Molecular Details of Polyester Decrystallization via Molecular Simulation

Waste polyesters are a potential feedstock for recycled
and upcycled
products. These polymers are generally semicrystalline, which presents
a challenge for chemical and biological recycling to monomers, and
thus the thermodynamic work associated with polyester decrystallization
is an important consideration in some depolymerization strategies.
Here, we use molecular dynamics simulations to calculate the free
energy required to decrystallize a single chain from the crystal surface
of five commercially and scientifically important, semiaromatic polyesters
(PET, PTT, PBT, PEN, and PEF) in water. Our results indicate the decrystallization
work ranges from approximately 15 kcal/mol (PEN) to 8 kcal/mol (PEF)
per repeat unit for chains in the middle of a crystal surface. The
insight gained into the molecular interactions that form the structural
basis of semicrystalline synthetic polyesters can guide the pursuit
of more efficient plastic processing, which could include catalyst
development, optimizing recycling conditions including pretreatment,
enzyme and solvent selections, and design of new materials.