Research on the quality of long glass fiber‐reinforced polypropylene pipes formed via fluid‐assisted co‐injection molding

Abstract Fluid‐assisted co‐injection molding (FACIM) processes can be divided into water‐assisted co‐injection molding (WACIM) and gas‐assisted co‐injection molding (GACIM) processes. This study focuses on evaluating the quality of pipes formed through four distinct processes: water‐assisted co‐injection molding overflow (WACIM‐O), water‐assisted co‐injection molding short shot (WACIM‐S), gas‐assisted co‐injection molding overflow (GACIM‐O), and gas‐assisted co‐injection molding short shot (GACIM‐S). Wall thickness, wall thickness uniformity, fiber morphology, and pressure resistance were studied. Long glass fiber‐reinforced polypropylene was the outer layer while polypropylene was the inner layer. The total wall thickness of the four types of pipes tends to decrease along the flow direction; however, the total wall thickness of the short‐shot pipes increases at the end. The wall thickness uniformity of the GACIM pipes is better than that of the WACIM pipes while the average fiberglass fracture length of the FACIM‐O pipes is longer than that of the FACIM‐S pipes. Also, the average fiber fracture length of the WACIM‐O pipes is the longest. The fiber orientation distribution can be divided into the near‐mold wall layer, the outer core layer, and the near‐interface layer. The degree of fiber orientation increases layer by layer along the flow direction. Glass fiber orientation is the highest for the WACIM‐O pipes; the pressure resistance of FACIM‐O pipes is better than that of the FACIM‐S pipes. Highlights Pipes were successfully prepared from long glass fiber‐reinforced polypropylene and polypropylene as the material. The wall thickness uniformity of the fluid‐assisted co‐injection molding (FACIM)‐overflow pipes is satisfactory. The total wall thickness of the FACIM‐short shot pipes have notable variations. The water‐assisted co‐injection molding‐overflow pipes present a longer average fiber breaking length. The pressure resistance of FACIM‐overflow pipes is better than that of FACIM‐short shot pipes.