201,736 research outputs found
Estudo de variáveis que modificam a cinética de cristalização do PLA em blendas PLA/PVAL e PLA-g-MA/PVAL
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Química, Florianópolis, 2015.A busca por materiais biodegradáveis tem sido intensificada nos últimos anos com o objetivo de reduzir impactos ambientais. O poli(vinil álcool) (PVAL) e o poli(ácido lático) (PLA) são polímeros biodegradáveis amplamente produzidos. Uma alternativa para a obtenção de um material com propriedades diferentes dos polímeros puros é a preparação de blendas poliméricas. O presente trabalho avaliou o efeito do enxerto de anidrido maleico (MA) na cadeia polimérica do PLA na morfologia de blendas PLA-g-MA/PVAL, em comparação às blendas PLA/PVAL, bem como a influência do processamento, do enxerto e da presença de PVAL na cinética de cristalização isotérmica do PLA. A reação de enxerto foi realizada em reômetro de torque e o produto caracterizado por espectroscopia de UV-Vis, sendo ácido maleico o grupo funcional enxertado. As blendas PLA/PVAL e PLA-g-MA/PVAL foram preparadas por extrusão, em diferentes composições. Uma análise morfológica comparativa dos sistemas PLA/PVAL e PLA-g-MA/PVAL mostrou uma mudança na forma dos domínios de PVAL, de domínios esféricos para domínios fibrilares de dispersão regular nas blendas com componente enxertado, sugerindo uma estabilização da interface entre os dois polímeros. Efeitos significativos do processamento na cinética de cristalização, com base nos parâmetros cinéticos de Avrami, foram associados à diminuição do emaranhamento das cadeias, devido ao cisalhamento dos materiais no processamento. Os resultados mostraram que o PVAL pode atuar como agente de nucleação e que a taxa de cristalização aumentou com a área superficial dos domínios. Em quantidades elevadas, o PVAL atuou inibindo o efeito causado pelo processamento. O enxerto também apresentou influência no mecanismo de nucleação, bem como na forma dos cristais, que passaram da forma esferulítica (PLA) para hexagonal (PLA-g-MA).Abstract : The search for biodegradable materials has been intensified in recent years in order to reduce environmental impacts. Poly(vinyl alcohol) (PVAL) and poly(lactic acid) (PLA) are widely produced biodegradable polymers. An alternative to materials with intermediate properties in relation to neat polymers is the formulation of polymer blends. The present study evaluated the effect of maleic anhydride (MA) graft on the PLA polymeric chain in the morphology of PLA-g-MA/PVAL blends compared to PLA/PVAL blends, as well as the effect of processing, graft, and the presence of PVAL in the isothermal crystallization kinetics of PLA. The graft reaction was performed in a torque rheometer, the product was characterized by UV-Vis spectroscopy, and the maleic acid was the grafted functional group. Blends of PLA/PVAL and PLA-g-MA/PVAL were prepared through extrusion of the materials at different compositions. A comparative morphological analysis of the systems PLA/PVAL and PLA-g-MA/PVAL shows that there was a change in the form of PVAL domains, from spherical to fibrilar domains of regular dispersion in blends with a grafted component, suggesting some interface stabilization between the polymers. Significant processing effects in the crystallization kinetics, based on the Avrami kinetic parameters, were associated to a reduction of chain entanglement due to a high shearing of the materials in the processing. The results shows that the PVAL can act as a nucleating agent, and the crystallization rate increases with the surface area of the PVAL domains. PVAL acted by inhibiting the processing effect in blends of high PVAL proportion. The graft also showed an influence on the nucleation mechanism, as the PLA-g-MA presented a hexagonal spherulitic shape (PLA)
Fiber association and network formation in PLA/lignocellulosic fiber composites.
