Scielo RSS <![CDATA[Polímeros]]> vol. 25 num. 1 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[LIÇÃO DE VIDA: 90 ANOS DA PROFESSORA ELOISA MANO]]> <![CDATA[Vegetal fibers in polymeric composites: a review]]> The need to develop and commercialize materials containing vegetal fibers has grown in order to reduce environmental impact and reach sustainability. Large amounts of lignocellulosic materials are generated around the world from several human activities. The lignocellulosic materials are composed of cellulose, hemicellulose, lignin, extractives and ashes. Recently these constituents have been used in different applications; in particular, cellulose has been the subject of numerous works on the development of composite materials reinforced with natural fibers. Many studies have led to composite materials reinforced with fibers to improve the mechanical, physical, and thermal properties. Furthermore, lignocellulosic materials have been treated to apply in innovative solutions for efficient and sustainable systems. This paper aims to review the lignocellulosic fibers characteristics, as well as to present their applications as reinforcement in composites of different polymeric matrices. <![CDATA[Preparation of PLLA/PMMA and PLLA/PS binary blend nanoparticles by incorporation of PLLA in methyl methacrylate or styrene miniemulsion homopolymerization]]> Miniemulsion homopolymerization reactions of methyl methacrylate (MMA) and styrene (STY) using poly(L-lactide) as co-stabilizer were carried out in order to prepare poly(L-lactide)/poly(methyl methacrylate) (PLLA/PMMA) and poly(L-lactide)/polystyrene (PLLA/PS) binary blend nanoparticles. The effect of PLLA concentration on methyl methacrylate (MMA) and styrene (STY) homopolymerization reactions was evaluated. It was found that the incorporation of PLLA resulted on acceleration of MMA and STY homopolymerization reactions and led to a molar mass increase of up to 70% for PS in PLLA/PS blend nanoparticles in relation to those prepared without PLLA, which can be attributed to an increase of reaction loci viscosity (gel effect). PLLA also acted as an efficient co-stabilizer, since it was able to retard diffusional degradation of droplets when no other kind of co-stabilizer was used. Two isolated Tgs were found in both PLLA/PMMA and PLLA/PS blend nanoparticles which can be associated to blend immiscibility. TEM images corroborate these results, suggesting that immiscible PLLA/PMMA and PLLA/PS blend nanoparticles could be formed with two segregated phases and core-shell morphology. <![CDATA[Biodegradation of films of low density polyethylene (LDPE), poly(hydroxibutyrate-co-valerate) (PHBV), and LDPE/PHBV (70/30) blend with Paecilomyces variotii]]> The increased consumption of plastics in the world has been a subject of great concern and special attention by the scientific community. The aim is to promote development of materials that are biodegradable in a shorter time upon disposal in the environment. The most used synthetic plastics are difficult to biodegrade because they are made of long hydrocarbon chains, such as polyethylene (PE), polypropylene (PP), poly(vinyl chloride) (PVC), which are hydrophobic and resistant to the action of microbial enzymes. The use of alternative materials (natural polyesters) can minimize the harm to dumps and landfills upon their disposal, because they are susceptible to the action of microorganisms. In this study we evaluated the biodegradation/biodeterioration of PHBV (poly(3-hydroxybutyrate-co-hydroxyvalerate) films, LDPE (low density polyethylene) and the blend of LDPE/PHBV (70/30) by the fungus Paecilomyces variotii, using different methods: optical microscopy (OM), scanning electronic microscopy (SEM) and Fourier Transform Infrared spectroscopy (FTIR). <![CDATA[The use of lysozyme to prepare biologically active chitooligomers]]> Two types of crustacean commercial chitosans (CS1, CS2) were dissolved in lactic acid solutions, hydrolysed by lysozyme and finally fractioned by methanol solutions into two parts containing chito-oligomers (CS-O1, CS-O2). The antioxidant power and antimicrobial properties of both fractions were studied and compared with non-hydrolysed CS1 