Effects of composition, moisture and stearic acid on the plasto-elasticity and tableting of paracetamol-microcrystalline cellulose mixtures.

Measurements were made under various conditions of the stress relaxation (SR) and elastic recovery (ER) of mixtures of paracetamol and microcrystalline cellulose (Avicel) and of the tensile strengths (T) of their tablets. T was inversely proportional to ER/SR. Tablets laminated or capped when they contained less than 25% w/w of cellulose and the value of ER/SR measured at 20 kN over a compression/decompression/ejection cycle of 2 min, was greater than 9. Addition of between 2 and 4% w/w of water increased the tensile strengths of tablets, provided they contained less than 75% w/w of cellulose, but more water caused decreases in T. Additions of up to 10% w/w stearic acid also caused decreases in T. Explanations are provided for the results.