Polymer Degradation and Stability (v.81, #3)
FTIR imaging of oxidation of polyisoprene 2. The role of N-phenyl-N′-dimethyl-butyl-p-phenylenediamine antioxidant by Gui-Yang Li; J.L Koenig (377-385).
The thermal aging of polyisoprene (PI) rubber with different concentrations of the antioxidant N-phenyl-N′-dimethyl-butyl-p-phenylenediamine (6-PPD) in hot air (140 °C) has been studied using the FTIR imaging technique. These FTIR imaging results are interpreted using the diffusion-limited oxidation theory and mechanism. Antioxidant concentrations of 0.5 wt.% or larger protect the PI rubber surface at a temperature of 140 °C for up to 10 h (the oxidation inhibiting effect), but the self-protective crosslinked oxidation layer is also retarded by the antioxidant and therefore a larger amount of oxygen diffuses into the rubber which causes increases in the total amount of oxidation (the oxygen permeation effect). Using the spatial sensitivity of FTIR imaging, it is possible to observe the chemical results of these two competing effects at different distances from the rubber surface.
Keywords: PI rubber; Oxidation; Antioxidant; FTIR imaging; Thermal aging;
Thermal, oxidative and radiation stability of polyimides II. Polyimides based on bismaleimidohexane and bismaleimidodiphenylsulphone with different diamines by Milena Marinovic-Cincovic; Dragan Babic; Renata Jovanovic; Katarina Popov-Pergal; Miroslav Pergal (387-392).
Different polyimide resins were synthesized using 1,6-bis-maleimidohexane and the following compounds with terminal amino groups: 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulphone, 1,4-bis-(3-aminopropyl)-piperazine and 4,4′NN′-bismaleimidodiphenylsulphone and 1,2-diaminoehtane and 1,4-bis-(3-aminopropyl)-piperazine. The thermal and thermooxidative behaviour of the polyimide resins was studied by thermogravimetric measurements (TG) in oxygen and nitrogen. Polyimide resins have been irradiated and their radiation stability evaluated on the basis of thermal and thermooxidative behaviour of irradiated samples.
Keywords: Polyimide resins; Thermal and thermooxidative behaviour; Radiation stability;
Numerical simulation for enzymatic degradation of poly(vinyl alcohol) by Masaji Watanabe; Fusako Kawai (393-399).
We have studied the enzymatic degradation of polymeric compounds. We propose a mathematical model that governs the temporal change of the weight distribution with respect to the molecular weight. We deal with a particular case in which the molecules are degraded randomly, and develop a technique to solve the inverse problem to determine the degradation rate numerically. We illustrate our technique with an example in which GPC profiles of polyvinyl alcohol are introduced into the numerical computation. PVA is degraded by random oxidation of hydroxyl groups and following cleavage of carbon–carbon chain between two carbonyl groups/a carbonyl group and an adjacent hydroxymethine group either by hydrolase or aldolase.
Keywords: Polyvinyl alcohol; Enzymatic random depolymerization; Mathematical model;
Flammability characterization and synergistic effects of expandable graphite with magnesium hydroxide in halogen-free flame-retardant EVA blends by Zhenzhong Li; Baojun Qu (401-408).
The flammability characterization and synergistic effects of different types of expandable graphite (EG) with magnesium hydroxide (MH) in halogen-free flame-retardant (HFFR) ethylene vinyl acetate (EVA) blends have been studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and UL-94 test. The results show that the particle size and expansion ratio of EG have a great effect on the flammability of the HFFR EVA/MH/EG blends. The EG with bigger particle size and higher expansion ratio can apparently increase the LOI value and improve the UL-94 flammability properties of EVA blends. The data obtained from the CCT indicate that the heat release rate (HRR), the effective heat of combustion (EHC), and the mass loss rate (MLR) of EVA/MH/EG blends decrease remarkably with increasing the particle size and expansion ratio of EG. However, the specific extinction area (SEA) data show that the addition of EG can apparently increase the smoke emission of EVA/MH/EG blends. The TGA results show that the thermal stability of EVA/MH/EG blends increase with increasing the EG particle size and expansion ratio.
