A facile alternative strategy of upcycling mixed plastic waste into vitrimers.

Chemical depolymerization has been identified as a promising approach towards recycling of plastic waste. However, complete depolymerization may be energy intensive with complications in purification. In this work, we have demonstrated upcycling of mixed plastic waste comprising a mixture of polyester, polyamide, and polyurethane through a reprocessable vitrimer of the depolymerized oligomers. Using poly(ethylene terephthalate) (PET) as a model polymer, we first demonstrated partial controlled depolymerization, using glycerol as a cleaving agent, to obtain branched PET oligomers. Recovered PET (RPET) oligomer was then used as a feedstock to produce a crosslinked yet reprocessable vitrimer (vRPET) despite having a wide molecular weight distribution using a solventless melt processing approach. Crosslinking and dynamic interactions were observed through rheology and dynamic mechanical analysis (DMA). Tensile mechanical studies showed no noticeable decrease in mechanical strength over multiple repeated melt processing cycles. Consequently, we have clearly demonstrated the applicability of the above method to upcycle mixed plastic wastes into vitrimers and reprocessable composites. This work also afforded insights into a potentially viable alternative route for utilization of depolymerized plastic/mixed plastic waste into crosslinked vitrimer resins manifesting excellent mechanical strength, while remaining reprocessable/ recyclable for cyclical lifetime use.

The molecular design of photo-curable and high-strength benzoxazine for 3D printing.

Low viscosity photo-curable benzoxazines (BZs) are designed and synthesized for use in stereolithography 3D printing. An initial investigation shows that the thermally polymerized polybenzoxazines (PBZs) have remarkably high Tg (264 °C) and flexural modulus (4.91 GPa) values. Subsequently, the formulated photoprintable resins are employed for use in high-resolution projection micro-stereolithography (PµSL) printing. Complex PBZ 3D structures can be achieved from the as-printed objects after they are thermally treated. These findings advance the design of BZ monomers for photopolymerization-based 3D printing and offer a method for the efficient fabrication of high-performance thermosets for various demanding engineering applications.