Polymer Degradation and Stability (v.87, #3)

Positron annihilation lifetime (PAL) spectroscopy has been used to investigate microstructural properties of carbon black–silica–styrene butadiene rubber (SBR) composites. The positron annihilation lifetime shows a direct dependence on the carbon black type as well as the silica content added to the rubber compound. The effect of the tensile strain (ε=0–150%) on the positron annihilation parameters has been investigated by constructing a small load frame to permit the measurement of positron lifetime in situ. The variations in the o-Ps lifetime τ 3 and its intensity I 3 with deformation are discussed in the framework of free volume theories. A simple illustrative sketch for the rubber–filler matrix is proposed.
Keywords: Positron annihilation; Deformation; Styrene butadiene rubber; Carbon black; Silica;

Kinetic studies on the pyrolysis of chitin and chitosan by Tang Wanjun; Wang Cunxin; Chen Donghua (389-394).
The thermal degradation of chitin and chitosan have been studied by using simultaneous TG and DSC in nitrogen atmosphere. The model-free iso-conversional method has been employed to evaluate the activation energies as a function of the extent of degradation. The obtained dependencies are interpreted in terms of degradation mechanisms. Under nitrogen, the thermal degradation of chitin and chitosan follows a random scission pathway, which is initiated at weak links. The activation energies of thermal degradation of chitin are constant and this process follows 1.23 order reaction. As for chitosan, the activation energies of thermal decomposition are obviously dependent on the extent of conversion. The pyrolysis reaction of chitosan is analysed by using a distributed activation energy model (DAEM) because the residual N-acetylated side-chains are randomly distributed on the chitosan main chains. Also, the parameters of the DAEM are evaluated.
Keywords: Chitin; Chitosan; Pyrolysis; Activation energy; DAEM;

Compatible thermoplastic starch (TPS)/linear low density polyethylene (LLDPE) blends were prepared by one-step reactive extrusion in a single-screw extruder and characterized by means of mechanical properties, thermogravimetry (TG), scanning electron microscopy (SEM), rheological properties and Fourier transform infrared spectroscopy (FTIR). The thermal plasticisation of starch and its compatibilising modification with polyethylene were accomplished simultaneously in a single-screw extruder. The FTIR analysis showed that maleic anhydride (MAH) could graft onto the polyethylene chain using the same operational conditions as the preparation of the blends. The blends with MAH had better mechanical properties than the blends without MAH. From TG analysis, we concluded that the thermal stability of the compatible blends was higher than the incompatible blends. The FTIR results also indicated that with the addition of MAH, the compatibility between thermoplastic starch and polyethylene in the blends was truly improved.
Keywords: Thermoplastic starch (TPS); Polyethylene (PE); Maleic anhydride (MAH); One-step reactive extrusion; Compatibility;

Degradation of carrageenan by radiation by L. Relleve; N. Nagasawa; L.Q. Luan; T. Yagi; C. Aranilla; L. Abad; T. Kume; F. Yoshii; A. dela Rosa (403-410).
κ-, ι- and λ-Carrageenans were degraded by irradiation with gamma rays in the solid state, gel state or solution with various doses in air at ambient temperature. The molecular weights obtained were in the range of 10.5 × 104 to 0.8 × 104 of narrow molecular weight distribution. The chemical structural changes of carrageenans were accompanied by appearance of UV absorbance peak at 260 nm and a characteristic FT-IR band at 1728 cm−1. Due to radiation-induced desulfation, carrageenan oligomer has lower sulfate content. From comparison of radiation degradation yield (G d ), susceptibility to degradation of the three types of carrageenans in aqueous form follows the order of λ > ι > κ which could have been influenced by their conformational state. The oligomer obtained from κ-carrageenan with molecular weight of 1.0 × 104 showed a strong growth promotion effect on potato in tissue culture. Degradation of κ-carrageenan solution using vessel-type low energy electron beam accelerator (LEEB) (250 kV, 10 mA) was investigated. LEEB irradiation reduced the molecular weight of carrageenan though the electron beams have a depth penetration range of less than 3 mm in distilled water.
Keywords: Carrageenan; Gamma rays; Low energy electron beam accelerator; Desulfation; Conformational state; G-value;

