Control of 3D oriented strain-induced natural rubber crystallites under spatial confinement: cellulose nanocrystal networks and thickness dependence

New insights into 3D-oriented strain-induced crystallization of natural rubber/cellulose nanocrystal (NR/CNC) composites have been obtained by 2D wide-angle X-ray diffraction (2D-WAXD). Upon CNC content exceeding 10 wt%, the mechanical behavior of the material exhibits a yield point that resembles those observed in plastics. Taking into account the influence of filler content of CNCs and thickness, the three-dimensional orientation degree of NR crystallites can be quantitatively assessed. The formation of 3D NR crystallites can be established when the CNC content surpasses 10%, and concurrently, the degree of three-dimensional orientation of crystallites increases as thickness decreases. It was found that not only do CNCs enhance the confinement effect, leading to a decrease in the onset strain, but it is also beneficial for the formation of 3D-oriented strain-induced NR crystallites. The current study not only helps in the comprehensive understanding of the mechanism of 3D-oriented strain-induced NR crystallites by the constrained rigid filler network, but also provides the potential application of uniaxial tensile stretching in creating 3D functional materials.