the crystallization of PET.
Keywords: Recycled poly(ethylene terephthalate); Linear low density polyethylene; Polymeric methylene diphenyl diisocyanate; Chain extension; Compatibilization;

The degraded Eucalyptus pellita kraft lignin from the black liquor of KP-AQ pulping was precipitated directly at pH ∼2.0 without further purifying, since the lignin obtained is more representative with a whole distribution of molecular weight. The precipitated lignin was fractionated into six fractions by successive extraction with organic solvents. A comparison study of the lignin heterogeneity between the fractions was made in terms of fractional yield, content of associated polysaccharides, alkaline nitrobenzene oxidation, molecular weight distribution, 1H NMR and 13C NMR spectroscopy and thermal stability. It was found that the lignin fractions contained higher associated hemicelluloses and ratios of non-condensed syringyl/guaiacyl units which were extracted by organic solvents with higher Hildebrand solubility parameters. The results from GPC and TGA showed that the polydispersity and the thermal stability of the lignin fractions increased with increasing molecular weight. In the low molecular weight fraction, small amounts of β-aryl ether bond (β-O-4) surviving the KP-AQ pulping were detected by both 1H and 13C NMR spectra.
Keywords: Degraded lignins; Eucalyptus pellita; Fractionation; 1H NMR and 13C NMR; Thermal stability;

Seawater ageing of flax/poly(lactic acid) biocomposites by A. Le Duigou; P. Davies; C. Baley (1151-1162).
Natural fibre reinforced biopolymer composites, or biocomposites, are an alternative to the glass fibre reinforced thermoset composites widely used today in marine applications. Biocomposites offer good mechanical properties and total biodegradability, but if they are to be adopted for marine structures their durability in a seawater environment must be demonstrated. In the present study unreinforced PLLA (Poly(l-Lactic acid)), injected and film stacked flax composites with the same PLLA matrix have been examined. All the samples were aged in natural seawater at different temperatures in order to accelerate hygrothermal ageing. Changes to physico-chemical and mechanical behaviour have been followed by weight measurements, thermal and gel permeation chromatography (GPC) analyses, and tensile testing, completed by acoustic emission recording and scanning electron microscopy (SEM) examination. The matrix tensile stiffness is hardly affected by seawater at temperatures to 40 °C but the composite loses stiffness and strength. Fibre/matrix interface weakening is the main damage mechanism induced by wet ageing, but both matrix and fibre cracks also appear at longer periods.
Keywords: Composites; Natural fibre; Biopolymer; Hygrothermal ageing; Mechanical properties;

Accelerated ageing conditions with chlorinated water were identified that minimize variations in solution chemistry and water sorption, and that also enable the interpretation of HDPE physical and chemical changes during 20 week (3884 h) immersion periods. Of the ten conditions tested, three conditions with an alkalinity concentration of 50 ppm as CaCO3 at pH 6.5 and at 23 and 37 °C performed best. These three conditions exhibited stable pH, free available chlorine, and alkalinity concentration during 20 weeks of HDPE immersion with 72 h changes of ageing solution. HDPE was periodically characterized using differential scanning calorimetry, thermogravimetric analysis, tensile analysis, a density gradient column, moisture analysis, and optical and infrared spectroscopy. Formation of surface carbonyl bonds and gradual reductions in oxidation induction time were detected, as well as water sorption into HDPE. Ageing solution and water sorption monitoring recommendations from this work should be incorporated into accelerated ageing protocols and considered when characterizing aged PE drinking water pipe.
Keywords: Ageing; Chlorine; Oxidation; Polyethylene; Sorption; Water;

Thermal degradation and combustion of a novel UV curable coating containing phosphorus by WeiYi Xing; Yuan Hu; Lei Song; XiLei Chen; Ping Zhang; JianXiong Ni (1176-1182).
A novel phosphorus monomer (BDEEP) has been synthesized by allowing phosphorus oxychloride to react with 2-hydroxyethyl acrylate (HEA) and 1,4-Butane diol. Its structure was characterized by Fourier transformed infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance spectroscopy (1H NMR). The UV-curing behavior was investigated by FTIR. The combustibility was examined by microscale combustion colorimeter (MCC). The heat release rate (HRR) and heat release capacity (HRC) are 42.1 w/g and 44.0 J/g K, respectively. The thermal degradation was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR). The curve of TGA indicates that there are three characteristic degradation temperature stages for the cured film, which was further characterized by real time Fourier transform infrared (RTFTIR) measurement. It is proposed that the flame retardant action results from decomposition of phosphate to form poly(phosphoric acid), which catalyses the breakage of bonds adjacent to carbonyl groups to form the char, preventing the sample from burning further. The volatilized products formed on thermal degradation of BDEEP indicated that the volatilized products are CO, CO2, water, alkane, carbonyl, phosphorus compounds and aromatic compounds according to the temperature of onset formation.
Keywords: UV-curing; Phosphorus; Thermal degradation; Combustibility; TG-IR;