A hundred years ago, Messrs Kerr, Teas, Levi, Alsop, Reed et al were sitting in a St Louis hotel holding the first ALCA convention. At the time, the ALCA had 19 active members and nine associates. According to the JALCA, most of the early conventions discussed the by-laws of the fledgling society and the standardisation of commercial methods. However, there were papers read, such as ‘A method for the detection and estimation of soluble leather in tanyard liquors’ and the ‘Curiosities of cutch’ (a weed), which apparently was causing trouble for Kent fishermen drying their nets!

Anyway, what they weren’t talking much about was the structure of what they were tanning and it was not really until John Arthur Wilson came along a few years later that the science of leather technology took off in America.

Wilson was a superb leather chemist who investigated many areas of leather science and its application to the leather industry of his time. He is commemorated annually in a lecture given by an eminent scientist of the current age. This year, the committee chose Dr Jaume Cot of the CSIC, Barcelona, Spain, current president of the IULTCS and a leading leather chemist, who spoke about ‘An imaginary journey to the collagen molecule for a better understanding of leather waste treatments.’

He said: ‘Like a Jules Verne novel, this lecture pretends to conduct a virtual journey around the collagen molecule, in order to focus on the most important features of this unique protein.’ The journey started by discussing the modifications to the protocollagen polypeptide in the endoplasmic reticulum, which include hydroxylation, glycosylation and disulfide-bond formation. Interchain disulfide links between three of these peptide chains aligns them to form the triple helix.

Cot said that all the modifications occur in a precise sequence so allowing lateral alignment and the formation of the triple helix. The structure is then built up using lateral alignment and formation of covalent crosslinks enables the helixes to pack into 50nm diameter fibrils. How the staggered arrangement of collagen molecules gives rise to the striated appearance of the negatively stained fibril was also discussed, the 67nm periodicity, collagen types, the importance of hydroxyproline content, and the non-collageneous proteins such as the glycosaminoglycans, elastin etc, were also fully investigated.

He then reviewed chrome-tanned collagenic wastes and the different treatments available for this type of waste. The main ones, he said are: strong chrome complexing agents; calcium hydroxide hydrolysis at 100ºC; and alkaline oxidation of chromium (III) to chromium (VI) by the action of hydrogen peroxide. Being part of CSIC’s work, this technology was described in detail.

The lecture also reviewed dechroming processes; chromium (VI) recovery through an ion-exchange resin; the isolation of new biopolymers; and defined some options for different industrial uses of the waste materials. He said that the biopolymer isolated from chrome-tanned collagenic wastes could be applied directly to the paper, wood, ink, textile and leather industries as binders, biodegradable biopolymers, and protein-based self-feeding biodegradable flower pots, fillers, retanning agents; as a casein substitute in photography, adhesives etc. A second possibility would be to produce low formaldehyde content eco-adhesives and collagen-based ‘smart’ fabrics etc by chemical reaction with these biopolymers.

Unlike the first few conventions, papers at the 100th were presented on a wide variety of topics including beamhouse operations, the chemistry of tanning, automotive finishing and upgrading systems, a geopolitical summary of the leather industry over the past 50 years and a number of papers dealing with waste reduction. In addition, there were several papers presented regarding lean manufacturing practices, a discussion of technology management in complex leather networks and several presentations regarding the very latest technology and equipment for both tanning and drying. Obviously, it would be impossible to review all the papers here, but I hope that this short piece will encourage readers to join the ALCA.

Improving hide quality

M A Bonds, C R Richardson, and D C Shelly from Texas Tech University in Lubbock, discussed the nutritional and production influences on hide quality in cattle. They said that hide defects in feedlot cattle continue to steal potential profits from the beef cattle industry in the US through management and nutrition-related practices. Some of these hide damaging practices include branding, failure to dehorn, scratching and scarring from use of poorly-designed fencing and handling equipment, by not controlling parasites and blood vessel veining from extended time in feedlots.

