Effect of the structure on the morphology and spherulitic growth kinetics of polyolefin in‐reactor alloys

Abstract

Four polyolefin in-reactor alloys with different compositions and structures were prepared by sequential polymerization. All the alloys were fractionated into five fractions: a random copolymer of ethylene and propylene (25°C fraction), an ethylene-propylene segmented copolymer (90°C fraction), an ethylene homopolymer (110°C fraction), an ethylene-propylene block copolymer (120°C fraction), and a propylene homopolymer plus a minor ethylene homopolymer of high molecular weight (Ͼ120°C fraction). The effect of the structure on the morphology and spherulitic growth kinetics of the polypropylene (PP) component in the alloys was investigated. The polyolefin alloys containing a suitable block copolymer fraction and a larger amount of PP had a more homogeneous morphology, and the crystalline particles were smaller. Quenching the polyolefin alloys led to smaller crystallites and a more homogeneous morphology as well. Isothermal crystallization was carried out above the melting temperature of polyethylene, and the growth of PP spherulites was monitored with polarized optical microscopy with a hot stage. The alloys with higher propylene contents exhibited a faster spherulitic growth rate. The fold surface free energy was derived, and it was found that a large amount of block copolymer fractions and random copolymer fractions could reduce the fold surface free energy. The structure of the alloys also affected the crystallization regime of PP.

Effect of phase separation on overall isothermal crystallization kinetics of PP/EPR in‐reactor alloys

“…Similar phenomenon was observed isotactic PP/poly(ethylene‐ co ‐octene) (iPP/PEOc) in‐reactor alloys 56–58. So far, although there are some studies on crystallization kinetics of PP/EPR in‐reactor alloys,59–61 the effect of phase separation is seldom considered in this type of in‐reactor alloy. In our previous work, we reported the effect of phase separation in the melt on the linear spherulitic growth rate ( G ) of a PP/EPR in‐reactor alloy prepared by MSSP process 62.…”

Structural parameters in relation to the rheological behavior and properties of PP/EPR in‐reactor alloy synthesized by multi‐stage sequential polymerization

“…When dispersed phase is created in the copolymerization stage, each particle of dispersed phase is surrounded by some b‐ copolymers rich in PP produced acting as compatiblizing entities. Also, as particle size becomes smaller, the compatibility of the two phases increases, which is also in accordance with the findings reported by Xu et al,7 Jiang et al,9 and Li et al15…”

“…When dispersed phase is created in the copolymerization stage, each particle of dispersed phase is surrounded by some b-copolymers rich in PP produced acting as compatiblizing entities. Also, as particle size becomes smaller, the compatibility of the two phases increases, which is also in accordance with the findings reported by Xu et al, 7 Jiang et al, 9 and Li et al 15 The rheological results match the 13 C NMR results shown in Figure 3. According to these results the higher interfacial adhesion between the two phases of EP5, revealed in the storage modulus and Cole-Cole graph, may be due to greater entanglements between the matrix and dispersed phase particles which are evident in 13 C NMR spectra.…”

“…5 Lin et al 6 investigated the ethylene component in the PP CATALLOY (a polypropylene polymer production process in gaseous phase) and showed that while it acts as a nucleating agent and induces higher crystallization rate, it reduces the crystallinity and spherulite size. Xu et al 7 showed that alloys with smaller crystalline particles enhance compatibility between the matrix and dispersed phases. Chen et al 8 showed that the dispersed phase in high-impact polypropylene (HIPP) exhibits a multilayered core-shell structure including the inner core, intermediate layer, and outer shell, which were mainly composed of PE (including PE long blocks), EPR and PE-PP multi-block copolymers, respectively.…”

From Multisite Polymerization Catalysis to Sustainable Materials and All-Polyolefin Composites

“…According to Ryan, shear flow leads to stretching of the longest polyethylene chains, thus forming the “shish”, that nucleates crystallization of the lower molar-mass polyethylenes to afford the “kebab” . Several other groups have investigated shear-induced 1D crystallization and confirmed the prominent role of bimodal polyolefin MWDs. ,− Special injection molding processes, among them “shear-controlled orientation in injection molding” (SCORIM) , and “oscillating packing injection molding” (OPIM), , have been developed to fabricate all-polyolefin composites. Farah and Bretas used a slit die for polypropylene extrusion to prepare “all-polypropylene” composites with 2D self-reinforcement by shear-induced crystallization to form layered structures .…”