Friction Property Between Fabric And Human Skin

With the increasing pursuit of the clothing contact comfort, the friction behavior between fabric and human skin has attracted widespread attention in recent years. In daily life, interactive friction between human skin and clothing fabric would inevitably occur. Some troubles such as clothing style deformation and skin pruritus would arouse when the friction is relatively large. During the process of heavy labor, athletic sports and field march, human skin will be severely stimulated by the cloth when the external environment temperature rises or the body activity increases. In the flood relief, skin irritation, blistering and abrasions caused by intense friction between clothing and skin are common occurrence. Besides, due to the heavy pressure of the body and the interactive friction between clothing and skin, bedsore disease will be aroused which adding to a long-term bedridden. patient’s agony. Therefore, it is necessary and significant to investigate the tribological properties between fabric and human skin so as to develop more suitable underwear and bedding materials, protect the skin healthy as well as improve the wearing comfort. So far, material friction tester and skin tribometer have been used to indirectly measure the friction properties. However, it is difficult to simulate the curve friction behavior and dynamic interaction between clothing and human skin. The specialized tester and the universal applicable measurement system are absent.In order to investigate the friction property between fabric and human skin, a new fabric-skin friction tester was designed. And the experimental methods including the variation regularity of friction, test conditions, characterization indexes between fabric and skin under dry or wet conditions were introduced. On this basis, the friction property differences and the influence factors between various fabric and different skin were investigated. The main work and the results of this thesis will be presented in the following.(1) Friction experimental method between fabric and skin in dry condition The frictional test equipment was installed on the basis of existing strength tester. The load-elongation system was refitted into friction-displacement system between fabric and skin. It could directly measure the static and dynamic friction between fabric and human skin (simulated skin). It provided a practicable experimental instrument to investigate tribological behavior between fabric and human skin. The maximum friction range is3000cN and the maximum displacement range is500mm. The friction velocity is configured from100mm/min to1000mm/min. Friction experiments in dry condition (normal temperature) were carried out in a climatic chamber with the temperature at20±3℃and the relative humidity at50±5%. Some healthy students aged from20to30yrs were invited to be the subjects. The friction position is selected from the middle of lateral skin of forearm. In order to characterize the friction property between fabric and human skin, four friction indexes (static friction, turning point between static friction and dynamic friction, average dynamic friction and its coefficient of mean deviation) were defined. And the coefficient of variation is introduced to characterize the dispersion degree of several friction curves. Besides, friction coefficient was calculated by the frictional Euler Formula of the flexible belt.In order to recommend the suitable test parameters, the variation regularity of friction properties (average dynamic friction, coefficient of mean deviation and the coefficient of variation) between fabric and skin were compared under different test conditions. It was found that the average dynamic friction increased along with tension (or the normal pressure between fabric and skin) and sample width, basically had no effect on its velocity. According to the comprehensive comparison and practical test condition, the appropriate test conditions were recommended for the conventional fabric. The test tension of woven fabric was200cN, while the test tension of knitted fabric was60cN. The friction velocity of both kinds of fabric was500mm/min and the sample width was100mm. Under these conditions, the fluctuation of single friction curve and dispersion degree of several friction curves in repeated trials were both smallest. The fiction signal was stable and the fabric deformation was small. The experiment operability and reproducibility were relatively strong. It was considered that5times of friction test of each friction pair would meet the requirement during the95%confidence interval.(2) Differences of friction properties between fabric and individual human skinThe human skin roughness is diverse in different gender, age, height and weight. According to the comparison of the average dynamic friction and its coefficient of mean deviation per unit area, the friction properties differences and its influence factor between fabric and various human skin was analyzed.20volunteers (10male,10female) and various fabrics (6kinds of woven fabrics and6kinds of knitted fabric) were chose to take the friction experiments. It was found that the average dynamic friction between the fabric and female skin were significantly larger than that of male. There was a significant difference in average dynamic friction between female and male skin when rubbing with some fine and smooth fabrics. On the contrary, there was no significant difference in friction between female and male skin when rubbing with some uneven and crinkled fabric. There was no significant difference of gender impact on the coefficient of mean deviation of average dynamic friction between fabric and human skin.During the20-30year-old, there was not any significant correlation between body height (weight, age) and average dynamic friction (coefficient of mean deviation of average dynamic friction). While there was a significant correlation between body mass index and the average dynamic friction of woven fabric and skin during the95%confidence interval. Besides, gender difference basically had no influence on the relationship between body parameters (height, weight, age and body mass index) and friction properties (average dynamic friction and its coefficient of mean deviation). It showed that the friction between fabric and skin was small in dry condition. Friction effect within short time would not arouse intense discomfort and hurt human skin.