Quantifying effect of inorganic filler geometry on the structural, rheological and viscoelastic properties of polypropylene-based thermoplastic elastomers

In this study, polypropylene-based thermoplastic elastomer compounds (TPEs) were formulated by using isotactic polypropylene (i-PP), poly(styrene-b-ethylene/butylene-b-styrene) (SEBS), paraffinic oil and three different inorganic fillers; calcite, organo-clay, and halloysite. Structural, thermal, and rheological properties of TPEs were characterized by SEM, XRD, DSC analysis and rheological measurements in melt state. Effect of geometric features of fillers (as 1D, 2D, and 3D structure) on viscoelastic properties of TPEs was quantified by applying different test procedures and modeling approaches such as Williamson model and discrete retardation spectrum, and utilization of cross-over frequency. It was found that reinforcing effect of fillers decreased in the order of org-clay>halloysite>calcite in the case of same loading amount (5 wt%) into TPE compositions. It was found that 2D structure of org-clay layers led to a significant increase in melt viscosity and melt elasticity, creep strength, and relaxation time but reduced the relaxation rate of TPEs, compared to halloysite and calcite used in a particular amount.