Recipient Organization
LOUISIANA STATE UNIVERSITY
202 HIMES HALL
BATON ROUGE,LA 70803-0100
Performing Department
School of Nutrition and Food Sciences
Non Technical Summary
A change in knowledge will result by performing the tasks of this project due to the fact that the literature is scarce regarding physical properties of alligator skins: There are no publications on the strength, viscoelastic characteristics and thermal transitions of finishedAlligator mississippiensisleather. Therefore the primary objective of this project is to determine these characteristics and relate the data to the leather end use (apparel, shoes, etc.). Additionally, since chromium may be present in the tanned leather as trivalent Cr3+or hexavalent Cr6+cationic species (Cr6+ is toxic to humans), the proposed work will probe if the leather samples under investigation were chrome tanned (with Cr3+ compounds) and if hexavalent Cr6+ is present both in the tanned samples (which might be in direct contact with the human body, depending on the end use and design) and in the waste waters from Louisiana tanneries. The educational objective of this project is the training of students in obtaining and use of sustainable materials from Louisiana agriculture.
Animal Health Component
80%
Research Effort Categories
Basic
10%
Applied
80%
Developmental
10%
Goals / Objectives
The Louisiana Department of Wildlife and Fisheries (Department) manages the American alligator (Alligator mississippiensis) as a commercial, renewable natural resource conservatively estimated at over $704,000,000, providing significant, direct economic benefit to Louisiana. Louisiana's wild and farm alligator harvests currently exceed 300,000 animals annually, while the population level remains stable. As shown in the 2012 Annual Report of Alligator Advisory Council, Louisiana leads the country in the production of alligator skins. In recent years the United States tanned less than 10% of all alligator skins produced in Louisiana. Tanneries convert the raw hides into finished alligator leather. Once alligator hides have been tanned, they are used to make all types of products varying in size from earrings to sofas.It is the finished alligator leather produced in Louisiana the present project is focused on. Only alligator skins provided by Louisiana producers, the first beneficiaries of the projected investigations, will be analyzed. Because of this sustainable and substantial availability of alligator skins, diversification and expansion of markets for alligator leather goods is a logical next step. The goal is to find more opportunities for Louisiana's alligator business. Tests will be conducted on alligator skins according to the objectives outlined in the following. Since the testing leather coupons will be practically sampled from the entire skin surface, the data collected might be correlated with the end use of the particular part of the skin, knowing that the preferred alligator skin is its belly. This project aims at a complete characterization of finished American alligator (Alligator mississippiensis, named in the following only asalligator) leather regarding its strength and elasticity. Since the alligator leather samples analyzed several years ago were stored in the PI's conditioning laboratory in standard conditions, re-testing of these leathers after a long term aging will be both of academic and practical interests. Therefore several samples will be re-tested after a time span of 12 years to learn about how aging of alligator leather might affect mechanical characteristics. Data will be compared with that collected for other traditional leathers, such as cowhide and pig. The following objectives will be addressed in the project:1. Investigation of Physical and Mechanical Characteristics:Morphological evaluation of leather structureDetermination of physical characteristicsDetermination of tensile resistance (Stress and strain at break)Determination of tearing forceDetermination of viscoelastic parametersDetermination of thermal transitions 2. Investigation of the chemistry of chromium tanned leather3. Increasing of awareness of Louisiana alligator leather through publications and presentations.
