Heat shrinkable properties

The heat shrinkable properties of these tubes are demonstrated in... 

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. 

Fluorocarbons (PTFE, FEP, PVF2) Powder, emulsions Excellent high temperature properties. TFE to 500 F. FEP is easier to mold, but maximum use temperature is 400 F. Nearly inert chemically. Nonflammable. Loading with conductive filler improves creep resistance. Low coefficient of friction. High-temperature cable shielding, gaskets, heat-shrinkable tubing. 

PVC, PVA, PVAC, Copolymers) organosols forms available including hard and flexible types. Properties are highly dependent on plasticizer used. May be injection, extrusion, compression molded, vacuum formed. Low cost. antistatic sheet and hose, RF gaskets, heat-shrinkable tubing. 

The radiation-treated cables find wide applications in control instmmentation of nuclear power reactors, particle accelerators, aviation, and telephone equipments. Usually PE and PVC are radiation cross-linked for production of such cables. The heat shrinkable foils are widely used in packaging, electrical and electronic industries. The radiation cross-linked PE possesses the property of elastic memory which is utilized to produce heat shrinkable products. 

Irradiation of thermoplastics leads to cross-linking and thus imparts the properties of a thermosetting plastic. Tubing which has been expanded after the radiation treatment has a memory of its former size and will shrink to its original size when heated. Shrinkable tubing is available in a number of different plastics.2... 

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... 

Morshedian, J. Khonakdar, H.A. Mehrabzadeh, M. Eslami, H. Preparation and properties of heat-shrinkable cross-linked low-density polyethylene. Adv. Polym. Technol. 2003, 22 (2), 112-119. 

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). 

Slot liners, for example, are used in motor and generator construction to separate and insulate coils of magnet wire from the slot walls in the steel stator, and films are also used to separate different coils of wire from one another (phase separation) in motors. For these applications, materials with good electrical, thermal, and mechanical properties are required. Special grades are applied in capacitors and heat-shrinkable tubing. 

Cheng et al. [1990] refer to several possible polymeric blends, consisting of fluorinated and non-fluorinated, elastomeric and non-elastomeric, polymers and copolymers, which may also contain crosslinking agents and other additives, for use in cable jackets and heat-recoverable e.g., heat-shrinkable) articles. They point out that PVDF, and copolymers of ethylene and tetrafluo-roethylene (ETFE) have many desirable properties but their high stiffness can be undesirable for certain applications. However, their blends with some thermoplastic elastomers show markedly reduced stiffness, while substantially retaining their other desirable properties. Cheng et al. 

Shrinkablefilm and tubing Cross linked semicrystalline thermoplastics display rubberlike properties at temperatures above their melting points. On deformation followed by fast cooling the polymer maintains its deformed shape. The polymer returns to its original shape when reheated. This memory effect is applied in the production of heat shrinkable films and tubing. Radiation doses of the order of 40 — 1(X) kGy are used in the production of heat shrinkable products. 

Antistatic packaging materials come in a variety of forms, including Him, foam, bubble wrap, and containers. ESD films in heat-shrinkable form are designed to minimize static generation by friction within the bag, as well as transmission of static charges from outside the bag. These materials are often tinted pink as a visible signal of their antistatic properties. 

Deviees designed to transmit information by means of photons now incorporate polymeric materials with the appropriate structures. Passive applications include the eoating of optieal fibers by UV eurable epoxy aerylates, thermal curing silicones, or heat-shrinkable polyethylene, to protect them from mechanical wear. Polymers have also been used in the manufaeture of wave guides. Suitable polymers can now be synthesized having aetive nonhnear optical properties, which depend on the eleetronie exeitation of the 7t-electron system. 

In the field of aerospace applications, the reliability of materials under extreme exposure conditions is of prime importance. The high- and low-temperature properties of the fluoroelastomers have permitted them to give reliable performance in a number of aircraft and missile components, specifically manifold gaskets, coated fabrics, firewall seals, heat-shrinkable tubing and fittings for wire and cable, mastic adhesive sealants, protective coatings, and numerous types of O-ring seals. 

The effect of radiation on materials has importance in the areas of wire and cable insulation, heat-shrinkable articles, curing of elastomers, plastics, paints and inks, electron beam lithography, medical sterilization, polymer property control, and outer space applications. 

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