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Glutaraldehyde-tanned leather treated with tocopherol.
Article in Journal- American Leather Chemists Association · March 2005
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102
GLUTARALDEHYDE-TANNED LEATHER TREATED
WITH TOCOPHEROLa
by
CHENG-KUNG LIU,* NICHOLAS P. LATONA, AND JOSEPH LEE
United States Department of Agriculture,** Agricultural Research Service
Eastern Regional Research Center
600 EAST MERMAID LANE
WYNDMOOR, PA 19038-8598
ABSTRACT
Non-chrome-tanned (chrome-free) leather has
gradually gained commercial importance, particularly for automobile upholstery applications. UV
and heat resistance are very important qualities for
automobile applications. We developed an environmentally friendly finishing process that will
improve the UV- and heat resistance of automobile
upholstery leather. Tocopherol (Vitamin E) is a
potent free radical scavenger and highly protective
agent for collagen fibers against UV damage. We
previously reported that the application of tocopherol to the grain layer of chrome-tanned leather
improved its durability. The current study focuses
on non-chrome-tanned leather made with a glutaraldehyde tanning process. We applied tocopherol to the grain layer of that leather and also
studied the addition of tocopherol to the fatliquoring drums. Following exposure in a Fade-Ometer,
the treated samples were evaluated by colorimetry
and mechanical testing for the efficacy of UV- and
heat resistance. A polarizing microscope equipped
with a Berek compensator was employed to determine the birefringence of the untreated and treated
leather collagen fibers to determine the treatment
effects on the degree of orientation. Data showed
that leather coated with tocopherol exhibited significant improvement in tensile strength retention
and color fading resistance against UV radiation
and heat. Leather fatliquored with tocopherol,
however, did not show a similar improvement.
INTRODUCTION
Glutaraldehyde tanning was developed by Filachione et al.
in the Eastern Regional Research Center (ARS, ERRC) in
the early 1960's.1-5 It has become the most common alternative tanning agent to chrome salts, because it is less
expensive, is readily available, and is highly soluble in
aqueous solution. In recent years, it has been the dominant
tanning agent for preparation of chrome-free leather. The
chemistry of fixation of glutaraldehyde to collagen is not
fully understood. Presumably, it involves crossslinking by
the reaction of an aldehyde group with an amino group of
lysine or hydroxylysine or an aldol condensation between
two adjacent aldehydes.6 Although the majority of leather
is tanned using Cr(III) salts, environmental concerns over
the use and disposal of chrome-tanned leather encourage the
use of chrome-free leather, particularly in the European
automotive leather markets.7 Presently there is an increasing demand for the domestic production of automotive
leather.8 The quality of chrome-free leather such as glutaraldehyde-tanned leather in some respects is inferior to
that of chrome-tanned leather, for example in colorfastness
and thermal stability.9,10 Leather for car interiors is required
to meet exceptionally high quality standards. Consumers
expect leather to be able to withstand exposure to extreme
and varying temperatures, light, moisture and mechanical
loading conditions over time. Most automobile leather is
colored to improve its appearance and aesthetic value.
Sunlight on the other hand is a powerful form of energy that
can break up colored molecules into smaller pieces and can
cause a yellowing or bleaching effect. If chrome-free
leather is used for instrument panels and consoles, the problem of shrinkage due to poor heat resistance is especially
acute, as temperatures well over 100°C can be reached. The
poor lightfastness of crust leathers prevents the use of light
pigments or dyes and, therefore, more natural looking or
aniline finishes for leather. When using such leather in
automotive applications, these inadequacies are of paramount importance, and they need to be studied to find ways
of producing lightfast leather with improved thermostability.
*Corresponding Author. (e-mail address: [email protected]).
**Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and
does not imply recommendation or endorsement by the U.S. Department of Agriculture.
a
A Technical Paper based on a presentation at the 100th annual meeting of the American Leather Chemists Association at the
Chase Park Plaza, St. Louis, Missouri on June 16 - 20, 2004
JALCA, VOL. 100, 2005
103
UV AND HEAT RESISTANCE
Many studies demonstrated physico-chemical changes of
collagen induced by UV radiation.11,12 Sionkowska reported
that solar radiation induces photodegradation of collagen.13
Fujimori revealed that a solution of collagen, after UV irradiation, loses the ability to form natural fibrils.14 For synthetic polymers, UV absorbents such as hydroxybenzophenones have been widely used to improve the light stability
of both plastics and their colorants.15 UV absorbents are
also commonly used in skin care products such as sunscreens.16 They include benzophenones, cinnamates and
salicylates. Contact sensitivity or allergic reactions have
been reported with benzophenones.17 Cinnamates are effective UV blockers but have poor waterproofness. They are
generally used in combination with other agents; an example is octylmethyl cinnamate. Salicylates are also often
used in sunscreens, and they are water-insoluble.
Antioxidants are often included in sunscreens as free-radical scavengers. Tocopherol (vitamin E) is a potent free radical scavenger and a highly protective agent against UV skin
damage.18,19 It is a light yellow colored oil and a fat-soluble
vitamin. The principal role of tocopherol as an antioxidant
must be to neutralize free radicals that could initiate a chain
reaction, resulting in the formation of peroxides and products of their subsequent degradation.20 Thermal stability of
leather may be improved by using antioxidants such as toco-
pherols to protect against thermal oxidation, thereby
improving the stability of the triple helical structure of the
collagen molecules. We recently experimented with the
application of α-tocopherol to the grain layer of chrometanned leather. Results showed that chrome-tanned leather
treated with α-tocopherol yielded a significant improvement in mechanical strength and softness and, more importantly, increased strength retention and color fading resistance against UV radiation and heat. However, how the αtocopherol treatments affect the fine structure of collagen
fibers is unknown. Collagen fibers are the building blocks
of leather. The need to study the fine structure of collagen
fibers has led us to employ a polarizing microscope to measure the birefringence of fibers and thereby gain insights on
the effects of UV and heat on the fine structure of fibers.
Birefringence is a physical quantity associated with the
degree of orientation of the molecular chains in the fibers.
The current study focuses on the non-chrome-tanned leather
made with a glutaraldehyde tanning process. We applied
tocopherol to the grain layer of leather and also studied the
addition of tocopherol to the fatliquoring process.
Following exposure in a Fade-Ometer, the treated samples
were evaluated by colorimetry and mechanical testing for
their UV and heat resistance.
TABLE I
Deliming and Pretanning
Dilution
Process
Wash
Drain
Delime
Bate
Drain
Washed
Drain
Pickle
1:5
1:10
1:10
1:5
%
300
Product
Water
o
150
1
0.8
0.15
Water
Decatal ES-Deliming Agent
Decatal ES-Deliming Agent
Rohapon 6000-Bating Agent
27
200
Water
18
30
Water
7
Sodium Chloride
1
Lipoderm Liq NB1C-Fatliquor
0.5
Formic Acid
1.6
Sulfuric Acid
Pretannage
1.5
Sellatan CF Liq
2
Sellatan RL-Synth. Replacement Tannin
3
Sellatan FL-Synth. Replacement Tannin
0.1
Busan 30 L-Biocide
Basification
0.25
Sodium Bicarbonate
0.15
Sodium Bicarbonate
0.15
Sodium Bisulfite
Next day check pH. Horse up overnight
C
27
Time (min.)
15
15
30
120
pH
8.3-8.5
RPM
6
6
6
6
10
18
10
15
30
90
60
2.7-2.9
60
20
6
6
6
6
16
16
16
Overnight
6
3.8-4.0
JALCA, VOL. 100, 2005
104
UV AND HEAT RESISTANCE
EXPERIMENTAL
Materials And Procedures
Fresh hides were purchased from Moyer Packing Co.
