Preparation of adhesives from waste polystyrene plastic (top)

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, waste PS treatment methods include landfill, incineration, cracking, regeneration, and reuse [1]. 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 [2]. Comparing the solubility parameters of polystyrene and various solvents, we can see that aromatic hydrocarbons, chlorinated hydrocarbons, etc. have better solubility to polystyrene, such as benzene, toluene, xylene, chloroform, etc. [2]. 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 [3]. Studies have found that solvent gasoline, banana water, etc. are also effective components of mixed solvents [12].

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 [4,5,6]:

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 in construction and decoration industries [4 ].

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.

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