Study On The Properties Of Bioorigin Poly (γ-glutamic Acid) Aqueous Solutions

Firstly, the poly(glutamic acid) biosynthesized by Bacillus subtilis NX-2 was characterized by Fourier transform infrared spectrometry(FT-IR), 1H and 13C high resolution magic angle spinning nuclear magnetic resonance spectroscopy(HR/MAS NMR) andγ-glutamyltranspeptidase enzymatic hydrolysis, all the results can be summarized to confirm that the sample possesses the following chemical structure:Then the viscometric and rheological properties of bioorigin poly(γ-glutamic acid) (γ-PGA)dilute aqueous solutions are investigated systematically. Experiments shows that γ-PGA belongs to polyelectrolyte. The relationship between its reduced viscosity and polymer concentration doesn't coincide with Huggins equation, which can be changed by adding low-molecular-weight strong electrolyte such as NaCl with moderate ionic strength I , and herein the intrinsic viscosity [η] is directly proportional to - exponential of I. Furthermore, [η] value depends on time obviously, which may be caused by the biopolymer chain transition between spiral conformation and random coil arising from the reconstruction of intra-molecular synergic hydrogen bond. In addition, the rehological response ofγ-PGA dilute solutions at moderate shear rate has been measured using a capillary viscometer that provides for a fivefold variation in shear rate at each concentration. The non-Newtonian effects were found to be slight and negligible for biooriginγ-PGA, which brings out great convenience for intrinsic viscosity determination.Founding on the base of above-mentioned research work, the weight-average molecular weight dependence of intrinsic viscosity and structural parameters of bioorigin poly(γ-glutamic acid) was investigated by GPC-LLS method combinedwith viscometric measurements. The Mark-Houwink equation of poly(γ-glutamic acid) in 1.20 mol/L NaCl aqueous solution at 30℃ was estimated as follows:[η]=9.824×10-9Mw1.49, dL/g Finally the viscometric properties of γ-PGA extremely dilute aqueous solutions are investigated preliminarily. The measured reduced viscosity-concentration curves deviate from linear trend in dilute solution region and reveal downward turn in extremely dilute concentration region, the transition point being defined as critical concentration which may be regarded as the separating point between dilute solution and extremely dilute solution regions...