Crystalline melting temperature irradiation dose

Figure 9. Crystalline melting temperatures of the irradiated CL-AGE copolymer(6 mol% AGE) with increasing irradiation dose for the first and second DSC scans.

Polyethylene and polypropylene are mutually incompatible and the blend prepared from the melt of a mixture of the two polymers is, to a certain extent, hetmrgeneous. The transition of the original crystal structure of polyethylene into a pseudobexagonal modification depends on the irradiation dose, the dispersion method, and the conditions of the orientation of the macrcmudecule in the sample. Pseudobexagonal modification exists from S to 10 K over the melting temperature of a parent crystalline structure of polyethylene. 

The physical properties of polystyrene remain relatively stable even after high doses of irradiation. The hardness, tensile strength, and shear strength are all within 75% of the original values up to doses of lO MGy [177]. The glass transition temperature is reported to increase by about 10 °C and the crystalline melting point increases to 150 °C after the irradiation of crystalline isotactic polystyrene to 40 MGy [178]. 

The effect of gamma irradiation on the thermal characteristics of unreinforced highly crystalline polypropylene was studied by determination of melt temperature (TJ, melting enthalpy (AHJ, and degree of crystallinity values. All these values decrease with increasing radiation doses, indicating that the polymer becomes more amorphous during irradiation. 

Polar copolymers of ethylene, such as ethylene-vinyl acetate (EVA) and ethylene-ethyl acrylate (EEA), are readily crosslinked upon exposure to high energy irradiation [88]. In fact, the melt index of EVA can be controlled by the use of low doses (<50 kGy) of irradiation [89]. The presence in polar ethylene copolymers of comonomer units such as vinyl acetate or alkyl acrylates (methyl, ethyl and n-butyl) proportionately reduces the level of crystallinity, and since the majority of radiation responses of interest take place in the amorphous phase, the responses are more uniform throughout the polymer mass. When the irradiation is done at room temperature, the physical properties after irradiation follow the same trend as polyethylene [90]. 

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