Bao chunyang

(Heilongjiang Institute of Petroleum Chemistry, Harbin, Heilongjiang 150040)

Abstract: Styrofoam is widely used in packaging, thermal insulation, waterproof, thermal insulation, shock absorption and other fields because of its advantages of light weight, firmness, low hygroscopicity, easy molding, good water resistance, good thermal insulation and low price. PS are mostly disposable. Waste PS can neither rot nor degrade itself in nature, which not only wastes valuable non-renewable resources, but also causes serious environmental pollution. In order to save resources, protect the environment and turn waste into treasure, this paper studied the preparation of two kinds of adhesives with low toxicity, low cost and good performance with waste polystyrene as the main raw material and modified by modifiers. One of them is a solvent-based multifunctional adhesive with epoxy resin and toluene diisocyanate as modifiers, which can be used to bond metals, ceramics, glass, wood and so on. Its tensile shear strength is greater than 4.7MPa. The other is a graft emulsion adhesive with butyl acrylate and vinyl acetate mixed monomer as modifier. Its performance is better than that of white latex, and its compressive shear strength is as high as 10.4MPa, and its price is only 70% of that of white latex.

Keywords: waste polystyrene foam; Modifier; agglutinant

1 quotation

1. 1 Current situation at home and abroad

Expanded polystyrene (EPS) is a new material in the development of modern plastic industry. Since BASF Company of West Germany invented the foam molding method of volatile polystyrene beads in 195 1 and the United States invented the one-step molding method in the 1970s, its production has developed rapidly. From 65438 to 0985, China introduced five sets of polystyrene foam production devices from the United States and Japan, which promoted the development of China's plastic industry. Polystyrene foam is one of the most widely used plastics in the world. Because of its good water resistance, heat insulation, insulation, low hygroscopicity and strong seismic strength, as well as light weight, firmness, easy molding and low price, it is widely used in packaging, thermal insulation, waterproof, thermal insulation, shock absorption, decoration, catering industry and other fields, and has penetrated into all industries of the national economy. According to statistics, in recent ten years

In recent years, the average annual consumption of polystyrene plastics in China has increased by 10%. 1990 has reached 2 17000 tons. With the rapid development of electronic instruments and household appliances industry and the promotion of western development, the consumption of EPS will be increasing [1]. It is estimated that by 2005, China will need120,000 tons of polystyrene foam. Most of polystyrene foam plastics are disposable, and millions of tons of white garbage are scattered in nature, which will neither rot nor degrade and disappear on its own. On the one hand, it causes serious environmental pollution, on the other hand, it wastes valuable non-renewable resources. How to recycle waste polystyrene foam reasonably and effectively has attracted the attention of researchers all over the world, including China. Since 1970s, Japan, Western Europe and the United States have successively industrialized plastic waste. By the 1990s, the comprehensive utilization technology of plastic waste was mature, and the industrialization reached 80%. By the end of 1999, the recovery rate of plastic waste in the United States reached 50%, that in Britain reached 80% and that in Japan reached 49%. Italy not only recycles its own plastic waste, but also imports plastic waste from other European countries for recycling. China began to study the recycling technology of waste plastics in the late 1980s. After the 1990s, research became active, and the rate of technology industrialization was still very low. Only about 65,438+05% of waste plastics are recycled every year [2], and most of the rest are buried. The density of polystyrene foam is very small, only 0.02-0.04 g/cm3. So it's very big, and it will occupy a large area of land. Moreover, after the foam plastic enters the soil, it will not be degraded by microorganisms, which will make the air, moisture and nutrients in the soil unable to exchange normally. But also will gradually release some harmful substances, which will affect the normal cycle of the ecosystem and worsen the soil quality in the buried area and its surrounding Fiona Fang area.

1.2 recovery of polystyrene foam

There have been many patents and research reports on the recycling of polystyrene foam, and its application technology mainly focuses on the following aspects [4-9]:

1. Used for manufacturing lightweight building materials. Using expandable polystyrene pre-foamed particles or polystyrene foam waste crushed into small pieces as the main body, adding different fillers and using different binders, various light building materials are made. For example, using broken wood as filler, cement as binder, mixing with water, and then molding into various shapes of lightweight cement partition walls, or making artificial wood; Lightweight foam board supported by iron wire can be used as wallboard, countertop or decorative board; Using expanded perlite as filler can make roof insulation board; Using soil as binder and filler, evenly mixing with the same amount of polystyrene foam particles, pressing, molding, drying and calcining, can be made into light large blocks for high-rise buildings or permeable pipes for underground sewage drainage; Waste nylon yarn can be used as filler to make light bending castable. This recycling method is simple in process, large in recoverable amount and low in investment, and it is a good recycling method, but the only drawback is that the technical added value of the product is small.

