Modeling the properties of viscoelastic pharmaceutical and food compacts
Abstract
Although compaction of viscoelastic powders is an important process in food, pharmaceutical, ceramic and detergent industries, current scale-up methodologies are highly based on trial error. This research work aims to make compaction of viscoelastic powders more mechanistic by relating the microscopic phenomenon of contact area formation during powder consolidation, to the macroscopic compact properties, viz. density and tensile strength. Pharmaceutical (MCC-APAP) and food (Soy protein based) powders were selected for this purpose. Variation of compact density and tensile strength of MCC-APAP mixtures was studied as a function of compaction pressure, drug (APAP) and moisture contents. The density and tensile strength of Soy Flour and Soy Protein compacts was studied as a function of compaction pressure. Lower APAP and higher moisture contents were found to favor formation of denser compacts with higher tensile strength. Soy flour compacts were found to be slightly denser but exhibited much lower tensile strength compared to Soy Protein Concentrate. At a given compact porosity, the tensile strength of MCC based powders was found to be higher compared to Soy powders. The maximum viscoelastic contact area between two particles was estimated using Lum-Duncan Hewitt model (1999) combining viscoelastic properties, compaction pressure and time as input variables. Measurement of compaction and viscoelastic properties confirmed that while addition of drug and moisture decreased and increased the deformability of MCC particles, Soy Protein concentrate particles were much more deformable compared to Soy Flour. This claim of higher deformability was supported by higher true strains of individual powder beds and normalized contact area between two particles. It was also concluded that MCC particles are much more deformable compared to soy powders. Semi-analytical models were proposed to predict the density of compacts made from each powder, as a function of total viscoelastic contact area in the compact, bulk and maximum compact densities as well as coordination number. It was proposed that the rate of density increase was determined by the total contact area corresponding to the average of density range. The tensile strength was found to exponentially increase with contact area. However, compacts at same porosity were found to exhibit markedly different tensile strengths suggesting the importance of including particle bonding properties to estimate contact area. Thus, it was shown that contact area takes into account the important raw material and compaction variables hence enhancing the mechanistic understanding of viscoelastic powder compaction. Limitations of results were also discussed and specifics of future studies were proposed in order to develop more fundamental models to predict compact density and tensile strength.
Degree
Ph.D.
Advisors
Okos, Purdue University.
Subject Area
Food Science|Pharmacy sciences
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