Purpose: Solution-cast films are often used to predict performance in soft-shell capsule applications. This study is to measure and understand the mechanical and permeation behavior of DuPont’s SeaGel® carrageenan based film formulation with comparison to gelatin based films. More specifically, the present study characterizes the influence of relative humidity and temperature on oxygen and water vapor permeability of the films.
Methods: The films in this study were made either from a blend of carrageenan, a secondary film former and plasticizers (i.e. DuPont’s SeaGel® Technology) or a blend of gelatin and plasticizers. Oxygen permeability measurements were performed according to ASTM method D3985. Water vapor transmission rates (WVTR) of selected films were measured using a MOCON Permatran-W 3/33 (Moden Controls, Inc., Minneapolis, MN, USA) and the method as described in ASTM F1249-90. Water sorption characteristics of films were measured using a dynamic vapor sorption (DVS) analyzer by Surface Measurement Systems (Allentown, PA, USA). The sample was loaded into the DVS sample pan and immediately placed into the DVS with a 200-sccm stream of dry (~ 0.5% RH) nitrogen. Next, the sample was analyzed on a DVS-1 automated sorption analyzer at the desired temperature with a sample size between 5 and 20 mg. This sample size is sufficient due to the high sensitivity (< 0.1 μg) and the excellent baseline stability of the Cahn microbalance used in the DVS-1. Film puncture strength and distance were measured on a texture analyzer (Model TA.XT2, Texture Technologies, Scarsdale, NY) equipped with a 25-kg load cell. Film tensile modulus and strength were measured according to American Society of Testing and Materials Standard method D638. Films were punctured into dog-bone type-V tensile bars (gauge width = 0.125”, thickness = 0.0035±0.0010”, length = 0.375”) with cookie cutter, and tested for tensile properties using an Instron universal Machine (model 55R4507; Instron Corp., Canton, MA) with a 50-pound load cell.
Results: The equilibrium moisture content of the SeaGel® Technology and gelatin films generally increased with increasing relative humidity and decreased with increasing temperature. Both type of films exhibited a sorption hysteresis throughout whole relative humidity range. The magnitude of hysteresis decreased with increasing temperature. This hysteresis may have been caused by rearrangement of free volume and redistribution of pore size during the wetting process.
Oxygen permeability experiments were performed using ASTM method D3985 with 0% to 80% relative humidity at various temperatures. Oxygen permeation of SeaGel® Technology films were significantly increased when temperature increases. The water vapor transmission of both SeaGel® Technology and gelatin films increased with increasing relative humidity. The WVTR of gelatin film was slightly lower than previously reported by Martucci and others (1, 2, 3). This can be explained by the higher MW and thicker film those authors used.
Conclusion: A statistical model is developed to predict the permeability of SeaGel and gelatin films as a function of thickness, relative humidity and temperature. The equilibrium moisture content of SeaGel® Technology films increased with increasing relative humidity and decreased with increasing temperature. Oxygen and water vapor transmission of both SeaGel® Technology and gelatin films increased with increasing relative humidity. These results indicate that optimized SeaGel® Technology blends can improve mechanical and permeation properties of SeaGel® Technology free films. These improvements can be beneficial to film applications such as softshell capsules, oral film strips, and film coating.
Benjamin Roscoe– DUPONT NUTRITION & HEALTH
Andrew Horton– The Dow Chemical Company
Jattett Page– The Dow Chemical Company
Robert Gunther– The Dow Chemical Company
Harold Bernthal– The Dow Chemical Company