Heinz-Peter GERMANN Technology for Sustainability International Forum - Bologna 2011

1. SUSTAINABLE LEATHER MANUFACTURE:
REALISTIC OBJECTIVES AND FURTHER OPPORTUNITIES
Dr.-Ing. Heinz-Peter Germann
N-Zyme BioTec GmbH, Innovation Center Leather & Collagen,
Reutlingen / Germany
Sustainable development is a pattern of resource use that aims to meet human
needs while preserving the environment so that these needs can be met not only
in the present, but also for future generations.
The term was used by the Brundtland Commission – formally the World Commis-
sion on Environment and Development (chaired by the former Norwegian Prime
Minister Gro Harlem Brundtland) that was convened by the United Nations in 1983
– which coined what has become the most often-quoted definition of sustainable
development as
“Development that meets the needs of the present without compromising
the ability of future generations to meet their own needs”.
By IUCN, “The World Conservation Union”, it has been shown that the field of
sustainable development can be conceptually broken into three constituent parts
(see figure 1):
• environmental sustainability (objective: preserving nature and environment
for future generations)
• economic sustainability (i.e. a manner of economy enabling sound income
and prosperity)
• socio-political sustainability (i.e. development of the society as a way of
enabling participation for all members of a community)
Fig. 1: Scheme of sustainable development – at the confluence of
three constituent parts
Sustainability can be related to different levels of consideration, i.e. it can be
considered as a local, regional, national or global issue. While it is increasingly

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considered as a global issue from an ecological point of view, the focus of
economic and socio-political sustainability is often a national one.
Practical approaches to realizing the idea of sustainable development in manu-
facturing companies are followed up by cleaner production which includes
− reduction of energy use,
− use of renewable resources,
− minimization of water consumption a n d
− reduction of waste generation.
However, the ‘destination’ of sustainability is not a fixed place in the normal sense
that we understand destination. Instead, it is a set of wishful characteristics of a
future system as pointed out by A.M. Hasna in 2007.
“The origin of leather manufacture dates far back in the prehistoric ages, and was
probably one of the earliest arts practised by mankind” as already stated by Henry
Richardson Procter who has been called “the father of leather chemistry”.
Having a look some hundred thousand years back when stabilized animal skin by
chewing (principle of chamois tannage) and smoke tannage (following to the
discovery of fire) were discovered by mankind, this type of leather making and
using resources could certainly be considered a sustainable process, at that time.
And also the “Iceman”, a human being from Copper age, found in the European
Alps in the frontier area between Italy and Austria who has been reported as
wearing fur clothes “tanned” by a special fatliquor procedure that has to be seen
as an “impregnation” rather than a tannage, could still be seen as acting in the
same line.
But in those early times the (main) interest of mankind had been the stabilisation
of hides and skins – available from animals hunted for the need of nourishment –
just for their effective use in personal protection. From today’s scientific
perspectives, this could possibly be considered as the first attempt for pollution
prevention and control by avoiding uncontrolled rotting of hunting/slaughtering
waste in the environment.
And, indeed, leather manufacturing is in itself recycling – or as recently cited:
“Leather is a sustainable environmental solution to the very real disposal problem
of a large volume of hides and skins that originate from the meat industry …”.
On the other hand, leather production, like many other industrial processes, does
indeed involve the generation of polluted waste water and solid by-products or
wastes, so that an appropriate effluent treatment and waste management are the
subject of a must, nowadays. This also includes the reuse of valuable by-products
like e.g. splits or split off-cuts that can be used in the production of gelatine and
sausage casings. Fleshings e.g. can be used in biogas production or directly to
replace the fuel for energy generation after separation of fat, as recently

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demonstrated by Suedleder GmbH & Co. KG, a leading German contract tannery.
In Suedleder tannery this has resulted in 50% CO2-reduction (savings of 4.500 t/a
CO2).
Of course, some thousand years ago, by-products such as connective tissue
should not have created any problems since they were most probably consumed
as food.
However, factors like fashion, commercial interests and globalisation had not
existed yet. Even the rule of unhairing was not invented that time, a process which
later became a crucial step in leather manufacturing for generations of tanners.
Also preservation in today’s sense should not have played a major role; skins were
either used freshly enough after separation from the animal body or certain defects
resulting from putrefaction were probably considered as normal. Today, in the
preservation of hides and skins common salt is still the most extensively used
agent, although the 30-40% sodium chloride which is needed for this process is
causing serious problems, especially, in countries with warm and dry climate,
where fresh water resources are at a premium.
Obviously the best solution from the environmental point of view is the use of fresh
(green) uncured or chilled hides for processing wherever the proximity of the
tannery to the slaughterhouse is given. In other words, this will always be
restricted by the respective slaughtering and flaying conditions as well as the
climate in the place of processing. In those cases where preservation is
unavoidable new ways of raw hide curing like e.g. the proposed use of
wasserglass will have to be further investigated.
However, looking for a really sustainable leather manufacture, the sourcing of
hides and skins becomes of equal importance to controlling the manufacturing
process. This will always call for processing of raw hides at the place of origin.
The beamhouse processes have always been considered the most important
operations in leather production as far as quality and texture of the resulting
leather are concerned. On the other hand it is well known that the unhairing
process of hides and skins, including the removal of hair and epidermis as well as
the opening-up of the fibre-structure, ranks among the most polluting operations in
the tannery. Although there have been significant developments and
improvements, including e.g. the reduction of processing time and effluent load,
made in the past decades, we are still looking for a more desirable, cleaner
unhairing technology.
Development of the unhairing process:
• sweating process (hair-loosening by a “natural” bacterial process; difficult to
control)
• traditional liming (risk of uncontrolled bacterial growth and enzyme action
becomes unmanageable under the conditions of industrial production)