and CS2. The antioxidant properties were determined by the ferric ion reducing antioxidant power (FRAP) method while the bioactive properties were evaluated against a strain of Listeria monocytogenes. CS-O obtained from the solid fraction of the chito-oligomers solid fractions treated with 90% methanol showed the highest reducing power. Microbiological tests showed that CS-O exhibit higher antilisterial activity than CS. <![CDATA[Low Density Polyethylene (LDPE) blends based on Poly(3-Hydroxi-Butyrate) (PHB) and Guar Gum (GG) biodegradable polymers]]> LDPE blends based on PHB and GG biodegradable polymers were prepared by melt mixing in a twin screw extruder. The mechanical properties of the materials were evaluated. Preliminary information about the biodegradation behavior of the specimens was obtained by visual observation of samples removed from the simulated soil in 90 days. The results indicated that LDPE/PHB blends may be used for designing LDPE based materials with increased susceptibility to degradation, if elongation at break and impact properties are not determinant factors of their performance. LDPE based materials on GG present values of flexural and mechanical strength lower than those of LDPE/PHB blends. LDPE/PHB/GG blends exhibit unsatisfactory properties. Apparently, the effect of addition of GG to LDPE on the biodegradation behavior of LDPE/GG blends was less intense than the effect caused by addition of PHB to the blends. Similar observation has occurred with the partial replacement of GG by PHB in the ternary blends. <![CDATA[Evaluating the mechanical properties of E-Glass fiber/carbon fiber reinforced interpenetrating polymer networks]]> A series of vinyl ester and polyurethane interpenetrating polymer networks were prepared by changing the component ratios of VER (Vinyl ester) and PU (Polyurethane) and the polymerization process was confirmed with Fourier Transform infrared spectroscopy. IPN (Inter Penetrating Polymer Network - VER/PU) reinforced Glass and carbon fiber composite laminates were made using the Hand lay up technique. The Mechanical properties of the E-glass and carbon fiber specimens were compared from tests including Tensile, Compressive, Flexural, ILSS (Inter Laminar Shear Strength), Impact &amp; Head Deflection Test (HDT). The IPN Reinforced Carbon fiber specimen showed better results in all the tests than E-Glass fibre reinforced IPN laminate with same thickness of the specimen, according to ASTM standards. It was found that the combination of 60%VER and 40%PU IPN exhibits better impact strength and maximum elongation at break, but at the slight expense of mechanical properties such as tensile, compressive, flexural, ILSS properties. The morphology of the unreinforced and reinforced composites was analyzed with help of scanning electron microscopy. <![CDATA[Synthesis and film properties of chitosan and whey]]> El quitosano es un polímero natural derivado de la desacetilación de la quitina con propiedades tales como biocompatibilidad, biodegradabilidad y formación de filmes, de gran aplicación en el campo de la industria, alimentación y medicina. Los filmes a base de quitosano y lactosuero fueron preparados teniendo en cuenta la concentración de la solución de quitosano (1; 1.5 y 2% v/v), la relación en volumen de lactosuero (4:20, 6:20 y 8:20 v/v) y el tiempo de secado de 4.5, 5.0 y 5.5 horas. Estas condiciones de preparación se optimizaron empleando la metodología de la superficie de respuesta. La quitina extraída previamente de los exoesqueletos de camarón fue tratada con una solución acuosa de NaOH al 50% en masa, hasta obtener quitosano con un grado de desacetilación de 80.72%. El quitosano obtenido fue disuelto en ácido acético para obtener las distintas soluciones que posteriormente fueron combinadas con lactosuero. Los filmes sintetizados fueron caracterizados por espectroscopia en la región del infrarrojo y se evaluaron los parámetros de espesor, densidad, solubilidad, transparencia, hinchamiento y degradación. La degradación de los filmes quitosano/lactosuero disminuye con el aumento de la concentración de quitosano. El porcentaje de hinchamiento de los filmes se ve afectado por las proporciones de lactosuero. La concentración de lactosuero incide en el aumento del espesor y la densidad de los filmes.