Scielo RSS <![CDATA[Polímeros]]> vol. 25 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Editorial]]> <![CDATA[Development of dual-sensitive smart polymers by grafting chitosan with poly (<italic>N</italic>-isopropylacrylamide): an overview]]> <title>Abstract</title><p>A great deal of research on polymers over the past two decades has been focused on the development of stimuli-responsive polymers to obtain materials able to respond to specific surroundings. In this paper, an overview is presented of the concepts, behavior and applicability of these “smart polymers”. Polymers that are temperature- or pH-sensitive are discussed in detail, including the response mechanisms and types of macromolecules, because they are easy to handle and have a wide range of applications. Finally, the combination of pH and temperature responsive properties by means of graft copolymerization of chitosan with poly (<italic>N</italic>-isopropylacrylamide) (PNIPAM) was chosen to represent some synthetic routes and properties of dual-sensitive polymeric systems developed currently.</p> <![CDATA[TG/FT-IR characterization of additives typically employed in EPDM formulations]]> <title>Abstract</title><p>Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG/FT-IR) is a very popular technique for rubbers characterization. It involves analyses of the base polymer and additives. Ethylene–propylene–diene (EPDM) rubbers are frequently investigated by TG/FT-IR; however, the focus has been the degradation temperature range of the polymer. In this study, unvulcanized and vulcanized EPDM rubber and its additives were investigated by TG/FT-IR, without solvent extraction, and in a wide temperature range. Initially, the additives were individually characterized. TG/FT-IR identified the characteristic groups of all the additives analyzed and distinguished them from each other. Afterwards, unvulcanized and vulcanized EPDM rubbers were investigated without prior extraction.TG/FT-IR detected absorptions due to the additives tetramethylthiuram monosulfide and 2-mercaptobenzothiazole. Both of these sulfur-containing additives were present in the EPDM formulation at concentrations of 0.7 phr (0.63 wt %). The TG/FT-IR technique had some limitations, because not all the additives in EPDM rubber were detected. Paraffin oil, stearic acid and 2,2,4-trimethyl-1,2-dihydroquinoline functional groups were not observed in either the unvulcanized or vulcanized EPDM. Nevertheless, in addition to the ability of this method to detect sulfur-containing groups, the lack of a pre-extraction reduces the time and effort required for additive analysis in rubbers.</p> <![CDATA[Blends of ground tire rubber devulcanized by microwaves/HDPE - Part A: influence of devulcanization process]]> <title>Abstract</title><p>The main objective of this work is the study of the influence of microwaves devulcanization of the elastomeric phase on dynamically revulcanized blends based on Ground Tire Rubber (GTR)/High Density Polyethylene (HDPE). The devulcanization of the GTR was performed in a system comprised of a conventional microwave oven adapted with a motorized stirring at a constant microwaves power and at various exposure times. The influence of the devulcanization process on the final properties of the blends was evaluated in terms of mechanical, viscoelastic, thermal and rheological properties. The morphology was also studied.</p> <![CDATA[Immobilization of myoglobin in sodium alginate composite membranes]]> <title>Abstract</title><p>The immobilization of myoglobin in sodium alginate films was investigated with the aim of evaluating the protein stability in an ionic polymeric matrix. Myoglobin was chosen due to the resemblance to each hemoglobin tetramer. Sodium alginate, being a natural polysaccharide, was selected as the polymeric matrix because of its chemical structure and film-forming ability. To improve the mechanical resistance of sodium alginate films, the polymer was deposited over the surface of a cellulose acetate support by means of ultrafiltration. The ionic crosslink of sodium alginate was investigated by calcium ions. Composite membrane characterization comprised water swelling tests, water flux, SEM images and UV-visible spectroscopy. The electrostatic interaction between the protein and the polysaccharide did not damage the UV-visible pattern of native myoglobin. A good affinity between sodium alginate and cellulose acetate was observed. The top layer of the dense composite membrane successfully immobilized Myoglobin, retaining the native UV-visible pattern for two months.