PHARMACEUTICAL PROCESSING | MARCH 2015 33 n
n PHARMPRO. COM
sile strengths were measured using a TA.XT Plus Texture
Analyzer equipped with miniature tensile grips.
Physical Banding Properties
Banding Solution 1 containing 53% ethanol was applied
at room temperature to band HPMC capsules. The resultant
band was thin as compared with those produced with solutions 2 and 3 and mainly had smooth band edges (Table
1, approximately 5% of the banded capsules had irregular
edges). Almost no capsule deformation was observed (Fig
1a). As expected, band drying was faster with solution 1 as
compared with the other three banding solutions because
due to the presence of ethanol used.
Vacuum tests revealed that about 2% of the capsules
banded with solution #1 leaked at the capsule/body junction and compression tests indicated that no band/capsule
or cap/body separation was evident. Small air bubbles
were found at the cap/body junction of capsules that may
have resulted from air pressure release inside the capsule.
Banding Solution 2 a commonly used banding solution to
band gelatin capsules was assessed to its ability to band
HPMC capsules. Capsules were banded with solution 2 at
55oC (gelatin is liquid at this temperature). Approximately
8% of capsules banded with solution 2 showed an irregular
band edge. No air bubbles were observed. 21% of the capsules leaked. Compression tests revealed that the resultant
bands could be easily separated from capsule bodies using
low compression force. The poor banding properties resulted from a material incompatibility between gelatin and
HPMC. No observable fusion was observed between gelatin
band and the HPMC capsule shell.
Banding Solution 3 At beginning, two HPMC/water solutions (15% and 22%) were tested to assess the requirement
for ethanol in banding solutions used to band HPMC capsules. A 15% HPMC/water banding solution was evaluated
first. During drying at room temperature with the 15%
HPMC/water solution, banding solution appeared to accumulate at the bottom of some capsules (which were placed
horizontally in capsule carrier bars). This likely was caused
by gravity. Before drying, banding solution flows down and
accumulates at the bottom of the capsules and forms lump
after drying. Also, after drying, large air bubbles were observed in the banding areas of some capsules.
To overcome these banding problems, a 22% HPMC/
water solution was evaluated. The extremely high viscos-
ity (~800 cps) of this solution required that the solution be
heated to 50oC to lower the solution viscosity to ~300 cps
and then applied to HPMC capsules. Upon application of
the heated solution to HPMC capsules at room tempera-
ture, banding solution viscosity rapidly increases. While
this eliminated banding solution accumulation at the bot-
tom of the capsules, increasing viscosity during drying did
not prevent air bubble formation. Large air bubbles were
found on most capsule bands (Fig.1C). This caused 8% of
capsules to leak under vacuum. Moreover, some capsules
exhibited an irregular band edge and moderate shrinkage.
However, due to the good compatibility between solution 3
and HPMC capsules, no band/capsule separation was found
during capsule body compression tests. Finally, without the
addition of ethanol, the drying time was one minute longer
than that observed with solution 1.
Banding Solution 4 Gelling agent and gelling aids; including ~1% carrageenan, locust bean gum, and potassium
chloride were added to banding solution 4 to ensure that
rapidly after application it would form a solid gel at the
Upon application of banding solution 4 to HPMC capsules, gelling quickly formed and prevented large air
bubble formation at capsule cap/body junctions (Fig. 1D).
Only 4% of the capsules had air bubbles with only 3%
leaking primarily via unbanded areas at capsule cap/body
junctions. A few capsules banded with solution 4 exhibited
irregular edges and mild band area shrinkage whereas
compression tests revealed that there was no band/capsule
separation of HPMC capsules.
Microscopic examination of longitudinal cross sections
of HPMC capsules banded with each of the 4 banding solutions showed that band 1 (Fig 2A), 3 (Fig 2C) and 4 (Fig
2D) tightly fused with the capsule at cap/body junctions.
No gaps, air bubbles or separation was observed in bands
formed with solutions 1, 3 and 4. However, no capsule fusion was observed with banding solution 2 (Fig. 2B). These
observations were consistent with results from leak tests
and capsule body compression tests.
Tensile strength tests were used to assess how gelling agents and different solvent concentrations effected
band material mechanical properties. Results from tensile
strength tests revealed that HPMC–based banding solutions
1, 3 and 4 shared similar tensile strengths. In contrast, the
tensile strength of gelatin-based banding solution 2 was
determined to be approximately twice that of HPMC-based
banding materials. It is important to note that the addition
of gelling agents to solution 4 had no effect on its tensile
The high percentage of ethanol commonly used in HPMC
banding solutions is required to reduce drying times, minimize band shrinkage and air bubble formation and reduce
capsule leaks. However, the high percentage of ethanol required in these solutions can result in release in flammable
alcohol vapors. To alleviate these issues, 3 water-based
replacement banding agents were compared with an ethanol–containing HPMC banding agent routinely used to band
HPMC hard capsules.
As expected, HPMC capsules banded with ethanol-containing HPMC banding solution 1 yielded capsules with