摘要:

AbstractThe historical development of both main‐chain (M.C.) and side‐chain (S.C.) liquid crystalline polymers (LCPs) is presented. Synthetic routes and characterization techniques for LCPs are introduced. Various approaches to reduce the melting points of M.C. LCPs and to increase the mesogenic order of S.C. LCPs are reviewed and evaluated. The criteria to form a liquid crystalline phase are then discussed. Comparisons among thermotropic, lyotropic, and low‐molecular‐weight liquid crystals are also made. It is concluded that the preparation of LCPs has been well developed by the industry, but that the understanding of the formation of LC domains has not been completely understood. The theoretical explanations for some unexpected results are still not available. These anomalies are detailed in this work. Future research activity en LCPs for plastics engineers is also mentioned in this

ISSN:0032-3888    

DOI:10.1002/pen.760261302

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe biaxial tension stress‐strain‐yield behavior of glassy bisphenol A‐polycarbonate has been investigated at constant octahedral shear stress rate and at 25°C and −40°C. The specimens possess a small amount of anisotropy. Hill′s criterion for yielding of anisotropic materials is modified to take into account the sensitivity of the yield locus to the hydrostatic stress component. This modified yield criterion fits the 25°C data quite well. However, the data at −40°C cannot be fitted using reason

ISSN:0032-3888    

DOI:10.1002/pen.760261303

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe silicone elastomer RTV‐142 is often used as a particle‐getter material inside electronics packages. The adhesion mechanism that forms the bond between the particle and the cured adhesive has been investigated. One expects, theoretically, that polymer chains exhibit a temperature‐dependent mobility. This is consistent with the hypothesis that the flow of polymer chain segments around asperities on the foreign particles causes adhesion. Calculations of the surface energy of an idealized polymer system are presented which support the concept of a free‐energetically driven flow of chain segments into pores and around asperities. Polymer surface‐chain mobility is investigated experimentally by the scanning electron microscope analysis of a fractured, cut, and particle‐decorated surface. Surface appearance changes were noted as a function of temperature. Scanning electron micrographs indicate that polymer chain movement is temperature dependent. Such findings support the proposed adhesio

ISSN:0032-3888    

DOI:10.1002/pen.760261304

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe electrical conductivity and the dissipation factor of silicone rubber vulcanized by the condensation reaction of α,ω‐dihydroxypolysiloxane with ethoxysilane, using dibutyltin dilaurate as a catalyst, were studied. Rubber specimens, with different amounts of catalyst, were prepared using various vulcanization times and then heat treated in dry or wet atmospheres containing oxygen and nitrogen. The electrical properties of these specimens were measured at 20 to 200°C in dry air. The amounts of residual catalysts and unreacted ethoxy groups were analyzed by colorimetric and gas chromatographic methods. Factors influencing the specimen electrical properties were discussed in terms of preparation conditions and amount of residual compo

ISSN:0032-3888    

DOI:10.1002/pen.760261305

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe properties of poly(vinyl chlorlde)/ehlorinated poly(vinyl chloride) (61.6 percent C1) blends, prepared by melt and solution blending, were measured by various tests. Based on the chlorinated poly(vinyl chloride) (CPVC) composition, percent chlorine, and mole percent CC12groups, these blends were expected to show intermediate properties between miscible and immiscible systems. Indicative of miscible behavior were the single glass transition temperatures over the entire composition range for both melt and solution blended mixtures. A single phase was also indicated by transmission electron microscopy. However, the yield stress showed a minimum value less than either of the pure components in the 50 to 75 percent CPVC range, which is characteristic of two‐phased systems. Specific volume, glass transition temperature, and heat distortion temperature were linear with binary composition. The storage modulus showed a small maximum, suggesting a weak interaction between the two miscible polymers. Heats of melting for the residual PVC crystallinity were also less than expected from linear additivity. At 160°C and 210°C, the logarithm of the complex viscosity was essentially linear with volume fraction of CPVC, except for a very slight decrease in the 50 to 75 percent CPVC range, which may have been a result of lower crystallinity. At 140°C, the complex viscosity of the CPVC was less than that of PVC owing to the higher crystallinity of the latter. The viscosities were similar at 160°C, but at 210°C, where most of the crystallites had melted, the complex viscosity of the CPVC was higher because of its higher glass transition tempe

ISSN:0032-3888    

DOI:10.1002/pen.760261306

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractAn approximation method is proposed to predict the Mow rate‐pressure drop relation for isothermal laminar flow of any time‐independent fluid in wire coating extrusion. A geometric parameter method proposed earlier is used in predict the pressure‐driven flow in the annulus. The method is demonstrated for Newtonian, power law, and Ellis fluids. The accuracy of the method is shown by comparing the predictions with the theoretical and experimental results of Han and Rao. An expression for wire coating thickness is also

ISSN:0032-3888    

DOI:10.1002/pen.760261307

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractA common bond strength evaluation method is the tensile butt test. However, it is the opinion of the authors that the interpretation of the experimental results obtained from such a test often leaves much to be desired. The results of finite element analyses of butt tensile tests are presented, The stresses in the joints are not uniform as P/A would suggest. It can be argued that failure is more closely related to local extremes in stress than it is to the average stress generally reported. As added support for adhesive fracture mechanics, the analysis of butt tensile joints indicates that the maximum stress occurs at the edge of the joint. The location of the maximum energy release rate,G, varies with the ratio of thickness to diameter (h/D) of the adhesive. For a given “inherent flaw” size,Ghas a maximum value in the interior of the joint for smallh/dand at the bond edge for largeh/D.Studies of a transparent adhesive‐adherent system demonstrated that failure initiated at the points of maximum, energy release rate. The value of the failure load was also consistent with the trend predicted by fracture mech

ISSN:0032-3888    

DOI:10.1002/pen.760261308

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760261301

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY