Three major means of modification of polystyrene (PS)
Polystyrene , referred to as PS, transparent, insulated, lustre (easy to dye); low moisture absorption, low price. Therefore, it is often used in industries such as packaging, electronics, automobiles, construction, instrumentation, home appliances, toys, and daily necessities. Today we mainly look at the three major means of PS: blending modification, copolymerization modification and inorganic nanoparticle modification.
First, blending modification
Blending modification: two or more kinds of polymer materials, inorganic materials and additives are mechanically stirred to obtain materials with improved mechanical uniformity, thermal properties and optical properties.
Blending characteristics: Blending modification method has small investment and short production cycle, so it becomes a hot spot of PS modification. It is not only an important means of polymer modification, but also an important way to develop new materials.
PS/PE
Polyethylene (PE) has excellent flexibility and impact resistance, which is beneficial to improve the toughness of PS. However, PS and PE are two incompatible high polymers. When blending and modifying, a suitable compatibilizer is added. PS and PE blending can be achieved by two means, namely reactive blending and non-reactive blending.
In the study of reactive blending, reinforced PS (RPS), hydroxylated PE (CPE), PE and PS were simultaneously added to a twin-screw extruder for melt blending and extrusion to obtain a blended modified PS.
Note: The increase in the relative molecular weight of PE does not affect the tensile strength of the blend, and also increases the impact strength of the blend.
PS/PP
Polypropylene (PP) has higher tensile strength and surface hardness than PS, and its heat resistance is also good. Therefore, blending it with PS can improve the thermal properties of PS.
However, PP is incompatible with PS, so it is necessary to add a compatibilizer. The commonly used surface-treated silicon-filled PS/PP system can increase the adhesion between the polymer interfaces and increase the tensile strength of the PS/PP system. Maleic anhydride functionalized polypropylene (RPS-MPP) also has a good reaction compatibilizing effect on PS/PP.
PS/PC
Polycarbonate (PC) has excellent performance, good creep resistance, visible light transmittance of over 90%, similar to PS refractive index, and can be blended with PS to make PS thermal stability, strength and toughness Increased.
When the partially compatible PS/PC is subjected to external force, the stress distribution of the phase interface is uniform and continuous, so the impact and tensile force cause the blend to produce silver streaks and shear bands, thereby improving the mechanics of the PS/PC blend. performance.
Second, copolymerization modification
Copolymerization is one of the important methods for modifying PS. The flexible group is introduced by the method of copolymerizing monomer styrene and second monomer, so as to maintain the original excellent performance of PS, improve toughness and improve processing performance. . There are mainly two methods of block copolymerization and graft copolymerization.
1, block copolymerization
The compatibility of PS with other polyolefins is low, but the copolymerization of the two results in a product that combines rigidity and toughness. The second monomer is typically an alpha olefin. The metallocene catalyst catalyzes the copolymerization of styrene with the second monomer, which not only maintains the rigidity of the PS, but also enhances its flexibility.
2, graft copolymerization
A copolymer of styrene and its boron-containing derivative was synthesized by graft copolymerization using a metallocene catalyst, and the boron group of the product was oxidized and oxidized.
A series of PS graft copolymers were synthesized by atom transfer radical polymerization to realize the function of polystyrene, and the graft density and the length of the graft chain can be controlled by controlling the degree of bromination and the amount of monomers added.
Through the in situ chain transfer reaction, a PS graft copolymer containing a polar group at the end is synthesized under suitable reaction conditions and a catalytic system, and the functionalization of PS can be realized.
Third, inorganic nanoparticle modification
Inorganic nanoparticles have unique properties such as surface effects, volume effects, and quantum size effects, and their properties are significantly different from those of general powder and bulk materials. The composite of inorganic nanomaterials and PS under certain process conditions can greatly improve the strength, toughness, heat resistance and friction resistance of the polymer materials. There are many preparation methods for PS/inorganic nanoparticle composite materials, mainly the following.
1. Melt blending method
The modified nanoparticles are added to the molten resin, and after blending, the blended product is obtained. Since the nanoparticles are prone to agglomeration and the particles are difficult to be uniformly dispersed in the system, the key to the method is to surface-treat the nanoparticles before blending.
The PS/nanoparticle composites were prepared by mechanical blending method, which can significantly improve the tensile strength and notched impact strength of the composites and improve the thermal fluidity.
2, solution blending method
Solution blending method: the matrix resin is dissolved in a suitable solvent, the nanoparticles are added, and the nanoparticles are thoroughly stirred to uniformly disperse and mix the nanoparticles, and the solvent is removed to obtain a blended product. The acid-oxidized multi-walled carbon nanotubes MWNTs are immersed in a tetrahydrofuran solution, and then PS is dissolved in the solution, and ultrasonically treated for 3 hours to obtain a PS/multi-walled carbon nanotube composite conductive material, and the blending method can improve the material. Storage modulus and conductivity.
3. In-situ polymerization
In-situ polymerization method: refers to adding surface-treated nanoparticles into a monomer, mixing uniformly, and then initiating polymerization of the monomer under appropriate conditions, thereby preparing a PS/nano composite. The PS/vermiculite nanocomposites were prepared by in-situ method. Compared with PS, the decomposition temperature of the composites was significantly improved.
There are many methods for the modification of PS, but the comprehensive performance and modification mechanism of the modified products have to be further improved. Because the impact resistance, heat resistance, chemical resistance and processing properties of the modified products also need to meet higher requirements, in order to achieve a wider application of PS modified products.
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