Permeability of ethylcellulose microcapsules towards phenobarbital

Release characteristics of an azo dye from poly(ureaurethane) microcapsules

The time course for the transfer of azo dyes from the microcapsule core of dioctylphthalate to the dispersing medium of methanol through a poly(ureaurethane) (PUU) membrane was measured for various average size microcapsules with a size distribution. The dye release curves are represented by a stretched exponential function C(t)=C(eq)[1-exp [-(t/tau(eff))(alpha)]], where C(t) is the concentration of the dye in methanol, C(eq) that at the equilibrium state, and t the time. The exponent alpha decreased by increasing the variance of the size distribution of microcapsules. The effective time constant tau(eff) was expressed by tau(eff)=c(0)<R(2)>/kappa(alpha), where <R(2)> and kappa(alpha) are the mean square of microcapsule radius and a correction for the size distribution, respectively. The characteristic proportional constant, c(0), was determined as 2.6+/-0.2 min/microm(2). From the value of the constant, the diffusion coefficient of the azo dye in the PUU membrane was evaluated as 2.6 x 10(-12) cm(2)/s.

Permeability to solutes of polyamide capsules with different chemical compositions

The permeability of nylon capsule membranes with different chemical compositions to solutes was studied at different temperatures. The rate of solute permeation through the membrane decreased with increasing hydrophobicity of the membrane in the temperature range of 293-323 K. Increase in the size of permeant molecules caused a decreased in their rate of permeation through all capsule membranes at all temperatures studied. Higher permeation rates were observed for all permeants at higher temperatures. The activation energy of permeation was evaluated for the permeants from the Arrhenius plots of their permeation data. From the values of activation energy evaluated the solute permeation through the nylon capsule membranes was demonstrated to proceed by a pore mechanism.

An approach to prepare microparticles of uniform size

A novel emulsification method which employs a glass membrane of controlled pore size was adopted to prepare various types of microparticles. The microparticles thus obtained were uniform in size and the procedure proved applicable to a wide variety of microencapsulation processes. Furthermore, the particle size could be controlled by selecting preparative conditions.