Rheological characterization of cellulosic and alginate polymers

The purpose of this study was to assess the properties of aqueous solutions of various polymeric materials intended for use as components of a sustained release device for various proteins. Polymers that were studied included Sodium Carboxymethylcellulose (CMC), Methylcellulose (MC), Hydroxypropylmethylcellulose (HPMC) and Sodium Alginate (ALG). The effects of polymer concentration, temperature and autoclaving on solution viscosity were determined. With all the polymers, viscosity/ concentration relationships were linearized by using an equation of the type mu = (Ca + beta)gamma, where mu and C referred to solution viscosity and concentration, respectively. alpha and gamma were constants related to polymer type and molecular weight, whereas beta reflected viscosity of water at the temperature of measurement. gamma, which reflects the sensitivity of the viscosity/concentration relationship, was determined to be 4 for both low and high molecular weight CMC and ALG, and 8 for MC and HPMC. alpha, on the other hand, was directly proportional to polymer molecular weight. The same equation could also adequately describe viscosity/temperature relationships for each polymer. For both CMC and ALG, increasing solution concentration had a greater effect on the reduction of viscosity upon increasing temperature. A concentration dependent thermal "gelation" phenomena was observed with MC solutions. Autoclaving effects were more pronounced in ALG solutions as compared to CMC samples in the 0.5 to 3.0% w/v concentration range. No significant long term effects on solution viscosity were observed with MC and HPMC, however.