Preparation And Property Of Biodegradable Polypropylene/Lignin Composites

Wood-Plastic Composites, which use of wood material (lignin, wood flour, wood fiber or plant fibers, etc.) filled thermoplastic polymer, have the advantages of both wood and plastic. Lignin is an abundant, renewable and important resource, though the poor compatibiliity with polyolefin barriers its application. Polypropylene has great advantages to be the matrix of wood-plastic composites because of its low density, excellent mechanical properties and chemical stability. This paper studied on polypropylene/ lignin composites, the pre-graft (alkylation) of lignin to improve the compatibility of polypropylene and lignin, and the composites' biodegradability had also been studied.After the reaction of the lignin and dodecyl bromide, fourier transform infrared spectroscopy (FTIR) showed that the long-chain alkanes have been grafted to the lignin molecules. Modified lignin (alkylate lignin) has the better compatibility with PP. In PP/lignin composites, maximum content of modified lignin (neat lignin) was up to 70 wt%, maximum content of non-modified lignin was only 50 wt%.The results of mechanical properties showed that the composite with 10 wt% content of alkylate lignin got the best mechanical properties With increasing the lignin content, mechanical properties of the composites gradually decreased. The mechanical properties of PP/alkylate lignin composites were better than PP/neat lignin composites overall.Dynamic mechanical analysis (DMA) results showed that by adding lignin could increase the storage modulus of composites, which played a key role in enhancing the PP. However, the glass transition temperature (Tg ) of composites were slightly decreased.The study of differential scanning calorimetry (DSC) showed that lignin played a role of heterogeneous nucleation when the PP crystallization. When the content of neat lignin was 15wt%, the composites achieved the maximum crystallinity degree (61.3%); when the content of modified lignin was 50wt%, the composites achieved the maximum crystallinity degree (69.4%).Rheological behavior analysis showed that, non-Newtonian index of PP/alkylate lignin composites increased with adding alkylate lignin, and composites' processing performance mended, while the PP/neat lignin composites showed the opposite trend.Scanning electron microscopy (SEM) photos imaged that alkylate lignin had the better dispersion with PP matrix than non-modified lignin in the composites.Thermogravimetry analysis (TGA) showed that lignin enhanced the heat-resistant of PP matrix, and the heat-resistant of composites became better.After 50 days biological degradation, the maximum weight loss rate of composits was up to 9.61% (70 wt% content of alkylate lignin), IR analysis showed that the lignin of composites was degraded; DMA analysis showed that the storage modulus of composites was significantly decreased; SEM analysis showed that the micro-structure of composites was changed, which apparenting defects (empty and void); TG analysis showed that heat-resistant properties of composites essentially unchanged, but the residue at 600℃was significantly reduced; all of those proved composites can be degradation.