Abstract
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.
Highlights
Maleic anhydride (MAH) grafted polypropylene (PP) and polyethylene (PE) are semi-crystalline polymers with a wide range of applications in industry [1,2], such as chemical coupling agents [3], impact modifiers [4], and reactive compatibilizer precursors [5] for blends
The effects can be quite different for different polyolefins-g-MAH
The effects of MAH grafting on crystallization kinetics and melting behavior are studied with Differential scanning calorimetry (DSC), and the corresponding effects on crystalline structures and crystal packing structure are studied with Wide-Angle X-ray Diffraction (WAXD) and Small Angle X-ray Scattering (SAXS)
Summary
Maleic anhydride (MAH) grafted polypropylene (PP) and polyethylene (PE) are semi-crystalline polymers with a wide range of applications in industry [1,2], such as chemical coupling agents [3], impact modifiers [4], and reactive compatibilizer precursors [5] for blends. Their work on the blend suggested that the MAH grafting led to a lowered melting point of PP component, likely due to the co-crystallization of PP and PP-g-MAH. 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. Though double melting points of PP-g-MAH were reported in several studies in literature [15], it is not well understood what leads to the two distinct melting peaks for the grafted PP In literature, it is interpreted as the perfection of the crystal structure during the melting process [15]. A very different conclusion is made about the double melting points based on our studies with multiple techniques, including degradation characterization [18]
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