Polymer Degradation and Stability (v.90, #3)
Subject index for Volumes 87 - 90 (XVII-XXVI).
Contents of volumes 87-90 (III-XVI).
Accelerated aging and lifetime prediction: Review of non-Arrhenius behaviour due to two competing processes by M. Celina; K.T. Gillen; R.A. Assink (395-404).
Lifetime prediction of polymeric materials often requires extrapolation of accelerated aging data with the suitability and confidence in such approaches being subject to ongoing discussions. This paper reviews the evidence of non-Arrhenius behaviour (curvature) instead of linear extrapolations in polymer degradation studies. Several studies have emphasized mechanistic variations in the degradation mechanism and demonstrated changes in activation energies but often data have not been fully quantified. To improve predictive capabilities a simple approach for dealing with curvature in Arrhenius plots is examined on a basis of two competing reactions. This allows for excellent fitting of experimental data as shown for some elastomers, does not require complex kinetic modelling, and individual activation energies are easily determined. Reviewing literature data for the thermal degradation of polypropylene a crossover temperature (temperature at which the two processes equally contribute) of ∼83 °C was determined, with the high temperature process having a considerably higher activation energy (107–156 kJ/mol) than the low temperature process (35–50 kJ/mol). Since low activation energy processes can dominate at low temperatures and longer extrapolations result in larger uncertainties in lifetime predictions, experiments focused on estimating E a values at the lowest possible temperature instead of assuming straight line extrapolations will lead to more confident lifetime estimates.
Keywords: Accelerated aging; Polymer; Aging; Thermal degradation; Lifetime prediction; Extrapolation; Performance; Material selection; Arrhenius; Curvature;
Global weathering of aromatic engineering thermoplastics by J.E. Pickett; M.M. Gardner; D.A. Gibson; S.T. Rice (405-417).
The rates of gloss loss and color shift for 24 aromatic engineering thermoplastics at nine exposure sites world-wide have been compared relative to a commercial Miami exposure site. The scatter among individual samples was large, but on average, light dose alone was enough to account for almost all of the rate differences among the various sites for these materials. Temperature, humidity, rainfall, and acid rain seemed to play minor roles for most samples. Samples containing no particulate pigment had more erratic gloss loss and showed some dependency on the amount of rainfall. The overall “cleanliness” of the samples seemed to be an important factor in gloss retention, and washing protocols during the exposure period and before readings were important variables in cases of slow erosion and/or no particulate pigment. Microbial growth (fungus) was observed on Miami samples after 12–18 months of exposure, but none was seen at any other site.Relative to Miami defined as 1.0, the average rates of color shift and gloss loss were approximately 0.67 in the northern U.S., 0.8 in the central U.S., and 1.15 in the U.S. desert southwest. Southern Europe was nearly as harsh as Miami, while Northern Europe was comparable to the northern U.S. Northern Europe was found to be somewhat harsher than expected while the northern U.S. was slightly less harsh than expected based on light dose or temperature-weighted light dose. These conclusions apply only to aromatic engineering plastics and should not be assumed to hold for other kinds of materials, such as polyolefins or coatings, without experimental verification.
Keywords: Outdoor weathering; Plastics; Relative rates; Correlation;
Reproducibility of Florida weathering data by J.E. Pickett; M.M. Gardner (418-430).
We have investigated the consistency and reproducibility of Florida outdoor weathering data for aromatic engineering thermoplastics. Weather and broadband (295–385 nm) UV dose data for the 14-year period from 1989 to 2002 show that considerable variability is expected for exposures with duration < 1 year, but that standard deviations for UV exposure and temperature are approximately 7% of the mean at 1 year and <5% at 2 years and greater. Only rainfall shows significant long-term variability. Weathering data on pigmented aromatic engineering thermoplastics were consistent with these expectations. Overall trends and rates of color and gloss shifts were generally reproduced for samples exposed at different times. Color shift data were generally reproducible within a ΔE of 2 and 60° gloss loss within 10 units for samples beginning exposure 6 months apart. However, very large differences in absolute values for properties can occur for data taken near periods of rapid change, especially for gloss loss. Surprisingly, considering the data as a function of broadband UV dose rather than exposure time did not seem to reduce scatter. This emphasizes the problem of comparing results between data sets for exposure times < 1 year. We conclude that Florida data do provide a useful benchmark when rates and general trends are compared, but not for absolute values at arbitrary times.
