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Jun 2023
Rifkatu Kambel DogaraCorresponding author
The increasing demand for environmentally-friendly materials has led to a surge in research on the production of biodegradable polymers. In this study, we investigate the synthesis of a biodegradable polymer by graft copolymerization of gum Arabic (GA) and polyethylene glycol (PEG). GA, a natural polysaccharide and PEG, a synthetic water-soluble polymer, were used as the backbone and graft monomer, respectively. The graft copolymerization was carried out using benzoyl peroxide as an initiator and performed under nitrogen atmosphere. The resulting polymer was characterized by Fourier transform infrared (FTIR) spectroscopy, Xray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The FTIR spectra confirmed the formation of the graft copolymer, and TGA analysis showed that the copolymer had higher thermal stability than GA. The DTA thermograms indicated two thermal events. The evaporation of water and organic polyethylene glycol components was measured, and the first mass loss was due to the loss of adsorbed and structural water in the gum Arabic, which occurred between 31.87 and 180°C, while the second, corresponding to the pyrolysis of polyethylene glycol functional groups and polysaccharide decomposition, resulted in a 70% mass loss. SEM morphological analysis of gum Arabic showed aggregates of high irregularity in particle shape. The cracks and holes obtained in the Gum Arabic micrograph disappeared from the new gum Arabic-graft-polyethylene glycol, leaving a smooth surface with scattered particles in the image, which was due to the grafting copolymer. From the XRD patterns, the percentages of the amorphous and crystalline phases were determined. The results show that gum Arabic has a 78% degree of crystallinity, whereas gum Arabic-graft-polyethylene glycol has the lowest value of 51%. Biodegradation activity was observed using the fungus Aspergillus flavus on different days on gum Arabic-g-polyethylene glycol. The results clearly showed inhibition zones with a change in the state of the copolymer from solid to liquid from days 8 to 14. These results indicate that the GA-PEG copolymer has potential as a biodegradable material for use in various applications, such as packaging, agriculture, and medical industries.
Jul 2016 DOI 10.14302/issn.2473-1005.jdoi-16-1080
Guenka Palma-Dibb ReginaCorresponding author
Department of Restorative Dentistry, Ribeirão Preto School of Dentistry, University of São Paulo. Av. Café, s/nº - CEP: 14040-904 - Monte Alegre. Ribeirão Preto – SP, Brazil.
When a composite resin restoration is photopolymerized, a considerable amount of heat can be produced, potentially causing pulpal injury. Objective: Evaluate the influence of the type of light source and remaining dentin thickness on the temperature increase in the pulp chamber while curing composite resin restorations. Material and Methods: Ninety-six tooth fragments obtained from bovine incisors were divided into groups/subgroups (n=12), according to the light source (LED and halogen light) and remaining dentin thickness (3.5, 3, 2, and 1mm). Class I cavities were prepared and restored with a composite resin. A temperature increase was obtained during photopolymerization of the adhesive and each composite increment. Data were analyzed using ANOVA and Fisher’s Test (α=5%). Results: LED promoted higher temperature increments when compared with the halogen light. Temperature levels were the lowest for 3.5mm-thick and the highest for 1mm-thick remaining dentin. Levels registered during the photopolymerization of each composite increment were superior for LED. Conclusions: Both light sources result in temperature increases above 5.5°C. Additionally, the remaining dentin thickness of 1mm promoted the largest temperature increase.
Jun 2016 DOI 10.14302/issn.2473-1005.jdoi-16-1079
Guenka Palma-Dibb ReginaCorresponding author
Department of Restorative Dentistry, Ribeirão Preto School of Dentistry, University of São Paulo. Av. Café, s/nº - CEP: 14040-904 - Monte Alegre. Ribeirão Preto – SP, Brazil.
The present study evaluated in vitro the influence of two light sources in composite resin microhardness in different distances of photopolymerization. Two light sources were used (halogen, LED) to photopolymerize the composite resin (Filtek Z250; Esthet-X) in different distances surface (1,2,3 and 4 mm), totalizing 96 specimens. Microhardness Knoop test’ were made on the specimens top and bottom faces. The data were submitted to ANOVA and Fisher tests (α=5%). It was observed a significant difference (p<0.05) between the resins, in which Z250 presented higher values than Esthet-X (p<0.05). There was difference also between the halogen and LED, where the halogen showed better results with Z250 and the LED with Esthet-X. The top surface presented better value (p<0.05) compared to the bottom surface. It can be concluded that the light source and the photopolymerization distance influenced the composite resin microhardness, which it had lower proprieties with increase of the photopolymerization distance.
Sep 2021 DOI 10.14302/issn.2639-3166.jar-21-3955
Masoero GiorgioCorresponding author
Accademia di Agricoltura di Torino, Via A. Doria 10, 10123 Torino (Italy).
In the cultivation of vines the risk of hail appears to be increasing with the ongoing climate change. The use of protective plastic nets is spreading, but there is little knowledge on the additional processing costs and on the phenological and qualitative consequences, moreover, as depending on different colors of the nets. Thus, a randomized trial was carried out in Nebbiolo, a wine of great aging, testing three plastic anti-hail nets colored in green, gray and black. Results showed that 24% more-time was necessary for the canopy management practices under the nets. The black nets advanced the ripening process, with a berry weight decrease of about 13%. A significant decrease in the seed number per berry was observed under the black nets (-45%), while a rise (+102%) was observed under the green and gray nets with a parallel increase in the pH of the juice (+13%) and in malic acid (+28%) under the green nets. The berry skin did not show any significant differences in polyphenol and anthocyanin profiles, while the plants that matured in the upper part of the vineyard showed higher level in the berry skin extractable flavan-reactive to vanillin, and total polyphenol. On the other hand, in the seeds grown under green nets an increase in the extractable polyphenol compounds was observed, sign of a delay in seed ripening, with a higher tannin polymerization ratio, preserving the malic acid, and decreasing the acidity of the berry. In conclusion, the use of colored green may be a useful tool against excessive microclimatic warming and / or irradiation. The field internal variability affects much more the ripening dynamics than the nets used. A second aim was to develop a smart NIR SCiOTM model for polyphenols and the results were in line with the favorable expectations, providing R2 predictions of about 0.74 from the skin and 0.81 from the seeds.
Nov 2020 DOI 10.14302/issn.2689-2855.jan-20-3616
Hossien Hosseini SeyedCorresponding author
Department of Chemistry, Faculty of Science, Islamshahr Branch, Islamic Azad University, Tehran, Iran, Nika Pooyesh Strategic Sciences Research Institute, NBP Economic Group, Tehran-Iran
The composites of Cu, Carbonyl iron (CI), carbon nanofiber (CNF), graphite nanoflake (GNF)/polypyrrole (PPy) and [(Cu-CI-CNF-GNF) 0.5-PAA]-PPy0.5 were synthesized via different methods by in-situ polymerization on the surface of nanoparticles (NPs) with core-shell structure. This paper describes a method for polyacrylic acid (PAA) coating of NPs in aqueous solution. Then PPy coating was performed by template polymerization on NPs-PAA. Morphology, magnetic and conductivity properties were observed via scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and four probe method, respectively. The microwave characterization of nanocomposite was evaluated through arch test based on a network analyzer. The PPy nanocomposites possessed the excellent microwave multi absorbers properties in 2-18 GHz. It was also found that nanocomposites with 50% w/w and light weight exhibit good microwave absorbing properties in 2-3 GHz and 5-14 GHz frequency, so can be used to cellphone, radio frequency and radar shielding.