Francisco H. A. Rodrigues

Superabsorbent hydrogel nanocomposites based on starch-g-poly(sodium acrylate) matrix filled with cellulose nanowhiskers

Superabsorbents hydrogel nanocomposites based on starch-g-poly(sodium acrylate) and cellulose nanowhiskers (CNWs) were synthesized. A set of experiments was performed to evaluate the influence of some factors such as NaAc/starch mass ratio, crosslinker, and nanowhiskers amount in the swelling capacity and swelling kinetics. Increasing the NaAc/starch mass ratio up to 7 leads to an increase in the water uptake at a maximum value, however, higher ratios decreased that value due to the increase of crosslinking points. Similarly, the incorporation of CNWs up to 10 wt% provided an improvement in the swelling due to the hydrophilic groups from cellobiose units. Further, the incorporation of CNWs diminishes the water uptake. Besides, the CNWs improved the mechanical properties. SEM images showed that CNWs increase the average porous size of composites. The composites presented good responsive behavior in relation to pH and salt presence allowing those materials suitable for many potential applications.

Characterization of N-trimethyl chitosan/alginate complexes and curcumin release.

N-trimethyl chitosan of two quaternization degrees, DQ=20 and 80mol% and labeled as TMC20 and TMC80, were synthesized and characterized by (1)H NMR. Polyelectrolyte complexes (PECs) of TMC/alginate (TMC/ALG) were prepared at pHs 2, 7 and 10 by mixing the aqueous solutions of unlike polymers. The PECs were characterized through infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG) and wide-angle X-ray scattering (WAXS). Using the TMC of DQ=20 mol% and following the same methodology for preparing the PECs, beads of TMC20/ALG were obtained at pH 2 and loaded with curcumin (CUR) at pH 6.0-6.5. The morphology of the beads was evaluated by scanning electron microscopy (SEM). Studies in vitro of the controlled release of CUR from beads were investigated in simulated intestinal fluid (SIF) and simulated gastric fluid (SGF) and treated using conventional and partition-diffusion models. Results indicated that the beads based on TMC20 and ALG presented potential as drug-carrier to improve the solubility and biological activity of CUR at pH close to physiological one.

Fast dye removal from water by starch-based nanocomposites.

Robust and efficient methylene blue (MB) adsorbent was prepared based on starch/cellulose nanowhiskers hydrogel composite. Maximum MB adsorption capacity of ∼2050mgperg of dried hydrogel was obtained with the composite at 5wt.% of cellulose nanowhiskers and at pH 5. Adsorption capacity varied from 1450mg/g to 2050mg/g with increasing the initial MB concentration from 1500mg/L to 2500mg/L, respectively. For all the concentrations studied ca. 90% of MB was removed by the adsorbent. Optimal conditions were obtained at pH⩾5 due to the generation of negatively charged groups (COO(-)) in the adsorbent, which can strongly interact with the positive charges from MB. The main advantage of this system over other reported adsorbents, besides the fact of being synthesized from biodegradable polymers (starch and cellulose), is its fast adsorption kinetics that follows the pseudo-second order model, which is based on chimisorption phenomenon. Saturation condition was reached as fast as 1h of experiments owing to the formation of an adsorbed MB monolayer as suggested by the Langmuir isotherm model. Desorption experiments showed 60wt.% of MB loaded can be removed from the adsorbent by immersing it in a pH 1 solution, showing its feasibility to be reused. Therefore, starch/cellulose nanowhiskers hydrogel composite presents outstanding capacity to be employed in the remediation of MB contaminated wastewaters.

Cellulose nanowhiskers improve the methylene blue adsorption capacity of chitosan- g -poly(acrylic acid) hydrogel

Cellulose nanowhiskers (CNWs, 90% crystalline) were used to enhance the adsorption capacity of chitosan-g-poly(acrylic acid) hydrogel. The composites up to 20w/w-% CNWs showed improved adsorption capacity towards methylene blue (MB) as compared to the pristine hydrogel. At 5w/w-% CNWs the composite presented the highest adsorption capacity (1968mg/g). The maximum removal of MB (>98% of initial concentration 2000mg/L) was achieved quickly (60min) at room temperature, pH 6, and at low ionic strength (0.1M). Adsorption mechanism was explained with the Langmuir type I model suggesting the formation of a MB monolayer on the adsorbent surface. The interaction between the adsorbent and MB molecules was explained by chemisorption, as suggested by the pseudo-second-order kinetic model. Desorption experiments showed that 75% of loaded-MB could be recovered from the adsorbent by its immersion in a pH 1 solution. Additional experiments showed the post-utilized composite could be regenerated and reused for at least 5 consecutive adsorption/desorption cycles with minimum efficiency loss (∼2%).