Cooperative agreements were developed with feedlots in the Texas High Plains and Tyson/IBP to conduct a two-year study with finished feedlot cattle of known source, breed type, implant status, nutrition programme, and days on feed. The study, which is in progress, involves collecting information about groups (pens) of finished steers and heifers at market time from cooperating feedlots on carcase weights, carcase grade and yield, and hide defects.

All cattle are being fed under the same corporate management and feeding regimen, and detailed composition of the diets fed and complete hide quality information are being obtained from the cooperating agencies. Preliminary data collected from steers of similar breeding, nutrition and days on feed, but differing only in final weight at marketing, show hide quality differences.

The heavier steers (619kg) had higher percentages of hide damage due to veins (88% vs. 79%) and mechanical handling (40% vs. 22%) than the lighter steers (523kg). These data indicate that hide quality is different in feedlot steers of similar breeding and management and this results from increases in veins and mechanical damage as final body weight increases.

Investing in raw material

In discussing broader raw material quality issues, Phil Hadley, BLC Leather Technology Centre, said the investment in raw material represented by far the single largest cost to the leather processor yet. As Shelly and his co-workers have shown, it is the element that the tanner frequently has least control over.

The lifecycle of meat animals offers many opportunities for damage to occur including on the farm, during transport, slaughter and preservation. Work at the BLC has investigated the impact of ectoparasites, specifically the biting louse, Bovicola bovis, on hide quality and appropriate measures to control this commonly occurring pest.

In trials involving more than 500 cattle, the impact of exposure and treatment with commercial ectoparasiticides was evaluated and leather quality and value assessed accordingly. Animals slaughtered while infested with lice gave hides with low grades and significant levels of light spot and fleck damage. Animals slaughtered, having been cleared of lice for a minimum of six weeks, gave hides with reduced levels of fleck and this improved further up to 13 weeks, although full resolution of damage did not occur. Animals kept lice-free throughout their two-year life span consistently gave hides of high quality with no light spot damage.

A further trial evaluated the impact of treating calves at 12 weeks of age and keeping them lice free to slaughter at two years compared with calves that did not receive lice treatment. The untreated calves developed natural lice infestations and their hides displayed higher levels of light spot damage at both chrome tanned and dyed crust stages.

Hadley said the findings of the work suggested that lice cause damage to bovine hides that may demonstrate elements of resolution or healing but this is unlikely to resolve completely following treatment.

Recycling reagents

In the ‘good-old-days’, a beamhouse waste liquor would have consisted of arsenic, dog or pigeon dung and little regard for health and safety. However, as things have advanced, new and cleaner alternatives to lime and sulfide have been sought.

Rapid oxidative dehairing has been an ongoing project at the USDA, and Robert Dudley gave a paper that looked into the intricasies of recycling the dehairing reagents. He said there was a continuing interest by the packing industry in the use of rapid dehairing as a pathogen reduction step. However, any such procedure must not compromise the quality of the resulting hides.

The Eastern Regional Research Centre have been developing sulfide-free, oxidative processes for rapid dehairing, and recycling

of the oxidative dehairing mixture is required for the protocol to be a commercially viable option. Dudley said that in lab-scale experiments using a peroxide/cyanate system, the dehairing agent was successfully recycled five-to-seven times, and they found that a number of factors eventually affected the agent’s efficacy.

He said that after seven-to-nine cycles, NaOH, KOCN, and H2O2 were consumed and solubilised protein began to interfere as a buffer, dropping the pH below 13. The hydrogen peroxide concentration dramatically dropped during the first three cycles of the dehairing solution and then remained at a constant, but still effective, concentration of 1-2ppm.

The protein concentration was dependent upon the length of the hair, but generally after three cycles was between 24-40g/l. Removal of the insoluble hair (roughly 60% of the protein in the waste stream) did not affect the efficacy of the dehairing solution, but somewhat higher H2O2 concentrations (>10ppm) could be maintained when the solids were removed.

