Polymer Degradation and Stability (v.83, #1)

Thermal degradation of poly(ethylene terephthalate) at the processing temperature by Filippo Samperi; Concetto Puglisi; Rossana Alicata; Giorgio Montaudo (3-10).
Several isothermal degradation experiments on poly(ethylene terephthalate) (PET) were conducted in the temperature range of 270–370 °C, in order to simulate the reactions that take place during the processing of PET under inert atmosphere (N2). The structural characterisation of the reaction products was performed by MALDI mass spectrometry and by NMR analysis. The results indicate the formation of cyclic oligomers that decompose at higher temperature. Vinyl ester terminated oligomers could not be detected by MALDI and also by 1H and 13C NMR, whereas the formation of anhydride containing oligomers is well apparent. Formation of acetaldehyde in PET samples processed at various temperatures was detected by 1H NMR. We have also included in the present study a set of experiments where 0.5%w p-TsOH·H2O was added to PET. Our results show that the addition of small amounts of p-TsOH·H2O to PET, heated at 270 and 285 °C, induces a strong hydrolytic reaction with consequent increase of carboxyl terminated polyester chains.
Keywords: PET; Thermal degradation; MALDI–TOF MS; p-Toluene sulphonic acid;

Thermal degradation of poly(butylene terephthalate) at the processing temperature by Filippo Samperi; Concetto Puglisi; Rossana Alicata; Giorgio Montaudo (11-17).
In an accompanying paper [Samperi et al., Polym Degrad Stab (in press)] we have reported an investigation on the isothermal degradation of poly(ethylene terephthalate) (PET) and present here a parallel study on poly(butylene terephthalate) (PBT). Although the two aromatic polyesters are structurally quite similar, our results show that the presence of the butylene unit in PBT is apparently able to induce significant changes in the isothermal degradation of PBT compared to PET. A rationalisation of the differences observed is offered. Several isothermal degradation experiments on PBT were conducted in the temperature range of 270–350 °C, in order to simulate the reactions that take place in the actual processing of PBT. The structural characterisation of the reaction products was performed by MALDI Mass Spectrometry and by NMR analysis. The results indicate that the cyclic oligomers of PBT formed at temperatures below 290 °C by ring-chain equilibration mechanism undergo thermal decomposition at higher temperature by a β-hydrogen transfer mechanism, as well as the open PBT chains. The formation of unsaturated oligomers was detected by MALDI and also by 1H and 13C NMR techniques, whereas in contrast to the thermally degraded PET sample terephthalic anhydride-containing oligomers were not observed. Formation of butadiene was suggested by 1H NMR data on PBT samples processed at various temperatures.
Keywords: PBT; Thermal degradation; MALDI;

Vinyl acetate/butyl acrylate copolymers—part 1: mechanism of degradation by S Duquesne; J Lefebvre; R Delobel; G Camino; M LeBras; G Seeley (19-28).
This work deals with the mechanism of degradation of vinyl acetate/butyl acrylate (VA/BA) copolymers varying the VA/BA ratio. It is shown that for higher VA contents, the degradation starts at comparatively lower temperature but a more thermally stable material is formed. The mechanism of degradation of VA/BA copolymers is then compared with PVA and PBA homopolymers. It appears that the fractions of degradation (gases, high boiling products and residue) for VA/BA copolymer is a combination of those of polyvinyl acetate (PVA) and polybutyl acrylate (PBA). However, a slight stabilisation occurs when VA/BA are co-polymerised together compared with a VA and BA combination. Moreover, the comparison of the thermo-oxidative degradation with the pyrolysis demonstrates that the mechanisms are similar at least up to 450 °C.
Keywords: Thermal degradation; Vinyl acetate; Butyl acrylate; Copolymer;

Additional XPS studies on the degradation of poly(methyl methacrylate) and polystyrene nanocomposites by Jianxin Du; Jianqi Wang; Shengpei Su; Charles A. Wilkie (29-34).
XPS studies have been undertaken on exfoliated nanocomposites of polystyrene and poly(methyl methacrylate). One can clearly see that carbon is lost and that oxygen, silicon and aluminum accumulate at the surface of the degrading polymer. The concentration of aluminum at the surface is very low at the beginning of the experiment but makes a large jump at the same temperature at which carbon is lost and oxygen begins to accumulate at the surface. It appears that the ratio of silicon to aluminum changes as the polymer is lost. A brief discussion is given to explain the origin of oxygen at the surface.
Keywords: Thermal degradation; XPS; PMMA; PS; Nanocomposites;

