A molecular dynamics study of the effects of silane and cellulose nanocrystals at a glass fiber and epoxy interphase

Abstract Due to commonly observed adhesive fracture, the interphase regions between fibers and matrix have often been considered a critical design factor in polymer matrix composites. This study uses molecular dynamics simulation to explore the effects of two modifications at a glass fiber and epoxy interphase by adding a silane sizing and a cellulose nanocrystal particle. Based on the interphase density profile, the silane coating and the cellulose nanocrystal increase the interphase thickness and create an interpenetration region with the epoxy matrix. The results of shear deformation show that the main effect of the silane coating is to enhance the shear modulus and strength at the interphase and change the failure mode from adhesive to cohesive fracture. In addition, adding a rigid cellulose nanocrystal increases the interphase stiffness regardless of the silane environment, and it causes a similar transition to cohesive fracture when silane is absent. A trajectory analysis shows that the cellulose nanocrystal particle is physically absorbed on the glass fiber surface without silane, and it is physically confined in a region between silane and epoxy when silane is added. Overall, a cellulose nanocrystal particle increases the surface roughness at a glass fiber surface, leading to an improved shear modulus at the interphase of a glass fiber and epoxy composite.