(Souderton, PA ) and frozen at the ERRC. The hides were
thawed and cut into specimens. The hides were unhaired
using a sulfide-free unhairing process developed by Marmer
et al. at ERRC.23 The deliming and pretanning steps are listed in Table I. The sources of chemicals are: Decatal ES
(BASF, Charlotte, NC), Rohapon 6000 (TFL, Greensboro,
NC), Lipoderm NB1C (BASF, Charlotte, NC), Sellatan
CFL (TFL, Greensboro, NC), Irgatan RL (TFL, Greensboro,
NC), Irgatan FL (TFL, Greensboro, NC), Busan 30L
(Buckman Laboratories Inc., Memphis, TN). After unhairing the samples were lime-split to a thickness between 1.0
and 1.5 mm. The samples were then pretanned, retanned
and horsed up overnight. Table II lists the sequential
processes for tanning, retanning, dyeing and fatliquoring
used for the preparation of the chrome-free tocopherol-coated samples. The source of chemicals are: Saform acid
(Sentury Custom Services, Allamuchy, NJ), Sellatan CFL
(TFL, Greensboro, NC), Sellatan RL (TFL, Greensboro,
NC), Lipsol SQ (Strucktol/Schill and Seilacher, Stow, OH),
and Basyntan DLE (BASF, Charlotte, NC), Sellatan FL
(TFL, Greensboro, NC), Tara (Tannin Corp., Peabody, MA),
Eureka 950R (Atlas Refinery, Newark, NJ), Lipsol SQ,
Magnopol SOF-G (TFL, Greensboro, NC), Derma Red BG
(Clariant Corp., Fair Lawn, NJ). The leather was then
drained, washed at 50 °C and then drained again. The
leather was thereafter placed in plastic bags until it was toggle-dried at ambient temperature. The shrinkage temperature on the dried test pieces was found to be 85 °C. We
achieved a very consistent and good shrink temperature that
indicates uniform processing. The samples were then wet
TABLE II
Tanning, Retanning, and Fatliquoring Processes for Tocopherol Coatings
Dilution
1:10
1:5
1:5
1:5
1:10
Process
Wash
Drain
Float
%
200
150
0.4
Tannage
2
Basification
0.8
0.2
Retan
2
2
1
Retan
22
6
3
Fatliquoring
3
2
3.5
Dyeing
6
Next day check pH
Drain
Wash
200
Drain
Float
150
Fatliquoring
6
2.5
4
Retan
2
1
Add
0.5
Drain
Wash
200
Drain
JALCA, VOL. 100, 2005
Product
Water
o
Water
Sentry-Saform Acid-Non Swelling Acid
Sellatan CF Liq
Sodium Formate
Sodium Bicarbonate
Sellatan RL-Synth. Replacement Tannin
Lipsol SQ-Lecithin Fatliquor
Basyntan DLE
Sellatan RL-Synth. Replacement Tannin
Sellatan FL-Synth. Replacement Tannin
Tara-Vegetable Extract
Eureka 950R-Fatliquor
Lipsol SQ-Lecithin Fatliquor
Magnapol SOF-G-Polymeric Softener
Derma Red BG-Dye
20
C
20
Time (min.)
15
pH
RPM
16
10
60
3.2-3.4
16
16
20
3.7-4.0
16
20
16
90
16
60
overnight
16
6
4.0-4.2
Water
50
Water
Eureka 950R-Fatliquor
Lipsol SQ-Lecithin Fatliquor
Magnapol SOF-G-Polymeric Softener
Sellatan RL-Synth. Replacement Tannin
Basyntan DLE-White Tanning Agent
Formic Acid
50
Water
50
15
16
60
16
30
40
16
16
10
3.2-3.5
16
105
UV AND HEAT RESISTANCE
back and passed through a Molissa staking machine at a
medium setting (model 16370, Strojosuit, Czechoslovakia)
twice at a rate of 1.6 meters/min (5.3 ft/min). Six approximately 21.6 x 26.6-cm rectangular pieces were cut out near
the standard butt test area (ASTM D2813-97). We then
applied the dl-α-tocopherol (Sigma, St. Louis, MO) on the
surface of the grain in the amount of 7 g/ft2. The coated
leather samples were then conditioned in a conditioning
room at 23°C and 50 percent RH.
