The objective of this paper was to study the effect of pH, concentration and ionic species on the water absorption of the bionanocomposite hydrogels based on carboxymethylcellulose polysaccharide and laponite nanoclay. Bionanocomposite hydrogels were obtained via free radical polymerization. It was possible to observe that the swelling degree (Q) and kinetic properties were strongly influenced, and controlled, by the presence and quantity of ionic species, decreasing their water uptake when compared to the same values obtained in distilled water. Furthermore, the addition of nanoclay decreased the water uptake sensibility of the hydrogel in ionic media. It was also observed that the presence of the nanoclay decreased the Qeq distilled water values from 32.5 g g-1 to 22.5 g g-1. The pKa variation of the bionanocomposites was a good indication of the possible interaction of the nanoclay-polymeric chains. The possibility of the control of water absorption (velocity and quantity) whereas these nanocomposites are pH- and salt-responsive may potentiate their application in agriculture. Agronomical studies are in progress, which can confirm its applicability in this area.
The development of films from natural polymers is an alternative to reduce the consumption of packaging obtained from non-renewable sources. The formation of edible films requires a polymeric material that forms a homogeneous and continuous matrix. The gelatin is a natural polymer, cheap and abundant, characteristics that instigate its use. The aim of this study was preparing and characterize gelatin films and evaluate the influence of lemon essential oil nanoemulsion on gelatin matrix for an innovative application of the product. The films were characterized for their water vapor permeability (WVP) test, contact angle, thickness and mechanical analysis (tensile strength and elongation at break). The particle size showed an average of 170.6 nm and zeta potential around -10.9 mV. The incorporation of lemon nanoemulsion increased the water vapor permeability of the gelatin and the elongation, but decreased tensile strength due to the interaction with the hydrophobic portion of the polymer matrix.
In this work, nanocomposites formed from the natural polymer carboxymethylcellulose in combination with the polyacrylamide polymer and zeolite were obtained and characterized in relation to pesticide sorption capability. Hydrogels are three-dimensional network with large capacity of water or biological fluid adsorption. They have biocompatibility, biodegradability and non-toxicity properties, ensuring this class of polymers is widely used in different agriculture fields. Thus, the objective of the work was to investigate the process of paraquat sorption using a novel biodegradable nanocomposite. By mathematical modeling, it was possible to found that better models were the Freundlich-Langmuir isotherm and pseudosecond order kinetic, indicating that sorption is heterogeneous and similar to chemisorption process. Thus, such nanocomposites have great potential to be applied as an adsorbent material for removal of pesticides from contaminated water.
The aim of this work was to produce biodegradable films based on the pectin and cocoa puree reinforced with chitosan nanoparticles. Nanoparticles were obtained by the ionotropic gelation. Films were produced according to the "casting" method, through a colloidal solution composed of water, cocoa puree, chitosan nanoparticles solution and different concentrations of pectin (2% and 3% w/w). Films were analyzed by thickness measurements, water vapor permeability, mechanical properties and scanning electron microscopy. Nanoparticles were characterized by zeta potential and showed spherical shape with a diameter of about 110 nm and zeta potential value of approximately +30 mV. Pectin 2% and 3% cocoa films exhibited tensile strength (mPa) of 15.1 ± 0.7 and 22.9 ± 1.6, respectively. After nanostructures addition, values increased to 25.2 ± 0.7 and 29.8 ± 1.3. Increasing concentration polymer and chitosan nanoparticles to improve tensile strength values. Films contained 3% of pectin exhibited more significant decrease in water vapor permeability values when chitosan nanoparticles were added, from 2.470 ± 0.101 to 1.904 ± 0.125 g mm / kPa h m2. Results of the analyzes demonstrated that nanocomposites produced with pectin of different concentration showed satisfactory properties for application as packaging for food.
