Polymer Degradation and Stability (v.80, #1)

Thermal degradation of traditional poly(methyl methacrylate) (PMMA) results in the evolution of MMA monomer with two steps including end group scission and C–C chain homolysis by random scission. PMMA initiated by lactams and thiols has higher thermal stability and shows only C–C chain homolysis by random scission. The observed results are explained by a “blocking effect”. Three kinetic analysis methods have been used to describe the thermal degradation behaviour measured by weight loss. The Flynn method shows activation energy of 116–128 kJ/mol, higher than that of AIBN initiated poymer (78–91 kJ/mol). According to the Ozawa method the average activation energy is 222–236 kJ/mol, higher than other PMMA systems (126–169 kJ/mol). Finally, the method of Kissinger shows that this system has a frequency factor four orders of magnitude higher than conventional PMMA.
Keywords: PMMA degradation; Blocking effect; Activation energy;

Thermal degradation of poly (ε-caprolactone) by G Sivalingam; Giridhar Madras (11-16).
The thermal degradation kinetics of poly (ε-caprolactone) (PCL) in solution was investigated at various temperatures (170–245 °C). The degradation was also investigated by pyrolysis at various temperatures (280–330 °C). The time evolution of molecular weight distribution (MWD) was obtained using gel permeation chromatography. It was observed that in pyrolysis, PCL degrades by specific chain end scission by unzipping of monomers from the hydroxyl end of the polymer chains. In contrast, the degradation of PCL in solution is by random chain scission. A continuous distribution kinetics model is proposed to explain the observed behaviour under both conditions. The activation energy, determined from the temperature dependence of rate coefficients, was 61 kJ/mol and 201 kJ/mol for the degradation in solution and by pyrolysis, respectively.
Keywords: Poly (ε-caprolactone); Random chain scission; Specific chain scission; Pyrolysis; Degradation in solution; Continuous distribution kinetics;

This article describes a study on zinc hydroxystannate (ZHS) and zinc stannate (ZS) in combination with 1,2-bis(tribromophenoxy)ethane (BTBPE) for increasing flame retardancy and reduced smoke emission in an acrylonitrile-butadiene-styrene (ABS) copolymer. The combination between BTBPE, synergist and chlorinated polyethylene (CPE) yield a high value of LOI which for some proportions is higher than for commercial ABS.
Keywords: Flame retardant; LOI; Zinc stannate; ABS;

Modifications of ZSM-5 zeolites and their applications in catalytic degradation of LDPE by Qian Zhou; Yu-Zhong Wang; Chao Tang; Yu-Hua Zhang (23-30).
The combination of two modification techniques developed for the ZSM-5 zeolite, i.e., desilication and incorporation of lanthanum under microwave irradiation, has produced a highly efficient catalyst, DeLaZSM-5, for catalytic degradation of low-density polyethylene (LDPE). Its performance on the degradation was studied at 390 °C and compared with the parent ZSM-5 and the modified intermediate products desilicated ZSM-5 (DeZSM-5) and LaZSM-5. Among the catalysts tested, DeLaZSM-5 showed the highest catalytic degradation rate. In addition, on DeLaZSM-5 the liquid yield was slightly increased and the isoparaffin index of the liquid was almost doubled, which indicated higher liquid quality compared with the parent ZSM-5 zeolite. The high catalytic activity of DeLaZSM-5 could be explained by its unique acidic properties with a sharp increase of the number and strength of weak acid sites and a decrease of strong acid sites.
Keywords: DeLaZSM-5 zeolite; Catalytic degradation; LDPE;

We have studied the degradation resulting from reprocessing of post-consumer HDPE in order to verify its re-stabilization needs. Cone-plate rheometry was used to provide information about the molar mass and the molar mass distribution after reprocessing and stabilizing the material. Infrared spectroscopy (FTIR), oxidation induction time (OIT), melt flow index (MFI) and cone-plate rheometry measurements were performed. Also, atomic absorption spectrophotometry tests were carried out to verify which catalytic residue was present in the recycled HDPE so as to correlate it to the degradation processes taking place in the polymer. The results showed that in this case the post-consumer HDPE displayed cross-linking when reprocessed, indicating the need for re-stabilization. They also showed that the use of 0.2% antioxidant was efficient in blocking these processes, and that the cone-plate rheometry technique was powerful in assessing degradative processes.