2. It is used to manufacture general polystyrene. After high temperature defoaming and cooling, polystyrene foam waste is mechanically crushed, extruded into strips, and then granulated to make universal polystyrene. The main problem of this method is that because the waste foam is not cleaned before crushing and the local temperature is too high during baking and extrusion, the appearance of recycled materials may be brown, losing the colorless and transparent characteristics of new polystyrene. Its impact resistance is also poor, and it can only be used as some low-value plastic parts, which is difficult to compare with ordinary plastics such as polyethylene, polypropylene and polyvinyl chloride products.

3. Used to regenerate expandable polystyrene. Recycling waste PS foam to make e PS or reshape foam products should be said to be the most reasonable utilization direction of waste PS foam. Because the surface of waste polystyrene foam material is slightly deteriorated due to environmental pollution, the internal properties of the original polystyrene foam are maintained, creating conditions for reuse. Only in this way can we reshape or manufacture EPS and give full play to the excellent characteristics of polystyrene foam in many aspects. There are several ways to make EPS or reshape it with waste polystyrene foam: one is solution polymerization. Dissolving waste carbonized foam material in styrene monomer, adding dispersant to make styrene solution of polystyrene suspend in water, heating and polymerizing, and then adding foaming agent to continue polymerization to prepare bead foam material. The advantage of this method is that part of styrene is replaced by waste PS, which can reduce the cost. The disadvantage is that styrene monomer is consumed, and it is difficult to prepare uniform products because of the influence of unstable PS surface cleanliness on initiator activity. Second, spheroidization and re-foaming. Generally, polystyrene is cut into cylindrical particles, suspended in dispersant aqueous solution, heated to melt and spheroidize the cylinder, then cooled, pressurized with foaming agent, cooled, filtered, washed and dried at low temperature to make EPS beads [10]. The key of this method lies in the quality of raw materials, otherwise it is difficult to ensure the quality of new EPS. Third, the method of crushing and transforming beads. Selecting suitable softener, surfactant and defoamer in liquid medium, selectively crushing large pieces of waste PS foam into spherical beads with a diameter of 4-8 mm, and adding foaming agent to form foam products. This method is simple in process, consumes less additional materials, and the physical properties of molded products are close to the original waste, with small investment and great benefits, which is worth popularizing.

4. Preparation of flame retardant by bromination modification. The molecule of polystyrene contains benzene ring structure, and the hydrogen atom on benzene ring can be replaced by electrophilic reagent. Someone cleaned and dried the recycled polystyrene foam, dissolved it in dichloromethane solution, and electrophilic substituted it with liquid bromine under the catalysis of aluminum trichloride to prepare flame retardant brominated polystyrene. The bromine content can be as high as 6%. It can be used as flame retardant for PVC, ABS, polypropylene and other plastic products. Compared with other organic flame retardants, brominated polystyrene has low dosage, good flame retardant effect, and does not release toxic carcinogens such as dioxin when burning, especially when it is used in combination with antimony trioxide, its synergistic flame retardant effect is better, and it is a flame retardant with good performance. The performance of brominated polystyrene prepared by this process is comparable to that of commercial brominated polystyrene flame retardant, and the cost is low [1 1]. However, because the amount of flame retardant itself is not very large, this method can not meet the recovery of a large number of waste PS.

5. Thermal decomposition technology. On the one hand, styrene monomer can be produced by pyrolysis, that is, by selecting a suitable catalyst, waste polystyrene foam is pyrolyzed into styrene monomer under heating conditions. Under the tight supply of styrene, it is a reasonable way to prepare styrene by depolymerization of polystyrene foam waste to meet the market demand. The United States, France and Japan have also carried out a large number of experiments, but there are no reports of industrialization. The main problem of producing styrene by depolymerization is that the conversion rate of styrene is relatively low, only about 70% under good conditions, generally only about 40%, which not only affects the production cost, but also makes the cleaning and continuous operation of cracking equipment difficult [12]. On the other hand, it can be cracked into oil. A mixture of low-molecular-weight hydrocarbons can be obtained by heating foamed plastics in the absence of air or decomposing them under steam, and then the mixture can be decomposed and reformed by a catalyst to obtain a sulfur-free gasoline fraction, a kerosene fraction and some gases. 1 1 kg plastic can get 1 oil, and the rest is mainly carbon residue [13]. Japan has done a lot of research in this field, and China has made some achievements in this field, and now it is being industrialized.

