Relationship between Filler Loading and Morphology of the Interphase in Polyethylene-Chalk Composites

Mineral fillers such as kaolin or chalk have been commonly used in the polymer industry as additives to improve polymer mechanical properties and, at the same time, reduce the cost of raw materials. The problem is that the hydrophilic surface of the filler hinders its introduction into the polymer matrix. The paper reports a study of low density polyethylene (LDPE) composites with a natural chalk content of up to 40% wt. The morphology of the filler molecules and the microstructure of the composites were determined by scanning electron microscopy (SEM). The distribution of the filler molecules was estimated by light scattering. The mean diameter of the filler particles was 926.3 nm and their polydispersity was 0.101. The thermal and mechanical properties of the composites were characterised by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The enthalpy of melting, ΔH ^* , decreased by about 8% when the amount of filler was 10 wt% in the sample (PE ₁₀ ). However, no difference was recorded between the ΔH _m value of the sample with 40 wt% content of filler (PE ₄₀ ), and the value for PE ₁₀ . In LDPE composites with 40% of chalk, the free space in the interphase is reduced, slightly increasing the chain mobility in comparison with that in the composite with 10% of chalk.