In this study, a fully biobased composite reinforced by cotton fabrics was successfully fabricated by copolymerizing a bioderived unsaturated polyester (PEOI) with a green diluent, dimethyl itaconate (DI). The PEOI prepolymer was synthesized from itaconic acid (IA), oxalic acid (OA), and ethylene glycol (EG) via a simple polycondensation process and was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and viscosity measurements. Subsequently, the prepolymer was dissolved in DI to prepare a polymerizable unsaturated polyester resin (UPE) with low viscosity, excellent reactivity for free radical polymerization, and good compatibility with cotton fibers. After being reinforced by cotton fabrics, the resulting composites showed satisfactory material performance, including a strong tensile strength at break of approximately 34 MPa, a glass transition temperature (T g) of approximately 108 °C, and thermal decomposition temperatures (T d5%) ranging from 224 to 276 °C. These green composites derived from renewable resources are hopeful candidates for replacing petroleum-based UPE resins, and the family of IA derivatives may play promising roles in fabricating fully biobased composites.

To improve processability of benzoxazine monomer in preparation of composites, a water-slurry strategy was examined using several laboratory-scale instances. The water slurries were fabricated by mixing solid resin powder of 3-furfury-8-methoxy-3,4-dihydro-2H-1,3-benzoxazine with water and one type of filler particle, i.e., calcium carbonate, montmorillonite, or hollow glass beads. Experimental data show that approving liquidity can be achieved when more than 180 phr of water was mixed in the solid mixtures containing the resin powder and 100 phr of solid filler. The biobased composite prepared using the optimized condition exhibits outstanding mechanical properties and antifatigue performance as the composites prepared via solvent method. This water-slurry approach provides an environmentally friendly strategy to manuscript benzoxazine composites, offering benzoxazine with more promising applications in many industries such as building, wind energy, aircraft, and automobile.

Ring-opening polymerization of bifunctional benzoxazine has long been thought to produce a permanent network structure without reprocessing ability. Here, we demonstrate that surprising healability can be achieved by a controlled polymerization of an ortho-blocked bifunctional benzoxazine poly(oC-hda). The cured resin possesses a crosslinked structure, but can be deformed, remolded from crushed pieces or healed from mechanical damage. Based on a series of intensive experiments, we show that the healability can be explained by a dynamic bonding exchange mechanism between the phenoxy structures existing during the curing process. Moreover, we verify the possibility to heal the fatigue damaged poly(oC-hda) based composite to extend its service life. Our study provides another dynamic covalent bond to synthesize healable polymers, offering a broad platform for combining healability and desired thermosetting features together.

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A reactive diluent for the preparation of a fully biobased unsaturated polyester resin (UPR) was developed and is presented here. The diluent, 4-vinylguaiacol acetyl ester (AC4VG), was obtained via a simple two-step synthesis: decarboxylation from ferulic acid (FA) and acetylation of the decarboxylated product, 4-vinylguaiacol (4VG). This diluent shows excellent miscibility with biobased unsaturated polyester prepolymer (UPP) that had been synthesized from succinic acid (SA), 1,3-dihydroxypropane (PD), and itaconic acid (IA). A mixed solution of these possessed a very low viscosity at 174 mPa·s at room temperature when 40 wt% AC4VG was added. Moreover, its vinyl group brought high reactivity for free radical copolymerization with the UPP, and the benzene ring structure enabled a high glass transition temperature (T g) of the cured UPR. When the fully biobased UPR was reinforced by cotton fabric, a strong tensile strength at the break of approximately 65.8 MPa, a T g of 135 °C, and a T d5% of 276 °C were achieved. This work suggests that the fully biobased UPR reported here is a promising candidate for replacing petroleum-based ones, and the diluent AC4VG played an important role in the performance of this biobased UPR.