Polyolefins Journal
Volume:8 Issue: 1, Winter-Spring 2021

Melt free-radical grafting reactions between ethylene-propylene-dieneterpolymer (EPDM) and glycidyl methacrylate (GMA) were investigated in a batch mixer (170°C, 60rpm). Effect of dicumylperoxide (DCP) initiator and GMA functionalizing monomer concentrations was studied on the grafted EPDM characteristics. Titration results indicated an increase in the graft degree (GD) and gel content (GC) values with increasing DCP concentration as a result of increasing primary free radical concentration and strengthening cross-linking side reaction. FTIR spectrums confirmed that GMA functionalities have been grafted onto EPDM with appearing carbonyl (C=O) peak. After that, the resultant EPDM-g-GMA was used as compatibilizer in PS(polystyrene)/EPDM/PA6 (polyamide6) ternary blends. The effect of rubbery compatibilizer on the blend morphology and mechanical properties was studied. The ATR-FTIR spectra of ternary blends, etched to remove unreacted PA6, demonstrated that the compatibilizing reactions occurred during melt blending. By investigating the SEM micrographs it was revealed that the EPDM-g-GMA compatibilizer at the concentration range of 5 wt.% to 15 wt.% changed the size and type of the blend morphology from separated dispersed to multicore-shell morphology. The finest morphology was achieved by using 7.5 wt.% EPDM-g-GMA. Also, the presence of compatibilizer up to 7.5 wt.% could improve the tensile modulus, yield stress and impact strength, but a decreasing trend was observed at higher concentration of the compatibilizer.

In this work, the grafting of maleic anhydride onto two types of linear low density polyethylene with hexene-1 comonomer (LLDPE-H1) and butene-1 comonomer (LLDPE-B1), in the presence of styrene monomer (St) and dicumyl peroxide initiator (DCP) has been studied. The combined influences of MAH, St and DCP on the grafting efficiency via a melt reactive mixing process have been investigated using response surface methodology and the central cubic design has been employed for experimental design and data analysis. IR spectroscopy, contact angle measurements and adhesion test have been used to evaluate the extent of grafting reaction. The results showed that LLDPE-H1 with a 2.2% maximum grafting content showed more grafting content than the LLDPE-B1 (1.86%). This effect could be attributed to the type of comonomer in LLDPE-H1 which made it more prone to chain scission than LLDPE-B1, and a higher level of grafting was achieved. The gel content measurement showed that lower cross-linked structure was formed during the grafting process in the LLDP-H1 than that in the LLDPE-B1. The optimum conditions of maximum grafting and minimum gel content were statically investigated. The optimum percentage of grafting for LLDPE-H1 was 1.82% and it was 1.74% for LLDPE-B1, with the minimum gel content of 6.5% and 9%, respectively. It was found that the amount of grafted percentage was sensitive to the concentrations of the MAH, DCP, and St, while the extent of the gel content was more sensitive to the percentage of DCP.

In this work, the compatibility and crystallinity of low density polyethylene (LDPE) and polybutene-1 (PB-1) blends were studied. Various blends of LDPE/PB-1 containing 5, 10 and 20 wt.% PB-1 were prepared in a corotating twin-screw extruder and characterized by scanning electron microscopy (SEM), shear oscillation rheology and wide-angle X-ray diffractometry (WAXD). A matrix-droplet morphology was observed in SEM images, indicating incompatibility of the two polymers in the solid state. Compared to neat LDPE, the relaxation spectra of the blends were broadened, and a slight increase in their relaxation times was observed. The relaxation time of the blends was enhanced by increasing PB-1 content, which was further proved by fitting rheological data in the Carreau-Yasuda model. Deviation of Cole-Cole diagrams from circular shape means that the blend samples were not miscible and the positive-deviation behavior of the complex viscosity and storage modulus from the mixing rule revealed the formation of strong interfacial interactions. The crystallinity of both LLDPE and PB-1 was decreased as a result of blending. The peaks attributed to the form II of PB-1 crystals were eliminated and the peaks related to LDPE were obviously weakened, suggesting to prevent crystallinity of polymers which is associated with a reduction in the total crystallinity percentage for the blend. The reduction of crystallinity was more pronounced in PB-1 phase.