Thermo-oxidative degradation of polyethylene films containing pro-oxidant has been studied at three temperatures that normally occur during composting conditions. Besides temperature, oxygen concentration was also varied. After various periods, the effects of thermo-oxidation were evaluated by measurements of molecular mass of the materials. It is shown that while temperature is the most important factor influencing the rate of thermo-oxidative degradation of the materials, oxygen concentration is of negligible importance. The investigation has also shown that when the material is degraded into low molecular mass products, it is bioassimilated. The rate of aerobic biodegradation of the oxidation products was evaluated under controlled composting conditions using measurements of produced carbon dioxide. The degree of bioassimilation in our case was about 60%, and still increasing, after 180 days.
Keywords: Degradable polyethylene; Thermo-oxidation; Pro-oxidant; Molecular weight; Biodegradation; Mineralization; Activation energy;

ESR studies on collagen irradiated with protons by M. Chipara; J. Reyes Romero; M. Ignat; B. Constantinescu; C. Secu (45-49).
Electron spin resonance investigations on collagen irradiated with protons are reported. The resonance spectra were assigned to a convolution of lines due to ∼CH2–CH2 • residues and peroxy radicals. Raising the temperature of the sample (in air), the concentration of ∼CH2–CH2 • residues decreases while, the concentration of peroxy radicals increases due to the denaturation induced enhancement of the oxidation process. An increase in the apparent intensity of the recorded spectrum has been observed around 100 °C and ascribed to the release of adsorbed water molecules.
Keywords: Collagen; Irradiation; Electron spin resonance; Radicals; Thermo-oxidative degradation;

Degradation of low gloss polyurethane aircraft coatings under UV and prohesion alternating exposures by X.F. Yang; J. Li; S.G. Croll; D.E. Tallman; G.P. Bierwagen (51-58).
In this work, scanning electron microscopy (SEM)/energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) were used to study the accelerated weathering coating degradation that occurred in two low gloss polyurethane aircraft coating systems. One was epoxy primer with a traditional matte polyurethane topcoat and the other was the epoxy primer with a fluorinated polyurethane topcoat. The coated panels were exposed in a QUV chamber and a Prohesion chamber alternately. It was found that the primer with the matte topcoat system could not stop water penetration effectively, and the coating system was destroyed after 25 weeks. In contrast, the primer with the fluorinated polyurethane topcoat system formed a good barrier of water on the substrate, and the coating system was still functional after 2 years of exposure. Adhesion tests showed that the loss of coating adhesion caused the eventual failure of the low gloss coatings.
Keywords: Polyurethane; Coating degradation; AFM; SEM; EIS;

Changes in physical and mechanical properties of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) during degradation in a composting medium were studied. Effect of composting of up to 50 days was studied. Specimen weight loss, scanning electron microscopy (SEM), capillary viscometry, Fourier-transform infrared spectroscopy with accessory for attenuated total reflectance (FTIR-ATR), differential scanning calorimetry (DSC) and tensile testing were performed to characterize the changes in the physical and mechanical properties of PHBV during its degradation in the composting medium. The results from the analysis of weight loss, SEM, molecular weight, FTIR, DSC and tensile testing, particularly the physical and mechanical properties, suggest that the degradation of PHBV in compost medium is enzymatic rather than hydrolytic and occurs from surface and the degraded material leaches out.
Keywords: Poly(hydroxybutyrate-co-hydroxyvalerate); Degradation; Physical and mechanical properties; Composting;

