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Development of hot-melt extrusion as a novel technique for the ...

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2.3 Flory Huggins (F-H) <strong>the</strong>ory <strong>for</strong> <strong>the</strong> prediction <strong>of</strong> drug/polymer interactionparameterThe F–H interaction parameter, , w<strong>as</strong> correlated with temperature dependence, <strong>as</strong> inmany simplified c<strong>as</strong>es. The interaction parameter <strong>of</strong> <strong>the</strong> model system w<strong>as</strong> determined at twodifferent conditions using <strong>the</strong> Nishi–Wang [24] Eq. 7.1 equation b<strong>as</strong>ed on <strong>melt</strong>ing pointdepression data and Hildebrand and Scott [25] Eq. 7.2 correlations with solubility parameter,respectively. The F-H interaction parameter () <strong>for</strong> all <strong>of</strong> <strong>the</strong> drug/polymers binary mixtureswere calculated by using <strong>the</strong> following equations. The value determined by Eq. 7.1 represents<strong>the</strong> interactions between <strong>the</strong> two substances, specifically at <strong>the</strong> <strong>melt</strong>ing temperature, whichmay not be extrapolated to o<strong>the</strong>r temperatures.1 1 Rdrug12 [ln (1 ) (1 ) (1 ) ]0 drug drug drugpolydrugT T Hmmmdrugpolypoly(7.1)Where, is <strong>the</strong> molar volume <strong>of</strong> <strong>the</strong> repeating unit, m is <strong>the</strong> degree <strong>of</strong> polymerization, is<strong>the</strong> volume fraction and is <strong>the</strong> crystalline– amorphous polymer interaction parameter, T mand T o m is <strong>the</strong> crystalline <strong>melt</strong>ing peak and amorphous Tg in <strong>the</strong> system, respectively.F-H interaction parameter () can be also estimated by <strong>the</strong> method developed byHildebrand and Scott according to Eq. 7.2 [25] .( drug poly) RT2(7.2)Where, R is <strong>the</strong> g<strong>as</strong> constant, T is <strong>the</strong> absolute temperature, and v <strong>the</strong> volume per lattice siteand drug and poly are solubility parameters <strong>of</strong> drugs and polymers respectively.2.4 Differential Scanning Calorimetry (DSC)The physical state <strong>of</strong> <strong>the</strong> pure drug, physical mixtures and extrudates were examinedby using a Mettler-Toledo 823e (Greifensee, Switzerland) differential scanning calorimeter.Samples were prepared in sealed aluminum pans (3-5 mg) with a pierced lid. The sampleswere heated at 10 o C/min in a temperature range between 0 and 220 o C under nitrogenatmosphere.130 | P a g e

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