Polymer blend preparation
Prior processing, polymers were dried overnight at 80 C in a
ventilated oven. CA-based compositions were obtained by melt-compounding
of plasticized polymer pellets using the Brabender
bench-scale kneader at 190 C, first for 3 min at 30 rpm, followed by
6 min at 60 rpm.
As example of blend formulation, CA/PVOH (52/48)(w/w) blend
was prepared by mixing 51.7 parts of plasticized CA (pCA) with 48.3
parts of plasticized PVOH (pPVOH) leading to total plasticizer
content in the blend of 27.5 wt% (Note that the plasticizer content is
not considered in the blend nomenclature). When a compatibilizer
was used, it was mixed with the water soluble polymer and added
together into the kneader. Plasticized CA/PVOH blends were also
prepared in the Leistritz ZSE 18HP-40D twin-screw extruder
equipped with two pellet feeders. Plasticized polymers, pCA and
pPVOH, were fed together into the feeder hopper and blend
compositionwas adjusted by varying feeder rates. A screw speed of
150 rpm and constant barrel temperature of 185 C were selected.
Extruded material was collected by a moving belt, cold down by air
ejectors and pelletized downstream.