a b s t r a c tThis work aimed to evaluate the effect of including different concentrations of bamboo nanofibrils on physical, mechanical, morphological and structural properties of nanocomposites from cassava starch and polyvinyl alcohol (PVA). Nanocomposites were prepared with blends of starch/PVA and nanofibrils of bamboo. Chemical pre-treatments and mechanical defibrillation were used to obtain the nanofibrils. The mixture containing 3% of starch and 4% of PVA in the proportion of 20/80 (starch/PVA) were chosen after preliminary testing. Atomic force microscopy (AFM) and transmission electronic microscopy (TEM) were used to characterize the bamboo nanofibrils. Microstructure of the nanocomposites was evaluated using scanning electron microscopy (SEM) and X-ray diffractrometry (XRD). Physical and mechanical properties were also evaluated. Results showed that pre-chemical treatments increased the content of the alpha-cellulose in bleached pulp by approximately 112% in relation to the native fiber. Increasing the number of passages through the defibrillator reduced the average diameter of the bamboo nanofibrils (from 82 ± 29 nm to 10 ± 6 nm). Addition of 6.5% nanofibrils improved the tensile strength and elongation at the break of the nanocomposite by 24 and 51%, respectively, but reduced the tensile modulus by 40% in relation to control (unreinforced) blend. Nanofibrils decreased the transparency of the nanocomposite films. The water vapor permeability and water solubility of the nanocomposite containing high contents of nanofibrils decreased up to 20% and 30%, respectively, in relation to the control blend.

No abstract

The expansion of Brazilian agricultural production was very important in the last decade. A number of waste residues were produced showing an enormous potential for industrial crops and products. Sugarcane bagasse is the most important one and it has been investigated for chipboard panel's preparation. In this sense, this work aims to develop, characterize and compare chipboard panels made with sugarcane bagasse with urea formaldehyde (UF) and melamine formaldehyde (MF) resins. Panels were obtained with a mixture of sugarcane bagasse and particles, like pine or eucalyptus, with and without paraffin in the formulation. Nine different types of panels have been made, all with 9% in resin mix, under a pressing cycle of 4.0 MPa cm 2 , and temperature of 160 • C. Under physical tests, the panels complied with the American Standard CS 236-66 for trading chipboards of medium density and, in most cases the results obtained were lower than the ones raised in the literature. Under mechanical tests, that same standard was not complied with and, in most cases the results were close to or higher than those obtained in the literature.

No abstract

Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix.

There is a growing interest in cellulose nanofibrils from renewable sources for various industrial applications. However, there is a lack of information on cellulose arising from bamboo pulps. Nanofibrils from refined bamboo pulps, including bleached, unbleached, and unrefined/unbleached, were obtained by mechanical defibrillation for use in biodegradable composites. The influence of industrial processes, such as pulping and refining of unbleached pulps, as well as of alkali pretreatments and bleaching of refined pulps, on the chemical composition of the samples was analyzed. Morphological, structural, thermal, optical and viscometric properties were investigated as a function of the number of passages of refined/bleached suspensions through a defibrillator. For the unbleached suspensions, the effects of refining and bleaching on the properties of nanofibrils were evaluated, fixing the number of passages through the defibrillator. Microscopic studies demonstrated that nanoscale cellulose fibers were obtained from both pulps, with a higher yield for the refined/bleached and refined/unbleached pulp, at the expense of the unbleached/unrefined pulps. The study showed that, in addition to the effectiveness of the pre-treatments, there was an increase in the production efficiency of nanofibrils, as well as in the transparency of the bleached suspensions, while viscosity, thermal stability and crystallinity had reduced levels as the number of passages through the defibrillator increased, showing a gradual improvement in the transition from the micro- to the nano-scale. The present study contributed to the different methods that are available for the production of bamboo cellulose nanofibrils, which can be used in the production of biodegradable composites for various applications.

No abstract

No abstract