NovoCor AX is an exciting new enzyme product that can be used to increase area and softness during post tanning operations without compromising quality. The product, developed and patented by BLC Leathersellers Research Centre Ltd and Novozymes A/S, is a groundbreaking enzyme product for use on chrome tanned leather to give typical area increases of 3% within commercial production, although the original development work did indicate that the potential gains may be higher. Other benefits include improvements in softness, with no associated grain damage or looseness. The enzyme is effective on chrome tanned substrates and the technology is particularly beneficial for the softer leather types, including upholstery, wool-on and clothing leather production1.

Commercially this novel solution has already proven its success by being the single largest selling enzyme in Novozymes’ leather enzyme product range. And this only in the second year after commercial launch – a very extraordinary situation for Novozymes.

Tanneries representing all regions of the world are taking advantage of the benefits from applying this new innovative enzyme and many more are in the trial stage. Tanners are applying NovoCor AX both for quality improvement and for improved area.

NovoCor AX is marketed directly by Novozymes to selected tanneries and distributors in Asia and China and exclusive by German Trumpler in Europe, North and Latin America and Africa. This dual distribution set-up has proven its success in getting this novel technology out working in the leather industry as fast as possible.

How it works

Leather area and to a degree its softness are primarily controlled by the structural proteins and their distribution and alignment within the three principal layers of the hide or skin. The flesh layer is composed of collagen fibres that have a distinctly low angle of weave, lying almost parallel to the surfaces of the hide or skin. This layer therefore has a limited ability to stretch though a distortion of the collagen in the horizontal plane.

The corium layer is the thickest part of the skin and is composed of a matrix of interconnecting collagen fibres, which have an angle of weave approximating 45°. The area of the hide can be increased if the fibres are relaxed or stretched or equally decreased if the angle of weave is raised during processing, for example during swelling.

The grain layer has a larger area than the underlying corium because it is composed of finer fibres. In addition it adopts a convoluted arrangement, which allows it to stretch without rupturing. The reversibility of the stretching mechanism is controlled by the presence of elastin protein.

The final area of a piece of leather is dictated by the interaction of these three layers (if all present) with the grain layer and its component elastin playing the most important role within this process.

In the commonest industrial situation, the grain split of cattle hide, elastin plays the most important role in controlling the corium angle of weave and, hence, determining the area. If the flesh layer remains, as is likely in light leathers, area gain will be limited, but the softening effect will remain because the stiff nature of the grain layer will be changed.

Key to success

Area yield can be manipulated through degradation of the elastin protein thereby allowing the hide to relax. Elastin is an integral component of connective tissue, which includes skin. The protein has long range reversible deformability similar in many ways to rubber and can stretch to several times its normal length. The concept of elastin degradation to increase area is not new. Commercial enzyme formulations exist to enhance area yield prior to tanning. A practical challenge when applying enzymes to untanned hides and skins is the sensitivity of the collagen protein, which can be degraded if the process is not properly controlled. The consequence of this can be grain damage and looseness to the resulting leather.

The key to the success of NovoCor AX is the fact the component enzymes (mixture of at least one proteolytic enzyme and one elastolytic enzyme) target the structural proteins following chrome tannage. The NovoCor AX process exploits the difference in chemistry of the collagen and elastin proteins.

During conventional chrome tanning, chromium III is fixed to the collagen at the acidic side chains. This renders the collagen protein resistant (unless exposed to extreme conditions) to the effects of proeolytic enzymes (either through direct application or via microbial attack). By comparison, the lack of acidic groups in elastin means that chrome tanning has little effect on elastin which is still susceptible to hydrolysis by elastin specific enzymes. The net effect of treating chrome tanned leather with an elastase containing enzyme formulation is elastin degradation and removal without damage to the collagen and other tanned structural proteins. The chrome tanning reaction on collagen provides the safety to the NovoCor AX process: in this state, collagen is highly resistant to proteolytic enzyme attack and will only be adversely affected if the tanned collagen is damaged by heat or strong alkali, conditions unlikely to occur during post tanning processing.

Because the corium and remaining non structural proteins are fixed by the chrome tanning reaction, the whole corium structure is resistant to enzymatic attack. The looseness associated with such an attack prior to tanning cannot occur, as this arises from degradation of these components. This means tanners can use NovoCor AX safe in the knowledge that it will not damage their leather.

The enzymatic treatment does not apply to other tannages. Other tanning reactions, such as vegetable or syntan based tannages, rely in part for their effect on hydrophobic reactions with both collagen and elastin, therefore not differentiating the effects of the tanning process on the two proteins. This means the elastin would also be protected against enzymatic attack. Then, either the process of area gain will fail or the elastin can only be degraded under conditions that will also cause damage to the collagen. A consequence is that the enzymatic process must be applied to leather that has only been chrome tanned, ie during neutralisation of wet-blue, and not after retanning.

Simple to Use

The real beauty of the NovoCor AX process is its simplicity, merely requiring the enzymes to be added to the leather during the normal process of neutralisation prior to conventional post tanning operations. There is, therefore, no extra process step and the processing time remains largely unaffected.

The enzyme works effectively within a temperature range of 35-45°C, but preferably around 40°C, a pH range of 6-7 and a reaction time of 60-90 minutes. Draining the float with an optional wash to remove the enzyme terminates the process. Any residual enzyme activity will be inactivated during the retanning operations.

During trials there have been some limitations on certain types of leather, most notably within the light leather sector. The reason for this is presently unclear and further investigations are ongoing.