It is stated that the higher the degree of expansion, the less the penetration to the core of leather, and thus the lower the colloidal dispersion to the leather fiber, the lower the softness of leather, but the grain surface compactness; On the contrary, the lower the degree of expansion, the stronger the colloidal dispersion to the leather fiber, the softer the leather, the more elastic and extendable.
Some traditional views in China believe that to make leather plump and soft, we must increase the amount of lime and increase the degree of expansion. I have seen that a domestic production area of goat garment leather, most manufacturers have not hesitate to use a large amount of lime to increase the expansion of the skin, based on their years of experience that only in this way to obtain soft and plump products.
I think there is no right or wrong between above two kinds of views, just each emphasized a side of question, if look from dialectical angle, we can carry on comprehensive expression from the following 4 respects.
(1) expansion in a certain extent can give a lose effect to the fiber, because after the naked skin filling water and expansion, the distance between the fiber and the fiber will be enlarged, make the connection of weak keys between the fiber are "tear", which make the cohesion of collagen fiber damaged on a certain extent, the extent of damage is related to the degree of expansion, after the expansion eliminate, the bonding between the fiber will be difficult to recover to the original extent, this is the reason why inflation can get plump and soft effect. But if the expansion is too strong, the cohesion between the fibers will be seriously damaged, it will bring structural relaxation and other adverse bad consequences.
(2) The rapid and premature expansion is not conductive to the uniform looseness of collagen fibers. If you use too much alkali when liming, add the alkaline materials at one time and liquid ratio complete once, it can make the bare skin surface expand swiftly and violently, intense and rapid expansion led to the blockage of the entrance to the fiber structure, and will affect the alkaline materials to permeate to the deep skin and tight part of skin, cause poor dispersing effect to inner collagen fiber, at the same time it also affect fibers dissolved and saponification of oils and fats, that is the reason why some people emphasizes the expansion degree is higher, the softness of the leather will be lower.
(3) Moderate and uniform step-by-step expansion method is beneficial to the looseness of collagen fibers, because before the expansion of bare skin, most alkaline materials have been evenly infiltrated into all parts of the skin, and there will be no obvious problem that the core of the skin contact less chemical materials, so the looseness of fibers in all parts of the skin is more uniform and consistent. In this way, the above two different views can be unified.
(4) inflation is not the only way scattered collagen fiber, by liming we can use four ways to make collagen fiber separate from each other, namely removing the fibroglia, dispelling some connection between fiber keys and expansion effect, saponification oil, of which dissolution the fibroglia is the most important form, someone says "without expansion, we can make soft leather", this words makes sense, but also we cannot ignore the expansion effect of uniform expansion to collagen fibers. For example, in the production of pig leather, whenever the expansion of grey bare skin is not good, it is bound to bring a series of problems in softness, fullness, leather yield, velvet effect and dyeing and refueling effect.