Cooperative Effects of Epoxide Functional Groups on Natural Rubber and Silane Coupling Agents on Reinforcing Efficiency of Silica

Abstract

Polar functionality attached onto natural rubber has a significant impact on the reinforcing efficiency of silica. Parallel studies involving various levels of epoxidation on natural rubber (ENR) in the absence of bis-(triethoxysilylpropyl) tetrasulfide (TESPT) coupling agent, as well as a combination of ENRs with different loadings of TESPT, provide a better understanding of the various factors that influence the properties of silica-filled ENR compounds. Based on the overall properties, the best possible combination to optimize processability, to reduce filler–filler interaction, and improve vulcanization rate as well as vulcanizate properties, is to use ENR with an epoxide content in the range of 20–30 mol%, together with a small portion of TESPT, that is, 2–4 wt% relative to the silica content. This leads to a reduction of approximately 60–80% of TESPT when compared with the conventional NR compounds, where the optimal loading of TESPT was 9.0 wt% relative to the silica content.

The behavior of natural rubber–epoxidized natural rubber–silica composites based on wet masterbatch technique

“…In the DE compounds, the addition of ENR decreases the fillerfiller interaction dramatically; 10 phr ENR has the optimal effect, and more ENR content has an adverse effect. That is because large amounts of epoxide groups can create additional interactions or linkages between themselves, as previously reported by Kaewsakul et al 6 But, in WE composites, the Payne effect slightly increases with the addition of ENR, and this may be due to the additional interactions or linkages between ENR molecules. However, the Payne effects in WE compounds dramatically decrease compared to that in DE compounds.…”

“…absence of a silane coupling agent, [6][7][8][9][10][11][12] as shown in Scheme 1. 10,12 Although its application has been limited by its high cost and poor aging properties, [13][14][15] there are still reports of ENR being employed as a compatibilizer for silica-filled rubber.…”

“…5 Moreover, there is also a disadvantage in using Si-69: a high processing temperature is needed to obtain the chemical reactions, which consume more energy. 6 Epoxidized NR (ENR) is a kind of non-petroleum-based elastomer from NR modification. Its special molecular structure leads to both good compatibility with NR and a reactive possibility with silica.…”

Biologically sustainable rubber resin and rubber‐filler promoter: a precursor study

“…This behavior is clearly evident as the HDS was dispersed more consistently and more certainly bonding through polar groups on the rubber network, eventually tending to create a chemical linkage between the HDS surface and the rubbery macromolecules. This reaction condenses the hydrophilic character of the HDS and increases its compatibility with the rubbery macromolecules . This bio‐resin offers a wide array of property improvements at very low concentration loadings, owing to the high degree of dispersion of HDS as compared to the silane coupling agent and process oil loaded compound.…”

“…In ENR, a high degree of reinforcement is achieved with silica filler without the requirement of silane; ENR can be activated by the hydroxyl groups on the silica . Kaewsakul et al stated the role of epoxide functionality on silica reinforcement and reduction or possible replacement of conventional silane coupling agent . On the other hand, ENR is the most favored rubber for the construction of green tire tread due to the low rolling resistance combined with high traction properties .…”