Abstract
Halloysite Nanotubes (HNT) are chemically similar to clay, which makes them incompatible with non-polar rubbers such as natural rubber (NR). Modification of NR into a polar rubber is of interest. In this work, Epoxidized Natural Rubber (ENR) was prepared in order to obtain a composite that could assure filler–matrix compatibility. However, the performance of this composite was still not satisfactory, so an alternative to the basic HNT filler was pursued. The surface area of HNT was further increased by etching with acid; the specific surface increased with treatment time. The FTIR spectra confirmed selective etching on the Al–OH surface of HNT with reduction in peak intensity in the regions 3750–3600 cm−1 and 825–725 cm−1, indicating decrease in Al–OH structures. The use of acid-treated HNT improved modulus, tensile strength, and tear strength of the filled composites. This was attributed to the filler–matrix interactions of acid-treated HNT with ENR. Further evidence was found from the Payne effect being reduced to 44.2% through acid treatment of the filler. As for the strain-induced crystallization (SIC) in the composites, the stress–strain curves correlated well with the degree of crystallinity observed from synchrotron wide-angle X-ray scattering.
Highlights
Filler has become a major ingredient in compounding rubber
The results explored in this study give an improved scientific understanding of the role of acid-treated Halloysite nanotubes (HNT) in affecting the overall properties of Epoxidized Natural Rubber (ENR)/HNT composites, and will be useful for the manufacturing of rubber products based on ENR/HNT composites
The reductions in peak intensity in the regions 3750–3600 cm−1 and 825–725 cm−1 were attributed to decreased numbers of Al–OH structures, while the increased absorption intensity in the region 1250–1100 cm−1 was associated with siliconrich nanoparticles [27] formed after the destruction of HNT structures by acid treatment
Summary
Filler has become a major ingredient in compounding rubber. The main reasons for adding filler to rubber are to improve mechanical properties or thermal stability, and to lower the manufacturing costs [1]. NR was modified into an Epoxidized Natural Rubber (ENR) and was further used as a matrix to assure HNT–rubber compatibility This solution is well reported in terms of performance [8]. The aim of this study was to increase the surface area of HNT by using sulfuric acid and further incorporate it into an ENR matrix to test for improvement in the overall properties of the composites. The last method is considered interesting and not many reports have yet addressed it It can only be correlated for certain types of rubber, such as NR [11,12,13], because NR has very long polymer chains that crystallize under stretching [14]. The results explored in this study give an improved scientific understanding of the role of acid-treated HNT in affecting the overall properties of ENR/HNT composites, and will be useful for the manufacturing of rubber products based on ENR/HNT composites
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