Compaction resistance

In 1966, Cadotte developed a method for casting mlcroporous support film from polysulfone, polycarbonate, and polyphenylene oxide plastics ( ). Of these, polysulfone (Union Carbide Corporation, Udel P-3500) proved to have the best combination of compaction resistance and surface microporosity. Use of the mlcroporous sheet as a support for ultrathin cellulose acetate membranes produced fluxes of 10 to 15 gfd, an increase of about five-fold over that of the original mlcroporous asymmetric cellulose acetate support. Since that time, mlcroporous polysulfone has been widely adopted as the material of choice for the support film in composite membranes, while finding use itself in many ultrafiltration processes. 

Tablet dosage forms have to satisfy a unique design compromise. The desired properties of rapid or controlled disintegration and dissolution of the primary constituent particles must be balanced with the manufacturability and esthetics of a solid compact resistant to mechanical attrition.

In other respects, it also shared the favorable characteristics of the NS-100 membrane. That is, it was resistant to pH 3 to 12, and showed far better compaction resistance than cellulose acetate. Also, it possessed the capability to operate at elevated temperatures, though some irreversible flux decline could still occur.34 Rejections of various organics were also good, as shown in Table 5.1 These were in sharp contrast to organic rejection data on cellulose acetate membranes. Initially, PA-300 was also postulated to possess good chlorine resistance.31 Subsequent experience showed it to be equally sensitive to chlorine as NS-100. 

In preparing membranes via the phase inversion process for applications in pressure-driven processes, the formation of macrovoids should be avoided completely. These finger-like pores of the type present in the substructure of membranes (b) and (c) of Fig. 3.6-1, severely Hmit the compaction resistance of the membrane. Membranes with a sponge-Hke structure (Fig. 3.6-la) are to be preferred. 

The polymers must possess the necessary mechanical properties required for the dosage form design, such as elasticity, compactability, resistance to tensile, swelling and shear stresses, and resistance to tear and fatigue. 

The as-formed DAF dlaminopyrene and benzidine polymers have a two-probe compaction resistivity of > 10 Qcm. Exposure of the DAF solid to hydrogen chloride causes its resistivity to decrease to 10 - lO Qcm, PANI... 

Compact resistant Powder decomposes Reacts, SiCl4 and BCI3 liberated... 

A potentially very useful apphcation of UTDR is to design membranes that offer improved resistance to compaction. Kelley et al. (2002) smdied the effect of cross-linking on the compaction resistance of cellulose-acetate membranes. Figure 33.6 shows the compressive strain as a function of time for pure water permeation through a cellulose-acetate membrane at 4.1 MHz that has been exposed for different periods of time at 23°C to a titanium-isopropoxide cross-hnking agent. Sufficient cross-linking time can reduce the compressive strain by 65% and nearly totally eliminate the elastic compaction. 

The studies of Aerts et al. (2001) and Kelley et al. (2002) discussed in Section 33.5 demonstrated that UTDR can be used to determine the effectiveness of fillers and cross-linking to improve the compaction resistance of membranes. This application needs to be explored by membrane manufacturers in order to create a new generation of more robust membranes. 

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