Note on the Use of Diametrical Compression to Determine Tablet Tensile Strength.
The diametrical compression (DC) test, as defined in United States Pharmacopeia <1217> and in American Society for Testing and Materials testing standard D 3967, has been used extensively to derive the tensile strength (TS) of pharmaceutical tablets from the measured breaking force. DC-derived TSs provide a good approach to measuring the consistency of tablet mechanical properties from one batch to the next. For these quality control type applications, method precision is required, but accuracy is not. In addition, DC has been used to calibrate parameters of the Druker Prager Cap model, a yield criterion expressing the failure of a powder compact under arbitrary 3D loading conditions. For this application, the DC method must not only provide suitable precision but also provide accuracy. In this work, we explore the accuracy of the DC method by comparing TS results to those of the 3-point bend test method (also defined in United States Pharmacopeia <1217>). We conclude that the true TS of a powder compact is approximately double the DC-derived value. Although historical literature assumes that tablets fracture under tension along the centerline of the tablet, analysis of the stress state suggests that tablets are likely to fracture under shear. The impact of this ∼50% error should be considered when accuracy of the TS result is required.
Small Molecule Design and Development, Eli Lilly and Company, Indianapolis, Indiana 46285.
Jon
J
Hilden
Small Molecule Design and Development, Eli Lilly and Company, Indianapolis, Indiana 46285.
Mark
M
Polizzi
Small Molecule Design and Development, Eli Lilly and Company, Indianapolis, Indiana 46285. Electronic address: zettler_aaron_m@lilly.com.
Aaron
A
Zettler
D002482:Cellulose / Q000737:chemistry*; D019245:Compressive Strength; D004339:Drug Compounding / Q000295:instrumentation; D004867:Equipment Design; D005079:Excipients / Q000737:chemistry; D007785:Lactose / Q000737:chemistry*; D011208:Powders; D013314:Stress, Mechanical; D013607:Tablets / Q000737:chemistry*; D013678:Technology, Pharmaceutical / Q000295:instrumentation; D013718:Tensile Strength
D005079:Excipients; D011208:Powders; D013607:Tablets; D002482:Cellulose; D007785:Lactose; C109691:microcrystalline cellulose
compaction; compression; materials science; mathematical model; mechanical properties; powder technology