Resumo em Inglês:

Abstract The objective of this work was to investigate the effects of mercerization on chemical, morphological and thermal properties of Amazon Piassava Fibers. The effect of this treatment was studied using XRF, SEM, XRD and TGA. The fibers have been treated in 5% and 10% NaOH for 60 min. The XRF results for treated and untreated fibers showed that there is a decrease in the amount of SiO 2 by increasing the NaOH concentration. It has been possible to observe through SEM in untreated fiber that the surface presents a well arranged pattern of silicon rich star-like protrusions. For the two concentrations, SEM allowed to notice that the removal of deleterious surface impurities and fiber roughness was enhanced. The removal of organic material after treatment can be observed in the TGA analysis. XRD analysis indicate an increase in the crystallinity index, 0.19 to 0.31 after the treatment for 10% concentration solutions.

Resumo em Inglês:

Abstract Cellulose is the most abundant renewable resource in nature, it has various industrial applications due to its promising properties. Retama raetam is a wild plant belonging to the Fabaceae family, largely abundant in arid area which makes it a good candidate for industrial utilization. In the present study, highly crystalline cellulose microfibers (77.8% CrI) were extracted from Retama Raetam stems as a novel renewable source. The samples underwent a dewaxing process, then the microfibers were extracted using 7 wt% sodium hydroxide followed by a bleaching treatment. The extracted cellulose microfibers were characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray Diffraction and thermo-gravimetric analysis.

Resumo em Inglês:

Abstract Ballistic armor has been manufactured primarily based on polyaramide (Kevlar and Twaron) or Dyneema but the lifespan warranty in Brazil is only 5 years and after this time period they are incinerated or comminuted and ground up. This study aims to evaluate the changes on the physical, mechanical and morphological properties of polyaramide fibers of ballistic armor after natural aging. These samples with different fabrication (2005 and 2010) and usage time were exposed to natural weathering in the city of Porto Alegre, southern Brazil, during the period of one year. Morphology fiber results surfaced after ageing, it showed fiber swelling, stress cracking and defibrillation, and the results of the mechanical tensile testing of the polyaramide fibers showed a pronounced decrease (80%) in tensile strength. It can be concluded that the weight, the dtex of the fiber and the kind of fabric can influence the degradation degree under natural exposure.

Resumo em Inglês:

Abstract Three methods to obtain isoprene oligomers were evaluated: chemical degradation of non-vulcanized coagulated natural rubber; chemical degradation of natural rubber latex; and oligomerization of the isoprene monomer. The products were characterized by infrared spectrometry (FTIR), nuclear magnetic resonance (NMR) and size-exclusion chromatography (SEC). All the three processes were efficient and can be controlled in order to obtain products with desired molar mass. Among the degradation processes, the reaction with the non-vulcanized rubber led to the purest products, but this process has the disadvantage of relatively higher catalyst cost of the catalyst. Reactions of isoprene with free radical initiation produced oligomers under specific conditions: low isoprene concentration, low initiator concentration, and xylene as solvent. The results discussed here allows the readers to have a chemistry overview and experimental insights about different chemical routes to obtain isoprene oligomers, compiled together in the same work. It shall be helpful for applied chemistry researches.

Resumo em Inglês:

Abstract Nonisothermal crystallization and melting of the biodegradable thermoplastics poly(3-hydroxybutyrate) (PHB), poly(butylene adipate-co-terephthalate) (PBAT), and a 1:1 PHB/PBAT blend were investigated by differential scanning calorimetry (DSC) over an extensive range of heating/cooling rates (2 to 64°C/min). The different phase transition behavior of the neat components was reflected in the mixture and suggest an immiscible blend. Pseudo-Avrami, Ozawa and Mo classical macrokinetic models were used to describe the evolution of the melt crystallization process. Results suggest that none of these models could be used to predict the experimental results of crystallization kinetics of the blend with sufficient precision for polymer processing applications. However, some methods may be of used for the neat resins over restricted ranges of cooling rate, temperature or conversion (e.g., Ozawa for PHB at low cooling rate, Mo for PBAT).

