Poly(lactic acid) (PLA) fiber was developed more than a decade ago. It has been regarded as the most promising sustainable and biodegradable fiber to replace conventional polyethylene terephthalate (PET) polyester fiber in textile products. This paper reviews recent developments in PLA polymerization, PLA filament and fiber spinning, staple yarn spinning, fabric production, dyeing and finishing and aftercare procedures. The properties of PLA fiber are broadly similar to those of PET fiber; however, the properties of PLA fiber that differ, including thermal degradation and low hydrolytic resistance to strong alkaline, significantly affect the method selection and parameter setting of production and processing of PLA fibers and fabrics. PLA filaments are mainly produced by two-step melt spinning to get fibers with stable quality, but degradation at high temperature is still a problem. PLA staple yarns are normally spun using ring spinning. Currently existing knitting or weaving techniques can be used to produce PLA fabrics. PLA fabrics can be dyed with disperse dyes at 110°C, but their color fastness and shades are different from PET fabrics when using the same dyes. The scouring and dyeing of PLA/cotton blended fabrics and the reductive clearing after dyeing remain to be improved. As a new fiber, the entry of PLA fiber into the textile market faces difficult challenges as well as great opportunities in the future.
This paper presents a comparative study on natural indigo and indirubin in terms of molecular structures and spectral properties by using both computational and experimental methods. The spectral properties were analyzed with Fourier transform infrared (FTIR), Raman, UV-Visible, and fluorescence techniques. The density functional theory (DFT) method with B3LYP using 6-311G(d,p) basis set was utilized to obtain their optimized geometric structures and calculate the molecular electrostatic potential, frontier molecular orbitals, FTIR, and Raman spectra. The single-excitation configuration interaction (CIS), time-dependent density functional theory (TD-DFT), and polarization continuum model (PCM) were used to optimize the excited state structure and calculate the UV-Visible absorption and fluorescence spectra of the two molecules at B3LYP/6-311G(d,p) level. The results showed that all computational spectra agreed well with the experimental results. It was found that the same vibrational mode presents a lower frequency in indigo than that in indirubin. The frontier molecular orbital analysis demonstrated that the UV-Visible absorption and fluorescence bands of indigo and indirubin are mainly derived from π → π* transition. The results also implied that the indigo molecule is more conjugated and planar than indirubin, thereby exhibiting a longer maximum absorption wavelength and stronger fluorescence peak.
Sustainable poly(lactic acid) multifilaments are a new type of biodegradable fibers that have gained increasing attention in textile product development. However, low moisture management performance has hindered their application in high added-value textile products such as functional garments and sportswear. In this work, profiled poly(lactic acid) multifilaments with “+” cross-section and “Y” cross-section were developed by the melt spinning process in order to improve their moisture management properties. The cross-sectional and longitudinal morphologies of the produced profiled poly(lactic acid) multifilaments were first examined and their non-circularity degrees were calculated. The moisture-absorbing and fast-drying properties of both the poly(lactic acid) multifilaments and knitted fabrics, including vertical wicking, in-plane wicking, water absorption and evaporation, and water vapor transmission were then evaluated, and the effects of fiber cross-section shape and yarn texturing were analyzed. The results show that the moisture management performances of the knitted fabrics made with profiled poly(lactic acid) multifilaments are significantly improved when compared with those of the fabric made with circular cross-section poly(lactic acid) multifilaments. The results also show that moisture management performances of the knitted fabrics made with profiled poly(lactic acid) multifilaments are comparable or even better than those of the fabrics made of polyester multifilaments. The study suggests that poly(lactic acid) fibers can be applied for the development of textile products with high added value and substitute the large amounts of petroleum-based PET fiber in apparel end-use.
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