REACTIVE EXTRUSION: Unleashing the future of advanced materials
Reactive Extrusion has been presented in recent years as a key technology for the synthesis and chemical modification of polymers. Reactive extrusion is a ground-breaking process in the manufacturing industry that combines the principles of traditional extrusion with real-time chemical reactions. It is a highly specialized method that enables the production of advanced materials with unique properties and characteristics.
What is Reactive Extrusion?
Reactive extrusion (REX) is a continuous process in which an extruder is used as a chemical reactor, allowing process intensification by the combining the chemical synthesis / modification with conventional processes carried out in extruders like compounding, devolatilization and granulation in only one step. As a result, new/modified polymers or compounds suitable for transforming by subsequent polymer processes (e.g. injection moulding, extrusion) are obtained.
Generally, the reactive extrusion is carried out in co-rotating Twin Screw Extruders (TSE), due to its high mixing capacity, good ability to handle high viscosity polymers and high versatility in the process design. Nevertheless, there are other types of extruders that are also used for REX process but at lower extent (e.g. counter-rotating TSE, single screw extruders, planetary extruders, and multi screw extruders).
Reactive extrusion process
In these extruders, the monomers and/or polymers and other reagents are feed in a continue mode at the beginning of the extruder, where they are molten, mixed, and react along the extruder length such as in a tubular reactor. Along this process, additives, fillers and reinforcing agents can incorporated downstream, if it is allowed by the reaction kinetics, to obtain the final compound. In addition, the obtained polymer or compound can be devolatilised in the last part of the extruder to remove unreacted monomers or volatiles generated during the process. Finally, then molten material is compressed and discharged through the extruder die or underwater pelletizer, cooled and cut into pellets for further processing.
Another great advantage is that the reactive extrusion allows to carry out polymerization reactions in the absence or in presence of little amount of solvents in comparison with typical batch polymerization. This fact allows considerable savings by avoiding the extraction and recovery of solvent after the polymerization process.
Exploring the versatility of REX in advanced industries
Thanks to reactive extrusion, it is possible to:
- Produce materials with superior mechanical properties
- Increased heat resistance
- Enhanced corrosion resistance or flame retardancy
- Improved electrical insulation
- And a wide range of customizable characteristics.
These materials can be used to manufacture lightweight yet strong structural components, high-performance electronic devices, customized medical implants, and many other innovative applications. Its impact on the industry is remarkable. This process has opened up a wide range of possibilities for designing and manufacturing advanced materials in various sectors, including automotive, aerospace, electronics, packaging and medical industries.
Nevertheless, the application of reactive extrusion is limited by the residence time that can be achieved in the extruder ( from as low as 1 min up 15 – 20 minutes). So, in general it is indicated for polymerization or chemical modifications with fast kinetics. For this reason, long extruders with high length to diameter ratio are used (L/D > 44 up to 90). Other approach to increase the residence time is to assemble two or more extruders in tandem or cascade system.
Therefore, in order to design a REX process, it is absolutely necessary to carry out studies to understand and/or predict the required residence time in the extruder to achieve the expected conversion.
Reactive extrusion opens up a world of possibilities by enabling a wide range of chemical reactions to take place during the extrusion process. Through this innovative technique, polymer blends can undergo reactions such as grafting, crosslinking, chain extension, and copolymerization. These reactions occur in real-time as the materials are being extruded, leading to the formation of new chemical structures and the enhancement of material properties. Whether it is the functionalization of polymers, the synthesis of hybrid materials, or the production of tailored composites, reactive extrusion offers a versatile platform for designing and manufacturing advanced materials with precise control over their chemical composition and performance characteristics.
Reactive extrusion applications
The most common reactions that are reported as suitable to be carried out by reactive extrusion are the following:
- Polyaddition: to obtain thermoplastic polyurethanes (TPUs) of different hardness.
- Polycondensation: synthesis of polyesters such as polyethene terephthalate (PET), polybutylene terephthalate(PBT) and polyamides (Pas).
- Graft reactions and functionalization: functionalization of polyolefins with maleic anhydride and other acrylic monomers (for example PE-g-MAH, PP-g-MAH, PE-g-AA, PE-g-GMA).
- Free radical: production of styrenic and acrylic polymers, polystyrene (PS), polymethyl metacrylate (PMMA), Styrene Acrylonitrile (SAN), Styrene maleic anhydride copolymers (SMAC).
- Crosslinking: formulation of thermoplastic vulcanizates (TPVs) from polyolefins, rubbers, oils, and cross-linking agents. Crosslink of polyethene with vinyl silanes and peroxides.
- Controlled rheology: viscosity reduction of recycled PP (vis-breaking), PAs.
- Ionic polymerization: production of polylactic acid (PLA), polycaprolactone (PCL) and polyamide 6 (PA6) by ring opening polymerization reactions.
- Glycolysis: chemical recycling of PET.
- Hydrolysis: chemical recycling of PLA, PUs, Pas to obtain lactic acid, polyols, amines and acids.
- Reactive coupling: production of polymer blends, or in-situ compatibilization with fillers, fibres, nanoparticles, etc.
- Transesterification reactions: production of ethylene vinyl alcohol (EVAL) by transesterification of ethylene vinyl acetate (EVA) copolymers with alcohols.
- Saponification: Synthesis of elastomeric ionomers from ethylene acrylate copolymers (EMA, EBA).
Unlocking Potential: Impactful Case Studies
AIMPLAS has gained and increased experience in this area due to the execution of different projects throughout recent years, where the reactive extrusion has been the key technology. Between them they found the following projects:
- BIOVEGE, in which long chain alcohols were grafted in PLA and biopolymers for its use in packaging for vegetables.
- BIOBOTTLE, in which the reactive compatibilization and the increase of temperature resistance of biodegradable materials was carried out for applications in packaging of dairy products.
- BIOREFINE 2G, in which copolymers of PLA with polyesters of dicarboxylic acids obtained from lignocellulosic materials were obtained.
- PERCAL, in which hot-melt adhesives based on polylactic acid obtained from the organic fraction of municipal solid waste were obtained.
- BIOMAC, in which AIMPLAS is developing PLA and PLA based copolymers and nanocomposites by reactive extrusion for packaging and agricultural applications.
Leading the way: AIMPLAS Capabilities in Reactive Extrusion capacities of AIMPLAS
AIMPLAS has the following capacities to carry out the process of reactive extrusion:
- Synthesis laboratory with batch reactors and mini-compounder TSE.
- Torque rheometers of different capacities.
- Possibility to scale up the reaction to pilot plant scale with the help of simulation software.
- Different co-rotating TSE with screw diameters from 16 to 27 mm and L/D ratios from 25 to 56, completely modular that allow the incorporation of solids and liquids in different points of the extruder.
- Use of special dosing systems such as heated reactors and gravimetric feeders for both solids and liquids, vacuum pumps for extraction of unreacted monomers, , reaction by-products and other volatiles.
- Possibility of the customer to assist to the trials in the pilot plants.
- Characterization laboratory for complete analysis of the obtained products.