Project Methods
The specific instrumentations of methods presented in the following are available at LSU.Physical Characteristics Measurements. The thickness and the specific weight will be determined according to specific ASTM specifications. Collagen fibril diameter distribution will be investigated by Scanning Electron Microscopy. Prior to SEM measurements the alligator samples will be freeze-dried and sputter-coated with a thin layer of gold.Determination of Tensile Characteristics: Stress and Strain at Break. Tensile samples will be tested in two directions at 90o from each other, like the warp and filling of a fabric. The determinations will be performed according to ASTM Standard Test Method for Breaking Strength and Elongation of Textile Fabrics (Grab Test) with the dimension of tensile samples adapted to the dimensions of available skins. An Instron Model 4301 tensile tester will be used to measure breaking stress, breaking strain, Young's modulus and the energy at break at a crosshead speed and a load cell chosen according to sample resistance.Determination of Tearing Strength of Leather Samples. This test will determine the force required to propagate a single-rip tear starting from a cut in the sample and using a falling-pendulum (Elmendorf-Type) apparatus. The standard method will be applied to leather samples without any modifications, provided the sample does not tear in the direction crosswise to the direction of the force application during the test. It has been found that there was a significant difference in tear and tensile strengths of footwear goat leather produced using trivalent chromium salts, indicating that the percentage of chromium used in tanning influenced the physical strengths of the leather. This finding should be related to tearing of alligator leathers.Investigation of Viscoelastic Behavior of Alligator Leather. Leathers are not elastic bodies; they are viscoelastic materials because there is a phase shift between the force applied (stress) and the deformation (strain) which occurs in response. In dynamic mechanical analysis, DMA, measurements are represented as a complex modulus E* reflecting both the elastic (E') and the viscous (E") behavior of the material. The viscoelastic characteristics, as well as the thermal transitions of leathers (any), depend to a large extent on the presence of the water associated with constituting collagen biopolymer. The bound water plasticizes the leather at sub-freezing temperatures and dictates the viscoelastic properties. The content of water will be monitored by thermogravimetric analysis (TGA). Viscoelastic characteristics of alligator leather samples will be investigated by DMA in dry nitrogen both in heating and cooling modes from -40oC to 80oC using a train of frequency from 0.1 to 10 Hz.Thermogravimetric Analysis. Drying and thermal degradation of leather samples will be performed under nitrogen using a heating rate of 10oC/min. Modulated thermogravimetric analysis will be conducted in order to determine the activation energy of different processes involved in the thermal events using the program: 1) High resolution sensitivity 1; 2) Modulate +/- 5oC every 200 seconds; and 3) Ramp 2.00oC/min res 4 to 600oC.Investigation of Thermal Transitions in Alligator Leather. Thermal transitions of interest in leather are related to glass-transition (Tg), melting (Tm), crystallization (Tc) and denaturation (Td) temperatures of the collagen molecular chains within the leather matrix. When leather is exposed to temperatures below the Tg, the constituting collagen becomes very rigid and brittle, while at temperatures above Tg, the chain segments start moving and a transition from the glassy state to a rubbery-like state takes place. Tg is influenced by certain factors, such as cross-linking (tanned leather is a crosslinked polymer). The melting of collagen helix and aggregates of helices to gelatin can be considered as the melting of a polymer crystal. Cross-links cause an increase in Tm because they affect the entropy of melting. Thermal analysis of leather is performed by means of thermogravimetry and differential scanning calorimetry (DSC) analyzes and the collection of data should be related to the heating rate (the faster the heating rate, the higher the transition temperature) and the moisture content of samples. Tg, observed with difficulty by DSC technique because no enthalpic (heat) changes are associated to this transition, is clearly evidenced by DMA. Any secondary thermal transition observed as a step change in the DSC baseline will generate a peak for tan d and E" in DMA plots. To the PI's best knowledge there are no DSC and/or DMA investigations on glass-transition, melting, and crystallization of collagen from alligator leather.DSC analysis will be performed at a variable scan rate of 2-10°C/min, under nitrogen, for both heating and cooling runs.Chemistry of Alligator Tanned Skins. Determination of Chromium Species in Tanned Leather Samples and in Wastewaters from Louisiana Tanneries. The chromium salts are used extensively in the leather industry as a tanning agent. A series of ASTM methods cover wet procedures for determination of chromium in tanning liqueurs and wastewater, surface water, and drinking water but not in the tanned leather. The chromium content of the liquors determines the amount to be used to obtain the desired degree of tannage, and hence may be a matter for specification in the purchase of leather. Chromium may be present in the finished leather as trivalent Cr3+or hexavalent Cr6+cationic species. It has been proved that hexavalent chromium Cr6+ is toxic to humans, animals, and aquatic life. It can produce lung tumors when inhaled and readily induces skin sensitization. Therefore Cr6+ is closely monitored by U.S. Department of Health and Human Services. A wet field method has been proposed, but it is cumbersome and refers only to soluble Cr6+ species. However, the X-ray absorption spectroscopy technique which is divided into X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure can readily distinguish between different oxidations states of Chromium. The XANES region is roughly 50 eV within the edge and provides information about the chemical speciation of an element, while the EXAFS can extend 1,000 eV or higher from the edge and provides information about the interatomic spacing of the near neighbors of an atom. XANES is an element-specific technique and allows detection of the structure of elements directly, without any sample preparation or wet chemistry. XANES will probe if the leather samples under investigation were chrome tanned (with trivalent Cr3+ compounds, usually sulfate) or otherwise and if hexavalent Cr6+ is present both in the tanned samples and in the waste waters from Louisiana tanneries.