NOVEL SUPERABSORBENT HYDROGEL COMPOSITE BASED ON POLY(ACRYLAMIDE-CO-ACRYLATE)/NONTRONITE: CHARACTERIZATION AND SWELLING PERFORMANCE

A novel superabsorbent hydrogel (SH) composite based on a poly(acrylamide-co-acrylate) matrix filled with nontronite (NONT), a Fe(III)-rich member of the smectite group of clay minerals, is described in this manuscript. A variety of techniques, including FTIR, XRD, TGA, and SEM/EDX, were utilized to characterize this original composite. Experimental data confirmed the SH composite formation and suggested NONT was completely dispersed in the polymeric matrix. Additionally, NONT improved the water uptake capacity of the final material, which exhibited fast absorption, low sensitivity to the presence of salt, high water retention and a pH sensitive properties. These preliminary data showed that the original SH composite prepared here possesses highly attractive properties for applications in areas such as the agriculture field, particularly as a soil conditioner.

Síntese e caracterização de hidrogéis compósitos a partir de copolímeros acrilamida-acrilato e caulim: efeito da constituição de diferentes caulins do nordeste brasileiro

Superabsorbent hydrogels based on poly (acrylamide-co-acrylate) and different kaolins, were prepared by free-radical aqueous copolymerization. FTIR and WAXS techniques were employed for characterization of a series of hydrogels, obtained by varying the percentage of clay, crosslinking and constitution of kaolin. The water absorbency at equilibrium (Weq) decreased with increasing clay content and the amount of crosslinking agent. Superabsorbent hydrogel (Weq > 1084 g H2O/g gel) was obtained as 10 wt% of white kaolin and 0.05 mol% of crosslinking agent were used. The hydrogel proved sensitive to pH variation and the presence of salts.

Thermal Oligomerisation of Cardanol

Abstract Cardanol was extracted from technical Cashew Nut Shell Liquid (CNSL), a naturally occurring meta-substituted long chain phenol and oligomerized by heating at 140 °C. Products were characterized by rheology, infrared and 1H NMR spectroscopy and thermogravimetric analysis (TGA). Increase in viscosity and the flow activation energy was found with increasing time of heating. The relative absorbance of double bond of the hydrocarbon chain decreased with time of heating and indicated that the oligomerization is taking place through the unsaturation of the side chain. Decrease in internal double bond as well as in vinyl bond, observed by 1H NMR, pointed out to the participation of these two kinds of unsaturation as well as monoene, diene and triene. The oligomerization is a slow process. With 40 h of heating, the average molecular weight increases only by 46%. Great differences were found in TGA curves of cardanol with different times of oligomerization. Thermal stability increases with time of heating. The degree of oligomerization could be determined from relative mass loss of the first event of TG, or from flow activation energy.

Novos surfactantes alquil poliglicosídicos à base de amilose extraída da batata inglesa (Solanum tuberosum L.)

Alkyl polyglycosides (APGs) are new biodegradable surfactants, non-toxic, synthesized from abundant renewable sources, potentially more appropriate than anionic surfactants. A range of glycosides denoted APG-Cy was synthesized by the Koenig-Knorr reaction using C10, C16 and C18 alcohols and derived from the degradation of amylose from English potato. The molecular structures of the glycosides were characterized by Nuclear Magnetic Resonance (1H and 13C NMR) together with Infrared Spectroscopy (FTIR) and Gel Permeation Chromatography (GPC). The study by NMR allowed the junctions between hydrophilic head groups and hydrophobic tail-groups to be characterized in detail. Conformation of the glycosidic units is 4C1 type with a b anomeric configuration. The formation of glycosides with five glucose rings linked to the alkyl chain was confirmed by 1H NMR and GPC. Liquid crystals identified by the presence of double melting points were observed by Differential Scanning Calorimetry (DSC) showing thermotropic properties. The surface tension (γ) and critical micelle concentration (cmc) were determined by du Nouy method, noting that increasing the length of alkyl chain led to the expected reduction in the cmc. The energies of adsorption and micellization processes calculated from isotherms γ versus ln c (g.dm-3) indicate cooperativeness of hydrophilic and hydrophobic groups.