Effect of lubrication on the distribution of force between spherical agglomerates during compression

Abstract

PostprintThis is the accepted version of a paper published in Powder Technology. This paper has been peerreviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Mahmoodi, F., Alderborn, G., Frenning, G. (2010) Effect of lubrication on the distribution of force between spherical agglomerates during compression.Powder Technology, 198 (1) We employ the carbon paper technique to aid understanding of in die force and spatial distributions, upon compression of approximately 1 mm sized spherical agglomerates (pellets) of microcrystalline cellulose (MCC). The aim in this study was to test for the effect of lubricant film on force and spatial distributions. Pellets of MCC were formed via granulation and extrusion/spheronisation. Investigation of pellet bed compression was performed on a materials tester. Prior to compression studies the pellets were characterised for bulk density, size and deformability. Two pellet types were investigated; MCC and MCC lubricated with magnesium stearate. The carbon paper technique relies upon carbon paper as the medium for transferring imprints from compressed pellets onto photo quality paper. The digitised images of these imprints form the basis of analysis through the use of image processing software. Using the carbon paper technique within the range of 10-30 MPa indicates that lubrication does not have a significant effect on the distribution of forces between spherical agglomerates during uniaxial compression. 2 Spatial analysis of the imprints revealed that the lubricated pellets exhibited a higher packing order than the unlubricated ones at low applied pressures (10 and 20 MPa), a difference that could not be observed at 30 MPa. Hence interparticle friction and/or cohesion appear to influence the initial particle rearrangement, whereas confinement is suggested to dominate at higher pressures.

The degree of compression of spherical granular solids controls the evolution of microstructure and bond probability during compaction

“…This procedure was used to decrease bonding between the pellets in the formed tablets to enable mechanical deaggregation of the tablets without crushing the pellets forming the tablet. According to previous experiences (Mahmoodi et al, 2010), admixing a lubricant to microcrystalline cellulose pellets under these conditions will only marginally affect the compression behaviour of the pellets, in terms of the degree of compression as a function of compression pressure, compared with unlubricated pellets. The tablets prepared from lubricated pellets were gently deaggregated by manually shaking them in a petri dish.…”

Effect of spherical-agglomerate strength on the distribution of force during uniaxial compression

“…The slopes of the initial linear region of the force displacement plots, which represent plastic deformation prior to fracture, were used in the calculation of yield stress through the equation [11,20,21]:…”

“…Once bulk compression is carried out the resulting imprints are analysed through image analysis and the calibration curve is applied to convert the imprint areas into forces. As calibration, bulk compression and carbon paper analysis methodologies have been described in a previous article [11], only a brief description will be given here.…”

“…This arrangement was used for both the calibration and bulk compression procedures. Calibration was carried out on single pellets placed in a rig specifically designed to mimic a physically constraining environment (cylindrical die of diameter ≈ 1 mm with teflon walls) [11], with compression being applied via the Stable Microsystems TA HDi texture analyser equipped with a 50 N load cell. Forces between 2 and 50 N were applied with 10 repetitions for each step.…”

“…To the best of our knowledge, this is the first study in which the carbon paper technique is used in the determination of force distributions of pharmaceutical materials with differing mechanical properties. Non ideal pellets of a single type were also used in previous carbon paper based studies [10,11] conducted by our group.…”