Authors:K. Ito, Li Hong-ling, Y. Saito, T Yamamoto, Y. Nishihara, Y. Ujihira, and K. Nomura
The free-volume, of size ranging from 0.2 to 0.4 nm in radius, in an ethylene-vinyl alcohol copolymer was estimated using positronium lifetime measurement to elucidate the dependence of oxygen permeability on the free-volume size and fraction, on the ethylene content and on the crystallinity. The permeability and the free-volume fraction with varying the ethylene content were well related and the relation was interpreted based on the free-volume theory near below and above the glass transition temperature. On the other hand, the crystallinity significantly influenced the fraction of the amorphous region, where the free-volume hole exists, along with a slight change of the free-volume size. The variation of the permeability with the crystalline degree cannot be explained from the averaged free-volume fraction estimated by the whole volume of the polymer, but the permeability correlated with the free-volume size apparently.
Authors:K. Ito, H.-L. Li, Y. Saito, T. Yamamoto, Y. Nishihara, Y. Ujihira, and K. Nomura
The size distribution of free-volume (<~0.1 nm3) of ethylene-vinyl alcohol copolymer with various crystalline degrees was estimated by positronium lifetime measurement. With increasing degree of crystallinity, the size distribution significantly narrowed and the intensity of positronium decreased. This indicates that the inhomogeneity reduces with the increase of the degree of crystallinity. It is found that the free-volume fraction estimated is reflected by the fraction of the amorphous region.
Authors:M. Dolores Fernández and M. Jesús Fernández
The thermal degradation of ethylene-vinyl acetate (EVA), ethylene-vinyl-3,5-dinitrobenzoate (EVDNB) and ethylene-vinyl alcohol
(EVAL) copolymers have been studied using differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and
dynamic conditions in nitrogen. Thermal analysis indicates that EVA copolymers are thermally more stable than EVDNB samples.
The degradation of the copolymers considered occurs as an additive degradation of each component polyethylene (PE) and poly(vinyl
acetate) (PVA), poly(vinyl-3,5-dinitrobenzoate) (PVDNB) or poly(vinyl alcohol) (PVAL). The apparent activation energy of the
decomposition was determined by the Kissinger and Flynn-Wall methods which agree well.