Polymer Degradation and Stability (v.92, #4)
Editorial board (IFC).
Investigation of thermal degradation mechanism of an aliphatic polyester using pyrolysis–gas chromatography–mass spectrometry and a kinetic study of the effect of the amount of polymerisation catalyst by D.N. Bikiaris; K. Chrissafis; K.M. Paraskevopoulos; K.S. Triantafyllidis; E.V. Antonakou (525-536).
The thermal degradation mechanism of the aliphatic biodegradable polyester poly(propylene succinate) (PPSu) and the effect of the polymerisation catalyst (tetrabutyl titanate, TBT) were studied using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) and TGA analysis. It is found from mass ions detection, that the decomposition takes place, mainly, through β-hydrogen bond scission and secondarily by α-hydrogen bond scission. At low pyrolysis temperatures (360 and 385 °C) gases as well as succinic anhydride, succinic acid and propanoic acid are mainly produced while allyl and diallyl succinates are formed in smaller quantities. At high temperatures (450 °C) the behaviour is inverted. Using the isoconversional methods of Ozawa and Friedman it is founded that PPSu degrades by two consecutive mechanisms. According to this analysis the first mechanism that takes place at low temperatures is autocatalysis with an activation energy of about E = 110–120 kJ/mol. The second mechanism is a first-order reaction with E of 220 kJ/mol, and corresponds to the extended β- and α-hydrogen bond scissions. These activation energies are slightly dependent on the catalyst amount and are shifted towards lower values with an increase of TBT content from 3 × 10−4 to 3 × 10−1 mol TBT/mol succinic acid (SA).
Keywords: Poly(propylene succinate); Degradation mechanism; Pyrolysis; Thermogravimetry;
Investigation on water treeing behaviors of thermally aged XLPE cable insulation by Chonung Kim; Zhijian Jin; Xingyi Huang; Pingkai Jiang; Qingquan Ke (537-544).
The power cable insulation is in permanence subjected to thermal aging during its operating service. Thermal aging may influence not only the electrical, physicochemical and other properties of the XLPE cable insulation, but also the initiation and propagation of water tree inside it. Our research on the influence of thermal degradation to the water treeing behavior of XLPE cable insulation shows that thermal oxidation is the most influential to the initiation and growth of water treeing from the surface of XLPE cable insulation among all the probable factors caused during thermal aging.
Keywords: Water treeing; XLPE cable insulation; Thermal aging; Weibull statistical parameter;
Degradation and thermal properties of in situ compatibilized PS/POE blends by Zhenghong Guo; Zhengping Fang; Lifang Tong; Zhongbin Xu (545-551).
This paper reported the degradation behaviors and thermal properties of polystyrene (PS)/polyolefin elastomer (POE) blends with AlCl3 as the catalyst of Friedel–Crafts alkylation reaction. Gel permeation chromatography (GPC) and thermogravimetric analysis (TGA) were adopted to reveal the effects of in situ grafting reaction and degradation of blending compounds on the thermal properties of PS/POE blends. It was found that the changes in both catalyst content and blend composition influenced the competition between in situ grafting reaction and degradation, resulting in the complexity of the thermal properties of PS/POE/AlCl3 blends.
Keywords: Polystyrene; Polyolefin elastomer; In situ compatibilization; Degradation; Thermal properties;
Racemization behavior of l,l-lactide during heating by Takayuki Tsukegi; Toru Motoyama; Yoshihito Shirai; Haruo Nishida; Takeshi Endo (552-559).
To control the depolymerization process of poly(l-lactic acid) into l,l-lactide for feedstock recycling, the racemization of l,l-lactide as a post-depolymerization reaction was investigated. In the absence of a catalyst, the conversion to meso-lactide increased with increase in the heating temperature and time at a higher rate than the conversion into oligomers. The resulting high composition of meso-lactide suggests that the direct racemization of l,l-lactide had occurred in addition to the known racemization mechanism that occurs on the oligomer chains. In the presence of MgO, the oligomerization rapidly proceeded to reach an equilibrium state between monomers and oligomers. The equilibrium among l,l-, meso-, and d,d-lactides was found to be a convergent composition ratio l,l-:meso-:d,d-lactides = 1:1.22:0.99 (wt/wt/wt) after 120 min at 300 °C. This composition ratio also indicates that in addition to the known racemization reaction on the oligomer chains, direct racemization among the lactides is also a frequent occurrence.
