Tablets & Capsules

TC0117

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Tablets & Capsules January 2017 17 Differential scanning calorimetry (DSC) is helpful in assessing gelatin performance. DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and a ref- erence are measured as a function of temperature. The prin- ciple underlying this technique is that when the sample undergoes a physical transformation, such as phase transi- tions, more or less heat will need to flow to it than to the reference in order to maintain both at the same tempera- ture. Figure 4 shows a DSC diagram for gelatin. Note three singularities: 1. The Tg at which the sample undergoes a change in heat capacity 2. Crystallization (melt temperature 1 in the figure), the point at which the molecules obtain freedom of motion and spontaneously arrange themselves into a crystalline form. This peak can be used to confirm that crystallization occurs in the sample, and the area under curve gives information about the quantity of this phase. 3. The melting point (melt temperature 2) at which the polymer chains can move freely. We conducted an in-house study using two gelatin sam- ples—Gelatin 6 and Gelatin 15—that had different degrees of brittleness. Capsules made from each were analyzed for their thermal properties using DSC. Figure 5 shows the results. As Table 1 shows, Gelatin 15 has a slightly lower Tg but is less homogenous, and its crystallinity is three times higher than that of Gelatin 6. Therefore, we concluded that the mechanical properties of Gelatin 6 are superior to those of Gelatin 15. The effect of pigments Pigments provide opacity and create a protective barrier to harmful radiation, typically from the sun or other light sources. Titanium dioxide (TiO 2 )—the most common pig- ment in capsules—has a refractive index of 2.27 to 2.71, which differs markedly from that of gelatin (1.24). This dif- ference helps protect the gelatin because when a ray of light passes from a substance of low refractive index to a substance of high refractive index, a structure with a high radiation barrier is formed [8, 9]. Pigments also have a significant impact on mechanical properties: The higher the pigment content, the greater the brittleness. Therefore, it's critical to formulate the capsules using the optimal amount of pigment. The UV-Vis spectra for gelatin capsules shown in Figure 6 indicate that when the TiO 2 concentration is around 3 percent, light transmission is very low. They also show that adding pigment in excess of that amount doesn't protect the capsules or their contents any better. In fact, the perfor- mance of the gelatin capsules decreases in terms of brittle- ness, so avoid using more of this additive than is necessary. Manufacturing conditions It's well known that molecular weight and molecular weight distribution can markedly affect the mechanical properties of a polymer. Therefore, seek a polymer of opti- mal molecular weight: high enough to provide good Table 1 Tg and crystallinity of two gelatins Figure 4 DSC for gelatin 1.0 0.5 0.0 -0.5 -1.0 -1.5 Glass transition temperature Melt temperature 1 Melt temperature 2 0 20 40 60 80 100 120 140 160 180 Temperature (°C) Heat flow (W/g) Source: Unpublished ACG study Figure 5 DSC for two gelatins 1.0 0.5 0.0 -0.5 -1.0 -1.5 Cooling Heating 0 20 40 60 80 100 120 140 160 180 Temperature (°C) Heat flow (W/g) Source: Unpublished ACG study Note: Gelatin 6 results are shown in green and Gelatin 15 results in red. Circled areas denote Tg for heating and cooling cycles. Note: Gelatins are the same ones assessed in Figure 5. Confidence interval was calculated from Student distribution for probability of 95 percent. N=3. Crystallinity is expressed in relative units. Gelatin type Tg, heating cycle (C ° ) Tg, cooling cycle (C ° ) Crystallinity (J/s) 6 62 48 1 (2,303) 15 61 44 3 (7,585)

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