The Crystallinity of Ethylene-Vinyl Alcohol Copolymers

The effect of the composition on the properties of?-irradiated ethylenevinyl alcohol copolymers

“…The Figure 3 shows the glass transition temperature glass transition temperature, T_, has been taken as the values vs. the radiation dose for all the samples as said point where a change in the slope is observed in the above. According with the ethylene and vinyl alcohol specific heat -temperature plot, while the melting content and with the Tg values of the homopolymers, the glass transition temperature of Eval F, prior of the irradiation, is higher than that of the not irradiated Eval E [14,15]. It is worth noticing that crosslinking is the main effect however for both copolymers in the whole investigated dose range and indeed the T~ values are always larger than those corresponding to the not irradiated samples.…”

“…More particularly figure 4 shows the melting temperatures of the samples in the first heating run. A large difference (-20 ~ exists in the melting temperatures of Eval E and Eval F according to the differences in T m of the two homopolymer parents [14] and to their composition. A slight change of T m is present for both copolymers at large irradiation doses, which however seems to indicate a not significant modification of crystals perfection.…”

The effect of annealing on the structure and relaxation processes of vinyl alcohol-ethylene copolymers

“…Moreover, a shift of the glass transition temperature to higher temperatures is observed in the annealed specimens because development of crystallites has imposed on the annealed amorphous phase restraints greater than those present before the annealing process was applied, as observed in Table III. A detailed analysis of crystalline structure in these VAE copolymers has pointed out that both the composition and the thermal history are determining factors. 1 Thus, previously reported maps of crystalline lattice versus composition 7,8 displayed that a pseudohexagonal lattice is obtained for composition ranged between 20 and 60 mol % vinyl alcohol (VAL), and that the crystalline regions are isomorphous to PVAL (monoclinic lattice) above 60 mol % VAL. In the VAE copolymers under study, it has been viewed that, on the one hand, slowly cooled VAE1 and VAE2 crystallized into a monoclinic lattice as PVAL homopolymer.…”

The effect of residual acetate groups on the structure and properties of vinyl alcohol-ethylene copolymers

“…2 Thus, previously reported maps of crystalline lattice versus composition 3,4 displayed that a pseudohexagonal lattice is obtained for compositions ranged between 20 and 60 mol % vinyl alcohol (VAL) and that the crystalline regions are isomorphous to PVAL (monoclinic lattice) above 60 mol % VAL. In the VAE copolymers, it has been viewed that, on the one hand, slowly cooled specimens with vinyl alcohol content of or higher than 0.73 crystallized into a monoclinic lattice as PVAL homopolymer.…”

“…As a consequence of the bulkier nature of acetate groups compared to hydroxyl ones, the crystallization process of VAEAc copolymers could be hindered and this possible feature will be assessed by X-ray diffraction, a technique previously used to establish the crystalline structure of vinyl alcohol-ethylene copolymers. [2][3][4] The structural modifications of these copolymers should affect the thermal and mechanical properties, which will be studied by differential scanning calorimetry, thermogravim-etry, drawing behavior, birefringence measurements, and dynamic mechanical analysis.…”