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 reports a novel method to fabricate auxetic warp knitted fabrics on a tricot warp knitting machine based on a special structure design and knitting process. Three auxetic warp knitted structures were successfully developed and all of them were designed to form a reentrant hexagonal geometry to acquire an auxetic effect. To provide the fabrics with reentrant frames, elastomeric yarns and stiff yarns were used to form the elastic underlaps and stiff underlaps, respectively. While the elastic underlaps can keep the reentrant structures stable, the stiff underlaps can support the reentrant structures to keep their reentrant frames. To alleviate the transfer of yarns in the loops under tension, an additional front yarn guide bar was used to feed binding yarns to basic reentrant structures. After knitting, all the fabrics were subjected to a heat setting process to keep their shape and a tensile test to assess their auxetic behavior. The experimental results showed that all the fabrics exhibited an obvious auxetic behavior within a wide range of strain. In particular, the fabrics retained auxetic behavior until breaking when stretched in the wale direction, and the Poisson’s ratio of the fabrics could be as low as –0.5. On the other hand, the fabrics exhibited a large tensile elongation when stretched in the course direction and their Poisson’s ratios changed from negative to positive after the tensile strain exceeded a certain value.

Auxetic woven fabrics made with special geometrical structures have gained the interest of textile scientists in recent years. This paper reports a study on auxetic woven fabric based on a double-directional parallel in-phase zig-zag foldable geometrical structure. Such a fabric has been already produced and investigated for its negative Poisson's ratio effect in two principal directions (weft and warp directions). However, its negative Poisson's ratio effect in biased tensile directions as well as under repeated tensile loading conditions has not been studied yet. Therefore, in this paper, these two limitations are addressed. The auxetic woven fabric was firstly fabricated, and then subjected not only to tensile tests in different tensile directions, including two principle directions and three biased directions, but also to repeated tensile loading. It was found that both the negative Poisson's ratio effect and the resistance to tensile deformation are dependent upon the tensile direction, and the highest negative Poisson's ratio effect and higher resistance to tensile deformation are obtained in two principal directions.

Auxetic woven fabrics made of non-auxetic yarns have gained the interest of textile scientists in recent times. Such fabrics have already been produced and investigated for their negative Poisson's ratio (NPR) effect in two principle directions. However, the NPR effect of these fabrics in different biased tensile directions has not been studied. In particular, the influence of repeated tensile loading on the NPR effect retention ability of fabric has not been explored yet. Therefore, this paper aims to report the NPR effect of auxetic woven fabric in different tensile directions and the influence of repeating tensile cycle tests on its NPR effect retention ability. The auxetic woven fabric is firstly fabricated based on a re-entrant hexagonal geometrical structure by using elastic and non-elastic yarns, and then subjected to single and repeating tensile tests in five different tensile directions, which include two principle directions and three biased directions. It is found that the NPR effect is largely dependent upon the tensile direction and the number of repeating tensile cycles.

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