Executive Summary: High-Value Ion Exchange Materials Derived from Collagens

Summary of Project and Key Findings:
Based on the need to focus on developing high value materials from low value feedstocks, the decision was made to explore development of this collagen-based ion exchange chemistry for ovine (sheep) hides. Bovine foetal tendon collagen like that used for the initial studies has significant commercial value, but the ovine hides are dumped in large quantities.

The collagens in tendons and hides are classified as fibrillar, constituting mostly type I and III collagens. Glycine-proline-hydroxyproline is the primary repeating unit in the amino acid sequence of collagen. The hydroxyl group (-OH) of hydroxyproline (Hyp) present in the side chains of collagen is targeted for functionalization. The modification process for the bovine foetal collagen is carried out in two steps: 1) activation of the hydroxyl (-OH) groups using sulfonyl chloride and 2) nucleophilic substitution by amines. The 1,4-bis(3-aminopropyl)piperazine functionalized materials (polyamine system) were tested for the ability to exchange anions, and the taurine (2-aminoethanesulfonic acid) functionalized materials (polysulfonate system) were tested for the ability to exchange cations.

The key challenge in developing similar chemistry for hides proved to be in processing the hides to produce materials suitable for the functionalisation chemistry. The commercially available bovine foetal tendon material comes as a powder, whereas the hides could only be processed to give much larger pieces, with an irregular size distribution. The presence of wool on these hides, or the chemical consequences of depilation procedures to remove the wool, also interfered with the functionalisation chemistry, to the extent that minimal or inconsistent ion exchange properties were observed.

It was determined that low value hide-based collagens could not be easily functionalised in the same way as the bovine tendon powders.