Ethylene vinyl acetate copolymer (EVA)/alumina trihydrate (ATH) nanocomposites were prepared by melt-blending. Two kinds of interfacial modifiers were used in this research, a titanate coupling agent and maleated ethylene vinyl acetate copolymer (MEVA), which acted as a compatibiliser. The effects of modifiers on the properties of EVA nanocomposites were studied by thermogravimetric analysis, tensile and combustion tests. The dispersion and adhesion patterns of the ATH nano-particles in EVA matrix were characterized through Molau solution test, TEM and SEM. The experimental results demonstrated that the use of untreated ATH could clearly decrease the tensile properties of EVA composites. It was found that the combined addition of the two kinds of interfacial modifiers led to a dramatic increase in tensile and flame retardant properties of the nanocomposites. Also the thermal stability of this system, in terms of the thermal degradation test, was enhanced. These effects would be diminished if only one modifier was used. The improvement in the properties of interfacial modified EVA/ATH nanocomposites is mostly attributed to a better dispersion of surface modified filler and a strong adhesion between the filler and matrix.
Keywords: Interfacial modification; ATH; EVA nanocomposites; Mechanical properties; Flame retardancy;

Effect of bleaching sequence on paper ageing by Mohamed El-Sakhawy (419-423).
High-yield bagasse pulp was prepared by mechanical treatment after soaking in cold 10% sodium hydroxide. One-, two- and three-stage bleaching of the pulp were investigated by using hydrogen peroxide (P) and/or sodium dithionite (D), in different sequences. Paper sheets were prepared and tested for the strength properties and brightness value. The effect of ageing on paper properties and brightness was investigated. It was found that three-stage bleaching by using two steps with hydrogen peroxide and one step with sodium dithionite provides the optimum bleaching results with regard to the strength properties and the brightness values. Comparable results were also obtained after paper ageing. The best bleaching sequence is PPD followed by DPP and then PDP.
Keywords: Paper; Aging; Yellowing; Bleaching;

Polychloroprene degradation by a Photo-Fenton process by A.R. Freitas; G.J. Vidotti; A.F. Rubira; E.C. Muniz (425-432).
The influence of iron(III)-chloride-6-hydrate, FeCl3·6H2O on the photodegradation of polychloroprene under different conditions has been investigated. The effects of polymer concentration (Cp), temperature (T), and polychromatic light exposure (L) on polymer degradation were evaluated using a 23 factorial design. The photodegradation rate constant was determined through solution efflux time data in an Ubbelohde capillary viscometer and FTIR spectroscopy. Polychloroprene/FeCl3·6H2O photodegradation residues were investigated by GC–MS and FTIR spectroscopy. By efflux time data, it was verified that in contrast to Cp and light exposure, which play a significant role in polychloroprene degradation, temperature does not affect it. Degradation does not occur in the absence of light. Efflux time and FTIR data characterized the reaction as having second-order kinetics. Exposure of polychloroprene/FeCl3·6H2O solution to polychromatic light induces polymer structure changes, as observed by GC–MS and FTIR. After photodegradation, intense spectral changes in conjugated carbonyl and hydroxyl bands were observed by FTIR. One of the degradation products was characterized as acid chloride (C3H5ClO). Due to the influence of water and light on FeCl3 catalyses, the reaction was characterized as a Photo-Fenton process.
Keywords: Polychloroprene; Degradation; FeCl3·6H2O; Photo-Fenton process;

