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Effects of drying processes and fatliquring on resiliency of leather
Abstract
Resiliency is the important quality characterizing the dimensional stability of leather. It expresses the ability of materials such as leather to recover from deformation after being subjected to a strain or stress. Resiliency is particularly important to automotive upholstery makers because poor recovery from deformation will create bagginess in car seats made with upholstery leather. We have designed a tensile method to characterize the resiliency of leather. Measurements showed that the resiliency of chrome-tanned leather is superior to chrome-free leather. Our studies also indicated that the physical properties of leather, particularly resiliency, were affected significantly by the drying and fatliquoring processes. Observations revealed that toggle drying may impair the resiliency of leather, while vacuum drying produced the best resilient leather in this study. In addition, data indicated that there is a close relationship between resiliency and fracture energy of leather.
... Suzana Mihanović, Franka Žuvela Bošnjak -Utjecaj temperature sušenja na sorpcijska svojstva hidrofobirane sintetski štavljene kože -K&O 69 (2020) [3][4][13][14][15] Utjecaj temperature sušenja na sorpcijska svojstva hidrofobirane sintetski štavljene kože Influence of drying temperature on sorption properties of hydrophobic synthetic tanned leather Suzana Mihanović* Psunj Tvornica koža d.o.o., Kožarska ulica 18, HR-35403 Rešetari Franka Žuvela Bošnjak Sveučilište u Zagrebu Tekstilno -tehnološki fakultet, studijska jedinica Varaždin, Hallerova aleja 6, HR-42000 Varaždin *e-pošta: produc�on@viviani.hr Sažetak U ovom radu je istražen utjecaj temperature sušenja na sorpcijska svojstva goveđe sintetski štavljene hidrofobirane kože. ...
... Na taj način je moguće reducirati upotrebu električne energije prilikom sušenja [14]. Liu i suradnici su istraživanjem različito štavljenih koža sušenih različitim metodama te mašćenjem koža različitom količinom masnoće, došli do zaključka da je elastičnost kože uvjetovana procesom sušenja i mašćenjem [15]. Xianglong i sur. ...
... Suzana Mihanović, Franka Žuvela Bošnjak -Utjecaj temperature sušenja na sorpcijska svojstva hidrofobirane sintetski štavljene kože -K&O 69 (2020)[3][4][13][14][15] ...
U ovom radu je istražen utjecaj temperature sušenja na sorpcijska svojstva goveđe sintetski štavljene hidrofobirane kože. Kože su sušene na uređaju za sušenje uz primjenu vakuuma pri temperaturi od 40, 45, 50 i 55 °C u vremenu od 90 sekundi nakon provedbe štavljenja, nadoštave, bojanja i mašćenja u realnom proizvodnom procesu. Ispitivanjem apsorpcije vlage te vremena propuštanja i apsorpcije vode kože tijekom dinamičkog gibanja na penetrometru utvrđen je značajan utjecaj temperature sušenja na sorpcijska svojstva kože.
... The research is well summarized in Lamb et al. 4 . From 1990 to 2015, Liu et al. worked to understand the mechanism of drying and the resulting leather physical properties [5][6][7][8][9][10][11][12][13] . Liu et al. established a mathematical model in low pressure conductive drying that is given in Equation 1 that allows a tannery to predict their vacuum drying rates from their drying parameters 14,15 ...
... Liu in a number of papers examined the physical properties of chromium-free and chromium containing leathers [7][8][9]15 . The research also looked at the properties of the leathers produced by 6. differing drying methods 3,5,6,9,10,12,13 . Fibre separation by any means whether it is liming, bating, over-drumming, solvent drying, staking, milling, or slow drying will result in leather with a low apparent density. ...
... and 47% gave 13.4±2.4%. 10. The post-tanned chromium leathers that were pre-conditioned showed variable levels of moisture content even though precautions were taken to prevent this. ...
