J. R. M. d'Almeida

Impact behavior of sugarcane bagasse waste–EVA composites

Abstract The impact performance of chopped bagasse–EVA matrix composites is evaluated and compared with the behavior of bagasse filled PP and PE matrix composites and wood-based materials. The volume fraction and size of the chopped bagasse used as filler was varied. The experimental results show that the incorporation of bagasse strongly reduces the deformation capacity of EVA polymer. The reduction of the deformation capacity of the composites was also inferred by solid-state NMR relaxation analysis. The impact strength was independent of the bagasse size, but varied with the volume fraction. As a function of the volume fraction it was shown that the mechanical performance of bagasse–EVA composites could be tailored to reproduce the behavior of wood-based particle boards.

An investigation on the tensile strength of particulate filled polymeric composites

The validity of a semi-empirical equation previously developed for the yield strength evaluation of particulate composites is extended to predict the ultimate tensile strength of composites that do not show large macroscopic plastic behaviour. A good correlation is obtained between the theoretical values derived from the equation proposed and the experimental results from composites filled with both surface treated and untreated particles. A dimensionless parameter related to the filler–matrix interface is obtained and used to judge how effective a surface treatment is in order to enhance the mechanical properties of several particulate filled composites.

Acetilação da fibra de bucha (Luffa cylindrica)

In this work the effect of a new chemical surface treatment on the structure and surface morphology of loofah fibers (Luffa cylindrica) was analyzed, using infrared spectroscopy and scanning electron microscopy. The chemical treatment is aimed at increasing loofah compatibility with the polymeric matrices commonly used in composites. It was shown that the treatment used caused a reduction on the polarity of cellulose molecules, and removed the outer surface layer of loofah fibers, exposing their internal fibrillar structure. As a consequence the treatment promoted an increase on the surface area available to adhesion.

Effect of the fiber reinforcement on the low energy impact behavior of fabric reinforced resin matrix composite materials

The influence of the fiber used as reinforcement in resin matrix composite materials submitted to repeated low energy impacts is analyzed. The aramid, glass and carbon fiber composites were submitted to drop weight tests from 0.5m and from 1m. The number of impact events necessary to cause failure was recorded, and the fracture characteristics of each composite were analyzed by optical microscopy and X-rays radiography. The results obtained showed that carbon fiber composites have better performance than the glass and aramid composites. This behavior was partially attributed to the higher elastic energy absorption of carbon fibers that delays the propagation of delamination, and fiber breakage. The failure mode of glass fiber composites was dominated by the higher number of glass fibers per surface area of the composites. The worst behavior shown by aramid composites was attributed to the intrinsic anisotropy of aramid fibers.

A solid state NMR carbon-13 high resolution study of natural fiber from sugar cane and their composites with EVA

Abstract Natural fibers obtained from sugar cane have been analysed by carbon-13 high resolution solid state nuclear magnetic resonance (NMR) employing different techniques such as: cross-polarisation magic angle spinning (CP/MAS); variable contact time experiment and proton spin-lattice relaxation time in the rotating frame. Molecular mobility information for distinct types of sugar cane fibers, as well as two different mixtures (one of the mixtures contains equal amounts of waste fibers and the other has a random distribution of these waste fibers) and their composites with poly(ethylene-co-vinyl acetate) (EVA) were obtained from those techniques. Mechanical measurements (stress–strain) were also recorded for all samples. Both NMR and mechanical measurements responses showed that the mixtures of natural fiber can be used as a matrix in the composites.

Carbon-13 high resolution solid state NMR study of natural fibres obtained from sugar cane without treatment and their composites with EVA

Abstract Natural fibres from three distinct type of sugar cane without any specific treatment to remove the sugar, lignin and impurities and their composites with EVA, have been analysed by carbon-13 high-resolution solid state nuclear magnetic resonance (NMR). The NMR techniques used were cross-polarization magic angle spinning (CP/MAS); variable contact-time and proton spin-lattice relaxation time in the rotating frame (T1Hρ). From those measurements it was observed that the molecular mobility of chains along the fibres has a particular behaviour.

Influence of Water Absorption and Pre-drying Conditions on the Tensile Mechanical Properties of Hybrid Lignocellulosic Fiber/Polyester Composites

It is well known that humidity can deleteriously affect composite mechanical properties. In the present study the tensile properties of hybrid jute/cotton and sisal/cotton fabrics— polyester matrix composites were analyzed as a function of fiber content, immersion time in distilled water and of fabric drying just prior to composite manufacture. The results indicate that, as expected, tensile properties increase with fiber content, and that sisal reinforced composites were slightly more affected by water exposure than jute reinforced ones. This behavior was attributed to the higher affinity of sisal fibers toward water absorption. Fabric drying immediately before their incorporation onto the composites was shown to play an important role on composite mechanical properties. Fabric pre-drying led to composites with lower water absorption and higher overall mechanical properties. These composites also displayed a smaller strain at rupture, evincing better fiber to polymer matrix interaction. The data obtained suggests that water acts as a plasticizer for the systems investigated and that plasticization occurred in the early stages of composite immersion in water.

Immersion Temperature Effects on the Water Absorption Behavior of Hybrid Lignocellulosic Fiber Reinforced-Polyester Matrix Composites

Although economic, ecological, processing and property considerations suggest that it is very attractive to use lignocellulosic fibers as reinforcement in polymer matrix composites, moisture can strongly and deleteriously affect their properties. In this work the water absorption behavior of sisal/cotton, jute/cotton and ramie/cotton hybrid fabric reinforced composites is evaluated. The effect of the temperature of immersion, fiber volume fraction, and predrying of the fabrics before their incorporation onto the composites are evaluated. Sisal was shown to be the most hygroscopic of the fibers analyzed, and its presence leads to higher values of the maximum water content and of the diffusion coefficient of sisal/cotton reinforced composites. Under the range of temperatures analyzed (30–60°C) the volume fraction of the fibers, rather than the temperature itself, was shown to be the main parameter governing water absorption. Predrying usually lowers maximum water content, although for sisal/cotton reinforced composites a reverse trend was observed for the composites with higher volume fractions. This behavior was again attributed to the higher hydrophilic behavior of sisal fibers.

13C solid-state NMR analysis of the DGEBA/TETA epoxy system

Mechanical properties measurements, like Charpy impact tests, provided evidence that the macromolecular network of the epoxy system formed by the hexafunctional triethylene tetramine hardener, TETA, with the diglycidyl ether of bisphenol A monomer, DGEBA, can be modified by changing the hardener content. The previously analyzed monomer-to-hardener ratios were here studied by 13C-NMR solid state techniques. The results from crosspolarization/magic angle spinning (CPMAS) 13C-NMR spectra, together with the evaluation of proton spin-lattice relaxation time in the rotating frame (Tρ), display the behavior of these epoxy/hardener mixtures considering the mobility and interaction of molecular segments present at the macromolecular structure. The results also show that the epoxy-rich mixtures form tight, and therefore brittle, structures as previously observed by mechanical tests. The stoichiometric monomer-to-hardener ratio is a transition point where an increase in the mobility was found. For the amine-rich mixtures the obtained results suggest the presence of domains with different segmental mobilities.

Low-Cost Processing of Plastic Waste Composites

The use of the compression molding technique to manufacture polymeric panels from recycled polymers was evaluated. polypropylene (PP), polyethylene (PE), and polystyrene (PS) single polymers and their blends were manufactured both with and without UV and flame-retardant additives. The materials were tested in three-point bending, and the incorporation of the additives always produced a decrease of the flexural strength. The results obtained were compared with the properties of commercially available materials. In particular, PP + PE blends showed a promising mechanical performance. For the amount of flame-retardant additive used in this study, none of the compositions analyzed exhibited flame resistance. The balance between loss of mechanical strength due to the increase of the amount of flame retardant additive and lack of flame resistance was obtained by incorporating more flame retardant through a paintinglike procedure. The method proved to be an efficient way to attend the standard for building construction panels.