| Abstract | dc.description.abstract | The aim of this work is to present a detailed
study of the changes introduced by gamma radiation on
several metallocenic polyethylene copolymers. Therefore,
metallocenic polyethylene and copolymers with 3.3, 9.2,
and 16.1 mol % of hexene comonomer content were synthesized
and irradiated with 60Co gamma radiation under vacuum
at room temperature with radiation doses ranging
from 0 to 100 kGy. Size Exclusion Chromatography data
show that crosslinking reactions predominate over scission,
even for the copolymer with the highest tertiary carbon
content. Over a certain critical dose, which depends on the
molecular weight and molecular structure of the initial
polymer, an insoluble gel forms. The irradiated polymers
also exhibit complex rheological behavior with increasing
melt viscosity and elasticity, consistent with long chain
branching and/or crosslinking. FTIR confirms depletion of
terminal vinyl groups and increase of trans unsaturations
with dose. The rate at which these two reactions evolve
seems to depend on the comonomer content of the irradiated
copolymers. Differential scanning calorimetry and
Raman spectroscopy analyzes indicate less crystallinity and
thicker interphases in irradiated materials. A mathematical
model, which accounts for scission and crosslinking reactions,
fitted well the evolution with radiation dose of the
measured molecular weight data. | en_US |