Keywords: Weathering; Outdoor; Reproducibility; Miami; Florida;
Thermal and hydrolytic stability of sulfonated polyimide membranes with varying chemical structure by Wonbong Jang; Choonkeun Lee; Saimani Sundar; Yong Gun Shul; Haksoo Han (431-440).
Many important properties required for fuel cell applications including hydrolytic stability, depend on various factors like flexibility of the polymer backbone, ring structure and phase separation. This paper is primarily focused on studying the effect of the chemical backbone structure on the hydrolytic stability and other properties. To study the difference in the hydrolytic stability with change in the chemical backbone structure of sulfonated polyimides we synthesized phthalic sulfonated polyimides and naphthalenic sulfonated polyimides. Two series of phthalic sulfonated polyimides were prepared using 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-methylene dianiline (MDA), and 4,4′-(hexafluoroisopropylidine) diphthalic anhydride (6FDA) and oxydianiline (ODA). 4,4′-Diaminobiphenyl-2,2′-disulfonic acid (BDSA) was used to introduce sulfonic acid group into both series. Naphthalenic polyimides were synthesized from 1,4,5,8-naphthalenetetra-carboxylic dianhydride, BDSA, MDA and ODA. Also to observe other properties according to variation of sulfonic acid content, the degree of functionalisation was effectively controlled by altering the mole ratio between the sulfonated and non-sulfonated diamine monomers in phthalic sulfonated polyimides. The hydrolytic stability of the polyimides was followed by FT-IR spectroscopy at regular intervals. Polyimides prepared using naphthalenic dianhydride, NTDA, exhibited higher hydrolytic stability than the phthalic dianhydrides. The proton conductivity, ion exchange capacity (IEC) and water uptake measurements revealed the dependence on the molecular weight of the repeating unit. The proton conductivity of the sulfonated polyimides was found to vary with chemical backbone structure.
Keywords: Sulfonated polyimides; Hydrolytic stability; Morphology; Proton conductivity; Fuel cells;
In vitro degradation behaviour of non-porous ultra-fine poly(glycolic acid)/poly(l-lactic acid) fibres and porous ultra-fine poly(glycolic acid) fibres by Young You; Sung Won Lee; Ji Ho Youk; Byung-Moo Min; Seung Jin Lee; Won Ho Park (441-448).
The in vitro degradation behaviour of non-porous ultra-fine poly(glycolic acid)/poly(l-lactic acid) (PGA/PLA) fibres and porous ultra-fine PGA fibres was investigated. The non-porous ultra-fine PGA/PLA fibres were prepared by electrospinning of a PGA/PLA solution in 1,1,1,3,3,3-hexafluoro-2-propanol and the porous ultra-fine PGA fibres were obtained from them via selective removal of PLA with chloroform. Since PLA has a lower degradation rate than PGA, the degradation rates of the ultra-fine PGA/PLA fibres decreased with increasing content of PLA. The porous ultra-fine PGA fibres were degraded in vitro in the order of non-porous PGA > P-PGA/PLA(90/10) > P-PGA/PLA(70/30) > P-PGA/PLA(50/50) > P-PGA/PLA(30/70) due to autocatalytic hydrolysis.
Keywords: Poly(glycolic acid); Poly(l-lactic acid); Electrospinning; Porous ultra-fine fibre; Biodegradability;
Thermal degradation of biodegradable edible films based on xanthan and starches from different sources by R.M.D. Soares; A.M.F. Lima; R.V.B. Oliveira; A.T.N. Pires; V. Soldi (449-454).
Films based on xanthan/wheat starch and xanthan/maize starch were prepared in different proportions and analysed in terms of thermal stability in relation to the degradation reaction in an inert atmosphere. The main gaseous decomposition products were identified by infrared spectroscopy. Xanthan was found to be less thermally stable than starch from different sources. The starch addition to xanthan induced an increase in the film thermal stabilities. The thermal degradation mechanism of xanthan starts with scission of the side chain groups with subsequent scission of the main chain. Starches from maize and wheat presented a constant mechanism of thermal degradation. The proportion of xanthan/starch (50/50) presented a synergistic behaviour which may be associated with changes in the mechanism of the thermal degradation process. The FTIR spectra of the gaseous products during thermal degradation of xanthan showed a broad absorption in the 2750–3300 cm−1 region, probably indicating decomposition of β-d-mannopyranosyl groups, present in xanthan side chains. For pure starches, absorptions related to alcohol O–H stretching (3500–3750 cm−1), C＝O stretching of CO2, CO and carbonyl compounds (2361, 2177 and 1743 cm−1, respectively) were observed. For xanthan/starch mixtures (50/50) the same compounds as those for the pure polymer degradation were evolved. However, a shift of the C＝O to higher wavenumber values indicates that new carbonyl compounds are being formed due to changes in the thermal degradation mechanism.
