Tabletting behaviour of aggregates : Mechanistical conception and modulation by variations in aggregate physical properties

Sammanfattning: The volume reduction mechanisms involved during compression of aggregates prepared from microcrystalline cellulose particles and effects of variations in their physical properties on their compression behaviour and compactability were studied in this thesis.The dominating volume reduction mechanisms during compression of aggregates prepared of MCC were deformation (bulk deformation and local deformation) parallel with densification, and generally the degree of fragmentation of the aggregates was minute. Decrease in volume during compression can be described by the degree of compression of the aggregates and, as the aggregates were not prone to fragmentation, the degree of compression was related to the degree of deformation and densification that the aggregates underwent during compression. The volume reduction mechanism controlling the degree of compression in the early compression phase(<4 MPa) is probably deformation of the aggregate surfaces, although the process in this initial phase might be described as a sequence of alternating events of surface deformation, attrition and repositioning. The degree of compression was dependent on the intragranular porosity and the voidage of the aggregates before compression. Neither the size or distribution of the pores within the aggregates nor the size or the resistance of the individual aggregates to fracture seemed to be related to the degree of compression.A high degree of compression gave a compact of a more closed intergranular pore structure and the structure of the intergranular pore system was of significant importance for the tensile strength of the compact. If the number of intergranular contact zones in a cross section of the compact is similar, the compact strength was governed by the bonding force between the intergranular contact zones. This bonding force increases during compression as the degree of compression increases. The compact strength was thus considered to depend on the intragranular porosity and the voidage of the aggregates before compression due to the relationship between the tensile strength and the degree of compression.The findings in this thesis also indicated that the deformation properties in the early compression phase correlate with the evolution of the physical structure of the tablet at high pressures and thus to the bond formation process between aggregates at higher pressures.