Keywords: Poly(l-lactic acid); l,l-[Lactide]; Chemical recycling; Racemization; Ester–semiacetal tautomerization;
Analysis of surface degradation of epoxy nanocomposite due to tracking under AC and DC voltages by R. Sarathi; P. Rajesh Kumar; R.K. Sahu (560-568).
The tracking phenomenon, a carbonaceous process, in epoxy nanocomposite material has been studied under the AC and DC voltage in the present work. It was observed that the tracking is more severe under the DC voltages, especially under positive DC voltage when compared to negative DC voltage. The leakage current during the tracking studies was measured and moving average technique was used to characterize the trend of current flow. It was noticed that an increase in nanoclay content to epoxy resin shows a reduction in magnitude of leakage current flow during tracking test. It was also observed that the magnitude of leakage current is more under negative DC voltage compared with positive DC/AC voltage. The magnitude of leakage current and the tracking time shows inverse relationship as evident from the present study. A drastic reduction in contact angle was observed for the specimens subjected to tracking test. It was confirmed that surface discharges also cause permanent damage to the insulating material. The WAXD studies indicated that up to 5 wt% of nanoclay in epoxy resin resulted in exfoliated structure. The TEM studies were carried out on the nanocomposite structures. The TG–DTA results showed that a maximum degradation of epoxy resin occurs at around 300 °C. From the EPR study it is realized that, in the tracking formed zone the spin concentration is more in epoxy nanocomposites indicating that tracking as a damage generating process.
Keywords: Epoxy resin; Nanocomposites; Insulation; Degradation; Tracking; Leakage current;
Effects of EG and MoSi2 on thermal degradation of intumescent coating by Guoxin Li; Guozheng Liang; Tingshu He; Qinli Yang; Xuefeng Song (569-579).
An intumescent flame retardant coating was prepared with resin, solvent and flame retardant system composed of ammonium polyphosphate-APP, pentaerythritol-PER and melamine-MEL. The modifiers such as molybdenum disilicide (MoSi2) and expandable graphite (EG) were used to improve the performances of the APP–PER–MEL coating. The effects of EG, MoSi2 and MoSi2/EG on the fireproofing time and char formation of the coating were investigated by using heat insulation test, thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electric microscope (SEM). The results showed that by adding modifiers, the fireproofing time was prolonged and char formation rate was evidently enhanced. The largest improvement was achieved with 9 wt.% MoSi2/5 wt.% EG, XPS analysis indicated that the performance of anti-oxidation of the coating was improved by adding EG and MoSi2, and SEM images showed that a good synergistic effect was obtained through a ceramic-like layer produced by MoSi2 covered on the surface of “open-cellular” structural char.
Keywords: APP–PER–MEL coating; Thermal degradation; Intumescent coating; Expandable graphite; Molybdenum disilicide;
Degradation of polyhydroxyalkanoates in eutrophic reservoir by T.G. Volova; M.I. Gladyshev; M.Y. Trusova; N.O. Zhila (580-586).
During the summers of 1999–2001 the dynamics of polyhydroxyalkanoate degradation in a small recreational eutrophic reservoir was studied experimentally. It has been shown that biodegradation of polyhydroxyalkanoates in the environment is determined by the structure and physicochemical properties of the polymer and by local weather conditions, which influence the state of the aquatic ecosystem. Species (clones) of bacteria able to utilize polyhydroxyalkanoates in the reservoir were identified using molecular phylogenetic analysis of 16S rRNA genes.
Keywords: 16S rDNA; Degradation; DGGE; Polyhydroxyalkanoates; Reservoir;
Organic thermal stabilizers for rigid poly(vinyl chloride). Part XIII: Eugenol (4-allyl-2-methoxy-phenol) by Magdy W. Sabaa; Riham R. Mohamed (587-595).