Jeyapalina et al. established that dynamic mechanical thermal analysis (DMTA) can be used to gauge the progression of leather drying. This work has now been advanced in order to understand the mechanism surrounding sorption/desorption of moisture during cell conditioning, e.g., cell rotary conditioning (CRC). This paper will demonstrate how the use of DMTA could be used to monitor changes in leather stiffness. A gravimetric moisture analysis was performed on identical leather samples to gauge the progression of desorption. The change in storage modulus (E') was coupled to the moisture content (leather moisture and atmospheric relative humidity) to obtain a better understanding of the physical properties (specifically stiffness) of leather during a drying process. The research presented illustrates how DMTA can indicate leather fiber response to changes in atmospheric humidity and facilitate real-time adaptation of drying conditions during leather dehydration. The use of a cell conditioning system allows a tanner to control the flexibility of the material through the tension applied and the drying conditions. DMTA shows that the favorable conditions inside a CRC unit result in detectable changes to the leather fiber, similar to findings by Abrahamson and Williams-Wynn. Using this technique a researcher can dry chromium-containing and chromium-free leathers in a manner that is highly customizable to produce desired physical properties. Difficulties experienced in chromium-free leathers can also be investigated in detail using this technique.
... leading to good quality leathers in terms of physical strength characteristics [21]. Influence of vacuum drying and fatliquoring on resiliency of leather was studied earlier, which show vacuum drying is preferred over toggle drying in order to provide better resiliency in leather [22]. Another study [23], showed that residual water content is important for softness, and vacuum drying without toggling provided better toughness and softness in dried leather. ...
... There are a range of fatliquors for car upholstery leather-like, Prinol CRC, Prinol F-GB, Provo CAD, etc. The emission behavior between vegetable and fish oil has not been studied so far, but the measurement of emission and fogging is very important for the car upholstery leather [50,63]. The enhancement of the waterproofing behavior of leather is one of the major functions for such fatliquors [14,52]. ...
“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.
... Drying in the artisanal leather making is achieved through sun-drying whilst variety of other drying methods such as vacuum drying, toggle drying, radiation drying and paste drying are employed in modern tanneries. The commonest method is, however, the vacuum drying method and it is known to produce highly resilient leathers [90]. ...
The production of leather from animal skins and hides through tanning processes began in the pre-historic ages. Despite the origination of new leather making techniques such as chrome tanning which is being employed extensively today, the traditional method of leather production primarily through vegetable tanning is still being practised mostly in artisanal tanneries in developing nations including Ghana. Artisanal leather making, thus, contributes beneficially to rural livelihood. Nevertheless, the growth of this sector has been stifled by the lack of innovative technologies to enhance productivity. This challenge could be partly linked to the knowledge gap on the scientific principles governing artisanal leather production processes. This study, therefore, elaborates on various process steps and materials employed in traditional leather making in Ghana and the scientific principles underlying each of the processes. It also makes a comparison between traditional and modern leather manufacturing processes and identifies knowledge and technological gaps which would inspire in-depth scientific research into artisanal leather making.
Graphical abstract
... We previously reported a method designed to measure the resiliency of leather. 5 Our studies showed that the resiliency of chrome-tanned leather is superior to chrome-free leather. Data also indicated that resiliency was affected significantly by the drying and fatliquoring processes. ...
Dynamic mechanical thermal analysis (DMTA) is routinely used for mechanical analysis by the polymer industry to provide information on the viscoelastic properties of a material. This report reveals how DMTA has been used to further previous studies by providing insight into the differences between post-tanned leathers (chromium and chromium-free). It demonstrates the potential to correlate the results with an industrial application such as optimization of the drying conditions during cell rotary conditioning (CRC). DMTA can indicate leather fiber response to changes in atmospheric humidity and temperature, potentially facilitating real-time adaptation of conditions during leather drying. Initial DMTA results show that post-tanning, particularly fatliquoring, changes the rate of drying and allows scientists to advise on optimal leather drying conditions based on viscoelastic changes.
