1-Experimental part

1.1 Main raw materials
Butyl acrylate (BA): technical grade, styrene (ST): technical grade, butyl methacrylate (MMA): technical grade, potassium persulfate: analytical grade, sodium lauryl sulfate: analytical grade, bicarbonate Sodium: analytically pure.

1.2 Synthesis of impact-resistant ACR
1.2.1 Seed preparation
In a four-neck flask equipped with a stirrer, thermometer, and condenser, add distilled water, emulsifier, sodium bicarbonate, and stir. After emulsification is uniform, add part of BA containing crosslinking agent. After nitrogen replacement, the temperature is at 75 ℃. Add initiator to initiate polymerization.
1.2.2 Nuclear polymerization
After the seed emulsion is kept warm, the remaining BA is added dropwise, and the reaction is kept warm for 1.5 hours.
1.2.3 Shell polymerization
After the end of the nuclear polymerization heat preservation, the secondary monomer methyl methacrylate/styrene was added dropwise to the above-mentioned system towel to initiate polymerization at 78 ℃, and the temperature was kept for 0.5 h at the end of the dripping. After the reaction was completed, the temperature was kept at 85 ℃ for another 2 h, and then cooled Unwind.
1.2.4 Demulsification
After the emulsion is cooled down, it is demulsified with 0.5% demulsifier, filtered, washed, and dried to obtain a white powder.

2- Modification mechanism of impact ACR
2.1 Adding ACR impact modifier to PVC products can promote the homogenization of PVC gel during processing, thereby improving the adhesion between resin molecules and improving the impact strength of products.
2.2 When the rubber phase in the ACR impact modifier is impacted, the rubber elastomer particles in the system become the stress concentration center, which induces a large amount of silver shear bands. The generation and development of a large amount of silver and shear bands consumes a lot of energy, absorbs a large amount of impact energy and converts most of it into heat energy and releases it into ductile fracture, thereby improving the impact strength.

3 performance test
3.1 Structural analysis
3.1.1 Determination of the size of latex particles: using dynamic light scattering method, the instrument is the United States COULTER MODEL N4MD SUB-M ICROW PARTICLE ANALYZER.
3.1.2 Gel content determination: acetone is used as the extractant, and the extraction method is used.
3.1.3 Determination of molecular weight: using viscosity determination method.
3.2 Impact performance test
The ACR, PVC resin and various additives are combined in a high-speed mixer at room temperature according to a certain ratio, and then mixed with two rollers, pressed into tablets, prepared according to the GB/T1043-93 standard, and milled out the gaps. The impact test was carried out on the XCJ-40 simply supported beam impact testing machine.

4 Results and discussion
4.1 The effect of latex particle size on notched impact strength In the three stages of ACR synthesis, the latex particles were taken to measure the latex particle size. It was found that the particle size of the latex particles gradually increased as the synthesis progressed, and showed a clear core-shell structure. In the experiment, we also investigated the influence of different rubber particle sizes on the toughness of the ACR/PVC blend system. The results show that the notched impact strength increases with the increase of the latex particle size. When the latex particle size exceeds 200nm, the impact strength decreases instead.
4.2 The influence of gel content on notched impact strength
Experiments show that the notched impact strength increases significantly with the increase of the finished gel content. The impact resistance effect is obvious when the rubber phase gel content exceeds 80, and the impact resistance effect is best when it reaches the range of (90±2).

4.3 The influence of ACR core-shell ratio on the notched impact strength of the system
In the experiment, we investigated the notched impact strength of the ACR/PVC blend system within the range of 20% to 70% in the core layer content. The results showed that the initial notched impact strength increased rapidly with the increase of PBA content, but exceeded 60% The impact strength of the rear notch began to decrease. When the PBA content is too small, the modification is mainly composed of hard components (shells), so that the initiation, branching and termination speed of crazing will decrease, which is not conducive to the improvement of impact strength. The content of PBA is too high. Because PBA is rubbery and has a high viscosity. When the core is too large, the hard shell will not be able to completely wrap it. When it is broken, it will be partially exposed and bonded into small clumps, so that ACR cannot be uniformly dispersed in PVC. The desired modification effect cannot be achieved.

4.4 The influence of the added amount of impact modifier on the notched impact strength of PVC
In the experiment, we investigated the impact of different additions on the impact strength of the blend system. The results showed that with the increase of the addition, the impact strength of the blend system gradually increased, and the impact strength increased the most in the range of 6-8 parts. Fast, the effect is not obvious after more than 8 servings.

5 Conclusion
5.1 The polyacrylate modifier with core/shell structure synthesized by seed emulsion polymerization-the blend of impact ACR with rigid PVC can significantly improve the impact resistance of PVC, and it also has processing aids. The characteristics of PVC hardly affect the inherent performance of PVC, and the modification effect is best when the amount of modifier added reaches 8 parts.
5.2 Using seed emulsion polymerization to synthesize polymers with core/shell structure, the key to operation is to strictly control the emulsifier concentration. That is, in the first step of seed polymerization, it is required to obtain a seed emulsion with a sufficient number of particles and a sufficiently small particle size; in the second step of polymerization, the concentration of the system emulsifier must be strictly controlled so that there are no new micelles, so that the monomer can only be Polymerization occurs on the surface of the seed particles without producing new colloidal particles.

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