Phosphite stabilization effects on two-step melt-spun fibers of polylactide

The effects of molecular weight stabilization on mechanical properties of polylactide (PLA) fibers are investigated. The textile-grade PLA contains a 98:02 ratio of L:D stereocenters and fibers are produced by the two step method, involving a primary quench and cold drawing. Molecular weight loss, which is approximately 30% for unstabilized PLA, can be eliminated by the addition of small amounts of tris(nonylphenyl) phosphite prior to processing. The thermal and mechanical properties of fibers produced with two different concentrations of TNPP are compared to those of unstabilized PLA. Faster crystallization rates are obtainable with addition of the stabilizer, but final crystallinities are unaffected. Mechanical properties of the TNPP-enriched fibers are greatly improved over their unstabilized counterparts. Tensile strengths can be improved by 10-30% at a given draw ratio, while modulus may be improved by 10-25%. Excessive amounts of TNPP or insufficient mixing result in inhomogeneities that are deleterious to mechanical properties. Based on the available information, chain extension is believed to be the most likely mechanism for the molecular weight stabilization. (C) 2002 Elsevier Science Ltd. All rights reserved.