Literature values of the induction time t i and maximum rate r S of oxygen absorption for unstabilised polyethylene samples have been compiled. In Arrhenius plots all of their representative points are close to straight lines of parameters:   Ln(ti0)≈−24.4; E i ≈116  kJ   mol −1   for  t i and     Ln(r S0)≈−34.2; E s ≈146  kJ   mol −1   for  r s It can be concluded that there is a quasi-universal behaviour, for the thermal oxidation of polyethylene, irrespective to branching and other structural irregularities or crystallinity. This result is consistent with the hypothesis that radical chain oxidation of PE is essentially initiated by the bimolecular decomposition of hydroperoxides provided that their initial concentration is not lower than 10−5 mol l−1 and not higher than 10−1 mol l−1.
Keywords: Polyethylene; Thermal oxidation; Kinetics;

The thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis of compatibilized blends of low density polyethylene (LDPE) and poly(dimethyl siloxane) rubber (PDMS) in the proportion of 50:50 containing different proportions of ethylene methyl acrylate co-polymer (EMA) as compatibilizer have been studied. EMA acts as a chemical polymeric compatibilizer for the binary blend system of LDPE and PDMS, the proportion of which varied from 0 to 15 wt.%. The TG and DTG of the blends show that the thermal degradation takes place in two stages, where as neat LDPE shows a three stage degradation and neat EMA and PDMS show only single stage degradations respectively. The activation energies at 10% degradation have been determined using Freeman and Carroll's method and found to be maximum (171 kJ/mol) for the blend containing 6 wt.% of EMA. Half life periods at 200 °C have been evaluated by the Flynn and Wall method and found to be maximum for the blend containing 6 wt.% of EMA.
Keywords: Thermogravimetric analysis; Activation energy; Half-life period; Compatibility and crosslinking;

Thermogravimetric study on the ageing of lime wood supports of old paintings by Irina Crina Anca Sandu; Mihai Brebu; Constantin Luca; Ion Sandu; Cornelia Vasile (83-91).
This paper presents thermogravimetric data of some samples of soft lime tree (Tillia cordata Mill) wood from the structure of the supports of old paintings (mobile icons and iconostasis) 100–200 years old. In order to determine the ageing processes, the physical, structural and chemical changes that have occurred in time under the influence of environment have been correlated with thermogravimetric data. It has been established that the thermal characteristics for the elimination of physically adsorbed water depend on the sample's age and on the conservation treatments. The variation of the thermal characteristics with the wood age is important for the main decomposition step. The temperatures for the onset and the maximum rate of degradation as well as the global activation energy increase with the wood's age while the weight loss decreases. These characteristics could be used to assess the age and conservation status of the paintings. The variation of the characteristics could be due both to the loss in time of the volatile compounds that lead to lower thermal characteristics and to the structural changes occurring in the wood that, for the highly deteriorated and/or degraded wood leads to a totally different thermal behaviour.
Keywords: Thermal degradation; Soft wood; Wood ageing; Conservation status; Collapsed wood; Old paintings;

Ozonization of electronic conducting polymersI. Copolymers based on poly[3-nonylthiophene] by Wojciech Czerwiñski; Jacek Nowaczyk; Krystyna Kania (93-101).
The ozonization of a group of new conducting copolymers based on 3-nonylthiophene and 2-substituted-3-ethylthiophene was investigated. The reaction products have been studied using solid state 13C NMR, and FTIR spectroscopy. Polymers ozonized were laboratory made copolymers: poly[3-(2-(9-anthrylcarboxy)ethyl)thiophene-co-3-nonylthiophene] (P[AET-co-3NT]), poly[3-(2-acetoxyethyl)thiophene-co-3-nonylthiophene] (P[AcET-co-3NT]), poly[3-(2-hydroxyethyl)thiophene-co-3-nonylthiophene] (P[HET-co-3NT]). Chemical and electrical stability of the polymers in ozonized air, was investigated. These properties are important due to potential application of such polymers as a electroactive components in manufacturing of light emitting diode devices (LED's). Ozone present in the troposphere is one of the strongest oxidizing agents acting on polymeric materials, especially those having unsaturated bonds. The results of this research indicate that there are no significant changes in chemical structure of P[AcET-co-3NT] after ozone treatment. But in the case of P[AET-co-3NT] and P[HET-co-3NT] significant changes in conjugated bonds system were observed. In consequence electrical properties of polymers changed. Additionally it was found that ozonization causes distinct deterioration of optical properties.
Keywords: Conjugated polymers; Substituted polythiophenes; Ozonization;

