Effects of take‐up speed on the structure and properties of melt‐spun poly(L‐lactic acid) fibers

Abstract

Poly(L-lactic acid) (PLLA) filament fibers were prepared by one-step melt spinning process and the effects of variations in take-up speed on their thermal properties, mechanical properties, and crystalline structures were investigated. Differential scanning calorimetry (DSC) results revealed that the PLLA fibers showed multiple melting peaks and that the melting peak appearing at a lower temperature moved lower while that at a higher temperature moved higher with increasing take-up speed. The glass transition temperature (T g ) obtained from dynamic mechanical analysis (DMA) increased with increasing take-up speed. The tenacity increased and the boiling water shrinkage (BWS) decreased with increasing take-up speed. However, these mechanical and thermal properties were stabilized at take-up speeds over 3500 m/min. The melt-spun PLLA fibers of this study showed an a-form crystal structure which was not affected by the take-up speed. The change in the tendency of the thermal and mechanical properties at around 3500 m/min did not appear to result from the change in crystal form but rather from the change in crystallite size and crystallite orientation.

Structure–property relationship for poly(lactic acid) (PLA) filaments: physical, thermomechanical and shape memory characterization

“…The measured linear densities, birefringence, refractive indices and overall orientation function of the T and J samples are presented in Table 1. The measured birefringence showed reasonable agreement with the reported literature data in the range of 0.015-0.025, increasing by the takeup speed [25]. The filaments appeared yellowish-red between cross-polarized optical microscope, which was consistent with the previous reports regarding samples with positive birefringence [9,13,25].…”

“…Detailed thermomechanical analysis of the PLA fibers revealed storage modulus, E′, loss modulus, E″ and tan δ curves sensitivity to fiber structure. The experimental results confirmed that the thermomechanical properties of PLA fiber were affected by changes in fiber collection speed, drawing force and physical aging due to the changes in the fiber structural features included crystallinity, molecular orientation [8,25], microfibril size [14] and crystal structure [27]. The enhanced fiber crystallinity and chain orientation restricted the amorphous phase molecular mobility and improved its glass transition and modulus profoundly [8,14].…”

“…However, the crystalline orientation has more significant effect on total fiber birefringence than its orientation in the amorphous regions [25]. The higher average value of the birefringence and the overall orientation function of the J sample confirmed its higher molecular orientation.…”

“…Strong correlation was observed between the tensile properties and birefringence of PLA fibers and then birefringence can be employed as a structural parameter for orientation study [11]. The lower extrusion temperature [12], collection speed increase [8,9,25], draw ratio increase and hot drawing [8] have strong effects on the tensile strength of PLA fibers due to higher molecular orientation, crystallinity development, crystal formation of the two kinds. The oriented polymer chains tend to coil up and shrink in boiling water, whereas the crystalline fraction leads to dimensional stability.…”

“…Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) have been used to ascertain the processing/crystallization effects on the fiber thermal [6,8,11,12,25,26] and thermomechanical properties [8,14,25]. Detailed thermomechanical analysis of the PLA fibers revealed storage modulus, E′, loss modulus, E″ and tan δ curves sensitivity to fiber structure.…”