Injection molded lightweight composites from tea-stem fiber and polypropylene: Effect of fiber loading on forming properties and cell structure

China boasts abundant tea resources and substantial production output. To facilitate the high-value utilization of by-products generated during tea production, such as tea stems, thereby reducing resource wastage, this study pioneered the preparation of tea-stem fiber-reinforced polypropylene (TF/PP) composites through microcellular injection and conventional molding processes. The effects of tea-stem fiber (TF) content on the formability of foamed and unfoamed composites were compared and analyzed. The findings reveal that the inclusion of TFs fostered the crystallization of polymer chains, decreased the flowability of the composites in their molten state, and enhanced the density, surface hydrophilicity, and thermal stability of the molded composites. In the unfoamed state, composites with 20 wt%, 40 wt%, and 30 wt% TF content exhibited optimal tensile (35.92 MPa), flexural (58.43 MPa), and impact (6.49 KJ/m2) 2 ) strength, respectively. Upon foaming, composites with TF contents of 30 wt%, 40 wt%, and 30 wt% demonstrated superior tensile (32.84 MPa), flexural (51.31 MPa), and impact (6.94 KJ/m2) 2 ) strength, respectively. A 30 % TF content in foamed composites yielded the best reinforcement effect, creating an ideal balance of internal interactions. This resulted in mechanical properties that were close to or even exceeded those of unfoamed PP while reducing the density by nearly 6 %. The results from this study contribute towards the high-value application of tea by-products, promoting the development of the global tea economy.