Gas barrier properties of natural rubber/kaolin composites prepared by melt blending

A series of highly filled natural rubber (NR) composites based on silane modified kaolin (SMK), precipitated silica (PS) and their mixed-compound additions (SMK + PS) were prepared by melt blending. The transmission electron microscopy (TEM) was employed to characterize the NR composites. The kaolinite particles were finely dispersed into the natural rubber matrix and arranged in parallel orientation. Compared to the pure NR, these highly filled NR/SMK composites exhibited outstanding mechanical properties, excellent gas barrier properties and much higher thermal stability. The gas barrier properties of NR composites with SMK and PS were much higher than those of NR/PS composites and better than those of NR/SMK. The nitrogen permeability of NR/SMK composites was decreased by 20–40% after filling with kaolin. The significant improvements in the mechanical properties, thermal stability and gas barrier properties may be attributed to the parallel kaolinite particles which restricted the free movement of rubber chains and retarded the diffusion of the gas molecules. Thus, the highly filled NR/SMK composites may be used to improve the air-tightness of rubber products.

Research Highlights
► The kaolinite particles were finely dispersed into NR matrix in parallel.
► The parallel kaolinite particles retarded the diffusion of the gas and the motion of rubber chains.
► The restriction improved the thermal stability and gas barrier properties of NR composites.
► NR/SMK composites can be used to improve the air-tightness of rubber products.