Nanoparticles comprised of the poly(ethylene oxide)-b-poly (lactic acid) diblock copolymer (PEO-b-PLA) with and without the incorporation of lavender oil were prepared by nanoprecipitation. Diblock copolymers based on a fixed PEO block (5KDa) and two different PLA segments (4.5 or 10KDa) were used. The morphology, encapsulation efficiency, essential oil-polymer interaction and the release kinetics of the active agent in the nanoparticles, were evaluated. The hydrodynamic radius of the nanoparticles determined by light scattering was affected by the size of the poly(lactic acid) (PLA) block. The lavender essential oil encapsulation efficiency (at a concentration of 0.4 µL mL-1) determined by UV-VIS spectroscopy was in the range of 70-75%. The in vitro release suggests that the polymeric barrier is able to control the oil release.

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.

Recentemente, foi desenvolvido em nosso grupo de pesquisas um modelo que prevê 100% do perfil de liberação de soluto a partir de hidrogel. Este considera os efeitos de difusão e de partição e permite obter os valores da atividade de partição, α, e da constante cinética de liberação, kR. Embora α e kR sejam dependentes de fatores diversos, a hipótese de que a razão α/kR não seja dependente do volume de fluido de intumescimento foi testada neste trabalho. Assim, foram determinados valores da razão α/kR para vitamina B12 (VitB12) e diclofenaco de potássio (DFK) que foram submetidos a ensaios de liberação em três temperaturas (25, 35 e 45 ºC), sendo avaliados, em cada temperatura, os volumes 250, 350 e 450 mL. O hidrogel utilizado é baseado na goma arábica quimicamente modificada copolimerizada com N, N-dimetilacrilamida (AGm-DMAAm), na razão 60-40 (m/m) sendo o carregamento dos solutos feito durante o processo de gelificação. Foi verificado que a razão α/kR não depende do volume do fluido de liberação para uma determinada temperatura. Mas a temperatura é um fator importante, influenciando fortemente o processo de liberação destes solutos. A variação da temperatura de 25 para 35 ºC afeta mais a liberação de DFK do que a liberação de VitB12. Isso foi atribuído a interações eletrostáticas entre os grupos (R-COO-) contidos nesse soluto e a grupos positivamente carregados na matriz. Foram calculados os valores de tempo de meia vida de liberação, t1/2, e a energia de ativação, EaR, do processo de liberação dos solutos.

Recently, a model predicting whole profile solute release from a hydrogel was developed. In such model, the partition activity, α, and release kinetic constant, kR, can be obtained. Although α and kR depend on many factors, the hypothesis that α/kR ratio does not depend on external fluid volume was tested in the present study. Thus, α/kR values for two distinct solutes, vitamin B12 (VitB12) and diclofenac potassium (DFK), were obtained at 25, 35 and 45 ºC using 250, 350 and 450 mL of external fluid. The hydrogel used in the experiments was obtained by the copolymerization of N, N-dimethylacrylamide-modified Arabic gum (AGm-DMAAm), at wt% ratio of 60-40. It was verified that α/kR ratio is not volume dependent, at a certain temperature, but the temperature strongly influences the α/kR ratio for both solutes. Changing temperature from 25 to 35 ºC affected DFK release much more than VitB12 release. This was attributed mainly to electrostatic interactions between (R-COO-) from DFK and the positively charged groups in the GAm-DMAAm matrix. Additionally, the values for the half-life time release, t1/2, equilibrium time release, t eq, as well as the activation energy for releasing, EaR, were determined and discussed in light of the partition-diffusion model.

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.

Nanocristais inorgânicos estáveis e suportados, como PbS ou outros quantum dots, são materiais extremamente importantes quando obtidos na forma de filmes finos para a aplicação em áreas tecnológicas. Neste trabalho, um método para o crescimento de cristais de PbS sobre filme ultrafino de poli(ácido acrílico) (PAA) covalentemente imobilizado na superfície de polietileno (PE) é descrito. O método utilizado permite a obtenção de materiais com diferentes formas e tamanhos pelo ajuste de variáveis experimentais. Os compostos mais homogêneos e com as menores partículas foram obtidos em pH 6 devido a remoção mais lenta de íons Pb2+ adsorvidos no filme ultrafino de PAA. Dessa forma, o PbS é formado in situ no interior do PAA. A análise da morfologia dos compósitos mostrou uma relação direta entre a concentração de Pb2+ e a concentração de tioacetamida (TAA). Compósitos mais homogêneos com as partículas menores foram obtidos na condição de menor concentração de Pb2+ e maior concentração de TAA ou na condição intermediária de Pb2+ e menor concentração de TAA.

Supported and stable inorganic crystals in nanometric size, such as PbS or other quantum dots, are very desired materials in the form of thin films for the application in technological areas. Herein, an approach to the growth of PbS crystals in poly(acrylic acid) (PAA) ultrathin film covalently immobilized in the polyethylene (PE) surface is described. The method used allows the obtaining of materials with different shapes and sizes by the adjustment of experimental variables. The more homogenous composites with the smallest particles were obtained at pH 6 due to the slower removal of Pb2+ ions from PAA ultrathin film. Hence, the PbS is formed in situ inside of PAA. A direct relationship between Pb2+ and thioacetamide (TAA) concentrations was observed by the analysis of the composite morphologies. More homogenous composites with the smallest particles were obtained in the lowest Pb2+ condition and the highest TAA concentration condition or in the intermediate Pb2+ condition and the lowest TAA concentration condition.

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.

The thermal degradation of miscible and immiscible poly (3-hidroxy butyrate) PHB/ poly (ethylene terephthalate) sulphonated (PETs) blends was investigated using thermogravimetric analyses. Model-free kinetic analysis, Vyazovkin and Flynn-Wall-Ozawa's methods, were used to determine the apparent activation energy in the whole interval of degradation of the pure polymers, immiscible blends, and miscible blends. The thermal stability of both polymers in their blends is higher when compared to the pure polymers. The synergistic effect in the thermal stability in the blends is higher for the miscible blend where the formation of the specific interaction between PHB and PETs occurs. The apparent activation energy of the individual polymers is higher in PETs/PHB blends, and this effect is potentiated by the miscibility of the blend.

No presente trabalho, foram sintetizados hidrogéis com ambas as propriedades, termo-sensíveis e pH-responsivos, pela formação de redes de alginato de cálcio (alginato-Ca) dentro de redes de poli(N-Isopropil Acrilamida) (PNIPAAm), resultando em um sistema IPN (sistema de redes poliméricas interpenetradas). Através das análises por microscopia de varredura eletrônica (MEV) e ensaios de intumescimento foi possível observar que os hidrogéis IPN exibiram forte contração quando aquecidos acima da LCST (temperatura critica inferior de solubilização) da PNIPAAm, ou seja, acima de temperaturas de 30-35 ºC. Observou-se ainda que devido à contração do hidrogel, houve uma diminuição significativa nos tamanhos de poros os quais foram observados pelas micrografias. Observou-se também que no intervalo de pH estudado os hidrogéis de IPN sofreram significativa variação da estrutura com a variação desse parâmetro. Tal efeito foi atribuído à presença de grupos químicos carregados com alginato, os quais possuem carga elétrica negativa. Os resultados indicaram que o hidrogel formado por alginato-Ca e PNIPAAm possuíram características especificas após variação de pH e temperatura, e que tais características são derivadas dos compostos individuais envolvidos na síntese. Nesse caso, as propriedades de alginato-Ca e PNIPAAm livres foram preservadas dentro do hidrogel. Tal hidrogel ficou mais resistente à aplicação de uma tensão de compressão. Como conclusão, observou-se que os hidrogéis apresentaram morfologia característica para variações controladas de pH e temperatura, podendo ser eficientemente aplicados como biomaterial na cultura de células.

In the present investigation, hydrogels with pH-responsive and temperature-sensitive properties were obtained by formation of alginate-Ca network inside the PNIPAAm network resulting in an interpenetrated network system (IPN). From scanning electron microscopy (SEM) images and water uptake (WU) tests one observed that IPN hydrogels exhibited a drastic shrinking when heated above 30-35 ºC. The shrinking resulted in decreased average pore size, thus affect the hydrogel morphology significantly. In the pH range studied, IPN hydrogels showed significant pH dependence, which was attributed to the charged alginate groups. The results indicated that the pH-responsiveness and temperature-dependence of alginate and PNIPAAm, respectively, were preserved in IPN hydrogels. In addition, such hydrogels become less deformable when subjected to compressive stress. These hydrogels presented porous morphology that may be tuned by controlling the temperature, and this makes them attractive for applications as biomaterial in cell growth.

The use of lignocellulosic fibers and their constituents, as raw materials in the production of polymeric and composite materials, represent an exceptional opportunity of sustainable technological development. In the present report works that discuss promising alternatives of obtaining and use of materials such as cellulose, hemicellulose, lignin, cellulose nanocrystals and biocomposites were revised. The advance in the use of biomass can be, in a near future, capable of going beyond the application difficulties of these vast materials, especially in relation to the economical unviability, by the production of high performance polymeric and composite materials. This advance would represent a higher profitability to some areas of agrobusiness, especially the sector of biofuels, which produces elevated amounts of biomass waste.

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.

Neste trabalho, a termossensibilidade dos hidrogéis do tipo semi-IPN baseados em rede de alginato-Ca2+com poli(N-isopropil acrilamida) (PNIPAAm) entrelaçado, com diferentes teores de alginato e de PNIPAAm, foi caracterizada por meio de medidas de grau de intumescimento (Q), microscopia eletrônica de varredura (MEV) e propriedades mecânicas [tensão máxima de compressão (σ), densidade aparente de reticulação (νe) e módulo de elasticidade (E)]. Os valores de Q variam inversamente com νe. Para o parâmetro νe contribuem as concentrações de retículos alginato-Ca2+ e de cadeias de PNIPAAm. Hidrogéis com maiores valores de Q possuem maiores poros. Resultados de propriedades mecânicas demonstraram que hidrogéis com maior νe apresentam maior rigidez e resistência à compressão, sendo este efeito mais intenso acima da LCST do PNIPAAm. O controle dessas propriedades nesses hidrogéis termos-sensíveis torna esses materiais potencialmente viáveis para aplicação em sistemas carreadores para liberação controlada e/ou prolongada de fármacos e substratos para crescimento e cultura de célula.

