Effect of polyethylenimine on properties of emulsion styrene butadiene rubber/butadiene rubber blends

The purpose of this study was to evaluate the effect of polyethylenimine (PEI) on the properties of emulsion styrene butadiene rubber (ESBR)/butadiene rubber (BR) blends. PEI with molecular weight (M w ) of 800, 2,000, 25,000, and 270,000 g/mol with various ratios was successfully incorporated into ESBR/BR blends via rubber compounding method. Study showed almost 100% decrease in scorch time, ts 2 in lower M w PEI (800 and 2000 g/mol), compared to higher M w PEI (25,000 and 270,000 g/mol) in ESBR/BR blends. PEI incorporated ESBR/BR blends showed an overall improvement in terms of tensile strength. Lower M w PEI induced better tensile strength with an optimum value at 1.22 MPa, while higher M w PEI induced better tear strength and self-healing ability. Incorporation of 5 phr PEI 270,000 g/mol in the blend successfully achieved the optimum self-healing efficiency of 71.5% at 160°C for 1 h. Phase separation occurred between higher M w viscous PEI with rubber matrix at crack region to promote thermal self-healing. PEI molecules were found to be accumulated and assembled on the interface of the rubber chain from scanning electron microscopy (SEM) images. It was suggested weak physical bond interaction such as Van der Waals holding both rubber chains and PEI together, without any changes in the rubber chain backbone.