</p> <![CDATA[Wear and friction of composites of an epoxy with boron containing wastes]]> <title>Abstract</title><p>Polymer surface coatings provide superior adhesion to substrates, some flexibility and corrosion resistance. On the other hand, 400,000 ton of boron wastes are generated each year. We have developed polymer composites based on epoxy resins containing up to 50 wt. % of boron wastes and determined their pin-on-disk dynamic friction, wear, Shore D hardness and surface roughness. The hardness and wear resistance increase with increasing boron waste concentration. An equation, with parameters dependent on the load, relating wear rate to hardness is provided. Dynamic friction increases with increasing surface roughness, as represented by the equation. Further, dynamic friction is an increasing function of the wear rate. Micrographs of pure epoxy without fillers shows traces after pin-on-disk testing, with tears, breaks and cracks. For the composites, we observe simpler and relatively homogeneous surfaces.</p> <![CDATA[Analysis of equations of state for polymers]]> <title>Abstract</title><p>In the literature there are several studies comparing the accuracy of various models in describing the PvT behavior of polymers. However, most of these studies do not provide information about the quality of the estimated parameters or the sensitivity of the prediction of thermodynamic properties to the parameters of the equations. Furthermore, there are few studies exploring the prediction of thermal expansion and compression coefficients. Based on these observations, the objective of this study is to deepen the analysis of Tait, HH (Hartmann-Haque), MCM (modified cell model) and SHT (simplified hole theory) equations of state in predicting the PvT behavior of polymers, for both molten and solid states. The results showed that all equations of state provide an adequate description of the PvT behavior in the molten state, with low standard deviations in the estimation of parameters, adequate sensitivity of their parameters and plausible prediction of specific volume, thermal expansion and isothermal compression coefficients. In the solid state the Tait equation exhibited similar performance to the molten state, while HH showed satisfactory results for amorphous polymers and difficulty in adjusting the PvT curve for semicrystalline polymers.</p> <![CDATA[Acacia bark residues as filler in polypropylene composites]]> <title>Abstract</title><p>Large amounts of acacia bark residues are produced each day after tannin extraction with hot water, being generally burned. This by-product was chemically characterized and used as filler in polypropylene (PP) composites, considering different particle sizes and concentrations. The materials produced by melt blending had their mechanical and thermal properties evaluated. It was verified that, even containing a significant amount of extractable compounds, the acacia bark particles can produce PP composites with higher impact properties, higher crystallization temperature and higher degradation temperature in comparison to the polymer matrix.</p> <![CDATA[Melting and crystallization of poly(3-hydroxybutyrate): effect of heating/cooling rates on phase transformation]]> <title>Abstract</title><p>We studied the crystallization and melting phenomena of poly (3- hydroxybutyrate) (PHB), a biodegradable and biocompatible semi-crystalline thermoplastic, obtained from renewable resources. Its high crystallinity motivated several studies on crystallization and melting behavior, and also on ways to increase the amorphous polymer fraction. The effect of heating and cooling rates on the crystallization and melting of commercial PHB was investigated by differential scanning calorimetry. Several rates, ranging from 2.5 to 20 °C min<sup>–1</sup>, were used to study the phase changes during heating/cooling/reheating cycles. The results showed that PHB partially crystallizes from the melt during the cooling cycle and partially cold crystallizes on reheating, and that the relative amount of polymer crystallizing in each stage strongly depends on the cooling rate. The melt and cold crystallization temperatures, as well as the rates of phase change, depend strongly on the cooling and heating rates.</p> <![CDATA[Development of paints with infrared radiation reflective properties]]> <title>Abstract</title><p>Large buildings situated in hot regions of the Globe need to be agreeable to their residents. Air conditioning is extensively used to make these buildings comfortable, with consequent energy consumption. Absorption of solar visible and infrared radiations are responsible for heating objects on the surface of the Earth, including houses and buildings. To avoid excessive energy consumption, it is possible to use coatings formulated with special pigments that are able to reflect the radiation in the near- infrared, NIR, spectrum. To evaluate this phenomenon an experimental study about the reflectivity of paints containing infrared-reflective pigments has been made. By irradiating with an IR source and by measuring the surface temperatures of the samples we evaluated: color according to ASTM D 2244-14, UV/VIS/NIR reflectance according to ASTM E 903-12 and thermal performance. Additionally, the spectral reflectance and the IR emittance were measured and the solar reflectance of the samples were calculated. The results showed that plates coated with paints containing IR-reflecting pigments displayed lower air temperature on the opposite side as compared to conventional coatings, indicating that they can be effective to reflect NIR and decrease the temperature of buildings when used in roofs and walls.