Resumo em Inglês:

Abstract Two series of polyurethane (PU) and carbon nanotubes (CNT) based composites with 0.0, 0.25, 0.5 and 1.0 mass% of CNT were obtained from diluting a commercial masterbatch with 30 mass% CNT and using two different dispersion methods. The quality of the dispersions was assessed using optical microscopy, and scanning and transmission electron microscopies. These tests showed that high controlled shear stress is necessary to produce composites with nanoscale dispersion: the elastic modulus improved by an average of 38% in the case of the high-shear dispersed materials in comparison with the neat polymer. A specific fatigue test conducted by dynamic mechanical analysis was first used in this work to compare the neat PU with the CNT/PU nanocomposites. The number of cycles to failure increased from 2700 for the neat polymer to 3200 for the 0.5 mass% CNT based nanocomposite; the elongation at failure increased by 145% in the test conditions.

Resumo em Inglês:

Abstract Industries and the scientific community currently focus on creating new ways to recycle and to reuse polymer waste that leads to serious socio-environmental risks. However, the quality of recycled polyethylenes depends strongly on their purity degree, but the distinction between Low Density Polyethylene (LDPE) and High Density Polyethylene (HDPE) by a fast and consistently good methodology is still an unsolved issue for the current recycling processes. In this study, confocal Raman spectroscopy and Competitive Adaptive Reweighted Sampling - Partial Least Squares (CARS-PLS) linear regression have been successfully applied to quantify the concentration of LDPE/HDPE blends. The effects of several regression parameters (pretreatment method, Monte Carlo sampling runs, k-fold and maximal number of latent variables for cross-validation) on the CARS-PLS model training and prediction performance were analyzed. The CARS-PLS-based models show root-mean-squared prediction error of 4.06 - 8.87 wt% of LDPE for the whole composition range of HDPE/LDPE blend.

Resumo em Inglês:

Abstract Electrospinning is a simple and low-cost way to fabricate fibers. Among the various polymers used in electrospinning, polycaprolactone (PCL) stands out due to its excellent biodegradability and biocompatibility. However, PCL has some limitations such as low bioactivity, hydrophobic surface, and long in vivo degradation. Calcium phosphate ceramics have been recognized as an attractive biomaterial. They are bioactive and osteoinductive, and some are even quite biodegradable. Different contents of particles of beta-tricalcium phosphate (β-TCP) were incorporated in polymer matrix to form fibers of PCL/β-TCP composites by electrospinning for possible application in tissue regeneration. The presence of β-TCP particles promoted some changes in the thermal properties of the fibers. The immersion of PCL/β-TCP 8 wt-% fibers in simulated body fluid (SBF) caused the formation of a denser and homogeneous apatite layer on its surface.

Resumo em Inglês:

Abstract The photoswitchable poly(methyl methacrylate-random-methacrylate spirooxazine) was synthesized via atom transfer radical polymerization with the feed mole ratio of MMA/MSp comonomer of about 5.5/1. Well-defined poly(methyl methacrylate- random-methacrylate spirooxazine) have been obtained with the average molecular weight (Mn) of 6500 g/mol and polydispersity of 1.21. The structure and properties of the resulting copolymers were characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography, Fourier Transform infrared, UV-visible spectroscopy, and differential scanning calorimetry. Moreover, the copolymer exhibited the erasable and rewritable photoimaging on the solid state film which could to be as potential candidate for optical data storage materials.

Resumo em Inglês:

Abstract Poly(ether ether ketone) (PEEK) has excellent properties, such as high biocompatibility and an elastic modulus similar to bone, which makes it a suitable biomaterial. When modified with sulfuric acid (H2SO4) and hydroxyapatite (HA), its workability and bioactivity is enhanced, and this makes it of great importance in medicine. This study investigates a better combination of process parameters to manufacture sulfonated PEEK/HA (SPEEK/HA) membranes for biomaterials. Chemical, thermal, and biological analyses were carried out on all samples. The sulfonated structure was observed to enhance wettability, adhesion, and cell viability. Furthermore, an increase in the degree of sulfonation facilitated their workability as required for biomaterials; making them suitable for osseointegration. Besides, the SPEEK/HA membranes presented cell adhesion, confirming the viability to use as biomaterial. This study presents a cheap alternative method to easily process biomaterials of improved workability.