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• rapid hair-destroying by sharpening agents (became most widely used
standard procedure as a consequence of economic considerations
including leather quality improvement)
Attention was then turned to the development of new liming systems to protect the
environment. These developments included reduced water consumption (e.g. by
replacing rinsing by washing processes, decreasing the float ratio and trials on the
recycling of lime and liming wash liquors), the reduction of sulphide and reduction
in COD loading of the effluent.
For environmental reasons new unhairing technologies have been developed:
• hair-saving liming systems (based on the principle of a partial immunization
of the hair)
• low sulphide liming systems (usually based on combination of certain
organic (thio-)compounds with inorganic sulphides)
…and also:
• oxidative unhairing process (applying hydrogen peroxide in alkaline media –
which has not been commercially adopted, for certain limitations)
At present, from a technological and ecological point of view low-sulphide
systems using either organic thio-compounds or amines, sometimes in
conjunction with enzymes, have to be considered as the best technologies
existing; and it is merely depending on regional and individual conditions
concerning possibilities of hair utilization and on the technical equipment
available, whether these systems should be used in hair-destroying or hair-
saving mode.
A number of leather scientists have proposed that hair-saving
• enzymatic unhairing
will someday replace sulphide unhairing as an ecological sound alternative, so
that the wheel would come full circle – the oldest method of hair-loosening,
after some improvements, would become the latest one. As early as 1910, Otto
Roehm had patented the unhairing with pancreas tryptases aiming at the
replacement of the almost uncontrollable sweating method by a much more
controllable process. Unfortunately, some of the disadvantages already
observed by O. Roehm still could not be fully overcome (incomplete removal of
short hair under practical conditions). For this reason the use of some sulphide
in enzymatic unhairing processes is indispensable, till the present time.
Regarding the tanning process itself, in the pre-industrial period lasting nearly till
the end of the 19th century, vegetable tannage or tanning with Aluminium (tawing)
have been the tanning techniques employed depending upon the intended use of
the resulting leather – i.e. based on the leather characteristics required.
Following the discovery of the tanning effect of chromium salts by the German
Friedrich Knapp in the 1850’s and further development of the process by
M. Dennis (1893) who brought it into a practical system, chrome tannage became
the worldwide accepted standard method of tanning, during the last century.

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It should be noted that in these times there were no significant environmental
concerns. The main interests were based on rationalisation of the tanning process,
the benefits in cost and speed of the reaction – hence faster throughput time – and
a highly versatile basis for leather manufacture. All of these factors represented
major steps towards industrialisation.
It has just been within the last few decades that the sensitivity to the ecology and
health concerns by the majority of people, starting from the highly developed
countries, has been steadily increased. In the tanning sector, this has resulted in
developing different approaches for an improved chrome management (see
figure 2).
Fig. 2 Within the last 50 years:
Different approaches for an improved
chrome management
• chrome recycling techniques
• better understanding on the influence of process
parameters:
– mechanical action – temperature – pH
– concentration – processing time – Cr offer
• development of high exhausting chrome tanning
systems … based on the general principles of:
low chrome offer, optimised process parameters and
application of special auxiliaries
This has involved chrome-recycling techniques as well as a better understanding
of the individual and combined influences of process parameters.
This also formed the basis of the development of the high exhausting chrome
tanning systems, based on the general principles of low chrome offer, optimised
process parameters and application of special auxiliaries (“crosslinking masking
agents”).
Today‘s “greener” way of thinking brings about new requirements on process-
chemicals and -technologies in leather manufacturing. Moreover, this way of
thinking has been much intensified by an increasing number of press reports and
television programmes raising questions concerning the environmental burden and
consumer health. In addition, there are the increasingly stringent requirements of
governing tannery effluents as regards to their chrome content and also certain
issues involving the disposal or utilization of by-products containing chrome for
which chromium tannage in particular has come under criticism.
Before considering any possible alternatives to chrome tannage, over and above
any basic technical limitations in terms of the tanning effect, the question of actual
ecological benefits gained from using a different tanning method has to be
considered.
In this event it is interesting to consider for instance the amount of tanning agent
required for converting a bovine hide into leather (see figure 3):