Keywords: Xanthan; Starch; Thermal degradation; Edible films;
Kinetics of isothermal thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends by Nataša Stipanelov Vrandečić; Branka Andričić; Ivka Klarić; Tonka Kovačić (455-460).
The thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends of different compositions was investigated by means of isothermal thermogravimetry in flowing atmosphere of synthetic air at temperatures 240–270 °C. The main degradation processes are dehydrochlorination of PVC and CPE. For calculation of the apparent activation energy and apparent pre-exponential factor two kinetic methods were used: isoconversional method and Prout–Tompkins method. True compensation dependency between Arrhenius parameters, obtained using Prout–Tompkins model, was found. Calculated kinetic parameters of isothermal thermooxidative degradation are close to those from non-isothermal degradation and confirm the assumption of the main degradation process in PVC/CPE blends.
Keywords: Isothermal thermogravimetry; Kinetic analysis; PVC/CPE blends; Thermooxidative degradation;
Photodegradation of polypropylene thermal bonded non-woven fabric by S. Aslanzadeh; M. Haghighat Kish (461-470).
Samples of thermal bonded polypropylene non-woven fabrics were exposed to light from two TUV 30W G30T8 Philips lamps (λ = 253.7 nm) in a covered open-air chamber at room temperature (25 °C and 55% relative humidity) for different periods of time. In order to determine the state of degradation, the samples were examined by optical microscopy, scanning electron microscopy, staining with an isopropanol solution of methylene blue and Sudan III, colourimetry, Fourier transform infrared (FTIR) spectroscopy and density measurements. Although the bonded areas formed under complex thermal and mechanical deformations during the fabric production, no localized staining was observed. The colour of the irradiated and stained fabrics changed uniformly due to the even production of polar groups in the process of irradiation. It was found that the change of redness and blueness of degraded and stained samples can be correlated linearly with the evolution of POOH groups as determined by FTIR spectroscopy. Products containing carbonyl (C＝O), hydroxyl and/or hydroperoxide (POOH) groups increase with time of degradation with a non-linear relation. It was also observed that the density and 997 cm−1/972 cm−1 FTIR absorbance ratio increases with degradation time. Density fluctuation and the build up of degradation products caused fibre cracks and embrittlement.
Keywords: Photodegradation; Photooxidation; Non-woven fabric; Isotactic polypropylene; Staining; Spectroscopy; Colourimetry;
Investigation of the hydrothermal stability of cross-linked liquid silicone rubber (LSR) by Afshin Ghanbari-Siahkali; Susanta Mitra; Peter Kingshott; Kristoffer Almdal; Carsten Bloch; Helle Kem Rehmeier (471-480).
We investigate the hydrothermal stability of cross-linked liquid silicone rubber (LSR) in water at 100 °C up to period of two years. Optical microscopy of cross-sections of the exposed samples reveal that only the outer 100 μm of the surface layer is affected after two years. However, the surface chemistry of the material after prolonged exposure becomes significantly modified, as monitored by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR), which probes depths of 10 nm and 1 μm, respectively. In addition, changes to the bulk physical properties of the rubber samples, prior to and after the exposure, were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Micro-hardness analysis showed that surface roughness of the two year exposed sample increased from 60 (IRHD) to 75 (IRHD). Furthermore, the volume change (%) measurement showed a significant decrease in the course of exposure at prolonged time. The results provide the experimental basis for development of LSR materials suitable for numerous technical applications.
Keywords: Chemical degradation; Liquid silicone rubber (LSR); Surface hardness; XPS; ATR-FTIR; TGA; DSC; Physical properties; Volume change;
Compatibility effect on the thermal degradation behaviour of polypropylene blends with polyamide 6, ethylene propylene diene copolymer and polyurethane by J. Roeder; R.V.B. Oliveira; D. Becker; M.W. Gonçalves; V. Soldi; A.T.N. Pires (481-487).
