Synthesis of a Novel Charring Agent Containing Lignin and Its Intumescent Flame Retardant Properties for Polypropylene

Abstract

A novel eco-friendly charring agent (L-OH) was successfully synthesized by combining pentaerythritol (PER) with lignin through a simple two-step reaction. The structure of L-OH was characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and EDS. In addition, L-OH was introduced into polypropylene (PP) together with melamine (MEL) and ammonium polyphosphate (APP) as an intumescent flame retardant (IFRR). The flame retardancy of PP/IFRR composites were investigated using limited oxygen index (LOI), UL-94, thermogravimetric analysis (TGA) and cone calorimeter (CC) test. The experimental results indicate that the PP/IFRR composites pass the V-0 grade of the UL-94 test when the addition amount of IFRR is no less than 20%, and the LOI value of the composite reaches 32.2% at 30% IFRR addition. The peak heat release rate (PHRR) and peak smoke production rate (PSPR) of the composite decrease by 72.8% and 70.4% compared with pure PP, respectively. The flame retardancy mechanism was investigated by TGA, TG-FTIR and residual carbon analysis. These analyses indicate that L-OH can form a more continuous and dense carbon layer during the combustion process, which is the main factor contributing to the improved flame retardancy of PP.

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