摘要:

Some polymers show varying dynamic responses according to the technique employed to measure them. The polyethylenes are a good example, with a wide range of circumstances complicating the analysis of mechanical and dielectric relaxation spectra. First, the polyethylenes are nonpolar polymers that require oxidation or chlorination to obtain consistent dielectric activity; second, the relaxation spectrum is highly complicated in each of the three characteristic zones (γ, β, and α); and finally, the response to an alternative stimulus differs according to its physical origin. Thus it is well known that differences arise between dynamic mechanical and dielectric spectra when they are compared (McCrum et al., 1967; Morozuni et al., 1970; Ribes-Greus, 1986). Moreover, to obtain reasonable conclusions, it is necessary to use the same type of polymer in all cases; and to control the crystalline morphology of the specimen, a constant thermal history is needed.

ISSN:0360-2559    

DOI:10.1080/03602558908049819

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Plastics degrade through the influence of such factors as the sun's radiation, temperature, humidity, rain, the oxygen content of the air, and atmospheric pollutants. The most deleterious of these effects is radiation, which is responsible for breaking up polymer chains. The sun emits a complete spectrum of energy radiation, with waves similar in physical structure but varying in length and therefore in photon energy. Wavelength has an inverse relationship to quantum energy, as shown in Fig. 1.

ISSN:0360-2559    

DOI:10.1080/03602558908049820

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A number of plastic materials, such as unplasticized poly(viny1 chloride) (uPVC), acrylonitrile-butadiene-styrene (ABS), high-density polyethylene (HDPE), poly-(vinylidene fluoride) (PVDF), and chlorinated poly(viny1 chloride) (cPVC), are available for numerous applications. uPVC and HDPE pipes are used in pressurized piping systems in Saudi Arabia for industrial, agricultural, domestic, and general-purpose applications. Some studies have been carried out to investigate the causes of failure in plastic pipes, which is very high in the area. In this chapter an overview of the failure of plastic pipes is presented, with emphasis given to failure of pipes due to severe weather conditions in Saudi Arabia.

ISSN:0360-2559    

DOI:10.1080/03602558908049821

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The ability of a screw to manufacture products of good quality with high productivity and low cost is called its performance. At the design stage of an extrusion process, evaluation of screw performance is very important and can be realized on the basis of experimental and theoretical investigations.

ISSN:0360-2559    

DOI:10.1080/03602558908049822

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The aesthetic qualities of extruded articles are critical in many consumer-oriented applications. One area where this has become a major concern is in the manufacture of various automotive rubber parts, such as glass run channels, weatherstrip seals, trunk seals, and others. Such parts are being required to stand up to increasingly stringent warrantees in providing multifunctional sealing, maintaining tight dimensional control with rather complex part profiles, as well as being capable of production at relatively high extrusion line speeds. The vast majority of these parts are manufactured from EPDM (ethylene-propylene-diene monomer) polymers. These terpolymers have been used extensively in manufacturing a variety of extrusion articles for over a quarter of a century because of their wide processing latitude and excellent resistance to ozone, weathering, and heat, in combination with their good physical properties.

ISSN:0360-2559    

DOI:10.1080/03602558908049823

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In recent years polymers have become versatile and widely accepted materials in almost every conceivable application. Many of these applications involve the possibility of exposure to fire hazards. Upon exposure to a sufficient heat source and sufficient atmospheric oxygen, these materials catch fire and bum. However, the rate of combustion varies from polymer to polymer. The overall fire hazard is therefore a function not only of the fire performance of a polymer, but also the degree of exposure of the polymer to fire.

ISSN:0360-2559    

DOI:10.1080/03602558908049824

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Natural rubber is the second most costly raw material, after petroleum, imported by the United States. The present annual demand in the United States is about 1,000,000 tons, all of which must be imported from countries having tropical rain forest climates. Annual demand projected for the 1990 period is about 920,000 metric tons/year [1]. At a projected cost of $1 per pound, the import cost is estimated to be $2.02 billion a year. It is estimated that commercialization would provide the state of Texas with a $250,000,000 agribusiness on land in the Permian Basin of West Texas.

ISSN:0360-2559    

DOI:10.1080/03602558908049825

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The initial components and films of varying refraction indices used in polysiloxane lenses used as artificial crystalline eye lenses have been studied systematically for the first time by means of vibrational spectroscopy. A reliable correlation of spectral data with a set of special toxicological tests has been obtained that allows the choice of artificial lenses and control of their quality before implantation. The advantages of vibrational spectroscopy in the study of the structure and uniformity of polymer materials are incontrovertible, and close control over lens quality has been demonstrated. Spectral sampling of implantates has been shown to have advantages and is required in the absence of criteria for selective toxicity of biotests and under the extremely weak action of low-intensity destructive factors.

ISSN:0360-2559    

DOI:10.1080/03602558908049826

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The increasing deficiency of natural woods has led to the use of agricultural residues in the preparation of pulp and boards. The important agricultural residues are bagasse, straws, and cotton stalks, which accumulate in vast amounts. Some studies concerning the use of bagasse (Lumen et al., 1963), rice straw (Mobarak et al., 1975; Fadl et al., 1984), cotton stalks (Mobarak and Nada, 1975), and other agricultural residues (Lathrop and Naffziger, 1949; Aronosky and Lathrop, 1949) for producing hardboards are available. Actually, resins are added to pulp before board formation to give a final board of high strength and water resistance. The common resins are phenol-formaldehyde, urea-formaldehyde, and melamine- formaldehyde. Also, in one of our previous works, whole black liquor (Nada et al., 1982), produced from rice straw pulping process or its separated components (lignin, hemicellulose, and silica) (El-Saied et al., 1982) in the presence or absence of phenol-formaldehyde resin during hardboard preparation, was used to improve the strength properties of board. Other treatments are used to modify the hardboard or paper sheet properties, by impregnation of the sheets in resin solution (Plomely and Cottstein, 1968; Nada et al., 1981) or by polymer solution (Calleton et al., 1970; Youssef et al., in press). In addition, chemical modifica-tions such as acetylation, grafting (Smraishi et al., 1982). and cyanoethylation are carried out on wood and hardboard to improve their dimensional stability.

ISSN:0360-2559    

DOI:10.1080/03602558908049827

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The low-energy electron beam (EB) curing process has been proposed as a new manufacturing method for papers, foils, and films which may substitute for the heating and ultraviolet (UV) process. Recently, the process was applied to the curing of magnetic media, pressure-sensitive adhesives, and high-gloss printing, because of its economic benefits and the improved mechanical property of the coatings. One advantage characteristic of the EB process is high-speed polymerization of 100% solids without heating. The EB process has been industrialized in manufacturing processes involving high-gloss printing and coating with thin films, which might deteriorate in processes involving heating.

ISSN:0360-2559    

DOI:10.1080/03602558908049828

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor