A non-bisphenol-A epoxy resin with high Tg derived from the bio-based protocatechuic Acid:Synthesis and properties

Preparation and Properties of Epoxy Adhesives with Fast Curing at Room Temperature and Low-Temperature Resistance

Developing a highly efficient multifunctional epoxy adhesive is still an enormous challenge, which can rapidly cure at room temperature and has excellent low-temperature resistance performance and is crucial for the epoxy adhesive and electrical sealing fields during severe cold seasons. Herein, diglycidyl phthalate (DP) was synthesized with phthalic anhydride (PA) and epichlorohydrin (ECH) to enhance the curing rate and low-temperature resistance of bisphenol A diglycidyl ether (DGEBA) adhesive. The modified DP/DGEBA adhesives were systematically analyzed by gel time, mechanical properties, and aging resistance (time, temperature, and dry/wet treatment). The results showed that DP with highly active ester groups significantly accelerates the curing speed of DP/DGEBA. DP's rigid aromatic ring-benzene ring and flexible group-ester group gave the adhesive better low-temperature resistance. When the addition of DP was 10 wt % (based on the mass of DGEBA), the gel time of DP/DGEBA epoxy adhesives was reduced by 58 min compared to unmodified DGEBA epoxy adhesive, and after aging at low temperature (-20 °C) for 7 days, the tensile shear strengths of polyvinyl chloride (PVC) and aluminum plate increased by 76.2 and 80.6%, respectively. The results of non-isothermal curing kinetics and dynamic mechanical analysis suggested that when the amount of DP was 10 wt %, the reaction activation energy of DP/DGEBA epoxy adhesive decreased by 4.0%, and the cross-linking density increased by 8.9%. Moreover, the toughness of the modified adhesive was also improved. This study opens up a feasible way for the development of a low temperature-resistant epoxy adhesive cured rapidly at room temperature in practical application.

Sustainable production of catechol derivatives from waste tung nutshell C/G-type lignin via heterogeneous Cu-NC catalytic oxidation

The sustainable production of catechol derivatives is a challenging task. Catechyl (C) and guaiacyl (G) lignins coexisting in waste tung nutshells are promising feedstocks to form valuable catechol derivatives, but the depolymerization of C/G lignin typically involves a catalytic reductive process that cannot produce these oxidized aromatic chemicals. Herein, we demonstrated that the sustainable production of catechol derivative aldehydes and acids from C/G lignin could be achieved through a heterogeneous copper-catalyzed oxidative process. Under optimized conditions, the Cu-NC-800 catalyst affords a 43.5 mg g-1 yield (8.9 wt%, based on Klason lignin) of aromatic aldehydes (protocatechuic aldehyde, vanillin) and acids (protocatechuic acid, vanillic acid). XRD and XPS analyses showed that CuO and Cu2O may be the active species during the heterogeneous oxidation of the Cu-NC-800 catalyst. This study opens new opportunities for the sustainable production of catechol derivatives from C/G-type lignin.

Efficient Toughening of DGEBA with a Bio-Based Protocatechuic Acid Derivative

In this work, a bio-based epoxy resin, protocatechuic acid diester epoxy resin, (PDEP), was synthesized using protocatechuic acid. The structure and properties of PDEP have been characterized by ¹H NMR, ¹³C NMR, and Fourier transform infrared. After different contents of PDEP were added to diglycidyl ether of bisphenol A (DGEBA), the modified epoxy resins were cured by 4,4'-diaminodiphenylmethane (DDM). With the addition of a flexible long-chain bio-based monomer to improve toughness, the impact strength was 50 kJ·m^-2 with only 5.0 wt % PDEP; compared with pure DGEBA, the impact strength was 27 kJ·m^-2. Further, an increase in T _g should be confirmed from the mechanical cross-linking density and rigidity group content. The single T _g proved the homogeneous phase structure of the PDEP-cured resin. Morphology exhibiting the ductile fracture of the cured resin was confirmed by scanning electron microscopy. Overall, this work demonstrates the utilization of renewable protocatechuic acid as an effective modifier for epoxy resin, which reflects its potential application.

Processing of Functional Composite Resins Using Deep Eutectic Solvent

Deep eutectic solvents (DESs)—a promising class of alternatives to conventional ionic liquids (ILs) that have freezing points lower than the individual components—are typically formed from two or more components through hydrogen bond interactions. Due to the remarkable advantages of biocompatibility, economical feasibility and environmental hospitality, DESs show great potentials for green production and manufacturing. In terms of the processing of functional composite resins, DESs have been applied for property modifications, recyclability enhancement and functionality endowment. In this review, the applications of DESs in the processing of multiple functional composite resins such as epoxy, phenolic, acrylic, polyester and imprinted resins, are covered. Functional composite resins processed with DESs have attracted much attention of researchers in both academic and industrial communities. The tailored properties of DESs for the design of functional composite resins—as well as the effects of hydrogen bond on the current polymeric systems—are highlighted. In addition to the review of current works, the future perspectives of applying DESs in the processing of functional composite resins are also presented.