W. Chen’s scientific contributions

Nowadays, the antimicrobial activities of traditional Chinese medicines,which have many advantages such as low toxicity and few side-effects, rare resistance to drugs, widely sourced and low price, are being increasingly recognized. In this study we investigated the possibilities of severa essential oils extracted from traditional Chinese medicinal materials as leather fungicides. The essential oils tested included cinnamon oil, garlic oil, clove oil and star anise oil. A 2-Thiocyano-methylthlobenzothiazole (TCMTB) containing commercial fungicide was used as control to inhibit the growth of moulds on wetblue. Results show that these essential oils have antifungal activities and their effect improves with increasing concentration. In particular, for garlic oil, clove oil and cinnamon oil, the dosage of 2% is enough to inhibit the growth of all the tested moulds on wet-blue whilst for star anise oil, more than 2% is required. Essential oils show different inhibitory effects on different moulds and in general, Penicillium citrinum and Alternaria alternate are the species most sensitive to the essential oils, Aspergillus niger is rated second, and Rhizopus stolonifer is the most resistant and most difficult strain to inhibit by the four essential oils. Considering their advantages of being eco-friendly natural products and their acceptable economic cost, these essential oils extracted from traditional Chinese medicinal materials should have potential as fungicides used in leather industry.

Pickled skins were individually tanned with different commercial tanning agents, including chromitan [chrometan], glutaraldehyde and vegetable tannin extracts. The flammability of the tanned leathers were tested by the Oxygen Index test method (ASTM D 2863-77) and the Vertical Flame test (ALCA Method E 50). The densities of the tanned leathers were also measured to show the relationship between fibre's tightness and leather's flammability. The results show that the three tannages can enhance the flame resistance of leather and that the performance of tanning agents on leather can be ranked as: tannin extracts>chromitan>glutaraldehyde. The ranking of the leather density results is the same as the flammability sequence. The results should be useful as a basis for the options in tanning fire-resistant leather.

The synergism index (SI, Formula (1)) and graphical method (Fig. 1) expressed by the minimum inhibitory concentrations (MIC) are often used to evaluate the type of action of combined leather fungicides. The determination of MIC is a complicated and time-consuming process and the exact value is difficult to determine, so a rapid, simple method would be useful to evaluate synergistic combinations. In this study, a formula of the synergism index (SI*, Formula (3)) and the graphical method (Fig. 3) expressed by the diameters of inhibition zones were defined. (2-thiocyanoethyl)-cinnamate (A) and a commercial product of Isothiazoline whose active ingredients are the mixture 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (B) were chosen for combination, and the diameters of inhibition zones and minimum inhibitory concentrations for the effectiveness of different combinations to nine fungi were determined to verify the feasibility of the two methods. Results show that the values of SI calculated by MIC and the value of SI* calculated by diameters of inhibition zones are only slightly different, but they both show the same tendency in that, to most fungi and for most proportions, the values of SI and SI* are all less than 1.0. So, the different combinations of A and B show a synergistic effect or additive effect and the method of SI* is viable to evaluate their action. The relation between the value of SI* and the type of action is same as that of SI. Regarding the graphical method, the results for MIC show a dramatic synergistic effect that is different from that of SI method, and the results of evaluation of diameters of inhibition zones is similar to that of SI* method. So the graphical method expressed by the diameters of inhibition zones is also usable. As the determination of inhibition zones is a relative simple process, the two new methods are very convenient for evaluating synergistic combinations of leather fungicides.

Wet-blue pieces were treated with isothiazolinone at different concentrations in a drum and then the treated pieces were washed. During the treating and washing, the absorptivity and wash-out rate of isothiazolinone from the wet-blue were tested by UV/VIS spectrophotometry. The results showed that the highest absorptivity was about 45% in 15 minutes and the wash-out rate reached nearly 55% after washing for only 15 minutes. Thus, when applied to wet-blue, isothiazolinone should be added at the later stage of chrome tanning and the wet-blue preserved without further washing because of its poor washability. To investigate the distribution of isothiazolinone, the wet-blue pieces treated with 0.25% isothiazolinone (solution concentration) were split into three layers and the inhibition zones of each layer against two fungi were measured. The inhibitory effects of the split layers were also determined by inoculating fungal spores on the wetblue discs with and without culture medium. The results showed that the standard deviations of diameters of inhibition zones among the three layers were low at close to 2mm, indicating that isothiazolinone is distributed uniformly in wet-blue. The finished leather and the shoe lining were also treated with different concentrations of isothiazolinone. The inhibitory effects of treated lining and finished leather were evaluated by inoculating fungal spores on sample discs with a culture medium. Evaluation of the finished leather coated with 135.95mg/m 2 isothiazolinone and the lining (with 77.16mg/g)isothiazolinone inhibited the growth of 8 different fungi for 60 days. The above results may contribute to the application of isothiazolinone to the leather industry.

Previous work from this laboratory has demonstrated that a collagen-TiO2 nanocomposite could be prepared via a sol-gel procedure. However, the shrinkage temperature produced by this kind of nanocomposite is low. In this experiment, the collagen-TiO2 nanocomposite was improved by adding glutaraldehyde and increasing the pH level. Results show that the optimum amount of glutaraldehyde is 6% (based on pickled pelt weight), and the optimal pH level for preparation is 3.5. These conditions raise the shrinkage temperature of the nanocomposite from 73.8°C to 82.2°C. Scanning Electron Micrographs (SEM) images indicate that the collagen fibril has been wrapped with nanoparticles. Meanwhile, results from Atomic Force Microscopy (AFM) suggest that nano-TiO2 with a particle size of 40nm can be formed in-situ in the collagen. Further experiments demonstrated that the introduction of nanoparticles endows the nanocomposite with antibacterial activity.