摘要:

The effect of processing on the structure and properties of polyethersulfone (PES) has been studied. Processing at normal processing temperature (315° – 335°C) has been carried out by kneading for different times and at various roller rotating speeds, and also by successive extrusion cycles. Changes in PES appearance, melt viscosity, molecular weight, and mechanical properties after processing were found. The thermal stability of PES during processing is different from that measured by thermal analysis. A phenomenon of thickening of melt during processing of PES was found by the present authors. It seems that this phenomenon was caused by prolonged shear, heat, and oxidation at the processing temperatures used.

ISSN:0360-2559    

DOI:10.1080/03602559408015290

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Sheets made from untreated and treated wood and bagasse pulps were subjected to thermal degradation in static air and monitored by the differential thermal analysis (DTA) technique. Percent of resin (resol or novolac) added to the pulps was chosen on the basis that maximum breaking length was achieved. The DTA profiles were obtained and analyzed using the Prout-Tompkins law. A computer program was developed to elucidate the appropriate order of reaction (n) and, consequently, the thermodynamic parameters. Infrared spectra of the samples, and their relation with the mechanical properties and the above thermodynamic parameters, were elucidated. It was found that resin addition (either novolvac or resol) to bagasse pulp led to increased thermal stability, mean hydrogen strength, and crystallinity index. In addition, the stretching vibration corresponding to OH groups was shifted to a lower wavenumber due to its bonding with the phenolic resin. However, no significant changes were observed (specially thermal stability) in the case of sheets made from treated wood pulp.

ISSN:0360-2559    

DOI:10.1080/03602559408015291

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The viscoelastic properties such as storage modulus (E′), loss modulus (E”) and damping (tan δ) of unfilled and silica-filled blends of natural rubber (NR) and ethylene-vinyl acetate copolymer (EVA) have been evaluated. The blends were crosslinked by a mixed system consisting of accelerated sulfur and peroxide. The tan δ values of unfilled blends showed two transitions corresponding to EVA and NR phases. This indicated that the blends are immiscible. The damping curves of EVA and EVA-rich blends possess three distinct regions: a rubbery plateau, a melt transition, and a viscous plateau. It is seen that the addition of silica decreased the tan δ values of the samples substantially except that of NR, where a slight increase in tan δ values can be observed at high temperatures. The sharp decrease in tan δ in filled EVA and EVA-rich blends is associated with the decrease in crystallinity of the EVA phase due to the presence of filler. Addition of silica filler increased the storage and loss modulus of all the samples.

ISSN:0360-2559    

DOI:10.1080/03602559408015292

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Measurements of the IR spectra of native cotton linters and hydroxyethyl cellulose samples of different ethoxyl contents indicated that weaker-bonded OH groups are present in hydroxyethylated cellulose of ethoxyl contents of 23.34—28.89%. Also, the crystallinity indices, mean hydrogen bond strengths, and asymmetry indices for these hydroxyethylated celluloses are 100 compared with native cellulose; however, at ethoxyl content 30.31%, the crystallinity index increased; that is, a higher state of order is formed. The dielectric constant, ′, of native and hydroxyethylated cotton linters was measured at different temperatures and frequencies. The results indicate that the values of the dielectric constants of all hydroxyethyl cellulose samples at a given frequency are increased with the increase of temperature and become greater than ′ of native cellulose. At relatively low ethoxyl contents, the dielectric constant depends mainly on increasing the formed amorphous regions of the cellulose as a result of hydroxy-

ISSN:0360-2559    

DOI:10.1080/03602559408015293

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

It has been shown that the use of metal complexes containing aliphatic amines, and organic acids, and dimethylformamide as the ligands—as a consequence of which they have low melting points—improves the compatibility of the chelates with epoxy oligomers. The metalliferous epoxy chelate polymers produced by hardening of epoxy resins with these complexes possess high mechanical strength and thermal stability.

ISSN:0360-2559    

DOI:10.1080/03602559408015294

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Flow behavior of NBR and chlorosulfonated polyethylene rubber (Hypalon rubber) blend has been studied throughout the entire composition range. The effect of preheating of the blend is also studied in order to understand the interchain crosslinking, which has a pronounced effect on the NBR/Hypalon blend properties. Preheated blends, 50:50, thus provide higher viscosity, stored elastic energy, shear modulus, and relaxation time, etc. Lowernvalue of the preheated blends indicates more pseudoplasticity. The shearing accompanied by blend ratio has a predominant effect on the preheated stock due to microgel formation. From the rheological behavior it appears that there is a phase inversion at 50:50 ratio where the maximum amount of interchain crosslinking is expected in the preheated stocks.

ISSN:0360-2559    

DOI:10.1080/03602559408015295

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The mechanism and kinetics of retardation of peroxydisulfate/thiourea-initiated polymerization of acrylonitrile (AN) by phenol have been studied in the temperature range of 40°–50°C. The effects of the concentration of retarder (phenol), monomer (M), peroxydisulfate (S2O82-), and thiourea (TU) on polymerization have been studied. The most remarkable observation in the present investigation is the positive intercept obtained from the plot of [M]/Rpvs. 1/[M]. A reaction mechanism has been suggested and a suitable rate law has been proposed on the basis of experimental findings.

ISSN:0360-2559    

DOI:10.1080/03602559408015296

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The acetal homopolymer is conventionally obtained by the polymerization of formaldehyde, following end capping using acetic anhydride. Asahi Chemical developed a new process to obtain an end-capped polymer during polymerization of highly purified formaldehyde using acetic anhydride as the chain-transfer agent. The use of highly purified formaldehyde and end capping during polymerization using acetic anhydride as a chain-transfer agent or an end-capping agent will provide a simple process for manufacturing the acetal homopolymer. The polymerization mechanism was confirmed by infrared spectroscopy analysis and proton nuclear magnetic resonance (NMR) analysis of the obtained polymer.

ISSN:0360-2559    

DOI:10.1080/03602559408015297

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The Annual Kargin's Readings were held in the Department of Chemistry of Moscow State University on January 23, 1992. They were organized by the Scientific Council on Macromolecules of the Division of General and Technical Chemistry of the Russian Academy of Sciences, the Department of Chemistry of Moscow State University (MSU), Karpov Research Institute of Physical Chemistry (RIPF), Institute of Petroleum Chemical Synthesis of the Russian Academy of Sciences, and the Kargin Research Institute of Chemistry and Technology of Polymers. Scientists of institutes of the Russian Academy of Sciences as well as experts in polymer chemistry from research institutes and universities in Moscow and other scientific centers of the Commonwealth of Independent States participated in these readings. The readings were opened by Professor V. Kabanov, who emphasized that the period of 22 years since the death of Professor Kargin is long enough to allow evaluation of contributions of his pupils in areas of polymer chemistry of which Professor V. Kargin was founder. Professor Kabanov mentioned three of these areas where achievements are the best. They are:

ISSN:0360-2559    

DOI:10.1080/03602559408015298

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0360-2559    

DOI:10.1080/03602559408015299

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor