Technique for measuring the low pull-out forces of bonded fibers: application to glue-based false eyelashes

Until now, no method has been reported for measuring fiber pull-out forces in false eyelashes. Many false eyelashes are handmade and are comprised of poly(butylene terephthalate) (PBT) lashes with glue bases. Due to their small size, delicate nature, and complexity with regards to varying depths of embedment, angle of attachment of fibers to the base, and physical interactions between fibers of false eyelashes, conventional tensile testing machines are not able to grip individual lashes and accurately measure the small forces of detachment. In this work, a custom tensile testing instrument was used to investigate the effect of an approximately 120 °C curling step on the strength of adhesion of PBT fibers to the glue base. To account for the effects of structural complexity on the mechanical pull-out strength of individual fibers, 20 individual fibers were pulled from 11 different models of eyelashes, both before and after curling. A Kolmogorov-Smirnov normality test was employed to assure the data collected were normally distributed, and means and standard deviations were calculated. A two-tailed t-test revealed that 10 of the 11 tested eyelash models showed no statistically significant difference in mechanical strength before versus after the curling process.