ArticlePDF Available

Comparable Evaluation of Leather Waterproofing Behaviour upon Hide Quality. I. Influence of Retanning and Fatliqouring Agents on Leather Structure and Properties

Authors:

Abstract and Figures

For military leather processing pinnacle technologies are applied, because the leather must have extreme hydrophobicity, herewith to maintain the breathability and moisture management capabilities. Therefore, leather producers must use such tanning chemicals, which are able to impart sufficient waterproofness and vapour permeability. In this study the influence of retanning and fatliquoring technologies for wet-blue hide conversion into finished military leather on its waterproofing behaviour and breathability has been studied. The comparable evaluation of leathers manufactured in Lithuanian and Kazakhstan tanneries was carried out. The leathers were characterized by chemical analysis and moisture absorption, water vapour permeability and water vapour absorption properties.
Content may be subject to copyright.
150
ISSN 1392–1320 MATERIALS SCIENCE (MEDŽIAGOTYRA). Vol. 18, No. 2. 2012
Comparable Evaluation of Leather Waterproofing Behaviour upon Hide Quality.
I. Influence of Retanning and Fatliqouring Agents on Leather Structure and
Properties
Virginija JANKAUSKAITĖ
1
, Indira JIYEMBETOVA
2
, Ada GULBINIENĖ
1
,
Justa ŠIRVAITYTĖ
3
, Kęstutis BELEŠKA
3
, Virginijus URBELIS
1
1
Department of Clothing and Polymer Products Technology, Faculty of Design and Technologies, Kaunas University of
Technology, Studentų str. 56, LT-51424 Kaunas, Lithuania
2
Department of Textile Products Technology,
Institute of Technology and Information Systems, M Kh. Dulaty Taraz State
University, Tolei bi str. 60, 080000 Taraz, Kazakhstan
3
Department of Organic Technology, Faculty of Chemical Technology, Kaunas University of Technology, Radvilėnų str. 1,
LT-50254 Kaunas, Lithuania
http://dx.doi.org/10.5755/j01.ms.18.2.1918
Received 30 December 2011; accepted 24 April 2012
For military leather processing pinnacle technologies are applied, because the leather must have extreme hydrophobicity,
herewith to maintain the breathability and moisture management capabilities. Therefore, leather producers must use such
tanning chemicals, which are able to impart sufficient waterproofness and vapour permeability. In this study the
influence of retanning and fatliquoring technologies for wet-blue hide conversion into finished military leather on its
waterproofing behaviour and breathability has been studied. The comparable evaluation of leathers manufactured in
Lithuanian and Kazakhstan tanneries was carried out. The leathers were characterized by chemical analysis and moisture
absorption, water vapour permeability and water vapour absorption properties.
Keywords: military leather, retanning and fatliqouring technologies, waterproofness, breathability.
1. INTRODUCTION
Water resistance of leather is an important property to
several applications, like footwear and clothing with high
wearing comfort even under wet and cold conditions.
Furthermore, leather, which has absorbed too much water,
loses its ability to insulate against heat and cold [1].
Therefore, waterproof leather used for footwear should not
uptake more than 25 %
30 % of water [2]. However, the
leather should allow additionally high water vapour
permeability and some reversible water up-take to remove
perspiration from body.
To understand how to prevent the wetting of leather, it
is necessary to understand the process of leather wetting.
Generally, it takes place in four-steps [2]:
– water spreads over and wets the leather surface;
– water penetrates into the leather;
– water wets the fibre network (i.
e. internal surface of
leather);
the leather soaks by water due to the attractive
interaction between water and leather. Not only collagen
backbone, but also tanning agents, dye molecules, salts,
and other materials which present in leather network,
might be involved in these interactions.
There are many polar functional groups in collagen
fibres such as –OH, –COOH, –NH
2
and –CONH–. The
chemical compounds to be added mostly are hydrophilic
and have good water affinity. Therefore, to improve water
resistance property several leather making processes and
leather surface modifications are applied [2
4]:
Corresponding author.Tel.:+370-37-300207, fax: +370-37-353989.
E-mail adress: virginija.jankauskaite@ktu.lt (V. Jankauskaitė)
1. Sealing the leather with an impermeable layer, i.
e. a
heavy polymer finish. A foil or thin laminate of waterproof
synthetic material can be attached to the surface of the
leather by adhesive, also [5]. The spreading of water over
the surface is prevented by film and the leather cannot be
wetted at least under static conditions. However, such film
reduces the water vapour permeability drastically even
produced using most modern technologies [5, 6].
2. Closed waterproofing – closing the spaces between
the leather fibres with water-repellent substances [3, 4]. It
might be achieved in two different ways: firstly, leather
impregnation by incorporation of water-insoluble sub-
stances, for example, solid fats, and molten waxes;
secondly, using hydrophilic waterproofing [7]. Grease
impregnation is a long established system, and gives a
special look and feel to the leather. However, the filling of
the gaps with grease prevents the penetration of water into
the fibre network, but the leather becomes extremely heavy
and completely blocks any air and water vapour
permeability. In the second case waterproofing of leather is
achieved by application of certain surfactants (e.
g.
hydroxycarboxylic acid derivatives, alkenyl-succinic acid
derivatives, hydroxyethylation fatty acid, etc.), which bind
to the leather and can absorb a certain quantity of water
[8]. The surfactants and water form highly viscous water-
in-oil emulsion, which fill the gaps in the fibre network.
These micelles are hydrophobic on their outer side and,
therefore, the gaps are filled with a hydrophobic material.
The problem with closed waterproofing is that it (partially)
seals the pores and, therefore, frequently impairs the water
vapour permeability and water vapour absorption of the
leather [2, 3].
151
3. Open waterproofing – creating a hydrophobic net
around the fibres without filling spaces – is smartest
approach to make waterproof leather [2
4]. Used low
surface energy (not higher than 30 mN/m) waterproof
agent binds to the fibres and fibrils through its functional
groups and forms hydrophobic layer. Water vapour can
penetrate into the fibre network, while water droplets
possess high surface tension and cannot spread over the
hydrophilic fibre and wet the internal surface. High
interaction between fibre and waterproof agent is required.
It can be realized by using chrome stearates, which consist
of hydrophilic and hydrophobic parts, hydrophobic esters
and silicone based products.
There are many other factors that influence the
waterproofness of leather not only chemical substances
used in leather manufacture (salts, tensides, tanning agents,
retanning agents, dyestuffs, fatliquoring agents and
finishing agents). The initial quality of skin or hide and
operation of each process of the skin/hide conversion to the
finished leather have significant influence on the
waterproofness degree of finished leather [9, 10].
The problems that affect leather quality begin when
the animal is still alive, and include, cuts resulted by
barbed wire; in-fighting among male members and thorn
scratches and cuts; brand marks made for ownership
purposes using hot iron; holes and spots from infections
and infestations, caused by ticks, horn flies, mange and
bot-flies, among others; abscesses resulted from wrong
vaccination techniques and natural growth marks or excess
weight related problems, like furrows and wrinkles [9].
During transportation, the animal skin may suffer deep
injures from nails and wood splints in the truck.
