Effects of poly(dimethylsiloxane) and inorganic fillers in halogen free flame retardant poly(ethylene-co-vinyl acetate) compound: A chemometric approach

Grafting of thermotropic fluorinated mesogens on polysiloxane to improve the processability of linear low-density polyethylene

In this study, a series of polysiloxane grafted with thermotropic fluorinated mesogens (TSCPFLCP) is designed and synthesized. The TSCPFLCP exhibits a typical smectic liquid crystal phase, and shows a high thermal decomposition temperature at 335.6 °C. After blending with LLDPE, the balance melt torque of LLDPE/TSCPFLCP is decreased by 42% at 0.5 wt% TSCPFLCP, and the corresponding power law index is increased to 0.45. The flowing activation energy of the optimized LLDPE/TSCPFLCP blend is lower than that of pure LLDPE at the same shear rate, indicating that TSCPFLCP reduced the sensitivity of the apparent melt viscosity of LLDPE to both shear rate and temperature. This contributes to the broadening of the LLDPE processing window. On the other hand, TSCPFLCP is also found beneficial in ameliorating melt fracture during LLDPE extrusion. Furthermore, the mechanical properties of LLDPE/TSCPFLCP blends, such as tensile strength, elastic modulus and elongation at break, are also enhanced significantly at 0.5 wt% TSCPFLCP. Altogether, TSCPFLCP has been proven an effective processing aid to improve the processability and toughness of LLDPE.

Development of Biodegradable Flame-Retardant Bamboo Charcoal Composites, Part I: Thermal and Elemental Analyses

In this study, bamboo charcoal (BC) was used as a substitute filler for bamboo powder (BP) in a lignocellulose-plastic composite made from polylactic acid (PLA), with aluminum hypophosphite (AHP) added as a fire retardant. A set of BC/PLA/AHP composites were successfully prepared and tested for flame-retardancy properties. Objectives were to (a) assess compatibility and dispersibility of BC and AHP fillers in PLA matrix, and (b) improve flame-retardant properties of PLA composite. BC reduced flexural properties while co-addition of AHP enhanced bonding between PLA and BC, improving strength and ductility properties. Adding AHP drastically reduced the heat release rate and total heat release of the composites by 72.2% compared with pure PLA. The formation of carbonized surface layers in the BC/PLA/AHP composites effectively improved the fire performance index (FPI) and reduced the fire growth index (FGI). Flame-retardant performance was significantly improved with limiting oxygen index (LOI) of BC/PLA/AHP composite increased to 31 vol%, providing a V-0 rating in UL-94 vertical flame test. Adding AHP promoted earlier initial thermal degradation of the surface of BC/PLA/AHP composites with a carbon residue rate up to 40.3%, providing a protective layer of char. Further raw material and char residue analysis are presented in Part II of this series.

Design and Synthesis of Polysiloxane Based Side Chain Liquid Crystal Polymer for Improving the Processability and Toughness of Magnesium Hydrate/Linear Low-Density Polyethylene Composites

In this study, a polysiloxane grafted by thermotropic liquid crystal polymer (PSCTLCP) is designed and synthesized to effectively improve the processability and toughness of magnesium hydroxide (MH)/linear low-density polyethylene (LLDPE) composites. The obtained PSCTLCP is a nematic liquid crystal polymer; the liquid crystal phase exists in a temperature range of 170 to 275 °C, and its initial thermal decomposition temperature is as high as 279.6 °C, which matches the processing temperature of MH/LLDPE composites. With the increase of PSCTLCP loading, the balance melt torque of MH/LLDPE/PSCTLCP composites is gradually decreased by 42% at 5 wt % PSCTLCP loading. Moreover, the power law index of MH/LLDPE/PSCTLCP composite melt is smaller than 1, but gradually increased with PSCTLCP, the flowing activation energy of PSCTLCP-1.0 is lower than that of MH/LLDPE at the same shear rate, indicating that the sensitivity of apparent melt viscosity of the composites to shear rate and to temperature is decreased with the increase of PSCTLCP, and the processing window is broadened by the addition of PSCTLCP. Besides, the elongation at break of MH/LLDPE/PSCTLCP composites increases from 6.85% of the baseline MH/LLDPE to 17.66% at 3 wt % PSCTLCP loading. All the results indicate that PSCTLCP can significantly improve the processability and toughness of MH/LLDPE composites.