No abstract

In the present work, the synergistic toughening effect of olefin block copolymer (OBC) and a highly effective β nucleating agent (NA)-Calcium salt of pimelic acid (CaPim) on polypropylene random copolymer (PPR) was studied. Mechanical tests showed that with the introduction of 0.1 wt % CaPim, there was almost no change in the low-temperature (below 0 °C) toughness of PPR. Although introduction of OBC could obviously improve the toughness at 23 °C, high content is needed to effectively toughen PPR at low temperature. By coadding OBC and CaPim, PPR/OBC/NA blends showed not only great enhancement of toughness over the temperature range tested but also lower OBC content of undergoing brittle-ductile transition compared with PPR/OBC blends. The crystalline structure, crystallization behavior and phase morphology were investigated to explore the possible synergistic toughening mechanism. The high β-crystal content formed in PPR matrix and the finer distribution of OBC phase might be responsible for the superior toughness achieved.

The physical network structure and mechanical properties of styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) were regulated through rational introduction of crystalline olefin multiblock copolymer (OBC). This copolymer comprised alternated crystallizable and amorphous blocks, both of which had similar composition with ethylene-cobutylene (EB) blocks of SEBS. Polarized optical microscope and atom force microscope observations revealed that OBC exhibited distinct crystalline morphologies in blends. On one hand, major OBC chains were macrophase separated with SEBS, generating bulk crystals. On the other hand, small OBC particle crystals with diameter around 10 nm could be distinguished in the SEBS matrix as well. Considering the unique multiblock architecture of OBC, particle crystals could be regarded as additional physical netpoints to SEBS networks as the corresponding amorphous blocks entangled with continuous EB blocks. Because of the interesting crystalline behaviors of OBC in the SEBS matrix, the blend exhibited dramatically elevated elongation at break at both room temperature and relatively high temperature without sacrifice of intrinsic elasticity. We believe this work sheds light on comprehending the interaction between triblock elastomers and blended polymers, and it also demonstrates the feasibility of regulating the apparent properties of triblock copolymers by the blending approach.

The nature of shear-induced crystallization precursors, especially their relaxation behaviour, is an important issue in polymer chemical physics. In our work, relaxation behavior of shear-induced crystallization precursors in isotactic polypropylene containing various sorbitol-based nucleating agents (NAs) with different nucleating abilities was investigated by using both rheological and in situ small angle X-ray scattering (SAXS) methods. Rheological crystallization kinetics results showed that the amount of shear-induced precursors, calculated separately from the total nuclei, decayed exponentially with relaxation time in both pure and nucleated iPP. By fitting the decay of shear-induced precursors with relaxation time, the relaxation rate of precursors in nucleated iPP was found to be slower than that in pure iPP. Interestingly, it further decreased with the increase in the nucleating ability of sorbitol-based NAs. Meanwhile, the life-time of precursors was prolonged in nucleated iPP with increasing nucleating ability. Similar results were also testified by in situ SAXS measurements. By investigating the life-times at different temperatures, the activation energy for the relaxation of precursors was calculated and found to increase with stronger nucleating abilities. Our results demonstrated that sorbitol-based NAs could stabilize the iPP precursors and the effect of stabilization enhanced with the increase in nucleating ability. We believe that our work can not only help better reveal the relaxation behavior of shear-induced precursors but also provides a new perspective for understanding the role of NAs in real processing.