Before tanning, three important processes, which can
also cause leather damage, happen: bleeding, skinning and
curing. Insufficient bleeding can cause vain marks, while
wrong skinning techniques may result in flaying cuts that,
in some cases, may turn unusable otherwise valuable parts
of the leather. As the raw hide is subjected to putrefaction,
as soon as the animal dies, the raw hide must be cured to
protect it until the tanning process begins, and this time can
take months. Improper curing may lead to rotting and
putrefaction. The defects during tanning and post-
processing are much less common, as they are controlled
by the tanneries, which have in the leather quality their
main business [9].
Waterproof leathers are commercially of high interest
because this leathers are sold at a relative high price due to
requirement of specialty products for tanning
(waterproofing, selected retanning, neutralization and
dispersing agents) [2]. The choice of waterproofing system
depends on the degree of water resistance required, the
purpose of leather, and price. Extreme hydrophobicity is
required for military footwear leather [11]. On the other
hand, attention must be paid to the breathability and rate of
drying out of leather. Therefore, for military leathers
pinnacle technologies can be applied.
The aim of this work was to evaluate the
waterproofing behaviour of the military leather upon
various combinations of retannage and fatliquoring agents.
The influence of hide quality on the military leather water
resistance and breathability were evaluated as well.
2. CHOISE OF RETANNING, FATLIQUORING
AND FILLING CHEMICALS
The skins and hides tanning with chromium salts
induces the collagen fibre to be resistant against bacterial
attack and increase resistance to temperature. However, this
process does not possess the physical and aesthetic
properties required to the products made from leather.
Therefore, after chrome tanning obtained wet blue is
converted to usable leather in a series of chemical and
mechanical operations (i.
e. retanning, fatliquoring, etc.) [1].
The highly complex chemical processing of the wet
blue involving retanning, dyeing and fatliquoring (RDF)
are used for manufacturing of leathers (Fig. 1). RDF
process commences with the neutralization, when pH is
raised to over 4.8 on purpose to provide even penetration
of subsequent chemicals into the leather [1, 8].
Fig. 1. Succession of chemical processes in the conversion of wet
blue to dyed crust and the finished leather
The choice of retanning and fatliquoring chemicals
depends on the desired properties (softness, touch, fullness,
grain firmness or looseness, smell, adhesion properties,
water uptake or release, and water repellency) of the final
leather.
Various retanning agents were developed to give the
chrome tanned leather fullness with selective filling of the
structure and to provide tight and uniform grain surface
[8, 12
14]. In general, retanning agents can be inorganic
mineral substances (chrome, aluminium, zirconium salts)
or organic materials (vegetable or synthetic). The synthetic
retanning organic agents can be divided into three main
Crust leather
(h=1.8 – 2.2 mm)
NEUTRALIZATION
(pH = 5.0)
RETTANNAGE
DYING
FATLIQUORING
FIXATION
(
hot water, acid, chrome)
FINISHING
(roller or spray)
Finished leather
Wet blue
152
groups: 1) syntans (condensation products of aromatic
compounds like phenol, naphthalene sulphonic acid with
formaldehyde or urea); 2) resins (condensation products
from formaldehyde with amino and amido compounds like
urea, melamine, and dicyandiamide); 3) polymers, mainly
acrylic (polymerization products from acrylic acid deriva-
tives). Syntans are better soluble in water than vegetable
tannins, because they molecules are smaller. Therefore,
vegetable tannins more difficult penetrate to leather matrix,
and leather tanning process runs longer [1, 8]. However,
vegetable tans can reduce or prevent the formation of
harmful Cr(VI), promote antioxidation properties, improve
burnishability and glazing, fix cationic dyes [15].
The wide use of acrylic acid derivatives is related to
the presence of many carboxylic acid side groups that can
give tanning property both reacting with multiple chrome
centers on the leather and chemical bounding to the
collagen groups [12]. Acrylic resin interaction mechanism
with chrome tanned leather is presented in Fig. 2 [7].
Fig. 2. Interaction of acrylic resin with peptide chain and
chromium [7]
Synthetic retanning materials also are used for filling
and softening, as auxiliaries during fatliquoring and
sometimes as replacements of tannins in combination with
vegetable extracts [12]. The filling improves the tightness
and fineness of the leather grain with mellow surface.
The retanning agents play important role in the final
degree of leather water repellency, also. Melamine-
dicyandiamide resin, acrylo-nitrile resin, styrene-maleic
copolymer, chestnut can significantly to lower water
absorption of leather [16].
In recent, many researches are focused on the leather
properties (such as reduction of water uptake) modification
by grafting to collagen of different monomers such as
styrene and acrylate derivatives [17, 18].
Fatliquoring agents are one of the important leather
chemicals that have great effect on leather performance. It can
penetrate into the interwoven structure of the collagen fibres,
prevent the leather fibers from putrefaction, make the fibres
stick together and improve their physical and mechanical
capabilities [7, 8, 19]. The fatliquoring is the main step in the
production of hydrophobic leather [7, 14, 16].
Generally, fatliquoring substances are divided into
hydrophobic (emulsified) components and hydrophilic
(emulsifying) components [1, 8]. In the last decades
several products have been applied to impart waterproofing
properties of the leather [14, 16, 20
22]: natural oils,
alkenyl succinic acids, polysiloxanes, chromium soaps
(stearates and oleates), phosphoric esters and reactive
agents or amphiphilic polymers.
Multifunction fatliquoring agents can offer more new
capabilities for leather. Besides fatliquoring function, they
can enhance segment mobility of molecular chain of
collagen fibers, and contribute higher level of softness,
flexibility, waterproofness, perspiration resistance, etc.
[20, 21]. Not only waterproofing but also repellent
properties to the leather confer silicone derivatives and
fluorcarbonated resin [2, 4]. Silicones may be applied from
hydro-carbon solvents on the dry leather by dipping or
spraying or a silicone emulsion may be applied in the drum
on the wet leather by a fatliquoring [23, 24]. Silicones have
very high interfacial tensions relative to water and these
are not very temperature sensitive. However, silicones are
not very effective as solo agents [1]. Fluorocarbons are
applied from solvent solutions and have equally high water
repellency and also oil repellency [25].
3. EXPERIMENTAL
3.1. Materials
For comparable evaluation the hydrophobic leathers
tanned with different type of retanning and fatliquoring
agents in JSC “Natūrali oda & Ko” (Kėdainiai, Lithuania)
and “TarazKozhObuv” company (Taraz, Kazakhstan) were
chosen. Characterization of fully finished leathers to be
investigated is presented in Table 1. As can be seen, NO-
type leathers are stiffer compared to that of TKO-type one.
Table 1. Characterization of hydrophobic leathers to be used for investigations
Leather producer Chemicals suppliers Type Sample Thickness, mm Stiffness, N
Natūrali oda & Ko
(Kėdainiai,
Lithuania)
Schill+ Seilacher (Germany) / Stahl
International (Netherlands) Black NO-1
2.2 ±0.1 3.5
Schill+ Seilacher (Germany) / BASF
Group (Germany) / Stahl International
(Netherlands)
Brown NO-2
2.1 ±0.1 2.7
TarazKozhObuv
(Taraz, Kazahstan)
Smit & Zoon (Holand) / Hayana Leather
Chemicals (Spain)
Black, with
embossed surface TKO-1 2.0 ±0.1 2.3
Smit & Zoon (Holand)/ Shelkovo
Agroxim (Russia)
Black, with
embossed surface TKO-2 1.9 ±0.1 2.4
153
Table 2. Chemical materials used in the RDF processing to obtain waterproof leather
RDF process
stage
Chemicals used for RDF of leather
NO-1 NO-2 TKO-1 TKO-2
Washing thoroughly at T = 35 °C–40 °C, drain float
I.