Resumo em Inglês:

Abstract Oily fractions of olive oil not suitable for human consumption used were: lamp oil (AL), olive pomace oil (OO) and clear oil lees (CB). Polyols were obtained by modifications of epoxidation with subsequent hydrolysis (ALH, OOH, CBH) and transesterification (ALHT, OOHT, CBHT) in order to favor, then, the polymerization reactions. The analysis of the physicochemical properties determined show the decrease of the unsaturations in the triglyceride and the increase of the OH concentration in the modified polyols as compared to the initial oils (from 16 to 380 for the AL and the ALHT; from 24 to 448 for the CB and the CBHT and from 3 to 430 for the OO and the OOHT, respectively) .The main objective of this work is to evaluate the stability of these oils over time and to provide an alternative synthesis of polyurethanes from a renewable resource, not previously used for this purpose.

Resumo em Inglês:

Abstract Polycaprolactone (PCL) to which has been added zinc oxide nanoparticles (ZnO NPs) produces nanocomposites (PCL/ZnO NCs). These nanocomposites can be used in biomedical applications and in the food packaging sector. However, for these materials to be used in these applications, they need to be sterilized. For this, gamma irradiation is the most common method. Thus it is important to evaluate the effects of gamma irradiation on the properties of PCL and PCL/ZnO that have been exposed to gamma irradiation. PCL/ZnO NCs films were obtained by solvent casting and exposed to gamma irradiation at 25 kGy and evaluated by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) scanning electron microscopy (SEM) and mechanical properties. Mechanical properties and crystallinity showed marginal variations for the irradiated samples. The results obtained demonstrate that gamma irradiation at 25 kGy, did not cause profound changes in nanocomposite properties.

Resumo em Inglês:

Abstract The main objective of the present work is to produce and characterize urea granules coated with polymers prepared with aqueous solutions of acrylic acid and glycerol. Both coating and drying of urea granules were performed in a fluidized bed reactor. Fourier transform infrared spectroscopy analyses indicated the presence of poly(acrylic acid) and acrylic acid / glycerol copolymers on the granule coating and the formation of chemical bonds between urea and the polymer coating. Scanning electron microscopy images showed that the original and coated urea granules presented different characteristics, reinforcing the idea that coating occurs in the fluidized bed. Finally, rates of urea release showed that the coated granules presented slightly slower rates of urea dissolution in water due to the presence of the coating layer. Therefore, it is shown that it is possible to produce coated urea granules through in-situ polymerization onto the granule surface using a fluidized bed.

Resumo em Inglês:

Abstract The life cycle of a product depends to a great extent on its reuse and ease of recycling. This work had developed of composite materials of reprocessed polypropylene composites with rice husk ash (RHA) and sugarcane bagasse ash (SBA) through the coextrusion and injection processes as main purpose. The polymeric matrix was reprocesed until six generations by the injection technique. The reprocessed PP was mixed in 80:20 proportions with respect to filler mineral, using maleic anhydride as coupling agent in a coextrusion machine. The new series of composite materials were analyzed thermal, mechanical, rheological and morphologically. The incorporation of ashes in the PP matrix achieved characteristics of improved tensile strength, conserving the thermal properties. For this reason, this work presents an alternative for the manufacture of composite materials from post-industrial waste.

Resumo em Inglês:

Abstract Cobalt/aluminum and nickel/aluminum layered double hydroxide (LDH - M+2:Al molar ratio of 3:1) were intercalated with dodecylsulphate (DDS), laurate (LAU), stearate (STE) and palmitate (PAL) and used as filler in low-density polyethylene (LDPE) in percentages between 0.2 and 7.0wt%. After injection molding, the samples were submitted to morphological characterization by scanning electron microscopy (SEM), analysis of thermal behavior by differential scanning calorimetry (DSC) and investigation of rheological properties. All Co/Al-LDPE samples showed the formation of a high temperature polymer crystal domain, induced by the LDH filler. The rheological properties indicated in general a reduction of shear modulus due to incompatibility between some regions of LDH and LDPE, which promoted phase separation. However, interaction with the LDH surface indicated higher affinity of the Ni/Al-LDH for the LDPE compared to Co/Al-LDH, forming permanent networks.