Microwave Devulcanized Crumb Rubbers in Polypropylene Based Thermoplastic Dynamic Vulcanizates

Effect of Ethylene-1-Butene as a Compatibilizer for the Optimization of Wood Flour and Ground Tyre Rubber in Polypropylene Composites

The use of waste materials to make eco-friendly wood-polymer composites has been explored by many researchers for academic and industrial purposes due to the low cost, biodegradability, and availability of waste wood flour. Polypropylene (PP)/ground tyre rubber (GTR)/wood flour (WF) composites were prepared using an internal batch mixer at a temperature of 165 °C for 8 min, and the samples were injection-moulded at 190 °C with a pressure of 6 MPa. The design of the experimental approach was used to determine and optimize the proportions of each component in the composites. The morphology of the untreated composites showed more voids and the agglomeration of fillers, namely WF and GTR, in the PP matrix. Fewer voids, as well as improved distribution, were observed in the compatibilized composites. The incorporation of ethylene-1-butene as a compatibilizer improved the thermal stability and elongation at the break of the composites. The addition of WF increased the elongation at break and decreased the tensile strength of the composites. Overall, the use of statistically designed experiments has aided in attaining the optimum formulations of the wood flour–polymer composites.

Thermomechanical Devulcanisation of Ethylene Propylene Diene Monomer (EPDM) Rubber and Its Subsequent Reintegration into Virgin Rubber

Rubber waste remains a challenge for material science because its covalently cross-linked structure hinders the establishment of the circular economy of rubber. Devulcanisation may provide a solution, as it converts rubber vulcanisates back into their original, uncured state. Devulcanised rubber may be revulcanised or incorporated into virgin rubber, thus waste is utilized and the use of primary resources is reduced at the same time. In this paper, we treated sulphur-cured EPDM (ethylene propylene diene monomer) rubber on a two-roll mill at various temperatures and frictions. We determined the effectiveness of devulcanisation via Horikx’s analysis, which suggested that low devulcanisation temperatures would result in a 50% decrease in cross-link density with minimal polymer degradation. The devulcanisate was recycled via two methods: (a) revulcanisation with extra curing agents, and (b) mixing it with various amounts of the original rubber mixture, preparing rubber samples with 25, 50, 75, and 100 wt% recycled content. Tensile tests revealed that the samples’ elastic properties were severely compromised at 75 and 100 wt% devulcanisate contents. However, tensile strength decreased only by 15% and 20% for revulcanisates containing 25% and 50% recycled rubber, respectively.

Devulcanization of ground tire rubber: microwave and thermomechanical approaches

We devulcanized ground tire rubber (GTR) in a laboratory microwave oven and an internal mixer, measured the soluble content and the cross-link density of the samples, and then used Horikx's analysis. The results showed that microwave treatment caused severe degradation of the polymer chains, while in the case of thermomechanical devulcanization, the selective scission of covalent cross-links is more common. Four devulcanized ground tire rubber (dGTR) samples were chosen for further study and three groups of samples were produced: dGTR samples containing vulcanizing agents and different amounts of paraffin oil (dGTR-based mixtures), natural rubber-based rubber mixtures with different dGTR contents and reference rubber mixtures with dGTR-based mixtures (increased vulcanizing agent contents). Cure characteristics showed a plasticizer-like effect of dGTR. Tensile and tear strength decreased drastically with increasing dGTR content; however, elongation at break values did not follow such a trend. Mechanical properties improved with increased vulcanizing agent contents. The examined properties of the samples improved even further with the use of thermomechanically devulcanized samples. Horikx's analysis showed that this is attributable to moderate polymer chain scission.

The Influence of UV-Accelerated Aging Process on Industrial Waste Containing EPDM

One of the most efficient ways to recycle elastomeric residues from industrial processes is to incorporate them into compositions. The study of these new compositions is interesting in terms of reducing cost, the consumption of raw materials, and the generation of new waste, working towards sustainable development. Thus, this research aimed to produce and characterize elastomeric blends containing one phase comprised of ethylene–propylene–diene monomer rubber (EPDM) industrial waste aged by the action of ultraviolet radiation (UV) in a UV chamber, and the other comprised of raw EPDM, containing different concentrations of residue. Therefore, the mechanical properties and the vulcanization characteristics of the blends containing different concentrations of EPDM residue—aged and un-aged—were analyzed and compared to the properties of a standard formulation (Control). The results showed that the aging of the waste for a period of 156 h did not trigger a severe degradation process. Additionally, its reuse into new compositions promoted improvements of the studied mechanical properties without compromising the vulcanization characteristics due to the higher molecular stiffness of the samples.