RESUMO

Hybrid coatings of SiO2 and recycled unsaturated polyester resin (R-UPR) from recycled polyethylene-terephthalate (PET) were prepared by the sol-gel process on glass substrates. First, SiO2 was synthesized by the sol-gel process using a tetraethyl orthosilicate (TEOS) solution. Next, bis(2-hydroxypropyl-terephthalate) (BHPT) was synthesized from mechanical and chemical recycling (glycolysis) of post-consumer PET bottles in propylene glycol (PG) using ZnA as catalyst, in a Vessel-type reactor (20-200 °C); maleic anhydride (MA) was added and, following the same procedure, the unsaturated polyester (UP) was synthetized, which was cooled to room temperature. Next, styrene (St) and benzoyl-peroxide (PBO)-initiator were added to obtain R-UPR. TEOS (T) and three hybrid solutions were synthesized, with molar ratios of 0:1:0 (T), 1:2:0.25 (H1), 1:1:0.25 (H2), and 1:0:0.25 (H3) for R-UPR:TEOS:3-trimethoxy-(silyl)-propyl-methacrylate (TMSPM), respectively, with which TC, HC1, HC2, and HC3 coatings were elaborated using the immersion technique and polymerized (120 °C for 24 h). The solutions were characterized by FT-IR and TGA, and the coatings by SEM, nanoindentation, AFM, adhesion, and contact angle. The results showed that SiO2 enhanced mechanical (hardness and Young's modulus) and thermal properties of the R-UPR. The coatings adhered perfectly to the substrate, with thicknesses of micrometer units and a flat surface; in addition, hydrophilicity decreased as SiO2 decreased.

RESUMO

This study aimed to evaluate the capacity of novel experimental hybrid coatings (HC) to reduce dentin permeability and to verify their resistance to erosive and abrasive challenges. Dentin disc specimens (1 mm thick) were treated with 0.5 M EDTA solution and randomly allocated into three experimental groups (n = 10): Control (Saliva); Concentrated Hybrid Coating (TEOS/GPTMS/Y-APS); and Diluted Hybrid Coating (1:3 ratio with distilled water). Dentin permeability was assessed by hydraulic conductance in the following experimental time periods: post-EDTA, post treatment, post erosion (5 min in 0.05 M citric acid solution, pH = 3.8), and post abrasion (toothbrushing for 3,900 cycles). Dentin permeability percent was calculated with respect the values of post-EDTA for each experimental time. The morphology of the surface of extra dentin specimens was examined by scanning electron microscopy (SEM) in the same time periods (n = 3). Permeability data were analyzed by two-way repeated measures ANOVA and Tukey tests (p < .05). Both HC presented significantly lower dentin permeability than control post treatment and post erosion (p < .05), without difference between them (p > .05). Post abrasion, there were no significant difference among groups (p > .05). Post treatment and post erosion, the HC seemed to flow into the tubules, occluding them, while the tubules in control remained opened. Post abrasion, the tubules appear to be occluded in all groups. In conclusion, the experimental hybrid coatings were capable of reducing dentin permeability after treatment. They were also able to resist to erosive and abrasive challenges, with the advantage of forming thinner and colorless films that can be potentially used to treat dentin hypersensitivity.

Assuntos

Ácido Cítrico/efeitos adversos , Permeabilidade da Dentina/efeitos dos fármacos , Sensibilidade da Dentina/prevenção & controle , Sensibilidade da Dentina/terapia , Teste de Materiais , Erosão Dentária/prevenção & controle , Erosão Dentária/terapia , Escovação Dentária/efeitos adversos , Dentina/efeitos dos fármacos , Humanos , Microscopia Eletrônica de Varredura , Distribuição Aleatória , Saliva , Propriedades de Superfície/efeitos dos fármacos

RESUMO

The demand for hydrophobic polymer-based protective coatings to impart high corrosion resistance has increased recently. The increase of the hydrophobicity in a hybrid coating is a new challenge, for that reason and in order to protect a metallic surface of oxidant agents, a poly (methyl methacrylate) (PMMA) coating with the addition of a different amount of silicon dioxide (SiO2) was developed. The hybrid coating was applied on a sample of stainless steel AISI 304 by the dip-coating method. The characterization of the coatings was determined by electrochemical impedance spectroscopy and with a scanning electrochemical microscopy. The best coatings were PMMA and PMMA + SiO2 0.01% that exhibits a real impedance in the Nyquist diagram of 760 and 427,800 MΩ⋅cm2, respectively, and the modulus of the real impedance in the Bode diagram present values of 2.2 × 108 and 3.3 × 108 Ω⋅cm2. Moreover, the phase angle presents constant values around 75° to 85° and 85° for the PMMA and PMMA + SiO2 0.01%, respectively. Moreover, the values of the real resistance for the PMMA + SiO2 0.01% coating present values in the order of Mega-ohms despite the coating exhibits an artificial defect in their surface. The contact angle test showed that the hydrophobicity of the hybrid PMMA + SiO2 0.01% coating is higher than that of the pure PMMA coatings. The hybrid PMMA + SiO2 coatings developed in this work are a very interesting and promising area of study in order to develop efficient products to protect metallic surfaces from corrosion phenomenon.