摘要:

AbstractInterpenetrating polymer networks (IPN's) can be defined as a combination of two polymers in network form, at least one of which was synthesized and/or crosslinked in the immediate presence of the other. Historically, the science of IPN's began with the papers of J. R. Millar in 1960 on homo‐IPN's made from polystyrene, but the first recorded publication is a patent by J. W. Aylsworth in 1914. This latter system was based on phenol‐formaldehyde for one network, and sulfur cured natural rubber for the other network. Early academic laboratories interested in IPN's include the Frisch team at Detroit and SUNY, who soon added their former student, Danny Klempner, and Yuri Lipatov's team at the Ukranian SSR Academy of Sciences in the USSR, as well as the author's laboratory. More recent academic teams interested in IPN's include Douglas Hourston at the University of Lancaster, England; Robert Cohen at MIT; S. C. Kim at the Korea Advanced Institute of Science and Technology, Seoul, Korea; G. Meyer and J. M. Widmaier in Strasbourg, France; and many others. Numerous industrial laboratories are interested, noting that about 90 U.S. patients have been granted, most of them in the past ten years. Systems of special interest include the new thermoplastic IPN's, which are really hybrid materials between polymer blends and IPN's, and the IPN‐based RIM (reaction injection molding) materials. Other materials include the sequential IPN's and the SIN's, which have both polymers simultaneously polymerized, and the latex IPN's, which often exhibit core‐shell characte

ISSN:0032-3888    

DOI:10.1002/pen.760250902

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractDiffusion of water in a glassy epoxy resin has been studied by the sorption method. Film thickness scaling is used as a diagnostic tool for non‐Fickian sorption processes. A sorptiondesorption cycle effectively increases the preexisting free volume in the resin and renders the subsequent sorption process different from the original. The effect is understood by considering the time scale for diffusion and that for molecular relaxation of the glassy polymer network. A non‐Fickian sorption process is observed for an insufficiently cured resin and is caused by the resin undergoing further postcuring in the sorption process. It is shown that oxidation of the resin during sorption also gives rise to non‐Fickian processes previously described in the literature as diffusion anomalies for epoxies. It is further shown that the difference between sorption and resorption curves is not caused by irreversible damage to the resin but due to reversible changes in network conforma

ISSN:0032-3888    

DOI:10.1002/pen.760250903

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractA model is proposed for the diffusion mechanism of water in glassy epoxy resins. The polymer network is assumed to consist of two regions in which water molecules possess different mobilities. By considering the distribution of water molecules among these regions it is possible to describe the concentration dependency of the diffusion coefficient in the sorption and resorption processes. The diffusion coefficient becomes constant when the sorption temperature is close to the effective glass transition temperature of the epoxy‐water binary mixture. An explanation of this effect is also provided by the mode

ISSN:0032-3888    

DOI:10.1002/pen.760250904

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractPolycarbonate (PC), one of the leading engineering plastics, suffers from deterioration under harsh environmental conditions. It is sensitive to the effects of light (UV) radiation, to thermal degradation, and to the attack of hot water, due to hydrolysis. By exposure of various commercial PC grades—at various molecular weights and stabilization—to either natural or accelerated conditions, a maximum lifetime of three years was predicted for the best‐behaving grades. The criterion for failure was mainly based on loss of ductility in tensile tests, as well as loss of optical clarity and chain scission. Hot water has a significant effect on the performance of PC samples, and this is considered to be its greatest weakness. Degradation after exposure at various temperatures (without UV or humidity) leads to estimation of a temperature‐endurance index, that may serve as a practical limiting criterion for polymer life exp

ISSN:0032-3888    

DOI:10.1002/pen.760250905

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe big success of the reaction injection molding (RIM) process has brought about a marked interest in reacting polymer processing. In the present work, we study the technical feasibility of a continuous process to coat metallic conductors using reacting polymers. In the envisioned system, RIM type reactants are mixed and then injected into a tubular reactor through the center of which we pass the cable to be coated. The predictions of the mathematical model developed show that a feasible process can be designed by adequate control of the heat transfer phenomena. The process needs in general, a low reactor temperature and a high cable temperature.

