Hans Arwidsson

Water solid interactions II. Effect of moisture sorption and glass transition temperature on compactibility of microcrystalline cellulose alone or in binary mixtures with polyvinyl pyrrolidone

The relation between the moisture sorption and compaction properties of microcrystalline cellulose, MCC, and binary mixtures of MCC with polyvinyl pyrrolidone, PVP, has been examined. PVP is a completely amorphous polymer, whereas MCC contains various fractions of amorphous structure depending not only on the quality used but also on the pharmaceutical processing. The tensile strength of tablets of MCC is shown to depend upon the relative humidity, RH, prior to compaction. At an RH of about 70%, a decrease in strength is observed corresponding to the upward shift of the moisture sorption isotherm. For a dry blend of MCC and PVP as well as for a granulation, the tensile strength is determined by the properties of MCC at humidities below 70% RH. At humidities above 70%, a reduction of the glass transition temperature of PVP below the operating temperature (20°C) is the dominating factor, resulting in a decrease in tensile strength.

Water-Solid Interactions. III. Effect of Glass Transition Temperature, Tg, and Processing on Tensile Strength of Compacts of Lactose and Lactose/Polyvinyl Pyrrolidone

The effect of moisture sorption at different relative humidities on the tensile strength and the physical stability of compacts of crystalline and partly amorphous lactose, alone and in binary mixtures with PVP, has been studied. Furthermore, the role of moisture as a plasticizer and its effect on the glass transition temperature, Tg, are related to the compactibiltiy. Samples were conditioned for 2 hr using a climate test chamber at different relative humidities. Moisture sorption was determined, the radial crushing strength for compacts was measured immediately and after storage, and the tensile strength was calculated. The glass transition temperature, Tg, was determined using DSC. The tensile strength of the compacts was found to depend on both the conditioning humidity and the humidity during storage. An increase in humidity to a level at which the glass transition temperature, Tg, fell below the operating temperature, T, resulted in transition from a rigid glassy state to a mobile rubbery state. For compacts of partly amorphous lactose, an increase in the tensile strength was observed during storage of tablets, due to recrystallization of the amorphous regions above Tg. Tablets of mixtures of lactose and PVP exhibit a sharp decrease in tensile strength at humidities above 70% RH, due to the glass-to-rubber transition of PVP.

Water-solid interactions. I: A technique for studying moisture sorption/desorption

Abstract Moisture sorption and desorption have been characterized for active (naproxen and paracetamol) and inactive pharmaceutical solids by using a climatic test chamber. The relative humidity (RH) of the climatic test chamber was varied in the range from 15 to 90%. Equilibrium moisture content was achieved within a period of 2 h for slightly hygroscopic and moderately hygroscopic substances. For very hygroscopic substances equilibrium was reached within 2 h at low RH ( 60%). Moisture sorption isotherms were characterized by using the climatic test chamber and were found to be identical with moisture sorption isotherms characterized by desiccators.

Application of intrinsic viscosity and interaction constant as a formulation tool for film coating. III. Mechanical studies on free ethyl cellulose films, cast from organic solvents

Abstract The mechanical properties of ethyl cellulose films, cast from different solvent systems, have been determined and the structures of the films have been visualized in order to assess the solvent systems for use in a coating process. General relationships could not be found between intrinsic viscosity or interaction constant data and the mechanical properties. However, by using the two parameters in combination, favourable solvent systems could be selected e.g. methylene chloride and ethanol in the ratio of 60:40 (% w/w) or toluene and ethanol in the ratio of 80:20 (% w/w). Water should be avoided in solvent systems for ethyl cellulose since it accumulates in the evaporating solution and impairs the film properties by forming a spongy and porous film.