Plastics chemical modification techniques

Surface thermoplasticization of solid wood or particles is one of the more useful chemical modification techniques because most of the inherent properties of wood are retained. External plasticizers can only be applied to wood... 

Two important chemical modification techniques for PE arc chlorination and sulphochlorination [6,7,8]. Chlorinated-PE is used for a variety of different applications depending on the level of chlorine incorporation [6]. Chlorinated-PEs with mass fractions of (10 to 40) % chlorine are used as synthetic rubbers. Those with mass fractions of (25 to 50) % chlorine arc used as a high molecular weight plasticizer, and those with mass fractions of (40 to 75) % chlorine are used as a binder for paints. Chlorinated-PE is also used as an impact modifier for poly(vinyl chloride). 

The interface between plastic and wood fibres strongly influences the mechanical properties of a plastic/wood fibre composite. A means for evaluating the effectiveness of surface treatment on the wood fibres in the PVC/wood fibre composites is presented that investigated the adhesion between PVC and laminated wood veneers. Wood veneers were first treated with gamma-aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated PP for surface modification. The chemical modification made on the wood surfaces was then characterised by different complementary surface analytical techniques X-ray photoelectron spectroscopy and surface tension measurements. 63 refs. 

Moreover, wood has limited thermoplasticity. Although it can be bent under steam and chemical treatment, wood normally bums before it melts or becomes sufficiently plastic for heat molding or extrusion. These two techniques are important ways of shaping materials in high-speed composite production and are therefore keys to the cost-efficient penetration of lignocellulosic materials into the composites market. Chemical modification of wood offers a means of improving its thermoplasticity. 

The volume is divided into three parts Part I. Metallization Techniques and Properties of Metal Deposits, Part II, Investigation of Interfacial Interactions," and Part III, "Plastic Surface Modification and Adhesion Aspects of Metallized Plastics. The topics covered include various metallization techniques for a variety of plastic substrates various properties of metal deposits metal diffusion during metallization of high-temperature polymers investigation of metal/polymer inlerfacial interactions using a variety of techniques, viz., ESCA, SIMS, HREELS, UV photoemission theoretical studies of metal/polymer interfaces computer simulation of dielectric relaxation at metal/insulalor interfaces surface modification of plastics by a host of techniques including wet chemical, plasma, ion bombardment and its influence on adhesion adhesion aspects of metallized plastics including the use of blister test to study dynamic fracture mechanism of thin metallized plastics. 

Although chemical techniques can be used to modify the properties of biopolymers in order to expand their range of applications, this is not the unique way to improve biopolymer performance. There are different methods to transform biopolymers in sources of structural polymers that may supplant traditional commodity plastics, such as genetic manipulation of some plant species, polymerization of biological starting materials, or the creation of new gene sequences that can lead to novel protein polymers through the application of recombinant DNA methods. However, only biopolymer physical/chemical modifications will be discussed in this chapter. 

The origins of the plastics industry go back well over a century to the early exploitation of nitrocellulose but the manufacture and use of plastics in a large way came later with the development of petro-chemicals and the resulting ready availability of the many precursors required. Most of the polymers that are of commercial importance now were introduced in the period between the two world wars, or in the years immediately following. It seems reasonable to anticipate that the polymers sold in quantity at present are likely to remain significant for some time in the future newer materials may be added but changes perhaps will be linked mainly to the modification of existing types for more specific purposes and techniques of manufacture. 

It was noted by MacDiarmid and Epstein as early as 1989 that PAn salts may also be deposited as films on a variety of substrates by immersing the substrate in the polymerization mixture.29 In fact, during standard chemical polymerization, one often observes the deposition of a thin, extremely adherent green emeraldine salt (ES) film on the walls of glass reaction vessels, as well as the bulk precipitation of PAn/HA powder. By judicious manipulation of the polymerization conditions such as reagent concentrations/ratios and modification of the substrate surface, one can maximize the surface deposition as opposed to polymer precipitation.30 This phenomenon has been developed into a widely useful in situ polymerization technique for the preparation of PAn films on a variety of insulating surfaces such as glass and plastics, as well as on fibers and fabrics. 

One of the most important methods for controlling the yield behaviour of polymers is rubber modification, which is widely used to increase fracture resistance. The technique was first used in 1948 to modify the properties of polystyrene, and has since been extended to most of the major plastics, including polypropylene, polycarbonate, and rigid PVC, and to a number of the less highly crosslinked thermosets, notably epoxy resins. Between S and 20 % of a suitable rubber is added in the form of small particles, which are typically between 0.1 and S /im in diameter. Chemically reactive rubbers are preferred, because they form bonds with molecules of the surrounding matrix which can withstand tensile stress. The rubber particles have low moduli, and therefore act as stress concentrators. Accelerated deformation in the matrix adjacent to the rubber particles results in a lowering of the yield stress. 

The electron beam technique has often been utilized for surface modification and properly improvement of polymer materials like fibers, films, plastics, and composites in recent decades [104-107]. It may remove surface impurities and alter surface chemical characteristics at an appropriate irradiation condition. Electron beam processing is a dry, dean, and cold method with advantages such as energysaving, high throughput rate, uniform treatment, and envirorunental safety. 

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