Polymer Degradation and Stability (v.91, #3)

Calendar (I-II).

MoDeSt special edition by Norman Billingham (415).

Factors affecting accelerated testing of polymer photostability by J. Pospíšil; J. Pilař; N.C. Billingham; A. Marek; Z. Horák; S. Nešpůrek (417-422).
The effect of components of the atmosphere on photostabilized polymers and development of degradation phenomena is outlined. The processes are characteristic of heterogeneity in distribution of products of polymer degradation and stabilizer transformation or consumption. Concentration gradients of the products indicate preferential surface and near-surface changes having U-shaped characteristics and affected by the polymer material or sample thickness due to limited penetration of oxygen. Increased intensity of radiation in artificial sources induces material changes different from those resulting from natural weathering, complicating correlation between the two processes and lifetime prediction. Surface and near-surface analyses of tested samples provide a realistic insight into heterogeneity characteristic of photodegradation.
Keywords: Photodegradation; Photostabilization; Testing; Degradation analyses;

Simultaneous oxygen uptake and imaging chemiluminescence measurements by Pieter Gijsman; Mikael Hamskog (423-428).
There are several studies that make a comparison between chemiluminescence and oxygen uptake. Although, there are several reasons to perform this comparison on the same sample at the same conditions, these studies were done by comparing results from separate oxygen uptake and chemiluminescence experiments.It is also postulated that the shape of the chemiluminescence and oxygen uptake curves is not related to the kinetics of the degradation chemistry but to the oxidizing area. To be able to measure the luminescence and the oxygen uptake at the same sample under exactly the same conditions an apparatus is developed in which both measurements can be done simultaneously. To be able to get information on the oxidizing area too, this apparatus is based on imaging chemiluminescence. The induction times determined with chemiluminescence and oxygen uptake are about comparable, although at lower temperatures the induction time according to oxygen uptake is shorter, which might be due to a decrease of the sensitivity of chemiluminescence with temperature.For stabilized and unstabilized polypropylene it was shown that the luminescence curve is related to the amount of material degrading and that the shape of the oxygen uptake and luminescence curves is not related to the kinetics of the degradation chemistry.
Keywords: Polypropylene; Oxidation; Area; Kinetics; Heterogeneous;

The effect of adding virgin material or new stabilizers on the recyclability of polypropylene (PP) was determined. Stabilized PP was subjected to oven ageing at 130 °C for 100, 250 or 500 h before and after upgrading with virgin material (0, 20, 50, 80 or 100%) or additional stabilizer during reprocessing. The effect of upgrading recycled PP with extra stabilizer or virgin material was determined by measuring the elongation at break, yellowness change, oxidation induction time (OIT) or total luminous intensity (TLI) by chemiluminescence (CL) techniques. Selected specimens were analysed by microcalorimetry (MC).It has been shown that upgrading recycled PP with virgin material was not effective. Adding 80% virgin material did not increase the lifetime more than adding 20% virgin material. This indicates that a small amount of recycled material can induce degradation by contamination. Adding extra stabilizers instead of virgin material was much more effective. Of all techniques used the OIT as determined with CL showed a clear difference in residual stability of differently treated materials and seems to be the most valuable analytical method to determine the recyclability of PP. A comparison between CL and MC shows that MC is sensitive enough for measuring the solid-state oxidation of stabilized PP. Slightly lower OITs were detected by MC probably associated with the static atmosphere used during the measurements. The TLI method is not suitable to determine the degradation state of to be recycled material.
Keywords: Polypropylene; Recycling; Chemiluminescence; TAM III; Microcalorimetry; Oven ageing;

