Natural rubber latex nanocomposites : effect of montmorillonite clay structure on reinforcement and extractable proteins

Abstract

Natural rubber (NR) latex-clay nanocomposite (NRLCN) prepared with montmorillonite (MMT) clay aqueous dispersion was evaluated for reinforcement, extractable proteins and barrier properties. Physio-mechanical properties of the NRLCN were compared with conventional NR latex composites containing CaCC>3. The NRLCN structure was

characterized with X-ray diffraction and scanning electron microscope (SEM) techniques. X- ray diffraction data showed that, with a lower concentration of clay, highly exfoliated clay

structure was achieved whilst clay aggregation gradually resulted with a higher concentration of clay. Crosslink density and volume fraction ofrubber in the swollen gel as computed based on the solvent absorption data ofthe latex nanocomposite films increased while molar mass between crosslink ofthe rubber decreased with the increase of clay concentration. As a result of nano scale dispersion of montmorillonite clay and higher crosslink density of the latex nanocomposite films, resistance to permeation of small molecules through the NRLCN is significantly enhanced in comparison to conventional NR latex-CaC03 composites. Solid state mechanical properties ofNRLCNs have shown a significant reinforcement effect of dispersed nanoclay platelets but without sacrificing the elastic properties. Results have been explained in terms of degree of clay dispersion/exfoliation, crosslink density and strain induced crystallization. The extractable protein content was analysed for the NRLCN samples using the Modified Lowry Method. It had shown a significant reduction ofthe extractable protein content in the NR latex films when montmorillonite clay is introduced. The NRLCNs were leached using typical industrial leaching conditions and also tested for the extractable protein content which dropped well below the allergenicity level of human skin. The extractable protein content of raw NR latex-clay un-vulcanized films had shown similar results as the NRLCN which confirms the attraction of protein cations with the nanoclay platelets. The entrapped protein has accelerated the vulcanization reaction of the NRLCN which caused higher crosslink density. Higher mechanical properties, very low extractable protein content and improved barrier resistance indicated that NR latex nanocomposite containing montmorillonite clay is a potential replacement for conventional NR latex composites containing CaCC>3.