TFL believes in a strong future for enzymes
By Dr Jürgen Christner, TFL USA/Canada Inc.
The use of enzymes in the leather industry has been increasing continuously over the past
few decades. TFL (and one of its predecessors, the former Röhm GmbH), industry leader
in enzymes for leather, has contributed a lot to this development. Several landmarks were
set through major innovations while further focusing on enzyme applications.
Soaking.
Modern soaking acids consist of certain proteolytic enzyme preparations which are applied
at alkaline pH. They are formulated to speed up rehydration of the hide by removing blood,
dirt, grease and proteoglycans from it. At the same time they help degreasing. Shorter
soaking times (4-6hrs) and improved layout with reduced draw and wrinkling are the major
advantages which can be achieved by using products such as PELLVIT C®. There is
another feature which makes this product outstanding: its high dependability of results.
Even ten-fold the usual working concentration will not entail grain damage, impair physicomechanical properties or aggravate damage caused by poor preservation.
Degreasing.
Lipases can be advantageous for processing hides into waterproof leather or low fog
leather for automotive applications. They break down the natural grease into partially selfemulsifiable soaps and so reduce the need for surfactants.
At the end of the eighties TFL successfully introduced an alkaline lipase into the soaking
and liming process. Synergistic formulations of proteases and lipases ,as in PELLVIT LP®,
work well when used in the soaking process. Hides with a low to medium high fat content
can be processed without addition of further surfactants. The sole use of lipase however
may result in lower softness but a tighter grain. Acid lipases can be used for post
degreasing of poor wet blues. This may be important when surfactants could impair leather
quality, as in the case of waterproof leathers.
Unhairing.
Four decades ago Röhm, now TFL, introduced the famous Arazym products for unhairing
small skins like sheep and goat. The enzymes concerned were based on fungal proteases
from certain Aspergillus strains. The products were used at neutral to slightly alkaline pH
and resulted in almost complete unhairing. The process paid off when saving of the wool
was the primary goal. It even covered the cost of the extra manual labor involved in
scraping off the loosened hair. In the case of bovine hides unhairing with this type of
enzymes was less complete and sulfides were still needed to pulp the residual hairs.
In the 1970's a further milestone was the introduction of high alkaline proteases. They
helped to cut back on sulfide and to shorten the liming process by almost half. Layout was
greatly improved and in most cases a higher area yield was obtained. The dosage of these
proteases has to be chosen very carefully to avoid sueded grain, pronounced defects,
looser grain and empty flanks, depending on the state of the hides and the specific
process conditions.
More specific enzymes greatly helped to make enzyme assisted unhairing much safer.
Enzymes like the new ERHAVIT MC® have brought about many improvements. Its gentle
proteolytic action does not impair leather quality. ERHAVIT MC strongly assists the
removal of sebaceous grease and thus enables liming chemicals to penetrate more evenly
from both sides of the hides. The result is not only cleaner hides (fig 1) but also excellent
flatness. The product is effective not only in hair pulping but also in hair saving processes.
It helps to lower the COD and sulfide load in the liming effluent.
A very specific application of ERHAVIT MC is in TFL's patented shower process. High
amounts of the product are applied for a short time (2-3hrs) together with lime and a low
amount of sulfide. After the hair is off the hides are washed and relimed. Process times are
much shorter, flatness, cleanliness and area yield are improved, and dependability of
results is high (fig 2). In addition, the leathers from the shower process show excellent
penetration of the dyes.
When further reduction of the sulfide is necessary ERHAVIT MC is combined with
ERHAVIT FS®, which is a strong reducing agent based on formamidine sulfinic acid.
Sulfide can almost be dispensed with, depending on the amount of ERHAVIT FS used .
The hides processed in this way are very clean with a full temper and a regular break.