Eugenol (4-allyl-2-methoxy-phenol) has been examined as a thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high thermal stability value (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium–zinc soap and octyl tin mercaptide.Blending this organic stabilizer with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate together with the longer extent of discolouration of PVC stabilized by eugenol as compared with the blank and the samples stabilized with reference commercial stabilizers.A probable mechanism for the stabilizing action of eugenol has been proposed. The stabilizing efficiency is attributed partially to the stabilizer's ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.
Keywords: Poly(vinyl chloride); Eugenol; Induction period (Ts); Degradation; Thermal stability; Extent of discolouration;
The degradation of new thermally degradable thermosets obtained by cationic curing of mixtures of DGEBA and 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione) by Lidia González; Xavier Ramis; Josep Maria Salla; Ana Mantecón; Angels Serra (596-604).
The thermal degradation of thermosetting materials prepared by cationic copolymerization of mixtures of different proportions of diglycidylether of bisphenol A (DGEBA) with 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione) (MCP) initiated by ytterbium or lanthanum triflate or using a conventional initiator, BF3·MEA was investigated. To study the thermal degradation, several techniques were used such as thermogravimetry (TGA), infrared spectroscopy (FTIR) and calorimetry (DSC) and the volatiles evolved during degradation were identified by mass spectrometry. The materials prepared possess the characteristics of thermally degradable thermosets, due to the presence of ester groups in the polymer chain, which are broken at the beginning of degradation. The degradability increased when lanthanide triflates were used in the curing, especially the ytterbium salt and when the proportion of MCP in the material increased.
Keywords: Epoxy resins; Degradation; Thermosets; Cationic polymerizations; Reworkability;
Chemical and structural changes at the ABS polymer–copper metal interface by S. Kisin; F. Scaltro; P. Malanowski; P.G.Th. van der Varst; G. de With (605-610).
Creating oxygen containing moieties (hydroxyl or carbonyl) on polymer substrate surfaces is known to increase the adhesion strength of polymers to metals. However, we noticed adhesion increase with time even though no pre- or post-treatment of the polymer substrate was done. In the case of sputtered and galvanically strengthened copper coatings on acrylonitrile–butadiene–styrene polymer (ABS) substrate, the adhesion strength increased from approximately 6 J/m2 to 53 J/m2 during a 1008-h period. During this period structural and chemical changes of the polymer near the interface take place. Carbonyl functionalities developed on the ABS surface are most likely responsible for the large increase in the adhesion strength. Chemical changes of the polymer are probably a consequence of the galvanic deposition and a close contact of ABS with copper which is known to facilitate the oxidation of ABS.
Keywords: Adhesion; Metal–polymer interface; Oxidation; Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR);
Kinetics of poly(ethylene terephthalate) glycolysis by diethylene glycol. Part II: Effect of temperature, catalyst and polymer morphology by Francis Pardal; Gilles Tersac (611-616).
The influence of various parameters on the kinetics of poly(ethylene terephthalate) (PET) glycolysis by diethylene glycol (DEG), namely temperature (from 190 to 220 °C), temperature profile, catalysis and PET morphology has been studied.The results showed a strong influence of some experimental conditions (temperature and catalysis) on the mixture evolution during depolymerisation. The temperature study showed a critical temperature between 210 and 220 °C which seems to be the consequence of a better diffusion of DEG in PET, allowing easier reactions in solid phase. The initial morphology of PET scraps does not affect the rates of reactions much, in contrast to the temperature profile which has a great importance: time of PET dissolution at 220 °C is considerably shorter by heating PET and DEG separately at 220 °C before mixing, than by heating a cold mixture of the two reagents to 220 °C.
Keywords: Glycolysis; PET; Diethylene glycol; Kinetics;
Long-term performance of poly(vinyl chloride) cables. Part 1: Mechanical and electrical performances by M. Ekelund; H. Edin; U.W. Gedde (617-629).
