Issue link: https://www.e-digitaleditions.com/i/626800
Tablets & Capsules January 2016 45 impact Tg, and no thermal degrada- tion of the polymers was observed (Figure 3). Assessing pH-solubility behavior. Figure 4 shows the swelling curves of the initial HPMCAS polymer grades and their extrudate films in different pH solutions. It was seen that the swelling pH and the dissolution pH of the HPMCAS polymer grades before and after extrusion were unchanged. This indicates that the pH-solubility behavior of the LG, MG, and HG grades was unaffected by HME pro- cessing temperature. Determining chemical composi- tion and molecular weight. Quantitative analysis of molecular weight and substituent levels before and after extrusion at different HME Results and discussion: Evaluating the HPMCAS grades and their extrudates Evaluating melt rheology. Melt rheology showed all three grades had complex viscosities η*) of not more than 1,000 centipoise, which is desir- able for HME (Figure 2). The H grade of the polymer exhibited the most desirable melt rheology behavior. The HPMCAS extrudates' melt rheology behavior was similar to that of the HPMCAS polymers before extrusion. Determining glass transition tem- perature. DSC revealed that the HPMCAS grades and their corre- sponding extrudates have similar glass transition temperatures (Tg), indicat- ing that process temperature does not process temperatures was performed. HPMCAS LG grade showed a slight increase in the level of free acid from 0.0% to 0.6% and a corresponding decrease in succinoyl content from 16.1% to 15.8% above the extrusion temperature of 160°C. This indicates that—due to the higher concentration of more labile succinoyl groups—the LG grade is most susceptible to changes at higher temperatures during extrusion. Nonetheless, the change was minimal and the molecular weight determination before and after extru- sion showed no evidence of degrada- tion. In short, the chemical composi- tion and molecular weight of HPMCAS MG and HG appear to be unaffected by the HME processing temperatures and are stable. Figure 3 DSC of HPMCAS and HPMCAS extrudates produced at different temperatures Pure polymers MG extrudates LG extrudates HG extrudates XA1300-146A LG 140 XA1300-146B LG 160 XA1300-146C LG 180 0.00 -0.03 -0.06 -0.09 -0.12 -0.15 0.00 -0.02 -0.04 -0.06 -0.08 -0.10 0.00 -0.03 -0.06 -0.09 -0.12 -0.15 0.00 -0.03 -0.06 -0.09 -0.12 -0.15 Reversing heat flow (W/g) Reversing heat flow (W/g) Reversing heat flow (W/g) Reversing heat flow (W/g) -50 0 50 100 150 200 -50 0 50 100 150 200 -50 0 50 100 150 200 -50 0 50 100 150 200 Temperature (°C) Temperature (°C) Temperature (°C) Temperature (°C) X35270-79 LG X35270-77 MG X35270-78 HG XA1300-144A HG 120 XA1300-144B HG 140 XA1300-144C HG 160 XA1300-144D HG 180 XA1300-145A MG 140 XA1300-145B MG 160 XA1300-145C MG 180