6. Burn to recover energy. Because the main components of polystyrene foam are carbon and hydrogen, it can burn, and its total calorific value (about 4600 kJ/kg) is higher than that of standard coal (about 2600 kJ/kg) and fuel oil (about 4400 kJ/kg). Therefore, it is also an effective method to utilize its combustion heat by incineration. This method has been adopted by many developed countries with abundant funds and advanced equipment. For example, Japan Steel Pipe Company uses waste plastics instead of coke as fuel and reducing agent for ironmaking; A French air-conditioning company has developed a new process to produce steam by using the heat generated by waste plastic incineration. Steam can be used for production, saving energy. But as far as China is concerned, incineration still lags behind other methods. When plastics burn, the calorific value is large, and ordinary stoves are easy to burn out, so it is not easy to burn completely. Therefore, it is necessary to design a special combustion furnace, and the equipment maintenance cost is very high. The gas generated by combustion is easy to cause secondary pollution and needs to be treated.

7. Preparation of coating by grafting modification. Coatings are all made by adding pigments to the base material, stirring and grinding. The binder is a film-forming substance, and the polystyrene foam is composed of organic polymers. After being dissolved in solvent, it can be used as the base material of coatings with good water resistance and insulation. However, the coating based on PS has poor adhesion and film-forming property. By modifying it, adding proper amount of crosslinking agent and plasticizer to improve its film-forming property and film-forming quality, various coatings can be made. For example, Li et al. smashed waste polystyrene foam and dissolved it in xylene, added initiator, and dropwise added acrylic acid at a certain temperature for graft modification to obtain component A; Dissolving petroleum asphalt in xylene to obtain component b; Uniformly mixing water, emulsifier and auxiliary agent to obtain part C; Emulsifying the above three ingredients in an emulsifying kettle to prepare a waterproof coating. Grafting acrylic acid molecules on polystyrene molecular chain not only enhances the adhesion of coatings, but also improves the stability of emulsion. The prepared coating has good heat resistance, low temperature flexibility and bonding strength. In addition, the flexibility and adhesion of polystyrene can be improved by grafting flexible butyl acrylate on rigid polystyrene molecular chain, and anticorrosive coatings with good performance can be made by adding appropriate additives [14].

Progress of 1.3 polystyrene foam modified adhesive

Adhesives play an important role in all sectors of the national economy. Aerospace, aviation, architecture and decoration are all inseparable from adhesives. In the mid-1970s, the total output of adhesives in the world was close to 5 million tons. In recent years, it has continued to grow at a rate of about 300,000 tons per year. In all adhesive products, building adhesives account for about 25%-35%. With the rapid development of China's national economy, there is a big gap in building adhesives. It can kill two birds with one stone to prepare adhesive from waste PS to meet the market demand for high quality and low price adhesive. Chinese researchers began to engage in this research in the late 1980s, and made some achievements in the late 1990s. But there is still a lot of room for research. Therefore, this is a good research direction and the best direction for recycling waste PS.

Polystyrene is an amorphous linear nonpolar substance, which contains benzene rings in its molecules, so it is rigid and flexible, and its adhesion on the surface of polar substances is weak. The adhesive directly made of polystyrene is not strong enough, and the adhesive layer is hard and brittle. Therefore, it is necessary to introduce polar and flexible groups into the styrene chain to increase flexibility and improve adhesive strength, so as to obtain an adhesive with good adhesion and adhesiveness. The key technology of preparing adhesive from waste polystyrene foam is the selection of modifier. According to the literature report [15-35], there are the following modifiers:

1. phthalate modification. Polystyrene foam modified by plasticizer dibutyl phthalate. The solvent is acetone and magnesium oxide is used as filler. The adhesive can be used to bond loudspeaker circuits, and the bonding cost is reduced by about 70%. Wang Xiuyan smashed waste polystyrene foam, dissolved it in the innovative solvent 1, and then added dioctyl phthalate and essence to make a self-adhesive with good bonding effect, which can be reused and used to bond various labels, trademarks and paper products.

