Injection processing parameters directly influence the final fiber length and may have a negative effect on the mechanical properties of a part. The aim of the work is to investigate and quantify the effects of the injection rate (2/10/50 cm3/s) on the fiber length, the distribution, and orientation during injection molding and the mechanical properties of long‐glass‐fiber‐reinforced polypropylene (LGF/PP) by experimental and simulated methods. When the injection rate increases from 2 to 10 cm3/s, the fiber length sharply decreases from the original 11 mm to 3.43 mm at the nozzle and 1.30 mm at the filling end, and almost 88% of the fibers are less than 3 mm when the injection rate is 50 cm3/s. A distinct hierarchical orientation (skin‐shear‐core) for the fiber distribution in the thickness is obtained via a metallographic microscope, which shows that the shear layer (here the shear stress is larger and the fiber is more inclined to oriented along the flow direction) decreases with increasing injection rate. Moreover, the numerical results of the residual fiber length and orientation at different injection rates are in accord with the trend of the measured results. POLYM. ENG. SCI., 60:13–21, 2020. © 2019 Society of Plastics Engineers

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Poly (lactic acid) (PLA) is a biodegradable and environmentally friendly material.And the spent coffee grounds (SCG) are huge waste all over the world. Therefore, the issue that how to convert the low-value wastes SCG into more valuable products is attracting more research attention. In this work, we compounded PLA with SCG.Firstly, the efficiency of oil extraction from SCG was compared by different methods and solvents. Then, the biocomposites specimens of different SCG contents (0, 5, 10, and 15 wt%) were prepared by extrusion and injection molding. The effects of SCG particle size and content on the thermal and mechanical properties were investigated. Next, the effect of coupling agent (4,4-methylene diphenyl diisocyanate [MDI]) on the biocomposites properties at 10 wt% SCG was examined by Field emission-scanning electron microscope and Fourier transform infrared spectroscopy. The results show that the tensile strength and elongation at break of the PLA composites with the optimal contents are increased by about 50% and 120%, respectively, compared with untreated SCG.