Investigation of possible use of starch as tanning agent in leather industry

The aim of the starch modification is to introduce some functional groups into the starch molecule in order to enhance the physicochemical properties and obtain the expected properties depending on field of its use. As part of the thesis, firstly the native starch, which has too large molecular size to penetrate between skin fiber matrix, was oxidized with H2O2 and NaIO4 for disintegrating into appropriate molecular size that can be used in tanning process. According to the GPC results, the starch samples which their molecular weights were reduced for penetrating into skin fibers were selected and carboxymethylation process was also carried out. The product yields, water solubilities and degree of substitutions of oxidized and carboxymethylated starches were determined. Also the structures of native and modified starches were analyzed by FTIR and NMR analysis, therefore the changes occurring in native starch structure by oxidation and carboxymethylation processes were revealed. In the second stage of the thesis, pieces of pelts were tanned with selected oxidized starches and their carboxymethylated derivatives. The tanning effects were evaluated according to shrinkage temperatures and filling coefficients. Then, whole pelts were tanned with two starch samples having the best tanning effect and mechanical properties of the tanned leathers were tested. From the results, it was revealed that the native corn starch is modified in a controlled manner and the modified starch can be used as a tanning/retanning agent in leather making.