Characteristics of Ultradrawn Blend Films of Ethylene−Methyl Methacrylate Copolymer and Ultrahigh Molecular Weight Polyethylene Prepared by Gelation/Crystallization from Solutions Estimated by X-ray, Positron Annihilation, and 13C NMR

Abstract

Copolymer ethylene−methyl methacrylate (EMMA) and ultrahigh molecular weight polyethylene (UHMWPE) were blended in decalin solvent. Two kinds of EMMA films with different contents of the MMA side group were used as test specimens. A hot homogenized solution was poured into an aluminum tray to form gels, and the decalin was allowed to evaporate from the resultant gels under ambient condition. Surprisingly, the resultant dry blend films could be elongated up to more than 200-fold (λ = 200) at 135 °C. Such a great draw ratio could be realized even for a blend film with 90% EMMA content (the 9/1 film), although the maximum draw ratio of EMMA homopolymer films was 10-fold (λ = 10). The greatest drawability for the 9/1 films was attributed to large crystal lamellae of UHMWPE, ensuring a crystal transition from a folded to a fibrous type. Accordingly, EMMA chains were independent of the ultradrawing of UHMWPE and kept a random orientation under the ultradrawing process. The storage (Young's) moduli were 20−25 GPa at 20 °C. In contrast, EMMA chains within the 1/1 films were oriented drastically together with UHMWPE crystallites. The moduli of the 1/1 films at 20 °C reached 75−85 GPa, which are close to 100 GPa of UHMWPE homopolymer films with λ = 100 and are higher than the value (40 GPa) of polypropylene films with λ = 100 as well as the crystal lattice modulus (41−43 GPa) along the chain direction. The morphology of the blend films with such different orientation modes of EMMA chains was analyzed by using X-ray, 13C NMR, and positron annihilation. As a result, the drastic orientation of EMMA chains within the 1/1 film was thought to be due to the epitaxial nucleation surface for ethylene sequences of EMMA under the cooling process from 135 °C to room temperature after the elongation. However, the amount of EMMA content within the 9/1 film was obviously too much to develop the epitaxial nucleation surface effect. Even so, it was confirmed that most of the highly oriented ethylene sequences of EMMA within the 1/1 film exist as an amorphous phase, causing the β (mechanical) dispersion associated with a large (macro-Brownian) movement.