Biaxial orientation mechanism of drawn natural rubber. I. Appearance of the biaxial orientation

摘要

Triple centrifuged natural rubber (NR) film was crystallized at room temperature by uniaxial drawing at draw ratio (lambda) 6.0. Morphologies of the induced crystals were studied by wide angle X-ray diffraction (WAXD). Using a special drawing apparatus for shifting the X-ray beam positions, crystalline orientation was surveyed all over the drawn sample. WAXD results show the biaxial orientation (BO) with the c-axis being parallel to the draw direction and the a-axis parallel to the film surface. By means of the WAXD pattern with the incident beam perpendicular to the film, the drawn NR film was separated into three regions: (200+120) region indicating a low degree of BO, (200) region having a high degree of BO, and the intermediate region in between the above two regions. The degree of BO is enhanced from center to the clamping end depending on the increment of the sample width. At lower draw ratios (4.0 < lambda < 6.0), BO was developed with increasing draw ratio. In the intermediate region, BO increases sharply with a small increment of the width. The degree of BO is lowered at the periphery of the film.