Solvothermal Alcoholysis Routes for Recycling Polylactide Waste as Lactic Acid Esters

In
this work, we investigated the possible use of polylactide (PLA),
a biodegradable polymer obtained from renewable biofeedstock, to produce
a range of industrially useful lactic acid esters. We describe a simple
and convenient solvothermal alcoholysis method for large-scale recycling
of PLA resins or residues from disposable packaging in the presence
of the appropriate alcohol under catalyst-free or catalytic conditions.
This process proceeds easily both without and with a catalyst. The
results show that the best catalytic activities involve magnesium
and calcium alkoxides synthesized in situ from organometallic or metallic
precursors and an alcohol. We determined the crystal structure of
the chiral mononuclear postcatalyst [Ca­(LAc)2(EL)2] (1; LAc = lactic acid anion, EL = ethyl lactate),
obtained directly from the reactor. Particular emphasis is placed
on the operating conditions and high activity of the catalyst used.
Key factors that affect the catalytic activity and reaction mechanism
are also highlighted.