Effects of extruder screw configurations on thermal properties of glass fiber-reinforced polyamide 6 composites throughout the direct long-fiber-reinforced thermoplastics process

The direct long-fiber-reinforced thermoplastics (D-LFT) process is a series of processes involving two twin-screw extruders, a conveyer, and a compression molding machine. The second twin-screw extruder is designed for mixing continuous fibers with polymer melt and plays an important role in the D-LFT process. This study investigates effects of the screw configurations of the second extruder on thermal properties of glass fiber-reinforced polyamide 6 (PA6) composites throughout the D-LFT process. Two screw configurations, which generate low and high shear stress in composite melt (named the conveying and mixing screws, respectively), were used in the second twin-screw extruder. Samples were taken from four different locations along the D-LFT process and characterized using triple detection gel permeation chromatography (GPC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results suggested that the molecular weight of the PA6 matrix increased in the later stages of the D-LFT process (i.e., after the second extruder) by branching of PA6 molecules. In addition, the mixing screw decreased the molecular weight of the PA6 matrix more than the conveying screw. However, such a decrease in molecular weight had little influence on the thermal stability and crystallization behavior of the composites. POLYM. COMPOS., 40:3500-3509, 2019. (c) 2019 Society of Plastics Engineers