Neutralization Sodium formate
Sodium bicarbonate
Sodium formate
Sodium bicarbonate
Sodium formate
Sodium bicarbonate
Sodium formate
Sodium bicarbonate
Retanning Phenolic compound
(Ukatan NR)
Maleic acid styrene
copolymer ammonium
salt (Derugan NG)
Sodium salt of an amine
modified fatty acids
(Limanol PEW)
Aqueous anionic acrylic
polymer solution
(Densotan A)
Maleic acid styrene
copolymer ammonium
salt (Derugan NG)
Dicyandiamide resin
(Ukatan AG)
Aqueous polyacrylic
dispersion for retanning
(Retan 38)
Aqueous acrylic polymer
(Syntan RS 3)
Drain float, washing thoroughly at T = 25 °C–30 °C
II.
Retanning Dicyandiamide resin
(Ukatan AG)
Maleic acid styrene
copolymer ammonium
salt (Derugan NG)
Dicyandiamide resin
(Ukatan AG)
Maleic acid styrene
copolymer ammonium
salt (Derugan NG)
Aqueous acrylic polymer
(Syntan RS 3)
Mixture of lignin
sulphonate and phenolic
sulphonic acid
condensate (Syntan GP)
Emulsified synthetic oils
(Synthol EW 321)
Aqueous solution of
acrylic acid and ester
copolymer (Syncotan TL)
Mixture of lignin
sulphonate and phenolic
sulphonic acid
condensate (Syntan GP)
Aqueous acrylic polymer
(Syntan RS 3)
Filling Protein filling agent
(Synektan F)
Chestnut
Polyphenol copolymerized
with acrylic monomer
(Synektan R-982)
Chestnut
Melamine-urea-
formaldehyde condensate
(Syntan LF 187)
Dicyandiamide-urea-
formaldehyde condensate
(Syntan DF 585)
Melamine-urea-
formaldehyde condensate
(Syntan LF 187)
Dicyandiamide-urea-
formaldehyde condensate
(Syntan DF 585)
Quebracho
III. Washing at T = 40 °C
Fatliquoring
(water
repellants)
High molecular weight
paraffines and
hydrophobic emulsifiers
(Perfektol HQ)
Polymers combined with
highly effective silicone-
based additives
(Perfektol QX)
Unsaturated marine oil
(Perpristol COD)
High molecular weight
paraffines and
hydrophobic emulsifiers
(Perfektol HQ)
Silicone based water
repellent (Densodrin EP)
Aqueous anionic acrylic
polymer solution
(Densotan A)
Emulsified synthetic oils
(Synthol EW 321)
Aqueous solution of
acrylic acid and ester
copolymer (Syncotan TL)
Emulsified synthetic oils
(Synthol EW 321)
Concentrated anionic agent
(Paste VNIZ)
Drain float, twice washing thoroughly at T = 40 °C (first) and T = 20 °C–22 °C (second)
JSC “Natūrali oda & Ko” as a raw material for leather
manufacturing used local salted cattle hide not only high
quality, but second-rate as well. For the processing of
military leather with high waterproofness only top-quality
wet-blue hides were chosen.
“TarazKozhObuv” company for manufacturing of
military hydrophobic leather used only low quality skin
and hide. Overall, purely 1 %
5 % of Kazakhstan
skins/hides are second-rate. Wet blue produced from third-
rate (35 %
45 %) is realized to China. The main part of
skins/hides (50 %
60 %) is fourth-rate and only this raw
are used for the military leather manufacturing. Such low
quality of Kazakhstan skins and hides is related to the
insufficient structure evenness due to the intensive cattle
growth, various diseases of cattle, holes or spots obtained
from infections and infestations. Many injures are obtained
during bleeding, skinning, and curing.
3.2. Applied chemical processes of conversion wet-
blue to finished leather
Wet-blue hides shaved to 1.9 mm
2.2 mm were
tanned according to the conventional technology (Fig. 1).
Neutralization, retanning, filling and fatliquoring opera-
tions applied for leather manufacture to produce
waterproof leather are presented in Table 2. In all chemical
processing cases the neutralization is followed at
(35
40)
°C temperature using sodium formate and sodium
154
bicarbonate. During the neutralization the pH of leather
processing medium changed from 3.2
3.4 to 4.8
5.4.
As neutralization and retanning processes proceed
simultaneously, NO-type leathers additionally were
neutralized by retanning chemicals based on phenolic
compounds (Ukatan NR) and anionic acrylic polymer
solution (Densotan A). When pH is higher than 4.0, acrylic
compound Syntan RS 3 also acts as neutralization agent
(TKO-2 leather).
For the studied leathers the retanning both aromatic
(phenolic agents) and aliphatic tanning materials
(polycondensed and polymerized compounds) were applied.
TKO-type leathers were retanned using only aqueous acrylic
polymer dispersions (Retan 38 or Syntan RS 3). While in the
case of NO-type leathers not only polymers, such as styrene
copolymer and high molecular weight (above 100,000)
acrylic polymer (Derugan NG and Densotan A,
respectively), but also resins such as phenolic and
dicyandiamide (Ukatan NR and Ukatan AG) were applied as
retanning agents. In the case of NO-type leathers water
repellents were introduced already at the neutralization and
retanning stages: emulsifying amine modified fatty acids
(Limanol PEW) and acrylic polymer (Densotan A) were
used for the leathers NO-1 and NO-2, respectively.
After wet blue neutralization and retanning washing at
elevated temperature (T = 35
°C
40
°C) was performed.
Then follows second cycle of chemical processing to
increase leather fullness and impart water resistance
properties. In the case of NO-type leathers practically the
same resin and polymeric retanning agents as in previous
stage were used (Table 2). For retanning with acrylic
polymer to the TKO-type leathers additionally was added
polycondensation product – resin Syntan GP.
For selective filling in the loosely structured parts of
the leather, good grain tightness and fullness, high leveled
dying, better buffing and finishing filling agents were used.
In investigated cases were applied both types of fillers
(syntans and natural tannins, i.
e. vegetable).
The vegetable tans, such as hydrolysable tannin
(chestnut in NO-type leathers) and condensed tannin
(quebracho in TKO-2 leather) were applied. Lithuanian
leather tanner added additionally the resin-like vegetable
polymer, obtained by polyphenol copolymerization with an
acrylic monomer (Synektan R-982) and protein filling
agent (Synektan F).
The waterproofing of NO-type leathers were attempted
to impart by using high molecular weight paraffines,
silicone based additives and raw oil components (Table 2).
The aqueous acrylic polymer solution (Densotan A), used
in leather NO-2, has pronounced dispersing effect,
therefore make waterproofing much easier, especially in
the combination with Densodrin range products (BASF
Group). The waterproofness of the TKO-1 leather was
achieved by the repeated use of the mixture of emulsified
synthetic oils Synthol EW 321 with aqueous solution of
acrylic acid and ester copolymer Syncotan TL.