The morphology and thermal behaviour of polypropylene/polyamide 6 (PP/PA6), polypropylene/copolymer ethylene propylene diene (PP/PEBAX) and polypropylene/rigid polyurethane (PP/PUR) blends compatibilised with polypropylene-graft-maleic anhydride (PP-g-MA) were studied using scanning electron microscopy and thermogravimetric analyses. The study focuses on the influence of different blends obtained by mixing a thermoplastic, thermoplastic elastomer or thermoset with PP, compatibilised with PP-g-MA. The compatibilising effect of PP-g-MA in an immiscible PP/PA6 blend induces a homogeneous dispersion due to interfacial adhesion. For the PP/PEBAX and PP/PUR binary blends studied slight changes in the morphology were observed with a continuous phase but the PEBAX or PUR domains remained in the PP matrix. The deconvolution of the TGA curve permitted an evaluation of the decomposition stage of the undiluted and blend systems. Thermal stability is slightly influenced by the position of the maximum decomposition rate temperature of the first derivative thermogravimetric curve (DTG). However, the DTG curve profile remains consistent. The activation energy of undiluted PP was in the range of 162–169 kJ mol−1 determined by the Ozawa method. The stabilized activation energy value for all blends studied above a 0.4 weight-loss fraction is discussed.
Keywords: Polymer blends; Compatibiliser; Thermal decomposition;
Water absorption and enzymatic degradation of poly(lactic acid)/rice starch composites by G.H. Yew; A.M. Mohd Yusof; Z.A. Mohd Ishak; U.S. Ishiaku (488-500).
Poly(lactic acid) (PLA) composites consisting of PLA, rice starch (RS) (0–50 wt%) and epoxidised natural rubber (ENR50) were compounded by a twin-screw extruder and compression moulded into dumbbell specimens. Tensile tests were performed to characterize the mechanical properties of the PLA/RS composites. Morphological studies were done on the tensile fractured surface of the specimens by using scanning electron microscopy (SEM). Twenty weight percent of RS achieved a good balance of strength and stiffness. Beyond 20 wt% loading of RS, the tensile strength and elongation at break of PLA decreased drastically. This may be attributed to the agglomeration of RS, which could then act as stress concentrator. The incorporation of ENR50 increased the tensile strength and elongation at break of the PLA/RS composites remarkably, owing to the elastomeric behaviour and compatibilisation effects of ENR50. Interestingly, the morphology of PLA/RS composites transformed to a more ductile one with the addition of ENR. The kinetics of water absorption of the PLA/RS composites conforms to Fick's law. The M m and D values are dependent on the RS and ENR concentrations. The tensile properties of the PLA/RS composites deteriorated after water absorption. The retention-ability and recoverability of the PLA/RS composites are relatively low, attributed to the hydrolysis of PLA, degradation of the PLA–RS interface and leaching of the RS particles. In addition, the tensile properties of PLA/RS composites decreased drastically upon exposure to enzymatic degradation. Extensive pinhole and surface erosion on the PLA/RS composites indicate high degree of hydrolysis. Whilst the addition of ENR leads to some improvements in tensile properties, nevertheless, it enhanced the biodegradability of the PLA/RS composites when exposed to water and α-amylase enzymatic treatments.
Keywords: Polylactic acid (PLA); Rice starch (RS); Epoxidized natural rubber (ENR); Water absorption; Enzymatic degradation;
Ethanolamine as a novel plasticiser for thermoplastic starch by Mingfu Huang; Jiugao Yu; Xiaofei Ma (501-507).
Ethanolamine plasticised thermoplastic starch (ETPS) was prepared using a novel plasticiser ethanolamine. SEM images show that the native starch granules were destroyed, and the ethanolamine made them come into a uniform continuous phase. FTIR spectroscopy showed that the hydrogen bonds between the ethanolamine and starch molecules weakened the strong effect of starch intermolecular and intramolecular hydrogen bonds. The ETPS successfully restrains the re-crystallization of traditional thermoplastic starch plasticised by glycerol (GTPS), which was proved by XRD. The mechanical properties of ETPS, such as Young's modulus and breaking energy and the water absorption were improved. The glass-transition temperature (T g) and thermal stability were also studied by DSC and TGA.
