Influence of the process method on the properties of paper-fiber-reinforced composites

The application of pulp and paper fibers as reinforcement in thermoplastic composites involves several advantages, such as sustainability, constant fiber quality and high mechanical properties. This work compares three different processing methods for the production of paper-reinforced polypropylene composites. The composites were produced by (i) hot pressing, (ii) injection molding and (iii) a pre-coating process with fiber volume fractions between 10 and 65%. The mechanical properties were investigated by tensile and flexural testing. Furthermore, SEM analysis and porosity determination were carried out. The results were correlated with the according processing method and evaluated towards the highest composite performance. As a result, laminated composites with intact paper layers, showed significantly higher mechanical properties, due to the fiber orientation in the paper sheet and good adhesion between the matrix and the paper fibers. Compounded and injection molded composites showed a high degree of fiber agglomeration and less orientated fibers in the composite leading to reduced mechanical properties.