Comparison of application of different PVC impact modifiers

There are many types of PVC impact modifiers, including: CPE resin, ABS resin, MBS resin, EVA resin, NBR resin, ACR resin and so on. These modifiers have their own characteristics, advantages and disadvantages, so we have to choose the appropriate modifier according to the characteristics of the modifier and the final application of the processed product.

PVC impact modifiers sometimes also play a plasticizing role, so they can also be regarded as plasticizers. The main impact modifiers for PVC resin are as follows:

(1) CPE

CPE is chlorinated polyethylene, which is formed by chlorination of HDPE. Due to the presence of chlorine atoms, CPE has softness and some rubber properties, and makes CPE a polar polymer and has the same polar group with PVC, increasing the compatibility with PVC. Therefore, the polymer chain can maintain a large enough van der Waals force to improve the impact resistance of PVC, which plays a toughening role. Moreover. CPE has the function of promoting PVC melting and accelerating plasticization.With the increasing of the amount of CPE, the plasticizing torque is shortened, the balance torque is increased, and the viscosity of the plasticized melt is increased.

CPE used as a toughening agent generally contains 25-45% CL. CPE has wide source, low price, in addition to toughening effect, but also has cold resistance, weather resistance, fire resistance and chemical resistance. In the production of PVC pipes and profiles, most factories use CPE as an impact modifier, and the amount of addition is generally 5-15 parts. CPE can be used in conjunction with other toughening agents, such as rubber, EVA, etc., the effect is better, but the rubber additives are not resistant to aging.

(2) ACR

Acrylic Processing Aid is an acrylate copolymer. Currently There are two types of ACR used as PVC modifiers: one is to improve the processing properties of hard PVC; The other is an used to improve the impact strength of PVC products. The difference in chemical composition between the two is that ACR impact modifier contains a nucleus formed by acrylate-type crosslinked elastomer, and outside the nucleus is a shell composed of methyl methacrylate and ethyl acrylate copolymer. The impact strength of the good ACR + PVC blending system is more than 10 times higher than that of PVC, and the tensile property of PVC is also greatly improved, especially for outdoor hard PVC plastic products. Compared with other impact modifiers, ACR has good processing performance, obvious impact resistance, smooth and beautiful surface of the product and excellent aging resistance.

ACR is suitable for the impact modification of PVC plastic products for outdoor use, the use of ACR as an impact modifier in PVC plastic door and window profiles compared with other modifiers, ACR has the characteristics of good processing performance, smooth surface, good aging resistance, high welding Angle strength, but the price is about 1/3 higher than CPE. General 6-10 PHR in PVC application. In addition, under the same processing conditions, the impact strength of the blends prepared by different stabilizing systems of PVC+ACR is quite different. For example, under the same conditions, the use of barium stearate and cadmium stearate as the stabilizer has higher impact resistance than the use of lead salt stabilizer.

（3）MBS impact modifier

MBS impact modifier is a core-shell copolymer made of MMA graft styrene butadiene latex after salting out and drying. PVC can be modified with it to improve its impact strength and comprehensive properties. Due to its similar refractive index to PVC, the modified PVC has better transparency, so it is widely used in transparent products. Because it contains butadiene, it is easy to decompose and age in light, so it is not suitable for outdoor products.

Generally, adding MBS 10-17 PHR into PVC can increase the impact strength of PVC by 6-15 times, but when the amount of MBS is greater than 30 dosages, the impact strength of PVC decreases. MBS itself has good impact performance, good transparency, light transmittance can reach more than 90%, and while improving the impact property, it has little impact on other properties of the resin, such as tensile strength and elongation at break. MBS is expensive and often used with other impact modifiers, such as EAV, CPE, SBS, etc. MBS heat resistance is not good, poor weather resistance, not suitable for outdoor long-term use products, generally do not need to do the production of plastic door and window profile impact modifier use.