<hr/>Chitosan is a natural polymer derived from deacetylation of chitin, which exhibits properties such as biocompatibility, biodegradability and may form films, being applied in the food industry and medicine. Degradable chitosan films were prepared from chitosan extracted from shrimp shells and whey, using different concentrations of chitosan solution (1, 1.5, and 2% v/v), with (4:20, 6:20 and 8:20 v/v) whey proportions, for 4.5, 5.0 and 5.5 h at 60°C. Chitin extracted previously from shrimp shells was treated with a solution of 50% of NaOH to obtain chitosan with 80.72% deacetylation degree. This chitosan was dissolved in 1% (v/v) acetic acid, leading to the solutions that were then combined with whey. The films were characterized with infrared spectroscopy, and had thickness, density, solubility, transparency, swelling and degradability evaluated. The solubility and degradability of chitosan/whey films decreased with increasing chitosan concentration. The proportion of lactic serum affects the film swelling, and the thickness and density increased with whey relative concentration. <![CDATA[Materiais compósitos a base de fibras da cana-de-açúcar e polímeros reciclados obtidos através da técnica de extrusão]]> Os compósitos obtidos a partir de fibras de bagaço de cana-de-açúcar e polímeros reciclados (PEAD e PS) foram obtidos através da técnica de extrusão a quente e o planejamento fatorial possibilitou a análise dos fatores que influenciam a obtenção dos compósitos. As amostras contendo polietileno de alta densidade (PEAD), tanto com 30% como com 50% de fibras, mostraram-se mais impermeáveis na presença da água que as amostras obtidas com poliestireno (PS). Os compósitos obtidos com PEAD apresentaram resistência à flexão com uma tensão máxima aplicada de 45 MPa (50% de fibra) e de 39MPa (30% de fibra), esses valores são maiores que os apresentados pelos materiais obtidos com PS. Compósitos de polímeros e madeira (com 60% de serragem) apresenta resistência à flexão de aproximadamente 32 MPa e o MDF apresenta uma resistência à flexão de 36 MPa, esses resultados mostram que os compósitos obtidos possuem uma boa resistência a flexão.<hr/>The composites were obtained through hot extrusion of a mixture of recycled polymers (HDPE and PS) and sugar cane fibers. The extrusion technique resulted in homogeneous materials with good mechanical properties and the factorial design allowed the analysis of the factors that influence the process. Samples containing high density polyethylene (HDPE), both with 30% and 50% fibers were shown to be significantly more effective compared to polystyrene (PS) aiming at impermeability in the presence of water. The composites obtained with HDPE showed bending resistance, with 45 MPa (50% fiber) and 39MPa (30% fiber) maximum applied stress, these values are higher than those presented in the composites obtained with PS. Composites of polymers and wood (60% of sawdust) provide bending resistance of about 32 MPa and MDF has a bending resistance of 36 MPa, these results show that the compounds obtained have a good bending resistance. <![CDATA[Estudo da miscibilidade das misturas de PHB e PLA, com um PHB de alta polidispersividade]]> Neste trabalho, foi estudada a miscibilidade de misturas de um PHB constituído de frações de alta e baixa massa molar com um PLA de alta massa molar. Os materiais extrudados foram analisados pelas técnicas de calorimetria exploratória diferencial (DSC), espectroscopia dielétrica (DE) e análises dinâmico-mecânicas (DMA). A partir dos resultados observou-se o distinto comportamento cristalino das frações de PHB, assim como a miscibilidade parcial do PLA com o PHB de baixa massa molar.