Epoxidised natural rubber as adhesion promoter in natural rubber based compounds
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ORIGINAL PAPER
Epoxidised natural rubber as adhesion promoter in natural rubber based compounds Murat Öter1,2 · Bağdagül Karaağaç1,3 Received: 2 April 2020 / Accepted: 24 September 2020 © The Malaysian Rubber Board 2020
Abstract Natural rubber (NR) is the most preferred raw material for both tyre and non-tyre applications, which require good adhesion performance. It has a naturally sticky character to provide green tack. However, it has limitations to improve adhesion further due to its relatively low reactivity. In this study, epoxidised natural rubber (ENR) has been evaluated as an adhesion promoter for NR based model tyre compounds. ENR based adhesive compounds were prepared by blending NR with ENR in various ratios. Rheological, physical, and mechanical properties of NR/ENR compounds were studied. Sufficient cure rate and cure extent were achieved for elevated curing temperatures. The adhesion performance was measured with the T-peel adhesion test. In addition, thermodynamic work of adhesion (TWA) was calculated by using the surface free energy components of the compounds. The correlation between adhesion force and TWA was evaluated together with vulcanisation kinetic parameters in order to understand the adhesion mechanism. ENR incorporation was found to improve adhesion between selected tyre compounds, remarkably. Keywords Adhesion · Epoxidised natural rubber (ENR) · Thermodynamic work of adhesion · Vulcanisation kinetics
Introduction Natural rubber (NR) exhibits satisfactory mechanical and chemical properties such as elasticity, stickiness and resilience, which are emerging requirements in tyre compounds and the other rubber-based materials. However, in most of NR applications, low weathering stability, low oil resistance, and limited reactivity need to be improved. The chemical modification of NR along with double bonds is an effective strategy to obtain required properties [1]. Epoxidised natural rubber (ENR) is produced by epoxidation of NR in latex stage and introducing epoxy groups strongly affects the adhesion performance of NR as well as overall physical properties. Epoxidation is performed employing the hydrogen peroxide/formic acid via in-situ * Bağdagül Karaağaç [email protected]; [email protected] 1
Department of Chemical Engineering, Kocaeli University, Umuttepe Campus, 41380 Kocaeli, Turkey
2
Özka Tyre, Mahmut Paşa Mah. Kanalyolu Cad. No:178 Kullar, 41140 Kocaeli, Turkey
3
Department of Polymer Science and Technology, Kocaeli University, Umuttepe Campus, 41380 Kocaeli, Turkey
route with carefully controlled reaction conditions to avoid secondary ring-opening reactions. NR latex is first stabilised against acid coagulation by the addition of a non-ionic surfactant, and then the reaction is carried out at 60–70 °C. The epoxidised latex is neutralised prior to heat coagulation and thoroughly washed before drying in hot air. During epoxidation, some C=C double bonds on the NR main chain are converted to the polar epoxy groups; free volume between the rubber chain
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