Natural (outdoor) weathering test was performed to investigate the UV stability of thin films (0.06 mm) of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). The PE films were prepared from various formulations of LLDPE and LDPE resins. Some of these films contained a single high molecular mass HALS only, along with a primary antioxidant (i.e. Irganox 1010) and a secondary antioxidant (i.e. Irgafos 168 or Alkanox TNPP), while others contained HALS and UVA (i.e. Chimassorb 81 or Tinuvin P or Tinuvin 326) along with these antioxidants. The HALS used was either an oligomeric or a synergistic mixture of a high molecular mass (HMM) hindered amine stabilizer and co-additives. The UV stability was investigated by exposing the prepared films at 45° towards south in the direct sunshine up to 365 days. Fifty percent of tensile strength retention was determined for all these exposed films and it was found that the films containing a single HALS gained improved UV stability by about two to 12 fold over the pure films. On the other hand, films that contained a combination of HALS and UVA obtained further improved UV stability over the films containing a single HALS (both have antioxidants). Films containing a single HALS reached 50% TS retention within 205 days, whereas, films containing a combination of HALS and UVA reached 50% TS retention within 590 days, which is about three times further improvement in UV stability.
Keywords: Weathering; LLDPE; LDPE; Degradation; Retention; Formulations;

Spatial resolution of degradation in stabilized polystyrene and polypropylene plaques exposed to accelerated photodegradation or heat aging by A. Marek; L. Kaprálková; P. Schmidt; J. Pfleger; J. Humlíček; J. Pospíšil; J. Pilař (444-458).
Spatial resolution of photo and thermooxidation processes in polypropylene (PP) and polystyrene (PS) plaques was studied by electron spin resonance imaging (ESRI) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR FTIR). Polymer plaques made of PP and PS stabilized with various systems based on hindered amine stabilizers (HAS) were exposed to accelerated photodegradation and to heat aging in air atmosphere. Concentration profiles of nitroxides generated during the degradation process in the plaques were measured by ESRI, carbonyl and hydroxy groups were identified by ATR FTIR, transparency of the plaques in the actinic part of solar radiation, including a part of UV-B (295–315 nm), full range of UV-A (315–400 nm) and visible radiation was measured by optical techniques. A mechanism of the degradation consistent with all experimental data is suggested.
Keywords: Photodegradation; Photostabilization; HAS; Thermal aging; Polystyrene; Polypropylene;

Study on photodegradation of injection-moulded β-polypropylenes by Martin Obadal; Roman Čermák; Miroslav Raab; Vincent Verney; Sophie Commereuc; Frederic Fraïsse (459-463).
The effects of UV irradiation on β-nucleated injection-moulded polypropylenes (β-iPP) have been studied at several structural levels. Commercially available isotactic polypropylene was modified by 0.03 wt.% β-nucleating agent based on N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide. β-iPP specimens were injection-moulded using a processing set-up in which only mould temperature was varied. It was found that specimens consisted of a skin–core structure, which was strongly influenced by varying mould temperatures. The structural development consequently affected the specimen degradability as shown by wide-angle X-ray scattering, light microscopy and micro-infrared microscopy.
Keywords: β-Polypropylene; Injection moulding; Photo-oxidation; Skin–core morphology; Structure evolution;

The influence of reprocessing and thermooxidative ageing on the degradation behaviour of a commercial poly(oxymethylene) (POM) copolymer was studied by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. Five heating rates were used to evaluate activation energies at several degrees of conversion. TGA-measurements were accompanied by simultaneous monitoring of the evolved gases with a mass spectrometer (MS) coupled to the TGA-furnace outlet. The mass spectra showed that the main degradation product was formaldehyde and that in air further formation of water was detectable. In nitrogen atmosphere aged specimens emitted small amounts of carbon dioxide at the beginning of the mass loss. The activation energy for low degrees of conversion (<5%) increased in air and in nitrogen as a function of the conversion. For higher conversions a difference with progressing degradation emerged: in air, activation energies lowered continuously while they remained nearly constant under nitrogen.
Keywords: POM; Polyacetals; Reprocessing; Ageing; Degradation; Thermal analysis (TGA);

The efficiency of antioxidants in polymers is determined by three processes: the chemical reactivity, the physical loss and a minimal effective concentration. In most cases, loss of the stabiliser by physical processes (evaporation, leaching) is more significant than the loss by chemical consumption. In this paper, a model is proposed that relates the protection time of an antioxidant to the migration in a polymer matrix. The parameters that determine the migration, i.e. mobility (D) and solubility (S) are predicted using theoretical modelling. A linear correlation was found between the protection time and the function −S  ln(D). In some cases this correlation is better than that of the empirical model proposed by Moisan, ln(S 2/D).
Keywords: Stabilizers; Solubility; Mobility; Service life;

