Compaction of food powders: The influence of material properties and process parameters on product structure, strength, and dissolution

- Amorphous powders compacted at varying molecular size, aw, pressure, times.
- Temperature rise above Tg led to microsintering and strong bridge formation.
- Extent of sintering enhanced by increasing dwell times if T - Tg > 10 K.
- Dissolution regime of tablets determined by erosion vs. disintegration mechanisms.

During pressure agglomeration of food powders, it is often difficult to control the final product properties due to their complex material behaviours. The current study aims to better elucidate how the quality of a compact is impacted by the material characteristics of the raw materials as well as the process conditions applied.An amorphous powder was compacted under various conditions to investigate the influence of material properties, such as water activity and molecular weight, and process parameters (pressure and dwell time) on tablet porosity, tensile strength, and dissolution time.With increasing pressure, the porosity decreased and the strength increased, due to the formation of bridges between particles at their contact points. If the glass transition temperature (Tg) was low (due to moisture-induced plasticisation or more extensive enzyme hydrolysis) and the compaction pressure high, then the temperature of the powder surpassed its Tg; resulting in local occurrences of temporary glass transition within the powder bed, allowing for enhanced deformation and microsintering between particles. This led to stronger interparticle bridges and overall tablet crushing strength - this strength increase was particularly strong for longer dwell times, as the extent of microsintering was augmented.Tablets dissolved more quickly at higher water temperatures, but more slowly for higher compaction pressures - this may be explained by a change of dissolution regimes (erosion vs. disintegration). A higher molecular weight resulted in slower dissolution due to slower liquid penetration due to wetting, viscosity-building, and pore collapsing effects.The current work could be used to optimise the processing parameters, leading to improved product properties, particularly mechanical strength and reconstitution performance.

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