摘要:

AbstractAlthough polymeric materials have a relatively minor role in our solid waste disposal problems, they display a particular prominence as litter because of their environmental permanence, Photodegradation has been suggested as one possible solution, but considerable debate has centered on the need, costs, and limitations of such degradable systems. The chemical mechanisms involved in practical photodegradation are illustrated by a review of the oxidation schemes for normal and sensitized polystyrene. The different mechanisms associated with the use of additives, comonomers, and halogens are considered in some detail. A listing of patent literature relating specifically to photodegradable polystyrene is included in the review.

ISSN:0032-3888    

DOI:10.1002/pen.760160202

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe effect of thermal annealing and quenching on the notched Izod impact strength of several polymers has been studied. Primary emphasis was placed on polycarbonate, but ABS, PVC, polysulfone, and polymethylmethacrylate were also studied. It was determined that residual stresses created by thermal quenching from above the glass transition temperature can have a great effect on impact strength for the polycarbonate, PVC, and polysulfone polymers studied. In fact, it is shown that the thickness transition observed in impact strength for polycarbonates is governed by the residual stresses and not by thickness. In polycarbonates, quenched sheets up to 3/8 in. in thickness have shown impact strengths of 18 ft‐lb/in. whereas sheets 1/8 in. in thickness can be embrittled by annealing, showing an impact strength of 2 ft‐lb/in. However, it has been shown that this embrittlement results from the absence of residual stress. Residual stresses having maximum values up to 3000 psi (in Compression) have been determined at the polycarbonate sheet surface using birefringence measurement techniques. The existence of these compressive stresses is postulated to restrict the extent of craze growth at the notch tip, and the impact specimen can yield rather than fail in a brittle manner if the stress state is suffici

ISSN:0032-3888    

DOI:10.1002/pen.760160203

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractFor fabrication processes such as blow molding, vacuum forming, film blowing and fiber spinning, extensional flow is the dominate mode of melt deformation. Under these conditions, extensional viscosity is a significant rheological property. Thus, the biaxial extensional viscosity was measured for several samples of polypropylene. A technique based on the bubble inflation method of Denson and Gallo was used. Experimental values of biaxial extensional viscosities ranging from 1014to 1010poise as a function of strain rate, 10−5to 10−2reciprocal seconds, were obtained at 25°C. The technique used was critiqued and found to be useful in characterizing unoriented and biaxially oriented films, Uniaxially oriented films gave unsatisfactory results. It may be possible to use this testing method to assist in materials selection decis

ISSN:0032-3888    

DOI:10.1002/pen.760160204

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractPolymer blends and composites are composed of two different components, and usually, two different phases. Sometimes one phase is continuous and the other clearly discontinuous. Often, however, both phases retain some degree of continuity, as in certain fiber reinforced composites, block copolymers, materials composed of alternating lamellae structures and interpenetrating networks. A semi‐empirical theory is developed to express mathematically not only the known structures, but also two‐phase morphologies not yet synthesized or characterized. Many structures both real and proposed are shown to exhibit dual phase continuity, although for most systems, one phase can be said to be “more continuous” and the other “less co

ISSN:0032-3888    

DOI:10.1002/pen.760160205

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractChlorinated PVC is superior to unmodified PVC as a thermoplastic for use in thermoforming, especially if improved heat resistance and dimensional stability are required. In the present report, results tire given of a fundamental experimental study on the thermoformability of CPVC sheets obtained by calendering various formulations based on CPVC resins with at least 65 percent chlorine content. Extensibility as well as the relationship between stress and strain in uni‐ and biaxial stretching have been determined as a function of temperature and rate of stretching by means of specially devised, highly instrumented laboratory equipment. Stress‐strain relations under isothermal conditions and at constant strain rate are compared for the two modes of stretching, and the difference in behavior between PVC and CPVC, particularly with regard to the effect of temperature, is emphasized. Internal stresses frozen in during cooling, following rapid stretching at appropriate thermoforming temperatures, have been determined by means of a detailed analysis of retractive force measurements. The relationship between internal stress and molecular orientation is discussed as well as the effect of the latter parameters on various properties of technological interest: dimensional stability, impact resistance, and gas permeabil

ISSN:0032-3888    

DOI:10.1002/pen.760160206

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractA computer study was made to determine the thermal ignition criteria and ignition boundaries for chain‐addition polymerization in a well‐mixed batch system using a simple kinetic model. The occurrence of thermal runaway was shown to be a function of initiator type, feed conditions, and heat transport parameters. It was found that thermal runaway does not occur early with respect to monomer and initiator conversions and that for strongly dead‐ending systems, the sensitivity characteristic of ignition disappears. The role of various dimensionless parameters in characterizing reaction behavior is also disc

ISSN:0032-3888    

DOI:10.1002/pen.760160207

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThermal runaway arid parametric sensitivity were experimentally demonstrated in styrene polymerizations. Ignition boundaries were established for several initiator concentrations and a dimensionless boundary plotted. Runaway sensitivity was shown to disappear under specific conditions.

ISSN:0032-3888    

DOI:10.1002/pen.760160208

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760160201

出版商:Society of Plastics Engineers, Inc.    

年代:1976

数据来源: WILEY