(293h) Catalytic Dehydration of Evoh with Heterogeneous Acid Catalysts

Plastic blends have shown to be particularly difficult to recycle as impurities from tie layers and other polymers themselves downgrade the properties, preventing physical recycling. One option for recycling or upcycling multilayer films is selective conversion of a single polymer amongst many in the film for purposes of compatibilization or new functionalization. An example is the selective dehydration of vinyl alcohol groups in polyvinylalcohol-co-ethylene (EVOH) and polyethylene (PE) blends which are typically use for food preservation and wrapping. We have investigated the use of a series of heterogeneous acid catalysts (ZSM-5, TON, Beta, and amorphous silica alumina) with pure EVOH (in molten state) and with EVOH in solution (DMSO and Sulfolane). Studies have been carried out in a TGA with mass spectrometry detector, in a Parr reactor, and in a twin screw extruder. The catalyst:polymer mass ratio has been varied from 2% to 8% to keep the acid site concentration constant when comparing different catalysts. Catalysts were used at higher mass ratio in the twin screw extruder. Experiments were performed over a wide temperature range (100-250°C). Infrared spectroscopy, electron microscopy and elemental analysis have been used to characterize the reaction products. Results from the TGA and electron microscope show significant but incomplete dehydration of the vinyl alcohol groups. This conversion is coupled with concomitant rapid catalyst deactivation due to coking or fouling. Further evaluation of the catalyst will be performed by solvent extraction, TGA-TPO, FTIR and EM.