In this study, the thermosensitivity of semi-IPN hydrogels based on alginate-Ca2+ network and having PNIPAAm entangled was characterized by swelling degree (Q), scanning electron microscopy (SEM) and mechanical properties [compressive stress (σ), apparent cross-linking density (νe) and modulus of elasticity (E)]. The Q values change inversely to the νe ones. The concentrations of the alginate-Ca2+ cross-linking and of the PNIPAAm chains contribute to the νe parameter. Higher values of Q correlate to larger pores size in the hydrogel. Hydrogels richer in alginate and PNIPAAm were more rigid, highly resistant to deformation because of their higher compressive modulus of elasticity. This is more intense at temperatures above the LCST of PNIPAAm in water (32-35 °C). The control of thermosensitive properties by tailoring the alginate-Ca2+/PNIPAAm ratio and temperature allows the hydrogels studied in this paper to be applied as drug delivery devices and/or as substrate for cell growth.

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.

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.

CO2 supercrítico foi utilizado para preparar compósitos poliméricos com prata, prata/poli álcool vinílico e prata/ poli álcool vinílico/ poli (tereftalato de etileno) sulfonado, pela impregnação de um precursor de prata nas matrizes poliméricas no estado sólido seguida da redução térmica do precursor. Difração de raio X, microscopia eletrônica de varredura, espectroscopia de energia dispersiva, microscopia de força atômica, análise termogravimétrica e espectroscopia no UV/vis dos compósitos indicaram que as condições de preparação e a composição da matriz polimérica influenciam o tamanho e a forma das partículas de prata formadas, assim como, a uniformidade e a distribuição das partículas nas matrizes poliméricas. As partículas de prata nos compósitos ricos em PVA são menores, possuem formas mais uniformes e apresentam distribuição de tamanho mais estreita do que nos compósitos ricos em PETs.

Supercritical CO2 has been used to prepare silver polymer composites, silver/poly(vinyl alcohol) and silver/poly(vinyl alcohol)/sulfonated poly(ethylene terephthalate) through impregnation of a silver precursor in solid-state polymeric matrices followed by thermal reduction of the silver precursor. X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, thermogravimetric analysis and UV/vis spectroscopy indicate that synthesis conditions and polymeric matrix composition affect silver particle size, shape and distribution in polymeric matrices. Silver particles are smaller, have a more uniform shape and present narrower size distribution in PVA-rich than in PETs-rich composites.

PET pós-consumo foi modificado quimicamente através de reação com ácido sulfúrico por diferentes tempos. O material modificado foi caracterizado por DSC e FTIR-PAS e XPS. Verificou-se que a intensidade relativa do isômero trans diminui enquanto do isômero gauche aumenta para tempos de reação entre 0 e 60 minutos. Após 60 minutos de reação observou-se a presença de endotermas múltiplas que podem ser relacionadas com o desenvolvimento de estruturas intermediárias porque as intensidades relativas dos isômeros trans e gauche não apresentam variação significativa. O valor determinado de capacidade de troca iônica do PET pós-consumo modificado (PETS-pc) é comparável com os valores de resinas ácidas comerciais e não é afetado no intervalo de tempo de reação utilizado. Os valores da capacidade máxima de adsorção, qm, e do parâmetro de afinidade entre o adsorvente e o adsorvato, K, (111,18 ppm e 531,91 mg de corante/100g de adsorvente, respectivamente) para a adsorção do corante Remazol vermelho na amostra quimicamente modificada por 30 minutos foram calculados a partir da isoterma de adsorção de Langmuir. Os resultados indicam que esse material possui características adsorventes, podendo vir a ser utilizado para tratamento de efluente de indústria de tingimento têxtil.

Chemical modification of post consumer PET was carried out by reaction with sulfuric acid. The modified material was characterized by DSC, XPS and FTIR-PAS measurements. The relative intensity of trans isomer increases while it decreases for gauche isomer for reaction times from 0 up to 60 min. After 60 minutes of reaction multiple endotherms were observed, which may be related to the development of an intermediated structure, since the relative intensities of the trans and gauche isomers do not change. The ionic exchange capacity of the modified post consumer poly(ethylene terephthalate), PETS-pc, is comparable to commercial acid resins and is not affected by the reaction time. The maximum adsorption capacity, qm, and the affinity parameter, K, (111.18 ppm and 531.91 mg dye/100g adsorvent, respectively) due to the adsorption of Remazol Red were calculated for PET samples chemically modified during 30 minutes from the Langmuir adsorption isotherms. The results indicate that PETS-pc has excellent adsorvent capacity, and can be applied to treatment of textile dye effluents.