The biennial IULTCS International Congress is the most important international showcase for the leather industry and this year’s programme highlighted advancements in leather science and technology, industry, material testing, performance and applications, and sustainability. The event took place in Dresden on the 25-28 June 2019 with 450 delegates attending from 35 countries. The theme of the Congress was ‘Benign by Design’ – a principle in many green chemistry and sustainability initiatives. Modern chemical solutions should aim to end deterioration of the environment – this needs to be a clear message to scientists.

The keynote address, The Heidemann Lecture, was given by Dr Kheng-Lim Goh, Associate Professor, Mechanical Engineering & Director of Research, Newcastle University, Singapore. Dr Goh’s presentation “As tough as leather: Macro to nano scale perspectives of collagen stability” outlined findings from recent studies on the mechanics of collagen in connective tissues. In a deeply scientific paper, he looked at the factors affecting collagen stability in tissues and how to use this knowledge to understand and build structural applications to provide feedback for better product design. In concluding the 45-minute presentation, Dr Goh told delegates that his three takeaways from the presentation were to have a fresh look at the degree of collagen fibril alignment in tissue and rethinking the mechanics of crosslinking between collagen fibrils. He also stated that interfibrillar mechanics are governed by plastic stress transfer and the influence of fibril diameter on interfibrillar stress transfer.

LASRA was represented by a team of four scientists, who gave three oral presentations and one poster presentation. The oral presentations were:

Dr John Liu (Pictured)

Biotechnology for environment-friendly leather production

Abstract. LASRA research is guiding the application of biotechnology to help the New Zealand leather industry develop environmentally sustainable leather processes. Using 16S rRNA gene sequencing, we have isolated and identified a number of indigenous bacteria from the leather industry environment which are being adopted to develop benign leather processing technologies. We isolated and identified several Bacillus strains from a biofilter used in a leather manufacturing plant which exhibited sulphide oxidation activity, which are being applied in bioremediation of volatile organosulphur compounds emitted by leather products. We also discovered a strain of Stenotrophomonas spp. with significant and beneficial proteolytic activity in a tannery sludge. The identified strain not only displays collagenase activity but also the ability to reduce hexavalent chromium to trivalent chromium, making it an ideal candidate for biodegradation of tanned waste. Recently we revisited the natural autolytic processes of degradation of untreated pelts to guide a natural depilation method without any need for additional chemical treatment. In controlled experiments the wool could be removed completely from follicle after 2 days, without obvious damage and leathers could be processed with mechanical properties comparable to conventionally processed counterparts. The alkaline protease activity of the isolated bacteria is responsible for the observed natural unhairing.

Dr Sujay Prabakar

Towards a molecular level understanding of chrome tanning

Abstract. Synchrotron based small-angle X-ray scattering (SAXS) is a powerful technique that has helped us understand the changes in molecular-level collagen structure during tanning and denaturation (shrinkage). Based on SAXS results from real-time denaturation experiments on leather samples, we established a mechanistic model of chrome tanning indicated by the structural changes of collagen. It suggests that only a low level of chromium is effectively involved in cross-linking with collagen, highlighting the overuse of chrome during conventional tanning processes. Any extra amount of chrome added, however, can support the stabilisation of collagen – possibly via a non-covalent mechanism. Such a mechanism points towards a more environment-friendly tanning method by using suitable supplementary reagents to benefit the tanning effect non-covalently instead of by chrome. Also, by pre-treating with complexing agents such as sodium formate and disodium phthalate, as well as nanoclay (sodium montmorillonite), the uniformity of chrome penetration through the bovine hide collagen matrix can be improved significantly. These pre-treatments effectively reduce the reactivity of chromiumduring its cross-linking reaction with collagen while retaining bound water. However, collagen pre-treated with a covalent cross-linker (glutaraldehyde) results in a decrease in both the chromium-collagen cross-linking and bound water while improving uniformity. These molecular-level insights can be developed into metrics to guide us towards a more sustainable future for the leather industry. Further, coating on collagen fibrils can provide a pseudo stabilisation effect by increasing the hydrothermal heat resistance of collagen. Overall, synchrotron SAXS provides valuable information about changes in the collagen structure that could lead to more efficient use of chrome (or other tanning agents) in the global leather tanning industry.

Dr Rafea Naffa

Strong skin, not always thick: Comparative structural and molecular analysis of deer skin and cow hide

Abstract. A comprehensive analysis of the molecular and structural components of deer skin and cow hide was undertaken. These skins are known to be strong. However, they derive their strength from different combinations of molecular and structural properties. Firstly, the physical properties of deer skin and cow hide including tensile strength, tear strength, and denaturation temperature were measured. Secondly, the structure of the collagen fibrils and glycosaminoglycans was investigated using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Finally, the chemical composition of deer skin and cow hide, such as amino acids, crosslinks and glycosaminoglycans, were analyzed. Our results showed that the physical properties of deer skin and cow hide are derived from different combinations of several chemical components, resulting in a different architecture. It was found that the large and “wavy” collagen fibers in deer skin are made up of collagen fibrils with small diameters. Additionally, deer skin fibrils appeared to be linked by regular arrays of filaments of large glycosaminoglycans that are distributed uniformly. Deer skin contained a higher proportion of trivalent collagen crosslinks. In contrast, the collagen fibrils in cow hide were larger, contained a diverse glycosaminoglycan distribution and a higher proportion of tetravalent collagen crosslinks, resulting in straight collagen fibers. This study suggests that although deer skin and cow hide are both strong, they have different structural and molecular features.

Poster Presentation:

Mr Ethan Zhang

High-efficiency chrome tanning using pre-treatments: synchrotron SAXS and DSC study

Abstract. Pre-treatments are widely used during tanning processes to improve the performance of the main tannage. Synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to study four common types of pre-treatments, viz. a monodentate complexing agent (sodium formate, SF), chelating agent (disodium phthalate, DSP), covalent cross-linker (glutaraldehyde, GA) and nanoclay (sodium montmorillonite, MMT) to learn about their effects on chromium-collagen cross-linking reaction during tanning. Based on the results, the performance of chromium-collagen cross-linking with and without individual pre-treatments was presented based on five parameters: degree of cross-linking, level of hydration, hydrothermal stability, uniformity through the leather cross-section and the relative uptake of chrome. Comparison with ThruBlu chrome tanning, at the same chrome offer levels, on leather pre-treated with SF, DSP and MMT showed improved hydrothermal stability, uniformity and an increased level of hydration, while GA pre-treated leather showed a decreased level of hydration. All of the pre-treatments reduced surface fixation by decreasing the reactivity of chromium with collagen. Changes in the reaction performance can influence both the properties of the leather products as well as the efficiency of the leather manufacturing process. Insights into the structural changes of collagen during tanning with varied reaction conditions can help guide the design of novel, benign tanning processes with reduced environmental impact.