Rheology‐cell structure correlation for foam processing of polypropylene‐titanium dioxide and polypropylene‐graphene nanocomposites

Abstract This work focuses on understanding the effects of nanoparticle fillers (titanium dioxide (TiO 2 ) and graphene) on foam processing of polypropylene(PP) and makes an attempt to establish a rheology‐cell size correlation for PP‐TiO 2 and PP‐graphene nanocomposite foams. The establishment of such a correlation can help develop a precise model to predict optimum nanoparticle concentration in a polymer matrix to produce stable microcellular foams. The effects of adding TiO 2 and graphene nanoparticles on nanocomposite properties are studied through their thermal, mechanical, and rheological analysis. The nanocomposite/PP foams are prepared at various conditions, and their morphology and density are studied to obtain an understanding of the cell structure as a function of added nanoparticles. The optimized size/structure has also been correlated in terms of rheological and mechanical properties of the prepared nanocomposites to study the effects of variation in rheological properties on the resultant cell structure of prepared foams. Through the current work it was found that particle type/size plays the dominant factor in determining the cell size of resultant foam, although when comparing foams with varying filler concentration, it was established that a decrease in viscosity and storage modulus would create more cell stability by decreasing the applied stress and would lead to smaller cells. Highlights Rheological property variation can directly affect the polymer foamability Foaming of polymers can be closely simulated using the Maxwell model for polymers Reduction in viscosity leads to smaller and stable cells during foaming Stress relaxation rate determines the cell stabilization during expansion Agglomerate size plays a crucial role in determining cell size