Two stage extrusion of plasticized pectin/poly(vinyl alcohol) blends

Blends of pectin with starch (high amylose and normal), poly(vinyl alcohol) (PVOH), and glycerol were extruded in a twin screw extruder, pelletized, and then further processed into blown film and extruded sheet using a single screw extruder. The samples were analyzed using tensile measurements, dynamic mechanical analysis, and scanning electron microscopy. PVOH levels of 24% or greater were necessary to successfully make blown film, while extruded sheet could be made at a level of 16% PVOH. Tensile strength and initial modulus of the extruded sheets were slightly higher in the machine direction than in the cross direction, while the reverse was true for elongation to break. For the blown films tensile strength tended to be higher in the transverse direction than in the machine direction, while the reverse was seen for initial modulus. Increased levels of PVOH led to increases in tensile strength and elongation to break, while initial modulus was decreased. Morphology as determined by SEM visually indicated stretching in the transverse direction of the blown films. The second stage extrusion appeared to promote alpha-helix formation in the high amylose starch. (c) 2006 Published by Elsevier Ltd.