Herein a quenched-flow kinetic technique was applied to calculate the rate constants of 1-hexene and 1-octene oligomerization catalyzed by the Cp2ZrCl2 and Cp2HfCl2/MAO catalyst systems, and subsequently a mechanism for the higher α-olefin oligomerization reaction was proposed. The oligomerization results showed that Zr-based catalyst in the oligomerization of 1-octene had the highest activity of 17 in comparison to Hfbased one with an activity value of 15 g oligomer/(mmolCat.h)). According to the obtained results, increasing monomer length led to a shift in molecular weight and polydispersity index value (Mw/Mn) to lower values. Furthermore, the microstructure-viscosity relationship was followed by the calculation of branching ratio and short-chain branching percentage. The obtained results revealed that, the oligomers synthesized by the Cp2HfCl2 catalyst had lower short chain branching ratio value and short-chain branching percentages. According to the kinetic results, the initiation rate constant (ki) of Zr-based catalyst was higher than that of Hf-based catalyst, and the order of calculated propagation rate constants was Zr>Hf for both the 1-hexene and 1-octene-based oligomerizations.

Polyolefins have been widely used in the electrical insulation and cable industry in recent years. One of the main usages of these materials is dielectric insulation in coaxial cables. Low attenuation and high signal transmission speed are among the desired features in coaxial cables. The role of polyethylene foam on signal transmission speed in the coaxial cables is the main focus of this study. In the present study, the velocity factor of coaxial samples with different dielectric structures is investigated in both theoretical and experimental approaches. In theoretical formulation, only the void fraction of foam is taken into consideration and other foam properties such as cell density, cell size, and foam structure are neglected. This is the reason for the difference observed between theoretical and experimental results. In theoretical results, a linear increase in the velocity factor is witnessed with the increase of the void fraction while in experimental results there are some exceptions. The foaming degree of the samples was reached 63% causing a 37.7% decrease in theoretical relative permittivity and consequently a 26.8% increase in theoretical velocity factor. On the other hand, up to 36% increase is observed in the experimentally measured velocity factor of foamed dielectric samples compared to the samples with solid polyethylene dielectric.

Organocatalysts have attracted enormous interest in the water-crosslinking reaction in silane-grafted polyolefins(SGPOs) system owing to their simplicity, low toxicity and environmentally benign nature compared to theorganotin catalysts most commonly used in the SGPOs system. We focus on organophosphorus compounds includingfour structure types as organocatalysts; phosphoric acids, phosphoric esters, phosphine oxides and phosphine. Theircatalytic activities for the water-crosslinking reaction in the 3-methacryloxypropyltrimethoxysilane grafted thylenepropylene copolymer (EPR-g-MTMS) system were evaluated using the ATR-FTIR technique and the gel-fraction method. Phosphine oxides, phosphoric acids and phosphoric esters possessing an O=PR3 or O=P(OR’)3 unit were found to be an excellent catalyst for the water-crosslinking reaction in the EPR-g-MTMS system, while phosphine (PR3) showed no catalytic activity on the water-crosslinking reaction in this system, indicating that the phosphoryl (P=O) unit plays an important role on the catalytic performance of these compounds. In comparison, phosphine oxides showed considerably higher catalytic activities than phosphoric acids/esters. Density functional theory (DFT) calculations demonstrated that the difference in catalytic activity could be attributed to an electron density at P=O unit making the activation for water through hydrogen-bonding. Finally, a possible catalytic mechanism for phosphoryl compounds in the EPR-g-MTMS system was proposed on the basis of these results and the SN2-Si pathway in silicate sol-gel chemistry.