INFLUENCE OF SWEAT ON HIDE AND LEATHER

Transcription

1 INFLUENCE OF SWEAT ON HIDE AND LEATHER by KEYONG TANG, JINGLONG LIU AND FANG WANG Materials Engineering College, Zhengzhou University, Zhengzhou City, Henan Province, China and QUANJIE WANG State Research & Promotion Center of Leathermaking Technology Yantai City, Shandong Province, China ABSTRACT In this paper, some samples including un-tanned cattlehide collagen fibers, chrome tanned cattlehide collagen fibers, glutaraldehyde tanned cattlehide collagen fibers and formaldehyde tanned cattlehide collagen fibers are prepared and processed in man-made sweat, and preliminary studies on their dry heat shrinkage and thermal degradation behaviors are completed. The changes in thermal behaviors between samples before and after sweat process are studied. The mechanism of these changes when being processed in sweat is discussed. The influence of sweat process on the water vapor permeability and the hydrothermal stability of the crust leather are included as well. Key Words: Cattlehide collagen fibers; Leather; Sweat; Thermal degradation activation energy Hydrothermal stability INTRODUCTION As one of the most important clothing materials, leather has many excellent characteristics that no synthesis materials possess [1]. It is clear that leather goods may be penetrated by sweat in the process of being used. Therefore, the sweat resistance of leathers should be an important property too. Zhang Wenxiong and his colleagues studied the changes in physical properties of samples processed in sweat with different processing times. They found that, with the increase of sweat processed times, the chrome content and the denaturalization temperature decreases, the tanning degree of the leather decreases, and the mechanical properties decrease too. In the case of influencing mechanisms of sweat soaking on the structure and behaviors of leathers, no investigation may be found at all [2]. In this paper, some samples including un-tanned cattlehide collagen fibers, chrome tanned cattlehide collagen fibers, glutaraldehyde tanned cattlehide collagen fibers and formaldehyde tanned cattlehide collagen fibers are prepared and processed in man-made sweat and 1

2 preliminary studies on their hydrothermal shrinkage and thermal degradation behaviors are completed. The changes in thermal behaviors between samples before and after sweat process are studied. The mechanism of these changes is discussed. The influence of sweat soaking on the water vapor permeability and the hydrothermal stability of the crust leathers is included as well. EXPERIMENTAL Main Materials and Apparatus Sodium chloride, analytically pure, and sodium hydroxide, chemically pure, were made by Shanghai Chemical Reagent Co., Ltd. Silver nitrate, made by Shanghai Silica Gel Factory, is analytically pure. Glutaraldehyde solution (25%) and Formaldehyde solution(37%), which are biochemical reagent, were made by Shanghai Chemical Reagent Co., Ltd.. Sodium carbonate, which is analytically pure, was made by Tianjin Sitong Chemical plant. Chrome tanned liquor reduced by glucose, whose basicity is 38%, was prepared in our laboratory. Un-tanned cattlehide collagen fibers were prepared according to reference [3]. Chemically pure, Analytically pure, and Biochemical reagent are different grades of national reagent purity standards of China. Man-made sweat was made according to reference [4]. The crust leather samples used here were pigskin garment crust leather, which were provided by Sichuan University, China. PHS-2A ph value measurement instrument was made by Leici Instrument Plant, Shanghai, China. TG209 thermal analyzer was made by NETZSCH, Germany. THZ-82 water bath constant temperature oscillator was made by Fuhua Instrument Plant in Jiangsu province, China. Temperature & Humidity Controller was made by Chongqing Experimental Facilities Factory, China. Thermal platform microscope was made by Beijing No.3 Optical Instrument Factory, China. Procedures Preparation of Un-tanned Cattlehide Collagen Fibers After being prepared according to relevant reference [3], the samples of un-tanned cattlehide collagen fibers were put in a desiccator with silica gel in it for more than two weeks until the weight of the sample did not change anymore. It means that the moisture content in the sample reached a stable level. The sample was ready for subsequent process. Preparation of Chrome Tanned Cattlehide Collagen Fibers The chrome tanning process of the cattlehide collagen fibers was the same as reference [6]. Then the sample was ready for subsequent process. 2

