Phytic Acid Modified Boron Nitride Nanosheets as Sustainable Multifunctional Nanofillers for Enhanced Properties of Poly(l-lactide)

A sustainable multifunctional nanofiller (f-BNNSs) based on boron nitride nanosheets and biobased phytic acid was prepared using (γ-aminopropyl) triethoxysilane as a coupling agent. The structure of f-BNNSs was analyzed systematically using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental mapping. The influence of f-BNNSs on the crystallinity, polymorphism, crystallization kinetics, thermal stability, thermal conductivity, and flame retardant properties of poly(l-lactic acid) (PLLA) was systematically investigated. f-BNNSs show remarkable nucleating effects on the crystallization of PLLA, and the crystallization rate increases with increasing f-BNNSs loading. Upon addition of 20 wt % of f-BNNSs, the crystallization half-time of PLLA/f-BNNSs nanocomposite decreases from 12.0 to 1.0 min at 130 °C compared to PLLA. The presence of f-BNNSs in PLLA/f-BNNSs nanocomposites favors the formation of ordered α form irrespective of the loadings of f-BNNSs. Thermal stability and thermal conductivity of PLLA increased significantly due to the strong interfacial interactions between hydroxyl groups of f-BNNSs and the carboxyl groups of PLLA. The presence of phosphorus, nitrogen, silicon, and carbon elements in f-BNNSs improves the char forming capability of f-BNNSs leading to the enhancement of the flame retardancy of PLLA in PLLA/f-BNNSs nanocomposites. The limiting oxygen index (LOI) value of neat PLLA is 18.5% and it increases to 27.5% for PLLA nanocomposites containing 20 wt % of f-BNNSs. This work provides a new strategy toward the development of environmentally friendly multifunctional nanofiller for PLLA.