Keywords: Expandable graphite; Magnesium hydroxide; Synergistic effect; Halogen-free flame-retardant; Ethylene vinyl acetate copolymer;
New bifunctional antioxidants—intramolecular synergistic effects between chromanol and thiopropionate groups by Tomihiro Nishiyama; Yu Andoh; Taiji Sugimoto; Tomoyuki Okamoto (409-413).
We have examined the antioxidant activities, both in tetralin oxidation induced by an azo initiator and in tetralin under thermoxidative conditions of a series of tetramethyl-6-chromanols with a methyl thiomethyl, phenyl thiomethyl, methyl thiopropionate, and thiopropionate group. The antioxidants tested showed almost the same activity for the oxidation of tetralin induced by an azo initiator at 61 °C. At high temperature, we found that tetramethyl-6-chromanols with a thiopropionate group increased the induction period for ortho to the OH group by 7.5-fold and meta to the OH group by 10.7-fold, compared with that for pentamethyl-6-chromanol.
Keywords: Antioxidant activity; Chromanol; Synergistic effect; Thiopropionate group;
Thermogravimetric analysis of the decomposition of poly(1,4-dioxan-2-one)/starch blends by Xiu-Li Wang; Ke-Ke Yang; Yu-Zhong Wang; Bo Wu; Ya Liu; Bing Yang (415-421).
Thermal degradation of poly (1,4-dioxan-2-one)/starch was studied by thermogravimetric analysis in order to determine the actual reaction mechanism (RM) of the decomposition. The activation energy of the solid state process was determined using Kissinger's method, which does not require knowledge of the RM, whose result is 121 kJ/mol. Different integral and differential methods were used to compare with this value. Also, the experimental results were compared to master curve plots in the range of Doyle approximations. Analysis of experimental results suggests that in the range of conversions studied, 5–20%, the actual RM is D3 type, which is three-dimensional diffusion. The addition of starch will not change the recyclability of PPDO.
Keywords: Poly(1,4-dioxan-2-one); Starch; Thermogravimetry; Degradation kinetics; Activation energy;
Poly(bisphenol A)cyanurate network modified with poly(butylene glycol adipate). Thermal and mechanical properties by A. Fainleib; J. Grenet; M.R. Garda; J.M Saiter; O. Grigoryeva; V. Grytsenko; N. Popescu; M.C. Enescu (423-430).
A poly(bisphenol A)cyanurate (PCy) network was modified by a hydroxy-terminated oligoester, poly(butylene glycol adipate), PBGA, by polycyclotrimerization of bisphenol A dicyanate in the presence of the oligoester. The modified networks with PBGA content from 5 to 20% (w/w) were characterized by a combination of FTIR, DSC, TMA, TGA, impact testing and sol-gel analysis. It has been established that almost whole of the PBGA was chemically incorporated into the PCy network structure and that the higher the content of PBGA, the stronger the interaction between the components. It is shown that introducing PBGA does not drastically reduce thermal characteristics (temperature of the thermal degradation onset and glass transition temperature) of the PCy network while the impact properties are improved significantly. It is suggested that the modified PCy can be successfully used simultaneously at high temperatures and high loading.
Keywords: Modified polycyanurate networks; Polybutylene glycol adipate; DSC; TGA; TMA;
Organic thermal stabilizers for rigid poly(vinyl chloride) IX. N-Benzoyl-N′-p-substituted phenylthiourea derivatives by Magdy W. Sabaa; Riham R. Mohamed; Ahmady A. Yassin (431-440).