3 Preparation of Glutaraldehyde Tanned Cattlehide Collagen Fibers The tanning reagent used here was a solution that contained 25 percent of glutaraldehyde in weight grams of cattlehide collagen fibers were put into a solution with 3 grams of glutaraldehyde per liter and 30 milliliter of distilled water. In the normal temperature, the mixture was let alone for 14 hours and sufficiently shaking was needed. The ph value was adjusted to 8.5 with 20 percent of sodium carbonate in weight within 2 hours while the mixture was stirred well. After being taken out and filtered, the cake (glutaraldehyde tanned cattlehide collagen fibers) was washed with 20 milliliter distilled water for 10 times. The filtered cake was put in a desiccator with silica gel in it for more than two weeks until the weight of the sample didn t change anymore. It means that the moisture content in the sample didn t change anymore at all. Then the sample was ready for subsequent process. Preparation of Formaldehyde Tanned Cattlehide Collagen Fibers The tanning reagent used here was a solution that contained 37 percent of formaldehyde in weight grams of cattlehide collagen fibers were put into a solution with 10 grams of formaldehyde per liter and 30 milliliter of distilled water. In the normal temperature, the mixture was let alone for 14 hours and sufficiently shaking was needed. The ph value was adjusted to 7.0 with 20 percent of sodium carbonate in weight within 2 hours while the mixture was stirred well. After being taken out and filtered, the cake (formaldehyde cattlehide collagen fibers) was washed with 20 milliliter distilled water for 10 times. The filtered cake was put in a desiccator with silica gel in it for more than two weeks until the weight of the sample didn t change anymore. It means that the moisture content in the sample didn t change anymore at all. The sample was ready for subsequent process. Process of the Cattlehide Collagen Fibers Samples in Sweat The samples including un-tanned cattlehide collagen fibers, chrome tanned cattlehide collagen fibers, glutaraldehyde tanned cattlehide collagen fibers and formaldehyde tanned cattlehide collagen fibers were processed in man-made sweat. A few samples were taken out every three days. There were five times in all and the whole period was 15 days. After being washed with filtered water, the samples were put in a desiccator with silica gel in it for more than two weeks until the weight of the sample didn t change anymore. Some samples were tested on the thermal platform microscope according to reference [6]. Some samples were soaked in man-made sweat for 15 days. After being washed and processed according to reference [8], the samples were ready for Thermo-gravimetric (TG) analysis then. Water Vapor Permeability The determination of the water vapor permeability of the crust leather samples was conducted according to reference [5]. 3

4 Process of Crust Leather in Sweat Different samples were put into bottles with man-made sweat (20 times of the collagen fibers in weight) in it. After being soaked in sweat for 24 hours, the samples were taken out. After the samples having been conditioned in the environment of 20±1, R.H. =65%, for 24 hours, the water vapor permeability of the samples was determined. Determination of Chrome Content in the Crust Leather Samples The determination of chrome content in the samples was according to reference [5]. Hydrothermal Shrinkage Temperature of the Crust Leather Samples in Glycerin Different samples that had been processed in sweat were cut into a definite shape (2mm in width and 45mm in length).the shrinkage temperature and the shrinkage ratios of the samples were tested in glycerin with an instrument made by ourselves. Determination of Dry Heat Resistance of the Crust Leather Samples The thermal platform microscope was adjusted to the best condition. A collagen fiber was chosen among a few fibers. It was put on the glass slide and covered with a thin coverslip. The focus was adjusted to the best condition. They were dry heated from normal atmosphere temperature to 350 degree Centigrade at the temperature heating rate of 5 degree Centigrade per minute. All the changes taking place in this process, including the sample length at different temperatures and the changes in appearance of collagen fibers, were observed and recorded. Thermo-gravimetric (TG) Analysis The Thermo-gravimetric (TG) analysis was carried out on a TG209 thermal analyzer made by NETZSCH, Germany. The amount of the samples used here was 3-4 milligrams. The samples were put into aluminum capsules. After all the experimental parameters of the apparatus were regulated, the temperature was raised. The temperature heating rate procedures used here had been set up before the experiment, which were 5, 10, 15, 20 degree Kelvin per minute, respectively. Pure nitrogen gas was introduced in the aluminum capsules while the experiments were conducted. The experiment information was input into a computer and the thermo-gravimetric (TG) curves of all the samples were plot by computer automatically. RESULTS AND DISCUSSION Influence of Sweat and Tanning Agents on the Dry Heat Resistance of Samples Figure 1 shows the relation between the dry heat shrinkage temperatures and sweat soaking period. As shown in this figure, after being soaked in sweat, the dry heat shrinkage temperatures of all the samples drop more or less. The curves are almost alike for all the 4