Exfoliated polystyrene/ZnAl layered double hydroxide (PS/ZnAl LDH) nanocomposites were synthesised by a solution intercalation method and characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). It has been found that the exfoliated LDH layers with a thickness of less than 1 nm disorderedly disperse in the PS matrix. The XRD and TEM results show that the exfoliation of LDH can be divided into solvent swelling and layer breaking processes and is affected by several reaction parameters. Completely exfoliated LDH layers can be achieved by decreasing the content of LDH, elongating the refluxing time, and rapid precipitation. The TGA data show that the PS/ZnAl LDH nanocomposites have significantly enhanced thermal stability. When 50% weight loss was selected as a point of comparison, the thermal decomposition temperature of exfoliated PS/ZnAl LDH nanocomposites with 10 wt% ZnAl LDH is 39 °C higher than that of pure PS. The thermal stability of the exfoliated nanocomposites is usually better than that of intercalated composites.
Keywords: Layered double hydroxide; Polystyrene; Nanocomposite; Thermal stability;

Preparation and characterisation of low molecular weight chitosan and chito-oligomers by a commercial enzyme by Jin Li; Yumin Du; Jianhong Yang; Tao Feng; Aihua Li; Ping Chen (441-448).
Chitosan with 91.7% deacetylation was hydrolysed by a commercially available and efficient neutral protease. The degradation was monitored by gel permeation chromatography. Factors affecting the enzymatic hydrolysis of chitosan were studied. The structures of degraded chitosans were characterised by X-ray diffraction, Fourier transform infrared and MALDI-TOF mass spectrometry. Classical Michaelis–Menten kinetics parameters were measured by analysis of reducing sugars. The neutral protease showed optimum depolymerisation at pH 5.4 and 50 °C. Different reaction times gave chitosan with different molecular weights. Mn2+ was the most efficient activator of the enzymatic reaction. The enzymatic hydrolysis was endo-action and mainly occurred in a random fashion. The degree of deacetylation of the main hydrolysis products decreased compared with the initial chitosan. The decrease of molecular weight led to transformation of crystal structure and the increase of water solubility, but the chemical structures of residues were not modified. The degree of polymerisation of chito-oligomers was mainly from 3 to 8.
Keywords: Chitosan; Neutral protease; Enzymatic hydrolysis;

The work proposes a new model for polyethylene melt oxidation. It is aimed at understanding the experimental kinetics for polyethylene oxidation products. All the models envisaged previously and based on homogenous kinetics do not give a reasonable account of hydroperoxide and alcohol group formation. It is even so on superimposing geminate recombination of free radicals onto homogeneous kinetics. It is the mandatory assumption of geminate recombination of the chain propagating radicals that suggests an entirely heterogeneous oxidation model for polymer melts. It involves oxidation restricted to small portions of the melt, the oxidation volumes or domains in which clusters of oxidation products are formed. These elementary volumes contain the oxidation products resulting from the action of one pair of free radicals until their geminate recombination. At the beginning of the processing experiments the elementary oxidation volumes are mainly isolated. With advancing processing time, the new elementary oxidation volumes are formed increasingly in parts of the melt already oxidized previously. As a result, there is possibility of reaction between the new oxidation products and those present before in the elementary volumes. The kinetics of overlapping oxidation, i.e. of repeated oxidation of the same elementary oxidation volumes is straightforward. There results a simple mathematical model for the oxidation processes in polyethylene melts. This model accounts easily for the experimental kinetics of hydroperoxide and alcohol group formation.
Keywords: Polyethylene; Thermal oxidation; Processing; Oxidation products; Hydroperoxides; Alcohols; Mechanisms; Heterogeneous kinetics;

This study presents the effect of Phytagel® and stearic acid modification of soy protein isolate (SPI) based ‘green’ resins on their biodegradation in composting environment. The composting process was monitored for up to 10 weeks and the degradation of the resins was characterized by weight loss, attenuated total reflectance infrared spectroscopy, differential scanning calorimetry and sol–gel analysis. The changes in the resin surface topography and microstructure during composting were also characterized using scanning electron microscopy (SEM). The gel fraction in SPI resin reduced significantly as a function of composting time indicating its fast degradation within 21 days. The stearic acid modified SPI resin (SAM-SPI) degraded at a slower rate than the SPI resin and Phytagel® modified SPI (PM-SPI) resin degraded at the slowest rate. Based on the spectroscopic analysis and differential scanning calorimetric studies, it was found that stearic acid was among the main residue in the case of SAM-SPI resin after composting and Phytagel® in the case of PM-SPI resin. The results of this study suggest that the biodegradation and hence, the service life of the SPI based resins can be controlled by changing the concentration of stearic acid or Phytagel® in the SPI resin.
Keywords: Green plastics; Soy protein isolate; Stearic acid; Phytagel®; Composting; Biodegradation;

