Influence of two kinds of low dimensional nano-sized silicate clay on the flame retardancy of polypropylene

Abstract

Nano-rolled and nano-sheeted silicates were fabricated from nature kaolinite (Kaol). And their structure was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and so on. The two nano-sized silicates acted as synergists to enhance fire retardant performance of polypropylene (PP) with intumescent flame-retardants (IFR) together. The limited oxygen index (LOI) of PP is only 18%, incorporation of 25 wt% IFR lifted the LOI to 31.1%, further increase to 34.5 and 35.5% by 1.5 wt% substitution of nano-rolled Kaol (N-Kaol) or exfoliated Kaol (E-Kaol) with same amount of IFR, respectively. Moreover, each modified Kaol can effectively control melt dripping to help PP reach UL-94 V-0 grade. In cone test, the resultes showed that the peak heat release rate (pHRR) values of PP/IFR/N-Kaol (269 kW/m2) and PP/IFR/E-Kaol (319 kW/m2) composites were reduced by 38.6 and 27.2% compared to that of PP/IFR (438 kW/m2), respectively; the smoke release was similar to the heat release. Continue increased char percentage documented the promotion on charring from E-Kaol and N-Kaol. The PP/IFR/N-Kaol exhibited the best char strength. Morphology observation on macro/micro-structure of char and real-time FTIR demonstrated that N-Kaol can be beneficial to forming homogenous and compact intumescent char layer through “double effect” of barrier and pillar-like support during burning, especially after 340 s, compared with the PP/IFR containing E-Kaol. This special structure of char layer can effectively limit the flow and transfer of inflammable gases and heat between underlying matrix and outside environment.