Study of the effect of temperature, relative humidity and UV radiation on chrome-tanned leather ageing

Abstract

Since leather is strongly affected by three main environmental parameters: temperature, relative humidity and UV radiation, this piece of research focuses on the effect that these three factors have on chrome-tanned leather ageing. Chrome tanned leathers were exposed to weathering effects in a climatic chamber in order to identify the most important variables affecting this weathering process and also to check for any possible interactions. Both a multilevel centralized factorial experimental design and an analysis of variance (ANOVA) were used as statistical tools for estimating the effects of the parameters.

Full text

JALCA, VOL. 107, 2012
  179
Study of the effect of temperature, relative humidity
and uv radiation on chrome-tanned leather ageing
by
Anna Bacardit*, Montse Jorba1, Joaquim Font, and Luís Ollé
Igualada Engineering School (EEI). UPC.
Plaça del Rei, 15. 08700-Igualada (Spain)
1Asociación de Investigación de las Industrias de Curtidos y Anexas (AIICA).
Avda. Pla de la Massa s/n, 08700 Igualada, Spain
*Correspondingauthore-mail:annab@euetii.upc.edu;Tel.:+34-93-803-5300;
Fax:+34-93-803-1589ManuscriptreceivedNovember3,2011,acceptedforpublicationJanuary7,2012
Abstract
Sinceleatherisstronglyaffectedbythreemainenvironmental
parameters:temperature,relativehumidityandUVradiation,
thispieceofresearch focusesonthe effectthat thesethree
factorshaveonchrome-tannedleatherageing.Chrometanned
leat hers wer e expose d to weat herin g effect s in a cl imatic
chamber in order to identify the most important variables
affectingthisweatheringprocessandalsotocheckforany
possibleinteractions.Bothamultilevelcentralizedfactorial
experimentaldesign andananalysis ofvariance (ANOVA)
wereusedasstatisticaltoolsforestimatingtheeffectsofthe
parameters.
Resumen
Yaqueelcueroesfuertementeafectadoportresprincipales
parámetros ambientales: temperatura, humedad relativa, y
radiación UV [Ultra-Violeta],esta porcióninvestigativa se
enfoca en los efectosqueestos tresfactorestienensobreel
envejecimientodelcuerocurtidoalcromo.Cueroscurtidosal
cromofueronexpuestosalosefectosclimáticosenunacámara
climáticaconelfindeidentificarlasvariablesmásimportantes
queafectanaesteprocesoclimáticoyasítambiéninvestigar
cualesquier interacciones posibles. Ambos, un diseño
experimentalfactorialdemúltiplesnivelesconunanálisisde
var ianza (ANOVA) fu eron uti liza dos como  herra mient as
estadísticasparaestimarlosefectosdelosparámetros.

JALCA, VOL. 107, 2012
Introduction
Automotiveupholsteryleatherisamaterialthatcanbeusedin
differentenvironments.Therefore,thistypeofleathercanbe
subjected toaggressive environmental conditions that will
causeitsprematureageing.1-13Despitethefactthatdifferent
automobilebrandshavedescribedtheirownqualitystandards
andrequirementstobemetandcarriedoutstrictageingtests,
itisnotveryeasytoconductlabsimulationsduetothewide
variety of causesthatmay leadto prematureageing. Most
researchintoweatheringtestsmethodshasbeenconductedby
plastics,textile,andcoatingsindustries.Sunlight,temperature,
andmoistureoftenplaycriticalrolesindegradationofthese
materialsinend-use.Consequently,researchersincludethese
factorsinthedevelopmentofweatheringtestmethods.14-18
Inaddition,leatherisstronglyaffectedbythesethreemain
environmentalparameters:temperature,relativehumidity,and
UVradiation.19-30Anearlierpieceofworkstudiedtheeffectof
thetemperature,relativehumidity,andUVradiationonwet-
whiteleather.Accordingtothestudy,relativehumiditywas
thefactorwiththehighestimpactonmost oftheproperties
analyzed. Since it played a key role in weathering, it
consequentlydidsoinwet-whiteleatherageing.31However,as
ithasbeenreportedinotherstudies,chrome-tannedleather
and wet-white leather show a different behavior to the
parameters whichaffect the weathering process.32-35Inthe
presentwork,theleatherswithachrometannagewereexposed
tothethreemainenvironmentalparameters,i.e.,temperature,
relativehumidityandUVradiation.Aclimaticchamberwas
usedinordertoidentifythemostimportantvariablesaffecting
thechrome-tannedleatherageingandtocomparetheageing
processinbothtypesoftannage.
Experimental

