  Synthetic polymers constitute one of the main carbon-containing wastes
generated nowadays. In this study, combined hydrothermal liquefaction (co-HTL)
is evaluated for 1:1 mixtures of Miscanthus Giganteus and different synthetic
polymers including poly-acrylonitrile-butadiene-styrene (ABS), Bisphenol-A
based Epoxy resin, high density polyethylene (HDPE), low density polyethylene
(LDPE), polyamide 6 (PA6), polyamide 6/6 (PA66), polyethylene terephthalate
(PET), polycarbonate (PC), polypropylene (PP), polystyrene (PS) and
polyurethane foam (PUR), using batch HTL reactors at 350 {\deg}C. Based on mass
balances and oil composition, a comprehensive discussion of observed
interactions is presented. The results show that even though polyolefins do not
depolymerize under these conditions, the oil products depicts that these
materials interact with miscanthus oil changing its composition. Bisphenol-A
based polymers as PC and epoxy resins both contribute for the formation of
monomer-like structures in the oil. PET increases the presence of carboxyl
groups, while polyamides and PUR increase significantly the oil yield,
modifying oil composition towards nitrogen-containing molecules. PUR co-HTL was
found to increase both oil carbon and energy yields, leading to process
improvement when compared to pure miscanthus processing.