Efficiency and mechanism of phosphorous antioxidants in Phillips type polyethylene by Enikő Földes; Erik Maloschik; Ildikó Kriston; Peter Staniek; Béla Pukánszky (479-487).
The stabilising efficiency of three phosphorous secondary antioxidants of different chemical structures (phosphonite, phosphite and phosphine) was compared in a Phillips type polyethylene. The polymer was processed by six consecutive extrusions in the presence of 700 ppm primary antioxidant and 700 ppm phosphorous compound. The consumption of the secondary antioxidant was followed quantitatively by Fourier transform infrared (FTIR) spectroscopy. The properties of the polymer were characterised by FTIR spectroscopy, colour and rheological measurements, as well as by the determination of its residual thermo-oxidative stability. The results of the experiments proved that the chemical reactions occurring in the first extrusion of the polymer are different from those taking place in the further processing operations. The rate of antioxidant consumption and the chemical reactions of the polymer are strongly affected by the type of the phosphorous secondary antioxidant. The analysis of the results indicated that the three stabilisers must act according to different mechanisms. The investigated phosphine showed the best melt stabilising efficiency, while phosphonite was found to protect the polymer most effectively from discoloration.
Keywords: Polyethylene; Stabilisation; Phosphorous antioxidant; Phosphite; Phosphonite; Phosphine;

The lifetime of polymer materials predicted from the plots of log t f vs 1/T are in reasonable agreement with experimental data and users' observations, e.g. approximately 1 year for PC and unmodified PE-LLD both at 373 K (100 °C) and for PVC at temperature of outdoor conditions about 298 K (25 °C).
Keywords: DSC and TGA; Comparative thermal stability; Oxidation induction time (OIT); Activation energy of decomposition; Lifetime of polymer materials;

Thermal degradation behaviour of isotactic polypropylene blended with lignin by Maurizio Canetti; Fabio Bertini; Aurelio De Chirico; Guido Audisio (494-498).
The influence of lignin on the thermal degradation of isotactic polypropylene, investigated by thermogravimetric analysis, is reported in this article. Polypropylene blends containing 5 and 15 wt% of lignin were prepared by mixing the components in a screw mixer. An increase in the thermal degradation temperature of the blends was observed as a function of lignin content, in both oxidative and non-oxidative conditions. The increase is noticeably marked for the experiments carried out in air atmosphere, where the interactions between the polypropylene and the lignin lead to the formation of a protective surface able to reduce the oxygen diffusion towards the polymer bulk. Morphological analyses were carried out with optical and electronic microscopy, to evaluate the degree of dispersion of the lignin in the polypropylene matrix. X-ray techniques were employed to study the influence of lignin on the structure of the blended polypropylene.
Keywords: Degradation; Lignin; Polypropylene; Thermogravimetric analysis (TGA);

Thermal degradation of poly(vinyl chloride) synthesized with a titanocene catalyst by V.H. Ponce-Ibarra; R. Benavides; G. Cadenas-Pliego; I. Palos-Pizarro; B.M. Huerta (499-503).
PVC was synthesized using a trichloroindenyltitanium–methylaluminoxane catalyst at room temperature, and its degradation was monitored along with a commercial sample at 160, 170 and 180 °C under air or nitrogen atmosphere. The process was followed by HCl evolution, yellowing index, colour formation and thermogravimetric analysis. The produced polymer had a lower molecular weight and higher surface area, compared with a commercial PVC, while 1H NMR and T g values show minimal differences between materials. The HCl evolution degradation studies indicate that produced PVC has a lower thermal resistance than commercial PVC, while TGA reveals the opposite behaviour. Yellowing index and colour evaluation give evidence that nitrogen atmosphere and high surface area in produced PVC allow the polyene growth, whereas low surface area and air atmosphere generate shorter polyenes and chromophoric species. Differences in degradation performance are thought to be due to chemical origin, inherent morphology and differences in instrumentation.
Keywords: Synthesis; Poly(vinyl chloride); Degradation; Metallocene catalyst;

