Maleic anhydride (MAH) grafting to different polyolefins with similar grafting degree can have different effects on crystallization, crystal structure, and mechanical and thermal properties. The grafting leads to a smaller crystal size, less ordered lamellar structure, and a shorter long period for HDPE, LLDPE, and PP. The grafting makes PP lamellar packing less ordered the most and almost no effect to LLDPE. The grafting does not have that much impact on the crystallization ability of the HDPE, LLDPE, and HDPE/PP blend, but appreciably reduces the crystalline ability of PP-g-MAH, due to a dramatical drop in its molecular weight during the grafting process. As a result, the grafting makes PP a very brittle material with a lowered average melting point than the corresponding neat PP, but the grafting has almost no effect on elongation at break for LLDPE and some effect on HDPE (decreased by one-third). However, the PP degradation due to MAH grafting can be avoided in the presence of PE component, i.e., making the grafting of PP and PE at the same time with HDPE/PP blend. The grafted HDPE/PP blend shows a significantly improved compatibility, which leads to overall appreciably better mechanical properties than the neat HDPE/PP blend.Polymers 2020, 12, 675 2 of 13 slightly with addition of small amount of PP-g-MAH, while mechanical dampening decreased with addition of PP-g-MAH.It is well known that the degree of MAH grafting can have significant impact on the crystallization and structure of polyolefins. The melting temperature of HDPE-g-MAH decreases as increase in grafting content from 0.2% to 0.8%, [14] but increases with further increase in grafting degree. The crystallization, melting behavior and structures of PP with different maleic anhydride contents (AC = 0.5 mass%, 1 mass%, 3 mass%) was investigated by Menyhárd et al. [15] Liu et al. prepared and studied maleic anhydride/styrene-grafted PPR (polypropylene random copolymer) with grafting degrees of 1.38%, 2.25%, and 2.42%, respectively, and it is found that the crystallization rate of this MPP is higher than the neat PP and increases with the increase in grafting degree [16].Although there are quite a number of studies on MAH grafted polyolefins-including PP [15,16], high-density polyethylene (HDPE) [14], and linear low-density polyethylene (LLDPE) [17]-the different effects of similar MAH grafting degree on crystallization, structures, and properties of different polyolefins have not been explored. In the present work, a series of MAH grafted polyolefins are studied, including maleic anhydride grafted high-density polyethylene (HDPE-g-MAH), maleic anhydride grafted low-density polyethylene (LLDPE-g-MAH), PP-g-MAH and maleic anhydride grafted polypropylene/maleic anhydride grafted high-density polyethylene (PP-g-MAH/HDPE-g-MAH) blends (1:1). The crystallization kinetics, thermal behavior, crystal structure, lamellar packing, and crystal size of these grafted polyolefins, together with the corresponding non-grafted polymers, are discussed, which provides a ...

Crosslinking of polyolefin elastomer (POE, ENGAGE™ 8480) with Dicumyl Peroxide (DCP) can have effects on its crystallization dynamics, crystal structure, and properties. The POE crosslinked uniformly has significantly lower crystalline ability than the one with only amorphous phase crosslinked, which, in turn, has weaker crystalline ability than neat POE. The crystallinity and melting point depend on how the POE is crosslinked. The neat POE and POE crosslinked in amorphous phase only, are investigated with DSC and in‐situ tensile/synchrotron radiation (WAXD/SAXS). In situ tensile/synchrotron X‐ray during a uniaxial stretching process indicates that severe crystal fragmentation is observed at a strain around 45%, and with further increase in strain. The stress in the crosslinked POE is significantly larger than neat POE. For both samples, crystal orientation increases sharply within the strain range up to 88% where orientation‐induced new crystals aligned in stretching direction are observed. The long period increases more in stretching direction for the crosslinked POE, consistent with larger stress in this sample, and the stress difference is more pronounced at large strains (27.3 vs. 10.9 MPa at a strain 435%). Permanent set of the crosslinked POE is smaller, consistent with less oriented crystals observed after the test for permanent set.

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Controlling temperature and pressure during the supercritical carbon dioxide (scCO2) process can change the mount of CO2 entered in polypropylene (PP) phase, thereby changing the mechanical properties of materials. The effect of scCO2 treatment on the crystallization behavior is different in the semi-molten and molten states. This study investigates the PP treated with scCO2 near the melting point and at various pressures, and explores the effects of temperature and pressure on the crystal structure, lamellar structure, and thermodynamic properties of PP. The results show that at a melting temperature of 165 °C, scCO2 can enhances the ability of PP molecules to makes the PP crystal region more regular, and forms larger microcrystals and lamellae. Additionally, increasing the pressure can make more CO2 enter the PP crystal region and further improve the regularity of the crystal. At a semi-melting temperature of 155 °C, scCO2 is primarily in the amorphous region because it is difficult to enter the PP crystal region. Even if increasing the pressure, it has little effect on the crystal size and lamellar thickness of PP. The research has significant implications for developing and utilizing scCO2 to remove ash from materials.