Antioxidant activity of p-phenylenediamines studied by DSC by Z. Cibulková; P. Šimon; P. Lehocký; J. Balko (479-486).
The antioxidant activity of six N,N′-substituted p-phenylenediamines in polyisoprene rubber matrix has been studied by differential scanning calorimetry (DSC) under non-isothermal conditions. A method for obtaining the parameters from non-isothermal DSC measurements, based on the dependence of the onset temperature of the oxidation peak on heating rate, is presented. The parameters of an Arrhenius-like equation describing the temperature dependence of induction period have been obtained. The results show that the values of protection factors decrease with increasing temperature and decreasing concentration of the antioxidant. Two criteria characterizing the antioxidant effectiveness are proposed. Using both criteria, effectiveness of the antioxidants under study at 180 °C is in the order DPPD > SPPD > 6PPD > IPPD > MBPPD > CPPD. When DPPD is excluded, this order is inversely proportional to the dissociation energy of the C–H bond at the carbon atom in the neighbourhood of the nitrogen atom. Substitution of all hydrogen atoms at that carbon atom leads to a loss of antioxidant properties in the case of CPPD.
Keywords: Differential scanning calorimetry; Polyisoprene; Antioxidants; N,N′-substituted p-phenylenediamines; Induction period; Kinetics; Oxidation;

Biodegradable polymer scaffolds play a major role in the field of tissue engineering as they provide a three-dimensional template to regenerate desirable tissues for different applications. In this study, porous poly(dl-lactic-co-glycolic acid) (PLGA) scaffolds with four different pore sizes (150–180 μm, 180–250 μm, 250–280 μm and 280–400 μm) were fabricated using paraffin-spheres-dissolution technique. Paraffin spheres with the stated size range were bonded into a layer through a heat treatment to form a three-dimensional assembly. Biodegradable polymer PLGA (50/50) was dissolved in pyridine and cast into the paraffin sphere assembly. After dissolving the paraffin spheres, a porous polymer scaffold was formed. The morphology of the porous PLGA scaffolds was examined using scanning electron microscopy (SEM). Results showed that all four PLGA scaffolds had apparently uniform pore morphology with different pore diameters. The pores were mostly interconnected with diameters lying within the pore size range. Mercury intrusion porosimetry was also used to determine the median pore diameter, surface to volume ratio and the total porosity of the scaffolds. As compared with the size of the paraffin spheres used to generate the scaffolds, the median pore diameters measured by mercury porosimetry were smaller. This discrepancy could be explained by the presence of the smaller pores formed from the paraffin residues during dissolution and that the space between the paraffin spheres are not completely filled by the polymer before extraction. As the pore size range of the PLGA scaffolds increased, similar values of the surface to volume ratio were observed. All four different PLGA scaffolds are highly porous having nearly 90% porosity. It is believed that these parameters would significantly affect the transport processes through the scaffold as well as the structural properties of the scaffold.
Keywords: Poly(dl-lactic-co-glycolic acid) (PLGA); Scaffolds; Porosity; Morphology; Biomaterials;

Methacrylated phenolic melamine (MAPM) was synthesized as a flame retardant multifunctional oligomer for UV curable systems, and characterized by FTIR, 1H NMR and elemental analysis. A series of formulations was prepared based on MAPM and a commercial UV curable epoxy acrylate EB600. Their thermal behaviours were investigated by thermogravimetric analysis, indicating that MAPM had no effect on the char formation of EB600. The flammability was monitored by the limiting oxygen index (LOI); the LOI value of EB600 increased from 21.5 for pure EB600 to 26.5 for the blend containing 50% MAPM addition. The “composite bar test” result showed that the vapour phase action flame retardant mechanism was the dominant mode for MAPM. The thermal degradation mechanism of MAPM was investigated by in situ FTIR, DP–MS and elemental analysis. The results showed that MAPM first degraded to form melamine at around 300 °C, which would further undergo condensation on heating with elimination of ammonia. Nitrogen underwent about 19% conversion to the residue and 81% had vapourized below 500 °C.
Keywords: Flame retardant; Melamine; UV curing; Thermo-degradation;

