Chemical surface etching methods for ground tire rubber as sustainable approach for environmentally-friendly composites development– a review

Ground tire rubber (GTR) has been used as a sustainable low-cost modifier in various composites. However, due to the hydrophobic nature of GTR, it is in compatible with most matrices and results in deterioration in both mechanical and physical properties of composites. This necessitates pre-modification of the powdered rubber to improve the interfacial bonding at the rubber-matric interface. The most common GTR modification research relies on surface etching via use of various techniques. The current review aims to give a detailed overview of the surface etching chemical modification methods for GTR for incorporation into various matrices such as concrete, bitumen and polymers. The review will serve as a guide for engineers, chemists and manufactures with interest of including GTR in any type of composite for achieving compatibility with the main matrix. The surface chemical etching treatment methods such as acid etching, hydroxylation, oxidation, and radiation methods are discussed in this work. The characterization methods to confirm the functional groups on the modified GTR and the effect of the treatment on the resultant GTR composites are also highlighted. Finally, this review highlights the advantages and limitations of the chemical surface etching processes for GTR.