2.1.2 Selection of Modified Resin

Because waste polystyrene is a non-polar substance, its molecular structure contains a benzene ring which reduces the flexibility of the polymer chain, and has poor adhesion on the surface of steel, wood, etc., and it is necessary to use the polarity as a film-forming material for coating. The resin is modified to enhance the adhesion of the coating, which is the key to using waste plastics to produce coatings. Modifiers include TDI (toluene diisocyanate), phenolic resin, turpentine, rosin, isocyanate, and the like. Considering the cost issue, it is reasonable to use rosin or turpentine.

2.1.3 Selection of Plasticizers

Polystyrene is a linear structure, from the perspective of the three-dimensional structure, the position of the benzene ring side groups on the main chain is irregular, is a three-dimensional irregular polymer, it is not qualitative, benzene ring side groups will harden the main chain , resulting in a higher softening point (90-100 °C), more brittle at room temperature, so the outstanding characteristic of pure polystyrene is brittle. Therefore, in order to meet the requirements, polystyrene must be modified by adding plasticizer to polystyrene. Plasticizers are organic compounds with a certain polarity. When mixed with polymers, the temperature rises and the plasticizer molecules are drilled into the macromolecular polymer chain. Gravity due to the polarity of the plasticizer groups causes the polymer to swell, resulting in a strong, long-term mutual structure between the polymer chains and the plasticizer, and even hydrogen bonds. After cooling the system, the plasticizer remains Stay in the polymer chain. Due to the entry of the plasticizer molecules, the distance between the chains is increased, the van der Waals force is reduced, the activity of the segments is increased, and the softening temperature is reduced, thereby obtaining a tough coating. Plasticizers for polystyrene include phthalates, diterpenes, epoxidized soybean oils, epoxidized soybean octyl oleate, diesel aromatic plasticizers, alkylbenzene sulfonates, and the like. We chose a phthalate plasticizer for polystyrene. It has the characteristics of comprehensive performance, good compatibility with the resin, and low price. It not only has good plasticizing effect, but also has a small amount. The dosage is 6%-8%.

2.1.4 Selection of Emulsifiers

(1) Emulsifiers. The type of emulsifier directly affects the stability of the emulsion, the non-ionic emulsifier can give the emulsion a better chemical stability, and the anionic emulsifier can give the emulsion a better mechanical stability. Therefore, we use a composite system composed of non-ionic emulsifier OP 10 and anionic emulsifier to improve the stability of the emulsion. As the amount of emulsifier increases, the stability of the emulsion increases. When the amount of emulsifier reaches 2.4%, a stable emulsion coating can be obtained. The temperature of the emulsification process is 70-75°C, the stirring speed is 2000r/min, the ratio is 1/1, and the emulsification time is 2h. In the emulsification process, the organic solvent is slowly distilled out and recycled (see Table 3).

(2) The pH of the emulsion. The pH value has an important influence on the stability of the emulsion. Experiments have shown that when the pH value is 7-9, the stability of the emulsion is good. If the pH value is too high or too low, the stability of the emulsion will be reduced. This is because the emulsion is an electric double layer structure. When the concentration of H+ or OH− is too large, the negative ions or positive ions of the system are neutralized, the double electric layer disappears, and the emulsion is unstable.

2.1.5 Selection of Fillers and Antioxidants

The addition of filler not only reduces costs, but also improves performance by increasing the viscosity of the adhesive, heat resistance, mechanical strength, advection of the coating, enhancing the stability of the coating, and increasing the abrasion resistance. The fillers used in this experiment were: (1) active calcium carbonate: CaCO3, molecular weight 100.09, content ≥ 99.0%; (2) zinc oxide: ZnO, molecular weight 81.38, content ≥ 99.5%. This experiment used 60% ZnO, 40% CaCO3 as a filler. Anti-aging agents are added during the preparation of the coating to avoid excessive aging of the coating. Therefore, cyclohexanone is used as an antioxidant, and its anti-aging performance is very good.

2.2 Experimental results and product testing performance indicators

According to the structure and characteristics of polystyrene, xylene is the main solvent, and ethyl acetate and butanol are auxiliary solvents. Take xylene 50% - 80%, ethyl acetate 10% -30%, butanol 5% -20% for exploration experiments to determine the ratio of these three solvents. The best formula for the final adhesive and coating is shown in Table 4. Product performance indicators test results are shown in Table 5.

2.3 Economic Estimates The economic accounting indicators for coatings are shown in Table 6.

3 Conclusion

After experiments, we obtained the best formula for preparing coatings and adhesives. After testing and testing, the coating product has excellent performance, has a variety of functions, and fast drying at room temperature, waterproof anti-corrosion performance, adhesion, impact resistance, and its bright coating. It can be used as waterproof and anti-corrosive coatings, as well as various waterproof materials for carton and other packaging materials. It can also be used as an adhesive for interior wall coatings, building materials such as tiles and mosaics. The paint has excellent waterproof and anticorrosive properties, and the film is bright and beautiful. It can be widely used. In addition, these paints use waste polystyrene foam as raw materials, which are low in cost, low in investment, and easy to industrialize. This method of producing coatings creates a new path for the use of waste polystyrene foam, turning waste into treasure, saving energy and eliminating white pollution. Therefore, it has certain economic, social and environmental benefits. The use of waste polystyrene to obtain coatings has broad prospects and is suitable for widespread application.

Author/LI Wanhai, GUO Jinghai, WANG Hong, QI Aiyu (Department of Environmental Science and Engineering, Jilin Institute of Chemical Technology)