Leather is a natural material that can be used in different environments and often under aggressive environmental conditions that may cause premature ageing. The most important factors influencing the degradation of leather are temperature, relative humidity and UV radiation. Leathers with chrome tannage and wet-white leathers were exposed to weathering effects using a climatic chamber in order to identify the most important variables affecting this weathering process and to check for interactions.
Both a multilevel centralized factorial experimental design and an analysis of variance (ANOVA)
have been employed as statistical tools for estimating the effects of the parameters.Postprint (published version

Bacardit Dalmases, Anna

Castell, Joan Carles

Font Vallès, Joaquim

Jorba, Montse

Ollé Otero, Lluís

English

UPCommons. Portal del coneixement obert de la UPC

  XXXI IULTCS Congress Valencia (Spain) - September 27th-30th 2011   1  Paper B21  Comparison of the weathering variables on both chrome-tanned and wet-white leather ageing  Luis Ollé, Montse Jorba1, Joan Carles Castell1, Joaquim Font, Anna Bacardit Igualada Engineering School (EEI). UPC. Plaça del Rei, 15. 08700-Igualada (Spain) Tel.: +34-93-8035300, Fax: +34-93-8031589, e-mail: anna.bacardit@eei.upc.edu 1 Asociación de Investigación de las Industrias de Curtidos y Anexas (AIICA). Avda. Pla de la Massa s/n, 08700 Igualada, Spain   Abstract  Leather is a natural material that can be used in different environments and often under aggressive environmental conditions that may cause premature ageing. The most important factors influencing the degradation of leather are temperature, relative humidity and UV radiation. Leathers with chrome tannage and wet-white leathers were exposed to weathering effects using a climatic chamber in order to identify the most important variables affecting this weathering process and to check for interactions. Both a multilevel centralized factorial experimental design and an analysis of variance (ANOVA) have been employed as statistical tools for estimating the effects of the parameters.  1. Introduction As reported in previous studies, leather is strongly affected by three main environmental parameters: temperature, relative humidity and UV radiation 1-12.  When leather is exposed to sunlight or high temperatures, it absorbs energy which induces photochemical reactions by radical mechanisms. Firstly, chemical compounds split off and free radicals are formed. Secondly, these radicals react immediately with oxygen to form peroxide radicals. Peroxide radicals further react with the organic constituents of leather, and dyes, tanning agents and fatliquors, breaking some of the bonds between the said products and collagen13-15. It is known how insaturated oils form free radicals when exposed to light16-19. Results obtained in previous studies showed a different behaviour of both types of leather (i.e. chrome-tanned and wet-white) to leather ageing. As reported by G. Wolf et al., the resistance and dimensional stability of wet-white leathers is higher than that of chrome-tanned leathers. Therefore, wet-white tannage is increasingly used in the automotive sector following the European Union’s Legislation on End of Life Vehicles and the market trends for chrome free tanned leather 20,21. However, wet-white leather cannot withstand the simultaneous exposure to high temperatures and high relative humidity22-25.  2. Experimental 2.1. Material The tests were carried out on Spanish pickled cattle hides at pH = 3.2 – 3.5. Two types of tanned leather were tested: on the one hand, chrome tanned leather and on the other hand, wet-white tanned leather. In the latter case, the hides were tanned using tetrakishydroxymethylphosphonium sulphate (THPS) and silicate-phenolic synthetic. In both types of tanned leather, the hides were neutralized at pH = 5.3 and retanned using synthetic agents and resins; in wet-white hides, a total amount of 18% of protein-polyamide polymer was added as a retan agent. Then, the hides were 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 of applying a base coat using pigment, oil, wax, acrylic resin and two types of polyurethane (in total 3-4 dry grams of base coat per square foot of leather) by means of air spraying and pressing at 80 ºC / 80 bar / 1”. Afterwards, the leathers were top coated using two types of polyurethane and crosslinker (in total 0.5 dry grams of top coat per square   XXXI IULTCS Congress Valencia (Spain) - September 27th-30th 2011   2  foot of leather) by means of air spraying and pressing at 80 ºC / 80 bar / 1”. Finally, the leathers were milled and toggled.  