Research on recycled adhesives from waste polystyrene foam

Bao Chunyang

(Heilongjiang Petrochemical Research Institute, Harbin, Heilongjiang 150040)

Abstract: Polystyrene foam is widely used in packaging, thermal insulation, waterproofing, and heat insulation due to its light weight, solidity, shock absorption, low moisture absorption, easy molding, good water resistance, thermal insulation, and low price. , shock absorption and other fields. PS is mostly a one-time use. When discarded in nature, it cannot decay and transform, nor can it be degraded and disappear by itself. This not only wastes precious non-renewable resources, but also causes serious environmental pollution. This paper aims to save resources, protect the environment, and turn waste into treasure. It studies the preparation of two low-toxicity, low-cost, and good-performance adhesives using waste PS as the main raw material and modified by modifiers. One is a solvent-based multifunctional adhesive using epoxy resin and toluene diisocyanate as modifiers. It can be used for bonding metal, ceramics, glass, wood, etc., with a tensile shear strength greater than 4.7MPa; the other is It is a grafted polymer emulsion adhesive using a mixed monomer of butyl acrylate and vinyl acetate as a modifier. Its performance is better than that of commercially available milky white glue, with a compressive shear strength of up to 10.4MPa and a price of only 70% of milky white glue.

Keywords: waste polystyrene foam; modifier; adhesive

1 Introduction

1.1 Current situation at home and abroad

Polystyrene foam (Expanded Polystyrene, referred to as EPS) is a new material in the development of the modern plastics industry. Its production began in 1951 when West German BASF Company invented the volatile polystyrene bead foaming molding method. It has developed rapidly since the invention of the one-step forming method in the United States in the 1990s. In 1985, my country introduced five sets of polystyrene foam production equipment from the United States and Japan, which promoted the development of my country's plastics industry. Polystyrene foam is one of the most widely used plastics in the world today. It has good water resistance, heat insulation, insulation, low moisture absorption and strong earthquake strength, and is light, strong and easy to form. , low price and other characteristics, it is widely used in packaging, thermal insulation, waterproof, heat insulation, shock absorption, decoration, catering industry and other fields, and has penetrated into various sectors of the national economy. According to statistics, in the past ten years, my country's average annual consumption of polystyrene plastic has increased by 10%. In 1990, it reached 217,000 tons. With the rapid development of the electronic instrument and household appliance industries and the advancement of the development of the western region, the amount of EPS will become larger and larger [1]. It is estimated that by 2005, my country will need polystyrene 1.2 million tons of vinyl foam. Most polystyrene foam plastics are single-use. Millions of tons of white garbage are scattered in nature. They can neither rot, transform nor degrade on their own. This causes serious environmental pollution on the one hand and serious environmental pollution on the other. On the one hand, it is also a waste of precious non-renewable resources. How to recycle waste polystyrene foam reasonably and effectively has attracted widespread attention from scientific researchers around the world, including my country. Since the 1970s, Japan, Western Europe and the United States have successively carried out industrial processing of plastic waste. By the 1990s, the technology for comprehensive utilization of waste plastics has become mature, with industrialization reaching 80%. As of 1999, the plastic waste in the United States The plastic recycling rate reaches 50%, the UK reaches 80%, and Japan reaches 49%. Italy not only recycles its own plastic waste, but also imports waste plastics from other European countries for recycling. my country began to research waste plastic recycling technology in the late 1980s. After entering the 1990s, research became active, but the technology industrialization rate is still very low. Only about 15% of waste plastics are recycled every year [2]. The rest are mostly buried.

The density of polystyrene foam is very small, only 0.02-0.04g/cm3. Therefore, it is very large and will occupy a large area of ??land. Moreover, when the foam plastic enters the soil, it will basically not be degraded by microorganisms, causing the soil to The air, moisture, nutrients, etc. in the burial site cannot be circulated and exchanged normally, and it will gradually release some harmful substances, thereby affecting the normal cycle of the ecosystem, causing the soil quality of the burial site and its surrounding area to deteriorate, causing Tragedy[3].

1.2 Recycling of polystyrene foam

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

1. Used in the manufacture of lightweight building materials. Various lightweight building materials are made by using pre-expanded particles of expandable polystyrene or polystyrene foam waste broken into small pieces as the main body, adding different fillers, and using different binders. For example, use broken wood wire as filler, use cement as binder, add water to mix, and then mold it into various shapes of lightweight cement partitions, or make artificial wood; lightweight foam boards lined with wire supports It can be used as wall panels, countertops, or decorative panels; expanded perlite can be used as filler to make roof insulation panels; soil can be used as a binder and filler, mixed evenly with polystyrene foam particles in equal amounts, pressed and molded, and dried After calcination, it can be made into lightweight large blocks for high-rise buildings, or permeable pipes for underground wastewater drainage; using waste nylon wire as filler, it can be made into lightweight bending-resistant casting materials, etc. This recycling method has a simple process, large recyclable volume, and low investment. It is a better recycling method. The only disadvantage is that the technical added value of the product is small.