Besides coating tocopherol directly on the grain layer, in
another experiment, we added tocopherol to the fatliquoring
drum, instead of coating. Table III lists the various processes for tanning, retanning, dyeing and fatliquoring used for
the preparation of the chrome-free leather with tocopherol
added in the main fatliquoring step.
Measurements
Before physical property testing, the samples were stored in
a conditioned room at 23°C and 50% RH according to
ASTM D1610-96. Mechanical property measurements
included tensile strength and elongation. Tensile strength is
the maximum stress in tension that the leather may sustain
without breaking. Elongation is defined as the maximum
strain. Rectangular shaped leather samples (1 × 10 cm)
were cut near the standard test area as described in ASTM
D2813-97 with the long dimension parallel to the backbone.
These properties were measured with a sample length of 5
cm between the two grips. The strain rate (crosshead speed)
was set at 5 cm/min. An upgraded Instron mechanical prop-
TABLE III
Tanning, Retanning, and Fatliquoring Processes for Tocopherol added in Fatliquor
Dilution
1:10
1:5
1:5
1:5
Process
Wash
Drain
Float
150
0.4
Tannage
2
Basification
0.8
0.2
Retan
2
2
1
Retan
22
6
3
Fatliquoring
3
2
3.5
Dyeing
6
Next Day Check pH
Drain
Wash
200
Drain
Float
150
Fatliquoring
6
2.5
4
Retan
1:10
%
200
Add
Drain
Wash
Drain
0.5 to 10
2
1
0.5
200
Product
Water
o
Water
Sentry-Saform Acid-Non Swelling Acid
Sellatan CF Liq
Sodium Formate
Sodium Bicarbonate
Synth. Replacement Tannin
Lipsol SQ-Lecithin Fatliquor
Basyntan DLE-White Tanning Agent
Sellatan RL-Synth. Replacement Tannin
Sellatan FL-Synth. Replacement Tannin
Tara-Vegetable Extract
Eureka 950R-Fatliquor
Lipsol SQ-Lecithin Fatliquor
Magnapol SOF-G-Polymeric Softener
Derma Red BG-Dye
20
Water
50
C
20
Water
50
Eureka 950R-Fatliquor
Lipsol SQ-Lecithin Fatliquor
Magnapol SOF-G-Polymeric Softener
Tocopherol Emulsified with surfactant SDS 2:1
Tocopherol, Samples
Sellatan RL-Synth. Replacement Tannin
Basyntan DLE
Formic Acid
Water
50
Time (min.)
15
pH
RPM
16
10
60
3.2-3.4
16
16
20
3.7-4.0
16
20
16
90
16
60
Overnight
4.0-4.2
16
6
15
16
60
30
40
10
3.2-3.5
16
16
16
JALCA, VOL. 100, 2005
106
UV AND HEAT RESISTANCE
erty tester, model 1122, and Testworks 3.1 data acquisition
software (MTS Systems Corp., Minneapolis, MN) were
used throughout this work. Each test was conducted on four
samples to obtain an average value.
We used an Atlas Ci3000F, Xenon Arc Fade-Ometer
(Oxford, PA), to evaluate the UV- and heat resistance of the
leather samples. The samples were put inside the FadeOmeter that calibrated at 420nm, for total radiation dosage
of 225.6 kJ/m2 (about 72 h exposure). The settings for the
Fade-Ometer were as follows: black panel temperature100
± 2 oC, dry bulb temperature 65 ± 5 oC, radiation intensity
1.1 Watts/m2 and RH 20 ± 10%. These settings have been
commonly used in various industries for testing UV and
heat resistances. The colorfastness to light of the specimen
is evaluated by measuring the color change (∆E) between
the exposed samples and the unexposed original samples,
using the color-insights® QC Manager System (BYKGardner, Inc., Silver Spring, MD), which is an absorptiometric colorimeter often used for fabrics. We followed the
CIELAB colorimetric method; ∆E was calculated using the
following equation:24
∆E = (∆L*2+∆a*2+∆b*2)1/2
(1)
L* represents the difference between light and dark. A*
represents the difference between green (-a*) and red (+a*),
and b* represents the difference between yellow (+b*) and
blue (-b*). Measurements were conducted four times to
obtain an average value.
