Mechanical, crystallisation and moisture absorption properties of melt drawn polylactic acid fibres

Polylactic acid (PLA) fibres were produced with average diameter ranging from 11 to 38 μm via a melt drawing process employing increasing take-up velocities. The PLA fibres exhibited smooth surfaces and uniformity in diameter as determined by scanning electron (SEM) and optical microscopy (OM). Fourier Transform Infrared Spectroscopic (FTIR) analysis using the dichroic ratio demonstrated alignment of PLA chains with the draw direction, where the lower diameter PLA fibres exhibited a higher degree of chain orientation during the high speed melt drawing process. The crystallinity of the fibres also increased up to 34% with decreasing fibre diameter due to strain-induced crystallisation. The room temperature tensile strength and modulus of the smaller PLA fibres with an average diameter of 11 μm revealed values of 213 MPa and 4.8 GPa, respectively. These fibres revealed a significant decrease in their tensile strength (by 29%) when tested at 37 °C compared to the room temperature value. Comparatively larger diameter PLA fibres did not show any significant change in their mechanical properties at 37 °C. The variation in diameter of PLA fibres also revealed a noticeable influence in moisture absorption at various humidity levels believed to be due to the effect of crystallinity on water absorption.