N-Benzoyl-N′-p-substituted phenylthiourea derivatives have been investigated as thermal stabilizers or co-stabilizers for rigid PVC at 180 °C in air. The results reveal the higher stabilizing potency of the investigated organic stabilizers as compared with some of the commercially known reference stabilizers, which is proved by their greater induction period values (Ts), during which no detectable amount of hydrogen chloride gas could be detected, but with higher dehydrochlorination rate at the later stages of degradation. Complexation of these materials with the chlorides of Ni2+ and Cd2+ improved greatly the induction period values, however the dehydrochlorination rate is only slightly improved. On the other hand, blending these thermal stabilizers with some of the commercially known reference stabilizers in different proportions leads to a true synergistic effect. The induction period values and the degradation rate were remarkably improved. A probable ionic mechanism for the stabilizing action of N-Benzoyl-N′-p-substituted phenylthiourea derivatives is proposed. The stabilizing efficiency is attributed to the replacement of the labile chloride ions on the PVC chains by a relatively more stable moiety of the stabilizer.
Keywords: Poly(vinyl chloride); Dehydrochlorination; Thermal stabilization; Induction period; Blending;
Environmental biodegradation of polyethylene by S Bonhomme; A Cuer; A-M Delort; J Lemaire; M Sancelme; G Scott (441-452).
The degradation of a commercial environmentally degradable polyethylene was investigated in two stages. Firstly by abiotic oxidation in an air oven to simulate the effect of the compost environment and secondly in the presence of selected microorganisms. Initial biofilm formation was followed by fluorescence microscopy and the subsequent growth of bacteria on the surface of the plastic was observed by scanning electron microscopy (SEM). It was observed that microbial growth occurred on the presence of PE samples that had been compression moulded to thick sections but had not been deliberately pre-oxidised. Molecular enlargement and broadening of molecular weight distribution occurred after preheating in air at 60 °C but not at ambient temperatures but colonisation of microorganisms occurred on all samples. Erosion of the film surface was observed in the vicinity of the microorganisms and the decay of oxidation products in the surface of the polymer film was measured by FTIR measurements and was found to be associated with the formation of protein and polysaccharides, attributable to the growth of the microorganisms.
Keywords: Abiotic oxidation; Oxo-biodegradation; Polyethylene; Fluorescence microscopy; Scanning electron microscopy; FTIR spectroscopy;
New combined hindered phenol/hindered amine stabilizers for polymers based on diphenylmethane-4,4′-diisocyanate by Cs Kósa; Š Chmela; B Pawelke; G Theumer; W.D Habicher (453-461).
A new type of combined stabilizer based on hindered phenols and Hindered Amine Stabilizers (HAS) were synthesized and tested as light stabilizers. 2,4-Di-tert-butylphenol (I) and 2-tert-butyl-4-methylphenol (II) were coupled with 4-hydroxy-2,2,6,6-tetramethylpiperidine (TMP), 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMP), 4-amino-2,2,6,6-tetramethylpiperidine (ATP), 4-N-butyl-amino-2,2,6,6-tetramethylpiperidine (BATP) or 4-hydroxy-2,2,6,6-tetra-methyl-piperidin-N-oxyl (N-oxyl) through the reaction with diphenylmethane-4,4′-diisocyanate. The structure and purity of the synthesized compounds were proved by conventional analytical methods. They were tested as light stabilizers in polypropylene films. Stabilizing efficiency depends on the structure of the phenol as well as on the structure of the HAS. Derivatives of phenol I exhibited better efficiency compared with phenol II for all HAS used. Concerning the structure of HAS stabilizing activity increased in the following order ATP<BATP<N-oxyl<TMP=PMP. Much higher stabilizing performance of combined phenol I and II with TMP in comparison with the performance of their physical mixtures shows the quite strong synergistic effect arising from chemical bonding of both types of stabilizers in one molecule.
Keywords: Stabilization; Photooxidation; Combined stabilizers; Phenols; Hindered amines; Polypropylene;
Thermal degradation mechanism and rate constants of the thermal degradation of poly(epichlorohydrin-co-ethylene oxide), deduced from pyrolysis-GC-MS studies by M.A Soto-Oviedo; R.S Lehrle; I.W Parsons; M.-A De Paoli (463-472).
