Development of Waste Polystyrene Foam Recycled Adhesive II

1.3 Progress of Polystyrene Foam Modified Adhesives

Adhesives have a major role in all sectors of the national economy. Whether it is aerospace, aviation or construction, installation can not be separated from the adhesive. The total adhesive production in the world was close to 5 million tons in the mid-1970s. In recent years, the annual growth rate of 300,000 tons has continued to increase. Of all adhesive products, construction adhesives account for about 25%-35%. With the rapid development of China's national economy, there is a large gap in construction adhesives, and the use of waste PS to prepare adhesives to meet the market demand for high quality and low cost adhesives is a double-edged thing. Researchers in China started their studies in this area from the late 1980s and achieved some success in the late 1990s. However, the research space is still large. Therefore, this is a good research direction, and it is also the best direction for waste PS recycling.

Polystyrene is an amorphous linear non-polar substance. Its molecule contains a benzene ring. It has high rigidity and low flexibility. Its adhesive force on the surface of polar substances is very weak, and the adhesive strength obtained directly by it is used. It is not enough and the glue layer is hard and brittle, so it is necessary to introduce polar and flexible groups on the styrene links to increase the flexibility and improve the adhesive strength, so that adhesives with good adhesive force and adhesion can be obtained. The key technology for making adhesives from waste polystyrene foam is the choice of modifiers. According to literature reports [15-35], there are several modifiers:

1. Phthalate modification. Hu Guangjun modified the polystyrene foam with the plasticizer dibutyl phthalate. The solvent was acetone, and magnesium oxide was used as the filler. The obtained adhesive could be used to bond the speaker circuit, and the bonding cost was reduced by about 100%. 70;Wang Xiuyan Adds dioctyl phthalate and flavors after disintegration of waste polystyrene foam by adding an innovative solvent No.1, which can be made into self-adhesive. This kind of self-adhesive has good bonding effect. Can be reused, can be used for bonding of various labels, trademarks and paper products.

2. Isocyanate modification. Lei Yuying et al studied the isocyanate-modified PS adhesive: PS was dissolved in a mixed solvent of toluene, acetone, and ethyl acetate. After the reaction was completed, isocyanate was added for a certain period of time, and then the filler zinc oxide was added to obtain a solid content of about 30%. The adhesive has a viscosity of 0.5-1 Pa. s, the shear strength is 3.4 MPa, and the uneven peel strength is 1.2 KN/m. The adhesive can be used for the bonding of wood, paper products, daily-use plastics, and carpet backings.

3. Phenolic resin modification. Phenolic resin contains hydroxyl groups in its molecular structure and is an excellent modifier for polystyrene foam. Lu Youling et al. melted polystyrene foam in toluene, ethyl acetate, acetone and chloroform mixed solvent, and then stirred and added phenolic resin to react to obtain milky white PS modified adhesive. The adhesive has a shear strength of 3.47 MPa and an uneven peel strength of 14.8 KN/m, which can be used for the bonding of wood and household items. Shang Jinming and other studies have shown that when the amount of phenolic resin and polystyrene foam is equal, its adhesive strength is close to the phenolic resin adhesive. In order to increase the toughness of the adhesive after curing and the bonding strength to the adherend, a small amount of macromolecular cross-linking agent may be added as a modifier, so that the adhesive forms a network-like molecular layer on the surface of the adherend after curing. Li Jian et al. selected the isocyanate and phenolic resin modifiers containing strong polar groups to modify the waste polystyrene foam and achieved good results. The waste polystyrene foam is dissolved in a mixed solvent of toluene, acetone, chloroform, and ethyl acetate. The mechanical impurities are separated after complete dissolution, and an appropriate proportion of the crosslinker toluene diisocyanate and phenolic resin is added, and then the filler is added to obtain a sticky Thick red adhesive. The adhesive has a shear strength of 3.72 MPa and an uneven tear strength of 17.10 KN/m. The adhesive can replace the opal glue for wood bonding, the effect is good, and at the same time, it has good adhesion to plastics and porous materials.

4. Rosin modified. Qu Junjie et al studied adhesive preparation of waste styrofoam modified rosin resin. Xylene is used as a solvent, and the resulting adhesive can bond porcelain plates, mosaics, and plastic flooring. Chen Zhen et al studied the effect of rosin dosage on the performance of PS modified adhesive, and examined the influence of various solvents on the adhesive strength of PS modified adhesive. The results show that adding a small amount of rosin helps to improve the bonding strength, but because the phenanthrene ring in the rosin is easy to dissociate, with the increase in the amount of rosin, the bond strength is reduced; in all the solvents modified with polystyrene and ethyl acetate After the greatest bond strength.

