Development of a direct injection molding process for the production of long glass fiber-reinforced phenolic resins components

Parts made from phenolic molding compounds reinforced with glass fibers have a good heat resistance, a high dimensional accuracy, and an excellent chemical resistance. However, these parts typically have a low tensile strength. Conventional glass fiber-reinforced phenolic molding compounds have an average fiber length which is below the critical fiber length for this material combination. To increase the fiber length and to mitigate this disadvantage, a new injection molding process variant was developed, which allows the direct addition of long glass fibers. For opening and dispersing long fiber bundles, a thermoset-specific screw mixing element was developed and compared to the conventional conveying screw geometry. Despite the increased fiber shortening when using the mixing element, the mechanical properties were improved compared to the standard conveying screw geometry, which is attributed to the better fiber-matrix homogenization.