Preparation of gelatin solutions- A typical composition employed was as follows-
Gelatin 10.0 g
Metallic salt * 2.0 g
Glycerin 5.0 g
Methyl paraben (sodium salt) 0.18
Propyl paraben (sodium salt) 0.02
Demineralized water q.s. 100.0g (freshly boiled and cooled)
The study included the use of R.O (red oxide) at 1 %, 3% and 4 % w/w concentrations.
The required soluble and insoluble metallic salts including copper sulphate, potassium iodide, manganese oxide, zinc sulphate and dicalcium phosphate were added before adjusting the weight. Additional mixtures containing above components with mineral salts added to (a) R.O 1 % (w/w) and/or ferrous fumarate
1 % (w/w) were also prepared.
(i) Casting of films-
Free films 90.2 mm thick) of different compositions formulated as mentioned above were cat on a flat glass plate and were peeled. The films were conditioned in a desiccators at 30 + 1degC and 40 +1 degC at 72.8 % and 90.0 % RH. Moisture content of the films was determined by aquametry.
(ii) Dispersive infra- red spectra in Attenuated total reflectance (ATR) mode-
ATR-IR spectra of the films were recorded between 2000 and 615 cm-1 in IR spectrometer (Jasco model 810) previously validated using polystyrene standard) equipped with an integrating sphere using a krypton internal reflecting crystal.
Film strips (3x1 sqcm ) to fit the crystal dimensions were place on both sides of the crystal. An angle of incidence of 45 degree with minimal plate pressure were used to obtain the spectra at a scan of 1 cm/sec –1.
(iii) Thermal analysis – DSC studies-
Shimadzu DT- 40 Thermal analyzing system equipped with Chromatopac CR 6A integrator was employed using DSC module. Sample (5.0 mg) was taken in an aluminum cup (against an empty aluminum cup as reference) and was heated at a rate of 5 degK/min in an atmosphere of nitrogen (flow rate 30.0 ml/min) using temperature program of 35- 300 degC.
(iv) Rupture time dissolution tie of shell-
These were determined by suspending the conditioned fresh and aged films in 600 ml of modified dissolution medium comprising of 0.5 % alcalase and 1 % calcium chloride in demineralized water in 1.0 L beaker under stirring (100rpm).
Liquid phase interactions-
(i) pH changes-
pH of 6.67 % w/w gelatin gel containing 2 % w/v metallic salts under study was determined using a pH meter ( Elico model 101 ). The pH was recorded both for fresh samples as well as for those stored at 37 + 1 degC for 7 days.
Viscosity of selected solutions was determined at 30 + 2 degC in an Oswald viscometer (BSS-C) employing 6 % w/w aqueous solution containing 2 .0 % w/v of the salts under study. These determinations were made on the freshly prepared solutions as well as on those stored at 30 + 2 degC for a period varying between 3.0- 6.0 months.
To be continued in Part 5 of 5