On the use of black tea waste as a functional filler for manufacturing self-stabilizing polyethylene composites: In-depth thermal analysis

Thermal and oxidative stabilization are critical aspects in the processing and exploitation of polyolefins. Black tea contains many natural antioxidants, the largest group of compounds in its composition. When used as a filler for composite manufacturing, the thermo-oxidation process of polyethylene can be slowed down. Black tea waste (BTW) generated during the process of packing tea into sachets was introduced into a bio-based low-density polyethylene (LDPE) as a filler. The composites containing 1, 2, 5, and 10 wt% were produced by melt extrusion. In order to assess the antioxidant capacity of the used filler, an analysis was carried out using the DPPH solution on both the filler extracts and the produced composites. The total phenolic content and total flavonoid content analysis were also carried out on black tea waste extracts. Thermogravimetric analysis of composites was held in an inert and oxidative atmosphere, and data from the test in a nitrogen atmosphere was used to calculate degradation kinetics. The composites were also evaluated in terms of their thermal behavior by differential scanning calorimetry (DSC) to describe their crystallization process and oxidation induction time (OIT) to confirm stabilization effects caused by functional waste fillers on polyethylene. Adding 10 wt% of black tea waste elongates OIT nearly 36 times compared to LDPE. The thermo-oxidation process was also conducted at 90 °C for 1, 2, 4, 7, 11 and 15 days. The composites aged this way were subjected to the FTIR test. Thanks to this study, the carbonyl index (CI) was determined, which showed that adding tea waste limits the oxidation of polyethylene. • The evaluation of black tea waste antioxidant properties showed outstanding potential to scavenge free radicals. • Incorporating BTW into bioLDPE significantly elongates the composites' OIT, almost 36 times after adding 10 wt% of BTW. • The kinetic analysis of composite degradation showed that adding 5 and 10 wt% BTW to LDPE changes the decomposition model. • A thermal aging test showed the possibility of preventing material oxidation by BTW.