Thirty Boer x Spanish and 29 Spanish wethers were used in a trial to determine the effects of goat breed, supplementation level, and age on the mechanical properties of chrome-tanned and glutaraldehyde-tanned goat skin. Six Boer and five Spanish wethers were harvested at the beginning of the trial with the remaining animals assigned to four groups, having equal breed numbers, receiving either a high or low supplement amount daily. Two groups were harvested after 110 days and the remaining groups after an additional 108 days. Skins were removed by hand, split down the dorsal midline, and salted. The left half of each skin was chrome-tanned and the right half was tanned using a glutaraldehyde based tannage. Tanning goat skins using chromium resulted in stronger leather than that produced using glutaraldehyde. Increasing age led to decreased % elongation and increased leather stiffness. The effects of supplementation level were of lesser importance than tannage or age upon the strength characteristics of leather produced. Boer goat leather was thicker than Spanish goat leather, although tensile strength was unaffected by breed. Goat skins were not shaved to an equal thickness during the tanning process, perhaps leading to some of the breed differences seen, notably in % elongation and fracture energy. Therefore, further research is needed to evaluate characteristics of shaved skins.
'Knowledge Management' is a systematic practice which is quickly expanding in such application fields as production engineering and the planning business, that aims to define methods and procedures for giving a concrete direction to the organization of the competences, the multidisciplinary nature of information and lifelong learning. This manuscript purposes to give technicians and researchers in 'tanning technologies' an organizational instrument to structure their own heterogeneous knowledge by means of a 'common thread conductor'. This classifies the technical information and conforms their 'shape', presentation and manipulation through the elementary, basic elements of System Theory. So, a Best Technological Practice Managing System (BTPMS) can be suggested, following the familiar form of the usual Quality Management Systems for process improvements and quality assurance in specific areas of technical services. The study is mainly focussed on aspects such as identify, classify, represent, codify, create, capture, organise/structure data, distribute and finally enable adoption of the technical knowledge of tanning-processes.
The US is the world's 3rd largest hide producing country and currently produces approximately 35 million cattle hides annually. The majority of hides are tanned into leather, which is composed of collagen fibers interwoven into fibrous networks. Most leather products are constantly exposed to outdoor environments, therefore UV and heat resistance are very important qualities, particularly for nonchrome-tanned (chrome-free) leather. In recent years, we have focused on using environmentally friendly antioxidants that will improve the UV and heat resistance of chrome-free leather. Tocopherols are well-known antioxidants commonly used in the cosmetic and food industries. They are known as potent free radical scavengers and highly protective agents for collagen fibers against UV damage. We have investigated their potential to improve the UV and heat resistance of chrome-free leather. Experiments were conducted by adding 5–12% α-tocopherol to the polymeric topcoat on the grain of chrome-free leather. The treated samples were tested in a weatherometer, where they were exposed to artificial sunlight. Colorfastness and mechanical property tests showed that α-tocopherol significantly improved UV and heat resistance of leather. Dynamic mechanical tests showed that α-tocopherol reduced the hardening effects on leather caused by UV irradiation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Chrome-free leather such as glutaraldehyde-tanned leather behaves very differently from chrome-tanned leather. Information
regarding its viscoelasticity has not been previously reported. Hysteresis and stress relaxation are two essential properties
associated with viscoelasticity. We have designed a cyclic tensile test to measure these properties to gain insight into the
structural difference between chrome-free and chrome-tanned leather. Observations revealed that chrome-free leather tanned
with glutaraldehyde has a higher hysteresis than chrome-tanned leather. Stress relaxation experiments, on the other hand showed
chrome-free leather has very similar relaxation curves as chrome-tanned leather. Both leathers demonstrate a rapid decrease
in stress for the first few seconds followed by a much slower decay thereafter. The chrome-free leather, however, has a greater
initial stress than chrome-tanned leather, indicating a higher stiffness than chrome-tanned leather. Moreover, observations
showed the viscoelasticity of leather was affected significantly by its fatliquor content. A decrease of loading energy in
a cyclic stress–strain experiment resulted from higher fatliquor content in leather.