Glycolysis of waste flexible polyurethane foam by Chao-Hsiung Wu; Ching-Yuan Chang; Chien-Min Cheng; Hung-Chang Huang (103-111).
Glycolysis of flexible polyurethane (PU) was investigated to provide useful data for the recycling of waste cars. The glycolysis experiments were performed under atmospheric pressure and isothermal condition (220 °C). Diethylene glycol (DEG) and potassium acetate (KAc) were used as solvent and catalyst, respectively. The properties of glycolysis products were determined by analyzing the hydroxyl value, weight average molecular weight (M w), viscosity, and the conversion (X) of the –NCOO– functional group in PU. The results indicate that the adequate concentrations of DEG and KAc are about 150 and 1% of the mass of the PU and an adequate reaction time is 90 min. Purification experiments on the glycolysis products were carried out in a stirred flask with a shell and tube condenser. The distilled materials were collected at the gas-phase temperature ranges of <245, 245–260, 260–275, 275–290, and >290 °C. The polyol-containing products are mostly in the temperature range of 245–260 °C. The recovery of polyol-containing products can be achieved by the distillation of glycolysis products.
Keywords: Glycolysis; Polyurethane; Recycling; Waste cars;

New combined phenol/hindered amine photo- and thermal-stabilizers based on toluene-2,4-diisocyanate by J. Mosnáček; Š. Chmela; G. Theumer; W.D. Habicher; P. Hrdlovič (113-126).
Reactions of toluene-2,4-diisocyanate with different phenols and different HAS (hindered amine stabilizers) were used to prepare new combined phenol/HAS. As a phenol 2-tert-butyl-4-methoxyphenol (I); 2-tert-butyl-4-methylphenol (II); 2,4-di-tert-butyl-6-methylphenol (III) and 2,4-di-tert-butylphenol (IV) were used. HAS represented 4-hydroxy-2,2,6,6-tetramethylpiperidine (TMP), 4-hydroxy-1,2,2,6,6-pentamethyl-piperidine (PMP), 4-amino-2,2,6,6-tetramethylpiperidine (ATP), 4-N-butyl-amino-2,2,6,6-tetramethyl-piperidine (BATP) and 4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl (TMP-NO ·). Symmetrical phenol–phenol and HAS–HAS were also prepared. The synthesized compounds were tested as light and thermo stabilizers in polypropylene (PP). Non-oxidized as well as partially oxidized PP was used. The stabilizing efficiency depends on the structure of the phenol as well as the HAS. Concerning the phenol structure the best efficiency at photo oxidation was obtained with combined phenol/HAS containing 2,6-disubstituted phenol III for all HAS used. Efficiencies of phenols with just one substituent in the ortho position in combined additives were much lower. This difference was rather small in the case of thermo oxidation. Among the HAS the best performance was obtained from derivatives of TMP and PMP in photo oxidation of non-oxidized PP matrix. PMP derivatives in contrast to TMP ones did not stabilized partially oxidized PP very well. The efficiency of combined phenol/HAS was much higher than the efficiency of symmetrical HAS/HAS despite two times higher concentration of the active part in the symmetrical molecules. All combined additives showed very good ability to stabilize PP against thermo-oxidation. The highest efficiency was reached with TMP derivatives—about 12 000 to 14 000 h to reach carbonyl absorption 0.2 at 110 °C.
Keywords: Stabilization; Thermo-oxidation; Photo-oxidation; Combined stabilisers; Phenols; Hindered amines; Polypropylene;