The aim of this work was to study the thermo-oxidative dehydrochlorination of rigid and plasticised poly(vinyl chloride)/poly(methyl methacrylate) blends. For that purpose, blends of variable compositions from 0 to 100 wt% were prepared in the presence (15, 30 and 50 wt%) and in the absence of diethyl-2-hexyl phthalate as plasticiser. Their miscibility was investigated by using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). Their thermo-oxidative degradation at 180 ± 1 °C was studied and the amount of HCl released from PVC was measured by a continuous potentiometric method. Degraded samples were characterised, after purification, by FTIR spectroscopy and UV–visible spectroscopy. The results showed that the two polymers are miscible up to 60 wt% of poly(methyl methacrylate) (PMMA). This miscibility is due to a specific interaction of hydrogen bonding type between carbonyl groups (C=O) of PMMA and hydrogen (CHCl) groups of PVC as shown by FTIR analysis. On the other hand, PMMA exerted a stabilizing effect on the thermal degradation of PVC by reducing the zip dehydrochlorination, leading to the formation of shorter polyenes.
Keywords: PVC/PMMA blends; Miscibility; Thermo-oxidative; Dehydrochlorination;

Investigation on the thermal degradation of acrylic polymers with fluorinated side-chains by Vjacheslav V. Zuev; Fabio Bertini; Guido Audisio (512-516).
The thermal degradation of poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,7″-tridecafluoroheptylacrylate and poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′-dodecafluoroheptylmethacrylate has been studied in isothermal conditions at 450–750 °C using pyrolysis–gas chromatography. The type and composition of the pyrolysis products give useful information about mechanism of thermal degradation. It was shown that the main thermal degradation process for both polymers is random main-chain scission. The major degradation products for fluorinated polyacrylate are monomer, dimer, saturated diester, trimer, and corresponding methacrylate. The fluorinated polymethacrylate gives monomer as the main product of thermal destruction. As a result of side-chain reaction, the thermal degradation of the fluorinated polyacrylate also produces remarkable amounts of alcohol. On the other hand, the respective alcohol is only a minor component among the pyrolysis products of the fluorinated polymethacrylate. For both polymers, the main nontrivial degradation product coming from the alkyl ester decomposition is the corresponding fluorinated cyclohexane. The formation of the fluorinated cyclohexanes may be accounted for a nucleophilic bimolecular substitution pathway.
Keywords: Fluoropolymers; Acrylic polymers; Thermal degradation mechanism; Pyrolysis–gas chromatography; Poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,7″-tridecafluoroheptylacrylate; Poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′-dodecafluoroheptylmethacrylate;

Thermal degradation of waste polymers was carried out as a suitable technique for converting plastic polymers into liquid hydrocarbons, which could be used as feed stock materials. The catalytic degradation of waste plastics (polyethylene and polystyrene) was investigated in a batch reactor over different catalysts (FCC, ZSM-5 and clinoptillolite). The effects of catalysts and their average grain size on the properties of main degradation products (gases, gasoline, diesel oil) are discussed. The temperature range of 410–450 °C was used in the process. Both equilibrium FCC catalyst and natural clinoptilolite zeolite catalyst had good catalytic activity to produce light hydrocarbon liquids, and ZSM-5 catalyst produced the highest amount of gaseous products. Gases and liquids formed in cracking reactions were analyzed by gas chromatography. The liquid products consisted of a wide spectrum of hydrocarbons distributed within the C5–C28 carbon number range depending on the cracking parameters. The composition of hydrocarbons had linear non-branched structure in case of polyethylene, while from polystyrene more aromatics (ethyl-benzene, styrene, toluene, and benzene) were produced. The yields of volatile products increased with increasing degradation temperature. The olefin content of liquids was measured with an infrared technique and an olefin concentration of 50–60% was observed. The concentration of unsaturated compounds increased with decreasing temperature, and in the presence of catalysts. The activation energies were calculated on the basis of the composition of volatile products. The apparent activation energies were decreased by catalysts and catalyst caused both carbon-chain and double bond isomerisation.
Keywords: Waste polyethylene and polystyrene; Catalysts; Further utilization; Feed stocks; Fuel-like fractions; Octane number;

