Nucleating Agents to Enhance Poly(l-Lactide) Fiber Crystallization during Industrial-Scale Melt Spinning

Abstract

The nucleating agent N,N′-bis(2-hydroxyethyl)-terephthalamide (BHET) has promising effects on poly(l-lactide) (PLA) under quiescent conditions and for injection molding applications, but its suitability for industrial-scale fiber melt spinning is unclear. We therefore determined the effects of 1% and 2% (w/w) BHET on the crystallinity, tenacity, and elongation at break of PLA fibers compared to pure PLA and PLA plus talc as a reference nucleating agent. Fibers were spun at take-up velocities of 800, 1400 and 2000 m/min and at drawing at ratios of 1.1–4.0, reaching a final winding speed of 3600 m/min. The fibers were analyzed by differential scanning calorimetry, wide-angle X-ray diffraction, gel permeation chromatography and tensile testing. Statistical analysis of variance was used to determine the combined effects of the spin-line parameters on the material properties. We found that the fiber draw ratio and take-up velocity were the most important factors affecting tenacity and elongation, but the addition of BHET reduced the mechanical performance of the fibers. The self-organizing properties of BHET were not expressed due to the rapid quenching of the fibers, leading to the formation of α′-crystals. Understanding the behavior of BHET in the PLA matrix provides information on the performance of nucleation agents during high-speed processing that will allow processing improvements in the future.

Pilot-Scale Electrospinning of PLA Using Biobased Dyes as Multifunctional Additives

“…The crystallinity values of all fiber webs prepared from PLA composites were also similar, suggesting that varying the process parameters can reduce the fiber diameter, but the stress induced here was not sufficient to induce crystallization. Our crystallinity values were also similar to a partially oriented yarn prepared by melt spinning [ 35 , 36 ]. Our results show that pilot-scale electrospinning requires further optimization to achieve well-oriented fibers.…”

Effect of Colorants and Process Parameters on the Properties of Dope-Dyed Polylactic Acid Multifilament Yarns

“…We also observed a shoulder in the melting peak for PLA fibers at an SSD ratio of 3, probably reflecting the formation of imperfect α crystals during drawing, which melt at a temperature lower than α crystals. Similar melting behavior has previously been observed for drawn PLA chains [44,49].…”

“…However, at an SSD ratio of 3, the increase in tenacity was accompanied by a >1.5-fold increase in the degree of crystallinity, reaching 51.7% for the pure PLA fibers. Such an increase in drawing leading to increased crystallinity, to a maximum of 67%, was also reported by Mai et al [44,49] and was also anticipated because higher SSD ratios orient the polymer chains, creating a more ordered structure that induces crystallization during processing. We also observed a shoulder in the melting peak for PLA fibers at an SSD ratio of 3, probably reflecting the formation of imperfect α crystals during drawing, which melt at a temperature lower than α crystals.…”

“…At the same time, the elongation declined by 72% (from 94% to 26%). Increasing the SSD ratio was previously shown to increase tenacity and reduce elongation by stretching and orienting the polymer chains, leading to strain-induced crystallization [44,45]. The mechanical properties obtained from melt spun PLA yarn are similar to the values obtained by researchers in the past, when a maximum tenacity of about 30 cN/tex was reported [46,47].…”

“…We also observed a shoulder in th for PLA fibers at an SSD ratio of 3, probably reflecting the formation of im tals during drawing, which melt at a temperature lower than α crystals. S behavior has previously been observed for drawn PLA chains [44,49]. The higher crystallinity at an SSD ratio of 3 was also accompanied Cold crystallization occurs due to rapid quenching, when amorphous poly cannot crystallize during spinning relax and crystallize to form a more ord Two hypotheses could explain the lower Tcc.…”