The influence of Dunlop and air microbubbling manufacturing methods on the physical, microstructural and mechanical properties of nano-alumina filled natural rubber latex foam

Abstract

The impacts of nano-alumina (NA) as a filler and the manufacturing methods of Dunlop and air microbubbling on the physical, microstructural and mechanical properties of natural rubber latex foam (NRLF) were comprehensively investigated. The achieved crosslink density through the swelling method using the Flory–Rehner equation showed that the nano-alumina led to an increase in the crosslinking level in the foam. The foams prepared by the air microbubbling (BLF) had crosslink density 57–160% more than Dunlop (LF). Despite the fact that the nano-alumina enhanced the cell size and broadened their diameters probability distribution, the field-emission scanning electron microscopy illustrated that the air microbubbling resulted in the foams with 105% smaller cell size (0.113 mm) and 840% higher cell density (57.94·105 cell/mm3). In addition, the calculated specific tensile strength, modulus, toughness, and elongation at break proved that the metallic oxide filler of nano-alumina improved the tensile characteristics of the NRLF up to 60%. According to the results, adding 3 phr nano-alumina to the foam increased the compression recovery to 86 and 99.4% in the LF and BLF samples, respectively. Finally, the analysis of variance was performed to optimize the formulation of foams prepared by two manufacturing methods.