The properties of blends of polycaprolactone and starch (PCL/starch) and maleic anhydride (MAH)-grafted-polycaprolactone and starch (PCL-g-MAH/starch) were examined using Fourier transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (1H NMR), differential scanning calorimetry (DSC), and mechanical testing. Mechanical and thermal properties of PCL became noticeably worse when it was blended with starch, due to the poor compatibility between the two phases. The greater compatibility of PCL-g-MAH with starch, owing to the formation of an ester carbonyl group, led to a much better dispersion and homogeneity of starch in the PCL-g-MAH matrix and consequently to noticeably better properties. Furthermore, with a lower melt temperature, the PCL-g-MAH/starch blend is more easily processed than PCL/starch. Both blends were buried in soil to assess biodegradability. Water resistance of PCL-g-MAH/starch was higher than that of PCL/starch, although weight loss of blends buried in soil indicated that both were biodegradable, even at high levels of starch substitution. In soil, the mechanical properties of both blends, such as tensile strength and elongation at break, also deteriorated.
Keywords: Blends; PCL-g-MAH/starch; Mechanical and thermal properties; Biodegradability;

Kinetics of thermal degradation of flame retardant copolyesters containing phosphorus linked pendent groups by Hong Zhao; Yu-Zhong Wang; De-Yi Wang; Bo Wu; Dan-Qi Chen; Xiu-Li Wang; Ke-Ke Yang (135-140).
The thermal decomposition behaviour of phosphorus-containing copolyesters were studied using a conventional dynamic thermogravimetric analysis (TG) in a flowing air atmosphere at several heating rates between 10 and 40 °C/min. The activation energy was determined by using Kissinger method, Flynn–Wall–Ozawa method and Friedman method. The results for copolyesters with the phosphorus linkage as pendent groups, which were synthesized from the condensation of terephthalic acid (TPA), ethylene glycol(EG) and 9,10-dihydro-10 [2,3-di (hydroxy carbonyl) propyl] 10-phosphaphenanthrene-10-oxide (DDP), were compared with those of poly (ethylene terephthalate) (PET) and copolyesters with phosphorus linkage in the main chain, which were synthesized from TPA, EG and 2-carboxyethyl(phenylphosphinic) acid (CEPP). It is shown that the presence of the bulky pendent phosphorus side group in the copolyester tends to decrease the activation energy for decomposition in air.
Keywords: Thermal degradation kinetics; Phosphorus-containing copolyester; Flame retardant;

Thermal degradation kinetics of uncapped and end-capped poly(propylene carbonate) by Shuwen Peng; Yuxian An; Cheng Chen; Bin Fei; Yugang Zhuang; Lisong Dong (141-147).
In order to improve its thermal stability, poly(propylene carbonate)(PPC) was end-capped by different active agents. Thermogravimetric data show that the degradation temperature of uncapped PPC was lower than that of end-capped PPC. The kinetic parameters of thermal degradation of uncapped and end-capped PPC were calculated according to Chang's method. The results show that different mechanisms operate during the whole degradation temperature range for uncapped PPC. In the first stage, chain unzipping dominates the degradation. With increasing temperature, competing multi-step reactions occur. In the last stage, random chain scission plays an important role in degradation. For end-capped PPC, random chain scission dominates the whole degradation process.
Keywords: Poly(propylene carbonate); Thermal degradation; TG; Kinetics;