2.2. Methodology During a period of 7 days, the leathers were exposed to weathering effects using a climatic chamber 1000L / Dycometal model CCK 0/1000 with the aim to both identify the most important variables 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 estimating the effects of the parameters. 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 obtained as the average value of three different measurements  Table I. Experimental design TEST X1 X2 X3 T Hr UV* 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.  2.3. Evaluation In order to study the effect of temperature, relative humidity, and UV radiation on leather ageing, we carried 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.  IUP 36.  Measurement of leather softness.  IUF 450. Color fastness of leather to dry and wet rubbing (1000 and 50 rubs).  IUC 4. Determination of matter soluble in dichloromethane.  IUC 6.  Determination of water soluble matter, water 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 Infrared Spectrometer with Attenuated Total Reflectance (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.   XXXI IULTCS Congress Valencia (Spain) - September 27th-30th 2011   3    3. Results and discussion 3.1. Effect of the weathering variables on physical and fastness properties of the leather 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 on chrome tanned leather 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 describe the individual influence corresponding to each factor as well as their interactions on the measured properties.    Figure 1. - Statistical analysis of the effect of the weathering variables on physical and fastness properties of chrome tanned leather Standardized Pareto Chart for Shrinkage temperature0 1 2 3 4Standardized effectABA:TemperatureACB:Relative HumidityC:UV radiationBC +-Standardized Pareto Chart for Tear load0 1 2 3 4 5Standardized effectACABA:TemperatureBCB:Relative HumidityC:UV radiation +-Standardized Pareto Chart for Grain distension0 1 2 3 4Standardized effectACC:UV radiationB:Relative HumidityA:TemperatureABBC +-Standardized Pareto Chart for Dry rub0 2 4 6 8Standardized effectABACA:TemperatureBCB:Relative HumidityC:UV radiation +-Standardized Pareto Chart for Color loss0 1 2 3 4 5 6Standardized effectABACBCA:TemperatureB:Relative HumidityC:UV radiation +-Standardized Pareto Chart for Softness0 2 4 6 8Standardized effectB:Relative HumidityBCACA:TemperatureABC:UV radiation +-  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 shows a significant effect on tear load, dry rub and color loss. The analysis also indicates the possibility of a two-way interaction between UV radiation and relative humidity. This effect appears in shrinkage temperature, tear load and grain distension. The results of the main effects for each of the properties studied on wet-white leather are graphed in Figure 2. These results reveal several critical observations: relative humidity has, by far, the largest effect on all properties studied except for the tear load, color loss, and softness loss, in which any factor was found significant. Temperature also shows a significant effect on grain distension and wet rubbing. The analysis also indicates the possibility of a two-way interaction between relative humidity and temperature. However, this effect appears only in dry rubbing, wet rubbing, and color loss.   XXXI IULTCS Congress Valencia (Spain) - September 27th-30th 2011   4    Standardized Pareto Chart for Shrinkage T0 1 2 3 4 5Standardized effectA:TemperatureC:UV radiationACBCABB:Humidity +-Standardized Pareto Chart for Tear load0 0,5 1 1,5 2 2,5 3Standardized effectACC:UV radiationBCB:HumidityA:TemperatureAB +-Standardized Pareto Chart for Grain Distension0 0,5 1 1,5 2 2,5 3Standardized effectACABBCC:UV radiationA:TemperatureB:Humidity +-Standardized Pareto Chart for Dry rubbing0 1 2 3 4 5Standardized effectBCACA:TemperatureC:UV radiationABB:Humidity +-Standardized Pareto Chart for Wet rubbing0 2 4 6 8Standardized effectACBCC:UV radiationABA:TemperatureB:Humidity +-Standardized Pareto Chart for Color loss0 0,5 1 1,5 2 2,5 3Standardized effectACBCC:UV radiationA:TemperatureB:HumidityAB +-Standardized Pareto Chart for Softness loss0 0,5 1 1,5 2 2,5 3Standardized effectB:HumidityACBCA:TemperatureC:UV radiationAB +-Figure 2. - Statistical analysis of the effect of the weathering variables on physical and fastness properties of wet-white leather   As reported in previous studies22-24, 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.  