A novel disulfide-containing monomer for photoinitiator-free self-healable photocured coatings

Disulfide-containing coatings are gaining importance due to the peculiar properties and responsiveness of S-S bonds, which make them suitable for several applications, first among them self-healable materials. Herein, a novel UV-curable diacrylated polyurethane monomer containing disulfide bonds (DSPDA) was synthesized through a one-step process without the need for further purification, as assessed by NMR and HPLC analyses. The photopolymerization kinetics of the monomer was studied through real-time FTIR, highlighting a fast and complete conversion even in the absence of a photoinitiator, thus demonstrating the self-initiating capabilities of the synthesized monomer based on the disulfide cleavage upon UV light exposure. Clear coatings having a Tg = 72 °C were obtained. The self-healing ability of the films was assessed: thanks to the presence of disulfide bonds in the cured coating, a recovery of the damage was obtained in only 10 min by heating at 100 °C

Photocuring of Epoxidized Cardanol for Biobased Composites with Microfibrillated Cellulose

Cardanol is a natural alkylphenolic compound derived from Cashew NutShell Liquid (CNSL), a non-food annually renewable raw material extracted from cashew nutshells. In the quest for sustainable materials, the curing of biobased monomers and prepolymers with environmentally friendly processes attracts increasing interest. Photopolymerization is considered a green technology owing to low energy requirements, room temperature operation with high reaction rates, and absence of solvents. In this work we study the photocuring of a commercially available epoxidized cardanol, and explore its use in combination with microfibrillated cellulose (MFC) for the fabrication of fully biobased composites. Wet MFC mats were prepared by filtration, and then impregnated with the resin. The impregnated mats were then irradiated with UV light. Fourier Transform InfraRed (FTIR) spectroscopy was used to investigate the photocuring of the epoxidized cardanol, and of the composites. The thermomechanical properties of the composites were assessed by thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis. We confirmed that fully cured composites could be obtained, although a high photoinitiator concentration was needed, possibly due to a side reaction of the photoinitiator with MFC

Photoinduced Processes as a Way to Sustainable Polymers and Innovation in Polymeric Materials

Photoinduced processes have gained considerable attention in polymer science and have greatly implemented the technological developments of new products. Therefore, a large amount of research work is currently developed in this area: in this paper we illustrate the advantages of a chemistry driven by light, the present perspectives of the technology, and summarize some of our recent research works, honoring the memory of Prof. Aldo Priola who passed away in March 2021 and was one of the first scientists in Italy to contribute to the field

Enhancing properties and water resistance of PEO-based electrospun nanofibrous membranes by photo-crosslinking

Abstract In this study, modified fibrous mats of poly(ethylene oxide) (PEO) were fabricated through the versatile technique of electrospinning. Acrylic monomers were added to PEO with different composition ratios, and the mats were irradiated. The kinetics of photo-cross-linking reaction in the presence of the acrylic cross-linkers, as well as the structural, thermal and mechanical properties of the nanofibers, were studied. The morphology of the fibrous membranes before and after water treatment was monitored, and the insoluble fraction of the fibers was measured. As a result, by tuning the photo-cross-linking reaction, the control over fibers properties was feasible. The photo-cured PEO-based nanofibrous mats showed the solubility resistance needed to use them as membranes and to apply them in aqueous environments, as in water treatment processes and biomedical applications. Graphical Abstrac

Compositionally Graded Hydrophobic UV-Cured Coatings for the Prevention of Glass Stress Corrosion

The use of glass in architecture is growing and is moving towards structural applications. However, the tensile strength of glass cannot be fully exploited because of stress corrosion. This is a corrosion triggered by stress applied to the material and dependent on environmental factors such as humidity and temperature. To protect glass from stress corrosion, we developed a UV-cured coating, characterized by hydrophobicity, barrier to water vapor properties, and good adhesion to glass, thanks to a compositional profile. The coating was obtained by combining a cycloaliphatic diacrylate resin with a very low amount of a perfluoropolyether methacrylate co-monomer, which migrated to the free surface, creating a compositionally graded coating. The adhesion to glass was improved, using as a primer an acrylated silane able to co-react with the resins. With a mechanical load test using the coaxial double ring set-up, we proved that the coating is effective in the inhibition of stress corrosion of glass plates, with an increase of 76% of tensile strength

Characterization of a hybrid nano-silica waterborne polyurethane coating for clay bricks

A transparent hybrid organic–inorganic waterborne coating was evaluated for the protection of clay bricks. The nanocomposite film was prepared by combining an environmentally friendly process based on UV-curing of water-based acrylic resins and a mild thermal treatment to form nanosilica in situ from alkoxysilane precursors. Coated and uncoated facing bricks were compared by scanning electron microscopy, surface profilometry, water wettability, and capillary rise tests. The hybrid coatings act as a moderate water repellent; interestingly, no appreciable alteration of the aesthetic properties of the brick was observed, in particular no gloss or color change appeared after the treatment

Emulsion Polymerization of Dihydroeugenol-, Eugenol-, and Isoeugenol-Derived Methacrylates

International audienc

Controlled cationic curing of epoxy composites with photochemically modified silanol encapsulated carbon black

Epoxy resins have been an inspiration in adhesives and coatings, however, uneven photopolymerization kinetics result in wrinkled surface and filler segregation, causing aesthetic and mechanical damage. Hence a control over curing kinetics is required not only to dodge filler segregation but also to control composite surface smoothness. In this study, photochemical modification of carbon black with mercaptopropyltrimethoxysilane, has resulted in unique silanol dendrites exterior on carbon black. Kinetic investigation confirmed that E-a for cationic polymerization of modified CB composite is three folds less in comparison to neat matrix, and two folds less in comparison to unmodified CB composite. Silanol dendrites have contributed on epoxy curing kinetics, through activated monomer mechanism. Samples have been characterized through XPS, FTIR, SEM, TGA, DSC, Raman, and EDX

Novel perfluoropolyalkylethers monomers: synthesis and photo-induced cationic polymerization

Several difunctional oligomers were synthesized by functionalizing perfluoropolyalkylether (PFPAE) chains with different vinyl ethers and epoxides end-groups. Due to their innate synthetic challenges and demanding purification protocols, the PFPAE derivatives were obtained in low yield and with an average functionality lower than 2. However, the functionalized PFPAE oligomers were successful in being used in photo-induced cationic polymerization processes, obtaining transparent and soft films. The influences of the fluorinated chains, and various end-groups on the photopolymerization process were investigated, as well their chemical stability, thermal degradation, and surface properties