Macromolecular Symposia最新文献

Composites with polyaniline (Pani) in cellulosic matrices have been studied as Pani electrodes in many applications, but the presence of an insulating network causes a reduction in conductivity, and the electrochemical properties of the composites are difficult evaluate. This work, propose an easy synthesis of Pani into a membrane of bacterial nanocellulose produced from Kombucha tea fermentation by using the well-known aniline interfacial polymerization. To promote the polymer formation through all the large surface area of the three-dimensional (3D) membrane, the monomer and an oxidant are forced to penetrate the cellulosic matrix by vacuum filtration using different methodologies. Optical and scanning electron microscopies (SEMs) show that Pani is deposited even on the inner surface of the bacterial nanocellulose membrane, and cyclic voltammetry (CV) shows that the redox properties of Pani are maintained. Finally, higher current peaks are used to propose an easy methodology to produce Pani/bacterial nanocellulose electrodes with better electrochemical activity.

Brazil is the leading orange juice producer worldwide. Only about 50% of an orange is juice, so an enormous amount of waste is generated annually. In this context, studies involving alternatives for repurposing the remaining 50%, so it is not wasted or sent to landfill, are an issue of responsibility. In the present work, pectin is extracted to obtain a film-forming solution (FFS). The extracted pectin is classified as high ester pectin since its degree of esterification (%DE) is higher than 50%. The FFS gives rise to transparent films with a low yellowing index. The addition of CaCl₂ produces a crosslinked film with a 35% and 50% percentage increase in the contact angle and tensile strength, respectively. A FFS is proposed to be used without and with CaCl₂ as edible packaging material. Herein, it is applied as an edible coating (EC), directly onto the peeled apple slices, or as an edible wrapping film. Both strategies aim to delay the browning of apples, evaluated by the browning index (BI). This result is important for the marketing of fresh-cut fruits since the acceptance by consumers is strongly influenced by visual aspects.

The growing demand for carbon fiber-reinforced thermoplastic and thermoset (CFRT) composites, mainly in the aerospace, automotive, and energy industries, is due to obtaining lighter components. However, the amount of waste generated during the CFRT production process and at the end of its useful life has been increasing sharply, urgently requiring viable solutions that create less environmental impact in its final disposal. The mechanical recycling process has been presented as an economically and environmentally viable alternative to minimize the environmental impacts generated by the accumulation of this waste in the environment. Therefore, in this study, possible contaminations arising from the grinding process of waste composites reinforced with carbon fiber (CF) based on thermoplastics, polyamide 6 (CF/PA6), low melting poly (aryl ether ketone) (CF/PAEK), poly (phenylene sulfide) (CF/PPS), and fast-curing epoxy thermoset, are investigated. The composites are ground in a knife mill, resulting in materials measuring (2.6 ± 1) mm. Through differential scanning calorimetry (DSC) analysis, it is observed that the thermal profile of the ground composites is not changed; only the CF/PA6 composite shows an increase of 10% in the value of the degree of crystallinity. X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrometer show no metallic contamination from the grinding process. Only low levels of aluminum contamination are observed (below 2.7 wt%), attributed to the comminution step of the waste using an angle grinder adapted to cutting discs with abrasive aluminum oxide grains before the grounding process in the knife mill.

This study explores the potential of sustainable materials by combining biodegradable polymers with agro-industrial waste. It aims to offer alternatives to mitigate the adverse environmental impacts of single-use food packaging. The aim is to evaluate the potential of a composite material made from a polylactic acid (PLA)/polybutylene adipate-co-terephthalate (PBAT) blend, reinforced with rice husk (RH), as a viable alternative for food packaging. Two blends containing 10–20 wt% of PBAT (BL1 and BL2) and four composites with 10–20 wt% of RH reinforcement (CO1, CO2, CO3, and CO4) are tested to determine the most suitable formulation in terms of barrier properties. The samples are characterized using Fourier-Transform Infrared Spectroscopy (FTIR), contact angle measurements, Scanning Electron Microscopy (SEM), water absorption, and moisture absorption test. FTIR and SEM analyses reveal partial immiscibility between PLA and PBAT in blends BL1 and BL2. In the SEM analyses, composites CO1 and CO3 (10 wt% RH) exhibit better RH dispersion, resulting in lower water absorption and higher moisture barrier properties. However, the hydrophilic nature of RH indicates the need to improve the interaction at the fiber–matrix interface to optimize performance. Additional studies are ongoing to evaluate additional properties and feasibility for large-scale production, aiming at sustainable industrial applications.

