Influence of polypropylene topological structure evolution during melt branching reactive processing on its melt performances

Abstract

Gel-free long-chain-branched polypropylene (LCBPP) was prepared by the melt radical branching reaction in the presence of peroxide initiator 2,5-dimethyl-2,5-di(tertbutylperoxy) hexane peroxide, zinc dimethyldithiocarbamate, and trimethylolpropane triacrylate in a torque rheometer. It could be inferred that recombination between PP chains via radical coupled reaction took place and trimethylolpropane triacrylate was grafted onto PP backbone by the torque curves and Fourier transformed infrared spectroscopy results. The presence of long chain branches (LCB) for modified PP was verified by the gel permeation chromatography measurements and vGP plots. On the other hand, it was found that the topological structure of PP chains transformed from linear form to a long star-like shape during the reaction progress, and the topological structure was directly determined by the radical reaction time. The topological structure of PP would further impact its melt behaviour. After complete melting of raw PP, "sparse and long" LCBPP firstly generated which possessed high melt strength owing to the increasing entanglement of long branching chains. And at the time corresponding to the summit of reaction peak on the torque curve, the modified LCBPP possess the highest melt strength owing to its long star topological structure. While as reaction time was prolonged, severe degradation of the LCBPPs would take place under too long mixing time and "dense and short" branches generated due to the residual radicals, with a sharp decline in melt strength. KEYWORDS long chain branched (LCB), melt performance, polypropylene (PP), rheology, topological structure 1 | INTRODUCTION Isotactic polypropylene is one of the most widely used resins owing to its desirable and beneficial advantages such as low density, high melting point, wide sources, superior mechanical properties, and chemical stability. 1,2 However, ordinary commercial polypropylene, prepared by Ziegler-Natta or metallocene catalyst, cannot be applied into some processes where entanglement properties and melt strength are dominant, such as thermoforming, extrusion foaming, and blow molding, due to its linear structure and poor melt strength. Therefore, it is essential to improve the melt strength of PP. It was reported that fraction of long-chain-branched (LCB) or crosslinked structures in PP were able to enhance the melt strength remarkably owing to the augment of the entanglements among the macromolecule chains. 3 When LCB exists, PP can obviously exhibit strain hardening behaviour in the melt state. 4,5As a simple and effective way, melt radical addition is mostly applied to fabricate long-chain-branched polypropylene (LCBPP) recently. [5][6][7] Compared with in situ polymerization in a reactor and high-energy electron irradiation method, melt radical reaction has some unique advantages such as solvent-free process, short reactive time, and low cost. Nonetheless, the preparation technology and

Synergistic lignin construction of a long-chain branched polypropylene and its properties

“…The degree of deviation between the G 0 /G 00 curves is determined by differences in system compatibility, dispersion and platform modulus. 41 As shown in Fig. 3C, the difference between the G 0 / G 00 ratio between PP and the other samples gradually increased with the increasing interaction of xNBR with the PP substrate.…”

Preparation of polypropylene with high melt strength by wet reaction blending of lignin

“…After introduction of AM, PP 90 /XNBRL 10 /AM 5 curves deviates with reduced slope, compared with those of PP. It indicates that AM increased the interfacial interaction between the XNBRL particle and PP matrix, and the microscopic phase separation occurs 27 . After the addition of LS, the degree of deviation of tetrameric PP/XNBRL/AM/LS blend curve increased, indicating that the interfacial interaction was further enhanced by the introduction of LS.…”

Long-chain branched polypropylene: crystallization under high pressure and polymorphic composition

“…Long chain branches incorporated onto PP backbone can improve its melt processing properties, including melt strength, strain hardening and shear thinning, which leads to the broadening of end-uses and processing methods of PP [13,14]. LCB-PP is thought to exhibit different helical conformations and crystallites due to the specific chain structure [2].…”