Compressing polyethylene glycols: The effect of compression pressure and speed

Abstract

The effect of compression speed and pressure on the compaction properties of PEG 1500 (1638), 4000 (4129), 6000 (6343), 10 000 (12 774), 20 000 (23494) and 35 000 (34650) were investigated. Heckel analysis, pressure at zero porosity, crushing strength, tablet porosity, gross and net energy and net energy/crushing strength ratio have been investigated using a compaction simulator. Resistance to densification increases with molecular weight and compression speed and was confirmed by the increase in the mean yield pressure and the pressure at which they reach zero porosity and the increase in gross energy. PEGS have a melting range of approximately 48–67°C and increasing compression speed makes asperity melting more likely. Resolidification of melted material increases bonding which limits the disruptive effect of any elasticity. At any compression speed, low molecular weight PEGs undergo greater densification and form compacts of low porosity. Consistent with the time dependency of plastic materials, at any molecular weight the tablets made at 10 mm/s were harder than those made at 300 mm/s. PEG 12 774 gave the hardest tablets at all compression speeds. However, compressibility was less than lower molecular weight PEGs. The crushing strengths suggested that plastic deformation is not directly responsible for the harder tablets. PEG 34 650 is less plastic, but more resistant to densification and formed tablets with the highest porosity and produced the weakest tablets. A good correlation was found between the plastic energy/crushing strength ratio and compression speed and an equation is proposed to describe the relationship. The compactibility of the material may be estimated from the slope. The lowest slope was found for PEG 12 774 and the highest for PEG 34 650.