摘要:

AbstractThe effect of a diazide, chemically bonded to short polyamide fibers, has been investigated in order to establish if the diazide acts effectively as a bond bridge between the elastomeric matrix and the fibers. Composite properties, such as green strength, solvent swelling, tensile and tear strength, and elongation at break, which clearly manifest the existence of a strong interface, have been measured in comparison with those obtained in a similar composite with a conventional adhesive system. Likewise, the temperature dependence of tan δ showed a dispersion peak in the temperature range 30–90°C, which corresponds to the addition of the two relaxations related to the fiber and the interface. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070480301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractBlending of polystyrenes (PS) with a thermotropic liquid crystalline polymer (LCP) was performed by using a continuous corotating twin screw extruder. The influence of LCP content on the blending process was studied by changing the barrel heater temperature and the screw speed. The torque of screw shafts, generated during the blending process, was influenced by LCP content and its influence was not simple. The torque generated during the blending process was not directly related to the apparent melt viscosity of blends. Further, the effects of the matrix viscosity on the morphology and mechanical properties of the PS/LCP blends were studied using three grades of PS as matrix resins. It was found that the size of the LCP dispersed phase decreased with increasing matrix viscosity. Consequently, the mechanical properties of the PS/LCP blend were improved. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070480302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractCotton fibers were subjected to swelling in various concentrations of LiOH, NaOH, and KOH at 0°C. Swollen fibers were characterized by measurements of physical, mechanical, and fine structural properties. Slack swelling in LiOH and NaOH produced tremendous changes in fiber properties. Clear‐cut swelling maxima, disorientation, and subsequent deterioration in tensile properties at and near the swelling maxima were evident in both LiOH and NaOH. On the other hand, KOH swelling did not produce any clear swelling maximum. Fibers swollen in this reagent showed better retention of tensile properties due to conducive changes in the structural parameters resulting from a lower but more uniform swelling. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070480303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe single‐Li+conduction of the cross‐linking poly [oligo (oxyethylene) methacrylate‐co‐lithium methacryloyl hexylsulfonate]s was studied, and an Li+ionic transport number of 0.994 estimated from the isothermal transient ionic current (ITIC), in which an ion‐blocking platinum electrode was used. The results show that Li+‐ionic conduction can be reasonably described by Vogel–Tammann–Fulcher (VTF) equation, suggesting that there is close correlation between ionic migration and segmental motion in these polymers. The battery composed of lithium/this copolymer film/polyaniline supplied a constant short circuit current (JSC) of 45 μA/cm2and an open circuit potential (VOC) of 3.6 V at 25°C. © 1993 Jo

ISSN:0021-8995    

DOI:10.1002/app.1993.070480304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractBlends of propylene–ethylene block copolymer (PEB) and propylene homopolymer (PP) were prepared to give various rubber contents (4–20 wt %). By diluting the PEB with PP with molecular weight equal to that of the PEB matrix, molecular characteristics of all the blends were kept constant. The rubber particle size and size distribution of all the blends were almost constant, so that the interparticle distance decreased with increased rubber content. According to the observation of the fracture behavior at −20°C, a brittle to ductile transition was found at the rubber content of 16 wt %. Microdeformation behavior of the blends was investigated in the region of brittle to ductile transition by using transmission electron microscopy. In the case of the brittle sample with low rubber content, crazing and voiding were observed. Whereas even in the ductile sample with high rubber content, crazing certainly took place before shear yielding. The origin of ductile fracture could possibly be attributed to the relaxation of strain constraint by the microvoids contained in the craze. © 1993 John Wiley&So