The study of properties in waste polymeric materials is important for a further recycling and eventual reuse. The determination of thermal properties of PC–ABS mixtures obtained from waste electric and electronic equipment (WEEE) by using thermogravimetric analysis (TGA) has been carried out in this work. Kinetic parameters, such as apparent activation energies, have been calculated by using the autocatalytic model, which has shown a good correlation with experimental data. A good agreement between calculated and experimental results was observed for PC-based mixtures. This is an indication that the addition of a high amount of ABS permits the creation of a network formed by elastomeric domains which leads to a general increase in heterogeneity of the mixture.
Keywords: Thermal properties; Kinetic parameters; Polycarbonate; ABS; Thermogravimetric analysis;

Thermal behaviour of polyacrylamidoxime–copper chelates by Gabriela Moroi; Doina Bilba; Nicolae Bilba; Constantin Ciobanu (535-540).
The purpose of this work was to investigate the effect of several factors (anion type in the copper salt, pH and concentration of the salt solution) on the structure and thermo-oxidative degradation of the polyacrylamidoxime–copper chelates, by using elemental analysis, IR spectroscopy and dynamic thermogravimetry. The chelates containing copper ions as sulphate exhibit a better initial thermal stability than the polyacrylamidoxime fibre presumably due to the crosslinking generated by the intermolecular complexation of the ions; the removal of the sulphate anions takes place concomitantly with the second step of polymeric chain decomposition. The initial thermal decomposition of the chelates formed by copper ions as nitrate begins at lower temperatures as compared to the polyacrylamidoxime fibre, probably by the nitrate anion release, which partly overlaps the initial decomposition of the copper ion-crosslinked polymeric chains. Copper ions as either sulphate or nitrate catalyse the reactions involved in the main step of polyacrylamidoxime fibre decomposition; the higher the copper amount, the stronger the catalytic effect.
Keywords: Thermal degradation; Polyacrylamidoxime fibre; Copper chelates; Thermogravimetry; IR spectroscopy;

Solid state nuclear magnetic resonance techniques have been used to investigate aging mechanisms in a vinyl chloride:chlorotrifluoroethylene copolymer, FPC-461, due to exposure to γ-radiation. Solid state 1H MAS NMR spectra revealed structural changes in the polymer upon irradiation under both air and nitrogen atmospheres. Considerable degradation is seen with 1H NMR in the vinyl chloride region of the polymer, particularly in the samples irradiated in air. 19F MAS NMR was used to investigate speciation in the chlorotrifluoroethylene blocks, though negligible changes were seen. 1H and 19F NMR at elevated temperature revealed increased segmental mobility and decreased structural heterogeneity within the polymer, yielding significant resolution enhancement over room temperature solid state detection. The effects of multi-site exchange are manifested in both the 1H and 19F NMR spectra as a line broadening and change in peak position as a function of temperature.
Keywords: FPC-461; Fluoropolymer; Variable temperature NMR; Degradation;

The stability of poly(m-carborane-siloxane) elastomers exposed to heat and gamma radiation by Mogon Patel; Anthony C. Swain; Jenny L. Cunningham; Robert S. Maxwell; Sarah C. Chinn (548-554).
Poly(m-carboranyl-siloxane) elastomers containing a mixture of di-methyl- and methylphenyl-silyl units were synthesised using the ferric chloride catalysed condensation reaction between di-chloro-diorganosilane and bis(di-methylmethoxysilyl)-m-carborane. These elastomeric materials were originally developed to have greater stability to extreme thermal environments and retain tailorable physical and chemical properties relative to comparable non-carborane containing elastomers. Prepared samples were aged either by heating in air at elevated temperatures or by gamma irradiation from a 60Co source. Multinuclear (1H, 13C and 11B) solid and solution state nuclear magnetic resonance (NMR) was used to assess degradation. This included measurements of segmental chain dynamics using a solid-echo pulse sequence reflecting changes in crosslink density and assessing changes to the carborane fragment by 11B and 1H Magic Angle Spinning (MAS) methods. Thermogravimetric measurements were also performed to assess thermal stability. Gamma radiation (to a dose of 1 MGy) was found to induce only a small degree of elastomer hardening as evidenced by a reduction in segmental chain dynamics. The carborane cage however, remained intact at these dose levels. Thermal degradation was observed to lead to oxidative crosslinking, the degree of which is dependent on temperature. At temperatures below 350 °C, only small changes in segmental dynamics were observed commensurate with only minor weight loss at this temperature. At temperatures above 350 °C, the degradation of the elastomer increased dramatically with decreased segmental dynamics and presumed partial oxidation of the carborane cage. The integrity of the m-carborane cage and the segmental dynamics were found to be significantly reduced at temperatures above 580 °C, in line with the known cage rearrangement temperature for icosahedral carboranes.
Keywords: NMR; Poly(m-carboranyl-siloxane); Degradation; Chain dynamics;