For the purpose of increasing degradability of polystyrene (PS) and poly(vinyl chloride) (PVC), they were modified by means of introducing 1–5% addition of ketone (acetophenone or benzophenone). The influence of UV radiation on thin films of polymers modified in this way was studied. The changes in chemical structure of PS and PVC were studied using UV–vis and FTIR spectroscopy, the degradation reactions were monitored by determining the average molecular weights and polydispersity by gel chromatography, and the crosslinking reactions were estimated by determining the weight content of insoluble gel. The mechanical properties were studied by using standard tensile testing measurements. It was found that the ketones used, acting as sensitizers and/or initiators, caused some considerable changes of photochemical stability of both polymers. The oxidative photodegradation of PS, carried out in the same conditions and presence of the same quantity of modifying additives, is accelerated by a considerably higher rate in comparison to the analogous processes occurring in PVC. The differences in the course of photochemical processes of both irradiated polymers are related to the different miscibility of components. At the same time the limited efficiency of photocrosslinking and only slight deterioration of mechanical properties in PS with added acetophenone or benzophenone suggest the possibility of using such compositions for the manufacture of plastics degradable in natural environment.
Keywords: Polystyrene; Poly(vinylchloride); Photo-oxidative degeneration; Degradable packaging materials;

Degradation of wheat straw lignin and hemicellulosic polymers by a totally chlorine-free method by Xiao Feng Sun; R.C. Sun; J. Tomkinson; M.S. Baird (47-57).
Wheat straw lignin and hemicelluloses were degraded in a totally chlorine-free medium containing 80% acetic acid and 0.92–13.5% nitric acid. Effect of treatment time and temperature as well as nitric acid concentration on the efficiency of degradation of lignin and hemicellulosic polymers and on the yield of cellulose were comparatively investigated. The treatment with 80% acetic acid and 0.92% nitric acid as a catalyst at 120 °C for 20 min resulted in over 81% original hemicelluloses and 92% original lignin degradation. As the nitric acid concentration raises to 8.5%, over 96% original hemicelluloses and approximately 98% original lignin were degraded, yielding the cellulose approaching 96% purity. The characterisation of isolated cellulosic preparations was performed by their intrinsic viscosity, molecular weight, FT-IR, CP-MAS 13C-NMR, and thermal studies. The results showed that the treatment using 80% acetic acid and nitric acid as a catalyst under the conditions given also resulted in somewhat acetylation of the cellulose and decreased the degree of crystallinity of cellulose except for significant degradation of lignin and hemicellulosic polymers. The thermal stability of the cellulose declined with a decrease in its intrinsic viscosity
Keywords: Deagradation; Hemicelluloses; Lignin; Cellulose; Wheat straw; Chlorine-free; CP/MAS 13C-NMR;

α-Ethynylnaphthalene has been polymerized into poly(ethynylnaphthalene) (PEN) using [Rh(norbornadiene)Cl]2 in the presence of amines, such as triethylamine and/or S-(−)-methylbenzylamine, as co-catalyst in toluene. In these conditions the yields were low but the molecular weight was relatively high. Improved yields were obtained by polymerizing α-ethynylnaphthalene in tetrahydrofuran using a strong base such as t-BuOK; the molecular weight was low. PEN has been studied by FT-IR and electronic spectroscopy and also the optical activity has been checked polarimetrically but unsuccessfully on samples of PEN prepared in presence of the chiral amine S-(−)-methylbenzylamine. The thermal stability of PEN under nitrogen and air flow has been studied in detail by using TGA (thermogravimetry), DTG (derivative thermogravimetry) and DTA (differential thermal analysis) in comparison to poly(phenylacetylene) (PPA). It has been shown that the experimental results about the maximum decomposition rate and the char residue are in good agreement with theoretical calculations made with the group increment method of Van Krevelen. The oxygen index of PEN has been estimated together with that of PPA. It is concluded that PEN can be considered a non-flammable polymer.
Keywords: Ethynylnaphthalene; Arylacetylene; Polymerization; Rhodium; Chemical structure; Thermal properties;

