Blending refers to mixing together. It is a physical method to make several materials evenly mixed to improve the performance of the materials. In industry, using a rubber mixer to evenly mix different rubbers or rubber and plastic into rubber is a typical example. It is also possible to add certain special performance ingredients to the polymer to change the properties of the polymer, such as conductivity, etc.
Definition
Blending can improve the physical and mechanical properties and processing properties of polymer materials, reduce costs and expand the scope of application.
Blending is one of the important ways to achieve polymer modification and produce high-performance new materials.
According to the production method, it can be divided into mechanical blends, chemical blends, latex blends and solution blends.
Among them, mechanical blends, that is, blends obtained by mixing different polymer melts through rollers, extruders or intensive mixers, account for the main position.
Blends are generally multi-component, multi-phase systems whose properties depend on the properties, morphology and interfacial properties of the components they contain.
The use of two or more rubbers, or rubber and various plastics, can greatly expand the use of rubber products, significantly improve the quality and performance of rubber products, improve the process performance of rubber materials, reduce rubber consumption and reduce product costs. When different rubbers or rubber and plastics are blended, they should have good compatibility or use the best ratio to maximize the technical effect of blending.
Blending modification
Most existing membrane materials have strong hydrophobicity, which means that water needs to overcome high resistance to pass through the membrane, limiting its application in aqueous phase separation systems. Hydrophobicity also makes the membrane susceptible to membrane fouling, which deteriorates the separation performance of the membrane. At this time, it is particularly important to modify the membrane. There are many reports on polymer membrane modification, and its methods can be divided into two categories: chemical modification and physical modification. Physical modification methods mainly include surface coating and blending.
Blending is the simplest and most commonly used membrane modification method. Compared with other methods, blending modification has the following advantages: modification and membrane formation are carried out simultaneously, the process is simple, and no tedious post-processing steps are required; the modifier can simultaneously cover the membrane surface and the inner wall of the membrane pores, especially the inner wall of the hollow fiber membrane ; and it will not cause damage to the membrane structure. In recent years, the method of blending amphiphilic copolymers with traditional polymer membrane materials to prepare hydrophilic separation membranes has attracted people’s attention. Amphiphilic copolymer molecules contain both hydrophobic chains and hydrophilic chains. The hydrophobic chains make them have good compatibility with the membrane body material, while the hydrophilic chains make the membrane have higher hydrophilicity and stronger anti-fouling ability. Hydrophilically modified blended ultrafiltration and microfiltration membranes have a wide range of applications in wastewater treatment, protein filtration, hemodialysis, biological separation and other fields.
Selection of blending system
The following factors should be considered when selecting a blending system:
Compatibility factors
Compatibility is the basic condition for blending.
Good compatibility between the two phases is the prerequisite for the two-phase blend product to have good properties (especially mechanical properties).
Compatibility affects the difficulty of the blending process. In a two-phase system with good compatibility, the dispersed phase is easier to disperse during the blending process.
Therefore, polymer systems with better compatibility should generally be selected for blending.
Crystallinity factors
Crystalline plastics and non-crystalline plastics have obvious differences in performance. Blending polymers with different crystallinity properties can usually achieve some complementary properties.
Crystalline plastics usually have higher rigidity and hardness, better chemical resistance and wear resistance, and relatively good processing fluidity. The disadvantage of crystalline plastics is that they are brittle and the molding shrinkage of the products is high.
Non-crystalline engineering plastics have the characteristics of good dimensional stability but poor processing fluidity.
Improvement of performance or introduction of new performance
Performance factors mainly consider the complementary properties between the blend components, or improve a certain aspect of the polymer performance, or introduce some special properties.
Price factors
By blending expensive polymers with cheaper polymers, costs can be reduced without significantly affecting performance.
