Ethylene-Vinyl Acetate Copolymer (EVA, EAM)
Ethylene-Vinyl Acetate Copolymer (EVA, EAM)
Designation in ISO 1629 - EAM
The copolymerisation
of ethylene with vinyl acetate (VA) is another method by which the crystallinity of polyethylene can be reduced and a rubbery polymer obtained.
The final properties of the copolymer depend on the VA
content; at a VA level of 50% the copolymer is entirely
amorphous, and elastomeric grades generally contain 40-60% VA by weight. The oil resistance of the copolymer is also dependent
on the VA content; in general, however, this lies between that of SBR and polychloroprene. It is swollen by most organic solvents and not resistant
to animal and vegetable oils, but has some resistance to weak acids and alkalis at ambient temperature.
The saturated main chain of the copolymer
confers excellent resistance
to oxygen, ozone and light, but means that these
materials cannot
be crosslinked by sulphur.
Peroxides and radiation are the only methods by which crosslinking can be accomplished, and coagents are often required to achieve the required state of cure.
Uses
The main use of EVA is in wire and cable applications, although the electrical properties are inferior to those of EPDM. EVA is used for some medical extrusions and can be blended with other
polymers to improve ozone resistance.
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