Reactive extrusion vs. batch preparation of starch–g–polyacrylonitrile

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Abstract
Acrylonitrile (AN) was graft polymerized onto unmodified cornstarch by a continuous reactive extrusion process and, for comparison, by a typical batch reaction process. The effect of AN/starch weight ratios, level of ceric ammonium nitrate (CAN) initiator, starch in water concentration, reaction temperature, reaction time, and extruder screw speed in the reactive extrusion process was studied. Add‐on, reaction efficiency, grafting frequency, weight average molecular weight (MW) and MW distribution of polyacrylonitrile (PAN), and water absorbency of the saponified copolymers were determined. Processing times in the twin‐screw extruder (ZSK) were 2–3 min, and total reaction time was about 7 min before reaction of the extruded material was terminated, compared to a reaction time of 2 h used in the typical batch procedure. The continuous reactive extrusion process was found to be a rapid and efficient means of preparing St‐g‐PAN with high add‐on (% PAN of the grafted product). For example, 42% add‐on was achieved within the 7‐min reaction period using an AN/starch weight ratio of 1.0 (3.5% CAN, starch weight basis), as compared to 38–49% for the 2‐h batch process (0.75–1.5 AN/starch ratio). Percentages of homopolymer of the copolymers were low for both extrusion and batch processes. Grafting frequencies were substantially higher while MWs were significantly lower for grafts from the extrusion process. Water absorbency of the saponified St–g–PAN products was somewhat greater for the products prepared by the batch process.