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene was prepared by the reaction of hexachlorocyclotriphosphazene with the sodium salt of 4-hydroxybenzaldehyde and subsequent reduction of aldehyde groups to alcohol groups by using sodium borohydride. The hydroxyl-terminated star-shaped compound was studied as initiator for the synthesis of star-shaped poly(l-lactide)s and in the presence of stannous octanoate. Effects of molar ratios of monomer to initiator on polymerisation were investigated. The results indicated that the molecular weight of star-shaped poly(l-lactide)s and poly(d,l-lactide)s increased linearly with the molar ratio of monomer to initiator. Thermal analysis demonstrated that star-shaped poly(l-lactide)s possessed lower melting point, crystallinity and onset decomposition temperature but higher maximum decomposition temperature. Analysis of hydrolytic degradation of linear and star-shaped poly(d,l-lactide)s and poly(l-lactide) showed that star-shaped poly(d,l-lactide)s possessed the best degradability, while linear poly(l-lactide)s possessed the poorest degradability. Moreover, the star-shaped polylactide was degraded in two steps.
Keywords: Phosphazene; Star-shaped polylactide; Thermal stability; Degradation;

Epoxy resin was used as a compatibiliser to prepare poly(butylene terephthalate)/clay nanocomposites (PCN) via melt intercalation. The morphology of PCN hybrids was investigated using XRD and TEM. The results reveal that with the addition of epoxy, the silicates are easily intercalated and present a nice dispersion in the matrix. The linear viscoelastic behaviour of the nanocomposites was measured by the parallel plate rheometer. The ternary hybrids show a stronger solid-like response at terminal zone than that of the sample without epoxy. However, with the epoxy loading up to 6 wt% and above, the loss modulus and high-frequency storage modulus for ternary hybrids decline. Thermogravimetric analysis shows that only the hybrids with lower epoxy loading (2–4 wt%) show a higher thermal stability than that of the sample without epoxy, while with increase in epoxy content, the thermal stability of the ternary nanocomposites declines somewhat. The compatibiliser loadings do have an influence on the performance of nanocomposites and, the best compatibiliser dosage, 4 wt%, is decided by a new ‘crossover point’ rheological method.
Keywords: Poly(butylene terephthalate); Epoxy; Nanocomposites; Linear viscoelastic behaviour; Thermal stability;

Pulsed laser degradation of polyethylene oxide and polyacrylamide in aqueous solution by S.P. Vijayalakshmi; Dulal Senapati; Giridhar Madras (521-526).
The kinetics of degradation of polyethylene oxide (PEO) and polyacrylamide (PAM) was investigated using a pulsed Nd:YAG laser, operating at 266 nm wavelength with ∼6 ns pulses. Gel permeation chromatograph was used to monitor the change in molecular weight with time. Continuous distribution kinetics for random chain scission was used to obtain the rate coefficient for the degradation process. The measured rate coefficients for the degradation are 1.9 × 104 and 1.2 × 104  s−1 for PEO and PAM, respectively. A pathway for degradation has been proposed based on the experimental observations. The significance of polymer concentration and the laser light intensity along with the requirement of oxygen for degradation has been correlated to the mechanism of the degradation process. The degradation was found to decrease with increasing polymer concentration while a threshold light intensity was required to initiate the degradation process.
Keywords: Polymer degradation; Pulsed laser; Kinetics; Polyethylene oxide; Polyacrylamide;

