The adhesion properties of natural rubber pressure-sensitive adhesives using palm kernel oil-based alkyd resins as a tackifier

Alkyd resins, synthesized from palm kernel oil (PKO), were investigated as the tackifiers in the formulation of natural rubber (NR) based pressure-sensitive adhesives (PSA). PKO alkyd resins were prepared via a step-wise polymerization process where the esterification was completed with the presence of xylene (solvent cook). Two alkyds, namely Alk-26 and Alk-41, with respective short and medium oil lengths of 26 and 41, were synthesized in xylene. NR was isolated from latex, dried, milled and dissolved in xylene. The alkyd solutions were then blended with NR solution in various ratios. The blend solutions were coated onto strips of corona-treated polypropylene film and the solvent removed by evaporation. The peel and shear strengths of the PSA tapes were measured. Circular samples of the blends were cast onto release paper and tested for viscoelastic properties using dynamic mechanical analysis (DMA). It was found that Alk-26 increased the shear strength of NR while Alk-41 improved the peel strength of NR significantly. These adhesion properties were comparable to some of the commercial PSA tapes available on the market. DMA study revealed that both Alk-26 and Alk-41 were immiscible with NR and there was neither cross-linking nor entanglement present in the blends.