Ro. Sirotkin et Nw. Brooks, The dynamic mechanical relaxation behaviour of polyethylene copolymers cast from solution, POLYMER, 42(24), 2001, pp. 9801-9808
Three polyethylene copolymers, which differ widely with respect to their sh
ort chain branch content, have been cast from solution and subject to exten
sive structural and Dynamic Mechanic Thermal Analysis (DMTA) to establish t
he effect of the morphology on the alpha-, beta- and gamma -relaxations.
The results have shown that the alpha -relaxation temperature, T-alpha, inc
reases with the lamellar thickness, irrespective of grade, initial solvent
concentration or crystallinity and is associated with c-shear within the cr
ystalline lamellae. The beta -relaxation temperature, T-beta, shows a more
complex morphological dependence depending on the grade. The results indica
te that this relaxation is associated with interlamellar shear and is deter
mined, to some extent, by fold surface morphology.
The gamma -relaxation temperature, T-gamma, is shown to be dependent on the
initial solution concentration only. It is concluded that this relaxation
is associated with short-range motions in the amorphous region, with residu
al solvent acting to plasticise the amorphous regions. (C) 2001 Elsevier Sc
ience Ltd. All rights reserved.