Cables insulated with plasticized poly(vinyl chloride) were aged in air at temperatures between 80 °C and 180 °C and their conditions were assessed by indenter modulus measurements, tensile testing, infrared (IR) spectroscopy and differential scanning calorimetry (DSC). Electrical testing of oven-aged cable samples was performed in order to relate the electrical functionality during a high-energy line break (HELB) to the mechanical properties and to establish a lifetime criterion. The mechanical data taken at room temperature after ageing could be superimposed with regard to ageing time and temperature. The ageing–temperature shift factor showed an Arrhenius temperature dependence. The jacketing material showed an immediate increase in stiffness (indenter modulus and Young's modulus) and a decrease in the strain at break on ageing; these changes were dominated by loss of plasticizer by migration which was confirmed by IR spectroscopy and DSC. The core insulation showed smaller changes in these mechanical parameters; the loss of plasticizer by migration was greatly retarded by the closed environment, according to data obtained by IR spectroscopy and DSC, and the changes in the mechanical parameters were due to chemical degradation (dehydrochlorination). A comparison of data obtained from this study and data from other studies indicates that extrapolation of data for the jacketing insulation can be performed according to the Arrhenius equation even down to service temperatures (20–50 °C). The low-temperature deterioration of the jacketing is, according to this scheme, dominated by loss of plasticizer by migration.
Keywords: Poly(vinyl chloride) cables; Ageing; Mechanical properties; Plasticizer migration;
Durability of a starch-based biodegradable polymer by N. Tzankova Dintcheva; F.P. La Mantia (630-634).
The photo-oxidation and the photo-stabilization of a commercial biodegradable polymer have been investigated in order to establish the possibility of using this polymer as raw material for films for agriculture. The degradation has been followed by measuring the mechanical properties as a function of photo-oxidation time and in particular by following the elongation at break. The virgin polymer, made from maize starch and a synthetic biodegradable polyester, shows poor resistance to the UV irradiation as observed by the fast decay of the elongation at break, but the presence of small amounts of conventional UV stabilizers strongly improves the durability of this polymer. The UV stabilizers remarkably extend the induction time without modifying the photo-oxidation kinetics.Among the investigated stabilizers, the benzophenone compound seems to work slightly better than the benzotriazoles, than the triazine and than the sterically hindered amine. This behaviour has been attributed to the larger absorbance in the UV range of the biodegradable polymer.
Keywords: Starch-based biodegradable polymers; Durability; Anti-UV stabilizers; Mechanical properties;
Understanding the role of nanosilica particle surfaces in the thermal degradation of nanosilica–poly(methyl methacrylate) solution-blended nanocomposites: From low to high silica concentration by Nuria García; Teresa Corrales; Julio Guzmán; Pilar Tiemblo (635-643).
Nanocomposites of poly(methyl methacrylate) and 12 nm silica particles have been prepared by a casting procedure which allows the homogeneous dispersion of up to 35 wt% of silica. Twelve nanocomposites with compositions ranging from 1 to 35 wt% have been prepared and studied by Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, Thermogravimetric Analysis and Isothermal Chemiluminescence. Thermal stability increases outstandingly as soon as 1 wt% of silica is added to PMMA. This effect is well-known but had not been explained up to now. Of the two main processes which initiate degradation in PMMA, radical formation at labile chain ends and random chain scission, it is the former which disappears in composites with 3 wt% of silica. The origin of the thermal stabilization in these polymer composites is thus the blocking of the PMMA chain end by the silica particle. At the same time, viscous flow decreases progressively, and composites with 20 wt% of silica or over are dimensionally stable even if heated at 300 °C for several hours. The concomitant decrease of viscous flow and increase of low temperature thermal stability shift the temperature range of application of these composites strongly, and the understanding of the silica surface role allows envisaging the control of the behaviour.
Keywords: Poly(methyl methacrylate); Silica; Composites; Chain ends; Thermal stability;
In vitro screening of the action of non-steroidal anti-inflammatory drugs on hypochlorous acid-induced hyaluronan degradation by Monika Stankovská; Juergen Arnhold; Jozef Rychlý; Holger Spalteholz; Peter Gemeiner; Ladislav Šoltés (644-652).
