Preparation of Adhesives from Used Polystyrene Plastics (2)

2.3 Resin Modification

Rosin, phenolic resin, furan resin, epoxy resin, etc. are all good modifiers, and the heat resistance and water resistance are good. Compared with the phenolic resin, the two are better. For example, PSF is dissolved in a mixed solvent of toluene, ethyl acetate, acetone and chloroform, and the phenolic resin is added. The shear strength of the obtained adhesive can reach 3.47 MPa, and the uneven peel strength can reach 14.8 kN/m [ 4]. The lacquer can be prepared by adding rosin to the toluene or benzene solution of PSF, and then adding appropriate fillers and pigments to obtain colored paint [7]. Because the stability of rosin molecules is not very good, the amount of rosin should not be too large, otherwise the adhesive strength will decrease and the adhesive layer will be brittle. Resins and other modifiers can also be used for the modification of adhesives to achieve more satisfactory results. For example, ethyl acetate, acetone, cyclohexane, toluene as a mixed solvent, phenolic resin and isocyanate as modifiers, the resulting adhesive shear strength of up to 3.55-3.97MPa, uneven peel strength up to 15.2 -17.8 kN/m[6].

2.4 Phthalate Modification

Phthalates are plastic plasticizers that can improve the flexibility and toughness of adhesives. PS-based adhesives often use this type of modification, sometimes with other modifiers, such as Rosin and so on. For example, the composition and ratio of PS2.0-4.0kg, 2.5-3.5kg of dibutyl phthalate, 3.0-4.5kg of organic solvent, and 0.1-0.3kg of ethyl acetate can be pasted on glass, metal Surfaces of objects such as walls and walls, and can be reused [5]. Another example is the use of PSF, dibutyl phthalate, natural rubber, crude benzene, and rosin as raw materials to produce self-adhesives [7].

Appropriate fillers can be added to the adhesive to produce the corresponding sealant or coating product. For example, adhesives made of PSF, polyvinyl alcohol, No. 50 solvent oil, toluene, dibutyl phthalate, water, surfactant octyl ethoxylate and fillers can be used for the sealing of aluminum alloy doors and windows [8]. If the PS is dissolved in a mixed solvent composed of ethyl acetate and 200# gasoline, rosin is added, and bentonite, talc, light calcium, pigment, driers, etc. can be used to obtain interior and exterior wall paints. Strong, fast drying, smooth coating [5].

By chemical reaction, the reactive groups are grafted onto the polystyrene molecular chains to make them polar substances, which is called chemical modification. The adhesive prepared therefrom has good polarity and good adhesion to polar substrates. For example, after PS is dissolved in a mixed solvent of aromatic hydrocarbons and chlorinated hydrocarbons, activator Cu2Cl2 and initiator butyl benzoate are added, and acrylonitrile and allyl alcohol monomers are added at 100° C. After 2-4 hours of reaction, that is, PS chains are grafted with active acrylonitrile and allyl alcohol groups, and fillers are added to obtain adhesives with good water resistance and high bonding strength. They are widely used in construction, wood furniture and daily necessities [4]. For another example, graft modification of polystyrene with acrylates and reactive monomers, the presence of ester groups in acrylates greatly improves the adhesion of the coating to the substrate, and the active monomer N-alkyl acrylamide Addition can make the coating film cross-linking reaction during the filming process, giving the film a good mechanical properties and weather resistance. The paint can be used as a building wall paint [9]. In the above-mentioned adhesives and coatings, organic solvents are used as solvents, and they are highly toxic, contaminating producers, consumers, and the environment. Therefore, it is of great significance to explore water-based coatings.

3 Water-based polystyrene adhesives and coatings

Adding water, surfactant or emulsifier to the polystyrene adhesive can make the corresponding emulsion by emulsifying, thereby reducing the proportion of the organic solvent in the adhesive, reducing the hazard of the adhesive and reducing the cost. Surfactants may be sodium dodecylbenzene sulphonate, sodium lauryl sulphate, alkyl phenol polyoxyethylene ether, etc. [13]. After chemical modification, the grafted PS has good water solubility, and the water emulsion adhesive prepared therefrom has better stability. The water-emulsion adhesive can also be further processed to partially or completely separate the organic components therein to further reduce the organic content of the adhesive. For example, after PS is dissolved in 1,2-dichloroethane, it is sulfonated by a sulfonation reaction, then water is emulsified, and the organic solvent is distilled off under reduced pressure to obtain a water-based paint, which can be used for food packaging, Food tank internal coating, carton and other waterproof layer [10,11].

4 Future Development

In the use of waste PS to produce adhesives and their corresponding products, a lot of research work has been carried out, and gratifying results have been achieved, contributing to saving resources and reducing environmental pollution. Because of this simple method of reuse, the flow and technology are easy to grasp, and the investment is not large. Large, medium and small enterprises can produce it. Therefore, there are many such enterprises in China. At present, the inspection of adhesive products in China still performs only performance tests. The toxicity and contamination of products are not sufficiently tested, and the supervision and management system of environmental pollution of manufacturers is not sound enough. Therefore, it is common in the production and use of adhesive products. Environmental Pollution.

With the approaching of China's accession to the WTO, in addition to companies consciously comply with the state's laws and regulations concerning environmental protection or voluntarily perform ISO14000 environmental management system certification, China should strengthen the establishment of relevant indicators in the adhesive standard. With the improvement of people’s living standards and the strengthening of environmental protection awareness, while increasing the recycling rate of used plastics, the pollution problem of products will surely attract more and more attention from people. Therefore, the bonding performance is good, the utilization rate of waste materials is high, and pollution is high. Small adhesive products are people's trust. Therefore, the composition, stability, toxicity, or water-based adhesives and coatings are the trend of future development, and it is also the goal of our research workers in the future.

Source: China Plastics Additives Network