Polyolefin Grafted Maleic Anhydride as Compatibilizer for Lignin Polypropylene Composites

The mechanical and physical properties of polymer can be improved by adding lignin. Compared with inorganic fillers, lignin has the advantages of low density, low cost and renewable, so it is widely used in polymer fillers. However, because lignin has a large number of polar groups, its compatibility with PP is poor, so it is difficult to achieve the desired effect.

In this paper, PP/PP-MA/Lignin or PP/PB/Lignin was prepared by adding polypropylene grafted maleic anhydride (PP-g-MA) or polyolefin grafted maleic anhydride (PB) as compatibilizer to PP and lignin. From the fracture morphology of figure 1, it can be seen that after adding compatibilizer, the distribution of lignin in PP is more uniform than that without compatibilizer, and the particle size of lignin is smaller, which will help to improve the properties of lignin on PP. Figure 2 shows the tensile strength of the sample before and after the addition of compatibilizer. The figure shows that compared with pure PP, the Young's modulus and yield stress are increased after adding 2% lignin, but the elongation at break decreases obviously. After adding 10% compatibilizer, compared with pure PP, Young's modulus, yield stress and tensile fracture productivity are improved, indicating that the addition of compatibilizer will be beneficial to the dispersion of lignin in PP, thus further improving its mechanical properties. In addition, the addition of lignin will also improve the aging resistance of the materials.

Fig.1 SEM images showing the fractured surfaces of PP/lignin (a) and PP/PB/lignin composites (b) both containing 2 wt% lignin

Fig. 2. Tensile stress–strain curves of neat PP (i), PP/lignin composites with 2 wt % lignin (ii), PP/PB blend (iii), PP/PB/lignin composites containing 1 wt% (iv), 2 wt % lignin (v), and 4 wt% lignin (vi)；