Figure 4: Histograms of leaks in Pureflex™ Plus film detected after repeated flexing of
PureFlex™ films in accordance with ASTM F392.
Figure 3: Histograms of leaks detected in Pureflex™ film after repeated flexing of PureFlex™
films in accordance with ASTM F392.
Figure 2: Film resistance to defect formation from repeated abrasion.
were assessed and compared to the performance of the current PureFlex™ film.
Abrasion resistance was measured using a Taber Abrader.
The machine used a metal stylus to contact the film surface
under load and scrape across the sample in a repetitive motion until breakthrough was achieved. Once the stylus broke
through the film, it contacted a metal mandrel and completed an electrical circuit. By closing this loop the equipment stops its cycles, allowing a quantitative measurement
to be made. PureFlex™ Plus film demonstrated a significant
increase in abrasion resistance with a 3x increase in cycles
to failure over PureFlex™ film (Figure 2).
Repetitive folding and handling of a pharmaceutical film can
cause stress cracking and leak formation. To mimic this handling, a Gelbo flex tester was used in accordance with ASTM
F392. The apparatus used a mechanical arm that twists and
compressed a sheet of film for a prolonged number of cycles,
representing a severe challenge to film flexibility and strength.
Film samples were conditioned at 900 cycles before using a
dyed alcohol to detect pin holes. Figures 3 and 4 illustrate each
sample tested with the resulting number of defects detected
through a histogram plot. Pureflex™ Plus film demonstrates a
reproducibly higher resistance to pinhole leak formation.
Physical property testing in accordance with standard
test methods also showed an improvement in puncture
resistance and tensile strength. The new container film
recorded a 13% increase in puncture resistance (tested according to ASTM F1306) and a significant increase of tensile
strength (as measured by ASTM D882). The tensile strength
of Pureflex™ Plus film at yield was recorded at 27 lbf compared to Pureflex™ film at 23 lbf when tested in parallel.
Overall results indicate that this is new film represents a
significant improvement in robustness, leading to reduced
rates of leak formation.
A statistical design of experiments (DOE) study was performed on the blown-film, manufacturing line in order to assess and assure the process robustness and resulting quality
of PureFlex™ Plus film. In order to map the operating space of
the process, the draw down ratio was varied by changing the
speed of the nip rolls within the haul-off unit (See Figure 5).
This critical parameter was adjusted to control the extent
to which the film was stretched from the die, thus affecting
the cross-sectional area of the film. Low, nominal, and high
lots of film gauge thickness were produced with each lot
assessed against the film’s critical quality attributes. Screw
speed, barrel temperatures, die temperatures, air ring flow
rates and temperatures, and cooling temperatures within
the bubble were all adjusted accordingly to maintain the
thickness set point as well as to account for changes in environment. Within the limits of the critical control parameter
tested for the manufacturing process, the PureFlex™ Plus film
was able to meet the targets for its quality attributes.
PHARMACEUTICAL PROCESSING | OCTOBER 2014 15 ■