The development of more recyclable materials is a key requirement for a transition towards a more circular economy. Thanks to exchange reactions, vitrimer, an attractive alternative for recyclable materials, is an innovative class of polymers that is able to change its topology without decreasing its connectivity. In this work, a bisphenol compound (VP) was prepared from saturated cardanol, i.e., 3−pentadecylphenol and vanillyl alcohol. Then, VP was epoxidized to obtain epoxide (VPGE). Finally, VPGE and citric acid (CA) were polymerized in the presence of catalyst TBD to prepare a fully bio−based vitrimer based on transesterification. The results from differential scanning calorimetry (DSC) showed that the VPGE/CA system could be crosslinked at around 163 °C. The cardanol−derived vitrimers had good network rearrangement properties. Meanwhile, because of the dynamic structural elements in the network, the material was endowed with excellent self−healing, welding, and recyclability.

The need to improve the environmental friendliness and achieve the recycling of resins is an ongoing process for hot-melt adhesive technology. In this work, a new type of thermoreversible crosslinking hot-melt adhesive-based Diels Alder (DA) reaction was prepared. The critical idea was to efficiently initiate the esterification to yield furoic acid (FA)-grafted poly(vinyl alcohol) (PVA-g-FA), and then PVA-g-FA was mixed with N,N′-(4,4′-methylenediphenyl)dimaleimide (MDI) to finally obtain the thermoreversible crosslinking adhesive (PVA-g-FA/MDI). The experimental results indicated that the reversibility of the DA reaction between the furan rings and the maleimide groups allowed PVA-g-FA/MDI to be dynamically crosslinked. It was able to crosslink at a temperature of 80 °C and decrosslink at 120 °C. Moreover, the performances of hot-melt adhesive were investigated. The PVA-g-FA/MDI had a better peeling strength (43.33 N mm⁻¹), bond strength (11.84 MPa), and thermal conductivity (0.263 W m⁻¹ K⁻¹) than PVA resins. The light-transmittance and haze value were 52.8% and 12.24‰, respectively. The PVA-g-FA/MDI resin could be reused more than two times.

Improving the adhesion between layers and achieving the recycling of resins are challenges in additive manufacturing (AM) technology. In this work, a new type of photo-reversible crosslinking resin based on polyvinyl alcohol (PVA) and coumarin (HMC) was prepared via grafting reaction. The critical idea was to create a coumarin based photo-reversible crosslinking resin by carefully tailoring the photo-crosslinking time and temperature, so that the resin could be extruded through the nozzle and then maintain the proper shape during UV-curing. Photo-reversible crosslinking of AM resin was realized without the use of monomers, photo-initiators or propagating. A reasonable irradiation time with 354 nm (crosslink) or 254 nm UV light (cleavage) of 10 min was critical for photo-reversible crosslinking of PVA-g-HMC at 120 °C. An important result of this work was that the developed photo-reversible crosslinked resin could be reused and the printed resin exhibits excellent adhesion properties, thermal conductivity and oxygen barrier performance.