No full textPLA composites were prepared in an internal mixer with a lignocellulosic fiber having relatively large aspect ratio. Fiber content changed between 0 and 60 vol% and the homogenized material was compression molded to 1 mm thick plates. The composites showed anomalous behavior above certain fiber content. Their modulus and especially their strength decreased drastically and modeling also proved the loss of reinforcement at large fiber contents. Micromechanical testing showed that the mechanism of deformation and failure changes at a critical fiber content. Microscopic analysis indi-cated the formation of a network purely from geometrical reasons. The inherent strength of the network is very small because of the weak forces acting among the fibers. This weak inherent strength makes the structure of the composites very sensitive to pro-cessing conditions, and decreases strength, reproducibility as well as reliability
Chicken Feather Fibre Mat/PLA Composites for Thermal Insulation
No full textIn order to add more economic value to chicken feather, a waste material of the poultry industry, it has been researched to incorporate chicken feather fibre (CFF) into resin to produce value-added composites. In the present research, chicken feather fibre was separated from the rachises and used to produce fibre mats. Then fibre mats were incorporated into polylactic acid (PLA) to make composites with low thermal conductivity. The procedure for making chicken feather fibre mat using an automatic dynamic sheet former was explored. Two different composite fabrication methods were investigated. One involved fabricate composite samples by hot pressing chicken feather fibre mats with PLA sheet. The other involved making composite specimens by hot pressing PLA powder and chicken feather fibre mats. A decrease in tensile strength compared to PLA had been expected before composite specimen fabricating according to previous research and so alkali treated fibre mats were used to improve tensile strength of composites.
It was concluded that chicken feather fibre mats with uniform quality could be made by controlling the jet-to-spin ratio and water wall thickness of the dynamic sheet former cylinder. Stable mat/PLA composites could be fabricated by hot pressing chicken feather fibre mats with PLA powder. Results from tensile testing indicated that alkali treatment could improve tensile strength to a small degree. SEM image analysis revealed that poor interfacial bonding between fibre barbs and PLA matrix had occurred. Thermal conductivity testing demonstrated improved thermal insulation with addition of CFF to PLA
Improving interfacial adhesion in pla/wood biocomposites
No full textTwo reactive coupling agents, N,N-(1,3-phenylene dimaleiimide) (BMI) and 1,1-(methylenedi-4,1-phenylene)bismaleimide (DBMI) were used to improve interfacial adhesion in PLA/wood composites. First the effect of the coupling agents was established in a series of experiments in which the amount of coupling agent changed at constant wood content, and then the effect of coupling was determined at various wood loadings (0-60 vol%). Composites were homogenized in an internal mixer and compression molded to plates. Tensile properties were determined and micromechanical deformations were studied by acoustic emission measurements. The two compounds improved the properties of the composites. Stiffness, strength and deformability increased simultaneously supplying sufficient proof for coupling. Because of the flexibility of the molecule, DBMI is a more efficient coupling agent in the studied composites than BMI. However, the effect of coupling is small, because only a few very large particles debond under the effect of external load. Smaller particles adhere strongly to the matrix even without coupling proving that interfacial adhesion is strong in PLA/wood composites
La primavera republicana del 1931 al Pla d'Urgell
No full textLes eleccions municipals del 12 d'abril de 1931 atorgaren la majoria al republicanisme d'esquerres i conduïren al canvi de règim. A les comarques ponentines, com arreu del país, es visqué amb entusiasme la proclamació de la República el 14 i el 15 d'abril. Aquesta ponència, centrada en l'actual comarca del Pla d'Urgell, analitza: 1) l'impacte de l'adveniment de la República en els seus pobles; 2) la constitució dels ajuntaments republicans entre el 15 i el 17 d'abril; 3) el qüestionament de les eleccions que es produí en els municipis de Castellnou de Seana, Linyola i Mollerussa; 4) la posició dels nous alcaldes envers la República naixent; 5) els problemes que es consideraven heretats de la monarquia, i 6) la incidència que tingué el macianisme en el teixit sociopolític de la comarca. Com a corol·lari, proposa una aproximació a la pervivència de la primavera republicana de 1931en la memòria popular dels pladurgellencs.Municipal elections held on the 12th April 1931 revealed majoritarian support to left-wing republicanism and a regime change took place. The proclamation of the Second Spanish Republic (14th and 15th April 1931) was received with entusiasm both in the Ponent territories and the whole of Catalonia. This paper, focused in the current Pla d'Urgell county, analyses: 1) the impact of the Second Spanish Republic's proclamation in the Pla d'Urgell villages; 2) the formation of republican town councils between the 15th and the 17th April; 3) the questioning of the elections which took place in Castellnou de Seana, Linyola, and Mollerussa; 4) the new mayors' stance regarding the rising republic; 5) the problems that were considered as inherited from the previous monarchy, and 6) the impact that macianism had on Pla d'Urgell's sociopolitic networks. Finally, an approach to the survival of 1931's republican spring in local memory will be provided
PLA/WOOD BIOCOMPOSITES: IMPROVING COMPOSITE STRENGTH BY CHEMICAL TREATMENT OF THE FIBERS
No full textA resol type phenolic resin was prepared for the impregnation of wood particles used for the reinforcement of PLA. A preliminary study showed that the resin penetrates wood with rates depending on the concentration of the solution and on temperature. Treatment with a solution of 1 wt% resin resulted in a considerable increase of composite strength and decrease of water absorption. Composite strength improved as a result of increased inherent strength of the wood, but interfacial adhesion might be modified as well. When wood was treated with resin solutions of larger concentrations, the strength of the composites decreased, first slightly, then drastically to a very small value. A larger amount of resin results in a thick coating on wood with inferior mechanical properties. At large resin contents the mechanism of deformation changes; the thick coating breaks very easily leading to the catastrophic failure of the composites at very small loads
TEM images of Abam-PLA nanoparticles (a) and Abam-PLA-Tannin nanoparticles (b).
No full textTEM images of Abam-PLA nanoparticles (a) and Abam-PLA-Tannin nanoparticles (b).</p
Interactions, structure and properties in poly(lactic acid)/thermoplastic polymer blends
No full textBlends were prepared from poly(lactic acid) (PLA) and three thermoplastics, polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Rheological and mechanical properties, structure and component interactions were determined by various methods. The results showed that the structure and properties of the blends cover a relatively wide range. All three blends have heterogeneous structure, but the size of the dispersed particles differs by an order of magnitude indicating dissimilar interactions for the corresponding pairs. Properties change accordingly, the blend containing the smallest dispersed particles has the largest tensile strength, while PLA/PS blends with the coarsest structure have the smallest. The latter blends are also very brittle. Component interactions were estimated by four different methods, the determination of the size of the dispersed particles, the calculation of the Flory-Huggins interaction parameter from solvent absorption, from solubility parameters, and by the quantitative evaluation of the composition dependence of tensile strength. All approaches led to the same result indicating strong interaction for the PLA/PMMA pair and weak for PLA and PS. A general correlation was established between interactions and the mechanical properties of the blends
Romance, nuevo, y curioso de la Princesa Ismenia, hermana del gran Turco Osman, en que se declara, y da cuenta, de la Embajada que embió Osman á nuestro Rey de España Felipe Segundo ; a respuesta que se le bolvió, y el fin desesperado que tuvo la Princesa Ismenia
No full textSe ha respetado la puntuación originalSegún la BNE, en el módulo de autoridades, Vicente Verdaguer dirigirá, en Barcelona, el taller de la viuda de Pla, su cuñada, a partir de 1809, como "Imprenta de la Viuda de Pla" hasta 1845 en la que la imprenta empieza a llamarse "Herederos de la Viuda de Pla
Preparação e caracterização de blendas de amido termoplástico com poli (ácido lático) enxertado com anidrido maleico
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Química, Florianópolis, 2014.A utilização de materiais biodegradáveis e de fonte renovável, em diferentes setores industriais e comerciais, está em crescente avanço pela necessidade da diminuição dos impactos ambientais gerados em parte pela utilização de materiais petroquímicos não biodegradáveis. Neste cenário, o amido se destaca por ser renovável, ter baixo curto de produção e ser biodegradável. Entretanto, o amido termoplástico (ATp) apresenta características físico-químicas e mecânicas que inviabilizam a sua utilização, tornando-se necessária a incorporação de componentes que promovam mudanças nesta propriedades. A incorporação de poli(ácido lático) (PLA) a matriz de ATp vem despertando interesse dos pesquisadores por suas propriedades mecânicas e de barreira ao vapor de água. Neste trabalho foram estudadas blendas de ATp/PLA enxertado ou não com anidrido maleico (AM). A reação de enxerto e a formação da blenda ocorreram em meio fundido por extrusão ou reometria. Dois diferentes procedimentos experimentais foram utilizados para obtenção das blendas de ATp/PLA: i) PLA previamente enxertado com AM e posterior mistura com ATp e ii) simultâneo enxerto do PLA e obtenção das blendas. O enxerto de AM à cadeia polimérica de PLA foi maior nas amostras produzidas em uma única etapa em relação à amostra produzida com prévio enxerto do PLA. Os laminados produzidos em uma única etapa apresentaram maior deformação e menor tensão na ruptura quando comparados aos laminados de ATp/PLA sem enxerto de AM. O laminado produzido da amostra obtida por reômetria com prévio enxerto apresentou a maior deformação e uma tensão na ruptura na mesma magnitude que os laminados sem processamento. No que se refere à morfologia, os laminados das blendas obtidos com o PLA modificado apresentaram adesividade na interface e redução dos domínios de PLA na matriz de ATp. Os laminados obtidos por reometria apresentaram uma menor permeabilidade ao vapor de água quando comparados aos laminados obtidos por extrusão. O PLA extraído das blendas produzidas no reômetro apresentou uma redução significativa na massa molar em relação ao PLA sem processamento indicando uma degradação do material. A blenda obtida por reometria com prévio enxerto do PLA foi o que apresentou melhores resultados em todas as propriedades estudadas, destacando-a para possível aplicação como bandejas para a indústria de alimentos.Abstract : The use of biodegradable materials and renewable resources, in different industrial and commercial sectors, has been remarkably growing since there is a need for reduction of environmental impacts caused by the use of non-biodegradable petrochemical materials. In this scenario, starch points outdue to the characteristics of biodegradability, renewability and low cost. Starch has physico-chemical and mechanical properties which prevent their use, incorporation of components that promote changes in the physico-chemical properties. The incorporation of poly(lactic acid) in thermoplastic starch matrix has been attracting interest of researchers due to its improved mechanical properties and as a barrier to water vapor. In this study, blends of TPS/PLA with or without grafted maleic anhydride (MA ) were studied. The graft reaction and the formation of the blends were cast by using extruder and torque rheometer. Two different experimental procedures were used in order to obtain blends of TPS/PLA: i) PLA was previously grafted with MA and then blends were formed with TPS and ii) simultaneously obtainment of graft PLA and the blends in a single step. The MA graft into the polymer chain PLA was higher in samples produced in one step than in sample produced with prior graft PLA. The laminates produced in a single step showed higher elongation and lower tensile strength when compared to TPS/PLA without graft MA. The laminate produced samples taken in a torque rheometer with previous graft had the highest elongation and tensile stress in the same magnitude as the laminates without modification. The laminates of the blends obtained with the modified PLA showed morphologies with reduced areas of PLA and continuity at the interface between the domains of TPS matrix and PLA. The laminates obtained using the rheometer had a lower water vapor permeability as compared to laminates obtained in the extruder. PLA extracted from blends produced in rheometer showed significant reduction in molecular weight indicating a degradation of the material. The laminate prepared in advance of the rheometer with graft PLA showed the best results in all studied properties, highlighting it for possible application as trays in food industry
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