Films of poly-l-lactic acid were stretched under a novel dry-process. In the case of uniaxial stretching with free width, the stretching attained a stretch ratio up to MD×TD=3.5×1', in the case of uniaxial stretching with constant width, up to 3.0×1.0, and in the case of simultaneous-biaxial stretching, up to 2.5×2.5.
The crystalline phase of uniaxially stretched films with free width had uniaxial orientation, like a fiber. For the uniaxially stretched films with constant width, however, the crystalline phase had uniplanar-axial orientation, And, the crystalline phase of simultaneous-biaxially stretched films, showed uniplanar orientation at all stretch ratios.
The mechanical properties, transparency, crystallinity and degree of molecular orientation of the films were improved by this novel dry stretching process. Particularly, tensile strength and Young's modulus to machine direction increased for all the stretched films.
