Polymer processing heat shrinkability

Electron beam-initiated modification of polymers is a relatively new technique with certain advantages over conventional processes. Absence of catalyst residue, complete control of the temperature, a solvent-free system, and a source of an enormous amount of radicals and ions are some of the reasons why this technique has gained commercial importance in recent years. The modification of polyethylene (PE) for heat-shrinkable products using this technique has been recently reported [30,31]. Such modification is expected to alter the surface properties of PE and lead to improved adhesion and dyeability. 

Heat-shrinkable films, 28 46 Heat shrinkable polymers, 22 364 Heat sinks, 26 756 silver in, 22 658 Heatsink slugs, 24 864 Heats of reaction, in DR Processes,... 

Production and application of heat-shrinkable tubing on a wire splice. (Radiation Processing of Polymers (Singh, A., and Silverman, Eds.) Carl Hanser Publishers, p. 20 (1992). With permission from Carl Hanser Publishers.)... 

FIGURE 8.9 The process of producing heat-shrinkable polyethylene tubing and the use of the tubing to cover a wire joint Two-sided irradiation of a wire by electron beam. (Singh, A. and Silverman, 1, Eds., Radiation Processing of Polymers, Hanser, Munich, 1992. With permission.)... 

The use of radiation to modify the physical properties of polymers has become a very important industry with products such as electrical cables with insulation capable of withstanding high temperatures and heat-shrinkable polyethylene. However, of direct relevance to this symposium was the recognition in the early 1970 s that electron beam irradiation of pol3mier films could provide an important lithographic tool for the manufacture of microelectronic components. For consideration of the general principles of these processes see, for example, references (66) and (67). The products required In this field are complex requiring both microscopic... 

An example system is PVC and polyethylene wire and cabling irradiated to improve stresscracking resistance, abrasion resistance, high-temperature properties and flame retardance, via controlled electron-beam crosslinking (Loan, 1977). Additionally electron-beam crosslinking is utilized to impart memory into a polymer system, such as crosslinked PE materials for heat-shrinkable films and pipe applications (Baird, 1977). The control of electron-beam processing has advanced the quality of cell size and shape of PE foams via control of crosslink distribution (Paterson, 1984). 

The second method uses cross-linked polymers that have been processed to produce an extended form that, upon heating, shrinks to smaller dimensions. Suitable polymers for this type of heat-shrinkable tubing are radiation cross-linked polyolefins and halocarbons including poly(vinyl chloride) and poly(vinylidene fluoride). 

In other reports, a heat shrinkable (oriented) film was described in which the base resin was a copolymer of chlorotrifiuoroethylene and up to 5% of another monomer such as vinylidene fluoride. This film could be shrunk by the application of heat (about 2 minutes at 150°C), thus it was useful as a covering. To orient the film, it was wound around a pair of parallel rolls (similar to Fig. 6.26) in which the second roll (B in Fig. 6.26) moved at a faster rate than the first roll (A in Fig. 6.26). Heat was required to assist the stretching process and, to accomplish this, the rolls were heated to a temperature in the range of 85 °C to 130°C. The stretched film was cooled below the second transition temperature of the polymer while it was held under tension. Stretching the film in the... 

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