In this chemical processing stage the coloring of
leathers was performed as well (not discussed).
In the case of leathers NO-1, NO-2 and TKO-1
retanning, filling and fatliquoring proceeded in one
solution at temperature 50
°C
60
°C and pH = 3.7
3.8.
For leather TKO-2 filling was carried out at temperature
30
°C, and after washing the fatliquoring with synthetic
oils and anionic oiled paste was performed in distinct stage
at temperature 60
°C and pH = 3.6 value.
After wet blue chemical processing obtained crust
leather was finished using aqueous acrylic and
polyurethane emulsions.
3.3. Testing
Scanning electron microscopy (SEM). SEM analysis
of leather structure was performed using a microscope
Quanta 200 FEG (FEI, Netherlands). All microscopic
images were done on the same technical and technological
conditions: the electron beam heating voltage – 20.00 kV,
beam spot – 5.0, magnifications – 200× and 10000×, work
distance – 6.0 mm, low vacuum –80 Pa, detector – LFD.
For examination specimens about 1.2 mm thick crosscuts
were made with a hand microtome.
Leather chemical analyses. Chromium content was
determined according to the requirements of standard
LST EN ISO 5398-1, which describes a method of the
chromium in aqueous solution obtained from leather
determination by iodometric titration.
The method of the matter soluble in dichloromethane
(fatty substances) estimation specifies the standard
LST EN ISO 4048. The extraction of fatty substances was
carried out using Soxhlet apparatus.
The volatile matters, i.
e. moisture, were determined
using method described in LST EN ISO 4684. It is not
possible to determine the exact moisture content of leather
by this method. This is because at elevated temperatures
other volatile substances escape and tannins and fats can be
oxidized. Some absorbed water may be left in the leather
after drying.
Determination of water resistance. Before testing all
leathers were conditioned at standard atmosphere in
accordance with the requirements of LST EN 12222 at a
constant temperature T = 23
°C ±2
°C and relative humidity
RH = 50 % ±5 % (23/50). Dynamic water resistance of
leather using Bally Penetrometer, which specifies
standards LST EN ISO 5403 and LST EN ISO 20344 was
performed simulating conditions of wear. In this test a
piece of leather was formed into the shape of trough and
flexed whilst partially immersed in water. The water
absorption as a percentage gain in mass of test piece due to
the water uptake at the defined time was determined.
Testing was carried out at standard atmosphere 23/50.
Determination of leather breathability. The method
according to the requirements of standard LST EN
ISO 14268 and LST EN ISO 20344 was used to test the
water vapour permeability and absorption. The water
vapour permeability was measured when test piece was
fixed over the opening of a jar, which contains solid
desiccant. This unit was placed in a strong current of air in
a conditioned atmosphere (23/50). The air inside the
container was constantly agitated by the desiccant, which
was kept in movement by the rotation of the jar. The jar
was weighted to determine the mass of the moisture that
had passed through the test piece and had been absorbed
by the desiccant.
In the case of water vapour absorption determination
an impermeable material and the test piece was clamped
155
over the opening of container, which holds water, for
duration of the test (about 8 h). Water vapour coefficient
was calculated using obtained values of permeability and
absorption. Test piece was then weighted immediately and
the water absorption determined by the mass difference
before and after the test.
4. RESULTS AND DISCUSSIONS
Evaluation of the retanning and fatliquoring agents
(see Table 2) shows that the waterproofness for TKO-type
leathers mainly is achieved by filling the gaps in the fibre
network with water-in-oil emulsion, while in NO-type
leathers structure additionally is created using hydrophobic
material net around the fibres without spaces filling. It is
achieved by adding low surface energy silicone based
products and hydrophobic esters.
The chemical materials defined in finished leathers are
listed in Table 3. As it can be seen, in all leathers
chromium content is similar and vary in the range of
4.48 %
5.28 % (differs about 18 %). The same situation is
observed in the case of volatile matter content (variation
about 17 %). However, the matter soluble in dichloro-
methane (fatty substances) content in the leather depends
on the fatliquoring technology. In the case of NO-type and
TKO-1 leathers fatty substances content has close values
(2.64 %
3.82 %), while in the case of TKO-2 it is
approximately twice large and reaches 6.71 % value. It
may be supposed that such differences in dichloromethane
soluble materials can be related to the TKO-2 fatliquoring
in separate stage and influence of vegetable tannin
quebracho (see Table 2).
Table 3. Chemicals content in various leathers
Leather
type
Content of chemical materials in leather, %:
chromic
oxide
matter soluble in
dichloromethane
volatile
matter
NO-1 5.28 2.64 11.13
NO-2 4.56 3.34 11.24
TKO-1 5.09 3.82 12.39
TKO-2 4.48 6.71 13.00
Note: Cr(VI) content detected in of TKO-type leathers is in the
range of (0.3–1.9) mg/kg (requirement Cr(VI) < 10 mg/kg)
The fibres weaving, fibre bundles splitting, separation
and coalescence were investigated by SEM. The NO-type
and TKO-type leathers cross-sections are shown in Fig. 3.
Three-dimensional meshwork of modified collagen fibres
can be seen. Collagen fibres bundles diameter is
2 μm
5 μm and they are composed from many fibrils of
variable thickness. From Fig. 3, a, it is evident the
gradation in fibre size from coarse fibre bundles in the
flesh and corium (central) regions, to the much finer
fibrous structure found in the grain (outer surface) region.
Due to the loss of protein during the preliminary stages of
tanning, the regions between the top tightly-packed grain
layer and next layer of intermediate fibre size loses
cohesion and some delamination can occur. It is clearly
seen in TKO-type leather cross-sections (Fig. 3, a).
The properties of leather depend on the individual
fibres and their ability to move over each other. However,
appearance of the fibres and their interweaving also reveals
information about the processing through leather passes
[1, 8]. The fibre bundles in NO-type leathers are packed
more densely comparing to that of TKO-type leathers
(Fig. 3, b). No visible differences in the NO-1 and NO-2
cross-section are seen. TKO-type leathers have large voids
between fibre bundles; especially it is visible in TKO-2
leather. Besides, in some regions of TKO-1 leather the
adhering of fibres to each other is detected, supposing due
to the insufficient action of fatliquoring agents (Fig. 3, b).
On the other hand, it may be related to the discrete leather
quality, too [14, 16].
NO-1
NO-2
TKO-1
TKO-2
a b
Fig. 3. SEM images of various chrome tanned leathers cross-
section at different magnification: a – 200×;
b – 10 000×
156
Usually, it is required that military leathers would be
water resistant by six hours at least [11]. It means that after
six hours of dynamic testing that simulates conditions of
wear, water absorption should be not higher than
25 %
30 %. As it can be seen from Fig. 4, water
absorption of leathers differs significantly and is dependent
on leather quality, retanning and fatliquoring technologies.
However, no water penetration was detected for all leathers
during 7 h of testing.