Birefringence Measurement
We conducted birefringence (double refraction; n) measurements for the collagen fibers from various test specimens of leather.25 The apparatus was a Nikon polarizing
microscope (model E600 POL) equipped with a Berek compensator. The birefringence of a fiber was determined by
measuring the two principal refractive indices, nII and n⊥
(measured parallel and perpendicular to fiber axis, respectively) and subtracting one from the other:
∆n = nII - n⊥
(2)
When a fiber is viewed between crossed polars, interference
phenomena are observed. In the absence of a specimen, the
field of view with crossed polars is dark because the polarizer will pass only light polarized in one direction, and the
analyzer will pass only light polarized in a perpendicular
direction. The Berek compensator is capable of quantitatively determining the wavelength retardation of a crystal,
fiber, plastic film or other birefringent material. Provided
that the thickness of the material can be measured, a Berek
JALCA, VOL. 100, 2005
compensator can be utilized to ascertain the birefringence
value.
Tocopherol Quantification
Lipids were extracted from leather samples with hexane
using a Dionex ASE 200 Accelerated Solvent Extractor
using a previously described method.26 Duplicate 1-gram
samples were ground to 20 mesh using a Wiley Mill
(Thomas Scientific, Philadelphia). The extraction cells (11
ml) were loaded with the sample and the cell was topped off
with Ottawa sand to fill the void space. The extractions
were performed at a pressure of 1000 PSI and a temperature
of 100°C. Each extraction consisted of three 10-min static
cycles and a total volume of 22 ml hexane was used to
extract each sample. One ml of extract was removed for
HPLC, the remaining extract was dried under N2 and heat,
and the total mass was measured (correcting for the amount
removed). HPLC analysis was performed with an Agilent
1100 system, a LiChrsorb Diol column (3 x 100 mm), eluted isocratically with hexane/methyl t-butyl ether, 980/20,
v/v, and flow rate of 0.5 ml/min. Under these conditions
α-tocoopherol eluted at a retention time of 6 minutes and
was measured with an HP1100 Fluorescence detector operated at 294 nm excitation and 326 nm emission.
RESULTS AND DISCUSSION
Color Lightfastness and Tensile Strength Retention
Figure 1a demonstrates the effect of UV radiation on reddyed leather samples. It shows the samples coated with
tocopherol have much less color change than the samples
without the protective coating. Good resistance to color
fading in sunlight or artificial light is important for all
upholstery leather, but is particularly critical in automotive
leather, where the seats can be exposed to intense sunlight
at high temperatures for very long periods of time.
Adequate tensile strength is very important in manufacturing leather goods, where the leather is often subjected to a
tensile force during mechanical stretching or elongation.
Moreover, in a variety of end uses, leather goods must be
capable of resisting considerable stress without fracture.
Tensile strength determines the maximum tensile stress the
leather can sustain without fracture. Figure 1b shows the
resultant tensile strength retention (ratio of tensile strength
of samples before and after Fade-Ometer testing). For the
control samples, the tensile strength suffers a significant
loss. In contrast, tocopherol treatments yield greater tensile
strength retention. It is interesting to note that the value is
greater than 1, indicating tensile strength increased after
Fade-Ometer testing. This is probably due to the high temperature in the Fade-Ometer, which helps the penetration of
107
UV AND HEAT RESISTANCE
b.
a.
TENSILE STRENGTH RETENTION
32
COLOR CHANGE (delta E)
28
24
20
16
12
8
4
0
1.2
1.0
0.8
0.6
0.4
Control
Control Tocopherol
Tocopherol
TREATMENTS
Figure 1. - Color change (a) and tensile strength retention (b).
tocopherol, thereby increasing the lubrication of leather
fibers. As reported previously, besides its function as a free
radical scavenger, tocopherol may have a lubrication effect
toward the leather fibrous structure, which would result in
better tensile strength. Leather is made of bundles of interwoven collagen fibers. When leather is stretched, as done
in a tensile test, the fibers are aligned in the direction of
stretching. If the leather is not well lubricated, the fibers do
not slip over each other and some fibers will start to break,
which will break prematurely due to high friction resistance.
