Making organic coatings greener: Renewable resource, solvent-free synthesis, UV curing and repairability

Effect of Melamine Formaldehyde Resin Encapsulated UV Acrylic Resin Primer Microcapsules on the Properties of UV Primer Coating

Ultra-Violet (UV) coatings are widely adaptable of substrates and produce low emissions of volatile organic compounds. UV coatings can extend service life by adding self-healing microcapsules that restore integrity after sustaining damage. In this study, UV coating was used as a core material; microcapsules were produced and added to the UV coating to enhance its self-healing property, providing a good protection for both the UV coating and the substrate. UV primer microcapsules were prepared with UV primer as the core material and melamine formaldehyde resin as the wall material. The UV primer containing more than 98.0% solids content was mainly composed of epoxy acrylic resin, polyester acrylic resin, trihydroxy methacrylate, trimethyl methacrylate, and photo initiator. The preparation process of the UV primer microcapsules was optimized. Further, the UV coating was prepared with better UV primer microcapsules, and the effects of the UV primer microcapsules alongside the comprehensive properties of the coating were studied. The best preparation process for the UV primer microcapsules was as follows: the wall-core mass ratio was 1:0.50, Triton X-100 and Span-20 as emulsifiers with an HLB value of 10.04, the microcapsule reaction temperature was 70 °C, and the reaction time of the was 3.0 h. When the quantity of the UV primer microcapsules increased in the coating, color difference ΔE of the coating increased, gloss decreased, transmittance decreased, elongation at break increased and then decreased, roughness increased, and self-healing rate first increased and then decreased. When the addition of the UV primer microcapsules reached 2.0%, the color difference ΔE of the coating was 1.71, the gloss was 106.63 GU, the transmittance was 78.80%, the elongation at break was 3.62%, the roughness was 0.204 μm, and the self-healing rate was 28.56%, which were the best comprehensive properties of the UV primer. To improve the comprehensive properties of the UV coatings, the UV coatings were modified by a microcapsule technology, which gave the UV coatings a better self-healing property. The application range of microcapsules for the UV coatings was broadened. Based on the previous research of microcapsules in UV coatings, the results further refined the study of the effects of adding self-healing microcapsules to UV coatings using the UV coating itself as the core material.

Synthesis of Bio-Based Polyester Resins for Vat Photopolymerization 3D Printing

Driven by environmental considerations, the scientific community has directed great effort towards the synthesis of new materials derived from renewable resources. However, for photocurable resins, most commercially available building blocks still rely on petroleum-based precursors. Herein, we present a simple synthesis route for bio-based acrylate-modified polyester resins, whose viscosity is sufficiently low for processing them with vat photopolymerization 3D printing. The established synthesis route enables the gradual substitution of fossil-based raw materials with bio-based alternatives. The acid number, color and viscosity of the bio-based acrylic resins are characterized and photocurable formulations are prepared by adding a radical photoinitiator. The photopolymerization kinetics, and thermomechanical and mechanical properties of the photopolymers are investigated as a function of the resin structure and benchmarked against a commercially available petroleum-based counterpart. Finally, the processability of the new bio-based resins via digital light processing 3D printing is demonstrated and test specimens are successfully 3D printed with a resolution in the millimeter range.

A highly efficient and sustainable catalyst system for terminal epoxy-carboxylic acid ring opening reactions

The nucleophilic ring opening of epoxides by carboxylic acids is an indispensable transformation for materials science and coating technologies. Due to this industrial significance, improvements in operational energy consumption and catalyst sustainability are highly desirable for this transformation. Herein, an efficient, environmentally benign and non-toxic halide free cooperative catalyst system based on an iron(iii) benzoate complex and guanidinium carbonate is reported. The novel catalyst system shows improved activity over onium halide catalysts under neat conditions and in several solvents, including anisole and nBuOAc. Detailed mechanistic studies using FeCl3/DMAP as a catalyst revealed the importance of a carboxylate bridged cationic trinuclear μ3-oxo iron cluster and guanidinium carbonate or DMAP as a carboxylate reservoir due to its superior activity.