<hr/>In this work, the miscibility of a PHB formed by high and low molar mass fractions and a low molar mass PLA was studied. The extruded materials were analyzed by differential scanning calorimetry (DSC), dielectric spectroscopy (DS) and dynamic mechanical analysis (DMA). From these results, it was observed an unique behavior from the PHB fractions, and the partial miscibility of PLA onto low molar mass PHB. <![CDATA[Estudo comparativo da influência da razão de sopro nas propriedades de filmes tubulares de PEBD e PEAD]]> O objetivo deste trabalho é avaliar a influência do tipo de poliolefina e da razão de sopro (RS) nas propriedades físicas e térmicas de filmes produzidos em processo de extrusão tubular. No processamento foram utilizados um polietileno de baixa densidade (PEBD) e um polietileno de alta densidade (PEAD) transformados numa linha de extrusão de filme tubular com três RS de 1,5:1; 2,5:1 e 3,5:1. Os resultados das caracterizações físicas dos filmes mostraram maior variação de espessura no perímetro dos filmes tubulares de PEAD, quando comparados aos de PEBD. O aumento da RS causou uma diminuição de amplitude desta variação nos filmes tubulares de PEBD e diferenças nas propriedades ópticas. O coeficiente de atrito (COF) dos filmes foi menor para o PEAD e não teve variação significativa com o aumento da RS utilizada. Em relação às propriedades mecânicas, os filmes de PEAD apresentaram maior resistência à tração e menores valores de deformação no ponto de escoamento em ambas as direções. As RS maiores apresentaram similaridade nas tensões e nas deformações entre as direções da máquina (DM) e transversal (DT). A RS ideal, constatada para os filmes processados com PEBD, é 2,5:1 e com PEAD, é 3,5:1. Os filmes de PEAD apresentaram opacidade maior e menor brilho, quando comparados aos filmes de PEBD. Os resultados comprovaram valores conhecidos na literatura, entretanto introduziu-se uma inovação neste estudo: a utilização da técnica termográfica digital portátil, que permite visualizar, de maneira instantânea (on-line), as variações de temperatura no perímetro do balão, na zona de névoa (região de cristalização ou solidificação do filme).<hr/>The purpose of this study is to evaluate the influence of the polyolefin type and the blow-up ratio (BUR) on the thermal physical properties of films produced in a blown film extrusion process. It was used low density polyethylene (LDPE) and high density polyethylene (HDPE) processed in a blown film extrusion line at three BUR of: 1.5:1; 2.5:1 and 3.5:1. The results of physical characterization on these films demonstrated that the increase in the BUR shows a higher thickness variation in the perimeter of tubular films and, therefore, optical properties variation. The coefficient of friction (COF) of the films was smaller for HDPE and did not have significant variation with the increase in the BUR applied. Regarding mechanical properties, HDPE films showed higher tensile strength and lower strain values in the yield point, in both directions. The largest BUR showed higher similarity of the tensions and strains between the machine direction (MD) and transverse direction (TD). The ideal BUR observed for films processed with LDPE is 2.5:1, for HDPE this number is higher and close to 3.5:1. The HDPE films showed more opacities and less brightness when compared to LDPE films. The results prove well known values in the literature, however, there was an innovation introduced in this study which is the use of the portable digital thermo graphic technique that allows the instantaneous visualization (on-line) of the temperature variation in the bubble perimeter in the frost line (crystallization or solidification area of the film). <![CDATA[Estudo das propriedades elétricas e térmicas de compósitos nanoestruturados de poli(sulfeto de fenileno) reforçados com nanotubos de carbono]]> Neste trabalho o comportamento de cristalização e a condutividade elétrica de compósitos nanoestruturados de poli(sulfeto de fenileno) reforçado com nanotubos de carbono de paredes múltiplas obtidos através da técnica de mistura em fusão foram estudados. A incorporação do nanoreforço na matriz polimérica foi responsável por um aumento da cristalinidade devido ao fenômeno de nucleação heterogênea. A condutividade elétrica do PPS apresentou um aumento de 11 ordens de magnitude quando 2,0 m/m% de MWCNT foram adicionados a matriz polimérica. Além disso, o limite de percolação elétrica encontrado para este sistema foi de 1,4 m/m% de MWCNT, revelando a formação de uma rede condutiva tridimensional no interior da matriz polimérica.