Lecture 5- Mechanism Of Compaction Of Pharmaceutical Powders

Question 1

Successful tablet formulation

Answer 1

-understanding the mechanism etc is critical for this
-low tablet crushing strength, capping and lamination, high friability, poor coating uniformity= can all be avoided

Question 2

2 steps of compaction

Answer 2

*compression= reduction in bulk volume by eliminating voids and bringing particles into closer contact
-compressibility= ability of a powder to reduce in volume under pressure which occurs as a result of displacement of the gaseous phase

*consolidation= increased mechanical strength due to inter-particulate contact

Question 3

Material properties

Answer 3

*elastic= difficult to compress and tend to cap or laminate

*plastic= undergo deformation but are sensitive to lubrication and machine speed

*fragmenting= low sensitivity to additives, strain-rate insensitive, no effect of particle shape
-brittle materials tend to give high friability values + chip easily

-combo of plastic and brittle behaviour is very attractive and beneficial

Question 4

Assessment of plastic deformation;
Scanning electron microscopy

Answer 4

-size of particles after compression remains the same as before compression - change in particle shape can be observed

Question 5

Assessment of plastic deformation;
Percentage elastic recovery (%ER)

Answer 5

-plastically deforming material exhibits no/small increase in tablet thickness after tablet ejection/storage

%ER= [(Ha-Hb) / Hb] x 100
Ha; tablet thickness (24 hrs after tablet ejection)
Hb; tablet thickness after compression

Question 6

Assessment of plastic deformation;
Energy analysis

Answer 6

-relationship between upper punch force and upper punch displacement during compression
-high amount of gross energy is spent in bond formation; plastic energy

Question 7

Assessment of plastic deformation;
Force- volume relationships

Answer 7

-relationship between volume and applied pressure during compression

-strain rate sensitivity (SRS)- increase in compression speed increases the mean yield pressure

Slide 15- 18

Question 8

Assessment of plastic deformation;
Stress relaxation

Answer 8

-rapid reduction in the maximum applied compression force with time

-impacts on tablet hardness/strength = subject to change following compaction
-tablet strength may change during storage= due to polymorphic transformation

Question 9

Assessment of plastic deformation;
Reduction

Answer 9

-in tablet tensile strength / tablet hardness with increasing compression speed

Question 10

Assessment of elastic deformation;

Answer 10

*scanning electron microscopy + visual examination; capping and lamination

*percentage elastic recovery of the compressed tablets; increase in tablet thickness upon removal of the compression force or after storage

*energy analysis; force displacement profile; high amount of gross energy= spent in bonds disruption; elastic

*high % friability
*low tensile strength/ tablet hardness value

Question 11

Assessment of fragmentation

Answer 11

*scanning electron microscopy= impossible to find any original particle after compression

*increase specific surface area= due to decrease in geometric mean diameter of the particles after compression

*percentage elastic recovery= no change in tablet thickness upon removal of the compression force or after storage

Question 12

Assessment of elastic deformation;

Answer 12

*force; volume relationships; heckel analysis= high mean yield pressure value

*not strain rate sensitive= increase in compression speed- no effect on the mean yield pressure value; compaction properties = time independent

*stress relaxation= little/no decrease in the maximum applied compression force with time

*no reduction in tablet tensile strength with increasing compression speed

Question 13

Questions

Answer 13

Slide 26