MBS can not only give hard PVC good toughening effect and excellent light transmittivity, but also improve its processing performance, this is because MBS in the plasticizing process of PVC entanglement, friction with each other, the result not only promotes the disintegration of PVC particles, but also bonds with PVC particles, promoting the gelation of PVC. Therefore, the melting time is shortened, the residence time of the material in the extruder is reduced, the decomposition of PVC is prevented, and the processability of PVC is improved.

The main performance characteristics of PVC/MBS blends are as follows:

1. The impact strength is more than five times higher than PVC, and it can even be more than 30 times higher, and its toughness is also much higher than PVC /EVA and PVC/CPE blends;

2. Due to the introduction of MMA components in the dispersion structure, increasing its polarity and improving the compatibility with PVC, the light transmission of this blend not only greatly exceeds PVC/EVA and PVC/ CPE, but also exceeds PVC/ ABS;

3. Similarly, due to the improvement of compatibility, the stress whitening phenomenon of PVC/MBS blends is less than that of PVC/ABS when subjected to bending.

4. After a long time of mixing and natural aging test, the impact strength decreases a lot, so the waste can be recycled. Polymer blends similar in performance and composition to PVC/MBS also include:

1. MMA and AN are grafted onto SBR and blended with PVC;

2. MMA\AN and ST are grafted on SBR and blended with PVC;

3. MMA is grafted onto ABS and blended with PVC. These blends have excellent impact resistance and light transmission properties.

(4) SBS

SBS is styrene, butadiene, styrene ternary block copolymer, also known as thermoplastic styrene butadiene rubber, is a thermoplastic elastomer, its structure can be divided into two kinds of star and linear. The ratio of styrene and butadiene in SBS is 30/70, 40/60, 28/72 and 48/52. It is mainly used as impact modifier of HDPE, PP and PS, and its addition amount is 5-15 PHR. The main function of SBS is to improve its low temperature impact resistance. SBS has poor weather resistance and is not suitable for long-term outdoor use.

(5) ABS

ABS is terpolymer of styrene (40%-50%), butadiene (25%-30%), acrylonitrile (25%-30%) , mainly used in engineering plastics, but also used as PVC impact modification.And it’s low temperature impact modification effect is also very good. When the amount of ABS added reaches 50 PHR, the impact strength of PVC can be comparable to that of pure ABS. The amount of ABS added is generally 5-20PHR, the weather resistance of ABS is poor, it is not suitable for long-term outdoor use products, and it is generally not necessary to use impact modifiers for the production of plastic door and window profiles.

(6) EVA

EVA is a copolymer of ethylene and vinyl acetate. As the refractive index of EVA and PVC is different, it is difficult to get transparent products, therefore, EVA is often used with other impact resins. The amount of EVA added is less than 10 PHR.

In addition, rubber impact modifier is also an excellent toughening agent, the main varieties are: Ethylene-propylene rubber (EPR), EPDM (EPDM), nitrile butadiene rubber (NBR) and styrene butadiene rubber, natural rubber, butadiene rubber, neoprene rubber, polyisobutene, butadiene rubber, etc., of which EPR, EPDM, NBR three are most commonly used, which is to improve low temperature impact resistance is superior, but not resistant to aging. Plastic door and window profiles generally do not use such impact modifiers.

At present, CPE is mainly used as an impact resistant agent for PVC in China, while MBS and ACR(acrylate copolymer) are mainly used abroad, as well as ABS(acrylonitrile butadiene styrene copolymer) and EVA(ethylene vinyl acetate copolymer). By practical comparison, MBS resin is a kind of impact modifier with excellent comprehensive properties, especially its transparency and coordination.

The impact resistance of MBS resin is better than EVA, but worse than ACR, CPE and ABS. MBS is close to ABS in weather resistance, but inferior to the other three. In terms of light and thermal stability, MBS is close to ABS, but lower than ACR. With the CPE. It should be emphasized that the important role of MBS resin in the processing of transparent PVC resin products cannot be replaced. MBS resin can usually increase the impact strength of PVC by 5-6 times, and has little influence on tensile strength and elongation.