Chemical origins of permanent set in a peroxide cured filled silicone elastomer – tensile and 1H NMR analysis by Sarah Chinn; Steve DeTeresa; April Sawvel; Al Shields; Bryan Balazs; Robert S. Maxwell (555-564).
The aging of a commercial filled siloxane polymeric composite in states of high stress and Co-60 γ-radiation exposure has been studied. DC-745 is a commercially available silicone elastomer consisting of dimethyl, methyl-phenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is filled with ∼ 30 wt.% mixture of high and low surface area silicas. This filled material is shown to be subject to permanent set if exposed to radiation while under tensile stress. Tensile modulus measurements show that the material becomes marginally softer with combined radiation exposure and tensile strain as compared to material exposed to radiation without tensile strain. In addition, the segmental dynamics as measured by both uniaxial NMR relaxometry and Multiple Quantum NMR methods indicate that the material undergoes radiatively-induced crosslinking in the absence of tensile strain. In the presence of tensile strain, relaxometry and MQ NMR studies show a strain dependent change in the dynamic order parameter and in the number of polymer chains associated with the filler surface. Solvent swelling measurements indicated no dependence on network crosslink density on strain ratio. Variable tau CPMG echo experiments indicate that a fraction of the polymer chains diffuses through areas of strong magnetic field gradients both at the filler–polymer interface and adjacent to micro-voids within the network. The population of the polymer chains influenced by the field gradients was observed to be dependent on the cumulative dose and degree of tensile strain applied during exposure. The relative change in crosslink density from the NMR and solvent swelling data deviates from that predicted from the Tobolsky model, particularly at higher doses. The likely reasons for this deviation are changes in the filler–polymer interface, increasing deviation from Gaussian chain statistics, and/or the formation of increased numbers of elastically ineffective network chains.
Keywords: Siloxanes; Radiation; Multiple quantum NMR; Permanent set; Unilateral NMR;

Photophysical processes and photochemical reactions involved in poly(N-vinylcarbazole) and in copolymers with carbazole units by A. Rivaton; B. Mailhot; S. Robu; M. Lounaci; P.O. Bussière; J.-L. Gardette (565-572).
This paper is devoted to the analysis of the photochemical behaviour of copolymers with carbazole units exposed to long-wavelength radiation. These copolymers are constituted of two types of carbazolylethyl methacrylate units (CEM) with octyl methacrylate moieties (OMA). The exposure of copolymers and PVK to UV light results in dramatic modifications of the physical and photophysical properties of the polymer. These modifications can be correlated with modifications of the chemical structure of the matrix. The photoageing of copolymers and PVK has been analysed by fluorescence, ESR, UV–vis and infrared spectroscopies. The effects of crosslinking and chain scissions were determined by gel fraction measurements and size exclusion chromatography.
Keywords: Poly(N-vinylcarbazole); Copolymers; Photophysical processes; Photochemical reaction;

Photooxidation of poly[methyl(phenyl)silylene] and effect of photostabilizers by O. Meszároš; P. Schmidt; J. Pospíšil; S. Nešpůrek (573-578).
Poly[methyl(phenyl)silylene] (PMPSi) samples were irradiated in air atmosphere using either a weatherometer ATLAS Ci 3000+ or a mercury discharge lamp HBO 200. The kinetics of photodegradation was determined by FTIR and UV spectroscopies. The absorption changes in the siloxane, carbonyl and hydroxyl regions were monitored and analyzed. It is assumed that photodegradation of neat PMPSi in air atmosphere is an irreversible dual photoprocess consisting of primary photolysis followed by the photooxidation to oxygenated products such as siloxanes and species containing hydroxyl and carbonyl groups. Degradative changes can be retarded by the addition of photostabilizers. Triazine-based phenolic UV absorber protecting the polymer by the excited-state intramolecular proton transfer mechanism, bifunctional stabilizer (consisting of UV absorber and HAS functions) and the combination of triazine-based phenolic UV absorber with HAS was rather effective in retardation of photodegradation of PMPSi.
Keywords: Polysilane degradation; Poly[methyl(phenyl)silylene]; Photooxidation; Photostabilization;

