Biodegradable polylactic acids for use in forming fibers

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.

Description

Background of the invention

[0001] Biodegradable nonwoven webs have a wide variety of applications, such as in disposable absorbent products (eg, diapers, training pants, hygiene wipes, feminine pads and liners, adult incontinence pads, braces, garments, etc.). To facilitate nonwoven web formation, the selected biodegradable polymer should be melt processable and have good mechanical and physical properties. Polylactic acid ("PLA") is a common biodegradable and sustainable (renewable) polymer. Although various attempts have been made to use polylactic acid in the formation of nonwoven webs, its high molecular weight and viscosity tend to limit its use to only certain types of fiber forming processes. For example, conventional polylactic acid is generally not suitable for meltblowing processes, which require low polymer viscosity for efficient formation of microfibers. Therefore, there is still a need for biodegradable polylactic acid with good mechanical and physical propert...

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