December 2017 Abstracts

Calorimetric and Kinetic Analysis of Thermal Behaviors of Chrome-tanned Collagen Fibers Using Isoconversional and Multivariate Non-linear Regression Methods

by Wentao Liu, Yuanzhi Zhang and Guoying Li

To further understand the thermal stability of collagen in hide and leather, the thermal denaturation behaviors of chrome-tanned collagen fibers were studied by non-isothermal differential scanning calorimetry (DSC) using isoconversional and multivariate non-linear regression (Multivar-NLR) methods. The differential (Friedman) and the integral (Ozawa-Flynn-Wall) isoconversional methods as well as the Multivar-NLR method showed that the denaturation (or shrinkage) process could be best described by a three-step model, in which a reversible reaction was followed by a rate-limited irreversible step. The simulation of thermal behaviors of collagen at different temperature conditions indicated that the denaturation kinetics could be approximated to a one-step irreversible reaction at low heating rates or temperatures. For the design of new chrome-free tanning systems, which can endow collagen with high enough thermostability, the decrease in the rate of the irreversible denaturation of collagen might be an important criterion as well, besides the increases in the denaturation (or shrinkage) temperature, enthalpy and effective activation energy.

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Development and Characterization of Genipin Cross-linked Gelatin Based Composites Incorporated with Vegetable-tanned Collagen Fiber (VCF)

by Jie Liu, Cheng-Kung Liu, and Eleanor M. Brown

Collagen fibers obtained from solid fibrous wastes generated in tannery have a high potential of being used in developing green composites. Earlier studies in our laboratory demonstrate that nonwoven composites can be derived from collagen fiber network using paper-making technology. The purpose of this work was to fabricate green composites based on gelatin and vegetable-tanned collagen fibers (VCF), using a non-toxic and naturally occurring compound, genipin, as cross-linking agent. VCF were obtained from split hide that has been tanned with vegetable tannins by mechanical milling technique. The VCF content in the networks of gelatin was varied from 10 to 40% (w/w) in dry weight relative to that of the gelatin. The structure, mechanical properties, thermal properties and water resistance of the composite films have been investigated with Fourier transform infrared spectroscopy (FTIR), mechanical testing, thermogravimetric analysis and swelling measurement. The results from those studies revealed that VCF and gelatin could mix with each other homogeneously under alkaline condition and the mechanical properties of the composite films at wet state were improved significantly over that of pure gelatin film. In addition, the composite films showed higher water resistance and thermal resistance than the control. FTIR analysis confirmed the molecular interactions between gelatin and VCF and the formation of cross-links between primary amino groups on gelatin and VCF. Our results indicated that VCF can be used as environmentally friendly and cost-effective potential reinforcing agent for green composites, providing better properties than the original biopolymer matrix. The genipin cross-linked gelatin/VCF composite film can be a promising candidate for the biomedical and packaging applications.

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Penetration of the Polyflavonoids and Simple Phenolics: A Mechanistic Investigation of Vegetable Tanning

by Bo Teng, Jiacheng Wu and Wuyong Chen

Mechanisms of tanning are the fundamental base for predicting and developing new tanning agents and technologies. However, many mechanistic questions remain for us, such as: How does the penetration happen? How do the phenolic compounds work individually? In this study, penetration processes of the tannin extracts were investigated with the Bayberry extract (prodelphenidins), the Larch extract (procyanidins) and the Acacia Mangium extract (prodelphenidin-procyanidin complexes) used as tanning agents. During the process, the tanning liquids were regularly sampled and the simple phenolics and polyflavonoids were quantified respectively with a Prussian blue assay, a conductivity analysis, an acid-butanol assay as well as a HPLC analysis. The results showed that, during tannin, the concentration of polyflavonoids in the tanning liquid decreased continuously. In contrast, for the simple phenolics, the concentration decreased at first and later increased. Therefore, penetration processes of the tannin extracts can be described as: in the beginning, both simple phenolics and polyflavonoids started to penetrate; then the simple phenolics completed their penetration first and reversibly bound with collagens; in the meantime, the polyflavonoids were still penetrating and gradually replacing those simple ones from collagen matrix; at the end of the tanning processes, most of the simple phenolics were replaced by the polyflavonoids, meanwhile they were migrated back into the tanning liquids. The results will provide valuable information to help understanding the mechanism of vegetable tanning.

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Preparation and Characterization of Gelatin/Chitosan/Carbodiimide Films

by Maryann M. Taylor, Lorelie P. Bumanlag, Nicholas P. Latona, Eleanor M. Brown and Cheng-Kung Liu

In prior studies, we examined the effects of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and water-dispersible polycarbodiimides (pCDIs) on the properties of gels produced from gelatin and a gelatin/chitosan blend that may be suitable for a role in leather processing. Those studies showed major differences in gel properties as a function of the specific carbodiimide. In this continuing study, the gelable products formed from gelatin or a gelatin/chitosan blend modified with EDC or pCDIs were cast into films. The mechanical properties, hydrothermal stability, solubility, and water absorptivity of the films were examined. The range of values for mechanical properties (tensile strength, % elongation at break, Young’s modulus, and toughness) was small enough that it would likely not be a major consideration in the choice of carbodiimide for a particular application. Neither EDC nor the pCDIs at the concentrations tested in this work had any discernible effect on the hydrothermal stability of gelatin or gelatin/chitosan films. The effects of the pCDIs on solubility and water absorption properties of the films trended more closely with the concentration of the pCDI than did the effects of EDC. This preliminary study explores the potential for using the environmentally friendly, water-dispersible pCDIs in gelatin and gelatin/chitosan-based films for use in leather coating or packaging applications.

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