The thermal degradation mechanism and kinetic parameters for the overall degradation for the poly(epichlorohydrin-co-ethylene oxide) elastomer have been investigated by pyrolysis-gas chromatography-mass spectrometry (pyrolysis-GC-MS) techniques. In this study the total volatile products from the pyrolysis of the elastomer at different temperatures were measured as a Total Ion Current (TIC) in the mass spectrometer. Information about the components within the TIC was obtained from measurements of the Selected Ion Currents (SIC) of ions of different m/z ratios. Amongst the m/z ratios observed, those corresponding to ions of m/z of 35, 36, 37, and 38 confirmed that HCl is one of the pyrolysis products. SIC measurements for a wide range of other possible degradation products were examined in order to assess the general structures, and these revealed that a wide range of low molar mass hydrocarbons and chlorohydrocarbons are formed on thermal degradation of the elastomer. The results suggest that a major mechanistic process is the depolymerization of macroradicals, and that hydrogen abstraction from a carbon atom adjacent to a C–O bond is an important process in the formation of volatile products. This information has led to the postulation of a possible mechanism for the thermal degradation of the elastomer. Quantitative kinetic measurements were made by evaluating the overall rate of production of volatile products using the TIC obtained from sequence pyrolysis experiments. The data leading to this overall rate constant (k) was interpreted in several ways, i.e. according to the Ericsson, Guggenheim and Kezdy-Jaz-Bruylants methods. The average values obtained for this overall rate constant were 0.16±0.03, 0.25±0.03, and 0.55±0.20 s−1 for pyrolysis temperatures of 350, 387, and 400 °C, respectively.
Keywords: Pyrolysis-GC-MS; Poly(epichlorohydrin-co-ethylene oxide) elastomer; Thermal degradation mechanism; Kinetics; Rate constants;
Preparation and characterization of polystyrene/graphite oxide nanocomposite by emulsion polymerization by Rongfang Ding; Yuan Hu; Zhou Gui; Ruowen Zong; Zuyao Chen; Weicheng Fan (473-476).
Polystyrene intercalated graphite oxide (GO) nanocomposite was prepared by emulsion polymerization reaction and characterized by X-ray diffraction (XRD), high resolution electron microscopy (HREM), and thermogravimetric analysis (TGA). It was shown that polystyrene can be intercalated into the interlayer space of GO and form exfoliated and intercalated nanocomposites. The thermal analysis demonstrated that the presence of GO enhances the char residue of the nanocomposite.
Keywords: Polystyrene; Graphite oxide; Intercalation; Nanocomposites;
Investigation of the biodegradability of water-insoluble materials in a solid test based on the adaptation of a biological oxygen demand measuring system by Leonóra Száraz; Judit Beczner; Gernot Kayser (477-482).
The usual BOD measuring systems used for monitoring the degradation of biodegradable materials are applied for the assessment of biodegradation exclusively in aquatic tests by detecting the amount of O2 consumed during degradation. In our study, a new, solid test application of a BOD system optionally capable to detect CO2 evolved during degradation is presented. After the optimisation of sample concentration and test temperature, the measurement set-up possessing relatively small reaction vessels of 250 ml with 80 g of soil mix proved to supply reliable and reproducible results. The system was optimised with microcrystalline cellulose—used as reference material in aquatic and solid test as well—showing 89.3±3.2% degree of degradation after 21 days, and it was applied for the assessment of biodegradation of commercially available non-powdered (films and kraft-paper) samples indicating degrees of degradation between 24.9 and 55.4%.
Keywords: BOD measuring system; Soil mix; Starch-based biodegradable films; Assessment of biodegradation; Kraft-paper;
Aliphatic amines for use as long-term heat stabilizers for polypropylene by Pieter Gijsman; Magali Gitton-Chevalier (483-489).
