Investigating elastic relaxation effects on the optical properties of functionalised calcium carbonate compacts using optics-based Heckel analysis

Abstract

Heckel analysis is a widely used method for the characterisation of the compression behaviour of pharmaceutical samples during the preparation of solid dosage formulations. The present study introduces an optical version of the Heckel equation that is based on a combination of the conventional Heckel equation together with the linear relationship defined between the effective terahertz (THz) refractive index and the porosity of pharmaceutical tablets. The proposed optical Heckel equation allows us to, firstly, calculate the zero-porosity refractive index, and, secondly, predict the in-die development of the effective refractive index as a function of the compressive pressure during tablet compression. This was demonstrated for five batches of highly porous functionalised calcium carbonate (FCC) excipient compacts. The close match observed between the estimated in-die effective refractive index and the measured/out-of-die effective THz refractive index supports the validity of the proposed form of the equation. By comparing the measured and estimated in-die tablet properties, a clear change in the porosity and hence, the effective refractive index, due to post-compression elastic relaxation of the FCC compacts, has been observed. We have, therefore, proposed a THz-based compaction setup that will permit in-line monitoring of processes during tablet compression. We envisage that this new approach in tracking powder properties introduced in this preliminary study will lead to the onset of further extensive and detailed future studies.

Production of functional spherical particles with porous hollow structures in water via oiling-out directional agglomeration

“…46 where K is the Heckel slope depicting the development of a log-linear response of the structure to the application of pressure, and A is an intercept constant describing densification by particle movement and rearrangement. 47 The inverse of K is the mean yield pressure and it represents the limit of plastic deformation of materials or the resistance of a material to deformation. 48…”

Simultaneous investigation of the liquid transport and swelling performance during tablet disintegration

“…20 waveforms were co-averaged for each single measurement of the sample and the reference to improve the signal-to-noise ratio. The duration of each measurement was 40 s. The transmission system was purged with dry nitrogen gas throughout the measurements to minimise the impact of the water vapour on the transmission measurements (Bawuah et al, 2018). Any sample such as the porous medium of the tablet causes a delay of the terahertz pulse in the time-domain, ∆t, (see Figure 1).…”