Search

Controlled release systems were developed using biodegradable polymers/copolymers via polycondensation of glycerol with acids (citric, adipic, and succinic) with potassium chloride (KCl) 0, 10, 20, and 40 wt% followed by crosslinking at 120°C. Polymers were characterized by thermogravimetry, X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and UV‐Vis spectroscopy. All are thermally stable up to 200°C, therefore suitable for release in countries where temperatures reach 50°C. Fractographic analysis showed rubbery (rough and ductile) and hard (smooth and brittle) polymers depending on the acid used. The release profiles showed that hydrophilic (polar) polymers are easily hydrolyzed, generating faster release reaching 52% in 120 h. Less polar polymers delay KCl release below 20% at the same time. Therefore, it was possible to adjust the release by controlling the fertilizer content and the type of polymer, designing a fast or slow release to meet the needs of a given crop. [ABSTRACT FROM AUTHOR]

Biodegradable, renewable, and environmentally friendly glycerol-based wood adhesives were synthesized through polycondensation reaction between dicarboxylic acids (sebacic and citric acid) and glycerol using different molar ratios, i.e. poly(glycerol sebacate) – PGS, poly(glycerol citrate-co-sebacate) – PGCS, and poly(glycerol citrate) – PGC. Thermal properties of the synthesized polymers were evaluated after cross-linking. Results showed that thermal stability was influenced by polymer molecular structure, being lower for PGC due to the presence of quaternary carbons of citric acid. Differential scanning calorimetry analyses showed an intermediate glass transition for the copolymer in comparison with homopolymers. Tensile shear strength tests showed that the presence of citric acid in the polymer improves adhesion and reduces adhesive flexibility, contrary to what happens to polymers with sebacic acid. This behavior was also proved through morphological analyses of the fracture surface. Adhesives with tailor-made properties were produced from glycerol, opening up new revenues for a by-product of the biodiesel production chain. [ABSTRACT FROM AUTHOR]

In the present work, the electrical properties of a natural rubber‐based nanocomposite (NR) filled with cellulose nanowhiskers (CNW) coated with polyaniline (PANI) were studied. We developed a statistic model that simulates nanocomposite microstructure and conductivity, calculated using the transfer matrix technique. A two‐dimensional network of resistors representing a microstructure of both the insulating region (NR) and conductive fillers (cellulose nanowhiskers coated with polyaniline ‐ CNWP) was developed. The conductance of bond between two neighboring sites in the CNWP filler and two neighboring sites of the NR matrix was estimated using Drude's equation and Dyre's formula, respectively. Results of the simulations show that the conduction process between two sites of NR follows the modified Dyre model (RFEB), while between two CNWP sites follows the modified Drude model. The theoretical‐experimental adjustment shows that the electrical conduction process occurs via hopping and tunneling between states located inside the CNWP phase, randomly distributed in the rubber matrix. [ABSTRACT FROM AUTHOR]

This paper reports for the first time the facile synthesis of hollow F‐doped SnO2 nanofibers by solution blow spinning (SBS) and their ethanol sensing performance. The as‐prepared nanofibers were characterized using scanning electron microscopy (SEM), x‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier‐transform infrared spectroscopy (FTIR), and electrochemical impedance spectroscopy (EIS). The gas sensing behavior of the F‐doped SnO2 nanofibers was investigated using a homemade test chamber. The results revealed the preparation of mesoporous F‐doped SnO2 hollow fibers with a diameter ranging from 207 ± 43 to 355 ± 41 nm. The combination of nanocrystalline hollow structure and F doping led to fast high‐responsive ethanol sensors at room temperature (RT) with good reproducibility and long‐term stability. These results indicate that F‐doped SnO2 hollow nanofibers are good candidates for building practical low‐temperature ethanol gas sensors. [ABSTRACT FROM AUTHOR]