We present an assessment on error of the pre-exponential factor estimated from the isoconversional plot and the single heating rate plot for dynamic thermogravimetric measurement. It is found that the pre-exponential factor obtained at the correct reaction order usually has about −10% error in value. The use of a wrong reaction order can lead to a variation in the value of the pre-exponential factor by several times, sometimes even several hundred times. Curve simulation is a careful method for obtaining kinetics parameter values. Only perfect agreement of simulation curve with the experimental one can give the correct kinetic parameters.
Keywords: Arrhenius equation; Pre-exponential factor; Kinetics; nth-Order model; Reaction order;

The structure and thermal degradation of a boron-containing bisphenol-F formaldehyde resin (BBPFFR) synthesized by the formalin method have been studied. The results showed that a six-membered ring containing boron–oxygen coordinate linkage was formed in the thermosetting process, and the coordinated oxygen atom was provided by the phenolic hydroxyl. The degradation of this resin began with the oxidation and breakage of ether linkages and carbonyl groups. The kinetic parameters of thermal degradation were determined by thermogravimetric analysis.
Keywords: Boron-containing phenol-formaldehyde resin; Bisphenol-F; Boric acid; Thermal analysis;

High yield production of polyhydroxyalkanoates from soybean oil by Ralstonia eutropha and its recombinant strain by Prihardi Kahar; Takeharu Tsuge; Kazunori Taguchi; Yoshiharu Doi (79-86).
High yield production of polyhydroxyalkanoates (PHAs) by Ralstonia eutropha H16 and its recombinant strain PHB4/pJRDEE32d13 (a PHA-negative mutant harboring Aeromonas caviae PHA synthase gene, phaC Ac ) from renewable inexpensive soybean oil was investigated. The PHA production by the wild-type strain H16 was achieved with a high dry cells weight (118–126 g/l) and a high poly[(R)-3-hydroxybutyrate] [P(3HB)] content per dry cells of 72–76% (w/w). A copolymer of 3HB with 5 mol% (R)-3-hydroxyhexanoate, P(3HB-co-5 mol% 3HHx), could be produced from soybean oil as a sole carbon source by the recombinant strain PHB4/pJRDEE32d13 with a high dry cells weight (128–138 g/l) and a high PHA content of 71–74% (w/w). The reproducible results of PHA production in the presence of soybean oil as a sole carbon source was obtained with a high yield at a range of 0.72 to 0.76 g-PHA per g-soybean oil used.
Keywords: High yield production; Plant oils; Polyhydroxyalkanoates; Recombinant Ralstonia eutropha; Soybean oil;

Stabilization and mechanical properties of biodegradable aliphatic polyesteramide and its filled composites by Yaobang Zou; Lu Wang; Hailian Zhang; Zhiyong Qian; Li Mou; Jiyu Wang; Xiaobo Liu (87-92).
The stabilization of polyesteramide (PEA) was studied by TGA, melt index and intrinsic viscosity. Primary antioxidant A1010 (0.6 wt.%) combined with 0.2 wt.% of hydroperoxide decomposer A168 is effective in stabilizing PEA; but the holding life of PEA in the extruder barrel is only 30 min, and the antioxidants are completely consumed when it is extruded four times. Fillers including heavy calcium carbonate (HCC), tricalcium phosphate (TCP) and talc affect both the thermal stability and mechanical properties of the resultant composites, which are discussed in detail. The Turcsanyi model can best describe the composition dependence of tensile strength of the HCC and talc filled PEA, and the Sato-Furukawa can best predict the Young's modulus of HCC filled PEA, but is poor for the talc-filled material
Keywords: Polyesteramide; Talc; Calcium carbonate; Tricalcium phosphate; Composite; Stabilization; Mechanical properties;

