Reactive extrusion | processing feature Chain reaction
The intensive mixing performance of a twin-screw extrusion system and the ability the technology provides to optimise thermal and mechanical exposure of the polymer in the barrel makes it a good choice for reactive extrusion processing. Key applications include the chemical integration of bonding agents to improve adhesion between the polymer matrix and fibre or particulate fillers, and more recently the direct polymerisation of thermoplastic polyurethane (TPU) elastomers from liquid components. KraussMaffei Berstorff has developed systems for
the production of impact modifiers and bonding agents for used in applications such as WPC extrusion and highly filled compounds. The company says a prime consideration for this type of reactive extrusion applica- tion is the use of screws and barrels with a corrosion resistant coating. Typical screw configurations include LD ratios of up to 50, with the installed drives selected according to the specific melting and dwell times required for the individual processing requirements. The company has also developed systems for the
production of TPUs, comprising a twin-screw extrusion unit which is fed with the liquid components and catalysts. The reacted TPU polymer is extruded via an underwater pelletizing system. The TPU production lines require high precision
gravimetric or mass flow metering systems to ensure the liquid components are delivered to the extruder throat in the correct ratio. LD ratios of up to 60 are typical for such applications.
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The polymer modification potential of reactive extrusion is being used in a variety of applications ranging from polymerisation and polymer modification to the production of novel bio-based blends. Compounding World reports
According to KraussMaffei Berstorff, dynamic
regulation of melt temperature is a critical considera- tion in any reactive extrusion process. Its systems use direct heating of the barrel elements in combination with liquid cooling. Heating is performed using high power cartridge heaters or heater bands; cooling is achieved with either high pressure water or oil circu- lated through a network of cooling bores. French technology company Setup Performance
provides reactive extrusion technology support to a wide range of clients. Earlier this year, it commissioned a new 43 mm diameter LD 60 twin-screw extruder in its laboratory at Frontonas near Lyon to handle pre-indus- trial pilot volumes. Aside from expertise in TPU production and the
grafting of polyolefins with maleic anhydride, it has also August 2012 | COMPOUNDING WORLD 41
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