Time-dependent deformation of some direct compression excipients

Area of Science:

• Materials Science
• Pharmaceutical Sciences
• Solid-State Chemistry

Background:

• Understanding time-dependent deformation is crucial for pharmaceutical tablet formulation.
• Previous studies suggested certain materials behave as Maxwell bodies, necessitating further investigation.

Purpose of the Study:

• To compare the time-dependent deformation of microfine cellulose, anhydrous lactose, dicalcium phosphate dihydrate, modified starch, and sodium chloride.
• To investigate the influence of compression time and strain rate on material consolidation and deformation.

Main Methods:

• Stress-relaxation experiments using a reciprocating tablet machine.
• Heckel plot analysis with varying compression contact times (0.17 s and 10 s).
• Diametral compression tests on preformed compacts at different strain rates (0.05–6.5 mm/min).

Main Results:

• None of the tested materials behaved as Maxwell bodies, contrary to prior research.
• Increased compression time enhanced consolidation for starch, cellulose, lactose, and sodium chloride, but not dicalcium phosphate.
• Modified starch compacts displayed time-dependent deformation, while sodium chloride compacts showed brittle behavior attributed to work-hardening.

Conclusions:

• Material deformation is complex and deviates from simple models like the Maxwell body.
• Compression time significantly impacts the consolidation of most pharmaceutical excipients studied.
• Work-hardening in sodium chloride influences its brittle fracture behavior post-compaction.