Compression Molding Anisotropy of Natural Rubber Compounds

By studying the physical properties of natural rubber compounds cured by compression in a test mold which has a unidirectional outer flow of excess rubber from the mold when vulcanization starts, we found that the tear strength of the test pieces where the direction of the stretching was parallel to the outer flow was lower than that of the test pieces with the direction perpendicular to it. Similar anisotropies were also observed in tensile strength, modulus, tanδ, Payne's effect, etc. Some anisotropies similar to the experiments were observed in the OCTA calculation with a non-crosslinked natural rubber model. The causes of anisotropies were considered.