Grantee Research Project Results
Final Report: Environmentally Friendly Leather Tanning Using Enzymes
EPA Grant Number: SU835511Title: Environmentally Friendly Leather Tanning Using Enzymes
Investigators: Cao, Huantian , Wu, Changqing , Scudder, Crescent , Siron, Leslie , Xu, Wenqing
Institution: University of Delaware
EPA Project Officer: Packard, Benjamin H
Phase: I
Project Period: August 15, 2013 through August 14, 2014
Project Amount: $14,999
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2013) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Chemical Safety , P3 Awards , Sustainable and Healthy Communities
Objective:
The purpose of tanning animal hides is to achieve a stabilization of the collagen fibers imbedded within the skin and to prevent shrinkage of these fibers. The goal is to have a high hydrothermal stability (therefore the collagen fibers do not degrade in the heat), be resistant to microbial damage, while also being aesthetically ideal with high strength and softness. Currently, the industrial tanning methods use a high level of chemical agent inputs creating a lot of chemical output pollution. A common chemical used as a tanning agent is chromium (III), which if oxidized becomes chromium (VI), a known toxin and carcinogen. Leather tannery also produces hazardous wastewater effluent and solid waste, creates air pollutants, and it exposes workers to harmful chemicals.
This research explores a wide range of alternative naturally-derived chemicals as leather tanning agents and explores new processes for leather tanning using environmentally friendlier inputs. The leather produced from this research is applied to the fashion and apparel industry by creating products that adhere to the aesthetic and functional properties of leather widely used by this industry.
The goal of this project is to investigate environmentally friendly leather tanning process using enzymes, or a combination of enzymes and non-toxic chemicals. The research uses an interdisciplinary approach combining the knowledge from two departments at the University of Delaware, Fashion and Apparel Studies (FASH) and Animal and Food Sciences (ANFS). Dr. Eleanor Brown of United States Department of Agriculture Eastern Regional Research Center (USDA ERRC) served as the external collaborator/mentor of the project. Our objectives included: (a) selecting and obtaining raw goat hides for experimental treatments; (b) investigating enzymatic tanning processes using enzymes such as transglutanimase, laccase, protease, lipase, and phenol oxidase (tyrosinase); (c) investigating enzyme-assisted chemical tanning processes using a combination of enzymes and non-toxic chemicals such as plant polyphenols; (d) evaluating the tanning effectiveness, textile properties of the leather and environmental impact of the tanning process; (e) designing and developing leather accessories; (f) developing an educational tool.
Summary/Accomplishments (Outputs/Outcomes):
Conventionally dehaired and pickled goatskins were chosen as the raw material for this study. The chemicals used for tanning experiments included commercial grade vegetable tannins quebracho, food grade protein crosslinking transglutaminases (TG) additives, research agent grade tea extracts, protease, lipase, and laccase.
A shaken water bath was used to maintain temperature during tanning experiments. Tests for the effectiveness of tanning were determined by analysis of hydrothermal stability (shrinkage temperature Ts), exhaustion of spent liquor, and through observation of fiber bundles using scanning electron microscopic (SEM) analysis.
Using 20% quebracho solution as vegetable tannins, leather can be tanned with a shrinkage temperature of 79°C. This vegetable tanning was the control of the experiments in this research. Without vegetable tanning agent quebracho and used by itself, the enzymes protease, lipase, transglutaminases, laccase, a combination of laccase and transglutaminase, and tea extracts containing polyphenols do not have tanning effect with shrinkage temperature similar to the un-tanned skin of about 60°C. Enzymes and tea extracts were determined not adequate as tanning agents alone.
Pre-treatment of goatskins with lipase, protease, and a combination of lipase and protease followed by 20% quebracho vegetable tanning process resulted in shrinkage temperatures below the control (quebracho vegetable tanning only). When the enzyme concentration and treatment time were reduced, the Ts would be closer to 79°C (reached up to 78°C or 79°C). Pre-treatment with protein, fat degradation enzymes would not help tanning, and exhaustion of spent liquors was not conducted due to low shrinkage temperatures.
Quebracho vegetable tanning process followed by post-treatment with transglutaminases showed either the same shrinkage temperature or a slight improvement of 2°C when compared to the control. Exhaustion of spent liquor results indicated Ts increase was not associated to the difference in quebracho uptake, but could be the result of protein crosslinking in post-treatment. A combination of quebracho and transglutaminase or laccase (quebracho and one enzyme) in one-step tanning process resulted in Ts of 78°C-81°C, a slight increase of up to 2°C compared to the control of quebracho tanning. A combination of quebracho and transglutaminase with laccase (quebracho and two enzymes) in one-step tanning treatment ranged from Ts of 79°C- 84°C, indicating an up to 5°C increase in shrinkage temperature. A combination of quebracho and transglutaminase with a post-treatment of laccase showed a Ts range of 79°C-83°C, while quebracho and post-treatment of laccase being 81°C. This indicates an up to 4°C increase in shrinkage temperature with post-treatment of laccase.
With enzymes in the same tanning solution of quebracho, the % uptake of quebracho was slightly lower than quebracho alone. This indicated the enzyme assisted collagen crosslinking and/or phenol oxidizing may slightly block the vegetable tannins penetration, and the Ts increases were the result of crosslinking and oxidizing. From SEM images, researchers observed no significant differences in fiber bundles of the cross grain structure with enzyme additions. The researchers discovered the laccase treatment would make the leather darker. This could be the result of oxidizing. Traditionally, brown color was obtained from vegetable tanning. In combination with the vegetable tannin quebracho with enzymes, a wide spectrum from light brown to very dark brown (almost black) color were obtained in this project, which could replace subsequent leather dyeing process.
Upon completion of experimental trials, currently the research team has selected a sub-set of enzyme assisted vegetable tanning methods to develop fashionable leather products and to conduct physical and environmental testing (BOD/COD/TS) on larger leather samples. The leather and accessories samples and testing results will be presented in the EPA P3 National Sustainable Design Expo in Washington, DC in April 2014.
Conclusions:
This was a very successful interdisciplinary project that combined knowledge of faculty and students in FASH and ANFS. In addition, the research team visited USDA ERRC and learned a lot from our mentor Dr. Eleanor Brown and her colleagues at ERRC on leather science and processing. The team also learned to use the pilot tannery facility at USDA ERRC in the project.
This research project successfully addressed the potential for exploring environmentally friendlier chemicals used for the tanning of leather. This research investigated a variety of enzymes and the finding is consistent with a published research finding that transglutaminase treatment did not affect denaturation temperature of hides. Enzymes when used alone are not effective tanning agents. However, the research found that the existence of enzyme transglutaminase and laccase can help increase hydrothermal stability of vegetable tanning. The shrinkage temperature may increase up to 5°C. While the enzyme-assisted vegetable tanning did not find hydrothermal stability to compare to chrome tanning (Ts about 105°C), the mentor of our project Dr. Eleanor Brown indicated a shrinkage temperature of 83 to 84°C will be adequate for most fashion products. Among the five transglutaminase additives, TGTC, with ingredients of maltodextrin (a polysaccharide produced from starch) and sodium caseinate (a type of protein found in milk), is the most promising one.
In addition to increase hydrothermal stability, enzyme assisted vegetable tanning also helped obtain leather with a wide spectrum of color from light brown to very dark brown (almost black). This could replace subsequent leather dyeing process.
Supplemental Keywords:
Green chemistry, green manufacturing, environmentally benign substitute, biotechnology, toxic use reductionThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.