Recent advances in the development of green furan ring-containing polymeric materials based on renewable plant biomass

Fossil resources are rapidly depleting, forcing researchers in various fields of chemistry and materials science to switch to the use of renewable sources and the development of corresponding technologies. In this regard, the field of sustainable materials science is experiencing an extraordinary surge of interest in recent times due to the significant advances made in the development of new polymers with desired and controllable properties. This review summarizes important scientific reports in recent times dedicated to the synthesis, construction and computational studies of novel sustainable polymeric materials containing unchanged (pseudo)aromatic furan cores in their structure. Linear polymers for thermoplastics, branched polymers for thermosets and other crosslinked materials are emerging materials to highlight. Various polymer blends and composites based on sustainable polyfurans are also considered as pathways to achieve high-value-added products.

Synthesis of Hyperbranched Flame Retardants with Varied Branched Chains' Rigidity and Performance of Modified Epoxy Resins

To overcome the high flammability and brittleness of epoxy resins without sacrificing their glass transition temperature (Tg) and mechanical properties, three epoxy-terminated hyperbranched flame retardants (EHBFRs) with a rigid central core and different branches, named EHBFR-HB, EHBFR-HCM, and EHBFR-HBM, were synthesized. After chemical structure characterization, the synthesized EHBFRs were introduced into the diglycidyl ether of bisphenol A (DGEBA) and cured with 4, 4-diaminodiphenylmethane (DDM). The compatibility, thermal stability, mechanical properties, and flame retardancy of the resultant resins were evaluated. Results showed that all three EHBFRs could significantly improve the fire safety of cured resins, and 30 wt. % of EHBFRs (less than 1.0 wt. % phosphorus content) endowed cured DGEBA with a UL-94 V-0 rating. In addition, the increased rigidity of branches in EHBFRs could increase the flexural strength and modulus of cured resins, and the branches with appropriate rigidity were also beneficial for improving their room temperature impact strength and Tg.

Photocurable Glycerol- and Vanillin-Based Resins for the Synthesis of Vitrimers

In this study, photocurable resins based on glycerol and vanillin were designed, synthesized, and applied to digital light processing three-dimensional (3D) printing and vitrimeric abilities such as shape-memory, self-healing, and recyclability have been investigated. First, photocurable resins were prepared and synthesized by combining renewable resources and photocuring as an environmentally friendly strategy for the synthesis of vitrimers. Afterward, the most suitable resin for optical 3D printing was selected by photorheometry, and the thermal and mechanical properties of the resulting polymers were tested. Furthermore, by activating dynamic transesterification reactions at elevated temperatures, the photocured polymer exhibited self-healing, recyclability, and shape-memory properties. The vitrimer with a weight ratio of 8:2 of glycerol- and vanillin-based monomers demonstrated a welding efficiency of tensile strength up to 114.12%, 75% recyclability by alcoholysis, and shape-memory properties above and below two glass transition temperatures.

Biobased Composites by Photoinduced Polymerization of Cardanol Methacrylate with Microfibrillated Cellulose

Biobased monomers and green processes are key to producing sustainable materials. Cardanol, an aromatic compound obtained from cashew nut shells, may be conveniently functionalized, e.g., with epoxy or (meth)acrylate groups, to replace petroleum-based monomers. Photoinduced polymerization is recognized as a sustainable process, less energy intensive than thermal curing; however, cardanol-based UV-cured polymers have relatively low thermomechanical properties, making them mostly suitable as reactive diluents or in non-structural applications such as coatings. It is therefore convenient to combine them with biobased reinforcements, such as microfibrillated cellulose (MFC), to obtain composites with good mechanical properties. In this work a cardanol-based methacrylate monomer was photopolymerized in the presence of MFC to yield self-standing, flexible, and relatively transparent films with high thermal stability. The polymerization process was completed within few minutes even in the presence of filler, and the cellulosic filler was not affected by the photopolymerization process.

