Preparation and properties of dynamically cured polypropylene (PP)/maleic anhydride–grafted polypropylene (MAH-g-PP)/calcium carbonate (CaCO 3 )/epoxy composites

In this study, an epoxy resin was dynamically cured in a polypropylene (PP)/maleic anhydride–grafted polypropylene (MAH-g-PP)/calcium carbonate (CaCO 3 ) matrix to prepare dynamically cured PP/MAH-g-PP/CaCO 3 /epoxy composites. The torque measurement shows that the addition of epoxy resin into the PP/MAH-g-PP/CaCO 3 composites results in a slight increase in the torque at equilibrium, and epoxy resin in the composites has been cured by 2-ethylene-4-methane-imidazole (EMI-2,4). Scanning electron microscopic analysis shows that dual compatibilizers composed of MAH-g-PP and an epoxy resin were demonstrated to effectively compatibilize the immiscible PP/CaCO 3 composites. MAH-g-PP with a low MAH content is miscible with PP to make it quasi-functionalized, while the epoxy resin can react with MAH-g-PP and hydroxyl groups at the CaCO 3 surface. Thus the formed MAH-g-PP-co-epoxy-co-CaCO 3 copolymer at the interface is able to anchor along the interface and serve as an efficient compatibilizer. Dynamic cure of the epoxy resin can further increase the interaction adhesion in the PP/CaCO 3 composites. The epoxy resin does not show compatibilization effects for the PP/CaCO 3 composites without the presence of MAH-g-PP. The shift of crystallization peaks to the higher temperature suggests that the CaCO 3 filler in the composites can act as a nucleating agent, accelerating the crystallization of PP component, and the PP/CaCO 3 composites compatibilized by MAH-g-PP and the epoxy resin have higher crystallization peaks. This shows that an increase in the interaction adhesion between the CaCO 3 and PP matrix, improving the nucleating activity of the filler and promoting crystallization of PP. Thermogravimetric analysis shows that the incorporation of the CaCO 3 into the PP could improve the thermal stability of PP, and the addition of MAH-g-PP and the epoxy resin into the composites obviously could further improve the thermal stability. The mechanical properties of PP/MAH-g-PP/CaCO 3 and PP/MAH-g-PP/CaCO 3 /epoxy composites are better than that of the PP/CaCO 3 composites. The PP/MAH-g-PP/CaCO 3 /epoxy/EMI-2,4 composites have the best mechanical properties in all the PP/CaCO 3 composites, which is attributed to the better interaction adhesion. The suitable content of epoxy resin is about 5 wt% in the presence of MAH-g-PP in the PP/CaCO 3 composites, while an excess epoxy resin of above 5 wt% acts as an organic filler for PP.