<hr/>In this work, the crystallization behavior and electrical conductivity of multiwalled carbon nanotubes reinforced poly (phenylene sulfide) nanostructured composites obtained by melt mixing were investigated. The incorporation of nanofiller in polymeric matrix was responsible for an increase in crystallinity due heterogeneous nucleation phenomenon. The electrical conductivity of PPS showed an increase by 11 orders of magnitude when 2.0 wt% of MWCNT was considered. Moreover, the electrical percolation threshold found on this system was 1.4 wt%, suggesting the formation of three-dimensional conductive network within the polymeric matrix. <![CDATA[Influência de estabilizantes na degradação foto-oxidativa de filmes de compósitos de SWy-1/poli(óxido de etileno)]]> Compósitos de poli(óxido de etileno) (PEO) com argila montmorilonita SWy-1 e estabilizantes (2-hidroxibenzofenona e tinuvin 770) foram preparados pelo método de intercalação em solução. Os filmes obtidos foram expostos a irradiação UV, e os produtos da fotodegradação foram monitorados por FTIR (Fourier Transform Infrared Spectroscopy, ou Espectroscopia no infravermelho por transformada de Fourier) e SEC (Size Exclusion Chromatography, ou cromatografia de exclusão por tamanho). O PEO puro apresentou maior coeficiente de degradação, kd, comparado com as demais amostras. O sistema que apresentou o menor valor para o coeficiente de degradação (kd = 1,9×10–6 mol g–1 h-1) foi o compósito de PEO/5%SWy-1 com 0,25% de tinuvin 770. Nesse caso, a estabilização da matriz de PEO pode ser atribuída à argila juntamente com o tinuvin 770. A argila dispersa e absorve a irradiação UV, e o tinuvin age como estabilizante do tipo HALS (do inglês hindered amine light stabilizer, ou estabilizantes à luz tipo aminas impedidas).<hr/>Poly(ethylene oxide) (PEO) with SWy-1 montmorillonite and stabilizers (2-hydroxybenzophenone and tinuvin 770) composites were prepared by intercalation in solution method. The films of the composites were exposed to UV irradiation. The photodegradation products were monitored by FTIR (Fourier Transform Infrared Spectroscopy) and SEC (Size Exclusion Chromatography) method. The PEO pure showed higher degradation rate coefficients, kd , compared to the others samples. The system that showed the lowest value for the degradation rate coefficients (kd = 1.9×10–6 mol g –1 h –1) was the PEO/SWy-1 5% composite with 0.25% of tinuvin 770. In this case, the stabilization of the PEO matrix can be attributed to clay associated with tinuvin 770. The clay scatters and absorbs UV irradiation and tinuvin acts as a stabilizer of the HALS (hindered amine light stabilizers) kind. <![CDATA[Análise numérica da pressão de ruptura de tubos à base de borracha e cordonéis poliméricos]]> Este trabalho tem como objetivo estudar o efeito de cordonéis de poliéster, poliamida, poliaramida e híbrido poliamida/poliaramida como reforço de elastômeros utilizados na fabricação de mangotes. O comportamento do tubo elastomérico reforçado com cordonéis sob pressão interna foi simulado com análise por elementos finitos (FEA) utilizando-se elementos chamados reinforcement bars. Foram realizados ensaios para se obter as propriedades em tração dos cordonéis para alimentar o modelo. O cordonel de poliaramida apresentou a maior tensão de ruptura, o de poliamida maior deformação na ruptura, e o híbrido apresentou valores intermediários. O critério de falha adotado para o tubo consistiu na análise do nível de carga no cordonel. Foram avaliadas, principalmente, a pressão e a deformação de ruptura do tubo elastomérico simulado frente à variação do ângulo de orientação dos cordonéis. Os resultados mostraram que ângulos próximos a 55° tornam o tubo mais resistente porém menos rígido no sentido longitudinal.