Vegetable tannin extract has an important use as a tanning agent in leather industry. The colloidal properties of vegetable tannin extract solutions, as a critical factor, greatly affect vegetable tanning process. In this work, we have investigated the particle size and Zeta potential of Commercial Acacia Mangium extract solutions (CAME) and Commercial valonia extract solutions (CVE) under water bath heating and microwave irradiation. The selected conditions were as follows: time, 15 min, 30

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... , 60 min and 120 min; temperature, 30°C, 40°C and 50°C. It was found that the particle size of both CAME and CVE under microwave irradiation decreased while Zeta potential increased compared with water bath heating. Particularly, the extent of the decreased particle size and increased Zeta potential of CVE is bigger than CAME. Furthermore, the feature becomes more and more significant with the rise of temperature. In the vegetable tanning process, tannin extracts with small particle size can easily penetrate into the skin and then crosslink well with the collagen of skin. Therefore, as a novel, environmentally friendly and efficient thermal method, microwave irradiation may be used for the well-performance leather, less pollution and cleaner tanning process.