ISSN:0021-8995    

DOI:10.1002/app.1993.070480305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractCellulose acetate in acetone solution is known to show some peaks in its chromatogram as measured by gel‐permeation chromatography. These peaks are named from the shorter elution time as prehump I, prehump II, and main hump. In our previous paper, we characterized prehump I. In this study, the second peak, prehump II, was fractionated by using the large‐scale GPC column and its molecular properties were investigated. The results have shown that the molecules of prehump II are not aggregated but molecularly dispersed with some anionic residues. These anionic groups may be sulfuric acid groups introduced during the acetylation process as a catalyst that interact repulsively with the anionic groups of the GPC column gel. This resulted in the phenomenon that the prehump II elutes earlier than the main hump in the GPC chromatogram. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070480306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractPolystyrene terminated with an organic sulfide group was prepared by styrene bulk polymerization using three organic disulfides as initiators, and the content of the organic sulfide group (X̄n) was determined quantitatively from the data of UV and M̄n.Styrene–vinyl acetate block copolymer was prepared by using polystyrene ended with the organic sulfide group as the photosensitizer to initiate vinyl acetate polymerization. The copolymer was characterized by IR,1H‐NMR,13C‐NMR, DSC, and TEM, respectively.Different copolymerization conditions were investigated systematically. The result reveals that the X̄nvalue is a key factor in the copolymerization and the copolymerization proceeds via living radical mechanism. © 1993 John Wiley&

ISSN:0021-8995    

DOI:10.1002/app.1993.070480307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAqueous solutions of partly hydrolyzed polyvinyl acetate (polyvinyl alcohol, PVA) and hydroxypropyl methylcellulose (HPMC) are used together as dispersants in vinyl chloride suspension polymerization. Surface tension, viscosity, and cloud point (CP) of diluted PVA and HPMC solutions at room temperature, viscosity of concentrated solutions as a function of temperature, and incipient gelation temperatures (IGT) were determined. Viscosity measurements show synergism of binary polymer mixtures. The synergetic effect diminishes with rise of temperature. IGT of PVA–HPMC solutions do not differ remarkably from those of solutions containing only HPMC and are much higher than the corresponding CP. At definite relative concentrations of HPMC and PVA, separation of the mixtures into two immiscible phases occurs. Each phase contains both polymers, but in the denser and more concentrated phase (lower layer), PVA is the prevailing component. The mutual influence of the two polymers causes changes in solute–solvent interaction, that is, dehydration of the polymers' molecules. It is assumed that in the processes occurring in the system, preferential molecules of definite structure take part. The merits of a system using both polymers as dispersants in the vinyl chloride polymerization are discussed in the light of ascertained data. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070480308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe hydrolytic depolymerization of molten PET in excess water was studied using a 2 L stirred pressure reactor at temperatures of 250, 265, and 280°C. Rate constants for hydrolysis are calculated from the initial rate data. At initial water: PET charge ratios (w/w) exceeding 5.1, essentially complete depolymerization to monomer is possible at 265°C. At lower water: PET initial charges, an equilibrium is established. The equilibrium constants are calculated for 2 g water/g PET at three temperatures. A kinetic model is proposed to describe the hydrolysis reaction. The model is shown to fit experimental data and to yield good predictions for the equilibrium concentration of carboxyl groups. Carboxyl‐group concentrations are measured using an end‐group analysis technique. Potentiometric titrations are carried out in one of two solvent systems, dimethylphenol:chloroform or dimethylsulfoxide, depending on the extent of hydrolysis. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070480309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractVarious heat‐resistant thermosetting polyimides containing hexafluoroisopropylidene and keto and ether groups suitable for fiber‐reinforced composites development have been synthesised by thermal polymerization of maleimido and nadimido end capped polymer precursors. Thermal polymerization involving addition reactions was performed at 225°C for 1.5 h and post‐curing at 290°C for 0.5 h. Tough polymers XVIII to XXIII were obtained. The thermal polymerization was monitored using infrared spectroscopy. The polymer precursors were characterized by IR,1H‐NMR, and elemental analysis. The synthesized polymers were evaluated for thermal stability using dynamic thermogravimetric analysis (TGA). All the polymers showed thermal decomposition temperatures in the range of 430–435°C in nitrogen and in air. The char yield of the polymers was in the range of 60–67% in nitrogen at 800°C. This study indicated that thermally synthesized polymers from hexafluoroisopropylidene, keto, and ether containing polymides are potential candidates for the development of advanced materials for aerospace and high‐tech applications. © 1993 Jo

ISSN:0021-8995    

DOI:10.1002/app.1993.070480310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY