Abstract
l-Lactide/trimethylene carbonate copolymers have been produced as multifilament fibers by high-speed melt-spinning. The relationship existing between the composition, processing parameters and physical properties of the fibers has been disclosed by analyzing how the industrial process induced changes at the macromolecular level, i.e., the chain microstructure and crystallinity development. A poly(l-lactide) and three copolymers having trimethylene carbonate contents of 5, 10 and 18 mol % were synthesized with high molecular weight ( Mn) up to 377 kDa and narrow dispersity. Their microstructure, crystallinity and thermal properties were dictated by the composition. The spinnability was then assessed for all the as-polymerized materials: four melt-spun multifilament fibers with increasing linear density were collected for each (co)polymer at a fixed take-up speed of 1800 m min-1 varying the mass throughput during the extrusion. A linear correlation resulted between the as-spun fiber properties and the linear density. The as-spun fibers could be further oriented, developing more crystallinity and improving their tensile properties by a second stage of hot-drawing. This ability was dependent on the composition and crystallinity achieved during the melt-spinning and the parameters selected for the hot-drawing, such as temperature, draw ratio and input speed. The crystalline structure evolved to a more stable form, and the degree of crystallinity increased from 0-52% to 25-66%. Values of tensile strength and Young's modulus up to 0.32-0.61 GPa and 4.9-8.4 GPa were respectively achieved.
Highlights
Poly(lactic acid) or poly(lactide), PLA, is a biobased, degradable and thermoplastic polymer belonging to the family of the aliphatic polyesters
We have evaluated how the melt-extrusion and processing parameters, and the draw ratio, drawing temperature and speed modify the molecular weight and microstructure and induce crystallinity
The average block lengths of lactidyl (LLL) and trimethylene carbonate blocks (LT) were calculated from the methine and methylene region of the 13C NMR spectra according to the following equations: Table 2
Summary
Poly(lactic acid) or poly(lactide), PLA, is a biobased, degradable and thermoplastic polymer belonging to the family of the aliphatic polyesters. The poly(L-lactide), PLLA, usually prepared by ring-opening polymerization of the L-lactide monomer (LA), is a semicrystalline material having good mechanical properties with a melting point, Tm, of approximately 180 °C and a glass transition temperature, Tg, in the range 55−60 °C.3. Its features make it an ideal candidate for load-bearing applications.[4] PLA can form high-strength monofilament[5−7] and multifilament fibers,[8,9] as well as electrospun fibers[10−12] which have been investigated as scaffolding materials[13−16] and injectable micelles carrier.[17] The quality of PLA fibers makes them suitable for use in textile applications as well.[18]
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