Natural rubber-based solution adhesives: effect of carbon black on the adhesive properties

In the retreading industry, generally two types of adhesives say a solid adhesive (bonding gum) and a solution adhesive (black vulcanising cement) are mainly used. In this study, the performance of natural rubber (NR)-based solution adhesive for the rubber to rubber bonding was examined. The effect of different grades of carbon black (CB) say ISAF (N220), HAF (N330) and GPF (N660) as a reinforcing filler in adhesive was evaluated. The loading used was different for the three grades of CB to achieve the required level of hardness for the adhesive. A blend of natural rubber and butadiene rubber (BR) was used as the adherend substrate. The vulcanisation characteristics, mechanical properties, swelling measurements and adhesion strength of different CB-filled NR-based solution adhesive were studied. All the three grades of CB-filled NR-based adhesives showed an increase in the rheometer torque and crosslink density compared to unfilled NR-based adhesive. The incorporation of CB improved the mechanical properties, adhesion strength and thermal stability of NR-based adhesives. CB-filled NR adhesives showed lower solvent uptake compared to unfilled ones. The measured properties of all the three grades of CB-filled NR-based solution adhesives were found to be comparable at the fixed hardness level.