The antioxidative effect of two non-steroidal anti-inflammatory drugs was studied in vitro by measuring the kinetics of degradation of high-molecular weight hyaluronan (HA) in a system comprising hypochlorous acid + CuCl2 + ascorbic acid using a Brookfield rotational viscometer equipped with a Teflon cup and spindle of coaxial cylindrical geometry. The changes in HA chemical structure were investigated by chemiluminometry. When sodium naproxen was added to the system during a running degradative process its inhibitory effect was clearly shown. The inhibition was dependent on the drug concentration. However, when this drug was added to the system before the initiation of HA degradation, no inhibition was seen even at the highest drug concentration tested. The inhibitory effect of acetylsalicylic acid was achieved with a relatively low concentration of the drug and was independent of the experimental model used.
Keywords: Hyaluronan degradation; Hypochlorous acid; Non-steroidal anti-inflammatory drugs; Rotational viscometry; Chemiluminometry;
Evolution of wood surface free energy after heat treatment by Philippe Gérardin; Marko Petrič; Mathieu Petrissans; Jacques Lambert; Jean Jacques Ehrhrardt (653-657).
Surface free energies of pine and beech wood were investigated before and after heat treatment using the Lifshitz–van der Waals/acid–base approach from contact angles measured by the Wilhelmy method. The results obtained showed that the decrease of the electron-donating component of the acid–base component was the major parameter affecting the wetting of the modified wood's surface. The Lifshitz–van der Waals component was slightly modified after heat treatment indicating that the atomic and molecular interactions due to permanent or induced dipoles between wood macromolecules were weakly modified. Modification of the surface chemical composition was studied by X-ray photoelectron spectroscopy (XPS) and titration of acidity. XPS indicated an important decrease of the O/C ratio after heat treatment explaining the decrease of the electron-donating component (γ −) of the surface free energy. The decarboxylation and degradation of glucuronic acids present in hemicelluloses, demonstrated by titration of carboxylic acid functions of wood, had only limited effect on the electron-accepting component (γ +).
Keywords: Acidity; Heat treatment; Surface free energy; Wettability; Wood; X-ray photoelectron spectroscopy;
Enzymatic and anaerobic degradation of amylose based acrylic copolymers, for use as matrices for drug release by J. Alias; I. Goñi; M. Gurruchaga (658-666).
The aim of this investigation is the use of starch for effective colon-targeted drug delivery. To this end, high-amylose starch-based copolymers were tested as matrices for drug delivery. Ethyl methacrylate (EMA) was grafted onto a high-amylose starch (A). Copolymer synthesis and characterization as well as other experiments to test the enzymatic resistance and the capacity for fermentation of these products by colonic bacteria were carried out. Finally, tablets developed with our copolymers were tested to observe the dissolution behaviour of a model drug and a model protein. Our findings indicate that large quantities of grafted PEMA are not necessary to obtain high enzymatic resistance. Fermentation experiments indicate that the carbohydrate of A–EMA copolymers is susceptible to fermentation in spite of the EMA coating around the amylose backbone and that these materials could favour colon-targeted delivery.
Keywords: Enzymatic degradation; In vitro fermentation; Drug delivery; Starch copolymers; Colon delivery;
In vitro and in vivo degradation behaviors of synthetic absorbable bicomponent monofilament suture prepared with poly(p-dioxanone) and its copolymer by Jung Nam Im; Jeong Kyung Kim; Hyun-Kyoon Kim; Chang Hoon In; Kuen Yong Lee; Won Ho Park (667-674).
A synthetic absorbable bicomponent monofilament suture (MonoFlex), composed of poly(p-dioxanone) and its copolymer, was prepared by a conjugate spinning method, and its degradation behavior was investigated in vitro and in vivo. MonoFlex degraded by hydrolysis, and retained approximately 55% of its original strength after four weeks of incubation in PBS at 37 °C. About 70% of the original strength was maintained after four weeks of implantation in rats, and the suture material was completely absorbed after 180–210 days post-implantation in rats. No remarkable tissue reactions were observed during degradation, and foreign body reactions were similar to those of commercially available suture materials composed of poly(p-dioxanone). This study to monitor the degradation behavior of monofilament sutures in vitro as well as in vivo may be useful in the development of novel suture materials for extended wound support.
Keywords: Monofilament suture; Bicomponent; Degradation; Absorption; Tissue reaction;
Adjusting timing of weathering test to account for seasonal variations in UV exposure by A. Heikkilä; A. Tanskanen; P. Kärhä; K. Hanhi (675-683).
