Investigation of the mechanism and effectiveness of cationic polymer as a compatibilizer in microfibrillated cellulose-reinforced polyolefins

The reinforcement effect of microfibrillated cellulose (MFC) in high-density polyethylene (HDPE) was investigated by mechanical, thermal, and rheological analysis. The reinforcement effect using both maleic-anhydride-grafted polypropylene (MAPP) and cationic polymer using primary amine (CPPA) as coupling agents in MFC-reinforced polypropylene (PP) has been reported in our previous study (Suzuki et al. in Cellulose 21:507–518, 2014. doi:10.​1007/​s10570-013-0143-9). The combined use of MAPP and CPPA showed a greater reinforcement effect in the MFC-reinforced HDPE composite than in MFC-reinforced PP. The tensile modulus of MFC-reinforced HDPE was about 22 % higher than that of MFC-reinforced PP. Rheological analysis showed that there was a drastic improvement in the interaction between MFC and HDPE using CPPA and MAPP. The storage modulus of the MFC/HDPE composite in the melt state using MAPP and CPPA as coupling reagents was about three times higher than that without the coupling reagents. Furthermore, differential scanning calorimetry analysis suggested that a chemical reaction occurred between MAPP and CPPA. In addition, the thermal properties of MFC-reinforced HDPE were remarkably improved using MAPP and CPPA: the coefficient of thermal expansion of the composite decreased from 237.2 (HDPE) to 57.1 ppm/K (MFC/HDPE/MAPP/CPPA) and the heat distortion temperature under 0.45 MPa load improved from 67.4 (HDPE) to 116.7 °C (MFC/HDPE/MAPP/CPPA).