This paper describes a biodegradable fiber formed from a thermoplastic composition that contains a modified thermoplastic starch up to 45 wt.% and a modified aliphatic-aromatic copolyester up to 80 wt.%. The modified copolyester enhances the strength of the starch-containing fibers and also facilitates the ability of the starch to be melt processed. Due to its relatively low melting point (120 °C), the modified aliphatic-aromatic copolyester can be extruded with the modified thermoplastic starch at a temperature that is low enough to avoid substantial removal of the moisture found in the starch. The modification of aliphatic-aromatic copolyester is carried out by an alcohol in an extruder so that it contains one or more hydroxyalkyl or alkyl terminal groups. By selectively controlling the conditions of the alcoholysis reaction (e.g. alcohol and copolymer concentrations, temperature, etc.), the resulting modified aliphatic-aromatic copolyester could attain a molecular weight that is relatively low. Such low molecular weight polymers have the combination of a higher melt flow index and lower apparent viscosity, which is useful in a wide variety of fiber forming applications such as in conventional fiber spinning and meltblowing of nonwoven webs for hygiene product applications.
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