(3) Distribution and influence regularity of friction between fabric and skin in dry conditionIn order to survey the distribution of dynamic friction coefficient,74kind of woven fabric and25kind of knitted fabric which common contact with skin were collected to carry out the friction tests. The results showed that the dynamic friction coefficient between woven fabric and skin distributed at0.12-0.50. And the average value was0.38. The surface of filament woven fabric was smooth with less hairiness, the yarn was fine and the standard moisture regain was low. The dynamic friction coefficient between filament woven fabric and skin was generally smaller than0.34. While the surface of staple fiber woven fabric was rough with more hairiness, the yarn was thick and the standard moisture regain was high. The dynamic friction coefficient between staple fiber woven fabric and skin was generally larger than0.33. The dynamic friction coefficient between knitted fabric and skin distributed at0.15-0.71. And the average value was0.53. Also, the dynamic friction coefficient between staple fiber knitted fabric and skin was larger than that of the filament knitted fabric.To explore the major factor of the friction property between fabric and skin, classified by the materials and yarn type, pure cotton woven fabric, non-cotton staple fiber woven fabric and filament woven fabric were analyzed by single correction analysis and multiple linear stepwise regression analysis respectively. It showed that the larger the weft diameter, the smaller the distance among warps, the larger the average dynamic friction between pure cotton woven fabric and skin. The regression formula of pure cotton woven fabric was basically suitable for the non-cotton staple fiber woven fabric. It also found that the larger the weft diameter, the smaller the warp diameter, the larger the average dynamic friction between filament woven fabric and skin. The relationships between knitted fabric structural parameters and average dynamic friction were also investigated. It showed that the average dynamic friction between knitted fabric and skin mainly influenced by the horizontal dense. For plain knit fabric, the larger the vertical dense and yarn diameter, the larger the average dynamic friction.(4) Friction experimental method between fabric and skin in wet conditionWhen the human body sweats, costume will be wet after absorbing perspiration and stick to the skin surface immediately. It will make the friction increase sharply and seriously influence the skin comfort. In order to investigate the friction property between fabric and skin in wet state, the wet sample preparation method was explored firstly. The complete wetting fabrics were hung on the line for different time to get the testing fabrics with different water content (wet state). The relative hanging time was innovatively introduced to characterize the different wet states. The relative hanging time was defined by the quotient of actual hanging time and total hanging time. Friction experiments in wet condition were carried out in a climatic chamber with the temperature at25±3℃and the relative humidity at60±5%. The friction-sliding displacement curves between different kinds of fabric and skin in different dry and wet states were analyzed. It was found that there were4kinds of friction-sliding displacement curves. They were normal friction curve, arched friction curve, rising friction curve and decline friction curve. The normal friction curve and rising friction curve usually occurred on woven fabrics in different states and their probabilities were44percent and47percent, respectively. While only normal friction curve often occurred on knitted fabrics and its probability was92percent. According to the characteristic of various friction curves, based on the friction indexes defined in dry condition, another2kinds of friction indexes (maximum dynamic friction and variation rate of dynamic friction) were added to characterize the friction properties between fabric and skin in wet state.The whole variation trend of average dynamic friction between various fabric and skin during the total hanging process were investigated to recommend the suitable wet condition. When the wetting degree of the fabric (or the liquid content in fabric) decreased, the average dynamic friction between woven fabric and skin increased at first and then decreased. When the large droplets on the fabric almost dropt at the second relative hanging time node (T=0.2), the average dynamic friction reached the maximum value. The average dynamic friction decreased to minimum value until the fabric dried up. The friction variation trend of natural fiber knitted fabric was same as that of woven fabric. While the average dynamic friction between synthetic fiber knitted fabric and skin reached the maximum value when the water content in fabric was largest at first. Then it entered the stage of a stable buffer time since the second relative hanging time node (T=0.2). And it declined slowly until minimum value at dry condition. It was noted that the average dynamic friction of most of the fabric reached maximum value at the second relative hanging time node. Compared to the completed wetting state, the water content of fabric was easy to control at this time node. And the experiment is reproducible. Thus, this suitable relative hanging time (T=0.2) was recommended as the standard friction test condition between fabric and skin in wet state.It was found that average dynamic friction between fabric and skin at the recommended wet condition was3times as that of the dry condition. The average dynamic friction of some fabric was universally large at wet condition. The yarn was fine, the density was large and the fabric was thin and smooth. In contrast, the average dynamic friction of some other fabric was universally small at wet condition. The yarn was thick, the density was small and the fabric structure was loose. Besides, the average dynamic friction between natural fiber fabric and skin was universally larger than that of the synthetic fibre synthetic fibre fabric. At the recommended wet conditions for common woven fabric,10times of friction test of each friction pair would meet the requirement during the95%confidence interval. While for common knitted fabric,8times of friction test was requested. When the friction between fabric and skin exceed1200cN, skin would be stretched seriously and discomfort was obvious, even a feeling of intense burning would be aroused.