Due to its fast drying speed, vacuum drying has become one of the most popular drying methods in recent years for leather manufacture. However, information regarding how drying conditions affect the resulting leather mechanical properties is lacking. Without this information, drying operations often produce leather with poor mechanical properties. Therefore, we conducted a systematic vacuum drying study to gain a clear picture of how drying variables affect the mechanical properties of vacuum-dried leather. Data clearly indicate that a lower drying temperature, shorter drying time, and proper initial water content in leather are favorable conditions to produce stronger and softer leather. In this investigation we not only formulate the relationship between drying factors and mechanical properties, but also explore the possibility using a mass transfer quantity such as drying rate to generalize the complex relationship between drying variables and resultant mechanical properties. Observations showed that the rate of drying is one of key factors that governs the tear strength. This investigation may benefit the leather industry in optimizing drying conditions to obtain improved mechanical properties.
For thousands of years, collagen materials, such as leather, have been among the most dominant natural fibrous materials used by humans. Fatliquoring is one of the critical steps in the leather-making process, wherein oil or a lubricant is added to the leather to prevent the leather fibers from sticking together, thereby providing sufficient pliability to the leather. We have examined the feasibility of using the acoustic emission (AE) technique to characterize the degree of lubrication of leather produced with various fatliquor concentrations. In a tensile test, an acoustic transducer was contacted with the leather samples to collect their AE quantities and properties. The samples lubricated with a fatliquor concentration less than 10% showed twin peaks on the plot of hits rate versus time. This implied that a non-uniform fracture occurred in a leather structure that was not sufficiently lubricated. In contrast, a sufficiently lubricated leather structure showed a steady increase in hits rate with time until it fractured. Traditional stress-strain tests did not reflect these behaviors. Observations also showed a direct correlation between the cumulative hits and fatliquor concentration. The results of this work may provide a route to identify an adequate degree of lubrication in the leather.
The use of glutaraldehyde as a fixative in bioprostheses and drug delivery matrices is reviewed. The chemistry of glutaraldehyde cross-linking and its effect on the biological performance of a number of bioprostheses such as tissue heart valves, vascular grafts, pericardial patches, tendon grafts and drug delivery matrices are examined.
The adhesions among the fibers of dried calfskin were examined by measuring the acoustical pulses emitted when the skin was stretched. The rate of emission of the pulses and their energies were determined. The frequency distributions of the pulse amplitudes comprised spectra that were similar in shape for skin that had been dried from acetone, petroleum ether, and petroleum ether containing fatliquor. The separate contributions from the ruptures of adhesions and of fibers to these spectra were analyzed and related to the lubrication of the fibers by fatliquor. The method promises to be helpful in elucidating and following changes in fiber adhesion in tanning, drying, impregnation, filling, and finishing, and might serve as the basis of a field test in leather drying.
Staking is one of the key leather making operations to soften leather and to improve its pliability. Besides the number of staking passes, there are many other factors affecting the action of staking, and consequently the resultant physical properties of staked leather. Fatliquoring, for example, is another process to soften leather and will influence the results of staking. There is no report so far, however, to demonstrate the interaction of fatliquoring and staking on softening leather. This investigation is devoted to this important subject, aiming at a better understanding of their interaction on pliability and other important properties of concern to the leather industry, such as mechanical strength, elongation, toughness and area retention. We therefore have conducted a systematic study, using the SAS statistical program, to formulate their interactive relationship on the physical properties of leather. Observation showed that the tensile strength and tear strength both increase steadily with increasing number of staking passes. This trend slowly reverses, however, as the fatliquor concentration increases. Even more intricate is the effect of fatliquor on the behavior of staking softening. Without fatliquor, staking actually stiffens the leather. Data showed the softening action of staking only becomes effective after fatliquor concentration reaches a certain level. Area measurements showed no obvious link between the amount of staking and area retention. An association was observed, however, between the residual water content and area retention. The leather after vacuum drying with less residual water content shows better area yield.
