Selective laser crystallization and amorphization in polymer fibers

Abstract

Textile finishing is a huge industry for modification of textile surface properties to align with the desired end use spanning medical, engineering, and apparel applications. Laser-induced polymer morphology modification has been studied by researchers, with evidence suggesting a correlation between laser fluence and crystallinity. However, a lack of data has resulted in the mechanism for change remaining unknown. This paper aims to identify the mechanism of initial Young’s modulus control in polyethylene terephthalate (PET) monofilament yarn and explain the relationship between Young’s modulus and the degree of crystallinity using Takayanagi’s model. PET monofilament yarns were treated using a CO2 infrared laser at a 10.6  μm wavelength at fluences up to 0.086 J/mm2. Young’s modulus data obtained from stress-strain curves at 0.2% strain and fraction crystallinities obtained from differential scanning calorimetry were compared with Takayanagi’s series model. Laser surface treatment within a fluence range up to 0.087 J/mm2 on PET resulted in stable Young’s modulus values. A 3.5% reduction in Young’s modulus of PET was seen with a 6.1% reduction in crystallinity, which was in good agreement with Takayanagi’s series model. Lasers offer rapid material processing capable of increasing or decreasing fractional crystallinity selectively along the fiber where desired. Selective amorphization increases chemical absorption, allowing increased surface finishing uptake at milder processing conditions, whereas increasing fractional crystallinity imparts fiber strength. The relationship between fiber crystallinity and Young’s modulus for PET can be described by Takayanagi’s model, allowing a prediction of material properties, which can be extended from fibers to all thin-film polymers.