Hydrolytically degradable PET/PEG block copolymer was synthesized by the macromolecular transesterification method from PET and PEG. Non-isothermal crystallization behavior of the copolymers was investigated by differential scanning calorimetry (DSC). Water absorption and in vitro degradation behaviour of these copolymers were studied in detail. When hydrophilic PEG was incorporated into the PET chain, water absorption increased. With the increase in PEG concentration, the degradation rate increased accordingly. PEG molecular weight has different effects on PET/PEG copolymers’ degradation rate.
Keywords: Block copolymer; PET/PEG; Thermal property; Hydrolytic degradation; Poly(ether-ester)s;

Two series of poly(ester-urethane) block copolymers were synthesized from bacterial telechelics, hydroxylated poly[(R)-3-hydroxybutyrate] (PHB-diol), as hard segments, and either poly(butylene glycol adipate)-diol (PBA-diol) or poly(diethylene glycol adipate)-diol (PDEGA-diol), as soft segments, using 1,6-hexamethylene diisocyanate as a non-toxic connecting agent. The content of PHB hard segments systematically varied from 10 to 60 wt.%. The synthesized materials were characterized by 1H NMR, GPC, differential scanning calorimetry, thermogravimetric analysis, wide angle X-ray diffraction, and tensile properties. The crystallization characteristics, reflecting the segmented properties of the synthesized copolymers, are discussed. For poly(ester-urethane)s, based on PHB-diol and PBA-diol, with PHB content less than 50 wt.%, both PBA and PHB crystalline phases, were detected. In contrast, in poly(ester-urethane)s, derived from PHB-diol and PDEGA-diol, only one crystalline phase, corresponding to the PHB hard segments, was observed. The thermogravimetric results of the prepared copolymers showed three-step decomposition assigned to the thermal degradation of PHB hard, PBA or PDEGA soft blocks, and urethane linkage, respectively. The tensile properties indicated that the tensile strength and elongation at the break points of poly(ester-urethane)s, derived from PHB and PBA, are greater than those prepared from PHB and PDEGA. The biodegradability was studied in compost-derived culture. The extent of mineralization was dependent on the copolymer composition. At a comparable incubation time, the copolymers containing 50 wt.% PHB were mineralized to an extent similar to that of the PHB homopolymer.
Keywords: Poly(R-3-hydroxybutyrate)-diol; Poly(ester-urethane)s; Thermal behaviour; Mechanical properties; Biodegradability;

Stress relaxation and thermogravimetric studies on room temperature vulcanised polysiloxane rubbers by Mogon Patel; Mark Soames; Anthony R. Skinner; Thomas S. Stephens (111-116).
The stress relaxation properties of foamed polysiloxane rubbers are important as they can influence the useful life of components made from such a polymer system. Of particular interest is understanding the changes in properties with time and temperature and whether the mechanisms responsible for stress relaxation are able to induce other material property changes. The stress relaxation properties of Dow Corning S5370 polysiloxane samples, aged under controlled conditions, have been measured using a Thermomechanical analyser (TMA) at a number of different temperatures. The results were assessed using the principle of Time-Temperature Superposition. Derived acceleration factors showed good adherence to the Arrhenius relationship and showed two regions where processes with different activation energies dominate. A transition region where there is a change in the predominant degradation process is evident at around 120 °C. Thermogravimetric analysis (TGA) studies were used to provide an improved understanding of the degradation at elevated temperatures (>120 °C). Time-temperature superposition and Arrhenius treatment of the TGA results reveal an activation energy (75±6 kJ/mol) which correlates closely to that derived from stress relaxation (65±5 kJ/mol). Overall, these observations suggest that the degradation processes at elevated temperatures which influence stress relaxation also induce significant weight loss. The dominant degradation process at elevated temperatures(>120 °C) is most probably silicone head to tail unzipping reactions resulting in the production of volatile cyclic species.
Keywords: Polysiloxane rubber; Stress Relaxation; Weight loss;

Photochemical stability of collagen/poly (vinyl alcohol) blends by Alina Sionkowska; Joanna Skopińska; Marcin Wisniewski (117-125).
The photochemical stability of blends of collagen and poly(vinyl alcohol) has been studied by Fourier transform infrared spectroscopy (FTIR), UV–vis spectrophotometry, differential scanning calorimetry (DSC) and viscometry. Mechanical properties of the blends before and after UV irradiation were studied. Surface properties before and after UV irradiation were monitored using atomic force microscopy (AFM) and optical microscopy. The new materials obtained have different thermal, mechanical and photochemical stability than those of single components. They are more stable thermally and photochemically, but they have worse mechanical properties than pure collagen films.
Keywords: Collagen; Poly(vinyl alcohol); UV irradiation; Biomaterials;