the tests were carried out using Spanish chrome tanned cattle
hides shaved at 1.2-1.3 mm. The hides were neutralized at pH
= 5.5 and retanned using synthetic agents and resins. The
hides were then dyed using black dye and fatliquored using
oxi-sulphited marine oil, soya lecithin, and sulphonated beef
tallow. Finally, the hides were dried (vacuum-air) and milled.
The finishing consists in applying a base coat using pigment,
oil, wax, acrylic resin, and two types of polyurethane (3-4 dry
grams of base coat per square foot of leatherin total) by
means of air spraying and pressing at 80ºC / 80 bar / 1". After
that, the leathers were top coated using two types of
polyurethane and crosslinker (0.5 dr y grams of top coat per
square foot of leatherin total) by means of air spraying and
pressing at 80ºC / 80 bar / 1". Finally, the leathers were milled
and toggled.

During a period of 7 days, t he leathers were exposed to
weathering effects using a climatic chambe r 1000L /
Dycometal model CCK 0/1000 with the aim to both identify
the most impor tant var iables affecting this weathering
process and to check for any possible interactions.
A multilevel centralized factorial experimental design and an
analysis of variance (ANOVA) were employed as statistical
tools for estimat ing the effe cts of the par ameters. An
experimental design with 3 variables and 2 levels (23) was
chosen in order to carry out the experiment. The variables to
study were: temperature, relative humidity, and UV radiation.
Table I shows the twelve experiments required for this
experiment. High and low settings for each input variable
were selected according to Table I. The experimental results
were obtaine d as the average value of th ree different
measurements.


      
1 -1 -1 -1 0 0 0
2 1 -1 -1 70 0 0
3 -1 1 -1 0 95 0
4 1 1 -1 70 95 0
5 -1 -1 1 0 0 4
6 1 -1 1 70 0 4
7 -1 1 1 0 95 4
8 1 1 1 70 95 4
9 0 0 0 35 47.5 2
10 0 0 0 35 47.5 2
11 0 0 0 35 47.5 2
12 0 0 0 35 47.5 2
*The leathers were exposed to UV radiation for 4 days
(220 MJ/m2in total) and for 2 days (110 MJ/m2in total)
using a Suntest XLS+ Atlas equipped with a xenon lamp
and window glass filter.

Inordertostudytheeffectoftemperature,relativehumidity,
and UV radiation on leather ageing, we car ried out the
followingtests:
IUP8.Measurementoftearload.
IUP9.Measurementofdistensionandstrengthofgrain
bytheballbursttest.
IUP16.Measurementofshrinkagetemperature.
180 Environmental Parameters Effect on Chrome-tanned Leather

JALCA, VOL. 107, 2012
IUP36.Measurementofleathersoftness.
IUF450.Colorfastnessofleathertodryandwetrubbing
(1000and50rubs).
IUC 4. Det e r m i n ation of mat t er solubl e  in
dichloromethane.
IUC  6. Deter mina tion of wa ter solubl e matter, wate r
solubleinorganicmatter,andwatersolubleorganicmatter.
Coloroftheleatherswasmeasuredusingaspectrophotometer
(DatacolorInternational,SpectraflashSF300).
Theinfraredspectraofleathersurfacewererecordedusingan
In frar ed Spec tromet er with  Attenu ated Total  Refle ctanc e
(Perkin-ElmerSpectrumOneFTIRwithUATRaccessory)
andSpectrumv5.0.1.softwareforthevisualizationofchanges
amongspectra.
Toexaminethe changes in fibrous structure of the leather
samples,weusedthescanning electronmicroscopy JEOL
JSM6400.
Results and Discussion


TableIIpresentstheresultsobtainedforeachoftheproperties
analyzed.
Thestatisticalanalysisoftheresultsobtainedwascarriedout
usingtheStatgraphicsPlusProgram.Theresultsofthemain
effectsforeachofthepropertiesstudiedaregraphedinFigure
1,showingtheeffectofrelativehumidity,temperature,and
UV radiation factors analyzed in this experiment. The
coefficients of the main effects descr ibe the individual
influence corresponding to each factor as well as their
interactionsonthemeasuredproperties.Thestatisticallyvalid
regressioncoefficientsofthepolynomialmodelsfittedtothe
experimentaldataarethefollowing:
a.Shrinkage Temperature =107.8– 0.5*T+ 1.0*Hr–
1.5*UV+0.25*T*Hr–0.75*T*UV–1.75*Hr*UV
b.Tearload=126.9–10.25*T–15.85*Hr–19.15*UV+
9.45*T*Hr+8.7*T*UV+12.3*Hr*UV
c.Graindistension=16.9–0.25*T+0.22*Hr+0.12*UV
–0.27*T*Hr+0.07*T*UV+0.35*Hr*UV
d.Dry r ubbing = 4.2 – 0.2*T – 0.3*Hr – 0.6*U V –
0.06*T*Hr–0.06*T*UV–0.19*Hr*UV
e.Nofactorwasfoundsignificantinwetrubbing.
f.Color loss = 82.5 – 0.49*T – 0.5*Hr – 1.1*UV –
0.1*T*Hr+0.19*T*UV+0.42*Hr*UV
g.Softnessloss=2.6–0.04*T+0.01*Hr+0.1625*UV–
0.1*T*Hr-0.01*T*UV–0.01*Hr*UV
As can be seen in the Pareto charts shown in Figure 1, UV
radiation has, by far, the largest effect on all properties
studied except for the grain distension. Relative humidity also


