The Degradation And Cross-linking Study Of Poly-gamma-glutamic Acid On Cosmetics

Poly-gamma-glutamic acid (y-PGA) is one of the few available microbial polymerization of poly-amino acids so far[1]. There are a large number of hydrophilic groups in PGA molecule structure, including amino, carboxyl and hydroxyl groups. In addition, a large amount of hydrogen bonds exist in the y-PGA. The above two characteristics enhance the performance of super absorbent and improve the ability of locking water. At present, more and more manufacturers make full use of γ-PGAto produce cosmetic, so the increasingly sharp competitions and the homogenization of products have led to a downward on prices rapidly and a decline in profitability constantly respectively. In order to developing new type products of y-PGA, our research group take the research and development experiences of hyaluronic acid for reference to prepare two kinds of new type y-PGA products which are all easy to absorb and intensify texture by the methods of degradation and cross-linking respectively.The purpose of appropriate degradation was to improve the ability of absorption and utilization. The molecular weight of raw y-PGA was about 1000 kDa, by investigating the effect of conditions such as temperature, pH on the degradation of y-PGA, a series of low molecular weight y-PGA were prepared, then the moisturizing properties of different low molecular weights y-PGA in vivo and in vitro was investigated and compared. Experiment had proved that at the following experimental conditions 3％γ-PGA, pH 2.0, incubation 3 hours at 80 ℃, or 3％γ-PGA, pH 3.0, incubation 1 hours at 90℃,we could acquire the special low molecular weight(100 kDa)γ-PGA which had the best moisturizing properties. At the same time, to facilitate the selection and optimization conditions of degradation, as well as to control the degree of degradation in industrialized mass production timely, we modified and simplified the Ubbelohde Viscometer measured method. The characterization efflux time of viscosity and the relative average molecular weight of the GPC were fitting. We discovered that the method could be used to track the degradation degree of y-PGA quickly and efficiently.As for y-PGA cross-linking, we choose 1,4-butanediol diglycidyl ether as crosslinking agent. Cross-linking can improve the molecular weight to make up the inadequacy of natural degradation. But in actual production, we found some phenomena including the instability of the cross-linked PGA, the viscosity of the cPGA reduced easily after placing a few weeks and the color of the cPGA turned yellow, which all seriously impacted the sales of the products. So a method on preparing phase-stable cPGA-S has been urgently needed. The influences of dosage of cross-linking substrate and ratio of homogenate on the stability of the cPGA were studied. In 12％～-20％γ-PGA, the content of 1,4-butanediol diglycidyl ether is 5％～ 10％ of the monomer molar volume of y-PGA, the apparent visual results show that there were no stratification and precipitation phenomenon occurred after 12 months, that means we prepared phase-stable cPGA-S. By investigating the effects of thicker, pH and salt, we established a preparation progress on viscosity stability of cPGA-S, its viscosity change rate<5％ after 5 months. Furthermore, such suspension had been found features of dramatic increase in viscosity, rapid liquefaction on skin surface, which made it more suitable to be developed as a new medium in cosmetics field.