In this study, the hydrogel formulations based on polysaccharide sodium alginate were investigated for further development of intercalated nanocomposite hydrogels, for purposes of future applications in the areas of health as a carrier in drug delivery systems. Thus, the objective of the work dealt with in the optimization of hydrogels synthesis and obtaining nanostructured hydrogels with clay in an intercalated conformation. The optimization of the hydrogel synthesis was successful, and it is possible to define the materials and / or solutions to be used and concentrations of these solutions to the best formulations of hydrogels. The choice of the concentration of the polysaccharide, the type of crosslinking agent and nanofiller to continued development work, it was determined following criteria as the degree of swelling, and in some cases the physical properties, contributed to determine the best hydrogels. The development of intercalated nanocomposites hydrogel beads was confirmed by the X-ray diffraction technique, which thus could be used to observe evidence of effective incorporation or intercalation of the nanoclay in the hydrogel matrix.
In this study, a novel hybrid composite based on biodegradable hydrogel and Portland cement with promising technological properties was reported. In the first step, a full 23 with central point factorial design was utilized to obtain the enhanced polyacrylamide-carboxymethylcellulose hydrogel compositions. A mathematical model was devised, indicating that the 3 main variables were significant and the AAm and MBAAm variables positively contributed to the mode and showing that the CMC variable had the opposite contribution. In the second step, these compositions were mixed with Portland cement to obtain the hybrid composites. The presence of cement improved the mechanical properties of polymeric matrices, and electronic microscopic micrographics revealed that the hydrogels were well adhered to the cement phase and no phase separation between hydrogel and cement was detected. Finally, using the energy dispersive X-ray technique, the elements Na, Mg, Al, Si, S, K, Ca and Fe were detected in the polymeric matrix, consistent with the hybrid composite formation.
In this work, a novel device based on polyacrylamide (PAAm) hydrogels and KL - DeOH - H2O lyotropic liquid crystal (LLC), with potential for application as Polymer Dispersed Liquid Crystals (PDLC), was proposed and its properties characterized. The confinement of LLC promoted significant changes in spectroscopic, morphological, optical, hydrophilic, structural and mechanical properties due to the interaction between the LLC-PAAm matrix and entropic parameter changes. The mechanical and structural properties can be controlled by adjusting AAm, temperature and presence of LLC, which can be useful for technological applications of these systems in optical devices.
This work reported the characterization of hydrogels constituted by methylcellulose (MC) entrapped in polyacrylamide (PAAm) network prepared by cross-linking polymerization (gelling process). Spectroscopic and morphologic properties were investigated using Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Effects of AAm, MC contents, ionic charge of salt counter-ions (NaCl, KCl, NH4Cl, CaCl2, MnCl2, MgCl2, and AlCl3), and fertilizers [(NH4)2SO4 and KH2PO4] on kinetic and hydrophilic (swelling degree) properties were investigated in detail. By decreasing the MC content or by increasing acrylamide content, there was a pronounced decrease in water uptake by the hydrogels. The increase in counter-ion X-Cl salt and the presence of fertilizer on the external swelling medium also provoked a decrease in water uptake. The water uptake mechanism of PAAm-MC hydrogels swollen in water followed the Fickian diffusion, while the mechanisms of hydrogels swollen in salt or fertilizer aqueous media followed the anomalous transport process. With their fast and high water absorption, the porous, three-dimensional matrices containing PAAm and MC are promising for agriculture as carrier vehicles.
Neste trabalho foi reportada a caracterização de hidrogéis constituídos por metilcelulose (MC) e poliacrilamida (PAAm) preparados pelo processo de reticulação cruzada. As propriedades espectroscópicas e morfológicas foram investigadas por espectroscopia no infravermelho com transformada de Fourier e microscopia eletrônica de varredura, respectivamente. O efeito da carga iônica, presença de sais, concentrações de monômero AAm e polissacarídeo MC na absorção de água e nas propriedades cinéticas dos hidrogéis foi detalhadamente investigado. Os resultados indicaram que o decréscimo da concentração de MC ou aumento da concentração de AAm, carga iônica do contra-íon do sal de cloreto e a presença de fertilizante no meio externo de intumescimento provocaram diminuição significativa na absorção de água dos hidrogéis. O mecanismo de absorção de água dos hidrogéis de PAAm-MC em água seguiu o modelo de difusão Fickiana; já o mecanismo dos hidrogéis intumescidos em sais (cloreto ou fertilizante) seguiu o modelo de transporte anômalo. Pela alta e rápida absorção de água, as matrizes porosas e tridimensionais compostas por PAAm e MC podem em potencial ser aplicadas na agricultura como veículos carreadores.
