The optimization of epoxide-based tannage systems: an initial study

Liquid epoxide resins have an obvious potential as collagen crosslinkers, in particular as alternatives to the aldehydic-types used. In the work reported here, some conditions for the effective use of epoxides in tanning systems have been studied and identified based on hide powder trials. Few commercial aromatic epoxides are found to be water-soluble, and also have relatively low reaction rates, proving another disadvantage. In a series of screening tests, it has been found that an epoxide with aromatic groups in its backbone, used to treat collagen, produces higher hydrothermal stability than that treated with aliphatic epoxide. However, of the commercial aliphatic epoxide resins examined in this research, the water-soluble, tetra-functional pentaerythritol polyglycidyl ether, (e.g. Denacol EX 411), has been shown to be suitable for the leather tannage applications. Different types of waterborne epoxide resins, including emulsion and emulsifiable resins based on BDEGA (bisphenol A diglycidyl ether), have been examined but gave disappointing results. It is thought that difficulties here lie in trying to achieve good penetration into the collagen’s fibrous structure, of the particles that make up such emulsions. Late stage tannage, giving a leather product with high shrinkage temperature (Ts = 85ºC) has been achieved; here the system required catalyst to produce acceptable conversion within 3 hr at 50ºC. The important factors influencing the effectiveness of a particular tannage, are discussed.