3.2. Effect of the weathering variables in the modification of the leather composition In order to compare the chemical degradation of leather due to temperature, relative humidity and UV radiation, the following was determined: matter soluble in dichloromethane, water soluble inorganic matter, water soluble organic matter and IR spectra. For each of the studied properties, the standardized Pareto chart for chrome tanned leather is shown in Figure 3. Figure 4 shows the Pareto chart for wet-white leather.           Standardized Pareto Chart for IR 0 1 2 3 4 5 6 Standardized effect BC B:Relative HumidityAC A:TemperatureABC:UV radiation +- Figure 3. - Statistical analysis of the effect of the weathering variables on modification of the leather composition for chrome tanned leather  Standardized Pareto Chart for Inorganic substances0 2 4 6 8Standardized effectACBCC:UV radiationA:TemperatureABB:Relative Humidity +-Standardized Pareto Chart for Fatts0 1 2 3 4 5Standardized effectABACBCA:TemperatureB:Relative HumidityC:UV radiation +-Standardized Pareto Chart for Organic substances0 0,5 1 1,5 2 2,5 3Standardized effectB:Relative HumidityC:UV radiationABACBCA:Temperature +-  XXXI IULTCS Congress Valencia (Spain) - September 27th-30th 2011   5   As can be seen in the Pareto charts shown in Figure 3, UV radiation has again the largest effect on IR and on matter soluble in dichloromethane. Temperature 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.   Standardized Pareto Chart for IR0 1 2 3 4Standardized effectBCACC:UV radiationA:TemperatureB:HumidityAB +-Standardized Pareto Chart for Fatts0 2 4 6 8Standardized effectBCABB:HumidityA:TemperatureACC:UV radiation +-Figure 4. - Statistical analysis of the effect of the weathering variables on modification of the leather composition for wet-white leathers  Standardized Pareto Chart for Water soluble inorganics0 0,5 1 1,5 2 2,5 3Standardized effectBCC:UV radiationABACA:TemperatureB:Humidity +-Standardized Pareto Chart for Water soluble organics0 1 2 3 4Standardized effectA:TemperatureBCABACC:UV radiationB:Humidity +-  The results show a different behaviour of both types of tanned leather under the studied weathering variables. The analysis confirms again that relative humidity was found significant on all of the properties analyzed in wet-white leathers. Temperature shows a significant effect on water soluble inorganics, IR, and fats.   Through the analysis of variance for matter soluble in dichloromethane, it was observed that it is the only property affected by UV radiation, and emerges as the most important one. It is known how insaturated oils form free radicals when exposed to light13-19. 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 of all the components in the WW leather.  3.3. Changes in fibrous structure  Figure 5 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 UV 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.  4. Conclusions The aim of this study was to compare the effect of the temperature, relative humidity, and UV radiation on chrome-tanned leather and wet-white leather ageing. UV radiation was the factor with the highest impact on most of the properties analyzed on chrome-tanned leather. Therefore, it plays a key role in weathering and consequently in chrome-tanned leather ageing.    XXXI IULTCS Congress Valencia (Spain) - September 27th-30th 2011   6  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.   Figure 5. – Micrograph (SEM) of cross-section of leather samples no.1, 9, and 8  9 8 1 Wet-white leathers 8 9 1 Chrome tanned leathers   5. References [1] Kite, M.; Thomson, R.; Conservation of leather and related materials; Elsevier, Oxford. 2000 [2] Bickley, J.C.; Vegetable tannins. In Leather, its composition and changes with time; C. Calnan and B. Haines, eds. Northampton: The Leather Conservation Centre. 1991 [3] Bowes, J.H.; Raistrick, A.S.; The action of heat and moisture on leather. V. Chemical changes in collagen and tanned collagen, J. Soc. Leath. Tech. Ch., 29, 201, 1964 [4] Calnan, C.N.; Ageing of vegetable tanned leather in response to variations in climatic conditions. In Leather, its composition and changes with time; C. Calnan and B. Haines, eds. Northampton: The Leather Conservation Centre. 1991 [5] Chahine, C.; Acidic deterioration of vegetable tanned leather. In Leather, its composition and changes with time; C. Calnan and B. Haines, eds. Northampton: The Leather Conservation Centre. 