Polyaniline (Pani) is widely studied for power sources due to its easy synthesis, good chemical and thermal stabilities, high electrical conductivity and reversive oxidation/reduction processes. However, the interaction between Pani and the carbon substrate used as a current collector interferes with the efficiency of the final electrode. So, the present work aims at evaluating the effect of plasma functionalization of textile carbon fibers (CFs) with the intention of promoting conjugated covalent bonds between the substrate and the polymer chain, intensifying their interaction and electron transfer. The applied methodology is based on exposing CF to Ar/N₂ plasma to promote reactive groups on the surface and to create anchors to the growth of the polymer chain in the following interfacial synthesis of Pani. For comparison purposes, Pani electrodes are produced using CF with no treatment and CF with previously adsorbed aniline. The morphological characterization through scanning electron microscopy (SEM), allied with X-ray photoelectron spectroscopy (XPS), shows modifications in the fiber rugosity and the insertion of polar and N-functional groups on the surface. Finally, the electrochemical properties of the electrode are evaluated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show a lower impedance, a higher peak, and higher capacitive currents for the electrodes whose CF are treated by Ar/N₂ when compared with electrodes with untreated CF or with adsorbed aniline.

For decades, polyethylene terephthalate (PET) has been a prominent material for high-performance polymer fibers, finding widespread applications in offshore mooring. PET offers cost-effectiveness, high strength, ease of processing, compatibility with other fibers, and recyclability. This article presents the depolymerization of PET for material aging via hydrolysis conducted with seawater (South Atlantic) at three different elevated temperatures, with hydrolysis time of up to 100 days. Three PET fibers with different linear densities are used, and the experimental investigation involves measuring the breaking strength through yarn break load (YBL) tests to evaluate the effect of hydrolysis conditions (time, temperature) on the mechanical behavior of the multifilaments. A constant reduction in strength is observed for all PETs due to hydrolysis time. However, within the studied temperature range, the maximum strength loss is not always associated with the highest temperature. Additionally, several models are used to fit the effects of hydrolysis exposure time and temperature on yarn strength, providing both 2D and 3D models that describe the phenomenon.

Corrosion is a natural phenomenon that affects many sectors that use metallic materials in their industrial plants, including the oil industry. In this sector, corrosion phenomena occur frequently in metal pipes, generating economic losses, environmental damage, and safety risks in general. The aim of this study is to evaluate the addition of laboratory-synthesized reduced graphene oxide (rGO) to an epoxy resin on the corrosion resistance of coatings for use in the oil sector. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM) analyses are carried out on the synthesized nanoparticles and on the nanocomposite coatings, which are prepared with 0.1–0.5 wt% of rGO. SEM analysis shows that there is a decrease in the number of defects on the surface of the samples as the concentration of rGO increases up to 0.3 wt%. The corrosion resistance of the coatings is evaluated by electrochemical impedance spectroscopy (EIS), which shows that the addition of rGO to the epoxy matrix improves corrosion protection compared to the pure coating, as it increases the diffusive path of the corrosive agents. The nanocomposite coating with 0.3 wt% rGO shows better anti-corrosion performance. This material can be applied both as an external and internal anti-corrosion coating in any industrial sector, as well as in the oil and gas industry.

Environmental issues caused by polymeric materials residue are an emerging problem. Biodegradable and biobased materials are great alternatives that need improvement in their properties. The goal is to produce and characterize starch/PVA blend films with lignin to improve the properties of the blend and determine the optimum amount of lignin. Flexible films are produced by casting using 75% starch, 25% polyvinyl alcohol (PVA), and varying quantities of lignin (0%, 0.5%, 1%, and 2%). Optical, thermal, and water interaction properties are analyzed. The addition of lignin make the films more translucent and with red and yellow colors. Moisture absorption drops 34% with the incorporation of the additive. The film with 0.5% lignin shows significant improvement in all the properties tested, showing a potential to be applied as a flexible and biodegradable packaging material.

The study investigates the characterization and toxicity of two types of phenolic foams: Floral (FF) and Hydroponic (HF), used in floral arrangements and hydroponic structures. These foams contain a resin with a free phenol content ranging between 5.0% and 8.0%, a substance harmful to plant development and ecosystem contamination. Methods such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and gas chromatography-tandem mass spectrometry (GC-MS/MS) are used for characterization. Acute exposure ecotoxicological tests are conducted with Daphnia magna for the FF sample and lettuce seeds (Lactuca sativa) for both FF and HF samples. Results reveal structural similarities between the foams and phenolic resin, including the presence of residual free phenol at concentrations of 180 ppm in FF and 73 ppm in HF, and possibly different additive treatments between samples. The FF sample had a half maximal effective concentration (EC₅₀, 48 h) = 15.4 ± 2.7 g L⁻¹ for D. magna. Surprisingly, the HF sample proves more toxic to L. sativa than FF, suggesting a potential influence of additives released from the sample's composition beyond the free phenol. This study shows that improper phenolic foam disposal can harm both aquatic and land ecosystems.

Gaskets are sealing elements used in plate heat exchangers, which are subjected to aggressive conditions during service. In particular, the compression state, together alongside temperatures, can cause a premature deterioration of properties. To monitor and prevent such a situation, this study uses the TTS (time-temperature superposition) method and Arrhenius to predict the lifetime of FKM gaskets. For this purpose, thermo-oxidative aging is conducted at different temperatures for up to 6 months, monitoring compression set (CS) and Shore A hardness. The results indicate that the gasket can withstand periods of up to almost 300 days in service for an operating temperature of 140 °C.