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    Solid surface composite materials manufactured from syrup of polymethyl methacrylate, alumina trihydrate and natural mineral fillers
    (Universidade Federal do Rio de Janeiro, 2020-01-01)
    Se desarrolló un material compuesto a partir de un jarabe de polimetilmetacrilato (PMMA), trihidróxido de aluminio (ATH) y cargas minerales naturales (CMN) con propiedades similares al material comercial Krion®. Con este propósito, se fabricaron materiales compuestos en dos etapas: En la primera etapa, se realizó la polimerización parcial, en masa, vía radicales libres del metacrilato de metilo (MMA) para obtener un jarabe de polimetilmetacrilato y se determinaron los parámetros de la polimerización necesarios para evitar el efecto de autoaceleración y, al mismo tiempo, lograr un jarabe de un porcentaje de conversión de PMMA capaz de evitar la sedimentación de partículas de ATH. En la segunda etapa, se fabricaron y caracterizaron diversas muestras de materiales compuestos a partir de la mezcla del jarabe de PMMA obtenido anteriormente, partículas de ATH y CMN, con el propósito de determinar los parámetros adecuados para lograr propiedades similares al Krion®. Se ha demostrado que, para evitar la autoaceleración y la sedimentación de ATH, se debe lograr un jarabe con un porcentaje de conversión de MMA en PMMA entre 20% y 25% en peso y la polimerización parcial debe realizarse con 0,1% en peso de peróxido de benzoilo (PBO) y 0,2% en peso de etilenglicol dimercaptoacetato (EGDM) a 85°C durante 90 minutos. Similarmente, para obtener propiedades similares al Krion®, los parámetros para la fabricación de un material compuesto de PMMA reforzado con partículas de ATH y CMN son: 40% jarabe / 60% ATH / %CMN variable según el tipo de carga, 0,1% en peso de PBO adicional, 2,0% en peso de etilenglicol dimetacrilato (EGDMA) y 13 horas de curado en un horno a 85°C. Las propiedades del material compuesto con solo ATH fabricado bajo estas condiciones son: 53 MPa de resistencia a flexión, 8054 MPa de módulo elástico en flexión y 91 HRM de dureza. La calidad estética mejora con la incorporación de CMN pero las propiedades mecánicas disminuyen.
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    Synthesis and characterization of new interpenetrated hydrogels from N-isopropylacrylamide, 2-oxazoline macromonomer and acrylamide
    (Elsevier Ltd, 2022-08-15)
    New interpenetrated hydrogels (IPN), sensitive to pH and temperature, were synthesized by sequential free radical polymerizations in aqueous medium. In the first stage, a thermosensitive hydrogel of poly(N-isopropylacrylamide) (HG-PNiPAAm) was prepared, and in the second stage a hydrogel of acrylamide and 2-oxazoline macromonomer (MM) containing carboxylic acid ester groups was synthesized in the presence of the PNiPAAm hydrogel. In both stages, bisacrylamide was used as a crosslinker. The 2-oxazoline macromonomer was a random copolymer of methyl-3-(oxazol-2-yl)-propionate (EsterOxa) (23 % mol) and 2-methyl-2-oxazoline (MeOxa) (77 % mol) with a polymerization degree of 21 and contained a vinylbenzene end group for radical polymerization. Five different IPN-hydrogels were synthesized, the amount of the oxazoline was varied systematically, and the EsterOxa units were finally hydrolyzed to carboxylic acid groups. The structure of the IPNs was characterized by 1H HR-MAS NMR spectroscopy. All IPN hydrogels showed a conformational transition when varying the temperature or the pH value and these transitions were a function of the composition of the IPN hydrogel. While pure HG-PNiPAAm resulted in a transition temperature of 31 °C, this value rose to 50 °C and higher for MM-H containing IPNs. This property was shown macroscopically as a contraction or expansion of the hydrogel but also in the 1H HR-MAS NMR measurements. The sensitivity to pH in the IPN hydrogels was manifested as a contraction of the volume of the hydrogel at low pH. While introducing poly(acryl amide) PAAm increased the degree of water absorption, increasing the amount of hydrolyzed EsterOxa macromonomer within the hydrogel decreased this absorption at high pH values. These features were attributed to the formation of hydrogen bonds between the acid and amide or protonated amino groups. A lower initial swelling at elevated temperatures but constant switching pH value (pH = 6) supported this reasoning. Importantly, at 20 °C and pH = 5.7 all IPN had a similar degree of swelling Q of 34 to 39, strongly reduced due to the IPN structure compared to a PAAmMM hydrogel (Q > 200). The reported IPNs result from a straight forward synthesis and are thus an interesting material for future applications as potent actuator and sensor materials.