A polyamic acid suitable for either pretanning or retanning wet-blue in leather industry has been synthesized by polycondensing pyromellitic dianhydride with diaminodiphenyl ether. Its performances for improving physical properties of crust leather, reinforcing absorption and fixation of chromium were investigated by applying it in a reduced chromium offer system. The results show that the extension and tearing strength, especially thickness of crust leather can be significantly improved by the polyamic acid, and residual chromium in spent tanning bath could be reduced to below 40 mgCr+3/l by pretanning with the polyamic acid. The chromium released from wet-blue during fatliquoring can be reduced by 85.7%, and kept at a much lower limit of 6 mg/l by the polyamic acid. A much fuller crust leather with shrink temperature of over 95°C can be obtained with 3% of normal chrome powder by pretannig or retanning with the polyamic acid. Therefore, this polyamic acid has the good potential for industrial application in ecological leather.

A low molecular weight copolymer suitable for retanning wet-blue in leather industry has been synthesized by copolymerizing maleinuric acid with acrylic acid. Its performances for improving physical properties of crust leather, fixing the free chromium salt existed in wet-blue and scavenging the free formaldehyde introduced by other chemicals were investigated by applying it on goatskin wet-blue. The results show that the strengths and extensions, especially the softness of the crust leather can be significantly improved by the copolymer. The chromium released from wet-blue during retanning and free formaldehyde in leather can be reduced by 84.9% and 70.4% respectively with an offer of 3% the copolymer. Soft leather with very low levels of chromium release and free formaldehyde could be obtained by retanning with this copolymer. Therefore, this copolymer has the good potential for industrial application in ecological leather.