Blending and modification of PVC

Compatibility: ABS is an acrylonitrile-butadiene-styrene copolymer. Its structure is the same as MBS with rigid segments and flexible rubber segments. ABS is similar to PVC solubility parameters and is chemically thermodynamically compatible. From the molecular structure analysis, the ABS molecular chain contains a large number of acrylonitrile segments, and has a strong interaction with PVC molecules, which can form a good compatibility system.

Impact strength: The impact strength of this blend is greater than the impact strength of any of the raw materials; when PVC/ABS = 70/30, the impact strength of the blend reaches a maximum.

High temperature performance: PVC softening point is relatively low 75-85; ABS softening point is 105. Therefore, the high-temperature use performance of PVC can be improved after blending.

Processing performance: As the proportion of ABS increases, the melt index increases. Increased fluidity improves processability.

Additives: plasticizers, compatibilizers, heat stabilizers, antioxidants, tougheners, lubricants, etc.

Application: Extrusion molding produces plates, tubes and dissimilar materials. It can replace ABS in luggage products, and can also be used for injection molding to manufacture textile equipment, machine parts and instrument panels.

2, PVC / EPDM blend system

EPDM is an ethylene-propylene-diene terpolymer which is in a soft rubbery state at normal temperature. EPDM is a non-polar polymer, so when blended with PVC, the compatibility between the two is extremely poor. Zheng Changren et al [4] added a third component thiol compound as a compatibilizer in the blending system to improve the compatibility between the two phases. During the blending process, one end of the thiol compound reacted with PVC. The grafted material, at the other end, is entangled with EPDM and acts just like the coupling agent used in the polymer matrix composite. Through the action of the compatibilizer, the interface between PVC and EPDM is strengthened to achieve the purpose of modification and toughening. The notched impact strength of blends incorporating thiol compounds was more than 6 times higher than that of PVC matrix resins.

3, PVC / MBS blend system

MBS Resin is a type of polymer obtained by grafting a copolymer of methacrylic ACID and styrene onto polybutadiene or diphenyl rubber. In the polymer molecular chain, styrene is a rigid segment, polybutadiene or styrene-butadiene rubber is a soft segment, and the synergistic effect of the two gives the MBS molecule good flexibility.

MBS has similar solubility parameters to PVC, and a good compatibility blending system can be formed between the two. Both have a glass transition temperature Tg (89.14 °C) at high temperatures, between the Tg of the two.

It was found by SEM observation that in this system, the MS segment in the MBS phase forms a "continuous phase" with good compatibility with the PVC phase, while the rubber segment is dispersed in the continuous phase in the form of a microscopically dispersed phase. ". When subjected to an impact, crack absorption and transfer impact energy can be formed between the dispersed phase rubber segment and the continuous phase. Achieve a good toughening effect.

The addition of MBS makes it possible to obtain both toughness and light transmission properties of PVC, so MBS is called a transparent impact modifier for PVC.

4, PVC / NBR blend system

Compatibility: Nitrile rubber (NBR) is a polar polymer. The compatibility with PVC increases with the increase of acrylonitrile content in NBR. The compatibility is best when the AN content is 40%. When the PVC and NBR were mechanically blended at 150 °C, it was found that the PVC/NBR system could form a partial crosslinking system even if there was no crosslinking agent in the system.

Impact strength: When the content of AN is 20%, the impact strength of the blend with PVC is the highest.

Tensile strength: The tensile strength and impact strength of the blend of PVC/NBR are different: it increases with the increase of acrylonitrile content in NBR, and the linear relationship between the two when the AN content is less than 50%. .

application:

Compared with unmodified PVC, PVC/NBR blends have elasticity, tensile strength, abrasion resistance and oil resistance. Solvent resistance has been significantly improved. It is widely used in the production of oil-resistant, corrosion-resistant, non-slip work shoes, various sealing gaskets, bellows and other flexible pipes. Wire covering materials, electrical insulation parts, and foam plastics.

NBR is an unsaturated rubber, so it has poor weatherability and can be improved by vulcanization.

5, PVC / ACR blend system

As a modifier of rigid Pvc Resin, ACR can be divided into processing aids and anti-impact additives.

The processing aid is mainly to reduce the gel plasticization time of the rigid PVC material. It is convenient for secondary processing such as thermoforming.

The impact resistant ACR forms a "core-shell" structure. Its shell has good compatibility with PVC; its core plays an excellent toughening effect in the blend system.

ACR is the most successful transparency modifier after MBS.

6, PVC / EVA blend system

EVA is ethylene-vinyl acetate. The PVC/EVA blend can be produced by mechanical blending (mainly melt blending) and graft copolymerization-blending. PVC and EVA have only moderate compatibility, so the PVC/EVA blends obtained by mechanical blending method have coarse domains; the PVC/EVA blends obtained by graft copolymerization-blending method have fine domains.

The morphological structure of the PVC/EVA blend is also directly related to the blend ratio of the two polymers. If the EVA is less than 7-8% in the mechanical blending method PVC/EVA, the PVC is the continuous phase, which surrounds the EVA particles. However, when it exceeds 7 to 8%, the EVA is converted to the continuous opposite and surrounds the PVC particles, so the EVA content of 7 to 8% is the phase reversal zone of the blend.

An outstanding advantage of PVC/EVA blends is that flexibility is significantly better than PVC. Depending on the amount of EVA it contains, such blends are also classified into two main types, hard and soft, as PVC; soft PVC/EVA blends have a softness equivalent to 40 or 60 parts plasticized. The soft PVC of the agent is better than the low temperature characteristics of the latter, the plasticizing effect is stable, and it has a good hand feeling.

PVC/EVA graft copolymerization-blend

In the PVC/EVA graft copolymer-blend, as the EVA content increases, the plasticizing effect also increases, but the tensile strength decreases, the gas permeability increases, and the light transmittance decreases. Generally, the smaller the molecular weight of the EVA and EVA-PVC graft copolymer, the lower the hardness and softness of the PVC/EvA graft copolymerization blend.

application

PVC/EVA blends are used in a wide range of applications to produce hard and soft products. Hard products are mainly extruded and extruded, and are also used to produce impact plates and extruded profiles. Hard products also include low foam synthetic wood, injection molded products (impact pipe fittings, industrial parts) and the like. Soft products mainly include cold-resistant film, film, artificial leather, cable and foam.

At the same time, due to the poor thermal stability of PVC, it is necessary to add a corresponding stabilizer to repair the defects of the PVC chain, and at the same time absorb the HCL generated by the dechlorination of PVC. At the same time, due to the processing characteristics of PVC with high viscosity and large shear, it is necessary to add a corresponding lubricant such as polyethylene wax while adding a stabilizer.

Polyethylene wax, PE wax, low molecular weight polyethylene, is directly polymerized from ethylene. The products synthesized by different synthetic processes and catalytic systems have different molecular weight, molecular weight distribution and molecular chain structure. There will also be significant differences.

PE wax is usually a white powder with an average molecular weight of generally 1500-5000 and a melting point of 100-120 degrees. It has excellent external lubrication effect in PVC processing, which can effectively improve the fluidity, yield, dispersion, surface brightness and mold release of PVC processing. Due to its high molecular weight, high melting point and high temperature stability, it exhibits excellent external lubrication under high temperature and high shear conditions. Polyethylene wax products can effectively improve the dynamic thermal stability of PVC and the fluidity of the processing process, increase the extrusion efficiency of PVC products, improve the surface gloss of the products, and effectively reduce the appearance of PVC products during processing.