Degradable polyesteramide fibres were processed by melt-spinning. Tensile properties of as-spun and hot-drawn fibres were also investigated. After drawing, the overall crystallinity and the melting temperature of the copolymer increased. As a result, the tensile strength of the fibre increased, and the elongation at break decreased. The morphology of the surface and fracture cross section were studied by SEM. During alkaline degradation, the tensile strength and the elongation at break both decreased.
Keywords: Polyesteramide; Degradable polymer; Fibre; Thermal property; Tensile property;

The synthesis of acrylic weak base anion exchangers by the aminolysis reactions of ethylacrylate:acrylonitrile:divinylbenzene copolymers with ethylenediamine or triethylene-tetramine was performed. The resins were characterized by the density (W w), volume and weight exchange capacities (C v and C wt, respectively). Also, the chemical stability of the synthesized anion exchangers in aggressive media, such as H2O2; NaOCl; NaOCl+NaOH; NaOCl+FeSO4 was studied. The results are compared with those obtained for a commercial acrylic base anion exchanger, Purolite A-830. The most aggressive agent, which causes a serious degradation for all anion exchangers, is an aqueous solution of NaOCl, alone or in the mixture with 5 N NaOH or FeSO4. The acrylic weak base anion exchangers with permanent porosity have a higher resistance than those with the porosity in the swollen state. The resins with ethylenediamine functional groups have the highest chemical stability in the studied aggressive media.
Keywords: Acrylic weak base anion exchanger; Aminolysis–hydrolysis reaction; Chemical stability; Aggressive media;

Weathering tests were carried out on high-density polyethylene (HDPE) HDPE–CaCO3 composites exposed to tropical humid climate of Yucatan peninsula of Mexico, in two different environments: a rural–urban (RU) and marine–coastal (MC) one. The samples were analyzed for changes of physical and chemical properties, with respect to their thermal behavior, infrared absorption and molecular weight. Data obtained in this study, by means of FT-IR, DSC, and viscometry techniques, show that the actual weathering process can be extremely complex, involving a number of weathering factors acting together and resulting in other process interactions within or on the material. Despite the differences between RU and MC temperature–relative humidity daily values, the environmental temperature seems to be the key factor that impacts the rate of aging more than the ambient humidity. The presence of the mineral filler CaCO3 influences the HDPE degradation mechanism, whereas the environmental conditions only modify the rate of polymer degradation.
Keywords: High-density polyethylene; Mineral filler; Degradation; Natural weathering;

Computational study of metathesis degradation of rubber. distributions of products for the ethenolysis of 1,4-polyisoprene by Selena Gutierras; Sergio Martinez Vargas; Mikhail A. Tlenkopatchev (149-156).
The molecular modeling of the product distributions for the ethenolysis of 1,4-polyisoprene at 25 °C using the B3LYP/6-31G(d,p) level of theory reveals that chain–ring and chain–chain equilibria are completely shifted toward the formation of 2-methyl-1,5-hexadiene. The amount of cyclic oligomers at equilibrium with linear molecules is small. The concentration of 2-methyl-1,5-hexadiene at equilibrium with linear isoprene oligomers is of 90 mol%. The value of 1,5-hexadiene at equilibrium with butadiene oligomers for the ethenolysis of 1,4-polybutadiene corresponds to 46 mol%. These results are in agreement with experimental data.
Keywords: Ab initio calculations; Metathesis degradation; 1,4-Polyisoprene;