5. Styrene-butadiene-styrene (SBS) block copolymer modification. The styrene block of styrene-butadiene-styrene block copolymer is similar to that of polystyrene, and has good compatibility. Therefore, using SBS block copolymer as PS modifier can improve the peeling of the adhesive. Strength, reduce the hardness and brittleness of the adhesive layer. Bao Qifu chose ethyl acetate, No. 120 gasoline, toluene, and turpentine as mixed solvents. SBS block copolymer was used as a modifier, and rosin resin was used as a tackifier. The shear strength of the adhesive was 4.43 MPa. The uniform peel strength is 1.4 KN/m. The adhesive can be bonded with wood, ceramic tile and other materials, and can replace polyvinyl acetate emulsion glue for bonding furniture and toys, and can also replace neoprene for wood edge sealing.

6. Modified with maleic anhydride. Meng Yuezhong Dissolved waste polystyrene foam in organic solvent, added initiator and maleic anhydride for grafting reaction, and then emulsified with polyvinyl alcohol solution in emulsifying device to obtain PS modified white glue. , The shear strength is above 3.92MPa, the cost is only one-third of the polyvinyl acetate emulsion, and the production process is simple and the production cycle is short.

7. Polyvinyl acetal modification. Shi Shengxun used toluene and No. 70 gasoline as mixed solvents to dissolve the waste polystyrene foam, and then added polyvinyl acetal to modify it to obtain a thick white adhesive. The most important feature of this adhesive is the wide use temperature. It can be used at -40-40°C, and the shear strength is always kept at 8.7 MPa, while the commercially available white latex can only maintain the strength of 9.0 MPa between 0-40°C.

8. Polyvinyl alcohol modification. Chen Ende uses xylene to completely dissolve the polystyrene foam, and then adds polyvinyl alcohol to modify it to obtain a medical sealant. The medical sealant does not react with formalin, and it is heat-resistant, cold-resistant, and not Leaking water.

9. Graft modification of reactive monomers. The grafted copolymer of waste polystyrene and reactive monomer can be grafted onto the styrene mer to obtain a good adhesive with waste polystyrene foam. According to a patent report, 100 parts of PS are dissolved in mixed solvents of aromatic hydrocarbons and chlorinated hydrocarbons to form a glue solution, cuprous chloride is added as an activator, and butyl benzoate peroxide is used as an initiator. The temperature is increased to 90-120°C and 20-30 parts are added. Acrylonitrile, allyl alcohol monomer, grafting reaction for 2 hours, so that polystyrene grafted polar groups to change the nature of the PS, then add asbestos powder or calcium silicate, to form a good water resistance, adhesion Strong white visoid adhesive. Its water resistance and shear strength are 10 times and 3 times higher than that of polyvinyl acetate emulsion glue. The PS adhesive can be used as glue for wood, furniture and daily life, and can also be used to bond cement products, flooring, wallpaper and each Kinds of fabrics. The grafting of acrylonitrile and allyl alcohol on polystyrene macromolecules can significantly improve the adhesion, but the proportion of added monomers is very high, so the cost is higher, and the toxicity of acrylonitrile monomer is also very large. Bring certain difficulties to production. Therefore it is difficult to promote the application. Chen Kailai et al. studied the carboxylate monomers grafted onto the styrene links and succeeded in preparing a decorative waterproof adhesive for buildings. The waste polystyrene foam is dissolved in two organic solvents, A and B, to form a glue solution. Under the action of the initiator, a graft copolymerization reaction occurs with the unsaturated monomer, and a graft is made on the polystyrene macromolecular chain. The addition of tackifying resin to the viscosities can produce a brown glue with a shear strength of 4.4-4.7 MPa, and its fire resistance is much better than that of similar products. The strength can reach 4.5 MPa after water immersion. The water-resistant glue thus obtained can be used for the bonding of wallpapers, tiles, parquets, and floors. 1:1 into the cement, the construction performance is better, and does not affect the performance of bonding the floor, tile. Among these modifiers mentioned above, epoxy resin is not reported as a modifier. Epoxy resin is often referred to as “magnum” and has good adhesion to various metals and most non-metallic materials. Performance, widely used in aircraft, missiles, automobiles, construction, electronic appliances and wood processing and other industrial sectors, and epoxy resin has good process performance, high bonding strength, low shrinkage, excellent resistance to dielectric properties, good electrical insulation properties Such advantages [43]. Its molecules also contain polar groups. If it can be used to modify the PS glue, modified PS glue with good properties should be obtained. On the other hand, epoxy resin adhesives are generally relatively brittle. Therefore, adding a toughening agent that can both improve PS brittleness and improve brittleness of epoxy resins can solve this problem. I finally chose isocyanate to achieve satisfactory results. It not only improves the bonding strength but also shortens the curing time. It also saves solvent and reduces costs. In addition, I also tried to substantially reduce the amount of monomer in the formulation based on the formula of the white plastic, using PS instead of polymerized monomers, adding a plasticizer, and obtaining a wood adhesive with better performance than the white glue. Greatly reduce the cost of commercially available milk white glue, and at the same time achieve the purpose of waste utilization.

(to be continued)