Polystyrene, name: styrene, after free radical polymerization, into polystyrene. Its properties, transparent, insulating, lustre (easy to dye); low moisture absorption, the price is also cheap. Therefore, often sold to electronics, cars, 1. Packing, construction, instrumentation, home appliances, toys and daily necessities are hard work.
As the saying goes, cheap is not good, good goods are not cheap. The disadvantages of cheap polystyrene are also quite a lot, for example, not to be beaten (large brittleness), weak body, subject to environmental changes (durable environmental stress), stomach Cold, it is not enough to drink a variety of beverages (poor solvent resistance). Therefore, it is often necessary to treat these problems by taking medicine (modification). The three common methods are: blend modification, copolymer modification and inorganic nano Particle modification.
First, blending modification
Blending modification: Two or more 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 polymers. When blending and modifying, it is necessary to add suitable compatibilizer. 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 the twin-screw extruder for melt blending and extrusion to obtain blended modified PS.
Note: The increase in relative molecular weight of PE does not affect the tensile strength of the blend, and also improves 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 polymer interfaces and increase the tensile strength of PS/PP system. Maleic anhydride Functionalized polypropylene (RPS-MPP) also has a good reaction and compatibilization 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 Improved.
When the partially compatible PS/PC is subjected to an external force, the stress distribution on the 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 two main 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 can obtain a product with both rigidity and toughness. The second monomer is generally α-olefin. Catalyzed styrene and second single with metallocene catalyst Body copolymerization not only maintains the rigidity of PS, but also enhances its flexibility.
2, graft copolymerization
The copolymer of styrene and its boron-containing derivative was synthesized by graft copolymerization with 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 length of graft chains can be controlled by controlling the degree of bromination and the amount of monomers added.
Through the in situ chain transfer reaction, the PS graft copolymer with polar group at the end was synthesized under suitable reaction conditions and catalytic system, which can realize the functionalization of PS.
Third, inorganic nanoparticle modification
Inorganic nanoparticles have unique surface effects, volume effects, quantum size effects, etc., and their properties are significantly different from those of general powders and bulk materials. Inorganic nanomaterials and PS can be compounded under certain process conditions. The amplitude increases the strength, toughness, heat resistance, and friction resistance of the polymer material. PS/inorganic nanoparticle composites have many preparation methods, mainly the following.
1, melt blending
The modified nanoparticles are added to the molten resin and blended to form a blended product. Because 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 perform the nanoparticles before blending. Surface treatment.
The PS/nanoparticle composites were prepared by mechanical blending method, which can significantly improve the tensile strength and notched impact strength of composites and improve the thermal fluidity.
2, solution blending
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 then the solvent is removed to obtain a blended product. The acid-oxidized multi-walled carbon nanotubes MWNTs are infiltrated into tetrahydrofuran. In the solution, PS is dissolved in the solution and ultrasonically treated for 3 h to obtain a PS/multi-walled carbon nanotube composite conductive material. The blending method can improve the storage modulus and electrical conductivity of the material.
3, in situ polymerization
In-situ polymerization method: refers to adding surface-treated nanoparticles to a monomer, mixing uniformly, and then initiating polymerization of the monomer under appropriate conditions to prepare a PS/nano composite. PS/蛭 is prepared by in-situ method. Stone nanocomposites, relative to PS, the decomposition temperature of the composite product is significantly improved.
There are many methods for the modification of PS, but the comprehensive properties and modification mechanism of the modified products have to be further improved. Because of the impact resistance, heat resistance, chemical resistance and processing properties of the modified products, Meet higher requirements to achieve a wider range of applications for PS modified products.