 




    

1 108 198.8 16.7 5 1 85,57 2,3
2 106 138.8 17.0 5 1 84,15 2,5
3 114 120.4 17.4 5 1 83,62 2,6
4 111 104.6 15.8 4-5 1 82,31 2,3
5 108 115.3 16.5 4-5 1 81,80 2,7
6 107 96.5 16.3 4 1 81,67 2,8
7 108 92.5 17.8 3-4 1 82,04 2,9
8 104 105.1 17.3 3 1 81,00 2,6
9 107 137.7 17.0 4 1 82,20 2,6
10 107 137.5 16.9 4 1 82,00 2,5
11 107 137.1 17.1 4 1 82,15 2,6
12 107 138.0 17.0 4 1 81,90 2,7
*Theresultsareexpressedaspercentageofcolorvariationwithregardtothewhitetest
(i.e.,leathersamplewithoutweatheringexposure)
Environmental Parameters Effect on Chrome-tanned Leather 181

h. IR = 0.09 + 0.016*T + 0.01* Hr + 0.03*UV + 0.02*T*
Hr -0.015*T*UV – 0.008* Hr*UV
i. Water soluble inorganics = 0.5 – 0.025*T – 0.075*Hr +
0.025*UV – 0.05*T*Hr
j.No fact o r wa s fou n d si g nif ic ant in water
soluble organics
k. Fats = 9.2 – 0.2*T – 0.3*Hr – 0.8*UV + 0.01*T*Hr +
0.01*T*UV – 0.04*Hr*UV
As can be seen in the Pareto charts shown in Figure 2, UV
radiation has again the largest effect on IR and on matter
soluble in dichloromet hane. Temperat ure also shows a
significant effect on IR. The analysis also indicates the
possibility of a two-way interaction between temperature and
relative humidity, and between temperature andUV radiation.
The results obtained with the IR spectra are consistent with
those observed in matter soluble in dichloromethane, which
are responsible for a significant portion of the absorption
bands of the spectra. The results are also consistent with those
obser ved in the loss of leather softness since a fur ther
tightening of the skin implies a loss of signal in the spectra
obtained through the ATR technique used.
The amount of soluble organic matter content in the leathers
used is very low. It has also been observed that the processes
of ageing have not lead to the hydrolysis of the resin and
synthetic retanning agents that the leather contains. This
result could have been different if the formula had considered
shows a significant effect on tear load, dry rub and color loss.
The analysis also indicates the possibilit y of a two-way
interaction between UV radiation and relative humidity. This
effect appears in shrinkage temperature, tear load and grain
distension.
As reported in previous studies,31-35 wet-white leather and
chrome-tanned leather show a different behavior to leather
ageing. Relative humidity was the factor in wet-white leather
with the highest impact on most of the physical and fastness
properties analysed, whereas in chrome-tanned leather it was
UV radiation. This may be due to the fact that the substances
that act as tans and retans in wet-white leathers are not much
rich in chromophore groups likely to absorb energy in the
form of light. However, humidity accelerates the hydrolysis
processes involving the decomposition of these substances
(i.e. tans and retans in wet-white leathers). This is contrary to
what occurs with chrome complexes. Apart fromvisible light
absorption, chrome complexes have high UV light absorption.


Table III shows the results of the chemical analysis of the
leather samples.
For each of the studied properties, the standardized Pareto
cha rt is shown in Figure 2. In addition, the following
mathematic models for each of the properties analyzed were
established:
JALCA, VOL. 107, 2012
Figure1.Statisticalanalysisoftheeffectoftheweatheringvariablesonphysicalandfastnessproperties
182 Environmental Parameters Effect on Chrome-tanned Leather