The aggregation state of cellulose nanocrystals modified with surfactants (CNC/S) in water and CNC/S powder dispersion stability in chloroform were studied and correlated with mechanical properties of nanocomposites with poly(lactic acid) (PLA). Four types of nonionic surfactants were used: PEG 300, PEG 1000, poly(ethylene glycol) monooleate, and Pluronic® L44 (PL44). The CNC/PL44 showed the smallest size of CNC aggregates dispersed in water before freeze‐drying, as determined by atomic force microscopy. The respective powder also showed the lowest decay rate of relative turbidity among CNC/S dispersions in chloroform. This, together with the improved surface coverage of CNC by PL44, verified by zeta potential (large change in the zeta potential of CNC/S dispersion in chloroform) and thermogravimetric analysis (improved thermal stability of CNC/S powder), yielded the highest tensile strength at break (TS) among PLA/CNC/S nanocomposites. Despite none of surfactants produced nanocomposites with TS higher than PLA or PLA/CNC, the aggregation state of CNC/S in water is well correlated with mechanical properties of PLA/CNC/S nanocomposites prepared by solvent casting. This correlation indicates that hornification cannot be avoided for the conditions used to prepare CNC/S powder and that there are two opposite effects in preparation of PLA/CNC/S nanocomposites. First, the effectiveness of steric barrier of nonionic surfactants against aggregation during freeze‐drying depends on complete surface coverage of CNC, together with hydration of stabilizing chain. Since hydration depends on hydrophilicity of stabilizing chain and compatibility with PLA depends on its nonpolar nature, this strategy alone seems not to be efficient to produce high‐performance nanocomposites. POLYM. COMPOS., 40:E399–E408, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Copyright of Revista Eletrônica de Materiais e Processos is the property of Revista Eletronica de Materiaia e Processos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wood plastic composites (WPC), which are used in high‐value markets, contribute to solve some of the problems associated with municipal solid waste accumulation. In this study, the effect of cashew nutshell powder (CNSP) content on properties of formulations with recycled high‐density polyethylene, 5 wt% of maleic anhydride grafted polypropylene and 5 wt% of struktol TPW 113, a blend of complex, modified fatty acid ester, was evaluated. Mixtures containing from 20 to 60 wt% CNSP were melt‐processed, using a thermokinetic mixer. WPC's were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, and melt flow index (MFI) measurements. Composite morphology and mechanical properties were also accessed, respectively, by scanning electron microscopy and tensile tests. Results show that the tensile strength of composites decreased as the content of CNSP increased due to poor reinforcement–matrix interface and voids formed during residual cashew nutshell liquid (CNSL) vaporization. On the other hand, elastic modulus decreased and elongation at break increased, both indicating a plasticizing effect of the residual CNSL, confirmed by crystallinity and MFI data. Differences in the thermal stability of composites were restricted to thermal behavior of main components. POLYM. COMPOS., 39:2662–2673, 2018. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, nanofibrous mats of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) with different PLA/PEG ratios were prepared by solution blow spinning. Terpinen-4-ol, a major phytoconstituent from tea tree oil ( Melaleuca alternifolia) was added to the fibers and their antimicrobial activity against Aggregatibacter actinomycetemcomitans (ATCC 00078) was tested. Spun mats were characterized by scanning electron microscopy, thermogravimetric analyses, differential scanning calorimetry, Fourier-transform infrared spectroscopy (FTIR), and cell viability tests by biofilm grown on the surface of inhibitory fibers. Fibers had average diameters dependent on polymer ratio. PEG acted as a plasticizer resulting in a reduction in PLA crystallinity. Addition of PEG lead to a faster drug release. Fibrous mats with terpinen-4-ol, whose incorporation was verified by FTIR, showed an effective antimicrobial activity against A. actinomycetemcomitans, similar to those containing 0.12% chlorhexidine gluconate ( P < 0.05), used as both the positive control and the dose level recommended for patient treatment. These results confirm the potential of solution blow spun fibrous mats containing terpinen-4-ol in the treatment of aggressive periodontitis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45782. [ABSTRACT FROM AUTHOR]

In this study, blends based on a high density polyethylene (HDPE) and chitosan (CS) were successfully prepared by melt processing, in a laboratory internal mixer. The CS biopolymer content effect (up to maximum of 40%), and, the addition of bentonite clay modified with quaternary ammonium salt (CTAB) impregnated chitosan as a compatibilizing agent, on the properties of the blends was analyzed by Fourier transform-infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analyses (TG), tensile strength, and scanning electron microscopy (SEM). The use of clay modified with CTAB impregnated chitosan, employing a method developed here, improved the compatibility of HDPE with chitosan, and therefore the thermal and some of the mechanical properties were enhanced, making HDPE/chitosan blends suitable candidates for food packaging. It was possible to obtain products of synthetic polymer, HDPE, with natural polymer, chitosan, using a method very used industrially, with acceptable and more friendly properties to the environment, when compared to conventional synthetic polymers. In addition, due to the possibility of impregnated chitosan with quaternary ammonium salt exhibit higher antibacterial activity than neat chitosan, the HDPE/chitosan/organobentonite blends may be potentially applied in food containers to favor the preservation of food for a longer time in comparison to conventional materials. [ABSTRACT FROM AUTHOR]