Applications of cellulose acetate phthalate aqueous dispersion (Aquacoat CPD) for enteric coatin
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The research described in this dissertation systematically investigated the fundamental mechanical properties of cellulose acetate phthalate (CAP) aqueous based films and the influence of coating and curing conditions on the release of beads coated with this polymer. The investigation aimed to obtain a solution for the poor enteric performance of CAP aqueous-based films on coated beads. The influence of plasticization and curing conditions on the mechanical properties of CAP films was investigated by tensile testing. Among the three plasticizers investigated, triethyl citrate yielded softer films with lower values of tensile strength and elastic modulus compared to diethyl phthalate and triacetin. Triethyl citrate plasticized films were also less sensitive to changes in curing conditions compared to the films plasticized with the other two plasticizers. For vii all films, increasing the curing temperature decreased the percent elongation, and produced more brittle films. Therefore, a high curing temperature may not be the ideal curing temperature for CAP coated products. Theophylline beads were used as a model to investigate the influence of fluidized-bed processing and curing conditions on the in situ performance of CAP coated films. The processing temperature was identified as a critical factor influencing the film quality. Better film formation was obtained at a lower coating temperature. Curing using the conventional heat-only condition had minor influence on film coalescence; in contrast, curing using a heat-humidity condition irreversibly converted poor film formation into better coalescence, and produced beads with enteric release profiles. Free films of CAP produced by the spray method following heat-humidity curing demonstrated improved mechanical toughness, and decreased surface roughness and film permeability as compared to the films cured at the heat-only condition. Further investigation revealed that the heat-humidity curing was ineffective without the presence of plasticizers. Despite the difference in solubility, diethyl phthalate and triethyl citrate were both effective plasticizers for the heat-humidity curing process to improve film coalescence. The improved film quality by heat-humidity curing, in turn, required less plasticizer to be used for enteric coating. The release profiles of heat-humidity cured beads remained stable during long-term storage at a low-humidity environment.