Hydroxypropoxymethylcellulose phthalate (HPMCPH HP 55)
Inactive ingredient (tablet coating substance)
Measuring cells: DSC820 or TGA850
Pan: Aluminum 40 µl or 100 µl, both with pierced lids
Sample preparation: The samples were stored under different relative humidity conditions in exsiccators
DSC measurement: Heating from 30 °C to 150 °C, cooling to 30 °C, 5 minutes iso-thermally at 30 °C, then heating to 300 °C at 20 K/min
TGA measurement: Heating from 30 °C to 300 °C at 20 K/min
Atmosphere: Nitrogen, DSC: 50 cm3/min, TGA: 80 cm3/min
TGA (diagram 22a)
The diagram shows the TGA curves of samples that were stored under different relative humidity conditions. The moisture content of a sample can be determined from the first step of the corresponding TGA curve. The values obtained correlate with the storage conditions.
DSC (diagram 22b)
The diagram shows the first and second heating curves of two different samples. Since the measurements were done in a pans with pierced lids, the moisture was able to evaporate in the first heating run. This process can be observed as a large endothermic peak. This correlates with the amount of water released. Apart from this, the peak partially overlaps the glass transition of the ‘wet sample’. The glass transition (Tg) is therefore determined using the second heating run, in which the moisture has already escaped.
Storage
| TGA Step, % | DSC Tg midpoint, °C |
---|---|---|
7 days over P2O5 | 1.18 | 129.6 |
1 days over P2O5 | 1.39 | - |
Untreated | 2.50 | - |
1 day at 95% r. h. | 8.28 | - |
7 days at 95% r. h. | 9.50 | 130.7 |
Cellulose-based polymers take up moisture easily. The uptake is dependent on the storage conditions. The moisture-free sample is normally used for determining the glass transition temperature (Tg). This is done by evaluating the second heating run. If the glass transition temperature has to be determined with different moisture contents, then sealed pans have to be used.
Glass Transition and Moisture Content, Hydroxypropoxymethylcellulose Phthalate (HPMC-PH) | Thermal Analysis Application No. HB809 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals