Formulation Effects on the Thermomechanical Properties and Permeability of Free Films and Coating Films: Characterization of Cellulose Acetate Films - Pharmaceutical Technology

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Formulation Effects on the Thermomechanical Properties and Permeability of Free Films and Coating Films: Characterization of Cellulose Acetate Films
The authors investigate the effects of a polyethylene glycol plasticizer and water on cellulose acetate film properties.


Pharmaceutical Technology
Volume 33, Issue 3, pp. 88-100

Materials and methods

Materials. CA-398-10NF-EP with acetyl content at 39.4% and CA-398-10TG (technical grade) with acetyl content at 40.3% (Eastman Chemical Company, Kingsport, TN) were used in the study. The plasticizer (Pz) investigated was polyethylene glycol 3350 (PEG 3350, Sigma Aldrich, St Louis, MO). High-purity acetone (B&J Brand, Burdick & Jackson, Muskegon, MI) and deionized water (NANOpure water system, Barnstead, Van Nuys, CA) were used as the solvent system. When applying CA onto tablets, the coating formulations were the same as those casting films. The tablets to be coated consisted of 98.5% of POLYOX water-soluble resins with a molecular weight of 5,000,000 (Dow Chemical, Midland, MI), 0.5% of colorant (Sensient Technologies Corp., St. Louis, MO), and 1.0% of magnesium stearate (Mallinckrodt Baker Inc., Phillipsburg, NJ). All of these materials were used as received.


Table I: List of CA- free films studied.
Preparation of CA-free films. The CA-free films were prepared using a solvent evaporation method. PEG 3350 was dissolved in water for 1.5 h, then most of needed acetone was added to the PEG/water solution. CA was gradually added to the solvent system under stirring. After all CA was added, stirring continued for another 2 h to allow CA to dissolve completely. The remaining needed acetone was added to the above mixture, followed by stirring for 30 min. After the CA solution was degassed for about 3 h, the solution was ready to be used to cast films. The film-cast method and procedures can be found in reference (12). The film formulations were developed based on an experiment design; the design space was that water varied from 0.0–10.0% and the ratio of Pz to polymer varied from 0.00 to 0.29. There were three repeated points (center point) for CA-398-10NF-EP and one center point for CA-398-10TG. The design was constrained with water, which must be in the formulation whenever Pz is present. Table I lists all of the free films prepared.

Characterization of CA-free films. The prepared films were characterized, and film properties such as film morphology, glass transition temperature, oxidative and thermal stability, mechanical strength and elongation, contact angle, and water vapor transmission rate were determined according to the methods described in a previous article (12).

Preparation of model tablets. POLYOX with (molecular weight of 5,000,000), blue dye, and magnesium stearate were blended in a V-blender (The Patterson Kelly Co. Inc, East Stroudsburg, PA) for 3 min with the intensifying bar on for 15 s. The above mixture was then compressed into 250.0-mg tablets on a rotary tablet press (D3B 16 station, Manesty, England) under 200-lb compression force.


Table II: Coating formulations.
CA coated on the model tablets. The CA coating formulations at 6.0% solid level were prepared following the same procedures used to prepare CA-free film except there was no degas step. Table II lists the coating formulations having four repeat points (center point) for CA-398-10NF-EP and one center point for CA-398-10TG based on the same experimental design as the free films.


Table III: Coating processing conditions.
All of the coating runs, with a target coating weight at 10.0 wt% relative to the tablet weight, were performed in a pan coater (COMPU-LAB, Thomas Engineering, Inc., Hoffman Estates, IL) with one spray gun under the processing conditions indicated in Table III. For each run, 800.0 g of tablets were coated, and all coating runs were repeated at least twice.

Testing of CA-coated tablets. Eight tablets from each coating run were randomly selected and tested in deionized water at 37 C to determine water uptake using a standard disintegration tester. At selected time intervals, the tested tablets were taken out, gently dried with a tissue, and weighed. The water uptake was calculated using the following equation:

Water uptake at time t =
(tablet weight at time t) – (tablet weight at time 0)


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