2. isocyanate modification. Lei et al. studied the preparation of isocyanate modified PS adhesive: dissolving PS in the mixed solvent of toluene, acetone and ethyl acetate, then adding isocyanate to react for a period of time, and then adding zinc oxide as filler to prepare the adhesive with a solid content of about 30%. The viscosity of the adhesive is 0.5-65438 0 Pa s, the shear strength is 3.4MPa, and the uneven peeling strength is 65438 0.2 kn/m.

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 the mixed solvent of toluene, ethyl acetate, acetone and chloroform, fully stirred, and then added phenolic resin for reaction, thus obtaining the milky white PS modified adhesive. The shear strength of the adhesive is 3.47MPa, and the uneven peeling strength is 14.8 kn/m, which can be used to bond wood and daily necessities. The research shows that when the amount of phenolic resin and polystyrene foam is equal, the bonding strength is close to that of phenolic resin adhesive. In order to improve the toughness and bonding strength of the adhesive after curing, a small amount of polymer crosslinking agent can be added as a modifier, so that a network molecular layer can be formed on the surface of the adhesive after curing. Li Bangde and others selected isocyanate and phenolic resin as modifiers with strong polar groups to modify waste polystyrene foam, and achieved good results. The waste polystyrene foam was dissolved in the mixed solvent of toluene, acetone, chloroform and ethyl acetate, and the mechanical impurities were separated after complete dissolution. A sticky red adhesive was prepared by adding toluene diisocyanate and phenolic resin in a proper proportion, and then adding filler. The shear strength of the adhesive can reach 3.72 MPa, and the uneven tear strength is 17. 10kn/m ... The adhesive can be used to bond wood instead of white latex, with good effect, and also has good bonding performance to plastics and porous materials.

4. Modification of rosin resin. Qu et al. studied the preparation of adhesive by modifying waste polystyrene foam with rosin resin. The adhesive takes xylene as solvent and can be used to bond porcelain plates, mosaics and plastic floors. Marco et al. studied the influence of rosin content on the properties of PS modified adhesive, and also investigated the influence of various solvents on the adhesive strength of PS modified adhesive. The results show that adding a small amount of rosin is beneficial to improve the bonding strength, but because the phenanthrene ring in rosin is easy to dissociate, the bonding strength decreases with the increase of rosin dosage. Among all solvents, the adhesive strength of polystyrene mixed with ethyl acetate is the highest.

5. Modification of styrene-butadiene-styrene-ethylene (SBS) block polymer. The structure of styrene block in 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 strength of adhesive and reduce the hardness and brittleness of adhesive layer. Bao Qifu chose ethyl acetate, 120 gasoline, toluene and turpentine as mixed solvents, SBS block polymer as modifier and rosin resin as tackifier. The shear strength of the adhesive is 4.43 MPa, and the uneven peeling strength is1.4 kn/m. The adhesive can be used for bonding materials such as wood and ceramic tiles, and can be used for bonding furniture and toys instead of polyvinyl acetate white latex, and can also be used for edge sealing of wood instead of chloroprene rubber.

6. Modification with maleic anhydride. Meng dissolved waste polystyrene foam in organic solvent, added initiator and maleic anhydride for grafting reaction, and then emulsified it with polyvinyl alcohol aqueous solution in emulsifying device to prepare PS modified white adhesive. The shear strength is above 3.92MPa, and the cost is only one third of that of polyvinyl acetate emulsion. Moreover, the production process is simple and the production period is short.

7. Modification of polyvinyl acetal. Shi Shengxun used toluene and 70 # gasoline as mixed solvent to dissolve waste polystyrene foam, and then added polyvinyl acetal to modify it to obtain a white viscous adhesive. The biggest feature of this glue is that it can be used at -40-40℃, and the shear strength has been kept at 8.7 MPa, while the strength of white latex on the market can only be kept at 9.0MPa at 0-40℃.

8. Modification of polyvinyl alcohol. Chen Ende completely dissolved polystyrene foam with xylene, and then added polyvinyl alcohol to modify it to make medical sealant, which does not react with formalin, and is heat-resistant, cold-resistant and impervious.