JALCA, VOL. 107, 2012



TEST IR* Watersoluble
organics%
Watersoluble
inorganics%
Fats
%
1 0.0290 0.1 0.5 10.7
2 0.0651 0.1 0.6 10.4
3 0.0400 0.1 0.5 10.3
4 0.1306 0 0.3 9.6
5 0.1581 0.1 0.6 9.4
6 0.0916 0 0.6 8.7
7 0.0943 0.1 0.5 8.4
8 0.1680 0.1 0.4 8.2
9 0.0871 0.1 0.5 8.8
10 0.0871 0.1 0.5 8.7
11 0.0871 0.1 0.5 8.9
12 0.0871 0.1 0.5 8.8
*Absorbance of IR spectrumwascalculatedasthesumofthe
correctedabsorbanceat2923cm-1,1730cm-1,and798cm-1
oftheinfraredspectrumrecordedbyATRforeachsample
(Absorbance of IR spectrum=Abs2923c m-1+Abs1730cm-1+
Abs798cm-1)
temperature and relative humidity were found significant in
water soluble inorganic matter. On the other hand, matter
soluble in dichloromethane is affected by UV radiation. It is
known how nonsaturated oils can for m free radicals when
exposed to light.7,10-13 In the fattening formulation, a fish oil,
among others, has been used. Despite being a product that has
undergone a treatment of stabilization (it is oxi-sulphited), it
contains alkene groups. Therefore, it makes sense that such
component is the most sensitive to the effect of light. In the
case of water soluble inorganic matter relative humidity act as
a chemical reagent in hydrolytic weathering reactions.

Figure 3 shows the cross-section of leather samples no.1, no.8
and no.9 to examine the changes in fibrous structure due to
the effect of the temperature, relative humidity, and U V
radiation.
Sample no.1 was exposed to low settings for each factor
(i.e., 0ºC, 0% Hr, and without UV radiation).
Sample no.9 was exposed to medium settings for each factor
(i.e., 35ºC, 47,5 % Hr, and 110 MJ/m2).
Sample no.8 was exposed to high settings for each factor
(i.e., 70ºC, 95% Hr, and 220 MJ/m2).
A slight loss in compactness can be observed in the fibers
possibly as a result of the hydrolysis of collagen, since the
protein chain of collagen has been exposed to high levels of
humidity. However, this slight loss of compactness is almost
negligible compared with that obtained in the wet-white
leather (see Study of the effect of temperature, relative
humidity and UV radiation on wet-white leather ageing,
JALCA, Vol. 105, 2010, 334-341).
Figure2.Statisticalanalysisoftheeffectoftheweatheringvariablesonmodificationoftheleathercomposition
retanning agents with less fastness to environmental effects.
The results show that water soluble inorganic matter and
matter soluble in dichloromethane are affected by weathering
exposure. This conforms that weathering exposure causes
radical reactions in such a way that some of the bonds
between collagen and tanning agents and/or fatliquors break.
Interestingly, relative humidity and an interaction between
Environmental Parameters Effect on Chrome-tanned Leather 183

JALCA, VOL. 107, 2012
Conclusions
The  aim of this study was to examine t he effect of the
temperature,relativehumidity,andUVradiationonchrome-
tannedleatherageing.UVradiationwasthefactorwiththe
highestimpactonmostofthepropertiesanalyzed.Therefore,
itplaysakeyroleinweatheringandconsequentlyinleather
ageing.Chrome-tannedleatherandwet-whiteleathershowa
differentageingbehavior.Whereaschrome-tannedleathers
arestronglyaffectedbyUVradiation,wet-whiteleathersare
stronglyaffectedbyrelativehumidity.
No correlation has been found betweenageing caused by
naturalweatheringandthatcausedundercontrolledconditions
inthelaboratory.
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Environmental Parameters Effect on Chrome-tanned Leather 185

(onwet-blueweight)
  H2O30°C
 AceticAcid(1:5) rotate–15’
Drain
 H2O40°C
 Directblackdye rotate–15’
 Protein-polymide
polymer rotate–1h
 Sodiumformiate rotate–10’
 Soyalecithin rotate–10’
 Sodium
bicarbonate(1:5) slowly
rotate–2h(≠)
pH=5.2–5.4
Drain
  H2O25°C
 Protein-polyamide
polymer
 Prentrationblackdye
 Auxiliarsynthetic rotate–2h(≠)
pH=4.8–5.0
Drain/Wash
  H2O60°C
 Soyalecithin
 Sulphonated
beeftallow
 Oxi-sulphited
marineoil rotate–1h
 HCOOH(1:5) rotate–15’
pH=3.8–4.0

  Pigment
 Wax
 Proteinicbinder
 Water
 Acrylicresin
 Poliurethane1
 Poliurethane2
4xsprayingmachine(totaldry4g/ft2)
Press80°C/80bar/1"
  TopPoliurethane1
 TopPoliurethane2
 Silicone
 Water
Cross-linker
2xsprayingmachine(totaldry0.5g/ft2)
Press80°C/80bar/1"
Millingandtoggling