</p> <![CDATA[Bioactivity, biocompatibility and antimicrobial properties of a chitosan-mineral composite for periodontal tissue regeneration]]> <title>Abstract</title><p>A composite membrane of the polymer, chitosan, and the silver-exchanged mineral phase, tobermorite, was prepared by solvent casting and characterised by scanning electron microscopy and Fourier transform infrared spectroscopy. The <italic>in vitro</italic> bioactivity, cytocompatibility and antimicrobial activity of the composite were evaluated with respect to its potential application as a guided tissue regeneration (GTR) membrane. The <italic>in vitro</italic> bioactivity was verified by the formation of hydroxyapatite on the surface of the membrane in simulated body fluid and its cytocompatibility was established using MG63 human osteosarcoma cells. The presence of silver ions conferred significant antimicrobial activity against <italic>S. aureus, P. aeruginosa</italic> and <italic>E. coli</italic>. The findings of this investigation have indicated that the chitosan-silver-tobermorite composite is a prospective candidate for GTR applications.</p> <![CDATA[Development of methodology for the synthesis of poly(lactic acid-co-glycolic acid) for use in the production of radioactive sources]]> <title>Resumo</title><p>A Organização Mundial da Saúde (OMS) relata o câncer como uma das principais causas de morte no mundo. Uma modalidade de tratamento que vem sendo bastante utilizada no tratamento do câncer de próstata é a braquiterapia, que consiste na introdução de sementes com material radioativo no interior do orgão. Sementes de Iodo-125 podem ser inseridas soltas ou em cordas poliméricas fabricadas a partir do (poli(ácido lático-co-ácido glicólico)) (PLGA). Foi proposto neste trabalho, o estudo e desenvolvimento da metodologia de síntese do biopolímero PLGA. Os resultados obtidos demonstram que, através da metodologia utilizada, foi possível determinar os melhores parâmetros de reação (tempo e temperatura) para o PLGA na proporção 80/20 (lactídeo/glicolídeo). Com uma temperatura de 110 °C e tempo de reação 72h o rendimento da reação é superior a 90%. Os valores de massas moleculares obtidas entre os testes, ainda são baixos quando comparados com os valores obtidos por outros autores na literatura. Novos testes estão sendo conduzidos, utilizando dímeros preparados no laboratório. Testes substituindo o vácuo por uma atmosfera de nitrogênio também estão sendo realizados. Essas duas substituições podem aumentar o valor final da massa molecular do polímero. Em relação à caracterização, as técnicas utilizadas confirmaram a estrutura esperada do polímero.</p><hr/><title>Abstract</title><p>According to the World Health Organization, cancer is a leading cause of death worldwide. A radiotherapy method extensively used in prostate cancer is brachytherapy, where the area requiring treatment receives radioactive seeds. Iodine-125 seeds can be inserted loose or stranded in bioabsorbable polymers produced from poly(lactic-co-glycolic acid) (PLGA). We developed the synthesis methodology for PLGA and the results obtained show that it was possible to determine the optimal reaction parameters (time and temperature) for PLGA in 80/20 (lactide/glycolide) ratio. The yield was higher than 90% using a temperature of 110 °C and reaction time of 72 hours; however, the molecular weight values ​​obtained are very low compared to those obtained by other authors. New tests using previously synthesized dimers and nitrogen atmosphere are being performed. These conditions could potentially increase the molar mass of PLGA. All techniques used confirmed the expected structure of the polymer.</p> <![CDATA[Sheets of cassava starch - poly (vinyl alcohol) produced by extrusion: effect of formulation on the color and opacity]]> <title>Resumo</title><p>Foram produzidos 12 laminados com diferentes proporções de amido de mandioca, poli(vinil álcool) (PVA) e glicerol por extrusão usando um planejamento de mistura. A opacidade dos materiais variou entre 31 e 56%, e a concentração de PVA e a interação entre as concentrações de amido e PVA foram os principais responsáveis pelo aumento da opacidade. A diferença de cor (ΔE*) variou entre 20-30, sendo a concentração de amido o principal responsável pelo aumento da diferença de cor, por promover uma coloração mais amarelada nos laminados.</p><hr/><title>Abstract</title><p>Twelve sheets were produced by extrusion with different proportions of cassava starch, poly (vinyl alcohol) (PVA) and glycerol using a mixture design. The opacity of the materials ranged from 31 to 56%, and the concentration of PVA and the interaction between starch and PVA concentrations the mainly responsible for increasing opacity. The color difference (ΔE*) ranged from 20 to 30, the concentration of starch being primarily responsible for increasing in color difference by promoting a more yellowish color in sheets.</p>