Polypropylene/Layered Double Hydroxide Nanocomposites:Influence of LDH Intralayer Metal Constituents on the Properties ofPolypropylene

摘要

Sonication-assisted delamination of layered double hydroxides (LDHs) resulted in smaller-sized LDH nanoparticles (∼50–200 nm). Such delaminated Co–Al LDH, Zn–Al LDH, and Co–Zn–Al LDH solutions were used for the preparation of highly dispersed isotactic polypropylene (iPP) nanocomposites. Transmission electron microscopy and wide-angle X-ray diffraction results revealed that the LDH nanoparticles were well dispersed within the iPP matrix. The intention of this study is to understand the influence of the intralayer metal composition of LDH on the various properties of iPP/LDH nanocomposites. The sonicated LDH nanoparticles showed a significant increase in the crystallization rate of iPP; however, not much difference in the crystallization rate of iPP was observed in the presence of different types of LDH. The dynamic mechanical analysis results indicated that the storage modulus of iPP was increased significantly with the addition of LDH. The incorporation of different types of LDH showed no influence on the storage modulus of iPP. But considerable differences were observed in the flame retardancyand thermal stability of iPP with the type of LDH used for the preparationof nanocomposites. The thermal stability (50% weight loss temperature(T0.5)) of the iPP nanocomposite containingthree-metal LDH (Co–Zn–Al LDH) is superior to that ofthe nanocomposites made of two-metal LDH (Co–Al LDH and Zn–AlLDH). Preliminary studies on the flame-retardant properties of iPP/LDHnanocomposites using microscale combustion calorimetry showed thatthe peak heat release rate was reduced by 39% in the iPP/Co–Zn–AlLDH nanocomposite containing 6 wt % LDH, which is higher than thatof the two-metal LDH containing nanocomposites, iPP/Co–Al LDH(24%) and iPP/Zn–Al LDH (31%). These results demonstrated thatthe nanocomposites prepared using three-metal LDH showed better thermaland flame-retardant properties compared to the nanocomposites preparedusing two-metal LDH. This difference might be due to the better charformation capability of three-metal LDH compared to that of two-metalLDH.