Keywords: Themoplastic starch; Ethanolamine; Glycerol; Crystallization;
Synergistic effect of ferric chloride and silicon mixtures on the thermal stabilization enhancement of ABS by Junwon Jang; Jinhwan Kim; Jin-Young Bae (508-514).
A previous study from this laboratory has shown that Lewis acid-type transition metal chlorides (NiCl2, CoCl2, ZnCl2, and FeCl3) are effective char forming catalysts for ABS terpolymer in an inert atmosphere [Jang J, Kim JH, Bae JY. Polym Degrad Stab 2005;88(2):324.]. However, transition metal chloride catalysed char formation (and flame-retardance enhancement) of ABS in air was unsuccessful due to the oxidative degradation of the char at a higher temperature. In order to overcome these undesirable phenomena, we incorporated silicon with transition metal chlorides as co-catalyst and a series of ABS/transition metal chloride/silicon compounds were made from them and their flame retardancy was evaluated by measuring the limiting oxygen index (LOI) values. Our results showed that among various transition metal chloride/silicon catalyst systems the incorporated mixture of ferric chloride and silicon is very effective in enhancing the thermal stabilization of ABS and LOI value as high as 33 is obtained. The reason for this synergistic effect by ferric chloride and silicon was postulated to come from the interaction between ferric chloride and silicon at elevated temperatures, probably generating silicon tetrachloride and hydrogen chloride.
Keywords: ABS; Ferric chloride; Silicon; Synergism;
The effect of silicon sources on the mechanism of phosphorus–silicon synergism of flame retardation of epoxy resins by Ying-Ling Liu; Ching-I Chou (515-522).
The effect of silicon source on the mechanism and efficiency of silicon–phosphorus synergism of flame retardation was studied. The studied systems composed of a phosphorus-containing epoxy resin and various types of silicon additives including nanoscale colloidal silica (CS), tetraethoxysilane (TEOS), and diglycidylether terminated polydimethylsiloxane (PDMS-DG). Thermal stability and degradation kinetics of cured epoxy resins, elemental analysis of degraded residues, and evolved gases analysis of degradation reactions were conducted with a thermogravimetric analyser, energy-dispersive X-ray spectrometry, and gas chromatography–mass spectrometry, respectively. Addition of silicon compounds showed significant effect on enhancing the thermal stability and char yields of the cured epoxy resins. During thermal degradation, TEOS and PDMS-DG exhibited silicon migration to sample surface and CS did not. Self-degradation of PDMS-DG resulted in a silicon loss for PDMS-DG-containing epoxy resin. From the results it was concluded that using TEOS as an additive for epoxy resins and formation of epoxy-silica hybrid structure through sol–gel reactions was a good approach for achieving phosphorus–silicon synergism in flame retardation.
Keywords: Silicon; Flame retardation; Synergism; Thermal analysis;
Flammability and thermal degradation of flame retarded polypropylene composites containing melamine phosphate and pentaerythritol derivatives by Pin Lv; Zhengzhou Wang; Keliang Hu; Weicheng Fan (523-534).
The flammability of polypropylene (PP) composites containing intumescent flame retardant additives, i.e. melamine phosphate (MP) and pentaerythritol (PER), dipentaerythritol (DPER) or tripentaerythritol (TPER) was characterized by limiting oxygen index (LOI), UL 94 and the cone calorimeter, and the thermal degradation of the composites was studied using thermogravimetric analysis (TG) and real time Fourier transform infrared (RTFTIR). It has been found that the PP composite containing only MP does not show good flame retardancy even at 40% additive level. Compared with the PP/MP binary composite, the LOI values of the PP/MP/PER (PP/MP/DPER or PP/MP/TPER) ternary composites at the same additive loading are all increased, and UL 94 ratings of most ternary composites studied are raised to V-0 from no rating (PP/MP). The cone calorimeter results show that the heat release rate and smoke emission of some ternary composites decrease in comparison with the binary composite. It is noted from the TG data that initial decomposition temperatures of ternary composites are lower than that of the binary composite. The RTFTIR study indicates that the PP/IFR composites have higher thermal oxidative stability than the pure PP.
