Key Engineering Materials Vol. 668

Abstract: The present work analyses the behaviour of different binder matrices in order to implement the addition of paper pulp as reinforcement for cementitious composites and assesses the composites flexural properties with time. To prevent microfibers degradation in high-alkaline environments, lower alkaline matrices may be developed. In the present study ternary binder matrices containing ordinary Portland cement (OPC), gypsum (G) and fluid catalytic cracking catalyst residue (FC3R) are presented for that purpose. To assess the performance of the alternatives matrices, pH and conductivity evolution with time were monitored. Also flexural tests were carried out with the intention of evaluate the efficiency of the matrix to preserve fibres within the composite. According to pH and conductivity results is proved that this ternary system offers lower values at early stages (at 3 days) when compared to OPC systems. This inferior alkalinity might be associated to the better mechanical performance with time of the composites when the ternary matrix is used. After 10 months ageing, all the mechanical properties were higher when compared to composites using OPC. Particularly remarkable is the preservation after ageing of the specific energy and deflection at the modulus of rupture when the low-alkalinity matrices were employed, on the contrary what occurred with samples containing OPC where specific energy and deflection were nearly disappeared.

Abstract: Vegetal fibers are obtained from leaves, stalks, culms, fruit and seeds, and have been used in the macro, micro and nanoscale as partial replacement of synthetic fibers in organic and inorganic matrices. Bamboo has high strength fibers, and is one of main nonwood resources and is available in tropical areas worldwide. These characteristics justify the study and application of bamboo fiber as reinforcement in the macro, micro and nanoscale. The macrofibers were obtained from bamboo culms, the microfibers from the chemical pulping and the nanofibers were obtained from the mechanical nanofibrillation of the pulp. The fibers were subjected to chemical, physical, mechanical and morphological tests. There was modification in the chemical composition of the bamboo after pulping, such as decrease of amount of the lignin, hemicellulose and extractives in 42.4%, 33.3% and 83.7%, respectively.The bamboo fibers width have been reduced from 0.26 mm to 19.8 μm after pulping and after nanofibrillation process the width was reduced from 19.8 μm to 16.2 nm.The decrease of the fibers dimension can be seen from the micrographs and analyzing it mechanical properties, the bamboo fibers are a reinforcement potential in macro, micro and nanoscale to organic and inorganic matrices.

Abstract: Specimens of laminated bamboo Guadua angustifolia do not usually fail due to fiber breakage when submitted to shear stresses. The common failure mechanism in that case is slippage in the fiber-matrix interface, accompanied by degradation of the lignin matrix (parenchyma). In this study the shear strength of laminated bamboo Guadua angustifolia specimens was determined by tension tests reducing the cross section area. The perimeter of the slipped area was determined using digital image processing. Shear stresses were calculated taking into account the load and slipped area in specimens of two different groups, depending on the orientation of the laminated boards. It was found that the average value of the shear strength on pull out tests were 2.9 MPa, which is a mechanical property of the material that is useful, for example, in the analysis of the behavior of the joints, and analysis of the fracture process.

Abstract: Raw bamboo is a composite graded naturally material with variable distribution of fibers in the culm wall thickness and also in height. The strength and fiber volume fraction obtained in tests of round bamboo are very variable, while laminated bamboo has more uniform properties. The fiber volume fraction was determined in two groups of specimens of laminated bamboo Guadua angustifolia and also in two groups of bamboo clapboards. Although the average values of fiber volume fraction was around 45% for all cases, it was found that the coefficient of variation in the groups of specimens of laminated bamboo guadua was 6%, while in the groups of slats was 29%.

Abstract: The main objective of this investigation was to study the properties of composites of polypropylene (PP) containing different proportions (20, 40 and 60% wt%) of coir short fiber (natural vegetable fiber) without treatment of fibers, for use in products by injection with applications in the automotive industries, construction and other segments. Samples were prepared in a only stage using a high intensity thermokinetic mixer (K-Mixer). Additives were used in the mass fraction of 3 wt% compatibilizer (PP-g-MA), 2.2 wt% processing additive and 0.12 wt% thermal antioxidant. The composites were characterized by tensile test according to ASTM D638-10. The surface properties of the polymeric matrix with additives were studied by determining the contact angle (CA) in a sessile drop tensiometer and the carbonyl index (CI) by Fourier-transform infrared spectroscopy (FTIR). Thermal properties of the PP and the composition were evaluated by thermogravimetric test, and the interface of the fiber and the matrix in the composites were evaluated using images from scanning electron microscopy (SEM). The CA analysis showed that the PP matrix with additives has become less hydrophobic and the FTIR and the CI that there was a better stabilization of the PP with additives. There was an increase in thermal stability of the composites for all fiber content, which was up to 15 °C above PP for coir fiber composites. In the Young's modulus values showed that the inclusion of fibers reinforced the polymeric matrix and increased the stiffness of the composites, especially in composites containing 60% (wt%) in which the values were ~1.7 times greater than the polypropylene. Images of micrographs showed the interaction of the fiber in the matrix and that despite the hydrophilic character of the fibers and hydrophobic character of the PP, the composites showed non-homogeneous interfaces. These findings confirm the feasibility of using high level of coir fiber in polypropylene composites even without pretreatment of the fibers and the preparation of samples by injection.

