Modified abrasion testing of sheer knit textiles using
simulated movement and wear scenarios
Dave Cox
Senior Staff Technologist
Martindale abrasion testing was previously per- formed on Sheertex tights as well as on traditional tights, but ultimately found inconclusive due to the mild abrasive nature of the standard abradant. To better assess the resistance to abrasion in tights, modified Martindale testing was performed, and an apparatus using a robotic arm to simulate wear in use was designed. The Sheertex fabric was found to be significantly more resistant to abrasion compared to tested comparators.
When considering the durability of hosiery, abrasion re- sistance of the knit is an important factor. The more the tights can withstand rubbing action from, for example, a foot moving inside a shoe, a foot walking on a rough surface, or thighs rubbing against one another while walking, the more wears it will on average provide. Resistance to abrasion in fabric is typically measured using the Martindale method (ISO 12947 [1]). Under this method, the tested fabric is rubbed onto a standard abradant at relatively low pressure in continuously changing directions, tracing a Lissajous figure. Assessments—for example appearance change or specimen breakdown—are made after a predetermined number of rubs.
In prior testing, it was found that the standard Martindale method is not suitable for assessing abrasion resistance in tights. Firstly, the standard wool abradant is not sufficiently abrasive to produce a meaningful damage to the tights, even after 25,000 rubs. Secondly, the abrasion applied by the Martindale tester is not representative of the friction that occurs when worn by a user.
We believe that the abrasion resistance of Sheertex is at least ten times that of competitors.
A Robot Arm Abrasion tester was specifically designed to more accurately mimic rubbing that would occur when the foot of a user wearing tights is moving inside a shoe, or when the wearer is walking on a rough surface. The robot arm used was a Universal Robots UR-5ETM (Cobots Intelligence inc.), mounted to a table. A custom adapter was fabricated to attach a model foot to the end of the arm as an end effector. The model foot was made of solid foam overlaid with silicone, providing it a feel similar to that of a human foot. A camera was set up such that the arm’s digital outputs could control the shutter, allowing for photos to be taken automatically of the top and bottom of the foot between rubbing cycles.
Additionally, a Martindale apparatus (James Heal 1605 Midi-Martindale with five stations) was used, with the intent of providing a middle ground between the testing standard and a completely novel test.
Sheertex tights (referred to herein as Brand 1) were tested against competitor tights which are similar to Sheertex tights in sheerness and appearance (referred to herein as Brands 2, 3, and 4), as well as against disposable drugstore tights (referred to herein as Brand 5).
For each test, a new very fine (VF grit) non-woven abradant (Mirka Mirlon TotalTM) was installed onto the holding clamps on the test table. The foot portion of the tights under test was placed over the silicone foot, and held in place at the ankle region with a hook and loop fastener. The robot arm with the model foot attached thereto was programmed to carry out rubbing cycles.
Each rubbing cycle consisted of four rubs on the heel portion of the foot, followed by four rubs on the ball portion of the foot. After completion of each cycle, photos were taken of the top and bottom of the foot. The cycle was repeated until a hole was visible in any part of the fabric, at which point the robot arm was stopped and the number of cycles noted. This test was replicated three times for each brand of tights.
The Martindale method (ISO 12947 [1]) was used to assess abrasion resistance of tights, using the James Heal 1605 Midi- Martindale instrument. Instead of using the standard wool abradant, a more abrasive surface was used, Norton ProSand 320 Grit. The abradant was fixed using the ring clamp, and the felt backing fabric was omitted. The 9KPa weight was used. Tested samples were visually inspected using a progressive checking schedule - after 25, 50, 75, 100, 200, 300, 400, 500, 1000, 2000, 3000, 4000, 5000, and 10000 rubs. After 1000 rubs, any abraded fabric debris was cleared from the sample holders while checking the material.
Four stations were used, and a separate test was conducted for each brand. Samples were determined to have failed (and were thus removed from the apparatus) when visible holes appeared in the fabric. When all samples failed, the test was stopped.
Fig. 2. Rub cycles to failure, Modified Martindale Test
A 320 grit sandpaper was used as an abradant in place of the SM25 fabric specified in ISO 12947. Brands 2, 3, 4, and 5 failed at the first check interval at 25 rubs. It was not possible to observe any precursor states to failure (fuzzing, pilling) due to the fact that the samples failed at the first check interval.
While there was visible surface fuzzing due to the abradant in the Brand 1 (Sheertex) samples, actual holes did not occur until 5000 rubs, and it took 6000 rubs for all samples to have holes in them.
This result indicates that Sheertex tights (Brand 1) are at least 240 times more abrasion resistant than any of the chosen competitor tights.
There are several modes of fabric failure, which include but are not limited to fuzzing, pilling, and holes. When subjected to abrasive testing, most competing brands of tights immedi- ately developed holes, and completely bypass the fuzzing and pilling stage in this test.
As a longer-lasting fabric, the Sheertex knit did develop some fuzzing and (eventually) pilling, the fabric remained structurally intact and without holes for several thousand cycles, indicating that while there may eventually be visible wear in the fabric, it will continue to withstand wear for longer than the competition.
From these tests, it can be concluded that Sheertex tights are significantly more durable to abrasive breakdown. From the point of view of the consumer, and the environment, this substantial increase in resilience is a definite advantage. Tights which can better withstand these abrasion tests are also more likely to withstand the rigors of daily life, and many more wears than competitor tights, resulting in less waste and less inconvenience.
Many thanks to Amy Dam, Amanda Fleury, and Charlotte Fauqueux for their assistance with editing and adding clarity to this report.