It may be supposed that the cross-section of the NO-1
and NO-2 leathers is fully treated by retanning and
fatliquoring agents during chemical processes. Therefore,
even after 7 h under dynamic testing NO-1 and NO-2
leathers absorb only 5.7 % and 8.5 % of water,
respectively. It can be noted that the replacement of water
repellent silicone derivative and oil component
(Schill+Seilacher) with aqueous acrylic polymer solution
and silicone based component from BASF Group do not
impart higher water resistance properties to the leather.
The leather TKO-2 obtained by using three-stage
retanning and fatliquoring technology also shows high
waterproofness after 7 h of testing (water uptake is 15 %).
Another situation is observed with TKO-1 leather –
already after 1 h testing the water absorption reaches 9 %.
This value increases significantly during 4 h and 7 h of the
testing (up to 22 % and 40 %, respectively). Thus, the
waterproofness of TKO-1 leather is low, water repellant
treatment is insufficient and this leather does not meet
requirements for hydrophobic leather. Tough NO-type and
TKO-2 leathers meet the requirements, but NO-1 and
NO-2 leathers waterproofness is about 2
2.5 times higher.
It may be dependent not only on the differences in leathers
chemical processing, but mainly due to the low skin/hide
quality used for TKO-type leathers production [9, 10].
0
10
20
30
40
NO-1 NO-2 TKO-1 TKO-2
1 h
4 h
7 h
W, %
Fig. 4. Dependence of water absorption upon leather type at
dynamic testing
While the penetration of liquid water should be
prevented, water vapour should pass the leather as freely as
possible, or at least be absorbed, to ensure good
acclimatization inside of the footwear [4, 5]. Investigated
leathers breathability is presented in Fig. 5. As can be seen,
water vapour permeability (WVP) of leather TKO-1 is
notably low, although the water absorption and penetration
values are high (see Fig. 4). It may be related to the closed
waterproofing that causes the sealing of pores with oil
emulsions that impairs the water vapour permeability and
absorption [2, 3]. On the other hand, the adhering of fibre
bundles to each other due to the erratic penetration of
chemicals can also reduce leather breathability.
Meanwhile, WVP values for leathers NO-1 and NO-2 lies
in the range of (2.5
3.0) mg/(cm
2
h) and satisfies
requirements (WVP 0.8 mg/(cm
2
h)). The WVP value of
TKO-2 is 1.5
1.9 times lower (1.6 mg/(cm
2
h)), but
enough for perspiration evaporation.
From Fig. 5, a, it is evident that ability to absorb water
vapour almost does not depend on the leather quality.
WVA values are low and vary in the range of
(1.16
2.24) mg/cm
2
. It shows that after water repellent
treatment interfacial tension between investigated leather
fibres and water increases, and that significantly reduces or
eliminates interaction with water.
0
1
2
3
4
NO-1 NO-2 TKO-1 TKO-2
WVP
WVA
WVP, mg/(cm
2
h)
WVA, mg/cm
2
a
0
10
20
30
NO-1 NO-2 TKO-1 TKO-2
WVC
WVC, mg/cm
2
b
Fig. 5. Dependence of breathability upon leather type:
WVP – water vapour permeability; WVA – water vapour
absorption; WVC – water vapour coefficient
Water vapour coefficient depends upon water vapour
penetration and absorption values (WVC = 8WVP + WVA)
and requires to be not less than 15 mg/cm
2
. As can be
expected after the evaluation of leathers water vapour
penetration and absorption behaviour, TKO-1 leather
shows insufficient WVC value – only 9.5 mg/cm
2
(Fig. 5, b). The coefficient values of NO-1 and NO-2
leathers are high enough and exceed requirement in 30 %
and 60 %, respectively, while TKO-2 leather only scarcely
satisfies required value.
Comparing NO-type leathers waterproofness and
breathability behaviour it can be suspected that NO-2
leather has structure of less density, therefore show higher
157
water vapour permeability, but lower water resistance than
NO-1 leather.
5. CONCLUSIONS
The use of retanning compounds with free carboxylic
groups, complex emulsifiers, and hydrophobic products,
such as water insoluble fats and hydrophobic silicones
allows obtaining leather with high water repellency
properties and sufficient breathability. More effective are
multifunctional fatliquoring agents, which are capable to
surround the fibre with water repellent film and increase
the surface tension with water. The water repellent
treatment with chemical materials, which clog the
interfibrillar spaces by water absorption and emulsion
formation, ensures lower leather breathability.
Skin and hide quality influences on the finished leather
structure and waterproofness. Properly selected chemical
materials and their compositions with properly harmonized
properties, also sufficient selected methods of such
compositions application allow to produce leather with the
desired properties even from the hide of low quality.
REFERENCES
1. Covington, A. D. Tanning Chemistry – The Science of
Leather, Cambridge, RSC Publishing, 2009: 592 p.
2. Herrmann, W. Waterproof Leather – Requirements and
Technology Leather International 9 2006: pp. 56 58.
3. Beeby, R. Making Waterproof Footwear World Footwear
1996: pp. 14 22.
4. Silva, R. M., Pinto, V. V., Freitas, F., Ferreira, M. J.
Characterization of Barrier Effects in Footwear. In:
Multifuctional Barries for Flexible Structures (S. Duquesne,
C. Magniez, G. Camino, eds.). Springer, 2007, 292 p.:
pp. 229 268.
http://dx.doi.org/10.1007/978-3-540-71920-5_13
5. Gulbinienė, A., Jankauskaitė, V., Urbelis, V. The
Influence of Laminated Leather Structure on the Water
Vapour Absorption and Desorption Behaviour Materials
Science (Medziagotyra) 14 (1) 2008: pp. 44 50.
6. Fan, H., Li, L., Fan, X., Shi, B. The Water Vapour
Permeability of Leather Finished by Thermally-responsive
Polyurethane Journal of the American Leather Chemists
Association 89 (3) 2005: pp. 121 125.
7. Zhang, Y., Wang, L. Recent Research Progress on Leather
Fatliquoring Agents Polymer-Plastics Technology and
Engineering 48 (3) 2009: pp. 285 291.
8. Liao, L. L., Shan, Z. H. Leather Chemical and Technology.
Beijing: Chemical Industry Publishing Company, 2005.
9. Georgieva, L., Krastev, K., Angelov, N. Identification of
Surface Leather Defects. In: CompSysTech 03: Proceedings
of the 4th International Conference on Computer Systems
and Technologies New York, USA, 2003. ACM Press,
2003: pp. 303 307.
http://dx.doi.org/10.1145/973620.973670
10. Valeika, V., Širvaitytė, J., Beleška, K. Estimation of
Chrome-free Tanning Method Suitability in Conformity with
Physical and Chemical Properties of Leather Materials
Science (Medziagotyra) 16 (4) 2010: pp. 330 336.
11. Howard, E., Oakley, N. The Design and Function of
Military Footwear: a Review Following Experiences in the
South Atlantic Ergonomics 27 (6) 1984: pp. 631 637.
12. Naviglio, B., Calvanese, G., Tortora, G., Cipollaro, L.,
Pierri, G. Characterization of Tannery Chemicals:
Retanning Agents. e-book:
http://www.aaqtic.org.ar/congresos/istanbul2006/Visual%20
Displays/ (20011-09-15).
