Dry grape peel powder was extracted by three different techniques, stirred tank reactor, Soxhlet and ultrasound extraction. The composition, physical and chemical structure and inherent stability of the extracts were characterized by various methods. The extracts and reference compounds were added to polyethylene and their stabilization efficiency was determined in multiple extrusion experiments. The composition of the extracts was quite similar. Ten main compounds were identified in the extracts, which contained a considerable number of polyphenols, but only small amounts of quercetin and trans-resveratrol. The extracts proved to be more efficient processing stabilizers than trans-resveratrol and the commercial stabilizer, Irganox 1010, irrespective of the extraction technology used. In spite of their good processing stabilization effect, polymers containing the extracts had poor residual stability. The differences in processing and long-term stabilization must be related to the different structures of the polyphenols contained by the extracts and the reference compounds. The results clearly prove that the IC50 value determined by the DPPH assay is not suitable for the estimation of the efficiency of a compound as a stabilizer for polymers.
A new phosphine-type potential secondary stabilizer was synthesized successfully with large natural raw material content. The stabilizer is a waxy white powder with a relatively low melting temperature. Both the thermal and the storage stability of the stabilizer are sufficient for practical use. The new stabilizer was introduced into a Phillips-type high-density polyethylene, and its stabilizing efficiency was determined by multiple extrusions. Commercial phosphite and phosphonite stabilizers were used as references. The additive packages contained a primary antioxidant and a phosphorus compound, both added at 1000 ppm. The chemical structure of the polymer, viscosity, color, and residual stability were determined after each extrusion. The comparison of the stabilizing efficiency of the three secondary antioxidants showed that the phosphine stabilizer is at least as efficient as the phosphorous secondary stabilizers available in the market. The new stabilizer proved to be the most efficient in melt stabilization and in preventing discoloration; the residual stability of the polymer was similar in the presence of all three secondary antioxidants. This feasibility study proved that the new compound could be used as a potential stabilizer in practice.
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