Resumo em Inglês:

Abstract The objective of this research was to develop a more sustainable composite and still keep its characteristics. Fibers treated with NaOH at 5% w/w for 2 hours were incorporated into natural rubber in different proportions (0 phr, 24 phr, 36 phr, 48 phr and 60 phr). The mechanical properties of the composites suffered changes, increasing the hardness, young’s modulus and decreasing its tensile strength. All the physical properties were not statistically different. The coloration became less dark in the WF60/CB0 treatment, and the electrical properties presented better resistivity with the increase in the concentration of fibers in the composite. This presents a possibility of using WF for the production of wood-rubber composites for the production of rubber artifacts which do not require high rolling resistance. Based on the results from this research, we recommended the WF24/CB36 mix to produce antistatic floors.

Resumo em Inglês:

Abstract Aiming to produce an antimicrobial dressing for wound healing applications, in this work Tea Tree oil (TTO) was incorporated into PHBV nanofibers by absorption. It was observed increase in the nanofiber diameter due to 5% TTO absorption efficiency, which also led to a 54% decrease in the contact angle. The releasing assay indicates a 6.8% oil release in the first 24 h – being probably the oil deposited at the polymer surface – followed by a minimal release at 48 h. The set of antimicrobial assays performed suggests the incorporation of TTO optimized the antimicrobial activity of the polymer for E. coli and C. albicans, while against S. aureus no significant difference was observed. The MTT assay showed no cytotoxicity of PHBV, but the incubation of L929 fibroblast cells with PHBV-TTO reduced cell viability. Overall, the PHBV nanofibers containing TTO present great potential as an antimicrobial dressing.

Resumo em Inglês:

Abstract High-intensity ultrasound irradiation proved to be an effective method for modifying tara gum by generating low molecular weight products and better water solubility. The objectives of this research were to optimize the parameters for the high-intensity ultrasonic treatment with response surface methodology and improve the tara gum solubility. The results demonstrated that after the ultrasound treatment, the solubility of the tara gum had increased (17.7%) as a result of the reduced intrinsic viscosity (70%). The molecular weight of the untreated tara gum was 1.89 x 106 Da, and after ultrasound treatment, it was reduced to 0.47 x 106 Da. Rheological analyses confirmed the reduction in molecular weight for the modified and optimized tara gum and the resulting increase in solubility. This knowledge provides a better understanding of ultrasound treatment technology and increases the scope for use of tara gum in the food industry.

Resumo em Inglês:

Abstract Segmented polyurethanes based on poly(l-lactide)diol - PLLA, poly(ethylene-glycol) - PEG, poly(trimethylene-carbonate)diol - PTMC and hexamethylene diisocyanate were synthesized by a two-step polyaddition. Polyurethanes with variable compositions and molar mass were semi-crystalline and presented PLLA or PLLA + PEG crystalline phases and a heterogeneous amorphous phase. Sequential crystallization of PLLA and PEG resulted in a confined PEG crystallization into the PLLA crystalline phase. The random distribution of the segments in the polymer chains and the partial miscibility of the segments in the amorphous phase strongly influenced the morphology of the crystalline phase, and the kinetics of the crystallization. Morphology changed from not well-defined spherulites with Maltese cross to ring banded spherulites and axialites as the PLLA mass fraction decreased. PLLA nucleation and crystal growth rates varied with crystallization temperature similarly to homopolymers, presenting a bell-shaped curve, and the temperature for the maximum growth rate dependent on the polyurethanes composition.

Resumo em Inglês:

Abstract Thermally modification of wood is an environment-friendly alternative method for improving several properties of wood without the use of chemicals. The compressive strength (CS) parallel to the grain of reinforced laminated veneer lumber (LVL) manufactured from heat treated beech (Fagus orientalis) veneers and carbon fibre was determined. Thermally modification was performed at 140°C, 160°C, 180°C, and 200 °C according to thermal treatment process. Carbon fibre were added as a reinforcement layer between wood veneers bonded with phenol-formaldehyde (PF), polyvinyl acetate (PVAc) polyurethane adhesives (PU) to improve properties of LVL. Results showed that reinforcing LVL panels with carbon fibre increased both density and CS. The PF adhesive showed better results for reinforced LVL panels with carbon fibre. The anatomical structure and density of the wood material significantly affect its mechanical properties, including compressive strength parallel to the grains. Wood density had a strong significant linear relationship with CS.

Resumo em Inglês:

Abstract While numerous phenoxazine-based small molecules developed for organic electronic devices, very limited attention has been received on synthesized conjugated polymers containing this phenoxazine. Herein, we designed and synthesized two new low-bandgap donor−acceptor conjugated copolymers based on phenoxazine with different side chains and diketopyrrolopyrrole by Pd-catalyzed direct (hetero)arylation polycondensation using a Pd(OAc)2 catalyst and PCy3.HBF4 ligand. The effects of side chain branched alkyl and benzoyl of phenoxazine on the thermal, and optical properties of the polymers have been investigated. Both the polymers have a good yield 85%, high molecular weight up to 41500 g/mol, low dispersity index 1.91, excellent solubility in common organic solvents, and a broad absorption spectrum in the range of 500-900 nm with optical bandgaps as low as 1.40 eV. All these polymers possess good thermal stability with decomposition temperatures over 350 oC and no obvious thermal transitions.