13. Nashy, El-S. H. A., Hussein, A. I., Essa, M. M. Retanning
Agents for Chrome Tanned Leather Based on Emulsion
Nano-particles of Styrene/Butyl Acrylate Copolymers New
York Science Journal 3 (11) 2010: pp. 13 21.
14. Palop, R. A., Marsal, A. Factors Influencing the
Waterproofing Behaviour of Retanning-Fatliquoring
Polymers. Part I Journal of the American Leather Chemists
Association 99 (10) 2004: pp. 409 415.
15. Diaz, F. Today’s View on Vegetable Extracts in Wet-Blue
Processing World Leather 10 11 2011: pp. 19 23.
16. Palop, R. A., Marsal, A. Factors Influencing the
Waterproofing Behaviour of Retanning-Fatliquoring
Polymers. Part II Journal of the American Leather
Chemists Association 99 (11) 2004: pp. 461 467.
17. Mohamed, O. A., Moustafa, A. B., Mehawed, M. A.,
El-Sayed, N. H. Styrene and Butyl Methacrylate
Copolymers and Their Application in Leather Finishing
Journal of Applied Polymer Science 111 (3) 2009:
pp. 1488 1495.
18. Abd El-Ghaffar, M. A., El-Sayed, N. H., Masoud, R. A.
Modification of Leather Properties by Grafting. I. Effect of
Monomer Chain on the Physico-Mechanical Properties of
Grafted Leather Journal of Applied Polymer Science 89 (6)
2003: pp. 1478 1483.
19. Kaussen, M. Fatliquoring Agent for Improving the
Properties of Furniture and Automotive Leather Journal of
the American Leather Chemists Association 93 (1) 1998:
pp: 16 21.
20. Bin Lu, Jian-zhong Ma, Dang-ge Gao, Lei Hong, Jing
Zhang, Qun-na Xu. Synthesis and Properties of Modified
Rapeseed Oil/Montmorillonite Nanocomposite Fatliquoring
Agent Journal of Composite Materials 45 (24) 2011:
pp. 2573 2578.
http://dx.doi.org/10.1177/0021998311401110
21. Lihong, B., Yunjun, L., Shufen, Zh. Aliphatic Anionic
Polyurethane Microemulsion Leather Filling-Retanning
Agent Journal of the Society of Leather Technologists and
Chemists 91 (2) 2007: pp. 73 80.
22. Sivakumar, V., Poorna Prakash, R., Rao, P. G.,
Ramabrahmam, B. V., Swaminathan, G. Power
Ultrasound in Fatliquor Preparation Based on Vegetable Oil
for Leather Application Journal of Cleaner Production
16 (4) 2008: pp. 549 553.
23. United State Patent 5702490. Water Repellent Treatment of
Leather and Skin with Polysiloxanes Functionalized with
Carboxyl Groups in a Comb-like Manner, 1997.
24. European Patent Application EP 0 757 108 A2. Method for
Waterproofing Leather, 1997.
25. Luo, Z. Y., Fan, H. J., Lu, Y., Shi, B. Fluorine-containing
Aqueous Copolymer Emulsion for Waterproof Leather
Journal of the Society of Leather Technologists and
Chemists 92 (3) 2008: pp. 107 113.
... Increasing DS results in a decrease in the pI of the retanned leather. This is because the sulfonic acid and phenolic hydroxyl groups in PFS can combine with the amino groups of collagen and chrome in leather [25]. Within pH 4.5-6.5, the retanned leather possessed lower zeta potential with increasing DS, which should be helpful for the penetrations of PFS and other post-tanning agents in the leather. ...
Article
Full-text available
It is well-known that the sulfonation degree (DS) of aromatic syntan is an important factor affecting its retanning performances. But the quantitative relation between DS and syntan property and the influencing mechanism of DS on syntan property are not clarified. In this work, five phenolic formaldehyde syntans (PFSs) with the same polymerization degree but varying DS were prepared to investigate the effect of DS on the properties of syntan and crust leather. It was found that the absolute value of zeta potential and the particle size of PFS decreased with increasing DS in aqueous solution. Molecular dynamic simulation results proved that the DS of PFS was a major contributor to electrostatic interaction and hydrogen bonding in the PFS–water system and greatly affected the aggregation and dispersion of PFS in aqueous solution. The PFS with a low DS was prone to aggregate to large particles in aqueous solution because of low intermolecular electrostatic repulsion and less hydrogen bonds and therefore can be used to increase the thickness and tightness of leather. The PFS with a high DS presented a small particle size with more anionic groups in aqueous solution, thereby sharply decreasing the positive charge of leather surface and facilitating the penetration of the post-tanning agents into the leather. These results might be scientifically valid for rational molecular design of syntans and more productive use of syntans in leather making. Graphical Abstract
... Retanning agents influence the leather structure and properties. 7 Glutaraldehyde which is a well known tanning/retanning agent possesses unique characteristics that make it a most effective protein cross-linking agent. It can be present in at least 13 different forms (Fig. 1) depending on solution conditions such as pH, concentration, temperature, etc. 8 Glutaraldehyde is a 5-carbon dialdehyde with a linear structure and is mainly available as acidic aqueous solutions (pH3.0-4.0), in concentration ranging from less than 2% to 70% (w/v). ...
... Retanning agents influences the leather structure and properties (Jankauskaite et al., 2012). Phenol sulphonic acids are used as syntans in leather manufacturing. ...
Conference Paper
Full-text available
Two different samples of buff softy leather (i.e. BSPS0 and BSPS6) were prepared from a chrome tanned buffalo wet blue of Indian origin of substance 1.1-1.2 mm. BSPS0 was the control sample wherein no phenol sulfonic acid based synthetic tanning agent (syntan) was added. BSPS6 had 6% phenol sulfonic acid based syntan, in addition to the other common auxiliaries used in both the samples. Other unit operations (physical and chemical) for manufacturing leather were maintained same in both the samples. Thermal behavior of these samples was studied, and tried to be correlated with the crosslinking densities of the samples and theoretical predictions.
... But there are strong arguments against the use of vegetable oil also, a fatliquoring based on 50:50 synthetic and vegetable fatliquoring agent produces a satisfactory result. According to a report, the influence of sulfonated oil STO, SEO, sulfite fish oil, the hydrothermal stability is weak, but sulfated castor oil and sulfated fish oil can reduce the hydrothermal stability of chrome-free tanned leather [34,74]. The egg yolk is used for fatliquoring due to the presence of lecithin in it which is a high-quality emulsifier. ...
Article
Full-text available
“Fatliquor” is the most widely used wet chemical applied in the form of an emulsion at the end process of leather tanning. It keeps the leather soft, smooth, light, and heat fasting by preventing the fibrils from the aggregation and filling the voids. It pronounces most effectively on the softness, tensile properties, antifungal, and antimicrobial properties. Here this review article represents different fatliquors, its formation, applications and contemporary developments, and new challenges in producing the environment-friendly fatliquors. Applications of new novel classes of multifunctional fatliquors with excellent surface activities, biodegradability, antifungal, antimicrobial properties which are the keys to the effective fatliquoring have been focused.
... The oils cover the leather fibers with a hydrophobic layer with very low surface tension. Water vapor can enter between the fibers; however, hydrophilic water droplets have high surface tension and do not spread to the hydrophobic fiber surface and only wet the inner surface [7]. For these purposes different types of oils, natural and petroleum derivative fatliquors are being used in fatliquoring process [8]. ...
