An annual meeting of technical representatives from Member tanners and fellmongers is held at LASRA to steer all research projects for the following year, including agency-funded research. Results from the previous year’s work are reported on and discussed, and suggestions for follow-up work or new projects are proposed. A second meeting is held later in the year prior to the Conference to provide a running update on progress.
A rating scheme is used to prioritise the projects, ensuring only relevant research is conducted as a priority.
RESEARCH ACHIEVEMENTS 2017
The Industrial Technical Advisory Group (ITAG) biannual reporting programme provides more frequent updates to industry on current research.
The programme provides updates from the dedicated and professional research staff at LASRA on research activities carried out on behalf of Industry. The first meeting of the year is held in March at LASRA, identifying the priority areas for research over the coming year. Our committee use a rating scheme to prioritise on a scale of 1-3, where a rating of 1 means the research is of urgent need.
Summaries of a few of completed research projects from 2017 are provided below as examples of the breadth of research being carried out by LASRA scientists on behalf of the industry.
Proof of concept for the use of amino acid analysis to monitor the progress of liming
The liming process is used to remove hair and epidermis from hides/skins and to ‘open up’ the fibre structure. By measuring differences in the amino acid make-up of hide/skin processing liquors we can quantify the changes that occur during liming.
Aspects to potentially quantify include;
- The reduction of keratin specific amino acids from the skin, with an associated increase of keratin specific amino acids in the liquor
- The reduction of collagen specific amino acids from the skin, with an associated increase of collagen specific amino acids in the liquor
- The reduction of non-collagenous specific amino acids from the skin, with an associated increase of non-collagenous specific amino acids in the liquor
Through quantification of these indicators we intend to quantify changes in the liming process to the point where we can recommend best practice for maximum removal of epidermis and hair, while minimising the loss of collagen and enabling optimal ‘opening up’ of the structure.
Our preliminary amino acid analysis of the limed hide has identified a reduction in the keratin specific amino acid cysteine which occurs during liming.
Impact of float length on reagent diffusion time
In this work, the mathematical description of reagent diffusion was used to prepare a nomogram like Heisler charts already in use, for unsteady state heat transfer in simple shapes.
The goal was to apply the equations used in this work to previously published data for the diffusion of salt through hides during soaking, to determine the validity of the equations used and hence the validity of the chart that was developed.
By applying the equations published in Crank for reagent diffusion in one dimension, with a given float ratio to the data for salt removal in soaking published by O’Brien, the removal of brine salt into the wash water fits the data well.
Examination of the equations describing diffusion through a one-dimensional sheet has allowed for the development of a chart, which can be used to assess the impact of changes in float ratio on reagent penetration times.
The effect of long term storage on strength
Over the course of 18 months, skins held in the pickled condition lost less strength in comparison to those stored in the salted condition. The difference was significant in the first 6 months of storage.
Some mould was observed on pickled skins at 12 months. There was considerable mould observed on pickled pelt and some scattered mould on the salted skins after 18 months storage in these conditions.
We suspect that the relatively high temperatures observed resulted in destruction of protective TCMTB and subsequent moulding of the stored material. It is interesting to note that even in the relatively mild conditions of Palmerston North temperatures inside a storage container routinely reached above 40°C in summer.
Our animal study carried out in collaboration with AgResearch on FarmIQ sourced lamb skins concluded in 2017. These skins were processed as part of a pilot industrial trial to better understand the strength benefits of the LASRA footwear process.
Samples were taken from each skin and preserved in salt. Following processing of the skins to crust leather, each was assessed for its physical properties and the ten weakest and 10 strong lamb skins were identified, and the retained samples analysed to determine if there were any differences in the natural crosslink quantities between the two groups.
The types and amount of collagen crosslinks in the selected skins were measured using a method we have published. Overall, a strong correlation was found between the strength of the selected skins and the quantity of natural collagen crosslinks present, including both immature and mature crosslinks.
We have subsequently developed a process which allows these natural crosslinks to be measured at later process stages, even after tanning.
Although chrome is the most commonly used and versatile reagent in leather tanning, the stabilisation mechanism on collagen remains poorly understood, based on a lack of available molecular level information.
Small-angle X-ray scattering can detect changes in the collagen structure at the molecular level. The combined use of in-situ SAXS analysis and shrinkage determination by DSC enabled the effects of increasing chrome offers on the structure and physical performance of tanned hide to be measured.
Despite an observed increase in the shrinkage temperature of hide with increasing chrome offer, we saw that there were no noticeable changes in molecular stability beyond a chrome offer of 2.5%. Chrome is known to stabilise the collagen molecule by cross-linking to its active sites, so the lack of further change to the molecular stability indicates that these crosslinking sites must be fully occupied, at what would be considered a relatively low chrome offer.
We believe that instead of forming covalent cross-links the additional chrome interacts non-covalently with the collagen matrix, imparting improvements in the shrinkage temperature in a currently undetermined mechanism.
Evidence has been provided to support a causal relationship between a high edge-on collagen fibril Orientation Index (OI) and tear strength. A relationship is found between the amount of strain applied during tanning and the resultant thickness-normalized tear strength.
The tear strength depends on the relative directions of strain applied during tanning and the measured direction of tear strength. A greater in-plane OI produces greater tear strength in both the parallel and perpendicular tear directions to give a strong linear correlation between strength and collagen fibre orientation measured edge-on.
Previously, this relationship had been seen in a range of natural collagen materials, but in this instance a material has been manufactured with improved properties, demonstrating both the causal relationship and the ability to use this to modify natural materials.
Through our investigations to find an alternative, stronger tanning system than chrome, we have conducted SAXS analysis on several wet-white tannages, assessing the structural changes caused by tanning and retanning. Generally, no changes were observed using an aluminosilicate-based retanning agent after chrome tanning, since chrome provides a robust, strong tanning mechanism, but wet-white tanning systems are bound less strongly to collagen, allowing the retanning agent scope to cause further change to the structure during retanning. This indicates that aluminosilicate retanning agents can impart improvements in both the hydrothermal stability as well as the physical properties of chrome-free tanning systems.
The Selection Committee of the IULTCS Research Commission (IUR) recently announced LASRA’s Yi Zhang as the fourth recipient of the Young Leather Scientist Grant.
Ethan’s research topic is central to current MBIE-funded research and an area of great practical interest for the leather industry: “What makes leather stronger? A mechanistic study on the effect of natural/artificial cross-links on tensile strength using small-angle neutron scattering (SANS)”.
The aim of this research is to identify the mechanisms which directly contribute to the production of strong leather. The mechanisms will be further investigated by exploring novel syntans and tannages with similar cross-linking chemistry to the cross-links shown to work in this study. The project will also help us understand the role of mineral tannages on the physical properties of leather.
Dr. Luis Zugno, the IUR Chair, stated on this fourth year of the Young Leather Scientist Grant: “This year we have received many innovative research topics and the quality of the applications has also improved”. This indicates the growing importance and interest in this grant. The Selection Committee is chaired by Dr. Michael Meyer who oversees the necessary independence, confidentiality, and integrity of the selection process.