The Impact of Ground Tire Rubber Oxidation with H2O2 and KMnO4 on the Structure and Performance of Flexible Polyurethane/Ground Tire Rubber Composite Foams

Abstract

The use of waste tires is a very critical issue, considering their environmental and economic implications. One of the simplest and the least harmful methods is conversion of tires into ground tire rubber (GTR), which can be introduced into different polymer matrices as a filler. However, these applications often require proper modifications to provide compatibility with the polymer matrix. In this study, we examined the impact of GTR oxidation with hydrogen peroxide and potassium permanganate on the processing and properties of flexible polyurethane/GTR composite foams. Applied treatments caused oxidation and introduction of hydroxyl groups onto the surface of rubber particles, expressed by the broad range of their hydroxyl numbers. It resulted in noticeable differences in the processing of the polyurethane system and affected the structure of flexible composite foams. Treatment with H2O2 resulted in a 31% rise of apparent density, while the catalytic activity of potassium ions enhanced foaming of system decreased density by 25% and increased the open cell content. Better mechanical performance was noted for H2O2 modifications (even by 100% higher normalized compressive strength), because of the voids in cell walls and incompletely developed structure during polymerization, accelerated by KMnO4 treatment. This paper shows that modification of ground tire rubber is a very promising approach, and when properly performed may be applied to engineer the structure and performance of polyurethane composite foams.

Structural Changes and Their Implications in Foamed Flexible Polyurethane Composites Filled with Rapeseed Oil-Treated Ground Tire Rubber

“…The temperature was measured until reaching a plateau (variations lower than 0.5 • C for 10 s). It can be seen that for the unfilled polyurethane foam, the temperature reached almost 90 • C. The introduction of waste rubber resulted in the decrease of the maximum temperature, which confirms our previous results [27]. Moreover, for the unfilled foam, faster heat build-up was observed, indicating the system's higher reactivity.…”

“…In our previous work [26], we noted the increase in mechanical strength and an improvement in the material's thermal stability with the addition of GTR. In another paper [27], we reported that the partial oxidation of rubber surface might enhance the potential interactions with polyurethane matrix due to the increase in the GTR hydroxyl value measured by the titration-based method [28]. Depending on the level of modification, the mechanical properties of the resulting foams may be noticeably improved.…”

Ground Tire Rubber Filled Flexible Polyurethane Foam—Effect of Waste Rubber Treatment on Composite Performance

“…Nevertheless, our previous results [ 19 ] indicate that after modifications of GTR, the formulations of PU foams should be modified to adjust the proper ratio between isocyanate and hydroxyl groups in the system. Such a phenomenon was confirmed by our other work [ 20 ] dealing with the application of GTR oxidized with KMnO 4 and H 2 O 2 solutions. An excessive oxidation of GTR surface with potassium permanganate caused the disturbance of the NCO:OH ratio, which resulted in the weakening of polyurethane matrix and significant reduction in compressive strength.…”

“…Literature data indicate that it may beneficially affect the compressive strength and the damping properties considering the mechanical and acoustic vibrations [ 19 ]. Such effects play a vital role in the applications of PU foams in packaging, automotive, and construction industries or as soundproofing materials [ 20 ]. Gayathri et al [ 21 ] observed a substantial enhancement of tensile and compressive performance of foams with the addition of waste rubber.…”

Special Issue: Structure, Properties and Applications of Polymeric Foams

“…Alongside for the application of renewable raw materials, the use of recycled ones should be emphasized considering the current pro-ecological trends, as in the work of Hejna et al [10] dealing with structure and performance of flexible foamed polyurethane/ground tire rubber composites.…”