Title : Natural rubber nanocomposites with cellulose nanofiber reinforcements produced by latex mixing: Effects of fiber morphology and modification
Abstract:
The natural rubbers are versatile elastomeric natural polymers that are beneficially used in composites and coatings. The better understanding on processing and reinforcement effects of cellulose nanofibers in natural rubber blends are advantageous for the creation of mechanically more stable natural rubber compounds, in parallel with the reinforcement effects and better processability during latex mixing. The cellulose nanofibers were produced by mechanical homogenization of native kraft pulp fibers, through mechanical processing in a microfluidizer towards different degree of fibrillation, resulting in micro- to nanofibrillated fiber morphologies. A chemical surface modification of the fibers was subsequently performed by the deposition of hydrophobic nanoparticles at the fiber surface, including vegetable oils and styrene-maleimide. The effect of fiber morphologies and content (0 to 15 wt.-%) on mechanical reinforcement and structural variations were investigated by adding to different types of natural rubbers. After rheological characterization of the nanofiber suspensions, the nanocomposites were formed by appropriate mixing the fibers into the rubber latex phase and film casting. The rheological properties of the latex are dominated by the shear thinning effect of the cellulose nanofibers indicating the formation of an interpenetrating fiber network, which becomes more prevalent at the higher degree of fibrillation. Indeed, the fibers with low degree of fibrillation had a weak effect on mechanical reinforcement of the natural rubbers, while the medium degree of fibrillation indicated a strongest improvement in modulus and tensile strength with a decrease in elongation at break. Moreover, the fibrillated cellulose enhances the cross-linking with reduction in the double carbon bonds of the natural rubber and decrease in hydroxyl functions of the nanocellulose.