The effect of fatliquor was not included in our previous vacuum drying studies for chrome-tanned leather. Therefore, a follow-up vacuum drying study was performed to evaluate the effect of fatliquor. By using the SAS statistical program, we have formulated the relationship between fatliquor concentration and drying rate. This study also focused on how fatliquor affects the strength, elongation, stiffness and toughness of the vacuum dried leather. A second order polynomial regression equation was derived to plot 3-D response surfaces that clearly illustrate the relationship between the fatliquor concentration and drying rate, as well as the resultant physical properties. Measurements showed the drying rate decreases as the fatliquor concentration increases by a factor of (I-f)1/2, where f is the fatliquor concentration fraction. Observation showed that the tensile strength, elongation, and toughness all increase steadily with an increased fatliquor concentration, whereas the Young's modulus decreased. A correlation was observed between elongation and Young's modulus.
Liming is one of the key steps in the leather-making process - to remove hair and non-collagenous materials from the hide and, more importantly, to open up the fibrous structure for tanning and lubrication. However, the leather industry lacks an effective means to identify proper liming conditions that produce a sufficient degree of opening-up. As part of our effort to investigate the applications of acoustic emission technology to leather manufacture, we have examined the feasibility of using the acoustic emission (AE) technique to measure the degree of opening-up of leather produced with various liming times. Leather samples were stretched and contacted with an acoustic sensor to collect various acoustic quantities. Observations showed that a change in the degree of opening-up of the fiber structure associated with the increase of liming time can be detected by a history plot of acoustic emission counts. The samples with less than 24 hours liming show a relatively smooth history plot, whereas the samples with a liming time greater than 24 hours produce a pronounced saw-shaped pattern, and the longer the liming time, the more erratic the pattern becomes. This behavior mirrors the change in the extent of opening-up of the fibrous structure engendered by the lime action. We have concluded that a qualitative association exists between the degree of opening-up of leather and the acoustic counts patterns measured by an AE analyzer. The results of this work may provide a route to monitor the degree of opening-up of leather.
Stretching chrome-free leather tanned with glutaraldehyde during vacuum drying may possibly be the best drying method for this particular type of leather, because it results in an improved area yield and better mechanical properties due to a lower drying temperature. We explored this composite drying method and investigated how drying variables affect the drying rate and mechanical properties of chrome-free leather that was tanned with glutaraldehyde. Using a statistical experimental design, a second order polynomial equation was derived to quantitatively describe the relationship between the drying rate and three major independent variables: drying temperature, stretch %, and drying time. Drying rate models derived from this investigation provide a clear understanding of the drying process for chrome-free leather. The drying constant indicates that chrome free leather dries faster than chrome-tanned leather. These models will help the leather industry estimate the proper drying parameters. Our studies showed that stretch % during vacuum drying is the most significant variable affecting the stiffness and area retention of leather. This research indicated that stretching should not be overdone and the preferable length increase should not be greater than 10%; otherwise poor leather properties may result, such as an elongation less than 40% and toughness index less than 1.
The environmental and health concerns over the use and disposal of chrome-tanned leather have encouraged the use of non-chrome-tanned (chrome-free) leather. The drying operation is a critical leather-making step to attain the required physical properties for leather products. We recently conducted a drying study on non-chrome-tanned leather made with a glutaraldehyde-tanning process. Results showed that the physical properties of leather, such as area retention and softness, were affected significantly by the drying method. Data revealed that leather with inferior fracture energy often resulted in poor grainbreak. In addition, observations showed that drying methods using toggling produced higher areayield; however, it resulted in stiffer leather. Our research showed that residual water content plays an important role in controlling the softness of leather. Vacuum drying without toggling yields better toughness and softness. A dimensionless quantity "toughness index" showed a strong correlation with the resultant area retention, which agrees with our previous findings for chrome-tanned leather.