On the other hand, if the samples are well lubricated, then
the leather will bypass this premature breakage and have
more fibers to contribute to the resistance of deformation
until final fracture, resulting in better tensile strength retention.
Birefringence and Fiber Strength
Figure 2 shows the birefringence of the fibers from the different leather samples. It demonstrates that the UV and
heated samples after being run in the Fade-Ometer have a
It is well known that fibers are highly anisotropic and their
tenacity (the terminology used in textile industry for tensile
strength of fibers) is very sensitive to the change of bire-
nz
∆n=0
nII
∆ n = nII –nz
Figure 3. - Relationship between orientation and birefringence of fibers.
fringence. This is not surprising, because tensile strength is
a vector quantity. It only quantifies breaking stress in the
one direction that it is being stretched. Therefore, the resistance is given only by the vector components parallel to the
applied force direction. Obviously, the more molecular
chains that line up in this direction, the higher the tensile
strength that is attained. As illustrated in Figure 4, the birefringence data has a strong link to the tenacity of fibers.27
The higher birefringence values mean a greater degree of
orientation of the molecular chains in the fibers, consequently the more molecular chains to share the tensile force,
thus resulting in a better tensile strength.
0.04
BIREFRINGENCE
significant lower birefringence than the original non-irradiated samples. The difference in the refractive indices
depends on the relation between the direction of polarization of the light and the direction of alignment of the molecular chain. It is therefore to be expected that the birefringence will be greatest when the molecules are all lined up
parallel to the fiber axis and that will be zero when they are
randomly directed, as illustrated in Figure 3. This result
indicates that the UV-irradiated leather fibers lost a significant degree of orientation in their molecular chains.
Presumably, the UV radiation and heat caused disorientation in the collagen molecular chains, thereby resulting in a
lower birefringence. On the other hand, the sample coated
with tocopherol did not lose the degree of orientation as
drastically as the untreated samples after UV radiation in a
Fade-Ometer. Apparently, the tocopherol coating creates a
protective shield that minimizes the UV and heat damage.
0.03
0.02
0.01
0.00
CONTROL
UV/Heat
Toco Coat
Toco Coat, UV/Heat
SAMPLES
Figure 2. - Birefringence of leather fibers.
Wet Treatments
Besides coating the leather samples with tocopherol, a set of
JALCA, VOL. 100, 2005
108
UV AND HEAT RESISTANCE
Silk
Polyethylene
4
Cotton
3
2
Rayon
Wool
32
COLOR CHANGE (Delta E)
FIBER TENACITY (g/denier)
Nylon
5
30
28
26
24
1
0.01
0.02
0.03
0.04
0.05
0.06
BIREFRINGENCE
0
Figure 4. - The correlation between fiber tenacity and birefringence.
5
10
15
TOCOPHEROL CONTENT (mg/g)
15
TENSILE STRENGTH RETENTION
TOCOPHEROL CONTENT (mg/g)
Figure 6. - Color change as a function of tocopherol content
in the fatliquoring process.
10
5
0
0
2
4
6
8
1.7
1.4
1.1
0.8
0.5
0.2
10
0
TOCOPHEROL OFFERED (%)
Figure 5. - Tocopherol absorption as a function of tocopherol
offered in the fatliquoring.
15
(3)
Variance analysis showed that the p-value is less than 0.001,
confirming that this nonlinear model is highly justifiable.
P-value indicates the probability that effects originated from
experimental error (instead of factor itself); therefore a
smaller value of p indicates a greater significance of effects.
The value of 0.1 (or 10%) is a commonly used cutoff of pvalue for significance.
The colorfastness test results from those wet-treatments are
not as good as offered by the coated samples. As illustrated
2.0
ELONGATION RETENTION
As demonstrated in Figure 5, the absorbed tocopherol
increases as the tocopherol offered (denoted as X) in the
drum increases. Regression analysis gave the following
equation (Equation 3) with a coefficient of multiple determination (R2) of 0.98.
