Surfactant Chain Length and Tensile Properties of Calcium Carbonate‐Polyethylene Composites

Abstract

AbstractMicron‐sized CaCO3 particles free of milling additives were coated with a monolayer of aliphatic carboxylic acids of different chain length (C2, C4, C5, C10, and C18). CaCO3 was compounded with LDPE at different loading, and the tensile properties of the composites were measured and correlated to the length of the alkyl chains tethered to the particles' surface. SEM indicated that the particles are well dispersed (no agglomerates). The inclusions show little influence on the polymer crystallization, and the filler surface treatment leads to a slight decrease in polymer crystallinity that grows with increasing chain length of the fatty acid. The tensile modulus, yield stress, and maximum stress increase with increasing filler volume fraction ϕ, and the dependence is a function of the length of the alkyl chains tethered to the CaCO3 surface. It seems that the interphase thickness and properties depend on the alkyl chain length and strongly influence the modulus and stresses measured. With increasing chain length in the coated organic layer, the interfacial adhesion between the inclusions and the polymer matrix decreases, and the fibril formation increases. The tensile properties are the result of a superimposition of all these effects. The yield and ultimate strains are dominated by the interfacial slippage (increases with growing alkyl chain length) that leads to debonding at high deformations. Surface treatment of CaCO3 with valeric acid leads to the maximum possible tensile modulus, yield stress, and tensile strength combined with a relatively small loss in yield and ultimate strain.magnified image