Effects of washing and sun exposure on leather materials

Footwear has bred a rich and colorful shoe culture during the long development process. People who pay more attention to matching and dressing are more diligent in maintaining their shoes. The maintenance and cleaning of leather shoes is also completely different from that of other ordinary footwear. Leather shoes, mainly made of animal leather, are a special style of footwear.

In addition, leather shoes should not be brushed, soaked in rain or exposed to the hot sun. Exposure of leather shoes will make the leather hard, which will cause the leather fibers to become brittle and even break. But what kind of changes will the leather shoes be caused by the washing and drying methods like ordinary shoes? In this experiment, the upper materials for shoes are divided into several groups, which are respectively soaked in water and placed in a xenon arc testing machine to simulate During the sun exposure process, the softness of the leather after soaking and the folding fastness of the leather surface coating after sun exposure were measured respectively, which were intuitively reflected in the form of data, and the microscopic changes of the leather after soaking were observed.

1. Test materials and equipment:

1. Test materials: some sheepskin and cowhide for shoes.

2. Test equipment: softness tester, light fastness tester

2. Test and detection part:

1. Cut different leather samples into several 100mm×100mm samples, and divide the samples into 11 groups, of which 5 groups of samples were placed in (23±2)°C third-grade water for 24 hours (simulating leather shoes washing or soaking). );

2. Place the other 5 groups of samples in the xenon arc aging test machine for 12 hours in the sun, adjust the temperature (60±5) ℃, humidity (30±5)% (simulated leather shoes sunlight), and the remaining 1 group is a blank sample. Do nothing.

3. Put the soaked sample, the simulated sun-exposed sample and the blank sample in a constant temperature and humidity room with a temperature of 20°C and a humidity of 65% to dry for 48 hours.

4. Determination of the leather softness of 5 groups of samples and blank samples after simulated soaking and natural drying;

5. Put the 5 groups of samples and the blank sample after simulating sun exposure and natural drying in the leather flex test machine, according to the standard QB/T2714-2005 "Determination of the folding fastness of leather physical and mechanical tests" Dry test method, observe the change of the leather surface every 2000 times.

3. Results and discussion:

1. After simulated soaking of animal skin samples, regardless of whether it is cowhide or sheepskin, the softness of the leather after soaking and drying will decrease. The leather will become stiff and straight, and the softness will decrease by several to ten percent. How much. If it is leather shoes, the upper cortex of the leather shoes will become stiff and the wearing comfort will be reduced. Therefore, it can be seen that leather shoes are not suitable for washing or soaking in water. Part of the water-soluble lipids are easily dissolved in water during the water soaking process. Compared with before soaking, the soaked leather has more obvious gaps and ravines between the thicker collagen fiber bundles in the reticular layer, making the collagen fibers The absence of the "lubrication" of the fat between the bundles results in a sensory stiff leather. And the leather can restore its softness and elasticity by fatliquing it to absorb the right amount of oil, thus preventing the leather from becoming stiff, straight, or even cracked.

2. After simulating the sun exposure of the leather samples, it is found that the general trend of the leather samples is that the folding fastness of the surface coating has decreased, especially the folding fastness of the surface coating of the mirror leather has a more significant decrease and is easier to crack. This is because mirror leather has a relatively smoother surface and a thicker coating. Therefore, leather shoes should not be exposed to the sun during daily use, otherwise the folding fastness of the surface coating of leather shoes will be reduced, thus making the upper coating of leather shoes more likely to crack during wearing.

In short, leather shoes are not suitable for washing and exposure to the sun, because after washing, the leather skin will become stiff and the wearing comfort will be reduced; and exposure to the sun will reduce the folding fastness of the coating on the leather surface, making it easier to crack during wearing. So as to reduce the service life of leather shoes. Leather products can be manually brushed with a special leather cleaning agent. When the product is half dry, fat replenishment or fatliquoring treatment can restore the softness of the leather. During the tanning process, some lipids are added to the leather by emulsification. However, emulsified lipids are hydrophilic, and in the process of washing leather products, especially in the case of washing with high-concentration washing liquid, part of the lipids are easily washed off by the action of surfactants. Therefore, in order to restore the softness of the leather, it is necessary to replenish or add fat to the washed leather products. However, the folding fastness of leather products after exposure to the sun is irreversible, so leather shoes should not be exposed to the sun or close to heat sources.