It is well known that Hindered Amine Stabilizers (HAS) act as stabilizers preventing the thermo-oxidative degradation of polypropylene (PP). However, different commercial oligomeric HAS that contain a piperidinyl as well as a triazine moiety were found to differ in activity. The main difference between these types of HAS concerned the presence of different types of aliphatic amines in their backbones. We measured the influence of several aliphatic amines on the thermo-oxidative degradation of PP to find out whether this difference can explain the difference in activity of these commercial HAS. In the presence of a HAS or a phenolic antioxidant, aliphatic amines increase the thermo-oxidative stability of PP. This is probably due to their ability to react with aldehydes and in this way prevent the formation of peracids, which are known to increase the degradation rate of PP. The presence of primary or secondary amines in the chemical structure of a HAS in addition to the piperidinyl group has an influence on the activity of the HAS when it is used as a long-term heat stabilizer and may explain the difference in activity observed between some commercial HAS stabilizers.
Keywords: Hindered amine stabilizer; Phenolic antioxidant; Heterogeneous degradation; Thermo-oxidation;
Depth profile analysis of the photochemical degradation of polycarbonate by infrared spectroscopy by N Nagai; H Okumura; T Imai; I Nishiyama (491-496).
The depth profile of the chemical changes in polycarbonate after photochemical degradation was investigated by infrared reflection spectroscopy with gradient shaving preparation. In addition, a spectral simulation technique to interpret the infrared ATR spectra with multiple angles of incidence was applied. The polycarbonate plates were photo-irradiated for 24 and 72 h by a weather meter. A band at around 1600 cm−1 caused by photo-Fries rearrangement was observed, and a carboxylic acid band caused by side-chain photo-oxidation was also observed. These drastic changes in the surface occurred to a depth of at least 0.5 μm. A technique employing IR simulation demonstrated that the drastic chemical changes occurred in the surface to a depth of 0.2 μm for 24 and 72 h treated samples. For a treatment time of at least 72 h, the rate of degradation is extreme in the region of a depth of 0–0.2 μm.
Keywords: Polycarbonate; Photo-degradation; Infrared spectroscopy; Depth profile; Gradient shaving preparation; ATR;
Photo-oxidative degradation of polyethylene/montmorillonite nanocomposite by Huaili Qin; Chungui Zhao; Shimin Zhang; Guangming Chen; Mingshu Yang (497-500).
Photo-oxidative degradation is critical to polymer materials. It is even the case in polymer/layered silicate nanocomposites. A UV photo-oxidative degradation study on polyethylene/montmorillonite (PE/MMT) nanocomposite was carried out by FT-IR technique. It is indicated that the rate of photo-oxidative degradation of PE/MMT nanocomposite is much faster than that of pure PE. The acceleration of photo-oxidative degradation of PE/MMT nanocomposite is due to the effect of MMT and ammonium ion, in which the effect of ammonium ion is primary. It has been found that the dispersion state (either nano- or micro-) of MMT does not seem conclusive on the acceleration of degradation. Fe3+ modified MMT can also accelerate the photo-oxidative degradation of PE matrix.
Keywords: Polyethylene; Montmorillonite; Nanocomposite; Photo-oxidative; Degradation;
Poly(l-lactide) XI. Lactide formation by thermal depolymerisation of poly(l-lactide) in a closed system by Hideto Tsuji; Ippei Fukui; Hiroyuki Daimon; Koichi Fujie (501-509).
Thermal degradation (depolymerisation) of poly(l-lactide) [i.e., poly(l-lactic acid) (PLLA)] was carried out in a sealed tube as a closed system in the temperature range of 250–290 °C for 15 h without further addition of depolymerisation catalyst, and lactide formation by depolymerisation of PLLA was monitored using X-ray diffractometry, gel permeation chromatography (GPC), and gas chromatography (GC). The highest yields of lactides and l-lactide were as low as 14 and 8%, when thermal degradation was performed for 10 h at 270 and 250 °C, respectively. The fractions of l-lactide and of d- and meso-lactides respectively decreased and increased with increasing degradation temperature and time. The low yield of lactides in this study can be explained by polymerization of the formed lactide and by formation of low molecular weight compounds other than lactides, while the low yield of l-lactide is attributable to the formation of high amounts of meso- and d-lactides, in addition to the low yield of lactides. The probable pathways for the formation of D- and meso-lactides are discussed.