Finishing, the final step in the leather-making process, contributes to the beauty and durability of leather. Choosing the right coating is critical in obtaining a satisfactory finishing result, such as good flexing endurance and no surface cracking. Acoustic emission has been known to be a useful method to characterize the coating properties for the automobile industry. As a continuation of our efforts to investigate the applications of acoustic emission technology to leather manufacture, we exploited the AE technique to measure the flexing endurance of leather coatings. An acoustic sensor was clipped to the grain layer of finished leather in a tensile test to collect various acoustic quantities. Observations showed that differences in the flexibility of the coatings can be analyzed by examining the plot of the AE count rate as a function of time. We have concluded that a quantitative association exists between the flexibility of coatings and the cumulative acoustic counts produced at an initial tensile stretch. The results of this AE research may provide a route to examine the flexing endurance of leather coatings.
Leathers prepared from wet white are certain to become more prevalent. Modifications made by BASF to some products and services improve the quality of leather and offer economical and ecological advantages.
In our continuing investigation of the applications of acoustic emission technology to leather manufacture, we present in this report recent results on evaluating the possibility of using the acoustic emission technique to gain insights into reasons of tear failure. In a tear test, chrome-tanned leather samples were attached with an acoustic sensor to collect various acoustic quantities. Data showed that the samples stronger in tear strength gave a significantly lower acoustic count. In contrast, the samples with poor tear strength generated much more frequent sound waves, i.e., more acoustic counts. This is contrary to results from tensile tests, where the higher strength leather always produces more acoustic counts. Observations also showed that harsh drying conditions or thin corium can lead to a brittle structure, which consequently yields poor tear resistance. In an acoustic emission test, this can be reflected by high acoustic counts because of frequent fiber breaking and friction associated with the brittle structure.
We conducted a vacuum drying study for chrome-tanned leather, using the SAS statistical program to formulate the relationship between drying variables and residual water content, as well as the rate of drying. This study also focused on how drying variables affect the dimensional stability of leather and its mechanical properties such as stiffness. Using Box-Hunter's method, a second order polynomial equation was derived to precisely describe the relationship between the residual water content and three major independent variables: drying temperature, initial water content, and drying time. Area measurements right after vacuum drying showed very little change with all the applied drying conditions. However, a significant area change was observed after leather with various residual water contents was conditioned for two weeks. A correlation was observed between the residual water content and area retention. The vacuum dried leather with less residual water content yields better dimensional stability. Drying rate was also calculated from the residual water content as a function of drying variables. Contrary to conventional air drying, observation showed that vacuum drying does not start with a distinguishable constant drying rate. Drying directly goes to the 'falling rate period' and the rate of drying decreases with time. Finally, the study derived a simple mathematical model for drying rate as a function of a wider range of drying variables.
This investigation is to establish a foundation for developing a nondestructive tester with an acoustic analyzer for predicting the tensile strength of leather. Observations showed an excellent correlation between the tensile strength of leather and the corresponding acoustic cumulative energy at break, read from an acoustic emission analyzer. Moreover, a linear relationship was observed between the acoustic cumulative energy at break and the initial acoustic cumulative energy when leather was stretched to 10 percent of it original length. More importantly, a correlation was observed between the initial acoustic cumulative energy and the tensile strength of leather. The implication of these phenomena is that the tensile strength of leather may be predicted without breaking the leather, by measuring the initial acoustic cumulative energy. The result of this study thus provides an essential base facilitating the possible design of a portable leather stretcher attached with an acoustic sensor. This would allow the prediction of tensile strength by measuring the cumulative acoustic energy during initial stretching without breaking or damaging the leather.