<hr/>This work investigates the effect of polyamide, polyester, polyaramid and hybrid (polyamide and polyaramid) cords as reinforcement for elastomers used in the production of marine hoses. The behavior of the elastomeric pipe reinforced with these cords under internal pressure was simulated with finite element analysis (FEA) using elements called reinforcement bars. To obtain input data for the model, tensile properties of the cords were evaluated. The polyaramid cord showed the highest ultimate stress, the polyamide the largest elongation at break, and the hybrid cord showed intermediate values. The failure criterion adopted for the pipe consisted of examining the allowable force in the cord. The analyses focused on the variation of pressure and strain at burst of the pipe with the orientation angle of the cords along the elastomeric tube. The results showed that angles close to 55° yielded stronger pipes but less rigid in their longitudinal direction. <![CDATA[Preparação e avaliação de nanocompósitos de poliestireno - hidróxido duplo lamelar HDL de ZnAl – organofuncionalizado com laurato/palmitato]]> Este trabalho descreve a síntese e caracterização de nanocompósitos de poliestireno (PS) e hidróxido duplo lamelar (HDL) formado pelos cátions de ZnAl via polimerização in situ. O HDL utilizado neste trabalho foi modificado com uma mistura de dois ânions, laurato e palmitato. Para caracterização da estrutura e morfologia dos nanocompósitos sintetizados, foram realizadas análises por difração de raios X (DRX) e microscopia eletrônica de transmissão (MET). As caracterizações térmicas, mecânicas e de flamabilidade foram realizadas via análise termogravimétrica (TGA), ensaio de flexão e ensaio de flamabilidade, respectivamente. Os resultados obtidos neste trabalho sugerem que os nanocompósitos sintetizados possuem, de uma forma geral, uma morfologia intercalada/esfoliada com melhoras em suas propriedades térmicas e mecânicas, quando comparados com o PS puro. Entretanto, não foi observado melhora na propriedade de flamabilidade.<hr/>This work describes the synthesis and characterization of polystyrene (PS) and layered double hydroxide (LDH) nanocomposites formed by ZnAl cations via in situ polymerization. The LDH used in this study was modified with a mixture of two anions: laurate and palmitate. The characterization of structure and morphology for the synthesized nanocomposites was developed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal, mechanical and flammability characterizations properties were carried out via thermogravimetric analysis (TGA), bending test and flammability test, respectively. The results suggest that the nanocomposites have in general intercalated/exfoliated morphology with improvements in thermal and mechanical properties compared to the neat PS. However no significant improvement was observed on the flammability property. <![CDATA[Determinação e análise de parâmetros para o desenvolvimento de um processo de decoração de peças plásticas através da injeção sobre tecido]]> O processo de injeção sobre tecidos, utilizado na indústria automotiva, é caracterizado por modificações no processo de injeção convencional e possibilita o desenvolvimento de novos produtos com características diferenciadas. Devido às dificuldades de processamento, e tendo em vista as necessidades de adaptação dos parâmetros de injeção quando essa é feita sobre tecidos, foi desenvolvida uma metodologia de determinação e análise de parâmetros de processo que possibilitaram o desenvolvimento desta técnica. Os testes foram realizados inicialmente em uma indústria produtora de peças automotivas e a metodologia adotada foi repetida em uma instituição de ensino. Verificou-se, então, que controlando os parâmetros de injeção e fechamento do molde, foi possível obter, em ambos os casos, peças conforme as especificações de qualidade requeridas.<hr/>The injection molding process on fabrics used in the automotive industry is characterized by changes in conventional injection molding process and enables the development of new products with different characteristics. Due to processing difficulties, and considering the need for adaptation of injection parameters when it is done on fabrics, a method for determining and analyzing the process parameters was developed so that technique could be put into practice. Initially tests were conducted in an industry producing automotive parts and the method adopted was replicated in an educational institution. Then, it has been found, that through controlling the injection and mold closing parameters, it was possible to obtain, parts conforming to quality specifications required in both cases.