Influence of natural exposure on castor oil based polyurethane reinforced with waste tire rubber.

Waste tire rubber (WTR) has been extensively generated worldwide due to mobility needs growth. About 1.5 billion units are generated annually, constantly discharged in the environment with a few reusability alternatives. Therefore, rubber recovery methods and these residues' transformation into a cost-effective product have gained attention. Aiming to minimize the usage of fossil resources and contributes to a circular economy, it was analyzed the usage of WTR particles (5-20% by weight) in castor oil-based polyurethane foams under natural aging to promote a holistic view of all factors involved in the performance of the foams. Morphological, thermal, chemical, and mechanical properties were determined before and after exposure to open air to observe the impact of photo-oxidation and hydrolysis. The increase in viscosity of pre-polymer during the rubber loading produced greater density foams with smaller cell sizes than neat PU, in which the average cell size increased after the weathering. The rubber contributes to enhancing the compressive behavior in the non-exposed samples. After exposure, the results suggest that degradation may act to increase the crosslinking density even with the presented structural changes such as yellowing and voids. Regarding thermal stability, the rubber promotes a slight decay in the ability to resist a heat flow before and after weathering. Still, the char yield increased, showing a possibility of better fire retardancy for composites. FTIR and UV-vis showed chemical structure changes as Photo-Fries network rearrangement, Norrish I random chain scission, and Norrish II β-scission. Besides, UV-vis revealed the maximum absorbance in the UVB region, showing that the PU reinforced by WTR can be a promising material for civil coatings.