Polymer material mixing extrusion technology and complete equipment

Mixing extrusion process is the only way for polymer materials, especially plastics, to move from products to industrialization. Modern polymer materials are developing towards high-performance polymer structural materials, new polymer functional materials and general polymer materials with low cost and high performance. 

High performance polymer structural materials are characterized by high specific strength, excellent corrosion resistance, abrasion resistance and easy processing, which are of great significance to the development of national economy and national security. Due to its unique functional and special type, new polymer functional materials have been widely used in the industrial fields such as ecological environment protection, information functionalization, biomedical equipment, material separation membrane, energy conversion and energy storage technology. High performance of general polymer materials and low cost of engineering plastics are still the focus of current research and development of polymer materials and an important measure to expand the application scope of general plastics and engineering plastics.

In addition to some processing properties of traditional polymer materials, the new polymer materials have many differences in physical and chemical properties. Appeared with the development of new polymeric materials, the fields of application broadening, to high polymer material mixing extrusion are also put forward higher request, the traditional mixing technology and equipment have not well some new high polymer material to meet the demand of the mixing, therefore, the development of new type mixing extrusion technology and equipment, to meet the needs of the new polymer materials to industrialization, mixing equipment BNR; at the same time, also is inevitable trend of the development of polymer processing equipment today.

1.       Application of twin screw mixing extrusion technology

Modern mixing and mixing extrusion technology is to blend existing polymer materials with a variety of polymers or add other materials to optimize the combination of different materials, so as to significantly improve the material properties, or give raw materials with new properties, adding new varieties to the polymer family. In the whole plastics industry, about 60% of the plastics have to be mixed and modified to produce new materials. Most of these complex processing processes are completed in the mixing equipment represented by the twin screw extruder. Using the same direction twin screw to mix extrusion has the following advantages:

(1) excellent mixing and plasticizing performance, which can fully guarantee the dispersion uniformity and performance uniformity of various materials after mixing, and is suitable for complex operations such as filling, blending, glass fiber reinforcement, reactive extrusion and volatile removal of various resins and plastics.

(2) cylinder and screw can realize "building block" combination, so as to achieve multi-purpose, multi-function.

(3) screw meshing, self-cleaning effect is good; The material achieves superior surface renewal effect and excellent exhaust performance, which can eliminate the gas or monomer generated in the mixing and plasticizing process.

(4) high screw speed, large production capacity, low power consumption per unit production, obvious energy saving effect.

Based on the above advantages, the co-directional twin-screw mixing extrusion technology has an irreplaceable advantage in polymer material processing equipment and occupies a leading position in polymer material modification production.

At present, the new type twin-screw compounding and the latest application of extrusion technology is mainly manifested in the following aspects: the preparation of nanometer material modification is high polymer material rigid Gao Ren type of low cost, high polymer alloy materials, electromagnetic shielding polymeric materials, novel polymer materials for degradable plastics, electronic packaging, new masterbatch and various functional masterbatch, etc., can also be used to new composite materials (such as wood plastic composite) the production and preparation of new materials, in addition, can also be used for polymer grafting, polycondensation of reactive extrusion. The industries involved include household appliances, automobiles, communications, electronic technology, national defense, aerospace, environmental protection, chemical industry, building materials, electric power, etc.

2.       Development of new polymer material extrusion technology with twin screw

At present, the development direction of new polymer materials, which are mainly composed of nanomaterials, degradable plastics, modified asphalt and wood-plastic composite materials, centers on the industrialization of these materials, and the same-direction twin-screw extrusion technology becomes the key to realize the industrialization. Compared with ordinary polyolefin materials, these materials have great differences in material system composition, molecular structure and rheological properties.

(1)     Nanomaterials are becoming a new type of materials developed by various countries in the world. From the preparation of nanometer masterbatch to the production of nanometer modified plastics, twin-screw extruder plays an irreplaceable role in the industrialization of nanometer plastics. Firstly, due to the particle size distribution of nanomaterials, the mixing extrusion and dispersion effects are required to be high. Secondly, the preparation of nanometer masterbatch for inviscid melt characteristics, low toughness, contains a large amount of gas extrusion and additives in the process of removing products of decomposition, and the traditional polymer under different state of plasticizing characteristics such as high brittleness, cooling and finished product process is different from ordinary polyolefin masterbatch process. 

     From mixing and plasticizing extruder to cooling and granulation, many innovative developments are needed. Therefore, the general cooling method of molten polymer cannot be adopted. The final product is produced by adopting the closed feeding mode with powder collection, adopting the new high-efficiency dense rotor element in the screw, setting buffer type exhaust mode in the cylinder, and adopting the route of belt conveying and cooling, pre-crushing and crushing in the material strip cooling and crushing.

(2)     There are a lot of starch in the development of starch filled degradable plastics, double degradable plastics and whole starch thermoplastic plastics. In addition to plasticizing and mixing them, exhaust dehydration and residence time distribution in the extrusion process have become problems that need to be solved when mixing and granulating. Therefore, according to the specific materials, the appropriate host screw length-diameter ratio, exhaust location and quantity, screw structure and arrangement, additive adding mode and adding point should be selected to test and determine the configuration; At the same time, the operation technology and technology also become the key problem of the degradation plastic twin-screw extrusion. The above key technologies can be based on the existing successful experience, combined with extrusion process experiment and results analysis, finally determine the extrusion process equipment configuration.

(3)     Modified asphalt has become a new direction of polymer material modification. Focusing on its application in highway construction, airport reconstruction and expansion projects, improving its temperature resistance and low temperature brittle property is the main direction of improving its application value. Because of the extensive molecular weight distribution and the structure of macromolecule, the modification of asphalt has not been much improved. Modified asphalt is very special, has both belong to the characteristics of the rubber plastic blending, but also has the content of the product post-processing, transport of twin screw extruder, mixing elements of development, such as extrusion granulation are put forward new requirements, need innovation to develop new type structure and configuration of the screw element, console, selected double screw part in all kinds of test parameters, such as screw length to diameter ratio, number and position of exhaust section, shear rate, extruding form and structure, etc.

(4)     In terms of material science, WPC is a new material with great potential. It is reported that plant fiber composites have been widely used in automobile industry, construction industry, transportation industry, aviation industry and so on due to their high mechanical properties, specific hardness, specific strength, sound absorption and biodegradability. In wood fiber, wood powder mixed with resin matrix, the mixture of different methods of wood fiber in composite material obtained by dispersing uniformity of difference is very big, to realize the industrialization of the wood plastic composite this new material production is the key to the extrusion process and special structure form of extruder, the technology innovation point lies in the segmented charging ways, special screw type structure, TME and ZME element, high torque gear transmission system, large screw length to diameter ratio and D/Di = 1.55 free volume, the one-step method of twin-screw extrusion production.