About Pu Synthetic Leather Hydrolyzed Problem
Polymer decomposition process broken into small molecules of water and moisture in the environment, called hydrolysis.
PU synthetic leatheris essentially the use of polyurethane resin processed from synthetic leather, resin properties determine the final performance PU synthetic leather products, the current system is mainly polyether polyurethane and polyester types. Hydrolysis resistance polyether resin system is much better than polyester, the reason is: the molecular chains of linear polyester polyurethane contains a lot of the more polar ester group and carbamate group is easy to form hydrogen key, leading product easier compared to a lot of air to absorb water vapor infiltration, water molecules have an effect on the polymer, its mode of action are:
One is reversible, that polymers absorb water and moisture is reversible. After absorbing polyurethane moisture in the air, the spacing between macromolecular chains increases, the glass transition temperature of the material decreases, it played a plasticizing effect, so that the material becomes soft, swelling, and then deformed.
Another is irreversible, i.e., hydrolysis of the polymer. Cracking macromolecules hydrolysis caused a direct result of the tensile strength, modulus, hardness reduction, increased elongation at break, and then the adhesive strength decreases, resulting in breakage and coating delamination.
The two processes are the same is carried out simultaneously. Also in the polymer during synthesis of acid, alkali or metal catalyst added will lead to increased hydrolysis of the ester group with reverse reaction with the water at the catalyst, i.e. hydrolysis reaction, carboxyl group is produced after the hydrolysis of polyester-urethane, carboxyl groups further hydrolysis reaction as a catalyst to accelerate the hydrolysis reaction, resulting in further cleavage of molecular chains.
Faced with these problems, how we solve it?
On the one hand, compared to traditional PU synthetic leather, CPU molded synthetic leather change the way molecular segments fundamentally from a thermoplastic into a thermoset, namely the linear molecular structure into a three-dimensional crosslinked structure, which prevents good water molecules penetrate between the molecular chains to prevent moisture and macromolecular polyurethane segment hydrogen bond formation physical residence in the molecular chain, in turn causing the hydrolysis products. Also CPU products all use polyether resin material, the resin system further ease the problem occurs hydrolysis.
On the other hand, in order to further improve the hydrolysis resistance of the resin system, we can add the carbodiimide resin system for a class of hydrolysis aid, its mechanism is as acids and water removal agent, can effectively acid or converted into water and neutralized to a harmless ureido structure, and can be embedded in the molecular chain of the molecular chain cleavage padding caused due to hydrolysis.
The test results on the current terms, CPU products in case of hydrolysis without adding additives can have up to ten years in hydrolysis