Satellite-derived UV climatology has been used to design a timetable for the outdoor UV exposure of polymeric material specimens. By pre-exposure computation, fixed time increments are transformed into a schedule with a predicted average accumulation of UV dose. The method was applied to produce a timetable for an ongoing exposure programme in a network of seven European test sites over the latitude range 28.5–67.4°N. The effect of the average seasonal variability of solar UV irradiance on the predicted accumulated UV exposure is shown to be notably diminished by the method. Relative underestimations of 5–82% of cumulative UV stress are estimated to be avoided by extensions of 6–167 days exposure durations as suggested by the adjustment procedure. Hence, more reproducible degradation data are expected to be obtainable for exposures that are not multiples of the full annual cycle of UV, especially for those with a duration <1 year.
Keywords: Weathering; Outdoor; Timing; UV radiation;
Physico-chemical aspects of polyethylene processing in an open mixer. Part 31: Formal kinetics of γ-lactone formation from additional primary products by F. Gugumus (684-702).
The potential contribution of primary oxidation products to γ-lactone formation in polyethylene is discussed. The 1,4,6-hydroperoxy-keto-hydroperoxides and the 1,2,5-tris-hydroperoxides are investigated in this work. Their formation and decomposition is examined with respect to γ-lactone formation at increasing rates in the initial stages and possibly at constant rates in the advanced stages of polyethylene processing. The formal kinetics based on the mechanisms is used to check the effect of the temperature and of the oxygen concentration. It is found that the activation energy calculated for the two mechanisms envisaged can account for different experimental values valid in the initial or advanced stages of polyethylene processing. However, the calculated increase of the rate on passing from air to pure oxygen is always much larger than the experimental value. Hence, the mechanisms examined can contribute to part only of the γ-lactone found experimentally. They should necessarily be complemented by additional mechanisms that show smaller increase with the oxygen concentration than that found experimentally.
Keywords: Polyethylene; Thermal oxidation; Oxidation products; γ-Lactones; Mechanisms; Kinetics;
Physico-chemical aspects of polyethylene processing in an open mixer. Part 32: Formal kinetics of γ-lactone formation from secondary products. Heterogeneous kinetics by F. Gugumus (703-719).
Oxidation of aldehydes and γ-hydroxy-trans-vinylene groups can yield γ-lactones. These intermediates account for γ-lactone formation in the advanced stages of polyethylene processing in air. The acyl-peroxy radical formed on free radical induced oxidation of aldehydes can abstract intramolecularly a δ-hydrogen atom to yield a peracid. Reaction of the alkyl radical formed in this reaction with the hydroperoxide group of the peracid gives a γ-lactone with simultaneous release of a hydroxyl radical. The calculated rate of γ-lactone formation according to the mechanism envisaged decreases slightly with increasing temperature (activation energy of about −5 kcal/mol). It is in agreement with the experiments that do not show significant activation energy in the high temperature range for the advanced stages of polyethylene processing. The calculated rate of γ-lactone formation is found to increase by a factor of about 2.7 if the processing experiments are performed in pure oxygen instead of in air. This is close to the experimental factor of about 2.Peroxidation of γ-hydroxy-trans-vinylene groups can also yield γ-lactones. The first possibility involves addition of a peroxy radical to the double bond followed by oxygen addition to the alkyl radical. This reaction possibly yields an α-peroxy-hydroperoxide. Intramolecular decomposition involving the two reactive groups of the α-peroxy-hydroperoxide can give an ozonide that on thermal decomposition yields among others an acid group in 4-position to the alcohol. The activation energy calculated is strongly negative so that the rate should decrease strongly with increasing temperature. Hence, the mechanism cannot contribute significantly to γ-lactone formation in the whole temperature range of the experiments. This is so in spite of the fact that the rate is estimated to increase by a factor of about 1.7 on passing from air to pure oxygen, which is close to the experimental value of approximately 2. The second possibility of transformation of γ-hydroxy-trans-vinylene groups is based on stress-induced oxygen addition to the double bond. Acid catalyzed decomposition of the allylic hydroperoxide that is formed in the reaction yields a pair of aldehydes with one of the aldehyde groups in 4-position to the alcohol group. Peroxidation of the aldehyde pair can give an acid group in 4-position to the hydroxyl group so that a γ-lactone can be formed. The activation energy calculated for the process is very small and the effect of the oxygen concentration corresponds to an increase by a factor of approximately 4.5 on passing from air to pure oxygen. It is postulated that simultaneous contribution by different mechanisms might well account for the experimental value of about 2.The heterogeneous kinetics discussed in detail allows for complementary data interpretation. It is especially suited for the understanding of the advanced stages of polyethylene processing, after some induction time.
