In the high-viscosity reaction system, twin screw compounding plastic extruder has a range of advantages, such as strong heat and mass transfer and interface renewal ability, narrow residence time distribution, excellent heat exchange and devolatilization surface, easy continuous operation, etc.
Twin screw polymerization extruder (or twin screw reactor) not only has the physical processes of heat transfer, mixing, shearing, conveying, exhausting, extrusion, etc., but also runs through the polymerization. The reaction chemistry changes, so the process is more complicated and the technology is more intensive. This is not much but important. Different reaction types, the structural form and characteristic parameters of the unit are also different, and generally need to be tailored to the specific material system and polymerization process.
Typical application includes: TPU reactive extrusion (polyurethane fiber, elastomer and adhesive), PC melt phase polycondensation, PMMA bulk polymerization, acrylic resin polymerization, nylon polycondensation and different kinds of grafting reaction.
The whole reactive extrusion production line is divided into four parts, the constant temperature storage and transportation system for raw materials, high-precision dosing and mixing pouring system, co-rotating twin screw extruder reaction and melt granulation system, to produce TPU pellets in a continuous feeding. Because isocyanate and most polyols are solids, they need to be melted into a liquid before going to the extruder. The dosing system mainly makes the three raw materials continuously injected into the twin screw plastic extruder in high precision according to the ratio of raw materials. The reaction extruder is the key part of the whole line. All the raw material reactions and the formation of TPU are completed in the reactive extruder, so the screw element configuration of the extruder, screw speed and temperature control will affect the quality of TPU.
Adopting Chuangbo's twin screw extrusion reactive method to procude TPU continuously, a high-torque gearbox, high-precision screw elements and optimized screw element arrangement, are provided, which is beneficial to the complete reaction of the material and will not cause thermal decomposition. The whole system has the advantages of short process, high output, automation, stable quality and mature technology. And the whole process will not touch the solvent, and reach green environmental protection.
Flow Chart for TPU Reactive Extrusion Line
1.metering feeder system 2. material hopper 3. mixing head 4. main extruder 5. diverter valve 6. screen changer 7. underwater pelletizer 8. centrifugal dewatering 9.vibrating sieve 10.product silo
Maleic Anhydride Grafting
Graft compatibilizers give polarity and adhesion to the polymer (such as PE, PP, POE etc) mainly through the action of a maleic anhydride (MAH) group or a glycidyl methacrylate (GMA) group. Improve the interfacial bonding force between the polymer and glass fiber, calcium carbonate and other inorganic fillers, the plant fibers such as wood powder, straw etc, thereby significantly improving the mechanical properties of the composite material.
The main raw materials for the production of graft compatibilizer are: resin, graft monomer, initiator and other additives. Through the heating and shearing in the reactive extruder, the grafting monomer is grafted with the polymer under the action of the initiator.
Features of Grafting Material (Compatibilizers) Pelletizing Line:
1.High torque twin screw extruder. It is suitable for high melt viscosity of graft material.
2.Adopt Loss-in-weight feeding system, feed the resin granules, processing additives and diluted initiator liquid steply to meet the high accurate requirement to proportion of the initiator and polymer.
3.The barrel and screw with large L/D: L/D=48:1~52:1, provide longer residence time, which is conducive to the completion of melting homogenization and grafting reaction, and 1~2 sections of vacuum degassing barrel is equipped to eliminate by-products in reaction to reduce product odor.
4.The pelletizing method is selected according to the melt characteristics. Different raw materials and ratios in the formulation have large differences in melt characteristics. The higher hardness products can select water cooling strand pelletizer, and the low-viscosity and easy-adhesive products can adopt under water pelletizer.
We have developed the most advanced system configuration in China. By this new system design, we realized the target of no remained smell of maleic anhydride and the better grafting efficiency.
The extruder type we provided for customer is: TSH-65/400-110-80 meaning screw diameter of 62.4mm, screw speed of 400rpm, main motor of 110Kw and L/D of 80. It is characterized with high torque, long L/D, continuous dosing system of multi-components and high feeding accuracy, specially designed devolatilization and recycling system etc. The designed throughput is 150-200kg/h.
Supercritical CO2 Grafting
The reactive extrusion line aims at exploring the advantages of using supercritical carbon dioxide (scCO2) as an environmentally benign solvent and swelling agent for carrying out the grafting process of maleic anhydride onto polypropylene in the solid state. The effects of scCO2 on the melting temperature and melting enthalpy of an isotactic polypropylene (iPP) are investigated first in order to define the upper reaction temperature and CO2 pressure limits. The effects of various factors on the grafted anhydride content and on changes in the molecular-scale and microscale structures of the resulting iPP are then investigated. Those factors include the reaction time, monomer and initiator concentrations, reaction temperature, CO2 pressure, and size of the iPP particles. Results show that the scCO2-assisted solid-state grafting process of maleic anhydride onto iPP do have some scientifically interesting and industrially relevant advantages over the classical solid-state or melt process. Among them, it is worth pointing out that the CO2 pressure itself constituts an additional and sensitive process parameter capable of significantly modifying the overall reaction pathway and the product quality. For example, without CO2, the solid-state grafting process is diffusion-controlled. Under scCO2, it becomes reaction-controlled. The CO2 pressure can also regulate the anhydride content with ease. On the other hand, the degree of iPP chain scission is not reduced under scCO2 compared to that of the classical melt process.