Search

The aim of this study is to investigate the shape memory behavior and physical properties of crosslinked low density polyethylene (LDPE)/Octavinyl functionalized polyhedral oligomeric silsesquioxanes (OvPOSS)/triallyl isocyanurate (TAIC) composites. Shape memory polymer can return from its temporary shape to the original (permanent) shape upon heating. One of the most widely used shape memory polymers is crosslinked polyethylene. Polyhedral oligomeric silsesquioxanes (POSSs) organic/inorganic hybrid materials are new the generation of nanofillers that can be used to increase the crosslinking efficiency of LDPE. OvPOSS nanoparticles having reactive functional vinyl groups and TAIC were used as coagents. On the other hand, 1 phr of di tert-butyl cumyl peroxide (BCUP) was used as a crosslinking agent in this study. LDPE/OvPOSS/TAIC/Peroxide composites were prepared in an Xplore model twin screw micro-compounder at a screw speed of 50 rpm and 135°C barrel temperature. The crosslinking was carried out using a hot-press operated at 175°C. The composites were characterized by performing tensile tests, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), rheology and shape memory tests. Rheological test results showed that the degree of crosslinking, storage and loss modulus of LDPE/TAIC system increased by the addition of OvPOSS and TAIC. It was obtained from DSC analysis that LDPE/OvPOSS/TAIC/Peroxide composites exhibited lower melting enthalpy values, which can be attributed to the restricted chain mobility of LPDE in the presence of OvPOSS and PRX. [ABSTRACT FROM AUTHOR]

Shape memory polymers are smart materials having the ability to change their shape under external stimulus. One of the most widely used shape memory polymers is cross-linked polyethylene (PE). The cross-linked polyethylene can be triggered by temperature to transfer from its permanent shape to programmed shape. Polyhedral oligomeric silsesquioxanes (POSSs) are the new generation of hybrid nanoparticles that positively affect the thermal stability, thermo-mechanical strength, flow properties and crystallization rates of the polymers. POSSs can also be used as crosslinking agents. Besides, coagents are used in order to improve the crosslinking efficiency by reducing undesirable side reactions such as chain breakage or disproportionation. They form bridges between polymer chains to be cross-linked. The aim of this study is to investigate the synergistic effects between POSS and coagent on the physical and shape memory properties of cross-linked linear low-density polyethylene (LLDPE). Octavinyl POSS (OvPOSS) nanoparticles and poly(ethylene glycol) dimethacrylate (PEGDMA) were used as coagents in this study. The peroxide used in crosslinking was di tert-butyl cumyl peroxide (PRX). Its content was kept constant as 1 phr. LLDPE/OvPOSS/PRX, LLDPE/PEGDMA/PRX and LLDPE/OvPOSS/PEGDMA/PRX composites were prepared in an Xplore model micro-compounder at a screw speed of 50 rpm and 135°C barrel temperature. The crosslinking was carried out using a hot-press operated at 175°C. The samples were characterized by performing differential scanning calorimetry (DSC), scanning electron microscopy (SEM), rheology, tensile tests and shape memory tests. Rheological analysis showed that the degree of crosslinking, storage modulus and complex viscosity increased in the presence of OvPOSS and PEGDMA. A synergistic effect was observed between OvPOSS and PEGDMA coagents. [ABSTRACT FROM AUTHOR]

In this study, the influence of epoxy functionalized polyhedral oligomeric silsesquioxanes (G-POSS) loading level on the mechanical, thermal and rheological properties of poly(lactic acid) (PLA)/thermoplastic polyurethane (TPU) blends were investigated. The blends were prepared in an Xplore Instruments MC15 twin-screw microcompounder at 200°C barrel temperature and 100 rpm screw speed. Mechanical properties were characterized by tensile and impact tests, thermal properties were determined via differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). Rheological properties were examined by oscillatory rheometer. A decreasing trend in tensile strength and thermal degradation temperature were obtained for PLA/TPU blends at high G-POSS loading levels. G-POSS loading level did not exhibit significant effect on glass transition, crystallization and melting temperatures of the blends. [ABSTRACT FROM AUTHOR]

In this study, the correlation between crystallization behavior and surface chemistry of polyhedral oligomeric silsesquioxanes (POSS) for plasticized poly(lactic acid) (PLA)/POSS nanocomposites was investigated. Four different kinds of POSS particles having different chemical structures were used. Poly(ethylene glycol) (PEG, 8000 g/mol) was utilized as the plasticiser. The nanocomposites were melt-compounded in an Xplore Instruments 15 cc twin screw microcompounder at 180 C barrel temperature and 100 rpm screw speed. Non-isothermal crystallization behaviour of PLA/PEG/POSS nanocomposites were evaluated from common kinetic models such as Avrami and Avrami-Ozawa and Kissinger by using the thermal data obtained from differantial scanning calorimetry (DSC). A polarized optical microscope (POM) equipped with a hot-stage was used to examine the morphology during the crystal growth. In order to investigate the interfacial interactions between POSS particles and plasticized PLA, thermodynamic work of adhesion approach was adopted using the experimentally determined surface energies. A strong correlation was obtained between interfacial chemistry and the nucleation rate in plasticized PLA/POSS nanocomposites. It was found that the polar interactions were the dominating factor which determines the nucleation activity of the POSS particles. [ABSTRACT FROM AUTHOR]