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Fig. 3: Amount of tanning agent required for a bovine hide (40 kg pelt weight)
Considering the worldwide consumption of 350.000-400.000 tons/annum chrome
tanning agents used for the manufacture of ≥ 80% of the world’s leather
production and the consumption of vegetable tanning agents of approximately
200.000-250.000 tons/annum, it becomes more than evident that a (complete)
replacement of chromium by vegetable tannins is not realistic. Increasing the
production of vegetable tannin extracts by the necessary factor, in the case of wild
growing trees like Quebracho, would immediately decimate their existence and in
the case of trees (e.g. mimosa) grown in plantation, the required cultivation area
would not be available; or in other words: extending the plantation area of tannin
producing plants to the debit of agricultural food production may not in the least be
considered as sustainable – in a world where lots of people are still suffering from
hunger.
Experimental studies and an eco-efficiency analysis, which were carried out to
compare different tanning methods from an ecological viewpoint, showed that, in
practice, it is safe to assume that chrome tanned leather produced in accordance
with the ‘best available technique’ principle – including all environmental measures
– can be classified as environmentally compatible. Basically, the indication of the
tanning method in itself cannot be regarded as an ecological quality criterion
irrespective of the leather article.
Considering, however, the importance of the tanning methods today, it has to be
mentioned that although 80-85% of the worldwide leather production is based on
chromium tannage, there is an increasing share of chrome-free tannages. This is
mainly due to the growing demand for so-called free-of-chrome leathers (“FOC-
leathers”) in the automotive industry where the current share of FOC-leather is
about 25-30%.
The principle of FOC-leather production is based upon a wet-white pre-tannage by
e.g. glutaraldehyde tanning agents (partially modified), THPS or other reactive
organic-synthetic crosslinkers (all originating from fossil fuels), which is followed by
a retanning using polyphenols (vegetable and syntan tanning agents) and other
organic-synthetic retanning agents.
Compared to chrome leathers their advantages include

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− the absence of “heavy metal”,
− less problems in solid waste disposal (including sludge) and
− improved performance in dry-shrinking behaviour.
On the other hand, well-known disadvantages include
− higher COD in the effluent,
− reduced fixation of dyestuffs and fatliquoring agents,
− extremely difficult hydrophobing,
− more difficult “handling” in production and processing,
− lower stability and mould resistance of semi-finished products (wet-white).
In principal, the course of tanning in modern processing can be divided in 2 steps
(see figure 4):
Fig. 4 The course of tanning
in modern processing
Pre-tanning/Main Tanning Retanning/Filling
stabilisation for adjustment of the
mechanical treatment required leather
(sammying, shaving) characteristics
production of a storable (e.g. fullness, shape-
and transportable semi- retention ability, grain
finished leather product firmness, embossability,
(wet-blue, wet-white, …) buffability)
1. The pre-tanning or main tanning stage for the stabilisation in order to permit
mechanical treatment and the production of a storable and transportable semi-
finished leather product and
2. The retanning/filling process for adjustment of the required leather
characteristics.
The retanning step includes mainly the application of vegetable tannins and
synthetic tanning/auxiliary tanning agents like syntans, resins and polymers; but
also mineral tanning agents and aldehydes are applied.
At this stage of leather manufacturing, which is also connected to the processes of
fatliquoring and dyeing, the most important technical issues concerning ecology
and consumer health are
– avoiding chromium VI
– avoiding formaldehyde release
– avoiding carcinogenic amines (from azo dyes)
All of these can be achieved best by the right selection of process chemicals.
However, neither wet-blue nor wet-white production can be considered as
sustainable processes in the proper sense, since both chromium salts and
glutaraldehyde (or any other reactive organic-synthetic tanning agent) are non-
renewable raw materials.