In this paper, the effects of acrylamide (AAm), methylcellulose (MC) contents, pH and ionic strength on kinetic, network and hydrophilic properties of polyacrylamide and methylcellulose hydrogels were investigated. The hydrogels were characterized by evaluating of network [average molecular weight between crosslinks (M C), crosslink density (q) and the number of elastically effective chains (Ve)], and kinetic parameters [diffusional exponent (n), diffusion constant (k) and diffusion coefficient (D)]. Such properties were controlled by adjusting of the AAm, MC contents, pH and ionic strength factors. Due to high hydrophilicity and fast water-uptake, the PAAm-MC hydrogels can be considered as materials for potential applications in agricultural fields, mainly in controlled release of water or pesticides.
Conductive semi-IPN hydrogels made with polyacrylamide (PAAm) and the conductive polymer poly(3,4-ethylene dioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) were synthesized and the hydrophilicity, mechanical, ionic conductivity and optical properties were characterized through the 2³ factorial design. The experiments concerning the factorial design were randomly performed. The inputs were acrylamide (AAm), N,N’-methylene-bis-acrylamide (MBAAm) and PEDOT/PSS contents, each fixed in three levels, one being the central point. The outputs were the swelling degree, maximum compression stress, ionic conductance and relative intensity of light transmitted through the hydrogel. ANOVA was obtained using Statistical Software®. The results of the twelve runs from the factorial design (eight runs from 2³ plus four central point replicates) were applied to evaluate the main effects and their interaction, in addition to decide if they are statistically significant. The results demonstrated that mechanical stability of semi-IPN hydrogels is preserved, with PEDOT/PSS creating additional entanglements within the PAAm network. In addition, the optical properties are strongly influenced by the presence of PEDOT/PSS. In summary, hydrogels could be synthesized with controlled hydrophilicity, transparency and mechanical stability, which is important for optical devices.
Neste trabalho, hidrogéis condutores do tipo semi-IPN constituídos por poliacrilamida (PAAm) e polímero intrinsecamente condutor poli(3,4-etileno dioxitiofeno)/poli(estireno-sulfonato) (PEDOT/PSS) foram sintetizados e suas propriedades hidrofílicas, mecânicas, condutoras e ópticas foram caracterizadas por meio de planejamento fatorial completo 2³ com ponto central. Para isso, utilizaram-se três fatores: concentrações de acrilamida (AAm) e N,N’-metileno-bis-acrilamida (MBAAm), e quantidade de PEDOT/PSS, em três níveis, sendo um deles o ponto central. O planejamento foi construído para avaliar os efeitos desses fatores (efeitos principais e efeitos de interação entre os fatores) nas seguintes propriedades dos hidrogéis estudados (respostas): grau de intumescimento, tensão máxima de compressão, condutância iônica e intensidade relativa de luz transmitida através dos hidrogéis estudados. Os resultados demonstraram que a estabilidade mecânica dos hidrogéis semi-IPN é preservada e a presença de PEDOT/PSS aumenta o entrelaçamento na matriz de PAAm. Observou-se também que as propriedades ópticas são fortemente influenciadas com a presença de PEDOT/PSS. Dessa forma, torna-se possível obter hidrogéis com hidrofilicidade, estabilidade mecânica e transparência controladas, o que é importante para a aplicação desses materiais, principalmente como dispositivos ópticos.