Co-authors​ :

 Joanna ANIŚKO (POLAND), Paulina KOSMELA , Mateusz BARCZEWSKI (POLAND) 

Black tea contains many natural antioxidants, the largest group of compounds in its composition. Thanks to its antioxidant properties, in the case of its use as a filler of polyethylene composites, the thermo-oxidation process of the polymeric matrix can be slowed down. An extensive analysis was held to evaluate the possibility of stabilization of the polyethylene composite as a material for rotational molding. In the rotational molding technique, the material is kept at an elevated temperature in a molten state for a relatively long time, which can cause oxidation of the polymer. Black tea dust produced as waste in the process of packing tea into sachets was introduced into a matrix of low-density polyethylene. The used polyethylene is biobased low-density polyethylene (LDPE SEB 853 I'm Green®). The filler was introduced in 1, 2, 5, and 10 wt% in the extrusion process. The DPPH analysis was performed on both the filler extract and composites to assess the antioxidant capacity of the used filler. 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 melting properties and oxygen induction time (OIT) to confirm stabilization effects. Adding 10 wt% of black tea waste increases OIT nearly 36 times compared to LDPE. The thermo-oxidation process was also carried out, consisting of annealing the pressed samples at 90 ° C for 1, 2, 4, 7, 11 and 15 days. The aged composites were subjected to the FTIR test. Thanks to this study, the carbonyl index was determined, which shows that adding tea dust slows down the oxidation of polyethylene. This thoroughly investigated material was cryogenically milled using an ultra-centrifugal mill Retsch ZM 200 with a sieve of 500 µm. The uniaxial rotational molding was performed using a desktop rotational molding machine, 493K RotoRocket. The rotomolded samples were subjected to the Fourier transform infrared spectroscopy; it appears that the addition of 10 wt% black tea waste prevents the formation of carbonyl compounds in polyethylene, while the addition of 5 wt. % or more prevents the appearance of a peak corresponding to C-O stretching associated with LDPE degradation. The antioxidant properties of filler were also investigated for filler exposed to a temperature similar to ones during rotational molding, which did not cause significant deterioration of these properties and changes in chemical composition investigated via FTIR study. Instead, the addition of BTW deteriorates the mechanical properties of the composite, including Young's modulus and tensile strength, compared to pure bioLDPE.