Melt spinning of poly(L-lactic acid) and its biodegradability

The melt spinning and melt drawing of poly(L-lactic acid) (PLLA) were carried out with a melt-spinning machine, and the mechanical properties, structure, and biodegradability of PLLA fiber were investigated. PLLA fiber with a tensile strength of 0.81 GPa was successfully obtained through two steps of drawing at a draw ratio of 18 in hot water. This fiber had enough tensile strength for common engineering use. The fiber could be degraded under controlled composting conditions at 70 degrees C for 1 week. In scanning electron microscopy observations of the fiber, a regular pattern of cracks running along the vertical direction to the fiber axis was clearly observed. This suggested that the PLLA fiber built up a highly ordered structure arranged along the direction of the fiber axis. After the fiber was left to lie in the ground for 1 year, however, the surface of the fiber was still smooth, and the tensile strength did not decrease much. This PLLA fiber could not be hydrolyzed after 1 month of steeping in a buffer solution at 37 degrees C, but it was rapidly hydrolyzed at more than 60 degrees C. It was suggested that the degradation (hydrolysis) rate of PLLA depended on the glass-transition temperature. Upon hydrolysis at 80 degrees C for 48 h, a regular crack along the vertical direction to the fiber axis was found that was very similar to that observed in degradation under composting conditions. (C) 2005 Wiley Periodicals, Inc.