engleski

EFFECT OF SOLVENT ON RADIATION GRAFTING AND CROSSLINKING OF POLYETHYLENE

Termination reaction in grafting of liquid monomer onto polyethylene is in most cases viscosity dependent and diffusion controlled. The viscosity could be changed by changing the monomer concentration inside the film. Such behaviour was clearly demonstrated by grafting of polyethylene in a mixture of styrene and methanol. Crosllinking of polyethylene influences its swelling properties. It could be expected that pre-crosslinking of polyethylene influences the rate and yield of grafting as well. This is demonstrated by pre-crosslinking of polyethylene and by its subsequent grafting with styrene after the trapped radicals had been annealed out. Grafting was induced by simultaneous irradiation or by preirradiation in vacuum. For pre-crosslinked polyethylene the grafting rate is higher than for the uncrosslinked polymer. However, to high degree of crosslinking causes the grafting rate to fall below that of the native polymer. The increased grafting yield at low crosslinking density is interpreted in terms of gel-effect. In order to obtain more direct information about the influence of swelling agent on polyethylene crosslinking the elastic modulus of the crosslinked polyethylene was investigated. Stress-strain curve of polyethylene samples irradiated in different environments were recorded in molten state at 165 oC. The results show that irradiation of swollen polyethylene produces fewer effective crosslinks than does irradiation of dry polymer.

Radiation grafting; pre-crosslinking; swelling; tenzile properties; effective crosslinks

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