Interfacial interactions and mechanical properties of mineral filled polymer composites: wollastonite in PMMA polymer matrix

Abstract

The nature of stearic acid and polymethylmethacrylate (PMMA) adsorption onto wollastonite has been studied from basic, neutral and acidic organic solvents by infrared (IR) spectroscopy. The roles of acid-base interactions on adsorption and wollastonite dispersion in polymer matrix have been discussed with the determined mechanical properties of surface-treated (stearic acid) and untreated wollastonite-filled PMMA polymer composites. Maximum adsorption of either stearic acid or PMMA occurs from a nonpolar solvent, and the adsorption is found to decrease with increasing acidity or basicity of the solvents. The adsorption corresponds to two geometrical layers either from nonpolar (carbon tetrachloride) or from slightly basic (benzene) and acidic (methylene dichloride) solvents. Increased acidity (chloroform) or basicity (tetrahydrofuran) of solvents led to a monolayer or a fraction of the monolayer coverage. The primary adsorption of stearic acid is thought to be the formation of hydrogen bonds between surface hydroxyl groups and carboxylic acid groups. The tensile and impact strength properties of the composites that are filled with stearic acid-treated wollastonite are improved when compared to the untreated filled composite. The results suggest a stronger interfacial bonding between stearic acid and filler than that of polymer to the filler. Thus, the application of stearic acid for surface modification of acidic fillers such as wollastonite is emphasized.