Other polyolefin plastics

In addition to propylene polymers, the following polyolefins are produced commercially. 

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These rubbers are now also being blended on a large scale with polyolefin plastics, particularly polypropylene, to produce a range of materials which at one extreme are tough plastics and at the other the so-called thermoplastic polyolefin rubbers (TPORs) (.see Section 11.9.1). 

Larger 3- and 4-m.e.v. Dynamitron electron beam accelerators are likewise available commercially. Service capabilities increase with the m.e.v. level of the electron beam accelerator. A 3.0-m.e.v. Dynamitron electron beam accelerator furnishes radiation capable of penetrating a maximum 370 mils of a unit density material or 185 mils of 2.0-density material other performance capabilities are doubled as well. The overwhelming majority of polyolefin plastic products now being manufactured have section thicknesses which can be penetrated safely even by a 1.5-m.e.v. electron beam accelerator. Two possible exceptions would be printed circuit board and thick-walled pipe. A 3-m.e.v. accelerator could readily meet such requirements. The performance capabilities of the 3-m.e.v. accelerator (12-ma. power supply) are increased not only with respect to maximum depth of penetration but also processing capability, which amounts to 14,000 megarad-pounds per hour at 50% absorption efficiency. 

Transmaterialisation is a more fundamental approach to the problem, which, with the goal of sustainable development, would ultimately switch consumption to only those resources that are renewable on a short timescale. Clearly petroleum, which takes millions of years to form, is not an example of such a sustainable resource. For the method to be truly effective, the wastes associated with the conversion and consumption of such resources must also be environmentally compatible on a short timescale. The use of polyolefin plastic bags for example, which have lifetimes in the environment of hundreds of years, is not consistent with this (no matter how they compare with alternative packaging materials at other stages in their lifecycle), nor is the use of some hazardous process auxiliaries which are likely to cause rapid environmental damage on release into the environment. 

Ethylene Copolymers. Ethylene copolymers probably are the most important materials in hot-melt formulations. Ethylene-vinyl acetate and ethylene-ethyl acrylate polymers are very versatile and available in a wide range of grades offering different co-monomer contents and viscosities. The melts are stable and compatible with various modifying resins, waxes, extenders, and fillers. Adhesion to many substrates is good—including the polyolefin plastics, which are difficult to bond with most other types of adhesive unless the surfaces are pre-treated. 

The range of uses for polyolefin plastics, and for polypropylene in particular, has been expanded greatly in recent years one application of interest in this context comprised large mouldings (approximately 1 m by 0.5 m in area) designed to interlock and to be placed on football grounds or other sports fields... 

Chemical resistance and electrical properties of PMP are similar to those of the other polyolefins, except that it retains these properties at higher temperatures than do either PE or PP. In this respect PMP tends to compare well with PTFE up to 150C (300F). Molded parts made of this plastic are hard and shiny, yet their impact strength is high at temperatures down to -29C (-20F). Their specific gravity of 0.83 is the lowest of many commercial solid plastics. 

Polystyrene was commercialized by I. G. Farben in 1931 and it has long been used as a commodity plastic. Although polystyrene is endowed with excellent properties not found in other commodity plastics such as polyolefins, its amorphous nature (relatively low heat and solvent resistance) limits its use in some application areas. 

Pyrolysis treatments are interesting regarding the aforementioned plastic refuse makeup. Other successful treatments for feedstock recycling of condensation polymers (PET, ABS, etc.), that allows for the depolymerization and recovery of their constituent monomers (e.g. hydrolysis, alcoholysis, methanolysis, etc.), cannot be applied for polyolefin plastics recycling. In contrast, pyrolysis of polyolefins yields valuable hydrocarbon mixtures of... 

Considerable variation is, of course, possible among different grades of the same polyolefin, and useful modifications are obtained by copolymerization, blending with other polymers, and compounding with various additives. As with other crystalline plastics, the polyolefins are not benefited by addition of liquid plasticizers. Such "foreign" molecules are generally not accepted by the crystal lattice, or, if incorporated, cause excessive weakening. 

PP is used in impact modified forms in films, bottles and crates and in unmodified form in ropes and twines. It is frequently present in domestic and industrial waste plastics in association with the polyethylenes. Owing to its pendant methyl groups PP is more readily peroxidised than the other polyolefins and it is not normally separated from them in domestic packaging waste. 

T. McKee, Laser Marking of Polyethylene and Other Polyolefins with Additives, Plastics Formulating <6 Compounding. 

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