The effect of moisture on changing the properties of cellulose - based shoe cardboard

Recently, there has been an increase in the return of used shoes by consumers due to defects in the main insole. These defects include cracking, sagging, and breaks in the area where the molded sole grids are located. The shoe industry predominantly uses cardboard, an artificial material composed of glued short cellulose fibers, for the main insoles. The purpose of the work is to evaluate the effect of humidification on the properties of shoe cardboards and to verify the compliance of the quality assessment tests stipulated by the standards for insole cardboards with the actual operating conditions of shoes. Standard methods were employed to study the physical and mechanical properties of cardboard in a dry state and after exposure to water for 2 hours and 24 hours. Parameters such as moisture transfer and hygroscopicity, wetness, and changes in linear dimensions during moistening and drying were determined. An electron microscope was used to analyze the structure of the cardboards under study. The study indicates that the tests prescribed by the standards for assessing the quality of insole boards do not fully account for the real impacts on shoes during operation. Despite cardboard properties meeting the standards (with the exception of wetness), consumers report delamination and deformation of the main insole. Therefore, tt is necessary to develop new methods for assessing the quality of shoe cardboards that more closely resemble the operating conditions of shoes. It has been determined that during the moistening of cardboards, the adhesive bonds between the fiber and the impregnation weaken (Cellsan) or are partially destroyed (Flexan, Flexan 10, Texon, Konitex), which leads to a decrease in their strength characteristics. A high degree of wetness, coupled with a minimal moisture release, results in the destruction of cardboard. This is because everyday shoes are worn for extended periods throughout a day, and significant moisture accumulates in the cardboard from which the main insoles are made. A solution to this problem could be the development of a material for the main insoles that is more resistant to moisture and retains its strength when wet. Future research should assess the strength of shoeboards after repeated wetting and drying cycles. The results of this study are applicable to the shoe industry.