PHYSICAL AND CHEMICAL PROPERTIES


CARBOPOL

Carbopol 974P is a synthetic high molecular weight cross-linked polymer of acrylic acid. It is a safe and nontoxic. It is an excellent thickening, emulsifying, suspending and gelling agent. Because of its control release and gel formation properties, Carbopol 974P was chosen as the encapsulation polymer.

Appearance : Fluffy, white, mildly acidic polymer
Bulk Density : Approximately 208 kg/m3 (13 lbs.ft3)
Specific gravity : 1.41
Moisture content : 2.0% maximum
Equilibrium moisture content : 8-10% (at 50% relative humidity)
PKa : 6.0 ± 0.5
pH of 1.0% water dispersion : 2.5 - 3.0
pH of 0.5% water dispersion : 2.7 - 3.5
Equivalent weight : 76 ± 4
Ash content : 0.009 ppm (average)
Glass transition temperature : 100-105C (212-221F)


SODIUM ALGINATE

Alginates are a family of polysaccharides composed of α-L-glucoronic acid (G) and β-D-mannuronic acid (M) residues, arranged in homopolymeric blocks of each type (MM, GG) and in heteropolymeric blocks of each composition. Alginates form strong gels with divalent cations like Ca2+, giving both strength and flexibility. Such a cross-linking process stiffens and roughens the polymer and reduces the swelling in solvents. The soluble sodium alginate was cross-linked with calcium chloride, resulting in the formation of the insoluble calcium alginate. This strong thermo stable gel has properties that largely depend on the characteristics of the polymer and the preparation method.

Sodium alginate is the sodium salt of alginic acid.
Appearance : generally occurs in wh ite to yellowish brown powdered or granular form.
Solubility : dissolve easily in water to form a viscous solution. It is insoluble in ether and ethanol. Odor : It has no particular flavor.
Molecular Formula: C5H7O4COONa
storage temp. : Store at Room Temperature
Stability: Stable. Incompatible with strong acids, strong bases, strong oxidizing agents.

Formula of Microencapsulation of Rifampicin Using Combination of Sodium Alginate and Carbopol as Coat Materials
  • Carbopol
  • Sodium Alginate
  • Tween 80 1% w/v 10 ml
  • Purified Water 5 ml
  • Rifampicin 300 mg
  • Methanol 1 ml
  • Castor oil 250 ml
  • Calcium Chloride 20% w/v 40 ml
  • Petroleum Ether 60 ml
Procedure
The ionic gelation process, which has been used to prepare large sized alginate beads, was used to prepare the microcapsules.
  1. Carbopol 974P and sodium alginate in different ratios were soaked in 1% w/v Tween-80 (10 ml) and in purified water (5 ml) respectively, for overnight to form a homogenous polymer solution.
  2. The two polymers were uniformly mixed with the help of a stirrer.
  3. The core material rifampicin (0.3 g) was dissolved in methanol (1 ml) and added to the polymer solution and mixed thoroughly to form a smooth viscous dispersion.
  4. The resulting dispersion was then added in a thin stream with syringe to about 250 ml of castor oil contained in a 500 ml beaker, while stirring at 250±20 rpm.
  5. A Remi medium duty overhead stirrer with speed meter (Model RQT 124) was used for stirring.
  6. The stirring was continuous for 5 min to emulsify the added dispersion as fine droplets.
  7. Calcium chloride (20% w/v) solution (40 ml) was then added slowly while stirring for ionic gelation (or curing) reaction to occur.
  8. Stirring was continued for 20 min to complete the curing reaction and to produce spherical microcapsules.
  9. The microcapsules so obtained were filtered and washed thrice with petroleum ether (60 ml).
  10. Later they were dried in air for 3 h followed by hot air oven at 50° for 4 h and stored in a dessicator.

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