5 samples except chrome tanned cattlehide collagen fibers. In the case of chrome tanned Sharp shrinking temperature / untanned collagen fiber chrome tanned collagen fiber 170 glutaraldehyde tanned collagen fiber formaldehyde tanned collagen fiber Sweat soaking period / Days Figure 1 Relation between the dry heat shrinkage temperatures and sweat soaking period cattlehide collagen fibers, when being soaked in sweat, almost no changes may be found in dry heat shrinkage temperature in the first six days. After six days of being soaked in sweat, the dry heat shrinkage temperature decreases greatly. This shows that the chrome tanned cattlehide collagen fibers are good at dry heat resistance in the initial soaking in sweat. It is to say that, in the first six days of sweat soaking, little changes take place in the structure in the case of chrome tanned collagen. After soaked in sweat, for the un-tanned cattlehide collagen fibers, glutaraldehyde tanned cattlehide collagen fibers and formaldehyde tanned cattlehide collagen fibers, however, the dry heat shrinkage temperatures decrease about 30. In the case of chrome tanned cattlehide collagen fibers, however, the dry heat shrinkage temperature decreases about 40. Figure 2 ~5 show the dry heat shrinkage temperature curves (before and after being soaked in sweat for 15 days) of the un-tanned cattlehide collagen fibers, chrome tanned cattlehide collagen fibers, glutaraldehyde tanned cattlehide collagen fibers and formaldehyde tanned cattlehide collagen fibers, respectively. From 2 ~5, we can found that, for all the samples studied here, there are some changes in dry heat shrinkage temperature ranges and the shrinkage ratios. The dry heat shrinkage temperature range of the un-tanned cattlehide collagen fibers (Figure 2) is 23 before sweat process. After being soaked in sweat for 15 days, the shrinkage temperature range changes to 32. The dry heat shrinkage temperature of un-tanned cattlehide collagen fibers brings forward, and their dry heat shrinkage ratio increases from 52% to55% because of sweat soaking. The dry heat shrinkage temperature range of the glutaraldehyde tanned cattlehide collagen fibers (Figure 4) is 28 before being soaked in sweat. After soaked in sweat for 15 days, it changes to 24. Their shrinkage ratio increases from 32% to 35% because of the sweat process. It illuminates that sweat soaking 5

6 may lead to some changes in the structures of both un-tanned and Dry Heat Shrinkage Ratio / % Figure 2 0 untanned collagen fiber untanned collagen fiber soaked in sweat Temperature / Dry heat shrinkage temperature of un-tanned collagen fibers before and after being soaked in sweat for 15 days 50 chrome tanned collagen fiber chrome tanned collagen fiber soaked in sweat 40 Dry Heat Shrinkage Ratio / % Temperature / Figure 3 Dry heat shrinkage temperature of chrome tanned collagen fibers before and after being soaked in sweat for 15 days glutaraldehyde tanned cattlehide collagen fibers. The samples may shrink easily when being dry heated and the shrinkage ratios increase in the cases of the two samples. No changes may be found in the shrinkage temperature range of chrome tanned cattlehide collagen fibers (Figure 3), which is 36. Their dry heat shrinkage temperature brings forward, but the dry heat shrinkage ratio reduces from 46% to 35%. The shrinkage temperature range of formaldehyde tanned cattlehide collagen fibers (Figure5) is 28. After being soaked in sweat for 15 days, its dry heat shrinkage ratio reduces from 43% to 35%. Therefore, with the influence of tannage and soaking in sweat on the dry heat shrinkage of collagen fibers being considered, chrome tanned and formaldehyde tanned cattlehide collagen fibers possess the best ability of sweat resistance in all the four samples studied here. Perhaps it is 6

7 because the salinities (or other small molecules) in the sweat have some unknown reaction with the collagen, which may make their structure more stable Dry Heat Shrinkage Ratio / % glutaraldehyde tanned collagen fiber glutaraldehyde tanned collagen fiber soaked in sweat Temperature / Figure 4 Dry heat shrinkage temperature of glutaraldehyde tanned collagen fibers before and after being soaked in sweat for 15 days

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