ISSN:0032-3888    

DOI:10.1002/pen.760250906

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractAs an engineering thermoplastic acetal homopolymer is often used in the manufacture of parts subjected to fatigue. This article presents the results of flexural fatigue tests on acetal Delrin 550 under different environmental conditions, namely ambient air, forced‐air ventilation at ambient temperature, or oil kept at a constant temperature at 40°C. The fatigue tests were performed on specimens cut from extruded sheets at a constant frequency of 30 Hz. Surface temperatures of the test specimens were measured either optically or electrically, depending on the environment. The test results show that both acetal stress and surface temperature of specimen, which are somehow related, vary considerably from one type of environment to another. However, results show that the fatigue life of the specimen is mainly governed by the amplitude of the initial stress and is almost independent of the environment, Another subject examined was the effect of oil on acetal's mechanical properties. It was found that prolonged contact with oil produced slight variations in tensile properties, but no significant effect on fatigue, li

ISSN:0032-3888    

DOI:10.1002/pen.760250907

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractPolymer blends of thermosetting and thermoplastic polymers were developed by properly mixing them in the presence of compatibilizers. Two compatibilizers that are structurally and chemically similar to thermosetting and thermoplastic polymers and a compatibilizer that does not have such similarity were synthesized. Polymer blends of phenol formaldehydepoly(methyl methacrylate) and phenol formaldehyde‐polystyrene were prepared by using the compatibilizers, poly(phenol formal dehyde‐s‐triazine‐methyl methacrylate), P(PF‐g‐MMA), poly(phenol formaldehyde‐s‐triazine‐styrene), P(PF‐g‐S), and poly (cinnamaldehyde‐co‐oxy propylene oxy isophthaloyl‐cooxy propylene oxy fumaroyl), P(C‐g‐E). The effects of molecular weight and quantity of the copolymer on the compatibility of the polymer were examined. The optimum compatibility which leads to superior tensile properties of the present blends was observed with P(PF‐g‐MMA) and P(PF‐g‐S) copolymers. The superior properties were also found to occur only in the range of the optimum molecular weight and quantity of the copolymer present in the blend. The polymer blends were analyzed by differential scanning calorimetry (DSC) and Electron Microscopy. DSC scans of P(PF‐g‐MMA) and P(PF‐g‐S) copolymer blends showed a singleTgwhereas the scans of P(Cg‐E) copolymer blends showed an additionalTgfor unblended thermoplastic fractions. The electron microscopy studies also revealed good compatibility in P(PF‐g‐MMA) and P(PF‐g‐S) copolymer blends in which the unblended thermoplastic fractions are negligibly less. The UV‐vacuum and heat resistance of the P(PF

ISSN:0032-3888    

DOI:10.1002/pen.760250908

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe Differential Scanning Calorimeter (DSC) was used to discriminate among 25 commercial high density polyethylenes (HDPE) on the basis of their degree of crystallinity and melting temperature. The area under the melting endotherm correlated directly with density and inversely with creep and thermal expansion measurements. Since high crystallinity was related to the design required properties of density, creep, and thermal expansion, DSC studies readily identified eight of the more promising polymers from the group of 25. The overall crystallization kinetics of polyethylenes with 75 percent crystallinity were analyzed by the Avrami and Fischer‐Turnbull equations. Results indicate small disk‐like spherulites (Avramin= 2) following nucleation‐controlled growth kinetics. These conclusions are in reasonable agreement with polarizing microscope observations. An equilibrium melting temperature between 141 and 142°C was estimated from Hoffman‐Weeks plots. Processing thick parts from highly crystalline polyethylene is difficult because of the 14 percent volume change on crystallization. Higher degrees of crystallinity are associated with moderate molecular weight, so the viscosity range of these polyethylenes is not especially suited for processing by extrusion. These caveates necessitate tradeoffs between optimal design properties and processing requirements for HD

ISSN:0032-3888    

DOI:10.1002/pen.760250909

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractAn analysis is presented which allows the sheet or film die designer to estimate when inertial and gravitational effects are important. General theoretical equations are developed for end fed dies with arbitrary variation of the cavity cross sectional shape, cavity taper, slot length, and gap over the width. The method assumes viscous flow and a two dimensional approximation for the cavity flow. For fluid flow properties, it is assumed only that the apparent viscosity is a single valued function of the shear rate. In the important special case of constant die geometry and power law fluids, three dimensionless numbers plus the power law index are the parameters controlling the uniformity of flow from the die. Results are presented that illustrate when die orientations with respect to gravity and when fluid inertia are important. When they are not, simple expressions for die inlet pressure and uniformity index are given.

ISSN:0032-3888    

DOI:10.1002/pen.760250910

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY

摘要:

AbstractThe role of the size and type of residual stresses and their distribution in the interior of polycarbonate mold‐injected test bars was studied, in view of the interrelationship between toughness and thermal or environmental history. The large thermal gradient during solidification of the polymer in the mold builds up compressive stresses near the wall and tensile stresses in the core. Annealing followed by slow cooling may reverse the type of stresses near the surface, while quenching augments the compressive stress. The latter stress near the wall is responsible for the extraordinarily high impact strength of polycarbonate. Exposure to the atmosphere and immersion in hot water may affect the distribution of residual stresses and thus contribute to the embrittlement of the originally tough polymer. The importance of molecular weight and polymer stabilization is elucidate

ISSN:0032-3888    

DOI:10.1002/pen.760250911

出版商:Society of Plastics Engineers, Inc.    

年代:1985

数据来源: WILEY