Capping tendencies

Jetzer, W., and Leuenberger, H. (1984), Determination of capping tendency in pharmaceutical active ingredients and excipients, Pharm. Acta Helv., 59(1), 2-7. 

Mann, S.C. Roberts, R.J. Rowe, R.C. Hunter, B.M. Rees, J.E. The effect of high speed compression at sub-atmospheric pressures on the capping tendency of pharmaceutical tablets. J. Pharm. Pharmacol. 1983, 55, 44P. 

Punch displacement measurements are easily done on a single station press by attaching LVDT to the punch. On a rotary press, such measurements can be done by means of slip ring, telemetry, or instrumented punch. Punch displacement profiles may be used in conjunction with compression force to estimate work of compression and work of expansion (measure of elasticity). Because capping tendency increases with the punch penetration depth, it may be desirable to monitor actual punch movement into the die. The shape of a force-displacement curve is an indication of the relative elasticity or plasticity of the material whereas plastic deformation is desirable for stronger tablets, excess plasticity usually results in tablets that tend to cap and laminate. ... 

The degree of stress relaxation can be used to predict the capping tendency of a formulation. It occurs when the upper punch begins to move upwards in the die after reaching Upon removal of upper punch the tablet when outside the die will expand in the axial and radial directions to relieve stress resulting from ela.stic recovery after compaction which could eventually lead to problems like capping and lamination (163). 

As noted earlier, there is a tendency for PVC to undergo elimination of hydrogen chloride when heated. The most labile chlorine atoms are those at tertiary or terminal sites. Once the initial chloride is eliminated, continued unzipping occurs with the formation of unsaturated backbone sites and the evolution of hydrogen chloride. The purpose of the stabilizer is to cap unzipping sites by substitution of more stable groups for the evolved chloride as depicted in the following equation ... 

The G5 and G6 dendrons did not assemble into monolayers because of the tendency of the focal point to be encapsulated by the hydrophobic dendritic branches at higher generations. Similarly, Liskamp s group reported a series of amino acid based dendrons capped with Boc end groups and a focal fatty acid chain also formed stable monolayers however, the fatty acid group was not a significant improvement over a shorter linkage (Mulders et al. 1998). In the condensed mono-layer phase, the dendrons covered a smaller area than predicted for a fully spread... 

The apparatus shown in Fig. 3.5 was used, and was filled completely with cement paste. Admixture additions were made by injecting with a hypodermic needle through the rubber cap. Pastes prepared in this way had air contents of less than 0.6% by volume, were free from any premature stiffening tendencies and were homogeneous. 

On experimental grounds Le Roux [52] reports that the tendency of methylamine nitrate to detonation is not high. At a density of 0.9 g/cm3 it is completely decomposed by a 2-g detonating cap along a short space only. A much stronger detonator, con-... 

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