The effect of additives on the thermal degradation of cellulose acetate by Maria da Conceição C Lucena; Ana Ellen V. de Alencar; Selma Elaine Mazzeto; Sandra de A Soares (149-155).
The thermal degradation of pure cellulose acetate and cellulose acetate with mono ammonium phosphate and boric acid as physically incorporated additives, was investigated using thermogravimetry analysis, thermal volatilization analysis and characterization of the degradation products by infrared spectroscopy. The additives modified the degradation process by decreasing the thermal stability of the polymer, enhancing the char and reducing the volatile formation. The addition of ammonium phosphate and boric acid together showed a synergistic effect in increasing char quantity. In this case a decrease in thermal stability was not observed. The analysis of degradation products showed that the cellulose acetate decomposition occurred by scission of glycosidic linkages followed by pyranose ring rupture and acetic acid evolution. Kinetic parameters, like activation energy, were calculated following the Ozawa method using dynamic thermogravimetric data.
Keywords: Cellulose acetate; Thermal degradation; Additives; Synergistic effect; Kinetics of degradation;

Synthesis and characterization of polycarbonate/ABS/montmorillonite nanocomposites by Shaofeng Wang; Yuan Hu; Zhengzhou Wang; Tang Yong; Zuyao Chen; Weicheng Fan (157-161).
Polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) polymer alloy/montmorillonite (MMT) nanocomposites have been prepared by direct melt intercalation. Their structure and thermal properties are characterized by XRD, TEM, HREM and TGA. The results of XRD and HREM show that nanocomposite is a kind of intercalated structure and the gallery heights of PC/ABS/MMT nanocomposites are almost the same as that of PC/MMT nanocomposite, 3 nm; meanwhile, the nanocomposites improves the thermal stability of PC/ABS polymer alloy matrix.
Keywords: Nanocomposites; Intercalated; XRD; PC/ABS;

Polyethylene (PE)–clay nanocomposites have been prepared using melt blending in a Brabrender mixer. X-ray diffraction and transmission electron microscopy were used to characterize the nano-structure of these composites while the thermal stability was evaluated from thermogravimetric analysis and the flammability parameters using cone calorimetry. It is found that the PE–clay nanocomposites have a mixed immiscible-intercalated structure and there is better intercalation when maleic anhydride is combined with the polymer and clay to be melt blended. The reduction in peak heat release rate is 30–40%.
Keywords: Nanocomposites; Polyethylene; Cone calorimetry;

Nanocomposites of polystyrene and polypropylene with organically-modified clay may be prepared by melt blending in a Brabender mixer the clay and the polymer. The presence of maleic anhydride increases the likelihood of nanocomposite formation for polystyrene but is less important for polypropylene. The materials that result are immiscible materials, in that the clay is not uniformly distributed throughout the polymer matrix, but there is polymer inserted between the clay layers. The results from cone calorimetry suggest that nanocomposite formation has occurred, since there is a significant reduction in the peak heat release rate.

Large-scale fermentative production of poly(3-hydroxybutyrate-co-5mol% 3-hydroxyhexanoate) [P(3HB-co-5mol% 3HHx)] from soybean oil as sole carbon source is simulated using a recombinant strain of Ralstonia eutropha harboring a polyhydroxyalkanoate (PHA) synthase gene from Aeromonas caviae. Its production costs, life cycle inventories (LCI) of energy consumption and carbon dioxide emissions from the cradle-to-factory gate are calculated and compared with the counterparts for microbial production of poly(3-hydroxybutyrate) [P(3HB)] from glucose as sole carbon source. In addition, the values of bio-based polymers are compared with those of petrochemical polymers. Annual production of 5000 tonnes of P(3HB-co-5mol% 3HHx) is estimated to cost from 3.5 to 4.5 US$/kg, depending on presumed production performances. Similar scale production of P(3HB) from glucose is estimated to cost 3.8–4.2 US$/kg. In contrast to the comparable production costs between P(3HB-co-5mol% 3HHx) and P(3HB), life cycle inventories of energy consumption and carbon dioxide emissions favor the former product over the latter, reflecting smaller inventories and higher production yields of soybean oil compared to glucose. The life cycle inventories of energy consumption and carbon dioxide emissions of bio-based polymers are markedly lower than those of typical petrochemical polymers.
Keywords: Polyhydroxyalkanoates; Bio-based polymers; Renewable carbon sources; Production cost; Life cycle inventory; CO2 emissions;