Effect of manufacturing conditions and polymer ratio on the permeability and film morphology of ethyl cellulose and hydroxypropyl cellulose free-films produced by using a novel spray method.

Abstract: This thesis considers the effect of manufacturing conditions and polymer ratio on water permeability and morphology of free-films. A novel spray method for producing ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) free-films was developed where several process parameters was controlled. The process was optimised by pre-spraying solvent until the system reached a steady-state temperature. This minimised the variation of outlet air temperature to < 2.5 °C. Coating time was approximately 4 minutes excluding drying. Free-films were produced using 94 wt% solvent (95 %-ethanol) and 6 wt% polymer. The amount of HPC in the films was varied (wt% HPC defined as HPC/(HPC+EC)'100). Films with 30-40-50-57 wt% HPC were studied. Phase diagrams was constructed to study the phase transformation of polymer mixtures. Results show that all polymer mixtures with HPC content above 30 wt% were phase separated prior to film manufacturing. Temperature had an effect on the polymer phase transformation. In the phase diagram, the 2-phase area was larger for temperatures above 40 °C. The investigated manufacturing conditions were outlet air temperature (°C) and spray rate (g/min). Outlet air temperature was controlled by adjusting the inlet air temperature. The films were characterized by measuring water permeability (m2/s). Cross section structure of the films was analyzed with confocal laser scanning microscopy (CLSM). FITC-HPC was added for enhanced contrast between the domains. Higher outlet air temperature gave higher water permeability of the film whereas higher spray rate gave lower water permeability. The outlet air temperature had an impact on evaporation rate. The evaporation rate together with spray rate affected the solidification and hence the structure of the film. Images show that longer solidification time smeared the domains into larger domains. Lower water permeability was caused by less connectivity between the pores. In conclusion, experiments show that water permeability of EC/HPC free-films was highly dependent on the manufacturing conditions.