9. Graft modification of active monomers. Waste polystyrene grafted with active monomer can graft active groups on styrene chain, so that adhesive with good performance can be prepared from waste polystyrene foam. It is reported in the patent that 100 part of ps is dissolved in the mixed solvent of aromatic hydrocarbon and chlorinated hydrocarbon to form a colloidal solution, then the activator cuprous chloride and initiator butyl peroxide are added, the temperature is raised to 90- 120℃, and then 20-30 parts of acrylonitrile and propylene alcohol monomer are added for grafting reaction for 2 hours, so that the properties of PS are changed by grafting polar groups of polystyrene, and then asbestos powder or calcium silicate is added. Its water resistance and shear strength are 10 times and more than 3 times that of polyvinyl acetate white latex, respectively. PS glue can be used as glue for wood, furniture and daily life, and can also be used to bond cement products, floors, wallpapers and various fabrics. Grafting acrylonitrile and propylene alcohol on polystyrene macromolecules can obviously improve its adhesion, but the proportion of monomers added is high, so the cost is high, and the toxicity of acrylonitrile monomer is also great, which brings certain difficulties to production. Therefore, it is difficult to popularize and apply. Chen Kailai and others studied the grafting of carboxylate monomer on styrene chain and successfully prepared water-resistant adhesive for building interior decoration. Dissolve waste polystyrene foam in two organic solvents A and B to make glue solution. Under the action of initiator, unsaturated monomers were grafted onto the glue solution, and polar groups were grafted onto the polystyrene macromolecular chain. Adding tackifying resin to obtain brown glue solution. The shear strength is 4.4-4.7 MPa, and the flame retardant performance is far superior to that of similar products. Waterproof glue prepared by this method can reach 4.5 MPa after soaking. When 1: 1 is added to the cement, the construction performance is good, and the performance of bonding the floor and tiles will not be affected. Among these modifiers, there is no report that epoxy resin is used as modifier. Epoxy resin is often called "all-purpose adhesive", which has good adhesion to various metals and most nonmetallic materials, and is widely used in aircraft, missiles, automobiles, construction, electronic appliances, wood processing and other industrial fields. Moreover, epoxy resin adhesive has the advantages of good process performance, high bonding strength, small shrinkage, excellent dielectric resistance and good electrical insulation [43], and its molecule also contains polar groups. If it can be used to modify PS adhesive, a modified PS adhesive with excellent performance should be obtained. On the other hand, epoxy resin adhesive is generally brittle, and adding a toughening agent which can improve both PS brittleness and epoxy resin brittleness can solve this problem. Finally, isocyanate was selected and satisfactory results were obtained. It not only improves the bonding strength and shortens the curing time, but also saves the solvent and reduces the cost. In addition, based on the formula of white latex, I tried to make a wood adhesive with better performance than white latex by greatly reducing the amount of monomer in the formula, replacing polymerized monomer with PS and adding plasticizer. The cost of white latex in the market is greatly reduced, and the purpose of waste utilization is achieved.

Development of 2 PS modified adhesive

2. Development of1solvent PS modified adhesive

2. 1. 1 Instruments and pharmaceutical instruments: constant temperature water bath; Electric agitator; NDJ- 1 rotational viscometer; Instron 4467, 4505 universal material testing machine; Blowing oven; SC-7 gas chromatograph (hydrogen flame discriminator). Drugs: polystyrene foam; Epoxy resin (e-51); Toluene diisocyanate; Azodiisobutyronitrile; Ethyl acetate; Toluene; Talcum powder; Amine curing agent.

2. 1.2 experimental principle

Polystyrene is an amorphous linear nonpolar substance with benzene ring in its molecule, so it is rigid and flexible. The adhesion on the surface of polar substances is very weak, and the adhesive directly made of polystyrene is not strong enough, and the adhesive layer is brittle and hard. Therefore, it is necessary to add modifiers to PS glue solution for modification, and introduce polar groups into styrene chain to increase flexibility and improve bonding strength. I chose epoxy resin (E-5 1) and toluene diisocyanate as modifiers. Under the action of initiator azodiisobutyronitrile amide, toluene diisocyanate first reacts with polystyrene. The reaction formula is as follows:

(2) The chain radical is crosslinked with toluene 2,4-diisocyanate.