Impact of thermal ageing on the tin catalyst species in room temperature vulcanised polysiloxane rubbers by Mogon Patel; Anthony R Skinner; Amiya Chaudhry; Norman C Billingham; Bernard Mahieu (157-161).
Tin 2-ethylhexanoate is used as a catalyst in the synthesis of room temperature cured polysiloxane rubbers. The catalyst has the potential to influence the important load bearing and ageing properties of the rubber. In this study, the structure of the catalyst and the nature of the tin species in both fresh and thermally aged polysiloxane samples (RTV5370) have been investigated. Infra-red and 13C NMR of the catalyst confirms the presence of 2-ethyl hexanoate ligands on the tin. Mössbauer Spectroscopy of the catalyst shows that the tin exists predominantly in the tin(II) oxidation state with some residual tin(IV) impurities. The tin(IV) phase predominates in the as-synthesised rubber, representing some 67% of the total tin signal, with the remainder being unreacted tin(II) species. The tin(IV) phase in the catalyst and that in the rubber are different. Overall, our observations suggest that the catalyst has taken part in the cure reaction and has been chemically modified as a result. The isomer shift (IS) and the quadrupole splitting (QS) from Mössbauer Spectroscopy suggests that the tin (IV) phase in the rubber is most probably SnO2 (stannic oxide). Toluene extraction studies show that this phase is not extractable from the rubber network, whereas the tin(II) species is easily removed. Both high temperature and room temperature ageing increase the proportion of the tin(IV) in the rubber.
Keywords: Polysiloxane rubber; Tin catalyst; Mössbauer spectroscopy; Thermal ageing;

Technological parameters of pyrolysis of waste polytetrafluoroethylene by Egbert Meissner; Agnieszka Wróblewska; Eugeniusz Milchert (163-172).
The results of the pyrolysis of waste polytetrafluoroethylene (PTFE) to the useful compounds: tetrafluoroethylene, hexafluoropropylene, octafluorocyclobutane and heavy ends (mainly 1- and 2-octafluorobutylene) are presented. The studies were carried out in a two-stage reactor, where the second stage also consisted of two sections. The influence of temperature, pressure, nitrogen flow rate, PTFE feed rate, and residence time of the pyrolysis products in the high temperature reaction zone on the yields of the resulting compounds was investigated. The optimum parameters for the synthesis of these compounds were established using process optimisation by the method of rotary-uniform design of experiments.
Keywords: PTFE; Pyrolysis; Tetrafluoroethylene; Heksafluoropropylene; Octafluorocyclobutane;

Studies on tyre cords: degradation of polyester due to fatigue by Amit K. Naskar; A.K. Mukherjee; R. Mukhopadhyay (173-180).
A comparison of physical characteristics of nylon 6, nylon 66 and polyester tyre cords was made. Polyester was found to have excellent dimensional stability in comparison to others. Service conditions of the tyre cords were simulated by applying cyclic compression and tension onto the cord reinforced rubber composite specimens at different strain levels (±10 and ±15%) and time using a Goodrich compression and tension (C–T) fatigue tester. Fatigued cords were taken out from the composites and their tensile properties were measured. Polyester was found to have poor fatigue resistance. At very high strain level (±15%) and after 120 h continuous run nylon 66 registered very good fatigue strength retention (80%) while nylon 6 showed 62% retention but polyester cord failed and broke before taking out from the composite. Poor fatigue property of polyester was attributed to the degradation of the cord as observed by decrease in intrinsic viscosity with fatigue time and poor adhesion to matrix. Apart from heat generation, mechanical scission, organic amines present in the rubber compound possibly catalysed the degradation of the polyester cords. Scanning electron microscopy showed a combination of brittle and ductile failure in the polyester filament due to fatigue.
Keywords: Tyre cord; Polyester; Nylon; Degradation; Fatigue;

Several Si-containing methacrylates and acrylates have been free radically copolymerised with methyl methacrylate and with styrene. The copolymers have been examined by DSC to determine glass transition temperatures (T g), by TGA to determine thermal stabilities, and by measurements of limiting oxygen index (LOI) to determine ignitability/flame retardance. The copolymers are found to have T gs similar to those of the parent homopolymers suggesting that the mechanical properties are little affected by the incorporation of the Si-containing groups and to have slightly improved flame retardance. LOI and char yields suggest that the mechanism of flame retardance, i.e. whether vapour phase or condensed phase, depends upon the nature of the Si-containing substituent.
Keywords: Methyl methacrylate; Styrene; Silicon-containing monomer; Copolymerisation; Thermal degradation; Flame retardance;