Article
Full-text available
In this study, collagen hydrolysate from bovine shaving wastes of leather production with the alkali hydrolysis reaction was emulsified with amino functional silicone oils to prepare lubricating natural polymer (LNP). Particle size and zeta potential of the LNP were measured. Prepared LNP was used in the fatliquoring step of chromium tanned bovine leathers. Contact angle of the leather surfaces with water were employed to study hydrophobicity of treated leather. The water absorption behavior of leather was determined by dynamic water resistance (penetrometer test) and static water resistance tests (kubelka water up-take). Performance characterizations of leathers were carried out with tensile strength, tear strength, filling efficiency and water vapour permeability (WVP) analyses. The contact angle measurements showed that the hydrophilic property of leather surface decreased after LNP treatment. Both dynamic and static water absorption behaviour was lowered while the WVP of leathers was not significantly affected negatively except of 20% LNP. Only 20% LNP application slightly decreased the WVP of leathers. Moreover, new lubricating agent provided satisfactory strength performance and good filling effect on leathers.
... In order to meet customers' requirements, a wide variety of retanning agents is used in retanning process, such as mineral retanning agents 8 , vegetable tannins 9 , Syntans 10-12 , resins 8,13 , polymers 14,15 which could bring about a difference in adsorption capacity of leather to water and may influence the thermal stability closely related to the moisture content of leather 16 . ...
Conference Paper
Full-text available
The retanning process is considered as one of the most important processes in leather making, and it plays an important role in the modern leather industry. The fibre structure of hide or skin is not uniform and the retanning agent improves the properties of leather by filling the empty part of wet-blue leather. It could contribute to further stabilization of collagen fibres and give better handle properties to leather such as fullness and elasticity. In a conventional leather retanning process, retanning materials used include both inorganic salt like basic chromium salt, zirconium salt and aluminum salt and organic materials such as vegetable tanning agent, synthetic tanning agent, resin retanning and aldehyde tanning agent. Extract from the barks of Acacia seyal (Talh bark), widely distributed in Sudan, has been evaluated for its utilization in the retanning of the leather and presented in this paper. Barks of talh have been extracted for 1 hour with distilled water (1:10 w/v) at temperature above 80˚C. The talh extract prepared has been used for the retanning of wet blue leathers. The effectiveness of talh extract in retanning of wet blue leathers has been compared with mimosa retanning. The organoleptic properties of the leathers viz. softness, fullness, grain smoothness, grain tightness (break), general appearance, uniformity of dyeing of talh retanned leather have been evaluated in comparison with mimosa retanned leathers. Talh retanning resulted in leathers with good grain tightness. Dyeing characteristics of talh retanned leathers have been found to be better than mimosa retanned leathers. Also physical strength characteristic and shrinkage temperature and economic viability were noted. The effluent arising from this retanning system has been analyzed for its environmental impact.
Article
Realizing green processes in wet finishing (including tanning, retanning, and fatliquoring) has become a big concern in the leather industry. Although the development of chrome-free tanning agents has made great contributions to the cleaner production of leather in recent years, the retanning and fatliquoring processes matched with this promising system still have many disadvantages, such as low compatibility, complex processes, and high pollution. Here, a novel multifunctional amphoteric polyurethane (RAWPU, an amphoteric polyurethane modified by ricinoleic acid) was synthesized and applied in the processing of chrome-free tanned leather. As a result, this product has not only the retanning characteristics of leather but also the lubrication characteristics of leather, thus integrating the traditional retanning and fatliquoring processes into one step. In addition, the hygienic performance of leather treated with RAWPU is better than that of the leather treated by commercial agents. More interestingly, compared with commercial agents which are nondegradable, RAWPU synthesized in this work easily degrades. This work is of great significance to the practical production of leather.
Chapter
Full-text available
Leather tanning industries are known to generate substantial amounts of toxic wastes that pollute ecosystems and pose environmental and health risks to the human populations living in the surrounding areas. The need to optimise and manage the leather tanning processes and wastes generated is therefore in line with the United Nations (UN), encompassing 17 sustainable development goals (SDGs), and 169 targets. This study sought to find out the contribution of United Nations Industrial Development Organisation (UNIDO) and other agencies mandated to assist the rapidly expanding leather tanning industries in sub-Saharan Africa (SSA). Specifically, the study focused on how these institutions helped create quality leather awareness for decent jobs, integrated green value chain, with eco-friendly tanning processes; information technology; as well as set up technical training, research institutes, and eco-industrial parks. It investigated how these entities, promoted agroforestry, affordable energy, conserved indigenous knowledge and mainstreamed gender. It also looked at standards certification and labour laws that enable the tanning industries to attain sustainable development goals towards the 2030 agenda of the UN. The recent introduction of innovative bioprocessing and bioremediation techniques into this industry is also opening more opportunities for green leather development in line with the SDGs.
Article
Full-text available
The aim of this research was to determine the influence of pulsed CO 2 laser treatment on crust leather surface morphology and wettability. The obtained results revealed that pulsed CO 2 laser engraving can be used as an effective tool for crust leather surface treatment. Pulsed CO 2 laser treatment only negligible affects the macrostructure of leather, while the morphology and wetting of the leather surface after treatment were changed. It was found that an increase of laser pulses number increases the initial water contact angle value and intensifies the water droplet relaxation process. After laser treatment, the water droplet contact angle relaxation rate increases twofold compare to those for untreated leather. SEM micrographs showed increased defectiveness with rough surface patterns, thermally affected areas, and change of microstructure. The EDX analysis revealed that the engraved leather surface contains a significantly higher amount of carbon but smaller quantities of oxygen compared to those of untreated samples. It was found that only after laser treatment chromium and sulfur in the EDX spectra appear while for untreated samples these elements on the surface were not observed. The results indicate that for investigated samples laser engraving does not affect the concentration of hexavalent chromium and are in accordance with EU requirements.
Article
Full-text available
In this paper the experimental and theoretical investigations of moisture transfer through microporous film laminated leather are presented. The water vapour absorption and desorption processes of laminated leather are described. Water vapour absorption in the laminated leather and its separate layers may be classified as non-Fickian: sigmoidal - for microporous film and two-stage - for the leather of different structures. Water vapour desorption of leather changes according to the exponential law and for microporous film according to the linear one. Water vapour absorption/desorption mechanism depends on the leather permeability. Microporous film does not worsen moisture transfer properties of the laminated leather. However water vapour permeability decreases and absorption increases due to the nonporous adhesive layer used for microporous film bonding. The decrease of laminated leather permeability intensifies the formation of capillary moisture or water clusters and increases water accumulation.
Book
This book offers a state-of-the-art view of leather making, based on the scientific principles underpinning the technology. In particular, it contributes to the understanding of the modern leather industry, allowing practitioners to make judgements about day-to-day problems in the tannery and how change can be applied in a predictable way. Major themes running through the book are the economics and environmental impact of leather making and how these will ensure the sustainability of the industry. This second edition of Tony Covington’s Tanning Chemistry is a revision, update and extension in collaboration with a new co-author, Will Wise. The update reflects the advances made in the past decade, including a discussion of the impact of new information concerning the chemistry of sulfide. The original chapters have been re-organised and new chapters on novel modes of reagent delivery and the principles of finishing are now included. Enzymology is addressed as a separate topic, as are environmental impact and the future of leather. The book will be useful to all those involved in the supply chain, from farm, through students, chemical suppliers and tanners, to leather goods brands. Leather science is the key to understanding leather technology, to make it work, to make it work better and to keep it ahead of the competition.