The influence of methyl methacrylate–butadiene–styrene copolymer (MBS) on poly(vinyl chloride) (PVC) photodehydrochlorination and photooxidative degradation was investigated by UV–vis, FTIR and fluorescence spectra. The gel amount formed in exposed samples was estimated gravimetrically. It was found that MBS decelerates PVC photodehydrochlorination and photocrosslinking; the effect is caused by the fact that the Cl radicals react with H atoms at tertiary atoms in polystyrene of MBS and initiate the depolymerisation of the PMMA chains of MBS, then leads to reinitiation of PVC dehydrochlorination. The surface free energy of PVC/MBS blends was calculated on the basis of contact angle measurements. The rate of photocrosslinking and photodegradation distinctly influenced the surface free energy, which can reach a maximum value at an appropriate irradiation time.
Keywords: Dehydrochlorination; Photooxidation degradation; Photocrosslinking; PVC/MBS blends;

Polylactide/montmorillonite nanocomposites: study of the hydrolytic degradation by M.-A. Paul; C. Delcourt; M. Alexandre; Ph. Degée; F. Monteverde; Ph. Dubois (535-542).
Hydrolytic degradation of polymer layered silicate nanocomposites based on polylactide matrix (PLA) and (organo-modified) montmorillonites was investigated in phosphate buffer solution for more than five months. While natural unmodified montmorillonite-Na+ led to the formation of a microcomposite, mainly intercalated nanocomposites were prepared by melt blending PLA with 3 wt% of montmorillonite organo-modified either by 2-ethylhexyl (hydrogenated tallowalkyl) ammonium cations (Cloisite®25A) or by bis-(2-hydroxyethyl) methyl tallowalkyl ammonium cations (Cloisite®30B). The evolution of molecular weight of the matrix as well as its crystallinity with the hydrolysis time has been recorded by size exclusion chromatography (SEC) and differential scanning calorimetry (DSC), respectively. Thermogravimetric analyses (TGA) performed on the microcomposite based on Cloisite®Na+ has shown that the thermal stability of the materials decreased proportionally to the decreasing PLA molecular weight along the hydrolysis time. Moreover, in parallel to the morphology of the composites, the relative hydrophilicity of the clay layers has been shown to play a key role in the hydrolytic degradation of the PLA chains.
Keywords: Polylactide; Nanocomposite; Montmorillonite; Clay; Degradation; Hydrolysis;

The changes of the thermal (DSC) and the dynamic-mechanical (DMA) behaviour of a metallocene isotactic polypropylene (iPP2) have been followed during the first stages of low-temperature thermo-oxidation. This study aims to look for correlations between changes in the crystalline phase of the material and the characteristics of the α and γ relaxation processes.The DSC analysis of iPP2 samples heated up to induction and auto-accelerated stages, confirms the crystallinity changes found in a previous metallocene iPP1 (Polym Deg Stab 83 (2004) 509), in particular the involvement of the highest Tm crystals. Some differences concerning crystalline changes and carbonyl and degradation index build-ups are also commented upon.As for the DMA analysis, a correlative change of the α and γ relaxations is detected as associated with annealing and chemical reactions taking place during the induction and the first oxidation stages respectively. The interdependence of both relaxations appears together with crystalline changes produced by these physico-chemical processes.
Keywords: Metallocene polypropylene; Thermo-oxidation; Crystallinity; Dynamic-mechanical behaviour;

FTIR analysis of thermally processed PU foam by David W. Hatchett; Gayani Kodippili; John M. Kinyanjui; Flocerfida Benincasa; Linda Sapochak (555-561).
The chemical composition, density, and modulus of PU foam was examined as a function of processing temperature (25 °C, 45 °C, and 85 °C). Degradation of uretoneimine cross-links and the emergence of carbodiimide functional groups are monitored and the remaining composition in the PU foam is determined using FTIR spectroscopy. The density and modulus of the PU foams after thermal processing are measured and discussed with respect to the change in chemical composition of the materials. The data indicates that the composition of chemical cross-links, the density, and the modulus all decrease as a function of increasing processing temperature. The modulus of the PU foam shows a linear dependence of the processing temperature decreasing by 20% at the highest temperature. The results suggest that processing temperature may be used to target defined physical and mechanical properties of PU foams without changing the composition of reactants used.
Keywords: Polyurethane; Uretoneimine; FTIR;