(R stands for benzyl)

Then, add epoxy resin. The structure of epoxy resin contains -OH, and isocyanate can react with -OH in epoxy resin. The general reaction formula is as follows:

In this way, isocyanate modified PS and epoxy resin successively, and partially crosslinked them.

2. Preparation of1.3 adhesive

Put the reaction container in a constant temperature water bath, install a stirring bar, add 100 parts of mixed solvent (ethyl acetate: toluene = 4: 1), add 50 parts of washed and dried waste polystyrene foam chips in batches, and open them while adding.

Dynamically stirring, gradually raising the temperature to 70℃ after completely dissolving, adding 0.5 part of initiator azodiisobutyronitrile and 3 parts of toluene 2,4-diisocyanate, stirring at medium speed for about 1- 1.5 hours, and then adding 0.5 part.

1 part toluene 2,4-diisocyanate, cooling to 50℃, adding 10 part epoxy resin (6 10 1), continuing the reaction 1 hour, and adding 10 part filler after cooling.

2. 1.4 test method of various indicators of adhesive

The nonvolatile content, viscosity, tensile shear strength and harmful substances in the adhesive were determined according to GB/T 2793-95, GB7 124 and GB 18583-200 1 respectively.

2.2 Development of emulsion PS modified adhesive

2.2. 1 instruments and medicines

Instrument: electric mixer; Electric heating jacket; Four-necked flask; Spherical reflux condenser tube; Thermometer; Dropping funnel; Instron 4467, 4505 universal material testing machine; Blowing oven; SC-7 gas chromatograph; Infrared spectrometer.

Drugs: polystyrene foam; Butyl acrylate; Vinyl acetate; Dioctyl phthalate; Ethyl acetate; Toluene; Initiator ammonium persulfate; Mixed emulsifier (sodium dodecyl sulfate: OP- 10 =

1:2)

2.2.2 Preparation of water-soluble PS modified adhesive

Add 50 parts of mixed solvent (ethyl acetate: toluene: 4: 1) into a four-necked flask, add 40 parts of washed, dried and crushed waste polystyrene foam in batches with stirring, gradually raise the temperature to 40℃, completely dissolve into transparent viscous liquid, add 1 part of composite emulsifier, and stir and emulsify for 30 minutes. Add 40 parts of water (distilled water or deionized water) and 4 parts of mixed monomer (butyl acrylate: vinyl acrylate = 1: 1), raise the temperature to 60℃, increase the stirring speed, emulsify for 30-40 min, and drop part of initiator (ammonium persulfate 10% solution); During the reaction, heat is released and the temperature automatically rises. At this time, the temperature was heated to 75℃, and a solution consisting of 65,438+02 parts of mixed monomer and 80 parts of water was added dropwise. In the process of adding mixed monomer aqueous solution, a part of initiator (the total amount of initiator is 65,438+0 parts) is added intermittently, and the reaction temperature should be controlled between 75-85℃. After all the addition, add all the remaining initiators, raise the temperature to 90℃ and keep the temperature, stop heating when the solvent to be recovered reaches 80-85% of the added amount, then cool to 50℃, add two parts of plasticizer dioctyl phthalate, stir evenly, adjust the PH value to about 7, and cool to room temperature to obtain a white viscous liquid.

2.2.3 Test method of various performance indexes of PS modified emulsion adhesive

The nonvolatile content of the adhesive is determined according to GB/T 2793-95, the rotational viscosity of the adhesive is determined according to GB/T 2794-95, the compressive shear strength is determined according to Appendix B of Hg/T 2727, the ash content and PH value are determined according to GB1175, and the limit of harmful substances in the adhesive is determined according to GB65438.

3 Results and discussion

3. The results and discussion of1solvent PS modified adhesive.

3. The technical properties of 1.1PS modified adhesive are shown in table1.

3. 1.2 Selection of solvents

Styrofoam is soluble in aromatic hydrocarbons (such as benzene, toluene and xylene). ), chlorinated hydrocarbons (such as chloroform and trichloroethylene), carboxylic esters (such as ethyl acetate and butyl acetate) and ketones (such as acetone and butanone).

