Čes. slov. farm. 2008, 57(5):215-220
Characterization of celluloses by means of viscoelastic parameters
- Charles University in Prague, Faculty of Pharmacy in Hradec Králové, Department of Pharmaceutical Technology
In tablet formulation it is necessary to start from viscoelastic parameters of the excipients employed. Plasticity and elasticity of excipients are influenced by the type of bonds which are being formed in the course of the compaction process. The present paper evaluates the viscoelastic properties of selected fillers intended for direct compaction of tablets. The determinations included cellulose powder, microcrystalline celluloses Avicel PH 101, Avicel PH 102, Avicel PH 103, Avicel PH 200, Avicel PH 301, and Ceolus KG 802. Elasticity of the excipients was evaluated by means of Young's modulus of elasticity and differential elastic potential energy. Plasticity was evaluated by means of the stress relaxation test using the three-exponential equation following Maxwell's model. The method was supplemented with a novel original parameter, total plasticity PT. The study examined the effect of particle size of fillers, density, moisture content, and molecular weight on elasticity and plasticity of celluloses. The results of the paper revealed that particle size of celluloses did not influence elasticity and plasticity of excipients. With increasing density of celluloses, elasticity was increased and at the same time plasticity was decreased. The above-mentioned viscoelastic parameters were influenced by the content of moisture in fillers. With increasing amount of moisture in fillers, elasticity was decreased and plasticity increased. With increasing molecular weight of cellulose, elasticity was decreased and plasticity increased.
Keywords: Young's modulus of elasticity; differential elastic potential energy; three-exponential equation of plasticity; residual and total plasticity; celluloses
Grants and funding:
The paper was supported by the Research Project MSM 0021620822.
Received: August 11, 2008; Accepted: August 20, 2008; Published: May 1, 2008 Show citation
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