Microwave Devulcanization of Ground Tire Rubber and Its Improved Utilization in Natural Rubber Compounds

Abstract

We devulcanized ground tire rubber (GTR) with microwaves at different temperatures (140−200 °C) and heating rates (2−18 °C/min). We measured the soluble content and the cross-link density of the samples, and then evaluated them by Horikx's analysis and determined the specific microwave energy during devulcanization and the selectivity parameter of the treatments. We also introduced the K•D number that can be calculated as the product of the selectivity parameter (K) and the relative decrease in the cross-link density (D). The results showed that GTR devulcanized at lower temperatures, selectivity was very high, and the degree of devulcanization was adequate. At higher temperatures (180−200 °C), the degree of devulcanization reached 85%, but the selectivity parameter was low, which indicates severe degradation at this temperature range. At lower temperatures (140−160 °C) and decreasing heating rate, i.e., increasing residence time, the degree of devulcanization showed an increase, but at higher temperatures, the heating rate had no significant effect on the degree of devulcanization. We introduced different devulcanized GTRs (dGTRs) to natural rubber-based mixtures and produced samples with two different mixing methods: conventional mixing and so-called two-step mixing. In the latter one, in the first mixing step, we added vulcanizing agents to the dGTR, and in the second mixing step, we added this mixture to the reference mixture. Two-step mixing helped recover mechanical properties, especially tear strength. Scanning electron microscopy− energy-dispersive spectroscopy and atomic force microscopy showed that microwave devulcanization and the vulcanizing agents mixed with dGTR acted in the cross-section of dGTR.

Sustainable 3D printing with recycled tire rubber-based filaments: an investigation of process parameters and mechanical behaviour

“…To summarise, the use of video gauge is more reliable to estimate the Poisson’s ratio of 3D-printed TPU-WTR material (and in general for 3D-printed soft polymers) compared to strain gauges where the presence of cyanoacrylate adhesive in micro-voids negatively affects the accuracy of the analysis. In addition, the obtained Poisson’s ratio from the video gauge of 0.482 ± 0.025 is consistent with the Poisson’s ratio of compound rubber tire, which is 0.49 (Simon and Bárány, 2023). These preliminary findings could be valuable for expanding research on TPU-WTR performance, particularly in predicting its behaviour in specific fields of interest through computational studies such as finite element analysis.…”

Improving the mechanical properties of vulcanizates containing ground tire rubber: Recipe optimization with the Taguchi method

“…To do this, we applied an L8(2 7 ) orthogonal experimental design (Table 4). This means that we examined the effects of 7 different components in two different quantities, totaling 8 mixing scenarios.…”

“…Nowadays, waste tires are most commonly shredded into ground tire rubber (GTR), which is then used in a new matrix. The most common practice is to mix them into fresh rubber 1,7–10 . However, in most cases, there is poor compatibility between the matrix and the GTR in these new mixtures, resulting in materials that are not suitable for their intended applications 5,11,12 .…”

“…mon practice is to mix them into fresh rubber. 1,[7][8][9][10] However, in most cases, there is poor compatibility between the matrix and the GTR in these new mixtures, resulting in materials that are not suitable for their intended applications. 5,11,12 To address this issue, researchers have developed several compatibility-improving procedures in the past, but these can often be costly (devulcanization) 13 and have a significant environmental impact (chemical treatments).…”

High performance, self-adhesive and recyclable dynamic crosslinked waste rubber particle blends toward upcycling of waste rubber

“…8 To overcome this problem, a lot of efforts have been made by some researchers to enhance the interface interaction with the matrix by surface modification of WRP. 7,[9][10][11][12][13] Unfortunately, the above-mentioned problem of WRP makes it difficult to regain the mechanical performance of virgin rubber, let alone improve it. Another strategy for waste rubber recycling is to break the crosslinking network by devulcanization technologies such as the thermal method, the mechanical method, microwave irradiation and chemical reactions.…”