Real‐time observation of microcrack growth in thin film microtomed from rubber/nanocellulose composite sheets, during tensile deformation

Abstract

Rubber/nanocellulose composite sheets improve tensile properties compared with neat rubber sheets, when nanocellulose materials are suitably compounded with rubber matrices. First, two oven‐dried nanocellulose materials containing different additive components were prepared from nanocellulose/water dispersions, and the oven‐dried nanocellulose‐containing materials were compounded with rubber sheets under high shear forces by using a two‐roll mill. The tensile moduli and strength of the rubber/nanocellulose composite sheets were clearly better than those of the rubber sheet prepared without nanocellulose, while the elongations at break were similar. Thin films were cut from the rubber/nanocellulose composite sheets, and their real‐time tensile deformation processes were observed by transmission electron microscopy (TEM) to understand the time‐dependent patterns of crack propagation, void formations, and fusion between cracks and voids in the composites during tensile deformation. TEM observations showed that the composite sheets consisted of individual rubber/nanocellulose clusters. Voids initially formed inside the rubber/nanocellulose clusters, propagated to form cracks, fused with other voids or secondary cracks. There were slight differences between the crack‐propagation patterns of the two rubber composites, probably because of differences in the morphologies, sizes, distributions, and structures of the rubber/nanocellulose clusters, and surface chemical structures of individual nanocellulose elements between the composites.