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
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