Polyolefins Journal
Volume:11 Issue: 1, Winter 2024

Silane cross-linking of metallocene-based polyethylene-octene elastomer (POE)/linear low density polyethylene (LLDPE) blend was carried out using two-step Sioplas process in an industrial scale twin-screw extruder. In the study, grafting and cross-linking reactions of vinyl trimethoxy silane (VTMS) were analyzed using FTIR technique. It was found that the cured compound showed absorption peaks at 1078 cm-1 and 955 cm-1 related to Si-O-Si bonds. A peak was also observed at 3405 cm-1 of hydroxyl group produced from hydrolysis of methoxyethylene group during of curing process, reflecting that curing reaction was not completed. The samples were cured at different time intervals (15 min-16 hours). The gel content values determined by solvent extraction and FTIR were in good agreement at curing times more than 4 hours. The efficiency of the silane grafting reaction was determined using the ratio of the absorption peak at 1092 cm-1 characteristic of methoxy to the transmittance peak at 1378 cm-1 characteristic of methyl group, which  is considered as the internal standard. The results showed the highest efficiency of silane grafting reaction at 5 w% of VTMS with the least amount of internal standard ratio (0.029), at which the lowest MFI value, and the highest values for gel content, tear strength, compression set and hot set 200 °C were obtained.

Polypropylene (PP) is a strong, tough, crystalline thermoplastic material with high performance. Because of its diverse thermo-physical and mechanical properties, it is utilized in a wide variety of disciplines. In this study, the impact of free quenching on the thermo-physical characteristics of PP/calcium carbonate (CaCO3) composites was examined. Three distinct heating procedures were used. First, composites were cooled from their melting phase temperature to ambient temperature. Second, composites were cooled from 130°C to a pre-determined and controlled temperature (T: 0°, 20°, 30°, 40°, 50°, 60°, 70°, 80°C). Third, composites were temperature-tested using annealing. The findings suggest that the elongation-at-break and impact strength may be improved following an initial quenching process from the melting phase to ambient temperature. On the other hand, a second quenching process at 0°C produces superior results, and a correlation between mechanical and thermal characteristics is noted; however, while these qualities are increased, others, such as flexibility, density, Vicat softening temperature (VST), and heat distortion temperature (HDT) are negatively impacted.

Ultra-high molecular weight polyolefin (UHMWPO) has enormous potential applications due to their excellent mechanical properties such as tensile strength, flexural modulus, toughness and outstanding chemical resistance. But the processing of polyolefin, in particular, UHMWPO fibers cannot be processed by conventional methods due to its very high melt viscosity. In this work, we synthesized isotactic ultra-high molecular weight polypropylene (UHMWPP) resin and studied the processability of UHMWPP fibers using gel spinning and investigated physicomechanical properties. UHMWPP gel was made at various concentrations in decalin solvent at 150°C to produce consistent spinning dope solutions. The 7 wt.% concentration of UHMWPP was deemed best for fiber creation, compared to 3 wt.% and 5 wt.%. A rheological time sweep was done to ensure the gel's stability at 170°C before the spinning process. The UHMWPP's gelation and fiber formation were studied by tweaking the gel concentration and adjusting the processing temperature. The resulting UHMWPP monofilament had a measure of 220-250 denier. The hot stretched fibers were analyzed with the scanning electron microscope (SEM) to understand the surface morphology of the fibers. The crystal morphology of UHMWPP fibers was measured with wide-angle x-ray scattering (WAXS) and DSC. The X-ray measurement of hot stretched UHMWPP fibers showed crystalline peaks compared to those without stretched fibers.

The effect of calcium lactate (CL) and epoxidized soil bean (ESO) on the crystallization kinetics of polypropylene (PP) was investigated by using polarized optical microscope (POM) and differential scanning calorimetry (DSC). The experiments were performed under both non-isothermal and isothermal conditions. The development of spherulitic microstructure and crystallization kinetics were influenced by both CL and ESO. CL was an efficient nucleating agent for the crystallization of PP. The addition of CL facilitated faster spherulite growth and crystallization rate, while reduced the spherulite size. An opposite performance was discovered with the incorporation of ESO. Nucleation effect of CL on the PP crystallization was less effective with the presence of ESO. Compared with PP/CL, PP/CL/ESO provided a large spherulite size, slow spherulite growth, and a low crystallization rate. This is attributed to the ESO inhibited the nucleation site of CL. However, the degree of crystallinity and the Avrami exponents remained unchanged with the inclusion of both CL and ESO.

In this study, polypropylene (PP) was blended with polylactic acid (PLA) to enhance PP's mechanical properties, such as tensile strength and modulus, and to encourage the adoption of eco-friendly, renewable resource based material in polymer production. Even though PLA's biodegradability cannot be fully utilized in PP/PLA blends, but PLA can still improve PP's mechanical properties and provide an alternative resource for biobased raw materials. To meet the requirement, PP and PLA were blended in a 70:30 ratios with a compatibilizer and nanosilica at different loading levels by melt-blending. Blends of PP and PLA materials were processed without any problems, since both materials have melting points in the range of 170°C. Despite this, the properties of polymer blends are limited by the immiscibility between these neat polymers. To solve this problem, compatibilizers like polypropylene-grafted-maleic anhydride (PP-g-MA) were added to blends to improve their compatibility. Nanosilica was also added to this compatibilizer to study the system's compatibility and modify the hydrophobicity of PLA. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), tensile strength, and field emission scanning electron microscopy (FESEM) were used to analyze the polymer blend. Results indicate that compatibilizers play a significant role in improving tensile properties, thermal stability, and blend dispersion in the system, mainly in 5 parts compatibilizer-based systems. Composition with 5 parts compatibilizer increases tensile strength of 70/30 blend from 19.7 to 27 MPa, while elongation increases from 2.2 to 3.6 %. Additionally, a composition with 0.7 parts of nanosilica increases the modulus from 1488 to 1732 MPa when compared to the 70/30 blend.

Ultra-high molecular weight polyethylene (UHMWPE) was synthesized using Bi-supported SiO2/MgCl2/TiCl4 (Si-Mg-Ti) Ziegler-Natta catalyst in conjugation with triethyl aluminum (TEA). The impact of temperature and the presence of a chain-terminating agent were examined in the context of ethylene polymerization. The findings showed that as temperature decreases, the activity of the polymerization decreases, and the molecular weight of the polymer increases. Conversely, in the presence of a chain-terminating agent, the molecular weight of the polymer decreases. The introduction of Triethyl borate (TEB) and Tetraethoxy silane (TEOS) as an external donor has a pronounced effect on the catalyst activity, causing a significant decrease, while simultaneously leading to a substantial increase in the viscosity average molecular weight (Mv). Additionally, when a chain-terminating agent is added along with Triethyl borate (TEB) in the system, it results in a significant decrease in molecular weight, albeit with a slight increase in activity compared to a system without a donor. The crystallinity, particle size and bulk density of the polymer synthesized with and without external donor also investigated.