Because sulfide is considered the least environmentally friendly chemical in a tannery a lot
of R&D effort is still being put into research to find the ideal unhairing enzyme suitable for
sulfide free unhairing. It has to be said however that such a product is not yet in sight. It
has been found that even when very specific enzymes are used a very small amount of
younger and shorter hair is still left on the hide. Although this hair is loosened it is actually
entrapped and not easily removable by mechanical means. To remove this residual hair it
has to be pulped with a fairly high amount of sulfide.
Bating.
The bating process was actually the first technical process in which industrially
manufactured enzymes where used. These enzymes, introduced by Otto Röhm in 1907
under the famous OROPON® brandname, were based on pancreatin. Despite the
availability of modern bacterial and fungal enzymes manufactured by fermentation the
pancreatic bating agents have been able to maintain their strong position down to the
present and they are still the most commonly used bating enzymes for several reasons.
The pancreatic enzyme complex has a well balanced mixture of different proteases
(trypsin, chymotrypsin, elastase and various peptidases ) with a considerable content of
lipase as well, enabling it to perform several tasks at the same time.
The grain layer and the collagen fibre structure are relaxed without damaging them,
residual hair, pigments, fat and unstructured proteins are removed gently but efficiently.
This improves the tensile strength, tear resistance and the elastometre values.
Only a few years ago TFL introduced the second generation of pancreatic bating agents.
By modifying the extraction techniques the proportion of certain enzymes in the complex
can be increased and that of others reduced. With this improved specificity better
slackening of the hide structure could be achieved without impairing the grain enamel and
grain pattern. This means better softness while maintaining a uniform fine, tight break,
including in the flank areas of the hide. The elastin and collagen in the grain layer are
hydrolyzed more specifically and perhaps to a lesser extent than with some of the bacterial
proteases in use. This means the supportive function of these proteins is maintained and
the hair pores remain well opened, giving a finer and cleaner grain without the danger of
looseness (fig 3).
Elastin is a component of the blood vessels and if it is aggressively broken down the blood
vessels fold up. The cavity created results in the vein patterns becoming visible on the
hide surface.
TFL's new range of OROPON bating agents is composed of specifically designed
products. There are different bating products available for bovine, goat, sheep and pig
skins. All have a fairly broad pH activity range in common, usually between 6.5 and 9.5.
To allow safe handling all powder products are dedusted. Ten years ago a breakthrough in
liquid pancreatic product formulations was achieved when TFL introduced its OROPON
FM®. Pancreatic enzymes with their very limited stability in liquid form could be made
stable for a minimum of one year with an activity loss lower than 10% at a storage
temperature of 25°C. The same applies to products based on bacterial proteases and
lipases.
Acidic proteases from fungi with a pH optimum of 2-4 such as OROPON WB® were
developed for bating pickle pelts and to upgrade poor quality wet-blues. In the case of
pickle pelts the overall flatness is improved with fewer fold marks. The post treatment of
wet-blues results in improved dye levelness and less pronounced wrinkles. The enzyme
treatment is often given following an initial oxalic acid incubation. Addition of special
surfactants or acidic lipases (for waterproof leathers) can improve the removal of residual
excess natural grease.
Waste treatment.
Several patents taken out by Röhm, now TFL, in the late 70's dealt with the use of certain
proteases, e.g. ERHA PH 3985 for the treatment of lime fleshings, hide trimmings and wet
blue shavings. Lime fleshings and trimmings can be hydrolyzed at higher temperature and
alkaline pH into protein hydrolysate and fatty acids . The same is true for wet blue
shavings from which a higher quality chrome can be recovered in addition to the protein
hydrolysate.
As can be seen major improvements in enzyme technology for leather have been made
during the past three decades. Enzymes have become much more specific, safer and
reliable. They are an indispensible tool in the modern beamhouse. An exciting field of
research besides the quest for the perfect unhairing enzyme could well be enzymatic
tanning. Enzymes can not only hydrolyse peptide bonds but also help to form new ones.
Although such enzymes are already available they have yet to prove a serious alternative
to existing tanning methods.
Click here to view the figures (bilder>bad quality).