Process aspects of forming polyethylene-based composites filled with functional waste-plant fillers by rotational molding technology
Topic(s) : Material science
Co-authors :
Mateusz BARCZEWSKI (POLAND), Joanna ANIŚKO (POLAND), Paulina KOSMELA , Aleksander HEJNA (POLAND), Mariusz MARĆ , Wiktoria KANCIAK (POLAND), Adam PIASECKIAbstract :
The development of new sustainable material solutions in the processing of thermoplastic polymers concerns both the application of biopolymers and the use of valorized plant derivatives as fillers and modifiers of petrochemical polymers[1]. Considering the fragile nature and low thermal stability of organic compounds having functional features, including antioxidant effects, it is advisable to undertake research not only to determine the final properties of the composites containing them but also to qualitatively describe the degradation accompanying the processing. At the same time, due to the harsh processing environment in rotomolding technology resulting in the need for polymer stabilization, using functional fillers enabling the production of self-stabilizing wood-polymer composites requires combining the analysis of the structure-property relationship with a simultaneous comprehensive analysis of processing and active compounds passivation effects[2].
This study compares the impact of a one- or two-stage manufacturing processing procedure of high-density polyethylene-based (HDPE) composites filled with ground pecan (PES), pistachio (PS) shells (2-15 wt%; <400 μm) on the processing and mechanical properties with consideration of final quality and structure of rotomolded products. The investigations were supplemented with an analysis of changes in the resistance of polyethylene composites to oxidation induced by the migration of low molecular weight compounds with antioxidant activity from plant-based fillers to HDPE matrix.
The use of a two-stage composite processing method, including initial homogenization of the composition using twin-screw co-rotating extrusion before pulverization, allowed for improvement in processability (limited number of pores, pin-holes, and shorter densification time) and mechanical properties (higher tensile and impact strength ) of rotomolded products, compared to those made with the one-step procedure (physically mixed powdered polymer and fillers). Simultaneously, the oxidation resistance assessed by oxygen induction time (OIT-DSC) has been significantly reduced in the case of melt-mixed composites. Rheological analyses in an oxidizing atmosphere also allowed for qualitatively determining the material oxidation process under shearing conditions and correlated with OIT analysis. The PES-containing composites showed significantly higher oxidation resistance than the PS-filled series. Interestingly, the additional tests on the fillers exposed to elevated temperatures showed that their antioxidant capacity analyzed by the DPPH assay did not significantly change. It was found that a certain amount of antioxidants was consumed during melt-processing and rotomolding in the oxidative atmosphere, suppressing polyethylene process degradation, as a result of which the polymer was stabilized, but the number of active compounds in the final product was limited.
This study compares the impact of a one- or two-stage manufacturing processing procedure of high-density polyethylene-based (HDPE) composites filled with ground pecan (PES), pistachio (PS) shells (2-15 wt%; <400 μm) on the processing and mechanical properties with consideration of final quality and structure of rotomolded products. The investigations were supplemented with an analysis of changes in the resistance of polyethylene composites to oxidation induced by the migration of low molecular weight compounds with antioxidant activity from plant-based fillers to HDPE matrix.
The use of a two-stage composite processing method, including initial homogenization of the composition using twin-screw co-rotating extrusion before pulverization, allowed for improvement in processability (limited number of pores, pin-holes, and shorter densification time) and mechanical properties (higher tensile and impact strength ) of rotomolded products, compared to those made with the one-step procedure (physically mixed powdered polymer and fillers). Simultaneously, the oxidation resistance assessed by oxygen induction time (OIT-DSC) has been significantly reduced in the case of melt-mixed composites. Rheological analyses in an oxidizing atmosphere also allowed for qualitatively determining the material oxidation process under shearing conditions and correlated with OIT analysis. The PES-containing composites showed significantly higher oxidation resistance than the PS-filled series. Interestingly, the additional tests on the fillers exposed to elevated temperatures showed that their antioxidant capacity analyzed by the DPPH assay did not significantly change. It was found that a certain amount of antioxidants was consumed during melt-processing and rotomolding in the oxidative atmosphere, suppressing polyethylene process degradation, as a result of which the polymer was stabilized, but the number of active compounds in the final product was limited.