Keywords: Polypropylene; Intumescent flame retardation; Melamine phosphate; Pentaerythritol derivatives; Real time FTIR; Thermal degradation;
Study on the electrochemical degradation of poly-N-acetylaniline by electro-hydrolysis and electro-chlorination by Shouguo Wu; Xiaogang Han (535-539).
Poly-N-acetylaniline (PNAANI) film, an analogous polymer of polyaniline, was electrodeposited on a glassy carbon (GC) electrode by an electro-dynamic scan method. Cyclic voltammetry was used to characterize the electrochemical response. The cyclic voltammograms of PNAANI films after its electro-hydrolysis and electro-chlorination were interpreted. The electrode processes are discussed and the electrochemical degradation mechanism of PNAANI film proposed based on the experimental results.
Keywords: Poly-N-acetylaniline; Degradation; Electro-hydrolysis; Electro-chlorination;
Hygrothermal weathering of rice hull/HDPE composites under extreme climatic conditions by W. Wang; M. Sain; P.A. Cooper (540-545).
Natural fiber plastic composites (NFPCs) are mainly used in residential construction materials, especially as deck boards. Exposure of such composites with high fiber content and hollow profiles to variable climatic conditions raises questions about their moisture adsorption/desorption behavior and hygrothermal dimensional stability. In this study, commercial decking boards made from about 50% rice hull and about 50% high density polyethylene (HDPE) were investigated under simulated extreme climatic exposure conditions. The samples absorbed 4.5% moisture after 2000 h exposure to 93% relative humidity (RH) and 40 °C. At the same time, the walls of the samples swelled significantly (7.1%) in thickness and ultimately developed about 5.00 mm longitudinal bowing based on 61 cm long boards. Both expansion and bowing were partially recovered after another 2000 h exposure to 20% RH and 40 °C. It took more time for the samples to reach new moisture equilibrium than new dimensional equilibrium when exposed to different weathering conditions. Moisture content was the major factor causing deformation including swelling and bowing. Temperature also played a significant role by causing direct thermal expansion or contraction and by affecting the rate and the amount of moisture adsorption.
Keywords: Hygrothermal expansion; Natural fiber plastic composites; Moisture adsorption; Bowing;
Degradation of polyesteramides prepared by the anionic polymerisation of ɛ-caprolactam in the presence of poly(ɛ-caprolactone) by Daniela Chromcová; Alice Bernášková; Jiří Brožek; Irena Prokopová; Jan Roda; Josef Náhlík; Václav Šašek (546-554).
Poly[(ɛ-caprolactam)-co-(ɛ-caprolactone)] was prepared by the anionic polymerisation of ɛ-caprolactam in the presence of poly(ɛ-caprolactone) initiated by ɛ-caprolactam magnesium bromide. Copolymers with 10–25% ɛ-caprolactone structure units were subjected to degradation. After 8-weeks abiotic hydrolysis at 60 °C the molar mass of the copolymer was significantly reduced as seen from viscosity measurements. IR spectroscopy was employed to clarify the mechanism of hydrolysis. Only small changes in molar mass were observed after composting and fungal treatment. Therefore, the effect of degradation temperature was crucial. The thermal properties of polyesteramides were studied by DSC, which showed the shift of melting endotherm and enthalpy of fusion to higher values of degraded samples compared to original one. This indicated an increase in crystalline phase content caused by reorganization of amorphous phase. Physical degradation of films was observed using SEM. Film-surface changes were apparent mainly on samples with 25% ɛ-caprolactone units.
Keywords: Polyesteramides; Degradation; Composting; Fungal treatment;
Emission of possible odourous low molecular weight compounds in recycled biofibre/polypropylene composites monitored by head-space SPME-GC–MS by Ana Espert; Luis A. de las Heras; Sigbritt Karlsson (555-562).
A disadvantage of the use of natural fibres to reinforce polypropylene is their poor thermal stability, which results in their degradation at processing temperatures of the composites. As a result of this, there is a formation of low molecular weight compounds that are responsible for undesirable odours. Head-space-solid phase microextraction (HS-SPME) was used as a sample preparation technique and gas chromatography–mass spectrometry (GC–MS) was used to identify the low molecular weight compounds in natural polypropylene/polypropylene composites after simulating degradation. Among the compounds found in the samples, there are fragments of PP chains as heptadecane, compounds from antioxidants such as 2,4-bis(1,1-dimethylethyl)-phenol, and p-tert-butylphenol, and compounds from biofibres ageing, such as ethylparaben and vanillin. Numerous carboxylic acids were also identified, being these most probably the source of the undesirable odours.
