Brittleness in Gelatin Capsules: Effects of Pigments and Manufacturing Conditions

Pigments are used heavily during capsule manufacture. Colored capsules assist within the identification of dosage forms for patients. A uniquely colored capsule provides a robust anti-counterfeiting measure for a drug. Additionally, from a branding perspective, color creates a superb brand differentiation opportunity for drug manufacturers.

To manufacture colored capsules, pigments are usually preferred to water-soluble dyes. Pigments are water-insoluble colorants that selectively absorb a specific wavelength of sunshine and reflect others. This difference within the proportion of wavelength is perceived as color. By dispersing the sunshine , pigments produce opacity and make a barrier to guard gelatin against harmful radiation. The foremost common pigment utilized in capsules is titanium oxide. It’s a index of refraction (RI) of two .27–2.71, which is markedly different from that of gelatin (RI = 1.24). This difference in RI helps to make a high barrier to radiation, protecting the gelatin as light passes from gelatin (low RI) to titanium oxide (high RI).

From the attitude of capsule brittleness, pigments play a crucial role in mechanical properties; because the proportion of pigments is increased, brittleness is additionally increased. Hence, the pigment content may be a critical a part of capsule design. An insufficient amount of pigment may fail to guard the gelatin from UV radiation, whereas an excessive amount may end in brittle capsules.
The following figure shows the impact of the number of titanium oxide on the UV/VIS spectrum of gelatin capsules.

Titanium dioxide at a degree of roughly 3% shows very low light transmission. Increasing the pigment concentration further doesn't end in increased drug protection but increases the brittleness of the gelatin capsules. Hence, it's advisable to not use a high amount of titanium oxide to paint gelatin capsules.

Capsule manufacturers must closely consider the preparation conditions of the capsule shells, including the temperature and ratio of the capsule preparation area; we've already learned that gelatin shows many characteristics typical of an artificial polymer. Therefore, its mechanical properties are strongly influenced by the relative molecular mass and relative molecular mass distribution, almost like the other polymer. Accordingly, manufacturers must select an optimum relative molecular mass which will provide sufficient mechanical properties and even be easy to process.

Gelatin, when subjected to excessive heat for a protracted period, can cause polymer chain fragmentation, which, in turn, reduces the relative molecular mass. This will cause brittle capsules with a markedly lower capsule performance. Therefore, during manufacturing, when gelatin is required to be heated, it's recommended to stay the heating period as short as possible. Usually, gelatin is dissolved at 70°C to 80°C in demineralized water, in jacketed chrome steel tanks, which takes approximately 1 hour.
References
https://pharma-trends.com/2019/10/16/part-3-brittleness-in-gelatin-capsules-effects-of-pigments-and-manufacturing-conditions/