Study And Characterization Of Moisture Permeability Of Thin Natural Cow And Sheep Leather And Its Modified Coating

Based on the research theories and methods of fabric moisture permeability principle,least square fitting,and molecular dynamics simulation,this paper uses SEM,FTIR,and other instruments to characterize the thin natural cattle and sheep leather and modified leather,explore the relationship between its moisture permeability and internal and external factors,and elaborate its mechanism from a microscopic perspective.Firstly,the natural leather was cut into five kinds of thin cow and sheep leather with different thicknesses,and different modified coatings were added.The change of moisture permeability of different leather with nano-Ti O₂ mass fraction,temperature,thickness,and time was investigated by combining the characterization results;Secondly,the corresponding three-dimensional surface and mathematical model were established by MATLAB to explore the comprehensive impact of multiple factors on the leather moisture permeability and predict the leather moisture permeability under unknown conditions;Finally,the molecular dynamics simulation characterization was carried out by Gromacs to explore the change mechanism of moisture permeability of natural leather and modified leather from the molecular level.The specific research contents are as follows:（1）SEM characterization showed that the collagen fiber bundles of sheep leather were arranged more closely and the fiber gap was smaller than that of cattle leather,which led to the lower moisture permeability of sheep leather than cattle leather on the macro level.With the increase of nano-Ti O₂ mass fraction,the surface of the modified leather gradually became rough and agglomerated.FTIR analysis showed that the strength of the characteristic peak of Ti O₂/WPU at 1620 cm^-1 gradually increased,and the amide carbonyl peak at 1705 cm^-1weakened;The absorption peak of Ti O₂/WAA at 1625 cm^-1 becomes stronger,and the C=O at1725 cm^-1 decreases;Moreover,nano-Ti O₂reacts with WPU and WAA to form a kind of ether bond,which has strong interaction.（2）The moisture permeability of thin natural cattle and sheep leather decreased with the extension of time and tended to be stable at the end,and the time node to be stable was about2h.The relationship between moisture permeability（Y）and temperature（T）conforms to Y=a0)^{（7）,and the relationship between moisture permeability and thickness（x）conforms to Y=ax+b.For example,the regression equation of Y and T for 0.5mm cow leather is Y=1.15900.05093},and the regression equation of Y and x for cow leather at 60℃is Y=-11.06x+30.24.（3）The changing trend of moisture permeability of modified leather with various factors is consistent with that of thin natural leather,which increases with the increase of temperature,i.e.60℃>55℃>50℃>45℃>40℃;It decreases with the increase of thickness,i.e.0.5mm>0.6mm>0.7mm>0.8mm>0.9mm;It increases with the increase of nano-Ti O₂ mass fraction,i.e.6%>3%>1%>0%;Its"self hygroscopic time"is longer than that of thin natural leather for 2h.It was found that the moisture permeability of modified cow leather was better than that of modified sheep leather;When the mass fraction of nano-Ti O₂ is 0%,1%,and 3%,the moisture permeability of WAA-modified leather is better than that of WPU modified leather on the whole.When it is increased to 6%,the moisture permeability of the latter gradually equals or even exceeds the former;With the increase of nano-Ti O₂ mass fraction,the moisture permeability of modified leather gradually tends to natural leather.（4）Through 3D surface fitting,a total of 18 multiple regression equations between moisture permeability and temperature and thickness are obtained,for example,the regression equation of thin cow leather is Y₁=0.02987²-0.1679+0.03092²-0.8012-2.312+57.19.Through equation coefficient analysis,the influence on moisture permeability of thin natural leather was obtained,temperature>thickness;For modified leather,thickness>temperature.（5）Through molecular dynamics simulation and characterization,it was found that the changes of RMSD,Rg,Dis,RDF,and hydrogen bond physical quantities all showed that the molecular movement of leather protein was more intense,the structural stability was worse,the atomic binding tightness was weakened,the intermolecular force was reduced,and the molecular spacing was increased with the increase of temperature,which was confirmed by the experimental results.Compared with PU-1CGD and AA-1CGD,it was found that the RMSD of AA-1CGD fluctuated more with the rise of temperature,and Rg and Dis fluctuated more with the rise of temperature,and the value was greater;The probability of AA molecule distributing in a short distance and the number of hydrogen bonds of 1CGD protein molecule at five temperatures are less than PU molecule,which explains the reason why the moisture permeability of WAA modified leather is higher than that of WPU modified leather at five temperatures.This paper studies the moisture permeability of thin natural leather and modified leather,so that thin natural leather can maintain good moisture permeability while being endowed with excellent performance of finishing agent,which provides a theoretical basis for the research of leather clothing comfort,and helps enterprises learn from and improve to develop new products with better performance.