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More recent research and developments concerning ecologically beneficial
methods of pre-tanning or stabilising the skin (collagen matrix) include
− wasserglass stabilisation,
− enzymatic crosslinking and
− application of natural plant crosslinkers (especially, from olive waste)
There are three main objectives of these studies:
– To establish an innovative, sustainable and environmentally friendly
tanning system – as an appropriate complement to the existing tanning
methods
– The stabilisation/pre-tanning of the skin material – under the avoidance
of conventional chemical tanning agents – so that a satisfactory
mechanical processing (sammying/splitting and shaving) can be
achieved
– To obtain by-products/waste (shavings) enabling practically unlimited
usage
Skin stabilisation by wasserglass results in a white, stable and shaveable material
that proved to be storable for months. However, there is no significant increase in
the shrinkage temperature, and therefore reluctance for technical application.
The enzyme transglutaminase produces irreversible crosslinking with denaturated
collagen (gelatine). However, sufficient stabilisation (significant increase in the
shrinkage temperature) – as required for leather manufacture – could not be
achieved.
Application of an activated extract from olive solid waste produced technically
promising results. In the meantime, by serial trials at LGR, a stable leather
intermediate – called “wet-green®” – with good shaveability and a shrinkage
temperature of ≥70°C could be obtained. This new leather intermediate forms an
excellent basis for the production of crust leather (see figure 5).
Fig. 5 Natural plant crosslinkers
☺ Application of an activated extract from
olive solid waste produced technically Olea europea
promising results:
a stable leather intermediate (“wet-green®”)
with good shaveability
and TS ≥70°C
forming an excellent basis
for crust leather production

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Olive solid waste material includes leaves – originating from olive harvesting (see
figure 6) – as well as the effluent and residues from olive oil- and table olive
production.
Manual olive harvesting
Mechanical olive harvesting
Fig. 6 Generation of leaves and twigs during manual and especially, mechanical olive
harvesting
In Europe (>90% of world cultivation area for olive trees) approximately 30 million
tons of olive-solid waste materials are produced, annually.
The wet-green® technology uses a new innovative tanning agent based on an
aqueous olive leaf extract. The extract is produced from olive leaves that
accumulate in huge amounts as waste during the olive harvest and the trimming of
trees without any valorisation today. In the meantime, the new tanning agent can
be produced in industrial scale. Integration ability of the wet-green® tanning
process in leather production has been demonstrated within the scope of a
research project carried out by N-Zyme BioTec GmbH and Lederinstitut
Gerberschule Reutlingen.
Another issue to be dealt with in future is the undesirable problem of mould occur-
ring in the wet leather intermediate stage. A delay of further processing in the wet-
blue, wet-white or wet-green® stage can lead to mould growth and hence a
potential loss in quality and value. Avoiding such losses includes the use of
effective preservatives in the (pre-)tanning system. Although our former
investigations showed that the initial fungicide content is reduced significantly by
post-tanning operations and finishing, there is an interest in avoiding the presence
of those chemical agents mainly on behalf of consumer protection.
Therefore, further investigations included the development of an universal inter-
mediate stage (pre-/tanned) that requires no inclusion of preservatives / fungi-
cides. I.e., in addition, this product should allow drying, and subsequently wetting-
back without any problem.

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The aims of this approach are to avoid losses from mould attack, and avoid the
application of undesirable chemical agents.
This requires an appropriate stabilisation/crosslinking and sufficient increase in the
shrinkage temperature to enable sammying and shaving as well as appropriate
“fibre separation” (e.g. by the filling effect of certain tanning agents or fatliquors) to
enable drying without sticking within the fibrous collagen structure.
Although the new technology suggested will still need some optimisation, results
are extremely promising and giving inspiration about a further increase in the
sustainability of leather manufacture.
Cleaner production in finishing includes:
• avoidance / reduction of organic solvents
increasing application of water based systems
• avoidance / reduction of “overspray”
improvements in application techniques, e.g.
optimized spraying techniques (HVLP)
innovative roller coating technique
• ecological improvements in cross-linking
in-line cross-linking
substitution of harmful highly reactive crosslinkers
radiation curing (e.g. by UV)
• new innovative finishing technologies…?
Sustainable leather manufacturing: wishful thinking or realistic objective?
The ‘destination’ of sustainability is not a fixed place …
Instead, it is a set of wishful characteristics of a future system!
So, what are the future challenges for sustainable leather manufacture?
− In principle, leather manufacturing is in itself ‘recycling’ – i.e. it is a sustainable
solution to the disposal problem of a by-product that originates from the meat
industry.
− The concept of ‘globalization’ in leather production has to be updated / adjusted
by taking more into account additional factors like e.g. raw material sourcing
that is also relevant to the subject of sustainability.
− Sustainability of leather manufacture can be further increased by using
resources (i.e. water, fossil fuels and other natural resources) sparingly, which
includes controlling the production processes and improving the systematic re-
use of by-products whenever possible, and giving priority to the use of
renewable resources.
References see:
- H.-P. Germann, B.M. Das Memorial Lecture 2010: Sustainable leather
manufacture – Realistic objective or wishful thinking?, Leather 212, 4/2010,
28-30.
- H.-P. Germann et al., Heidemann Lecture: A natural plant crosslinker from olive
waste for leather tanning, Proceedings XXXI. IULTCS Congress, Valencia,
Spain, September 2011.