Keywords: Solid phase microextraction; Polypropylene/cellulose composites; Thermal degradation;
Reducing water absorption in compostable starch-based plastics by M. Gáspár; Zs. Benkő; G. Dogossy; K. Réczey; T. Czigány (563-569).
To improve the mechanical and physical properties of corn starch-based bioplastics the addition of natural polymers was investigated. Thermoplastic starch (TPS) was made of 70 g corn starch and 30 g glycerol. To this mixture 10–10 g of cellulose, hemicellulose and zein (protein) were added. Mechanical strength, water absorption and enzymatic degradation of composite materials were measured. Unfilled TPS and 10 w/w% polycaprolactone filled TPS were used as controls in the experiments. All the samples were biodegradable by enzymes. The tensile strength of unfilled and biopolymer filled TPS samples were significantly higher than that of the polycaprolactone filled one. Hemicellulose and zein composites had the best mechanical strength (10.4 and 11.5 MPa). Water uptake of each sample was measured using five different relative humidities. There were slight differences in water uptake of polycaprolactone, hemicellulose and zein filled TPS, however unfilled and cellulose filled samples absorbed more moisture than the polycaprolactone control in all the relative humidities used.
Keywords: Starch; TPS; Bioplastic; Biodegradable; Enzymatic hydrolysis; Polycaprolactone; Cellulose; Hemicellulose; Zein;
Depolymerisation of poly(ethylene terephthalate) fibre wastes using ethylene glycol by M. Ghaemy; K. Mossaddegh (570-576).
Poly(ethylene terephthalate) [PET] fibre wastes from an industrial manufacturer was depolymerised using excess ethylene glycol [EG] in the presence of metal acetate as a transesterification catalyst. The glycolysis reactions were carried out at the boiling point of ethylene glycol under nitrogen atmosphere up to 10 h. Influences of the reaction time, volume of EG, catalysts and their concentrations on the yield of the glycolysis products were investigated. The glycolysis products were analysed for hydroxyl and acid values and identified by different techniques, such as HPLC, 1H NMR and 13C NMR, mass spectra, and DSC. It was found that the glycolysis products consist mainly of bis(hydroxyethyl)terephthalate [BHET] monomer (>75%) which was effectively separated from dimer in quite pure crystalline form.
Keywords: PET; Depolymerisation; Glycolysis; Recycling of PET fibre wastes;
Effect of benzil and cobalt stearate on the aging of low-density polyethylene films by P.K. Roy; P. Surekha; C. Rajagopal; S.N. Chatterjee; V. Choudhary (577-585).
We report an investigation of the effect of benzil and cobalt stearate on the degradation behaviour of LDPE films. Thin films (70 μ) containing these additives were prepared by sheeting process. The effect of heating, exposure to UV-B and natural weathering of LDPE films in the presence/absence of additives was investigated. Changes in the tensile properties, carbonyl index and density were used to investigate the degradation behaviour. Attempts have been made to correlate the results as a function of mixed additives. In contrast to the activity of typical triplet activators, benzil was found to be incapable of initiating thermal- or photo-degradation of LDPE films. However, an accelerated rate of oxidation was observed, primarily due to cobalt stearate, in the case of compositions containing a combination of benzil and cobalt stearate. All samples were found to be more susceptible to thermo-oxidation than to UV or natural weathering.
Keywords: LDPE; Benzil; Weathering; Photo-oxidation; Thermo-oxidation;
New nanocomposites constituted of polyethylene and organically modified ZnAl-hydrotalcites by U. Costantino; A. Gallipoli; M. Nocchetti; G. Camino; F. Bellucci; A. Frache (586-590).
The thermal properties and combustion behaviour of new PE–hydrotalcites nanocomposites are described. Hydrotalcites were synthesized and then intercalated with stearate anion, because of the compatibility of long alkyl chain with polyethylene chains. The presence of inorganic filler shields PE from thermal oxidation, shifting the temperature range of volatilisation towards that of thermal degradation in nitrogen, and brings to a reduction of 55% in heat release rate during combustion.
Keywords: Nanocomposites; Layered double hydroxides; Organically modified hydrotalcites; Flame retardancy; Cone calorimetry; Thermal degradation;