CA2.5 and PVOH were plasticized in a Leistritz ZSE 18HP-40D
twin-screw extruder (L ¼ 40D) equipped with a liquid feeder for
plasticizer addition. Polymers were dried overnight at 80 C in a
ventilated oven before being introduced into polymer feeder. Screw
speed was fixed at 250 rpm and the barrel temperature profile was
set-up in function of the material to be processed. Extruded material
was cooled down in a water bath (CA) or by air ejectors over a
moving belt (PVOH) and pelletized downstream. Cellulose acetate
was plasticized with 30 wt% triacetin and PVOH with 25 wt%
glycerol.
HEC plasticization was conducted in a different manner using a
two-step process [9]. First, HEC was mixed with plasticizer and
water in beakers at room temperature and left to swell overnight to
form a premix. In a second step, the premix was melt-processed
using a Brabender bench-scale kneader (model 50 EHT, 80 cm3
free volume) with cam blades at 110 C for 6 min. Plasticizer content
was varied between 20 and 40 wt% and water was added at
concentrations of 10 or 15 wt%.