Negative Poisson’s Ratio Polyester Fibers

Abstract

Auxetic materials when stretched axially expand instead of contracting laterally. Following Lakes's [1] successful production of auxetic foams, a variety of auxetic products have been fabricated including honeycombs [2], polymeric and metallic foams [1] and microporous polymers [3,4]. An interesting feature of auxetic materials is that they are predicted [5], and have been found, to have enhanced properties. For example, it has been shown experimentally that the indentation resistance [6] of auxetic materials has been enhanced by up to four times when compared with the conventional equivalent. Other enhanced properties include plane strain fracture toughness [7], energy absorption [8], and shear modulus [9].The first synthetic auxetic microporous polymer was a particular form of polytetrafluoroethylene (PTFE) [10]. It was found that the auxeticity in this case was solely because of its complex microstructure [10]. This consisted of nodules interconnected by fibrils that react co-operatively to produce a negative Poisson's ratio. Similar microstructures have also been engineered in polymers such as ultra-high-molecular-weight polyethylene (UHMWPE) [3], polypropylene [4] and nylon [11], which were all produced by a novel thermal processing route consisting of three distinct stages; compaction [12], sintering [13] and ram extrusion [14]. The entire process takes place in a specially designed extrusion rig with extrudates produced in the form of cylindrical rods. Although having this special property, there were found to be limitations on the production of auxetic materials in the form of cylinders. In particular, the cylinders (having diameters varying between 9 and 15 mm) were found to be unsuitable for application-based research and were restricted to laboratory-based testing. Moreover, the process involved was not continuous and problems were envisaged in producing them on a large scale. 1 2 More recently, a novel thermal processing techniqueinvolving melt spinning has been employed to produce an auxetic product in a more useful and usable form, namely as a fiber [15]. This has led to auxetic polypropylene (PP) fibers being fabricated in a continuous process. Videoextensometry analysis was used to show the auxetic nature of the PP fiber. The processing route developed for auxetic polypropylene fibers is, in principle, flexible enough to be adapted to produce other polymeric fibers [15] and films [16] in auxetic form.This paper reports in detail the production of auxetic polyester fiber, including the characterization by videoextensometry.Abstract Auxetic materials are referred to as those having negative Poisson's ratio (ν). Initial work at Bolton successfully fabricated auxetic polypropylene fiber using a novel thermal meltspinning technique. This paper reports in detail both the methods and principles involved in screening polyester powder and also the manufacturing method for successful production of auxetic polyester fibers. Videoextensometry along with micro-tensile testing were used to measure the Poisson's...

Three decades of auxetic polymers: a review

“…(139), which were fabricated using a continuous partial melt extrusion process. To date, a variety of auxetic fibers, such as auxetic polyester fibers and nylon fibers (144)(145)(146)(147)(148), and fabrics made from auxetic yarns using knitting, weaving, and both the warp and the weft-knitting technologies based on different geometrical arrangements, have been developed (149-152).…”

Engineered Warp Knit Auxetic Fabrics

“…Such materials are increasingly attaining some prominence in ongoing research of technical textiles [1]. A major production route could be, first, to synthesize the auxetic polymers and then to produce the yarn [2,3] and knitted fabrics and thereafter, form composites from these polymers [4][5][6][7]. Efforts to fabricate auxetic fabric structures are limited.…”

Untitled

“…A large value of Poisson's ratio (v = -0.6) was obtained when measured by using video extensometry. A novel method to produce auxetic polyester fibres have been reported by Ravirala N et al [41]. The polyester granules were grinded by using an in-house cryogenic grinding and particles of less than 150µm were collected to carry out the extrusion.…”