PROCESSING | REACTIVE COMPOUNDING
plastic, starch-based blend using two successive compounding processes. In the first reactive compounding step, the blend partner is chemically modified; in the subsequent compounding step, the starch is plasticised and blended with the previously modified polymer. In the first iteration stage, two compounding steps with two cooling and melting processes and intermediate material drying were necessary. The researchers have combined these two individual compounding operations into a single processing step (Figure 2). In this new process, the blend material is modified and the starch and the required plasticisers are fed in the same twin-screw extruder at a later stage. Consequently, the optimised blend material can be formed ‘in one heat’ and energy equivalent to one drying and one melting process can be saved. Kenneth Russell, Reactive Extrusion Specialist at Optimized Compounds, says he is seeing strong interest from companies that currently undertake traditional compounding but are looking at reactive extrusion for certain speciality products, such as maleic anhydride grafted polyolefins and silane grafted polyethylene. One specific area of work at present is aimed at eliminating specks and gels during grafting of silane to HDPE, he says, where the crosslinking reaction competes with the grafting reaction resulting in defects in the polymer. Russell adds that another area of current interest is modification of recycled PET through reactive extrusion to alter its physical properties. While standard washing and reprocessing is well known technology for recycling PET bottle resin, melt modification using chain extenders and modifiers are now being explored to optimise properties for use in alternative applications, he says. Russell cites one project he was involved with – now a patented process (US 0072572) – in which
Figure 4: Effect of selective condensation on conversion level during scale up of a polymer functionalisation reactive extrusion process to production volumes Source: Optimized Compounds
selective condensation was used to extend an equilibrium reaction conducted in a reactive extruder (Figure 3). “A transesterification reaction was developed to add functionality to a polymer through reactive extrusion. A heavy alcohol was reacted with a methyl acrylate copolymer via transesterification, exchanging the alcohol with the polymer pendant group. It is an equilibrium reaction and as the process was scaled up from lab to pilot and then commercial scale, the conversion level decreased by as much as 65% from that obtained on the lab scale,” he says. “The installation of a condenser downstream of
the reaction section of a twin screw extruder shifts the equilibrium to extend the reaction. The reaction generates large amounts of methanol and other light alcohols as a by-product. The temperature of the ‘partial condenser’ is controlled such that the light alcohol is vented from the extruder but the heavy alcohol is recondensed back into the process. The result of this process improvement is an increase of the conversion back to the desired levels.” Conversion levels before and after the installation are shown in Figure 4. Optimized Compounds specialises in assisting companies develop new products through the use of reactive extrusion. Recent projects include work with TPVs, grafting of maleic anhydride onto polyolefins, and transesterification.
Figure 3: ] Selective condensation was used by an Optimized Compounds client to extend an equilibrium reaction conducted in a reactive extruder Source: Optimized Compounds
36 COMPOUNDING WORLD | September 2017
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.coperion.com �
www.centuryextrusion.com �
www.aimplas.net �
www.biorefine2g.eu �
www.thermofisher.com �
www.leistritz.com �
www.ict.fraunhofer.de �
www.optimizedcompounds.com
www.compoundingworld.com
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