Keywords: Polylactide; Poly(lactic acid); Lactide formation; Thermal degradation; Pyrolysis;
Isolation of a thermophilic bacterium degrading some nylons by Kosuke Tomita; Norihito Hayashi; Noritoshi Ikeda; Yumi Kikuchi (511-514).
A thermophilic strain capable of degrading nylon 12 was isolated from 100 soil samples by enrichment culture technique at 60 °C. At this temperature, the strain grew on nylon 12, accompanied by a marked decrease in molecular weight of nylon 12. It was identified as a neighboring species to Bacillus pallidus, which has an optimum growth temperature of around 60 °C. The strain was also found to degrade nylon 6 as well as nylon 12, but not nylon 66.
Keywords: Thermophilic bacterium; Nylon 12; Nylon 6; Biodegradation; Bacillus pallidus;
Effect of tin on poly(l-lactic acid) pyrolysis by Haruo Nishida; Tomokazu Mori; Shinya Hoshihara; Yujiang Fan; Yoshihito Shirai; Takeshi Endo (515-523).
Tin 2-ethylhexanoate is an indispensable component of commercially available poly(l-lactic acid) (PLLA). However, the thermal degradation kinetics of PLLA containing Sn have not yet clearly been established; in particular, whether the degradation mechanism is a 1st-order or a random reaction. To clarify the effects of residual Sn on PLLA pyrolysis, PLLA samples with different Sn contents from 20 to 607 ppm were prepared and subjected to pyrolysis analysed with pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS) and thermogravimetry (TG). The pyrolysis of PLLA Sn-607 (Sn content: 607 ppm) with Py-GC/MS in the temperature range of 40–400 °C selectively produced lactides. In contrast, the pyrolysis of PLLA Sn-20 (Sn content: 20 ppm) was accompanied by the production of cyclic oligomers. The dynamic pyrolysis of PLLA-Sn samples by TG clearly indicated that with an increase in Sn content there was a shift to a lower degradation temperature range and a decrease in activation energy Ea. The kinetic analysis of the dynamic pyrolysis data indicates that the Sn-catalyzed pyrolysis starts through a random degradation behaviour and then shifts to a zero-order weight loss as the main process. Three reactions were put forward as being possible mechanisms of the zero-order weight loss;, one being an unzipping reaction accompanying a random transesterification, the other two being the Sn-catalyzed pseudo-selective and selective lactide elimination reactions from random positions on a polymer chain. The kinetic parameter values obtained could be adequately explained for each degradation process.
Keywords: Poly(l-lactic acid); Poly(l-lactide); PLLA; Pyrolysis; Thermal decomposition; Kinetics; Simulation; Thermogravimetric analysis; Random degradation; Zero-order reaction;
Synthesis of high molecular weight poly(α,β-malic acid) for biomedical use by direct polycondensation by Tetsuto Kajiyama; Tetsushi Taguchi; Hisatoshi Kobayashi; Kazunori Kataoka; Junzo Tanaka (525-530).
Poly(malic acid) (PMA) is a biodegradable and bioabsorbable water-soluble polymer. In order to apply this compound in the biomedical field, many researchers have investigated the synthesis of PMA with high molecular weight by polymerization methods such as ring-opening and direct polycondensation. When the synthesis of high molecular weight PMA is performed by ring-opening polymerization, it is difficult because of the several steps involved in this reaction cycle, including a great deal of time for repeated purification. In contrast, direct polycondensation is a very useful method for the synthesis of polyesters since it is achieved by a one step reaction. In this report, we describe a new and simple method to synthesize high molecular weights compounds of α,β-PMA by direct polycondensation. The optimum reaction temperature for the synthesis of α,β-PMA by direct polycondensation was 120–130 °C, irrespective of reaction solvents or catalysts. From these results, we conclude that our approach efficiently synthesizes higher molecular weight compounds of α,β-PMA.