Resumo em Inglês:

Abstract Composite materials are used to repair cracks in pipelines that appear after a period of time. This study investigates the effect of hybridisation on the blister behaviour of composite repair by using the finite element method. The behaviour of the best hybridised stacking sequence is compared with the experimental results to validate the numerical outcomes. The effect of adding multiwall carbon nanotubes (MWCNTs) to the epoxy resin, used to stick the composite repair with the steel pipeline, is explored by combining the MWCNT and the epoxy through high shear mixing. The results showed that hybridisation has a great effect on improving the blistering behaviour of the composite repair. The preparation of nano-reinforced adhesive by shear mixing did not show noticeable improvement. Predicting the composite repair behaviour through blister test by using the finite element method can be used as a good indication of pipeline protection.

Resumo em Inglês:

Abstract Polyvinylidene fluoride (PVDF) is a polymer material that exhibits piezoelectricity, which is the ability of certain materials to generate an electric charge in response to applied mechanical stress. Electrospun nanofibers were prepared from a solution with 1800 mg PVDF (18 wt.%) powder dissolved in 7.5 ml of dimethylformamide (DMF) and 2.5 ml acetone. The experimental setup used in the electrostatic deposition process was developed in our laboratory. Atomic Force Microscopy (AFM) showed that the fibers vary from 100 nm to 200 nm. Scanning Electron Microscopy (SEM) measurements showed distributed and well-formed nanofibers, but with few incidences of beads. The Energy Dispersive Spectroscopy (EDX) results showed that all points of the formed nanofibers have very similar chemical compositions, based on carbon and fluorine. Raman and Fourier Transform Infrared (FTIR) Spectroscopic analysis revealed the characteristic bands related to β-phase in the sample, which is responsible for the piezoelectricity of PVDF.

Resumo em Inglês:

Abstract In this paper, the crystallization, fusion, and activation energy (Ea) of PBT/TiO2 were thoroughly evaluated using DSC. Increasing the rates shifted the peaks of melt crystallization to lower temperatures while the fusions were almost unaffected. TiO2 hindered the melt crystallization of PBT and lower crystallization rates, i.e., CMAX and K’ were acquired, in general, the crystallinity degree (Xc) was 4% higher in PBT/TiO2 which is in the marginal error. Pseudo-Avrami and Mo models were applied to evaluate the melt crystallization kinetics; both fitted the melt crystallization quite well; deviations were observed at the beginning and the crystallization end most due to the nucleation and spherulites impingement during the secondary crystallization. Ea was evaluated using the Friedman model, considering the values of Ea less energy has to be removed from PBT/TiO2 when compared to PBT, specifically at 1% of TiO2.

Resumo em Inglês:

Abstract Plastic wastes are generally not easily degradable under the action of environmental components. They are very much resistant to microbial attack too. These non-biodegradable plastics accumulate over a longer period of time on earth leading to environmental pollution. However, this may be avoided by using biodegradable polymers. Thus the demand for the preparation of biodegradable polymers has grown up. In recent years, researchers have developed a few biodegradable polymers from renewable sources; those find a large application in the field of packaging, agriculture, and biomedical fields. Starch is one such biopolymer, modification of which may lead to a semi-synthetic polymer with good properties with an edge of biodegradability. Poly(methyl methacrylate) is a good modifying agent for such modification as revealed by the literature search. This review report summarizes the preparation of such poly(methyl methacrylate) grafted starch polymers via different physical and chemical methods, their properties, and their applications.

Resumo em Inglês:

Abstract An overview perspective of the potential of chitin and chitosan biopolymers to promote economically and environmentally sustainable development poles, which could be exploited especially in developing countries, is presented. Their following advantages have been considered and briefly outlined: (i) the natural sources of chitin have a wide distribution on the entire planet and are usually accessible as inexpensive waste materials; (ii) the great versatility of these materials, with applications in diverse fields such as agriculture, water treatments, food industry, environment, petroleum, healthcare, energy, technology, etc., with some trials conducted even off-planet; (iii) the production and use of these materials could promote advances in the endogenous capacity of some countries to create own technologies and generate products and applications, basic and advanced, in sensitive sectors, i.e., health services, food, water treatments, etc., in addition to promoting the necessary integration of the academic sector with other sectors such as industry and business.

Resumo em Inglês:

Abstract Using natural fibers in composites presents a wide range of applications, from furniture to airplanes. In polymeric composite, the use of fiber is to boost strength and stiffness. However, this material presents low mechanical properties compared to virgin polymers due to hydrophilic nature of the fiber and hydrophobic nature of the polymer. It can result in weak bonding matrix/fiber which may cause incompatibility problem in bonding fibers with most of the polymer matrices. To achieve compatibility between surfaces there is a need to modify them, and one alternative is using coupling agents. Maleated coupling agents stand out as option, but their source is petroleum-derived polyolefin. Researchers have been seeking for more environmentally friendly alternatives to replace these materials. Therefore, this work aims to bring a comprehensive review of the mechanical behavior of maleated and ecological coupling agents. Based on the literature, resistance, flexural, and tensile strength were properties discussed.