Divided into organic solvents. Choosing a suitable solvent to dissolve foam plastics is mainly considered from the following aspects: first, the selected solvent should have good solubility in polystyrene and newly added modifiers, and good dispersibility in additives; Secondly, the properties of the solvent can best improve the performance of the adhesive. Thirdly, the selected solvent should be low toxic, cheap, easily available and safe. Based on the above factors, ethyl acetate or toluene is more suitable as solvent. However, considering that the solubility of mixed solvent is better than that of single solvent, and the boiling point, volatility and polarity are different, the adhesive can be adjusted by changing the mixing ratio.

Drying time can meet the needs of different occasions. Therefore, the mixture of ethyl acetate and toluene was selected as the solvent of polystyrene foam. The physical and chemical parameters of these two solvents are shown in Table 2.

The solubility parameter of polystyrene is 9. 1 1.

The selected solvent ratio is 3. 1.3.

Using ethyl acetate and toluene as mixed solvent, ethyl acetate contains polar groups, which is helpful to improve the properties of adhesive. Low boiling point and quick volatilization. Toluene is a nonpolar substance with high boiling point and relatively volatile.

Slow, the different ratio of the two will definitely affect the drying speed and adhesion of modified PS adhesive, so choose a more suitable solvent ratio.

It can be seen from the figure that the shear strength of the modified solution increases with the increase of the solvent ratio, that is, the ratio of ethyl acetate, and decreases after the solvent ratio is 4: 1. The reason may be due to

Ethyl acetate is polar, on the one hand, it can be modified, on the other hand, it can form intermolecular interaction with the surface of the adhered material, so the shear strength is improved; It volatilizes quickly and actively.

So as to meet the requirement of improving the shear strength of epoxy resin with less residual solvent after curing. Therefore, the ratio increases and the bonding strength increases. However, when the proportion of ethyl acetate is too large, because of its low boiling point and rapid volatilization, when

After the bonding edge is cured, the internal solvent may be in liquid or semi-solid state for a long time, which affects the bonding effect and slightly reduces the shear strength.

3. 1.4 Effect of the dosage of toluene diisocyanate on the shear strength of adhesive

Toluene diisocyanate (TDI) is a strong polar substance, and its modification effect is very obvious. Only a very small amount can obviously improve the properties of the adhesive, which has a good modification effect not only on polystyrene but also on epoxy resin. In the modification reaction of waste polystyrene, the modifier TDI has two functions: one is to introduce polar groups into polystyrene macromolecules to crosslink polystyrene macromolecules, and the other is to react with epoxy resin to modify epoxy resin to partially crosslink epoxy resin and polystyrene. The amount of TDI directly affects the properties of modified PS adhesive. If the amount of modifier is small, the polystyrene molecular chain contains less polar groups, the crosslinking degree is not enough, the toughness is not enough, the epoxy resin can not be well modified, and the adhesive layer is fragile. If the dosage is too much, the material will be excessively crosslinked, and even a network structure will be formed, which will reduce the shear strength. The experiment shows that the modification effect is better when the dosage of modifier is 2.0%. As shown in fig. 2

3. 1.5 The influence of the selection and dosage of epoxy resin on the properties of PS modified adhesive.

Epoxy resin is often called "all-purpose adhesive", which has good adhesion to various metals and most non-metallic materials, and is widely used in aircraft, missiles, automobiles, construction, electronic appliances and wood processing. Moreover, epoxy resin adhesive has the advantages of good process performance, high bonding strength, small shrinkage, excellent dielectric resistance and good electrical insulation. The modifiers of PS adhesive include phenolic resin, rosin resin, phthalate ester and so on. No one has tried to modify PS with epoxy resin. Because there are polar groups in epoxy resin, it should have a good modification effect on ps. So I tried to modify PS with epoxy resin. However, the effect of modifying PS with epoxy alone is not good, the adhesive layer is easy to peel off, the adhesive strength is not too great, and the adhesive layer is fragile, which may be caused by the factors of high rigidity. I added a third modifier to both of them and chose isocyanate successfully. The amount of epoxy resin also affects the properties of the adhesive solution. When the dosage is too small, the strength is not high, but when the dosage is slightly large, the shear strength will decrease. This may be because PS modified adhesive is a solvent-based adhesive. After the epoxy resin is cured, some solvents remain in the adhesive layer, which affects the performance of the adhesive. With the increase of the amount of epoxy resin, this effect is more obvious. Moreover, the addition amount is too large and the cost is high. The relationship between the amount of epoxy resin and the properties of adhesive is shown in Table 3.