Tailoring the crystalline morphology and mechanical property of olefin block copolymer via blending with a small amount of UHMWPE

The Influence of DMDBS on Crystallization Behavior and Crystalline Morphology of Weakly-Phase-Separated Olefin Block Copolymer

Olefin block copolymer (OBC), with its low hard segments, can form unique space-filling spherulites other than confined-crystallization morphologies, mainly due to its weak phase-separation. In this work, 1,3;2,4-Bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), a well-known nucleating agent, was used to tailor the crystallization behavior and crystalline morphology of OBC. It was found that DMDBS can precipitate within an OBC matrix and self-assemble into crystalline fibrils when cooling from the melt. A non-isothermal crystallization process exhibited an increased crystallization rate and strong composition dependence. During the isothermal crystallization process, DMDBS showed a more obvious nucleating efficiency at a higher crystallization temperature. OBC showed typical spherulites when DMDBS was added. Moreover, a low addition of DMDBS significantly decreased the crystal size, while a large addition of DMDBS induced aggregates, due to the limited miscibility of DMDBS with OBC. The efficient nucleating effect of DMDBS on OBC led to an increased optical transparency for OBC/DMDBS composites.

Highly improved mechanical and dielectric properties of paper-based composites with polyimide chopped fiber functionalized by ethylenediamine

In this study, polyimide (PI) chopped fibers were modified by ethylenediamine, and PI paper-based composites were fabricated using the as-modified PI chopped fibers and para-aramid fibrids which served as raw materials through the wet-forming process. The influence of different alkali treatment durations on the properties of PI fibers and composites was investigated. In sharp contrast with the pristine PI fibers, there was a satisfying difference in modified PI fibers including rougher surfaces and improved wettability due to the introduction of hydrophilic groups as confirmed by scanning electron microscope and Fourier transform infrared spectrometer. With increase in the modification time, the tensile index, the tearing index, and the internal bond strength of the composites were improved by 40.6, 27.0, and 103.57%, respectively, due to the hydrogen bonds. Meanwhile, the dielectric strength of the composites increased by 77.2% compared with the unmodified ones. These remarkable changes were mainly attributed to the enhanced interfacial bonding of the composites and decreased porosity in the three-dimensional network structure of the paper. Moreover, thermal stability was kept preferably within a certain range in spite of slight decrease.

Toward high-performance poly(para-phenylene terephthalamide) (PPTA)-based composite paper via hot-pressing: the key role of partial fibrillation and surface activation

Hot-pressing is in favor of fibrillation and property enhancement for para-aramid fiber based composite.