JALCA, VOL. 100, 2005
10
Figure 7. - Tensile strength retention as a function of tocopherol content
in the fatliquoring process.
experiments was also conducted by adding tocopherol to the
fatliquoring drum; the procedures are listed in Table III.
Tocopherol content (mg/g) = 3.96 X - 0.24 X2
5
TOCOPHEROL CONTENT (mg/g)
1.7
1.4
1.1
0.8
0.5
0.2
0
5
10
15
TOCOPHEROL CONTENT (mg/g)
Figure 8. - Elongation a function of tocopherol content
in the fatliquoring process.
in Figure 6, the colorfastness shows some degree of
improvement, but the beneficial effects of tocopherol are
not as obvious as the coated samples. On the other hand, the
increase in the strength retention ratio is rather evident as
UV AND HEAT RESISTANCE
with the percent tocopherol offered in the drum increases, as
shown in Figure 7. Tests also indicated that the samples
fatliquored with tocopherols have greater elongation retention, as demonstrated in Figure 8. This is largely due to the
lubrication function of tocopherol, with which the leather
fibers readily slip over one another, thereby increasing the
extensibility of leather.
CONCLUSIONS
This on-going research aims to develop a process treatment
that is environmentally friendly and yet significantly
increases the UV and heat resistance of chrome-free leather.
Data showed that coating leather with α-tocopherol significantly improves the color fading resistance and strength
retention against UV radiation and high temperature. We
also studied the addition of tocopherol to the fatliquoring
drums, but this treated leather did not show a similar
improvement. Our future work will explore the mixed α-,
β-, and γ-tocopherol for UV and heat resistance treatments,
the mixed isomers are less costly than α-tocopherol alone.
On the other hand, we will also investigate the fine structure
of treated leather fibers to gain a better understanding of the
structure/properties relationship. Moreover, we will explore
effectiveness of tocotrienols, which are believed to be
stronger antioxidants than tocopherols. The tocotrienols
differ from the tocopherols in the chemical nature of the
side chain (tail). Tocopherols have a saturated phytyl side
chain, whereas tocotrienols have an unsaturated isoprenoid
or farnesyl side chain possessing three double bonds.
ACKNOWLEDGMENTS
We thank Dr. Robert Moreau and Mr. Michael Powell of
ERRC for tocopherol quantitative measurements. We also
thank Mr. Jurgen Kuhnert of Cudahy Tanning Co., Dr.
David Coffin of ERRC, and Mr. James Haworth of Cargill
Nutriproducts for their invaluable information and comments.
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CONVENTION DISCUSSION
Stephen Yanek, Eagle Ottawa - Thank you very much C.-K.,
very nice. Two questions. Does the tocopherol have one or
more functional groups that could be used to help retain it
to the leather? In the one chart that you showed where it
peaked at about 8%, what method did you use to quantify
that?
We used hexane extraction and HPLC of the hexane extract
to quantify the level of tocopherol. I do not know which
functional groups in tocopherol react with the leather.
JALCA, VOL. 100, 2005
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Stephen Yanek, Eagle Ottawa - Was the concept that you
were relying on to have the tocopherol dissolve in the oil to
stay on the leather?
Yes.
Stephen Yanek, Eagle Ottawa - Was it a powder or a gel?
Tocopherol is an oil. We used a surfactant to help emulsification of the tocopherol in the fatliquor.
Rodney Hammond, Seton Co. - C.-K. have you looked at
whether the improved UV performance of the leather that is
treated with tocopherol continues if you put the leather
through climate testing where you go with high humidity
cycles, high humidity low temperature and then low humidity high temperature?
No we did not do that. We will do that in the future. Right
now we are testing with the humidity constant at 20%.
Rodney Hammond, Seton Co. - The reason I ask you that is
because you did not get the same results when you applied
the tocopherol in the fatliquor which suggests that it is the
surface coating itself that is giving the improved performance. Therefore, I would wonder if you do something that
would affect the surface coating whether you would continue to have the improved performance over time.
I intend to look at that in the next series of experiments.
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