1991 [6] Florian, M.-L.E.; A holistic interpretation of the deterioration of vegetable tanned leather; Leather Conservation News, 2, 1, 1985 [7] Haines, B.; Natural ageing of leather in libraries. In Leather, its composition and changes with time; C. Calnan and B. Haines, eds. Northampton: The Leather Conservation Centre. 1991 [8] Haines, B.; Deterioration under accelerated acidic ageing conditions. In Leather, its composition and changes with time; C. Calnan and B. Haines, eds. Northampton: The Leather Conservation Centre. 1991   XXXI IULTCS Congress Valencia (Spain) - September 27th-30th 2011   7  [9] Haines, B.; The structure of collagen. In Leather, its composition and changes with time; C. Calnan and B. Haines, eds. Northampton: The Leather Conservation Centre. 1991 [10] Larsen, R.; Experiments and observations in the study of environmental impact on historical vegetable tanned leathers; Thermochimica Acta, 365, 85, 2000 [11] Larsen, R.; Vest, M.; Nielsen, K.; Determination of hydrothermal stability (Shrinkage Temperature) of historical leather by the Micro Hot Table Technique, J. Soc. Leath. Tech. Ch., 77, 151, 1993 [12] Thomson, R.; Conserving historical leathers: Saving our past for the future, J. Am. Leather Chem. As., 97, 307, 2002 [13] Püntener, A.; The influence of fatliquors on the lightfastness of dyed leather, J. Am. Leather Chem. As., 91, 126, 1996 [14] Sammarco, U.; Formation of Cr (VI) in leather and possibility of elimination, Cuio, Pelli, Materie Concianti, 74, 83, 1998 [15] de Volder, N.; Hallmanns, M.; Levy, J.; Annoying energy. II. Solar heating of dark leather, in Proceedings of the XXIX International Union of Leather Technologists and Chemists Societies Congress, Washington, 2007 [16] Font, J.; Cuadros, R.M.; Reyes, M.R.; Costa-López, J.; Marsal, A.; Influence of various factors on chromium (VI) formation by photo-ageing, J. Soc. Leath. Tech. Ch., 83, 300, 1999 [17] Segura, R.; Palma, J.J.; Izquierdo, F.; Anti-aging in leather, in Proceedings of the 49º congreso AQEIC, Palma de Mallorca, España, 2000  [18] Palop, R.; Parareda, J.; Ballús, O.; Gomera, A.; Influence of fatliquoring products in leather aging and formation of Chromium VI. Part I, in Proceedings of the 56º Congreso AQEIC, Cartagena, España, 2007 [19] Palop, R.; Parareda, J.; Ballús, O.; Gomera, A.; Influence of fatliquoring products in leather aging and formation of Chromium VI. Part II, in Proceedings of the 56º Congreso AQEIC, Cartagena, España, 2007 [20] Wolf, G.; Breth, M.; Carle, J.; Igl, G.; New developments in wet white tanning technology, J. Am. Leather Chem. As., 96, 111, 2001 [21] Directive 2000/53/EC of the European Parliament and of the Council of 18 September 2000 on end-of life vehicles. [22] Bacardit, A.; Jorba, M.; Font, J.; Shendrik, A.; Ollé, L.; Biodegradation of leather tanned with inorganic salts, J. Soc. Leath. Tech. Ch., 95, 63, 2011 [23] Ollé, L.; Jorba, M.; Font, J.; Shendrik, A.; Bacardit, A.;  Biodegradation of wet-white leather, J. Soc. Leath. Tech. Ch., 95, accepted and pending of publication, 2011  [24] Ollé, L.; Jorba, M.; Font, J.; Bacardit, A.; Comparison of the effect of the tropical test on both chrome-tanned and wet-white upholstery leather, J. Soc. Leath. Tech. Ch., 95, accepted and pending of publication, 2011 [25] Bacardit, A.; Cobos, M.; Font, J.; Jorge, J. ; Ollé, L. ; Study of the effect of temperature, relative humidity and UV radiation on wet-white leather ageing, J. Am. Leather Chem. As., 105, 334, 2010. 

Comparison of the weathering variables on both chrome-tanned and wet-white leather ageing

Leather is a natural material that can be used in different environments and often under aggressive environmental conditions that may cause premature ageing. The most important factors influencing the degradation of leather are temperature, relative humidity and UV radiation. Leathers with chrome tannage and wet-white leathers were exposed to weathering effects using a climatic chamber in order to identify the most important variables affecting this weathering process and to check for interactions.

Both a multilevel centralized factorial experimental design and an analysis of variance (ANOVA)

have been employed as statistical tools for estimating the effects of the parameters

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Comparison of the weathering variables on both chrome-tanned and wet-white leather ageing

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