Preparation of Adhesives from Waste Polystyrene Plastics

Polystyrene plastic (hereinafter referred to as PS) and its foamed product Styrofoam (hereinafter referred to as PSF) have good water resistance, chemical resistance, electrical insulation, shock resistance, heat insulation, and production technology Its mature and low-cost features are a substitute for many materials. It is used in the manufacture of instrument housings, molds, models, heat-insulation materials, and shock-proof packaging and disposable lunch boxes. Growing year by year, it has become one of the four largest plastics in the world today.

The extensive application of PS has brought great progress to the society and brought great convenience to people's lives. However, due to its wide application and scattered consumers, it is not easy to collect after consumption, and it is also resistant to aging. , difficult to degrade, and other plastic sorting technology is still immature and perfect and other factors, waste PS has become a major public hazard, especially one-time use of PSF, light weight, low density, large size, constitutes World-famous white pollution.

Polystyrene is an important macromolecule compound that uses petroleum as raw material. Its one-time use will cause great waste of resources, and it also brings a series of pollution problems to the environment during its production and manufacturing process. Therefore, the recycling of waste PS is of great significance both to saving resources and saving energy, and to reducing the pressure on the environment caused by raw plastics and waste plastics. At present, the disposal methods for waste PS include landfill, incineration, cracking, regeneration, and reuse, among which the reuse method is an effective way to make full use of polystyrene as a chemical resource. The use of scrap PS to prepare adhesives and related products is a major aspect of reuse.

1 Simple polystyrene adhesive

PS is a thermoplastic that dissolves in a solvent and is a plastic adhesive. Comparing the solubility parameters of polystyrene and various solvents, it can be seen that aromatic hydrocarbons, chlorinated hydrocarbons, etc. have better solubility to polystyrene, such as benzene, toluene, xylene, and chloroform. The first method that people used was to dissolve PS in these solvents to make a simple adhesive. Since PS is a high-molecular polymer, it is a film-forming substance in itself. Therefore, this adhesive can be used to bond plastic products and painted cartons, wooden devices, floors, etc., but the solvent cost is high and the consumption is high. Taking into account the price of the solvent, the use of crude benzene and xylene is more economical, but the toxicity and odor of the product are large, which is detrimental to both producers and users.

The use of different solvents, the role and compatibility of solvents and PS, the use of mixed solvents can not only improve the odor of the adhesive and reduce the toxicity, but also improve the performance of the adhesive. For example, pure acetone does not dissolve PS well, and it volatilizes faster, affecting the coating and flatness of the glue. However, when it is added to other solvents, its presence and amount of addition to the dissolution rate are The quality of the product has a great influence. Studies have found that solvent gasoline, banana water, etc. are also active ingredients of the mixed solvent.

Since PS is a non-polar high-molecular polymer, it does not contain polar groups, and it contains a benzene ring with high rigidity and low flexibility. Therefore, an adhesive prepared by simply dissolving it in a solvent and a polar adherend are used. The adhesiveness is poor, the adhesive layer is brittle and hard, the effect is unsatisfactory and the application range is narrow. For this reason, a great deal of modification research work has been carried out. The purpose is to introduce polar groups and improve the adhesive strength and flexibility to adapt to various Adhesion needs to be adhered.

2 Modified polystyrene adhesive

According to the different modification methods, the modification can be divided into physical modification and chemical modification. The former refers to the introduction of polar substances only in the adhesive, and there is no change in the polystyrene molecule itself. This modification method is simple and generally requires only The simple stirring and mixing; while the latter is a chemical reaction with the modifier during the modification process, the polystyrene molecule is grafted with other groups to make it a polar molecule method.

The polar groups introduced in the adhesive can work well with the polar groups on the surface of the polar substrate, thereby strengthening the interaction between the two and making the bonding firm. The modified polystyrene adhesive can be applied to different adherends such as wood, plastics, building materials, daily necessities, and the like, respectively. The product can be an ordinary form of adhesive, such as construction glue, stickers, sealants, etc. It can also be made into paint products, such as anti-corrosion paint, bright oil, lacquer, color paint, etc., and can be used together with appropriate materials. For the production of waterproofing membranes and composite materials, etc., after the appropriate fillers and other components in the adhesive, you can obtain the appropriate coatings, such as waterproof coatings, road marking coatings, interior and exterior wall coatings, and moisture-proof coatings for cartons. Adding cross-linking agents, tackifiers, or plasticizers to plastics in PS's organic solution can all improve the performance of the adhesives, thereby expanding the scope of application of the adhesives. This modification can be divided into the following types]:

2.1 Ethyl acetate modification

Ethyl acetate is both a solvent and a modifier of PS, and its modification effect is superior to other solvents. For example, PSF 300 parts (parts by weight), 80 parts of ethyl acetate, acetone 120-140 parts, dissolved and mixed evenly, then add 400 parts of calcium carbonate and a small amount of stabilizer, the resulting adhesive can be used for building decoration and other industries.

2.2 Isocyanate Modification

The molecular formula of isocyanate is OCN-R-NCO. Its polarity is very strong. Adding it to the organic solution of PS can increase the polarity of the adhesive and enhance the bonding strength between the adhesive and the polar substrate.

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. Such as: PSF dissolved in toluene, ethyl acetate, acetone and chloroform mixed solvents, adding phenolic resin, the resulting adhesive shear strength of up to 3.47MPa, uneven peel strength up to 14.8kN /]. 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 paints.

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 -17.8kN/m.

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 The surface of objects such as walls and walls can be reused. For another example, PSF, dibutyl phthalate, natural rubber, crude benzene, and rosin can be used as raw materials.

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 . 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.

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, The PS chain segments are grafted with active acrylonitrile and allyl alcohol groups, and fillers are added to obtain adhesives with good water resistance and high bonding strength, which are widely used in construction, wood furniture and daily necessities. 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]. 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. The surfactant may be sodium dodecylbenzenesulfonate, sodium lauryl sulfate, alkylphenol polyoxyethylene ether, and the like. 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.

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.

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