NOVEL METHOD OF BREAKING DOWN RUBBER MOLECULES USING PEPTIZER AND THE PROPERTIES OF RESULTANT NATURAL RUBBER SOLVENT-BASED ADHESIVE

Abstract

The huge cost of energy associated with the breaking down of high molecular weight rubber during adhesive production has placed a demand for alternative processing technology. In this study, the use of benzoyl peroxide as a peptizer to lower the molecular weight of natural rubber has been reported. The properties of natural rubber-based solvent adhesive produced by mechanical mastication and peptizer were also compared. Natural rubber (NR) was masticated in a two-roll mill at 80oC for 30 mins and was processed into adhesive using xylene as solvent. Similarly, adhesives were formulated by chemical break down of the heavy natural rubber molecules using benzoyl peroxide as peptizer. The peptizer loading was varied from 0.2 – 1.0 parts per hundred rubber (phr) of rubber at 100oC in a water bath while other compounding additives were kept constants for all samples under study. The adhesives produced were subjected to the following test: viscosity, lap shear test, T-peel test and drying time test. Other properties studied are weathering resistance, heat resistance and effect of moisture on the adhesives bond on different substrates. The result shows that the viscosity of the adhesives increases with increasing peptizer loading and the masticated sample has a viscosity slightly lower than that of 0.8phr and 1.0phr peptizer loading. Furthermore, T-peel test shows that 0.4 phr peptizer loading has a better average T-peel strength for the bonds while the masticated sample had the least average T-peel strength when compared with all samples. The sample with 1.0phr peptizer loading had the least decrease in shear strength while the 0.2 peptizer loading had the maximum decrease in shear strength. Finally, the FT-IR spectra shows similarities in spectra but with difference in the intensity of the peaks, indicating the ability of the benzoyl peroxide to effectively oxidize the natural rubber as compared with the mechanical masticated sample. The peak of 1080 cm-1 in the peptized sample indicates a major difference with the spectra of mechanical masticated sample. Generally, the benzoyl peroxide effectively lowered the molecular weight of the natural rubber which is evident in the viscosity, reduced process time and ease of the adhesive formulation.