Keywords: Polyethylene; Thermal oxidation; Oxidation products; γ-lactones; Mechanisms; Kinetics;
A novel intumescent flame retardant: Synthesis and application in ABS copolymer by Haiyun Ma; Lifang Tong; Zhongbin Xu; Zhengping Fang; Yongming Jin; Fengzhu Lu (720-726).
A novel phosphorous–nitrogen structure containing intumescent flame retardant, poly(4,4-diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB) was synthesized and characterized. Thermal stability and flammability properties of ABS/PDSPB composites were investigated by thermogravimetric analysis (TGA) and cone calorimeter test, respectively. The results showed that the addition of PDSPB enhanced the thermal stability and flame retardancy of ABS significantly. The weight of residues improved greatly with the addition of PDSPB. FTIR and SEM investigations revealed that the residual chars contain polyphosphoric or phosphoric acid, which plays an important role in the process of carbonization. The intumescent chars formed from PDSPB and ABS/PDSPB composites were intact, multicellular and strong. It is confirmed that the char structure was a critical factor for flame retardancy of ABS resin.
Keywords: ABS; Intumescent flame retardant; Poly(4,4-diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate); Flammability; Thermal stability;
Thermal degradation analysis and XRD characterisation of fibre-forming synthetic polypropylene containing nanoclay by Sheng Zhang; T. Richard Hull; A. Richard Horrocks; Gill Smart; Baljinder K. Kandola; John Ebdon; Paul Joseph; Barry Hunt (727-732).
Flammability of synthetic fibres is significantly worse than that of bulk polymers because of the high surface area to volume ratio and the low tolerance to high filler loadings in the fibre production process. Introducing nanocomposite structures has the potential to enhance the char formation at relatively low loadings of nanoparticulate fillers and hence can reduce the flammability of synthetic polymers and fibres.This paper reports thermal degradation analysis results in conjunction with TG analysis under different atmospheres and further studies of X-ray diffraction characterisation of fibre-forming polypropylene containing selected dispersed nanoclays.The concentrations of hydrocarbons, carbon monoxide and carbon dioxide released during the TG analysis have been monitored and analysed by using a combined electrochemical infrared analyser. The intensity changes of the crystallinity peaks and nanoclay peaks in the polymer and composites are discussed.
Keywords: Polypropylene; Nanocomposites; Thermal degradation; XRD;
N-(Substituted phenyl) itaconimides as organic stabilizers for plasticized poly(vinyl chloride) against photo-degradation by Mona Mohamed Fahmi; Nadia Ahmed Mohamed (733-740).
Several N-(substituted phenyl)itaconimide derivatives, N-(RPh)II (R: –NO2, –COOH, –H, –OH, –OMe, –Me, –Cl, or –Br), have been investigated as organic photo-stabilizers for poly(vinyl chloride) (PVC) plasticized with dioctyl phthalate (DOP). Their stabilizing efficiencies are evaluated by measuring the length of the induction period (Ts), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination, and the extent of discolouration of the degraded polymer. The efficiencies are also evaluated by determining the amount of gel formation as well as the intrinsic viscosity of the insoluble and the soluble fractions of the degraded polymer, respectively. The results have proved the greater stabilizing efficiency of the N-(RPh)II derivatives relative to that of the phenyl salicylate UV absorber which is a commonly used industrial stabilizer. A radical mechanism is proposed to account for the stabilizing action of the investigated products.
Keywords: Plasticized poly(vinyl chloride); Organic photo-stabilizers; Photo-dehydrochlorination; Discolouration; Cross-linking; Stabilization mechanism;