Abstract: MDP (medium density particleboard) panels are normally graded in composition along their cross-section, using low-size particles and high concentration of adhesive on the particleboard surface (leading to improved physical and mechanical properties), and high-size particles in the particleboard core (interior), which provide higher porosity. Then, the aim of this study was to evaluate the impact of using different contents of bamboo particles in the particleboard core, on their physical and mechanical properties. The production of the panels was carried out using Pinus oocarpa (P) and Bambusa vulgaris var. Vittata (B) particles in different contents (100% P, 100% B, 50% de B e 50% de P, 25% de B e 75% de P, 75% de B e 25% de P) in the core of the particleboards. The face of the particleboards were composed of P particles. The panels were produced with nominal density of 0.70 g/cm³, 40:60 face:core relation, 11% urea-formaldehyde adhesive in the faces and 8% adhesive for the core, specific pressure of 3.92 MPa, 160 °C temperature and pressing time of 8 min. After seasoning, the panels were submitted to evaluation of the thickness swelling (TS) and water absorption (WA) after 2 and 24 h of immersion, apparent density (AD), internal bonding (IB), modulus of rupture (MOR) and modulus of elasticity (MOE) under static bending. There was no statistical difference between the treatments for AD, IB, MOR and MOE values. Panels produced with high contents of bamboo particles (100% B, 75% B e 50% B) in the core, presented the lower WA and TS values, leading to improved dimensional stability than panels with only pinus particles. The present results show the important impact of using functionally gradation and bamboo particles on the physical properties of the MDP panels produced.

Abstract: The objective of the present study was to verify the technical feasibility of using banana pseudostem fibers in the manufacture of MDP in intermediate panel layers, in different associations with wood from eucalyptus and banana pseudostem. The physical properties of water absorption and thickness swelling for immersion in water for both 2 and 24 hours were evaluated. Three panels were produced according to American Standard ASTM D 1037. 12% urea-formaldehyde adhesive were used for the production of panels. The pressing cycle was 4 MPa, with a temperature of 160°C for a period of 8 minutes. The panels were produced with a density of 0.70g/cm3 and had the following composition: 20/60/20 face/core, in which the face consisted of eucalyptus and varying proportions of pseudostem in the core (10%, 20% and 30%) and in eucalyptus. It is observed that the panels with 20% particles in the core showed the best results, compared to other panels evaluated.

Abstract: Poly (lactic acid) (PLA) is a biodegradable and high-cost polymer which is nevertheless replacing the use of commodities in applications like packaging films, and is widely discarded in the environment. In this work, PLA was homogenized in a K-Mixer with different proportions of thermoplastic starch (TPS), a material with lower cost, and these mixtures were reinforced with natural cotton fibers, seeking to increase the tensile strength without compromising biodegradation. To evaluate the degradation behavior of PLA-TPS-cotton composites, tests were performed to measure the contact angle as well as the effect of hydrolysis and degradation in simulated soil. All the materials showed peak mass retention when removed from the water at 28 days and from the simulated soil at 14 days. The results showed that varying the content of TPS (0, 3 and 5%) caused increased water absorption and rate of degradation, but the fiber content (0, 10 and 20%) can distinguish the influence observed by incorporation of starch. The samples immersed in water presented retention values near those of the PLA matrix itself only for the ratio between fiber and TPS of 2:1 in mass percentage, showing the increased stability of the composite in contact with water.

Abstract: Buriti (Mauritia flexuosa Mart.) is the most common and abundant palm tree in the Brazilian territory and it is present throughout South America. It is known as the "Tree of Life", because everything in it can be used and many residents of rural communities have this palm tree as their main source of income. In different Brazilian states, the fibers removed from young leaves of the Buriti palm tree are employed in the manufacturing of handicraft, being this fiber popularly known as "flax or silk" of buriti. In order to apply the “flax or silk” of buriti in new products, it is necessary to study their physiochemical characteristics, as well as to monitor the handling of the palm tree, the extraction process of the fiber and its application in handmade products. The buriti fiber analyzed in this study is from the Brazilian Cerrado biome, more specifically from the town of Barreirinhas (Maranhão State). The fibers were tested in order to determine tensile rupture strength, tenacity, elongation, Young’s modulus, cross microscopic structure and regain. In order to carry out the tests, the fibers were separated in 5 groups: 1) in natura fibers, 2) fibers boiled by the origin community, 3) fibers boiled in bleach, 4) fibers boiled in softener, and 5) fibers boiled in lemon juice, being the processing of last three groups done in the city of São Paulo. The group used for cross and longitudinal microscopy was in natura fibers. The groups of fibers referred were also maintained in water at 37°C for 21 days to determine its reaction and resistance to weather and were analyzed every 3 days. The results of tenacity, elongation and Young ́s modulus for each group were respectively: 1) 28.4±5.6 cN/tex (CV=20%), 8.3±0.6% (CV=7%), 6.1±0.8 N/tex (CV=13%); 2) 31.0±7.7 cN/tex (CV=25%), 8.4±0.8% (CV=9%), 7.2±0.7 N/tex (CV=10%); 3) 27.6±7.2 cN/tex (CV=26%), 7.9±0.6% (CV=7%), 6.0±1.2 N/tex (CV=20%); 4) 22.1±8.8 cN/tex (CV=40%), 8.6±1.9% (CV=22%), 5.0±1.0 N/tex (CV=20%); 5) 29.7±6.5 cN/tex (CV=22%), 8.6±0.6% (CV=7%), 5.8±0.8 N/tex (CV=13%). Through this study it could be possible to expand knowledge regarding the potential of the Brazilian biodiversity, presenting applications for the buriti fiber in the development of new products to be employed in design and industry as well as collaborating in the construction of social benefits by encouraging the recovery and strengthening of local cultural identity, community organization around solidarity economy and consequent generation of income for fibers extractive communities.