Rheological study of linear high density polyethylenes modified with organic peroxide

Preparation and properties of long chain branched high-density polyethylene based on nano-SiO2 grafted glycidyl methacrylate

A compounded nanoparticle with multiple double bonds (C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C) was prepared by grafting glycidyl methacrylate (GMA) onto the surface of nano-SiO₂. Then gel-free long chain branched polyethylene (LCBPE) was prepared by melt branching reaction in a Haake torque rheometer in the presence of initiator peroxide and GMA grafted nano-SiO₂ (SiO₂-g-GMA). The sampling time corresponded to the summit of the reaction peak in the torque curve. Fourier transform infrared results indicated that SiO₂-g-GMA had been grafted onto the HDPE backbone via radical reaction. The reaction mechanism and the topological structure of the PE products are also discussed. Rheological results showed that the relaxation time and molecular weight distribution of modified PE were increased owing to the introduction of LCB structure, and the more SiO₂-g-GMA was added, the more apparent variation could be observed. Compared with linear HDPE, both the melt strength and mechanical properties of LCBPE were improved obviously. From the differential scanning calorimetry and polarized optical microscopy results, smaller crystal size and lower growth rate were observed compared with linear HDPE, which are ascribed to the nucleation and restriction of long branching chains in the system. Well distributed nano-SiO₂ without any agglomeration in the PE matrix was observed in the scanning electron microscope images when the SiO₂-g-GMA content was less than 3 phr.

A compounded nanoparticle with multiple double bonds (CC) was prepared by grafting glycidyl methacrylate (GMA) onto the surface of nano-SiO₂.

Rheological properties and crystallization behaviors of long chain branched polyethylene prepared by melt branching reaction

Long chain branched polyethylene (LCBPE) without gel was prepared by melt branching reaction in a Haake torque rheometer in the presence of peroxide and different multi-functional acrylate monomers, and the optimal reaction time was determined according to the transient torque curves. The Fourier transform infrared (FTIR) results indicated that multi-functional monomers had been grafted onto HDPE backbone. Rheometer, 13C NMR, and high-temperature gel permeation chromatography (HT-GPC) coupled with triple detectors were used to characterize the microstructure of the LCBPE. The results showed the LCB content and the degree of branching increased with the increasing of functionality of the multi-functional monomers. Moreover, the LCBPE samples exhibited higher apparent zero shear rate activation energy and clear strain-hardening behavior compared with pure HDPE. Various rheological plots including viscosity, storage modulus, loss angle, and Cole-Cole plots were used to distinguish LCBPE from linear HDPE. A possible mechanism for melt branching reaction was also discussed in this paper. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were used to study the influences of LCB on the crystallization behavior and crystal morphology of all samples. It was found that the melt temperature and crystal morphologies of LCBPE were evidently different from that of pure HDPE due to the introduction of LCB.

Rheo-chemistry in Reactive Processing of Polyolefin

A brief review of reactive processing of polyolefins, which are the most widely used polymers today, is given in this paper from the role of flow field in processing and the characterization of the modified chain topologies. The materials are mainly focused on polyethylene (PE), polypropylene (PP) and polyolefin elastomer (POE) here. Aspects of reactions, coupling/crosslinking and scission are discussed both in terms of the mechanism and kinetics under different flow conditions.

Melt Strength and Thermal Properties of Organic Peroxide Modified Virgin and Recycled HDPE

Commercial blow moulding grade recycled high density polyethylene (r-HDPE) and blow moulding grade virgin HDPE were reactively extruded with various compositions (0.00 to 0.15 %) of different peroxides in a twin screw extruder. The aim was to improve the melt strength properties of a blow moulding grade HDPE homopolymer – a polymer resin comprising a significant part of the post consumer recycled plastic stream in Australia. Melting behaviour and crystallinity were investigated by modulated differential scanning calorimetry (MDSC). Uniaxial melt extensional (UME) measurement of the modified materials was carried out using Göttfert Rheotens melt strength tester to measure melt quality of the material. Melt strength and zero shear viscosity were also measured to assess and correlate changes in melt properties due to peroxide modification. Melt strength and zero shear viscosity of both recycled and virgin material were enhanced with the increase in composition of peroxide. However, addition of peroxide also brought with it flow instabilities like draw resonance and necking, both of which lead to limitations in polymer processing.