Improving beamhouse quality

There were also papers concerning the pre-tanning process or changes to the collagen structure. Trumpler’s Dr Thomas Feigel’s ‘Approach to negate quality problems in the beamhouse’, offered some practical hints on how some of the most typical quality problems from the beamhouse might be avoided or at least reduced in the production from green to blue. And Sam Mozersky, from ERRC, discussed the immunochemical estimation of the Decorin core-protein content of preparations of bovine Decorin.

One of the problems that leather scientists have had with investigating the tanning proces is that even in 1904, any tanner worth his salt could produce a piece of high quality leather, relatively low effluent discharge and yet not know what was going on at the fibril level.

Even now, there is no clear-cut answer but the latest ideas suggest that although different tanning agents are used, the mechanism of tanning may be the same regardless of whether it is a metal tannage or a non-metal one. Both Dr Ellie Brown from the ERRC and Professor Tony Covington, BSLT, spoke about the latest attempts to investigate just what does go on when leather is ‘tanned’.

Dr Brown, in her lecture ‘An approach to a tanning mechanism: Study of the interaction of aluminum sulfate with collagen’, said tanning is accomplished through the use of reagents that stabilise the collagen matrix.

The molecular characteristics of tanning agents are quite varied and led to the expectation that leathers produced with different tanning agents would have fundamentally different structures. However, current proposals suggest that the structural similarities between leathers produced with different tanning agents are likely to be greater than the differences.

She said that the goal of this work was to contribute to the elucidation of a general mechanism for tanning. In her study, the interaction of aluminum sulfate with collagen was investigated using techniques not even invented in Alsop’s day.

Brown said that in a model system, using soluble collagen 13C NMR spectroscopy showed that Al(III) formed a complex with carboxyl groups on collagen, while the spectra from 27Al NMR suggested the formation of a second sphere complex between collagen and aluminum.

The effects of Al(III) binding on the thermal stability of collagen were also studied, using circular dichroism spectroscopy of soluble complexes and differential scanning calorimetry of insoluble complexes. Dr Brown said she hoped a comparison of Al(III)-collagen interactions with Cr(III)-collagen interactions would provide an insight into a more generalised mechanism for tanning.

Collagen and plants

Prof Tony Covington spoke about ‘Collagen and plant polyphenols: new relationships and new outcomes’. The use of vegetable tannins was the main tannage 100 years ago, as many of the papers in the JALCA of that day highlight. This traditional process continues today in the production of native tanned skins and heavy leather.

However, Covington has recently used vegetable tannins in a different way: to develop organic tanning agents for modern purposes; ie with a high hydrothermal stability.

He said that a problem to overcome was the astringency of the tannins. But the use of non-tans, either from natural sources such as green tea or by degrading tannins into non-tannins, avoids the problem of hindered penetration through the pelt due to the reactivity of the polyphenols. He showed that both tannins and non-tannins are capable of engaging in combination tannage with aldehydic agents, and confer high hydro-thermal stability to collagen.

Therefore, the use of non-tannins provides a practical route to modern organic tanning. He pointed out that a feature of this type of stabilising mechanism for collagen is the creation of a polyphenol matrix around the triple helix, which has the added benefit of actually strengthening the leather. Since every traditional process step effectively weakens collagen, especially tanning, this is the first chemical reaction that has been shown to reverse that effect.

Other papers connected with the tanning process were the ‘Application of soluble silicates in leather production’ from Karl Heinz Munz; ‘Glutaraldehyde-tanned leather treated with tocopherols’ by Cheng Kung Liu from ERRC; and ‘A comparison of chemical, physical and enzymatic crosslinking of bovine type I collagen fibrils’ from Gennaro Maffia and co-workers at the department of chemical engineering, Widener University, Chester.

Increasing area yield

An area that the early 20th century tanner probably didn’t consider was maximising area yield. In those days, the markets were ‘local’ in comparison with the worldwide trade seen today, and given that most leathers were vegetable-tanned, the cutting area was less important than today.

