Polymer processing
Mehri Dana; Mohammad Reza Nabid; Gholamhossein Zohuri; Saeid Asadi Shahidi; Sohail Yazdanbakhsh
Abstract
Styrenic thermoplastic vulcanizates (STPV) consist of polypropylene (PP) and linear low density polyethylene (LLDPE) as the continuous phases and a crosslinked hydrogenated styrene block copolymer (SEBS) as the dispersed phase were prepared in an industrial scale using a corotating twin-screw extruder. ...
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Styrenic thermoplastic vulcanizates (STPV) consist of polypropylene (PP) and linear low density polyethylene (LLDPE) as the continuous phases and a crosslinked hydrogenated styrene block copolymer (SEBS) as the dispersed phase were prepared in an industrial scale using a corotating twin-screw extruder. Morphological study of the TPVs was carried out using a scanning electron microscope (SEM). Rheological study of the SEBS compounds carried with different content of 2,5-Dimethyl-2,5-di(tert-butylperoxy) hexane peroxide (0.5, 1, 2 and 4 wt. %). T90 appeared with 4 w% peroxide shows that curing has been completed. Effect of peroxide content (0.5 to 1.2 wt.%) on properties of the TPVs was led to an increase in tensile strength (from 5.6 to 7.4 MPa) and hardness to a certain extent (74 shore A). On the other hand, mechanical properties such as the elongation at break (from 592% to 284%), the melt flow index (MFI) (from 29.6 to 3.14 g/10 min at 190 °C, 10 kg) and tear strength (from 35 to 30 kg f/cm) are decreased. The compression set at low temperature (70 °C) is not changed so much, at high temperature (120 °C), while, is reduced due to higher curing (from 69% to 46%). Heat aging was carried out (at 85 °C for 168 h) on the TPVs which were prepared via the different content of peroxide (0.5 wt. % to 1.2 wt. %). It was found that the results of elongation and the hardness after aging have the lowest amount using 0.9 wt.% peroxide. However, the tensile strength after aging decreased with increasing the content of peroxide. As a result of increasing curing with increasing content of peroxide, the melting point of the prepared TPVs was disappears. The results of using triallylcyanurate (TAC) and bismaleimide (BMI) as a co-curing agent in peroxide curing indicate that all of the tensile strength, hardness and elongation at break (from 897 to 1082%) of the STPV were increased with BMI. Heat ageing study and compression set on the STPV with TAC was slightly raised compared to BMI. Also, the results of dynamic vulcanization on the properties of TPV based on SEBS/LLDPE/PP indicate that Crosslink density and gel content of TPV are close to that of EPDM rubber (fully crosslinked) and higher than that of TPE (without crosslinking). The results show that the tensile strength and density of the dynamically crosslinked blend have not changed significantly under peroxide curing.
Characterization
Mehri Dana; Gholam Hossein Zohuri; Navid Ramezanian; Saeid Asadi Shahidi; Sohail Yazdanbakhsh
Abstract
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 ...
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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.
