Estudo estrutural e morfológico de membranas de quitosana e de N,O-carboximetilquitosana

Abstract

In this work two sets of samples were evaluated according to their morphological and structural point of view. The first set is the powder samples: Chitosan (Q) purchased from Yue Planting – China; N,O-carboxymethyl sodium (NaCMQD) purchased on Dayang Chemicals – China and Heppe Medical – Germany. The second set of samples is in the form of membranes, which were synthesized in the laboratory from powder samples mentioned above: Chitosan Membrane (M-Q); Membrane of N,Ocarboxymethyl Chitosan synthesized from the Carboxymethyl Chitosan obtained at the Dayang Chemicals (M-CMQD) and N, O-carboxymethyl chitosan synthesized from the Carboxymethyl Chitosan obtained at the Heppe Medical (M-CMQH). Using NMR 13C the average degree of acetylation DA and substitution DS was determined for NaCMQD and NaCMQH samples, and as a tool to propose a molecular structure for each sample. The XRD patterns of powder samples (Q, NaCMQD and NaCMQH) and membranes (M-Q, M-CMQD and M-CMQH) showed for sample Q peaks located at (2 = 10:4, 19.8, 22.2, 29.6, 35.3 and 40:9 ), and the peaks related to their respective membrane (M-Q) was located at 2 = 10:4 and 15:1 , between 2 = 19:8 and 35:3 , and between 2 = 38:6 and 44:5 . The same was observed for NaCMQD sample (between 2 = 8:9 and 13:2 , 2 = 20:1 and between 2 = 33:2 and 42:2 ) and its respective membrane M-CMQD, with peaks located between 2 = 10:3 and 13:7 , 2 = 19:8 and 25:7 , 2 = 37:8 and 45:1 . The samples NaCMQH and M-CMQH showed similar XRD profiles (between 2 = 8:9 and 13:3 , 2 = 17:6 and 26:4 , 2 = 35:0 and 43:1 ). The percentage of crystallinity was estimated using the XRD profiles through Peak Fitting Module Program. For samples in the powder form the crystallinity percentages were found around 45, 40 and 30%, respectively. For samples in the form of membrane the crystallinity was about 35, 30 and 30, respectively. Chitosan powder and membrane (Q and M-Q) had higher percent of crystallinity due to the smaller size of its side groups, facilitating regular packing of their chains, since the carboxymethylchitosan showed extensive side groups, as evidenced by NMR¹³C, which hinders the packing of chains, decreasing its crystalline domains. The Le Bail method was performed using the FullProf program to refine the cell parameters initially found in literature, with orthorhombic space group. The refined cell parameters for Q and M-Q samples showed a = 9 ° A, b = 16 °A and c = 10 A° , approximately; for NaCMQD, NaCMQH, M-CMQD and M-CMQH, ten values of refined parameters were a = 13 A° , b = 19 °A and c = 10 A° , approximately. The average size of its crystallites/anisotropy of the samples Q, M-Q, NaCMQD, M-CMQD, NaCMQH and M-CMQH were 29 (4) A° , 16 (4) ° A, 32 (7) ° A, 23 (2) ° A, 20 (1) °A and 24 (1) A° , respectively. The increase of cell parameters a and b in the Carboxymethyl Chitosans occurred due to the insertion of side groups from carboxymethylation of chitosan, resulting in difficulty in packaging of the chains and therefore the crystallinity and the anisotropic dimensions of the crystallites. The morphologies of powders and membranes were evaluated by Scanning Electron Microscopy (SEM). Samples in powder form (Q, NaCMQD and NaCMQH) presented a variety of sizes of its grains, which showed no uniformity. Membranes (MQ, M-CMQD e M-CMQH) were classified according to their pore size and thickness of the fibers through the ImageJ software. All membranes had pores greater than 50 nm (macropores) and the thickness of fibers were found most frequently around 0.15 m (M-Q) between 5 and 10 m (M-CMQD) and about 5 m (M-CMQH). The thermal stability of the samples was assessed by Thermogravimetric Analysis (TGA/DTG). The physical form of the samples as well as their degree of crystallinity have influenced the main thermal events. Among the powder samples, chitosan showed greater thermal stability with a initial temperature of degradation around 283 C. Among the membranes, the M-Q and M-CMQH samples showed similar initial degradation temperature of around 233 C. Thus, this work presents a systematic evaluation of Chitosan and N,O-carboxymethyl chitosan, as well as their respective membranes, showing intrinsic characteristics of these samples according to their structural and morphological point of view.