A Self-Healing System Based on Ester Crosslinks for Carbon Black-Filled Rubber Compounds

Bashir Algaily,Wisut Kaewsakul,Siti Salina Sarkawi,Ekwipoo Kalkornsurapranee

doi:10.3390/jcs5030070

Abstract

Carbon black-reinforced rubber compounds based on the blends of natural rubber (NR) and butadiene rubber (BR) for tire sidewall applications were formulated to investigate the self-healing efficacy of a modifier called EMZ. This modifier is based on epoxidized natural rubber (ENR) modified with hydrolyzed maleic anhydride (HMA) as the ester crosslinking agent plus zinc acetate dihydrate (ZAD) as the transesterification catalyst. The influence of EMZ modifier content in sidewall compounds on processing characteristics, reinforcement, mechanical and fatigue properties, as well as property retentions, was investigated. Increasing the content of EMZ, the dump temperatures and Mooney viscosities of the compounds slightly increase, attributed to the presence of extra polymer networks and filler–rubber interactions. The bound rubber content and Payne effect show a good correction that essentially supports that the EMZ modifier gives enhanced filler–rubber interaction and reduced filler–filler interaction, reflecting the improved homogeneity of the composites. This is the key contribution to a better flex cracking resistance and a high fatigue-to-failure resistance when utilizing the EMZ modifier. To validate the property retentions, molecular damages were introduced to vulcanizates using a tensile stress–strain cyclic test following the Mullins effect concept. The property retentions are significantly enhanced with increasing EMZ content because the EMZ self-healing modifier provides reversible or dynamic ester linkages that potentially enable a bond-interchange mechanism of the crosslinks, leading to the intermolecular reparation of the rubber network.

Highlights

A sidewall is one of the crucial components in a tire, which protects the tire body plies from flex fatigue under a certain dynamic mechanical load of a running vehicle plus a driver, passengers, and their belongings
The rubber composites investigated in the present study were based on blends of natural rubber (NR) and butadiene rubber (BR), while the EMZ self-healing modifier at different amounts was added to the compounds via extra addition or blending
Increasing the content of EMZ, the dump temperatures and Mooney viscosities of the compounds slightly increased. This is because the extra polymer networks and filler–rubber interaction were generated due to the presence of the modifier, which was confirmed by the apparent crosslink densities and bound rubber contents, respectively

Summary

Introduction

A sidewall is one of the crucial components in a tire, which protects the tire body plies from flex fatigue under a certain dynamic mechanical load of a running vehicle plus a driver, passengers, and their belongings. Thereafter, the cracks propagate to a macroscopic level, leading to the failure of the sidewalls [1,2]. As the damages start from a molecular scale, the repeated dynamic operations of rubbers result in the progressive damages of rubber molecular networks, that grow to a larger defect scale, called macroscopic damages [3]. These initiated damages are cumulative under service circumstances and will not disappear at later stages even when an operation of rubbers, e.g., a running vehicle, stops. Current regulations demand tires to possess a longer lifetime and reduced fuel consumption without sacrificing car safety [5]

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Conclusion