Keywords: Poly(α,β-malic acid); Direct polycondensation; l-malic acid; Biodegradable polymer; Water-soluble polymer;
Photo- and thermo-oxidative degradation of photocrosslinked ethylene–propylene–diene terpolymer by Weizhi Wang; Baojun Qu (531-537).
Photocrosslinking of ethylene–propylene–diene terpolymer (EPDM), and photo- and thermo-oxidative degradation of photocrosslinked EPDM have been studied by photoacoustic Fourier transform infrared spectroscopy (PAS-FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The relative ratios of degradation to crosslinking for photocrosslinked EPDM by swelling measurement were estimated by Charlesby's random crosslinking theory to be 0.06 for EPDM 4770 and 0.1 for EPDM 4045. The PAS-FTIR and XPS data gave the evidence that the surface photo- and thermo-oxidation degradation of photocrosslinked EPDM samples with a given UV irradiation time apparently increase with aging time. The main photo-oxidation products were identified as hydroperoxides and various carbonyl compounds. The SEM measurements show that the photo-oxidative degradation of photocrosslinked EPDM has a crucial effect compared with thermo-oxidative degradation.
Keywords: Photo-oxidation; Thermo-oxidation; Degradation; Photocrosslinking; EPDM;
Flame retardancy of polystyrene nanocomposites based on an oligomeric organically-modified clay containing phosphate by Xiaoxia Zheng; Charles A Wilkie (539-550).
Novel modified clays, which may enable the formation of flame retarded polystyrene nanocomposites by melt or solution blending, have been prepared using an ammonium salt which contains an oligomeric material consisting of vinylbenzyl chloride, styrene and vinyl phosphate reacting with dimethylhexadecylamine. These nanocomposites have been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the evaluation of mechanical properties. Melt blending is an effective, economical way to produce intercalated nanocomposites with greatly reduced peak heat release rate and a decreased total heat release; the polymer does not all undergo thermal degradation.
Keywords: Flame retardancy; Nanocomposite; Polysytrene; Phosphate;
Synergy between conventional phosphorus fire retardants and organically-modified clays can lead to fire retardancy of styrenics by Grace Chigwada; Charles A Wilkie (551-557).
Polystyrene–clay nanocomposites combined with phosphorous-containing fire retardants have been prepared and used to explore the thermal stability and mechanical properties of the polymer formed. The amounts of fire retardants and clay used were varied to study the effect of each on thermal stability and mechanical properties of the polymer. The samples were prepared by bulk polymerization and analyzed by X-ray diffraction, thermogravimetric analysis, cone calorimetry, Fourier Transform infrared spectroscopy and the evaluation of mechanical properties. The thermal stability of the polymers is enhanced by the presence of the phosphorus-containing fire retardants.
Keywords: Polystyrene; Nanocomposites; Phosphorus fire retardants; Thermal stability;
The effects of various pulping conditions on crystalline structure of cellulose in cotton linters by Esat Gümüskaya; Mustafa Usta; Hüseyin Kirci (559-564).
In this study, we investigated that how the crystalline structure of cellulose in cotton linters changed during soda, sulfate and organosolve pulping processes by using X-ray diffraction and FT-IR spectroscopy. It was defined that crystalline structure of cellulose in cotton linters was more effected in organosolve pulping than in soda and sulfate pulping. It was found that the degree of crystallinity and crystallite size were higher in organosolve pulping than in soda and sulfate pulping. While cellulose I α (triclinic) was determined in all organosolve pulp samples, this unit cell structure was defined in only sulfate pulp samples obtained at 130 °C among other pulp samples. It was concluded that not only chemical agents, but also temperature and pressure in cooking digester had major effects on crystalline structure of cellulose in cotton linters during cooking.
Keywords: Cellulose; Polymer; Crystallinity; Pulping; Cotton linters; X-ray; FT-IR;
Calender of events (565-566).