| abstract |
A method for forming a biodegradable polylactic acid suitable for use in fibers is provided. Specifically, a polylactic acid is melt processed at a controlled water content to initiate a hydrolysis reaction. Without intending to be limited by theory, it is believed that the hydroxyl groups present in water are capable of attacking the ester linkage of polylactic acids, thereby leading to chain scission or 'depolymerization' of the polylactic acid molecule into one or more shorter ester chains. The shorter chains may include polylactic acids, as well as minor portions of lactic acid monomers or oligomers, and combinations of any of the foregoing. By selectively controlling the hydrolysis conditions (e.g., moisture and polymer concentrations, temperature, shear rate, etc.), a hydrolytically degraded polylactic acid may be achieved that has a molecular weight lower than the starting polymer. Such lower molecular weight polymers have a higher melt flow rate and lower apparent viscosity, which are useful in a wide variety of fiber forming applications, such as in the meltblowing of nonwoven webs. |