Natural Leather For Apparel And Its Modified Coating Moisture Permeability Study

Heat and moisture comfort is one of the important factors affecting the wearing comfort of natural leather,among which moisture permeability plays an important role.In this paper,we take natural cowhide and sheepskin,which is widely used in the apparel field,as the research object to explore the changes of its moisture permeability performance with internal and external factors.After the modified coating,the relationship between the moisture permeability of natural and modified cowhide and sheepskin with internal and external factors such as thickness and temperature was obtained experimentally.The two-factor regression equation of moisture permeability with temperature and thickness was obtained by using MATLAB to establish the fitted surface of moisture permeability with temperature and thickness.Further,gromacs molecular dynamics simulation method was used to investigate the causes of moisture permeability changes of natural leather in different environments and to explore the effect of temperature on the spatial structure of natural leather proteins at the microscopic level.The details of the study are as follows:(1)The scanning electron microscope test showed that the collagen fiber bundles inside sheep leather were tightly arranged,while the fiber bundles of cow leather were more loosely arranged with large fiber gaps.After analyzing the data,it is concluded that the moisture permeability of natural cow and sheep leather is inversely proportional to the thickness,and the overall trend is that the moisture permeability of cow leather>sheep leather.The moisture permeability of both cow and sheep leathers decreases with the increase of moisture permeability time and then tends to be constant,and both of them have the process of self-absorption for about 2 h.The moisture permeability of cow leather>sheep leather.The moisture permeability of cow and sheep leather increases exponentially and rapidly with the rise of temperature.The moisture permeability of cow leather basically remains at70(kg/m224h)when the temperature is higher than 60?,and that of sheep leather remains at65(kg/m224h)when the temperature is 60?,and the overall size of moisture permeability is cow leather>sheep leather.(2)Modified films were prepared using 0%,2%,5%,and 10%mass fraction of nano-Si O₂for waterborne polyurethane(WPU)modification,and the IR spectra showed that the two underwent chemical reactions to form ether bonds and strong interactions existed.The SEM images of the modified film showed that the surface of the modified film was smooth when the nano-Si O₂content was 0%and 2%;when the nano-Si O₂content increased to 5%and 10%,the nanoparticles agglomerated and local pores appeared.The variation of moisture permeability of modified cowhide and sheepskin is consistent with that of natural cowhide and sheepskin.The moisture permeability was proportional to the mass fraction of nano-Si O₂,proportional to the temperature and inversely proportional to the thickness.The moisture permeability of modified cowhide and sheepskin decreased with time and then stabilized,and there was a 1.5 h self-absorption stage,and the overall moisture permeability was modified cowhide>modified sheepskin.When the mass fraction of nano-Si O₂is 0%and 2%,the modified film pores are smaller than the pores of natural leather,and the moisture permeability is smaller than that of cowhide and sheepskin;when the mass fraction of nano-Si O₂is 5%and 10%,the nano-particle agglomeration on the coating surface destroys the film structure,and the moisture permeability is close to that of cowhide and sheepskin.(3)After surface fitting,10 regression equations between moisture permeability z and temperaturexandthicknessy,suchassheepskin equation:z46.7 62.281x8.288y0.03425x~20.3409xy1.198y~2were obtained.The effect of temperature change on the spatial conformation of natural leather proteins was microscopically simulated using gromacs,and the results showed that:the protein deformation increased with the increase of temperature,the mean value of RMSD increased from 0.25 nm to 0.28 nm,and the mean value of Rg increased from 2.55 nm to 2.575 nm;the molecular motion was accelerated,and the protein spatial structure was unstable,which was shown macroscopically that,with the increase of temperature,the leather structure is loosened and the moisture permeability increases.This paper studies the moisture permeability performance of natural and modified cowhide and sheepskin to provide a theoretical basis for the exploration of leather apparel comfort.To keep the excellent performance of natural leather in taking and optimization,and to further implement functional finishing in moisture permeability performance modification will help enterprises to learn from the improvement,so as to develop new products with better performance.