Rubber Seed Oil-Based UV-Curable Polyurethane Acrylate Resins for Digital Light Processing (DLP) 3D Printing

Novel UV-curable polyurethane acrylate (PUA) resins were developed from rubber seed oil (RSO). Firstly, hydroxylated rubber seed oil (HRSO) was prepared via an alcoholysis reaction of RSO with glycerol, and then HRSO was reacted with isophorone diisocyanate (IPDI) and hydroxyethyl acrylate (HEA) to produce the RSO-based PUA (RSO-PUA) oligomer. FT-IR and 1H NMR spectra collectively revealed that the obtained RSO-PUA was successfully synthesized, and the calculated C=C functionality of oligomer was 2.27 per fatty acid. Subsequently, a series of UV-curable resins were prepared and their ultimate properties, as well as UV-curing kinetics, were investigated. Notably, the UV-cured materials with 40% trimethylolpropane triacrylate (TMPTA) displayed a tensile strength of 11.7 MPa, an adhesion of 2 grade, a pencil hardness of 3H, a flexibility of 2 mm, and a glass transition temperature up to 109.4 °C. Finally, the optimal resin was used for digital light processing (DLP) 3D printing. The critical exposure energy of RSO-PUA (15.20 mJ/cm2) was lower than a commercial resin. In general, this work offered a simple method to prepare woody plant oil-based high-performance PUA resins that could be applied in the 3D printing industry.

Versatile Phosphate Diester-Based Flame Retardant Vitrimers via Catalyst-Free Mixed Transesterification

We herein report a new vitrimer system integrated with UV curability, recyclability, and flame retardancy. Energy-efficiency, sustainability, and safety have been required features for next-generation polymer materials. Various attempts have been made to endow thermoset polymers with rapid prototyping capacity, recyclability, and flame retardancy. Thermoset vitrimers based on covalent adaptable networks (CANs) are recyclable and remoldable but are generally not UV curable or flame retardant. Here, we present a conceptually novel option to achieve fast exchange reactions in CANs via catalyst-free mixed transesterification of a UV curable phosphate diester-based acrylate cross-linker. In this system, the phosphate diesters serve as reversible covalent bonds, hydrogen bonding ligands, and flame-retardant structures, while acrylate groups serve as UV curable units as well as transesterification collaborators. After the facile UV curing, an intrinsic flame-retardant and mechanically strong dynamic network was achieved due to abundant hydrogen bonds between P-OH and C═O structures. Additionally, this highly cross-linked network exhibited an attractive recyclability even at temperatures lower than T_g. This phosphate diester-based mixed transesterification concept represents an efficient approach for developing multifunctional vitrimers and can also be generalized into other thermally cured polymer systems.

Preparation and Characterization of Waterborne UV Lacquer Product Modified by Zinc Oxide with Flower Shape

In this paper, the waterborne UV lacquer product (WUV) was used as the main raw material, zinc oxide (ZnO) was used as the additive, and the stearic acid as the surface modifier. According to the method of spraying coating on the surface of poplar wood (Populus tomentosa), a simple and efficient preparation method was carried out to generate a super-hydrophobic surface and enhance the erosion resistance of the coating. By testing, the contact angle (CA) of water on the coating surface can reach 158.4°. The microstructure and chemical composition of the surface of coatings were studied by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The results showed that under acidic conditions, the non-polar long chain alkyl group of stearic acid vapor molecule reacted with the hydroxyl group in acetic acid, the metal ions of the ZnO were displaced to the stearic acid and generated globular zinc stearate (C₃₆H₇₀O₄Zn). The hydrophobic groups –CH₃ were grafted to the surface of zinc stearate (ZnSt2) particles and the micro/nano level of multistage flower zinc stearate coarse structure was successfully constructed on the surface of poplar wood, which endowed it with superhydrophobic properties. It is shown that the coating has good waterproof and erosion resistance.