TY - JOUR
T1 - Influence of elastic deformation of particles on Heckel analysis
AU - Sun, C.
AU - Grant, D. J.W.
PY - 2001
Y1 - 2001
N2 - The Heckel equation is one of the most useful equations for describing the compaction properties of pharmaceutical powders. Important material properties (e.g., yield strength) of powders can be derived using Heckel analysis. Two types of Heckel analysis are in common use. One is the "out-of-die," or "zero-pressure" method, the other is the "in-die" or "at-pressure" method. Because particles undergo elastic deformation under pressure, which tends to lower the porosity of the powder bed, the "out-of-die" method describes powder consolidation and compaction more accurately than the "in-die" method. However, "in-die" Heckel analysis has been widely used because of the speed and ease of data collection. Using L-lysine monohydrochloride dihydrate as a model compound, this work analyzes quantitatively the effects of elastic deformation on the calculation of porosity of a tablet, and therefore on the Heckel analysis. The effects of a small change in porosity, ε, on Heckel analysis are presented mathematically. It is found that a decrease in porosity of 0.001, when the porosity is lower than 0.05, causes a significant increase in the value of -ln ε. Therefore, data at ε < 0.05 should be interpreted with caution when using Heckel analysis. Elastic deformation causes positive deviations in the Heckel plot, and therefore leads to a yield strength that is lower than the true value. The lower the elastic modulus of the powder, the greater is the deviation from the true value. Therefore, the "in-die" method gives values of yield strength that are significantly lower than the true values for most pharmaceutical powders.
AB - The Heckel equation is one of the most useful equations for describing the compaction properties of pharmaceutical powders. Important material properties (e.g., yield strength) of powders can be derived using Heckel analysis. Two types of Heckel analysis are in common use. One is the "out-of-die," or "zero-pressure" method, the other is the "in-die" or "at-pressure" method. Because particles undergo elastic deformation under pressure, which tends to lower the porosity of the powder bed, the "out-of-die" method describes powder consolidation and compaction more accurately than the "in-die" method. However, "in-die" Heckel analysis has been widely used because of the speed and ease of data collection. Using L-lysine monohydrochloride dihydrate as a model compound, this work analyzes quantitatively the effects of elastic deformation on the calculation of porosity of a tablet, and therefore on the Heckel analysis. The effects of a small change in porosity, ε, on Heckel analysis are presented mathematically. It is found that a decrease in porosity of 0.001, when the porosity is lower than 0.05, causes a significant increase in the value of -ln ε. Therefore, data at ε < 0.05 should be interpreted with caution when using Heckel analysis. Elastic deformation causes positive deviations in the Heckel plot, and therefore leads to a yield strength that is lower than the true value. The lower the elastic modulus of the powder, the greater is the deviation from the true value. Therefore, the "in-die" method gives values of yield strength that are significantly lower than the true values for most pharmaceutical powders.
KW - Elastic deformation
KW - Elastic modulus
KW - Heckel analysis
KW - L-Lysine monohydrochloride dihydrate
KW - Yield strength
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U2 - 10.1081/PDT-100000738
DO - 10.1081/PDT-100000738
M3 - Article
C2 - 11416993
AN - SCOPUS:0035013530
SN - 1083-7450
VL - 6
SP - 193
EP - 200
JO - Pharmaceutical Development and Technology
JF - Pharmaceutical Development and Technology
IS - 2
ER -