The Effect of Titanium Dioxide on the Oxygen Permeability of Hydroxypropylmethyl Cellulose (HPMC) Films

Abstract

19741 P o r t e r 1980). The p a r t i c l e s being impermeable t o moisture, a r e considered t o i n c r e a s e t h e e f f e c t i v e d i f f u s i o n pathway s o decreasing permeability; above a c r i t i c a l pigment volume concentration (BVC) of between 5-15%V/v, t h e r e is i n s u f f i c i e n t polymer t o bind a l l t h e p a r t i c l e s t o g e t h e r , c r e a t i n g voids and i n c r e a s i n g permeability. T h e o r e t i c a l l y , t h e C h a t f i e l d theory should be v a l i d f o r a l l permeants,but we have observed t h i s t o be i n e r r o r f o r t h e oxygen p e r m e a b i l i t y o f HPMC f i l m s formed from suspensions of t i t a n i u m dioxide (Colorcon Ltd.) i n 5%W/v aqueous Pharmacoat 606 by c a s t i n g on t o g l a s s o r spraying on t o g l a s s o r 25.4m diameter calcium phosphatel a c t o s e t a b l e t c o r e s under c o a t i n g conditions designed t o mimic those i n a 24" Accela Cota ( P r a t e r e t a 1 1980). The t a b l e shows mean oxygen permeability c o e f f i c i e n t s a t 30° from a t l e a s t t h r e e r e p l i c a t e s determined by a mass spectrometry technique. With n e i t h e r type of sprayed f i l m does t i t a n i u m dioxide concentration m a t e r i a l l y a f f e c t oxygen permeability. For t h e c a s t f i l m s permeability remains e s s e n t i a l l y c o n s t a n t u n t i l t h e CPVC, when it r i s e s rapidly. The absence of t h e i n i t i a l permeability minimum found w i t h water vapour, can be a t t r i b u t e d t o t h e non p l a s t i c i s i n g n a t u r e of oxygen. The d i f f e r e n c e s between cast and sprayed f i l m s a t high f i l l e r content is probably due t o sedimentation of f i l l e r a s t h e s o l v e n t slowly evaporates during c a s t i n g , which cannot occur under spraying conditions. Ti02 Content Oxygen Permeability C o e f f i c i e n t (m2s-I x 1 0~3 ) (% Glass ( c a s t ) Glass (sprayed) T a b l e t Core (sprayed) n i l 7.79 (0.83) 7.89 (0.73) 7.18 (0.02) 3.0 8.39 (0.87) 7.61 (0.73) 6.97 (0.33) 15.6 13.28 (0.44) 8.58 (0.74) 6.18 (1.04) The E f f e c t of Titanium Dioxide Content (%v/v pigment:total s o l i d s r a t i o ) on the Oxygen Permeability a t 300 of HPMC Films formed on Glass and Calcium Phosphate-Lactose T a b l e t Core Substrates. (Figures i n b r a c k e t s a r e standard d e v i a t i o n s ) C h a t f i e l d ,