Recently, there have been a number of research projects to investigate increasing area yield, and one, from Novozymes, was presented at ALCA 100 entitled ‘The latest advances in enzymatic technology for area expansion’. Lars Rasmussen from the company said that although the main application for enzymes is related to the area yield increase of soft leathers – upholstery, automotive and garment – the shoe upper production using enzymes has proven its value regarding the upgrading of the finished leather.

He said the best area yield results on automotive and furniture upholstery leather were obtained at pH values around 6.4-7.0, during the neutralisation step. For many tanneries, this pH range is higher than that normally used, and the main concern is this pH range can lead to grain looseness. However, trials carried out on different raw material resulted in leather with tight grain and an improvement in area yield of up to 4%, compared with normal production values.

Rasmussen said that the production of shoe upper leather had benefited from the enzyme treatment, even working at lower pH values. In this case, higher dosages of enzymes are used because the main goal is to improve the grading of the finished leather.

The enzymatic treatment hydrolyses and removes the elastin fibres present in the hide. Since the elastin is more concentrated around scars, the enzymatic action relaxes the structure of the hide close to the scar tissue. This results in leather with flatter grain and improved printing quality and cutting area.

As ever, finishing threw up a crop of interesting papers with Jerry Levy, former ALCA president, leading the way. He talked about crosslinking and its effectiveness at coaxing the highest performance out of both on-site applied and industrially applied coatings in industrial fields as diverse as coating of spacecraft and finishing of leather. There has been an evolution in the nature of what is used by those who finish leather as: performance targets edge ever upward; tolerance for VOC edges ever downward; limitations on choices of organic carrier solvents and coalescents grow; acceptable chemistries narrow; and convenience and pot life re-emerge as important criteria.

His paper presented an overview of crosslinking in the context of the industry and compared the latest technological advances with respect to oligomeric polycarbodiimide and polyisocyanate types. A paper well worth looking out for in a future JALCA.

Another ALCA stalwart, Wolfgang Wenzel, from Bayer Chemicals, spoke about ‘Organic solvents in aqueous finishes for leather’. Strangely, so-called water-based systems contain a certain amount of organic solvents and other volatile organic compounds.

They are added to improve the physical properties of the finish, but as Wenzel said environmental legislation is forcing tanneries to reduce or avoid VOCs and especially organic solvents. His paper described the physical and technical background of the use of VOCs in finishing and discussed the possibilities of reducing them. There were also papers on finishing from TFL, Clariant and Rohm & Haas.

Another area that tanners in 1904 would have thought little about was the recycling or re-use of waste. As with everything, times change and Karol Kolomaznik, from Bata, Zlin, spoke about the ‘Total recycling technology of chromium from liquid and solid tannery wastes’, while Jack Gibbs from Auckland University of Technology investigated the ‘Recovery for re-use of vegetable tan liquors’.

This is something, thinking about it, our forefathers readily did when they used spent vegetable tan liquors either to mend other tanning baths, or to give hides a mild pretannage before they entererd the stronger liquor baths.

One piece of equipment the 1900 tanner had little control over was the drum, and I bet they didn’t have anything like the sophistication that Olcina’s Joaquin Paez showed the audience. Cangilones Drums, an Olcina-patented technology, has replaced centrifugal force as the main source of mechanical action with gravitational force and mass effect.

Thus, the drums allow excellent interaction between chemicals and hides at extremely low speeds, with all the advantages of water and chemical savings and reduced hide damage this entails.

Finally, in their usual nod to the past, the ALCA presented the Fred O’Flaherty Service Award. This year, the recipient was Frank Rutland, former head of the LIA, for his many contributions over the years to the association and the industry as a whole. Satyendra De, formerly with Garden State Tanning, was awarded the coveted Alsop Award, an award in memory of the ALCA’s first secretary.

The current president, Rodney Hammond was pleased to tell the audience that the association has seen a substantial gain in membership over the last year, with 54 new members, something I am sure delegates at the first ALCA Convention would be delighted about.