Commercial sunflower oil was epoxidised and used as organic co-stabiliser for rigid and plasticised poly(vinyl chloride) (PVC) containing Zn and Ca stearates as primary stabilisers and stearic acid as lubricant. For applications in the packaging of foodstuffs, migration testing must be performed. The detection and the quantification of contaminants migrating from the polymer into the food simulants are essential for the safety assessment of food contact plastic packaging materials. For that purpose, two food simulants were used: olive oil and 15% (v/v) aqueous ethanol. These represent fatty and moist food and beverages, respectively. The test conditions were 12 days at 40 °C. Circular samples of rigid PVC and PVC plasticised with dioctyl phthalate were immersed in a known volume of food simulant. A circular sample and 10 ml of food simulant were taken off every day to be analysed. Each sample was wiped and weighed. The rate of variation of the mass was determined as a function of time. The evolution of the peroxide index of olive oil with time was analysed. The specific migrations of the present additives were investigated by using two analytical methods (atomic absorption spectrometry and Fourier transform infrared spectroscopy). The influence of various parameters such as the nature of food simulant, the presence or the absence of the plasticiser, the agitation and time of contact was considered.
Keywords: PVC; Epoxidised sunflower oil; Migration; Food simulants;

Methods are proposed to synthesize efficient organophosphorous compounds and combine them with montmorillonite nanoparticles. The chemical–physical structure and mechanism of action of the new systems were studied in epoxy resin. Best results were achieved using the fully phosphorylated calixresorcinarene derivative: the heat release rate peak could be decreased by 61% and the LOI value was increased from 21 to 28. The salt form of additives in case of phosphorylated phloroglucine derivatives was not advantageous in epoxy resin, because the additives could not participate in the crosslinking process effectively due to their inhomogenous distribution in the matrix. The incorporation of the nanoparticles did not create the desired flame retardant effect which can be explained by the increased heat conductivity and lower mobility of the nanoparticles due to the crosslinked structure.
Keywords: Organophosphorous flame retardant; Epoxy resin; Intercalated montmorillonite; Cone calorimetry;

Role of montmorillonite in flame retardancy of ethylene–vinyl acetate copolymer by Andrea Szép; András Szabó; Nikoletta Tóth; Péter Anna; György Marosi (593-599).
The effects of non-treated (MMT), organophilic (OMM), and olefin/silicone polymer intercalated (IMM) montmorillonites on the thermal stability of ethylene–vinyl acetate copolymer (EVA) and on the flammability of magnesium hydroxide filled EVA were studied. The influence of various treatments on the delamination of montmorillonites in EVA was detected by rheological measurements and by Raman microscopy. The latter was a unique method for rapid detection of the dispersion also in highly filled EVA. Enhancement of thermo-oxidative stability of EVA and flame-retarded EVA could be observed by thermal analysis in the presence of variously treated montmorillonites. The flame-retardant efficiency of magnesium hydroxide was improved by simultaneous application of MMT and IMM. The increased performance of magnesium hydroxide was explained by the rheological effect of the IMM, catalytic effect of MMT and chemical interactions of montmorillonites with the metal hydroxide.
Keywords: Nanocomposite; Hydrated filler; Interface modification; Fire retardancy; Thermal degradation; Rheology;

