Ethylene-Propylene-Diene Terpolymer(EPDM)/Polyhedral Oligomeric Silsesquioxane(POSS) 나노복합체의 제조 및 특성

Abstract

This thesis studies on two different type of EPDM/POSS nanocomposites, one is EPDM/POSS nanocomposite vulcanizates and the other is melt-processible EPDM-g-POSS nanocomposites. In the studies on EPDM/POSS nanocomposite vulcanizates, effect of POSS on vulcanization behavior, mechanical properties and thermal stability of peroxide and sulfur cured EPDM was examined with an emphasis on the effect of functional group of POSS on these behaviors. In the studies on EPDM-g-POSS nanocomposites, reactive melt blending method to prepare the graft copolymer was explored. In peroxide vulcanized EPDM/POSS nanocomposites, it was observed that a POSS having acrylate group on its cage improves the crosslinking efficiency of EPDM rubber and the POSS is covalently grafted onto the EPDM chain during vulcanization. In order to prepare sulfur vulcanized EPDM/POSS nanocomposites, POSS containing disulfide group (POSS-SS) was incorporated into EPDM compounds. The POSS-SS was synthesized by oxidation of POSS containing thiol group on its cage. It was observed that the POSS-SS act as an accelerator for the sulfur vulcanization of EPDM, and the POSS is covalently grafted onto the rubber chain. Vulcanization kinetics studies performed using oscillating rheometer revealed that the addition of POSS-SS decrease the activation energy for the sulfur vulcanization of EPDM. In both peroxide cured and sulfur cured EPDM/POSS nanocomposite vulcanizates, the POSS molecules are dispersed in the rubber matrix as nanocrystalline domains, and tensile modulus, strength and resistance-to-crack growth of the nanocomposite vulcanizates increased with POSS with a concurrent increase in elongation-at-break. Enhanced thermal stability in the nanocomposite was also observed Thermal degradation kinetic studies was studied by means of thermogravimetry analysis (TGA) with sulfur vulcanized EPDM/POSS nanocomposite vulcanizate. Kissinger and Friedman method were used to obtain the non-isothermal degradation kinetic parameters, which revealed that the activation energy (Ea) for the thermal degradation increased with increasing POSS content in the nanocomposites. It was also revealed from this study that the POSS significantly prolonged the lifetime of EPDM under the thermal aging condition. The effective enhancement in the thermal stability of the nanocomposites can be achieved when the POSS is covalently bonded to the matrix rubber. EPDM-g-POSS was synthesized by reactive melt blending of maleated EPDM with aminopropylisobutyl POSS (amino-POSS) in an internal mixer. Chemical grafting of the aminoPOSS onto the maleated EPDM was confirmed by FTIR. In the EPDM-g-POSS, there are POSS-POSS interactions to form nanocrystal aggregates as well as hydrogen bonding and ionic interactions between the polymer chains, which provide physical crosslinking points to the rubber. It was shown that the EPDM-g-POSS obtained in this way exhibit a thermoplastic elastomer like behavior. The EPDM-g-POSS nanocomposites can also prepared by melt blending of EPDM with POSS-SS under a high shear stress. Labile disulfide group of POSS-SS can be broken to produce thiyl radical when it is subjected to a high shear stress, which can induce a grafting of POSS onto EPDM chain during the melt blending. The effect of shear stress, which was handled by a rotor speed in an internal mixer, on the grafting level was determined. It was revealed that the EPDM-g-POSS prepared by this way showed a thermoplastic elastomer like behavior. Mechanical properties, dynamic mechanical properties and elastic recoverability of the EPDM-g-POSS increased with increasing grafted POSS content. The melt rheological study revealed that the EPDM-g-POSS exhibit a more pronounced solid-like behavior and stronger shear thinning behavior as compared to neat EPDM.