ISSN:0032-3888    

DOI:10.1002/pen.760281302

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractProcessing plastics below their melting points has been shown to be an effective way to significantly enhance the mechanical, chemical, and physical properties of semi‐crystalline thermoplastics. A number of techniques have been developed that are capable of producing highly oriented fibers, films, and shapes. In general, these techniques can be classified as drawing, extrusion, arid rolling, with some very specific modifications having been made to each, that affects the performance of the process. Of particular interest is the rate of production, the range of thicknesses achievable, the uniformity of properties in the product, and the extent, if any, of biaxiality in the product. In recent years, the productivity of such forming processes has been increased by reducing the level of molecular entanglement among neighboring molecules. As an alternate to these orientation processes, techniques have been developed which rely on strain Induced crystallization to enhance the modulus of molded parts and extrudates from a melt. This paper constitutes a review of these techniques with emphasis on the process parameters, polymers investigated, and properties of the resulting material

ISSN:0032-3888    

DOI:10.1002/pen.760281303

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractIn this study, isotactic polypropylene (i‐PP) has been deformed by uniaxial compression to draw ratios up to 16×, and at draw temperatures from 30°C to 140°C. An order‐disorder transition in the crystals is observed at draw temperatures well above the stability limit, 70°C, reported for the disordered phase; Furthermore, this disordered phase (called smectic) is found to induce ductility and improve the efficiency of draw. The deformation induced smectic phase has been characterized using WAXS, DSC, and on‐line compression load versus draw ratio measurements. In consequence, a set of process conditions are offered to optimize draw. A mechanism for plastic deformation of i‐PP is also suggested, using the smectic phase

ISSN:0032-3888    

DOI:10.1002/pen.760281304

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe thermal and flow gradients present during thick polymer molding processes can produce layered structures through the thickness which vary in crystallinity, orientation, and axiality. Such structural complexity is difficult, expensive, and time consuming to characterize and presently impossible to predict. In order to overcome these problems emphasis in our laboratory has been directed toward the development of rapid, nondestructive techniques for the quantitative characterization of the structure of thick polymer samples. This includes the characterization of the average structure, the surface structure, and the internal layer structure. The present paper discusses some of these techniques and illustrates their application.

ISSN:0032-3888    

DOI:10.1002/pen.760281305

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is well known that orientation can produce, at a minimum, an order of magnitude improvement in physical properties of low cost plastic resins. A unique, large‐scale, commercial rolling mill process for continuous orientation of plastic sheet has been developed, A number of oriented materials have been commercially produced by this rolling mill process with a wide variety of physical properties attained. This has resulted in large volume sales of many interesting commercial products. Over the last thirty years, numerous researchers have conducted studies to evaluate the theoretical aspects of the rolling process, and the resultant properties. Most commercial oriented products are of relatively small cross sectional size such as fibers and film. The process reported herein produces heavy cross section oriented sheet. A new class of high strength thermoplastic materials is now available for design engineers to use. Long‐term strength properties are often 10 to 100 times better than with unoriented thermoplast

ISSN:0032-3888    

DOI:10.1002/pen.760281306

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe use of polymer dielectrics, particularly biaxially oriented polypropylene (BOPP), has revolutionized power distribution around the world. BOPP film of sub mil thickness has displaced impregnated Kraft paper because of superior dielectric performance, lower cost, and small volume. The polypropylene molecule has a unique set of properties which combine stable dielectric properties in the operating temperature and frequency range along with an adequate dielectric constant. High levels of orientation and a small unbalance of orientation are required to produce films of high dielectric strength over large areas of film. Control of thickness uniformities to approximately ± 5 percent are critical to the reliable operation of the capacitor under load and to control of capacitance in the product. A special fibrillated surface is required which promotes complete impregnation by the dielectric fluid.This surface is acquired by the development of a specific crystal morphology at one surface of the film. No additives are used to promote this crystalline structure since most additives effect dissipation factor and generate unwanted heat. Similarly, control of contamination (ppm and ppb) is a key factor in the manufacture of film power capacitors

ISSN:0032-3888    

DOI:10.1002/pen.760281307

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractAchievement of exceptional properties in films/fibers generally requires very high to ultra high molecular weights and very high degrees of orientation. A brief description of the fiber related technologies‐used to maximize orientation in high performance fibers, e.g., solid state extrusion, special drawing methods gel spinning, and liquid crystal spinning are reviewed. A detailed comparison of the fiber properties resulting from these technologies is also shown. Particular emphasis is.placed on describing the upgrading of polyethylene to a high performance fiber product through several of these technologies. Gel/solution spinning of ultra high molecular weight polyethylene (UHMWPE) is especially highlighted. The latest worldwide efforts to commercialize gel spun fibers are discussed as well as the applicability of the process to other thermoplastics. Applications illustrating the use of high performance fibers in various end use areas are summarized. The primary properties critical to each are also outline

ISSN:0032-3888    

DOI:10.1002/pen.760281308

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760281301

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY