Influence of Stacking Sequence on the Mechanical and Dynamic Mechanical Properties of Cotton/Glass Fiber Reinforced Polyester Composites

This study focuses on the use of waste cotton fiber from the textile industry to produce composites with unsaturated polyester and to evaluate the performance of glass (G) / cotton (C) fiber laminates, particularly their mechanical and dynamic mechanical properties. Distinct stacking sequences were studied but the overall fiber content was kept constant. In general, hybrid laminates exhibited intermediate mechanical properties compared to those of the pure laminates, and optimum performance was obtained when the glass fiber mats were placed on the surfaces of the composite. Furthermore, some hybrid laminates exhibited superior dynamic mechanical performance, even compared to the pure glass laminate. Lower tan delta peak height (related to better fiber-matrix interaction) values and higher Tg were reported for the [C/G/Ḡ]s and [G/C/C]s samples which, together with the [G/C/Ḡ]s sample, exhibited the best results for reinforcement effectiveness and loss modulus peak height. Therefore, it is found possible to partially replace the glass fiber by waste cotton fiber considering that the final product may be optimized for mechanical property, which requires glass fiber at the surface of the laminate, or for dynamic mechanical properties, that allows higher cotton fiber content

Preparation and characterization of ramie-glass fiber reinforced polymer matrix hybrid composites

The use of ramie fibers as reinforcement in hybrid composites is justified considering their satisfactory mechanical properties if compared with other natural fibers. This study aims to verify changes in chemical composition and thermal stability of the ramie fibers after washing with distilled water. One additional goal is to study glass fiber and washed ramie fiber composites focusing on the effect of varying both the fiber length (25, 35, 45 and 55 mm) and the fiber composition. The overall fiber loading was maintained constant (21 vol.%). Based on the results obtained, the washed ramie fiber may be considered as an alternative for the production of these composites. The higher flexural strength presented being observed for 45 mm fiber length composite, although this difference is not significant for lower glass fiber volume fractions: (0:100) and (25:75). Also, by increasing the relative volume fraction of glass fiber until an upper limit of 75%, higher flexural and impact properties were obtained

Materials produced from plant biomass: part II: evaluation of crystallinity and degradation kinetics of cellulose

In this study Eucalyptus grandis (CEG) and Pinus taeda (CPT) cellulose fibers obtained from kraft and sulfite pulping process, respectively, were characterized using Fourier transform infrared (FTIR) spectroscopy and thermogravimetry (TGA). The degradation kinetic parameters were determined by TGA using Coats and Redfern method. FTIR results showed that CPT presented a more ordered structure with higher crystallinity than CEG. Thermogravimetric results showed that CPT had a higher thermal stability than CEG. The kinetic results revel that for CEG the degradation mechanism occurs mainly by random nucleation, although phase boundary controlled reactions also occurs while for CPT the degradation process is more related with phase boundary controlled reactions. Results demonstrated that differences between thermal stability and degradation mechanisms might be associated with differences in the cellulose crystalline structure probably caused by different pulping processes used for obtaining the cellulose fibers

Estudo do reprocessamento de polietileno de baixa densidade (PEBD) reciclado do processamento de extrusão de filmes tubulares Study of the reprocessing of low density polyethylene (LDPE) recycled from extruded blown films

O mercado de reciclagem para os polímeros termoplásticos encontra-se atualmente em acentuada ascensão. Os materiais reciclados são vistos como materiais de propriedades inferiores em relação ao material virgem. O presente trabalho avaliou as características viscoelásticas e térmicas do polietileno de baixa densidade (PEBD) reciclado. As amostras foram reprocessadas até dez vezes em condições extremas de processamento (300 °C/80 rpm) em uma extrusora monorosca, a fim de avaliar modificações estruturais nas suas propriedades. Foram realizadas análises de reometria oscilatória de placas paralelas e calorimetria exploratória de varredura (DSC). A partir das análises de reometria oscilatória foram calculados espectros de relaxação e retardação pelo programa de regularização não-linear (NLREG) e através das análises de DSC no primeiro aquecimento foram calculados os parâmetros cinéticos pelos métodos de Avrami e Freeman-Carroll. Os resultados do estudo reológico demonstraram que as amostras reprocessadas acima de quatro vezes apresentaram aumento da viscosidade complexa e dos módulos de armazenamento e perda, além de fenômenos de relaxação e retardação mais largos. Entretanto, os termogramas de DSC e os parâmetros cinéticos de fusão demonstraram que o PEBD estudado manteve sua estabilidade térmica, independentemente da modificação de suas características viscoelásticas.<br>The recycling market of thermoplastic polymers is currently in a sharp increase. Recycled materials are regarded as having inferior properties compared to the virgin material. Here we investigated the viscoelastic and thermal properties of the recycled low density polyethylene (LDPE). The samples were reprocessed up to ten times under extreme processing conditions (300 °C/80 rpm) in a single screw extruder in order to evaluate structural changes in their properties. Analyses were performed in an oscillatory rheometer with parallel plates and in a differential scanning calorimeter (DSC). From the analysis of the oscillatory rheometry, relaxation and retardation spectra were obtained upon applying a non-linear adjustment using a computational program (NLREG), while the kinetics parameters were estimated from the results of the first DSC heating using the Avrami and Freeman-Carroll methods. From the rheological study we inferred that the samples reprocessed more than four times had an increase in complex viscosity, storage and loss moduli, also displaying wider relaxation and retardation phenomena. However, the DSC thermograms and the melt kinetic parameters showed that the LDPE studied maintained their thermal stability, regardless of the modification in their viscoelastic properties

Caracterização de resíduos de copolímeros de etileno-acetato de vinila - EVA Characterization of ethylene-vinyl acetate copolymer (EVA) residues

O poli[(etileno)-co-(acetato de vinila)] (EVA) possui grande aplicação na indústria calçadista, sendo utilizado na confecção de placas expandidas para posterior corte de palmilhas e entressolas. Estudos realizados na região sul do Brasil mostraram que os resíduos gerados pela indústria calçadista foram superiores a 200 toneladas/mês em 2001, sendo o maior volume oriundo de recortes de placas expandidas. Por isso, o objetivo deste trabalho foi o de caracterizar resíduos de EVA de chapas expandidas, visando à reciclagem mecânica desse material. Análises em MEV demonstraram que o resíduo de EVA apresenta uma morfologia microcelular que é destruída após o processo de moagem. O resíduo de EVA moído apresenta duas fases, uma reticulada (matriz) e uma não-reticulada (dispersa). O resíduo de EVA apresentou teor de gel de aproximadamente 75% em massa, cerca de 20% em massa de acetato de vinila (VAc), fora processado a partir de EVA com aproximadamente 28% de VAc e possui teor de carga inorgânica de 20% em massa, segundo análises em TGA. O EVA resíduo apresentou maiores valores de módulo elástico e de dureza, e menores valores de elongação na ruptura e de resistência ao impacto Izod. O custo energético da moagem do resíduo de EVA foi calculado como sendo inferior a 5% do valor do EVA virgem.<br>Poly[(ethylene)-co-(vinyl acetate)] (EVA) has large application in the shoes industries, especially as expanded sheets, in order to produce insoles and innersoles. Studies carried out in the south region of Brazil in 2001 have demonstrated that the residues generated by shoes industries were higher than 200 ton/month, the major part of which is composed by EVA expanded sheets. With this in mind, the objective of this work was to characterize the residues of expanded EVA and also to analyze the milling cost in order to make the recycling possible. The EVA residues presented originally a microcellular structure, which was destroyed after milling, according to SEM analysis. The EVA powder was found to be composed by two phases: a crosslinked phase (75wt%) and a soluble one (25wt%). The VAc content in EVA residues was found to be around 20wt% and it is believed that the EVA had originally ca. 28wt% of VAc before the crosslinking process, according to the TG analysis. Besides, it was found that the crosslinked structure of EVA residues make them stiffer than virgin EVA used for comparison, according to mechanical tests. The milling cost was estimated to be less than 5% compared to the virgin EVA

Effect of clay silylation on curing and mechanical and thermal properties of unsaturated polyester/montmorillonite nanocomposites

This workfocusesonthechemicalmodification ofmontmorillonite(MMT)(Cloisites Na) withcompa- tible silanes,vinyltriethoxysilane(CVTES)and γ-methacryloxypropyltrimethoxysilane(CMPS)inorderto preventagglomerationandtoimprovemontmorilloniteinteractionwithanunsaturatedpolyesterresin matrix seekingtoachieveamultifunctionalcomposite.Claysweredispersedintheresinbymechanical stirring andsonicationandthenanocompositeswerepreparedbyresintransferintoamold.Theme- chanical, morphological,thermaland flammability propertiesoftheobtainedcompositeswerecom- pared withthosepreparedusingcommercialCloisites 30B (C30B)andCloisites 15A(C15A)clays.Ad- vantagesofusingsilane-modified clays(CVTESandCMPS)ascomparedwithorganic-modified clays (C30B andC15A)canbesummarizedassimilar flexuralstrengthandlinearburningratebuthigher storagemodulusandimprovedadhesiontothepolyesterresinwithconsequenthigherthermalde- flection temperatureandreinforcementeffectivenessathighertemperatures.However,organicmodified claysshowedbetterdispersion(tendencytoexfoliate)andconsequentlydelayedthermalvolatilization due totheclaybarriereffect