Article
The influence of different factors on the waterproofing capacity of retanning-fatliquoring polymers was studied in an earlier work. In the present paper, given that the production of waterproofed leather articles requires the use of different retanning agents, the effect of these agents on water-repellency is evaluated. The variation of water repellency with time is also studied. It has been confirmed that the retanning agent plays an important role in the final degree of water repellency. Different retanning agents yielded varying water repellency rates. Time increased the waterproofing properties of the leather. However, the water-repellency values became uniform after subjecting the leather to a temperature of 80°C in an oven for 48 hours.
Article
In the last decades several products have been applied to confer waterproofing properties to the leather: natural oils, alkenyl succinic acids, poly-siloxanes, chromium soaps (stearates and oleates), phosphoric esters alone or in combination with alkenyl succinic acids and reactive agents or amphiphilic polymers. Other products (silicone derivative, fluorcarbonated resin) confer not only waterproofing but also oil repellent properties to the leather. In this work, the waterproofing behaviour of retanning-fatliquoring polymers alone or in combination with other hydrophobic products such as a silicone derivative and a fluorcarbonated resin is studied. The anionization of the tanned leather on the waterproofing performance of the retanning-fatliquoring polymer and the influence of the addition of fatliquoring auxiliaries to the tanning bath on the water repellent properties of the leather produced are also evaluated. A complete anionization of the tanned leather, by using a naphthalene sulphonic acid salt, is of paramount importance to obtain good water repellency. The addition of a sulphochlorinated paraffin and a phosphoric ester to the tanning bath reduced water-repellency values drastically.
Article
The retanning process plays an important role in optimizing the leather's colour, levelness, softness, fullness, and hydrophobicity. Polymer retanning agents are important materials for this process. The present study used maleic anhydride modified castor oil (MCO), PEG1000 (polyethylene glycol) and IPDI (isophorone diisocyanate) as main materials to synthesize polyurethane microemulsions (MC-PURs) and employed them to retan chrometanned leathers. The hydroxyl functionality of MCO was investigated by chemical and 1HNMR analysis, and confirmed to be about 2.0. The chemical structures of MCO, prepolymer and MC-PUR were characterized by IR. The optimized synthesis formulation and polyurethane microemulsion MC-PUR3 for MC-PURs as retanning agent was selected by comparing the properties of retanned leathers, such as softness, fullness, grain tightness, tensile strength, extension at break, depth of shade, waterproof properties et al. Then, MC-PUR3 was characterized by means of DSC, TG/DTG and TEM techniques. SEM microgram of MC-PUR3 retanned leather shows that the fibres are well dispersed.
Article
A novel fluorine-containing aqueous copolymer emulsion, which was used for waterproof leather fatliquoring, was prepared via free radical copolymerization from maleic anhydride and natural oil (rapeseed oil and fish oil) followed by an esterification reaction with dodecafluoro heptanol and octadecyl alcohol. The reaction was monitored on-line by FTIR analysis and the combining fastness [strength of the combination] between the fatliquoring agent and leather fibre was examined by extraction with dichloromethane and water. Simultaneously, the effects of the fluorine content on contact angle (water-surface of leather), dynamic waterproofness time and static water absorption ratio of leather were also investigated. The X-ray photoelectron spectroscopy (XPS) showed that most of the hydrophobic fluorine-containing groups were orientated onto the surface of the leather and formed a hydrophobic film layer, whilst the hydrophilic carboxyl groups were enveloped in the inner layer. The fact the combination fastness is greater for the fluorine-containing copolymer than for other types of fatliquoring agents, shows that the carboxyl groups in the inner layer have coordinated with chrome(III) in the form of chemical bonding rather than by physical absorption. Chrome tanned leather treated with this type of fluorine-containing copolymer fatliquoring agent shows good durable waterproofness. When the fluorine content in fatliquoring agent is varied from Owt% to 5wt% (based on solid content), the contact angle increases from 125° to 155°, the static water absorption ratio of leather is less than 9wt% and the dynamic waterproofness time reaches 55 minutes.
Article
The retanning process is a very important step in the leather manufacturing because it overcomes some of the disadvantages of chrome tannage. For this purpose, two different nano-emulsions of styrene/acrylate copolymers were prepared using seed emulsion polymerization technique. The main difference and characteristics of the two copolymer emulsions were studied. In addition, the morphology and the nano-particle size of the copolymer emulsions was proved by transmission electron microscope (TEM). The influence of the prepared copolymer emulsions as retanning agents for chrome tanned leather was also studied. The physico-mechanical properties of the retanned leather, namely, tensile strength, elongation at break and tear strength, were measured. Thermal stability and texture of grain surface and fibers of chrome tanned leather were examined using thermal gravimetric analysis (TGA) and scanning electron microscope (SEM), respectively. All these parameters were the main target of this work and used to evaluate the applicability of the copolymers as efficient retanning agents. The results showed an improvement in the physico-mechanical properties, softness, and firmness of grain as well as enhancement in thermal stability upon retanning by the prepared copolymer emulsions.
Article
A water-based thermally-responsive polyurethane (TRPU), based on the crystalline soft segment from the reaction of polycaprolactone diol (PCL) with isophorone diisocyanate (IPDI) and the crystalline hard segment from the reaction of IPDI -1,4-butanediol (BDO) together with dimethylolpropionic acid (DMPA), was synthesized and used in water vapour permeable leather finishing. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analyzer (DMTA), water swelling and water vapour permeability (WVP) were measured to evaluate how the structure of PU and the temperature influence the WVP of PU films and finished leathers. In contrast to common polyurethane elastomer (PUE) with an amorphous reversible phase, the TRPU with a crystalline reversible phase shows a phase-separated structure and a phased transition temperature (T trans) at normal use temperature. The water swelling and water vapour permeability of both TRPU film and finished leather are found to depend on the inner structure of the polymers and the temperature. When the temperature exceeds the Ttrans, a significant increase of WVP from 4100g/m 2/day to 10500g/m2/day was observed for finished leather in spite of some decrease of WVP compared with un-finished leather. Leather finished with common PUE appears to have a low WVP and only a slightly increased value over the temperature range.
Article
It is clear from experience in the Falklands that many of the longstanding problems associated with military footwear design remain unsolved. This review examines the aspects of design in relation to function and elucidates the many conflicting requirements of ideal boot design. Mobility, protection, insulation, waterproofing, vapour permeability, durability, weight, fit and supply, for instance, make contrasting demands upon the design of boots. Furthermore, failure to solve those conflicts, it is suggested, resulted in many non-freezing cold injuries in the South Atlantic and frequently leads to other injuries, including frostbite, when present boot designs are tested in action.An attempt is made to reconcile these and other criteria with the suggestion of a modular infantry ‘footwear package’ consisting of an inner and a number of different middle and outer boots.