Preparation and physicochemical characterization of binary composites palygorskite-chitosan for drug delivery

This work aimed the evaluation of pH influence in the obtainment of composites from palygorskite (PAL) and chitosan (CS). The materials PAL/CS-1 and PAL/CS-2 were obtained by similar methodology with modified pHs: 5.0 +/- 0.5 and 11.0 +/- 0.5, respectively. Both materials were evaluated for specific surface area analysis, elemental analysis, XRD, FTIR, thermal analysis, MEV and interaction drug composite, using 5-aminosalicylic acid (5-ASA) as model. The surface area analysis data showed the reduction in PAL/CS-2 related to CS presence on surface in contrast with PAL/CS-1, which corroborate with elemental analysis present nine times more of CS in PAL/CS-2 composition. Regarding to XRD data, the interaction of CS with PAL did not cause modification in clay structure in PAL/CS-2. These results were confirmed by FTIR data with the N-H deformation vibration in PAL/CS-2 while PAL/CS-1 was invariable to PAL. In thermal analysis, results were observed 60.2% residual mass to PAL/CS-2, which it was lower than PAL (87.2%) and PAL/CS-1 (86.7%), due to CS decomposition which had enthalpy energy of 62.1 J g(-1) K-1, confirming the data previously cited. PAL/CS-2 presented 5-ASA adsorption of 7.9 mg g(-1), which was inferior to others probably caused by scarcity of active sites of PAL already occupied by CS. These results showed that pH control was fundamental to enhance efficiency of obtainment of composite in basic pH because the decrease in CS protonation degree increasing interaction between this one and PAL, although it contributed to decrease in 5-ASA adsorption due to low availability of interaction sites.