Characterization and thermal degradation of polypropylene–montmorillonite nanocomposites by Fabio Bertini; Maurizio Canetti; Guido Audisio; Giovanna Costa; Luciano Falqui (600-605).
Polypropylene (PP)–montmorillonite nanocomposites have been prepared using isotactic PP homopolymers with different rheological properties, and a maleic anhydride grafted PP. Morphology and structure of the composites were investigated by using X-ray techniques (WAXD, SAXS) and transmission electron microscopy (TEM). The absence of pristine clusters of the clay and the presence of intercalated and exfoliated structures were shown for all the investigated samples. The nanocomposite prepared by using maleic anhydride grafted PP showed a widespread exfoliation. The thermal behaviour and degradation have been studied by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The incorporation of the montmorillonite improves the thermal stability in air atmosphere of all the investigated PPs, thanks to a physical barrier effect of the silicate layers.
Keywords: Thermal degradation; Thermogravimetric analysis; Nanocomposites; Polypropylene;

The work focuses on a mechanistic study of the title system with the aid of both TGA–FTIR (in the gas phase) and XPS (in the condensed phase). It is concluded that: (1) although the change in yield of char for PC/PPFBS is insignificant with respect to PC itself it appears that the majority of the crucial FR activity is in the condensed phase as indicated by the XPS data; (2) TGA–FTIR experiments support the view that the degradation of polycarbonate proceeds by the cleavage of the Cα–O and the Cβ–H bonds, leading to the formation of dienes, diols and carbon dioxide; (3) the reverse reaction of the intermediates, like phenols, may occur via the basic catalyst, possibly K-alkyl oxide, a weaker base is generated in the process; (4) voluminous evolution of CO2 accelerated by PPFBS may give flame retardance by way of intumescent action and its dilution into the gas phase.
Keywords: Flame retardant polycarbonate; Potassium perfluorobutane sulfonate; FTIR–TGA; XPS;

Swelling and hydrolytic degradation of poly(d,l-lactic acid) in aqueous solutions by C.S. Proikakis; N.J. Mamouzelos; P.A. Tarantili; A.G. Andreopoulos (614-619).
Low molecular weight poly(lactic acid) was synthesized by direct polycondensation of lactic acid. The oligomers were characterized by viscometry, light scattering, and gel permeation chromatography (GPC). The swelling behaviour of tablets made of the above polymer immersed in buffer solutions at 37 °C was studied. In the same experiments, the hydrolytic stability of d,l-PLA was assessed by measuring the weight loss after drying the tablets. In order to inhibit any degradation due to bacteria, formaldehyde was added in the solution as biostatic factor. The effect of an incorporated drug on the swelling behaviour of d,l-PLA tablets was also considered. It was found that the incorporation of drug in d,l-PLA tablets increases their swelling index, probably due to the creation of additional porosity in the specimens or other interaction between drug and polymeric matrix.
Keywords: Poly(d,l-lactic acid); Swelling; Hydrolysis; Erosion; Degradation;

Aerobic and anaerobic biodegradability of polymer films and physico-chemical characterization by V. Massardier-Nageotte; C. Pestre; T. Cruard-Pradet; R. Bayard (620-627).
Aerobic and anaerobic biodegradation of four different kinds of polymers, polylactic acid, polycaprolactone, a starch/polycaprolactone blend (Mater-bi®) and poly(butadiene adipate-co-terephthalate) (Eastar bio®) has been studied in the solid state under aerobic conditions and in the liquid phase under both aerobic and anaerobic conditions.Several standard test methods (ISO 14851, ISO 14853, ASTM G 21-90 and ASTM G 22-76 and NF X 41-514) were used to determine the biodegradability. To determine the efficiency of the biodegradation of polymers, quantitative (mass variations, oxygen uptake, pressure variations, biogas generation and composition, biodegradation percentages) and qualitative (variation of T g and T f, variation of molar mass by SEC, characterization by FTIR and NMR spectroscopy) analyses were made and materials were characterized before and after 28 days of degradation.After 28 days, the degradation of materials depends on the material and on the test conditions used. The degradation is better under aerobic conditions, in particular for Mater-bi and polycaprolactone. Nevertheless, we can notice that it is the amorphous part of the polymer which is more attacked by the micro-organisms but, after 28 days, they do not seem to cleave macromolecules inside the material: bacteria attack the surface of the polymer and seem to consume the macromolecules one after another (there is no significant variation in the molar mass and no difference between FTIR and NMR spectra before degradation and after 28 days of degradation).
Keywords: Polymers; Biodegradation tests; Aerobic and anaerobic conditions; SEC; DSC;