2. Used in the manufacture of general-purpose styrene polyethylene. After the polystyrene foam waste is defoamed and cooled at high temperature, it is mechanically crushed, extruded into strips, and then pelletized to make general-purpose polystyrene. The main problem with this method is that the appearance of the recycled material may be brown due to the waste foam not being washed before crushing and the local temperature being too high during the baking and extrusion process, losing the colorless and transparent characteristics of new polystyrene. Its impact resistance is also poor, and it can only be used for some low-value plastic parts, which is difficult to compare with general plastics such as polyethylene, polypropylene, and polyvinyl chloride products.

3． Used to recycle expandable polystyrene. Using waste PS foam to recycle EPS or re-mold foam products should be said to be the most reasonable utilization direction of waste PS foam. Because waste polystyrene foam materials, in addition to being slightly deteriorated by environmental pollution on the surface, still maintain the properties of the original polystyrene foam inside, which creates conditions for multiple uses. Only in this way can re-molding or manufacturing EPS best take advantage of the many excellent properties of polystyrene foam. There are several methods to use waste polystyrene foam to make EPS or re-mold it: first, solution polymerization method. Dissolve the waste foam material in styrene monomer, add a dispersant to make the PS styrene solution suspended in water in the form of beads, heat it to polymerize, then add a foaming agent, and continue polymerization to make bead foam. The advantage of this method is that waste PS is used to replace part of the styrene, which can reduce costs. The disadvantage is that it consumes styrene monomer. It is also affected by the unstable cleanliness of the PS surface on the initiator activity, making it difficult to produce a uniform product. products. Second, the spheroidization and then foaming method. General-purpose polystyrene is cut into cylindrical pellets, suspended in an aqueous solution of dispersant, heated to melt and spheroidize the cylinder, then cooled and pressurized to add a foaming agent, filtered, washed and dried at low temperature after cooling. into EPS beads [10]. The key to this method lies in the quality of raw materials, otherwise it will be difficult to guarantee the quality of new EPS. Third, the bead crushing and then molding method. It is to select appropriate softeners, surfactants and defoaming agents in the liquid medium to selectively break large pieces of waste PS foam into spherical beads with a diameter of 4-8mm, add foaming agents and then mold them into foam products. . This method has a simple process and consumes less additional materials. The physical properties of the molded products are close to those of the original waste materials. The investment is small and the benefits are high. It is worthy of promotion.

4. Bromination modification to prepare flame retardants. The polystyrene molecule contains a benzene ring structure, and the hydrogen atoms on the benzene ring can be replaced by electrophiles.

Some people wash and dry the recycled polystyrene foam and dissolve it in a dichloromethane solution. Under the catalysis of aluminum trichloride, an electrophilic substitution reaction occurs with liquid bromine to produce the flame retardant brominated polystyrene. The bromine content can be as high as 6%. It can be used as a flame retardant for plastic products such as polyvinyl chloride, ABS, and polypropylene. Compared with other organic flame retardants, brominated polystyrene has a low dosage and good flame retardant effect. It does not release toxic carcinogens such as dioxins during the combustion process. Especially when used in combination with antimony trioxide, it has synergistic retardant properties. It has better burning effect and 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 retardants, and the cost is low [11]. However, because the amount of flame retardant itself is not very large, this method cannot meet the recycling needs of large amounts of waste PS.

5. Thermal decomposition technology. On the one hand, styrene monomer can be produced by cracking, that is, waste polystyrene foam is heated under heating conditions and a suitable catalyst is selected to crack it to produce styrene monomer. When the supply of styrene is relatively tight, it is a reasonable way to use the depolymerization of polystyrene foam waste to make styrene to meet the needs of the market. The United States, France, and Japan have also conducted a large number of experiments, but there have been no reports of industrialization. The main problem in depolymerizing styrene is that the conversion rate of styrene is relatively low. In better cases, it is only about 70%. Generally, it is only about 40%. The conversion rate is low, which not only affects the production cost, but also leaves behind residues. This causes difficulties in the cleaning and continuous operation of cracking equipment [12]. On the other hand, it can be cracked to produce oil. A mixture of low molecular weight hydrocarbons can be obtained by heating the foam plastic in isolation from air or heating and decomposing it under water vapor, and then use a catalyst to decompose and reform it to obtain sulfur-free gasoline fractions, kerosene fractions and some gases. 11 oil products can be obtained from 1kg of plastic, and the rest is mainly carbon residue [13]. Japan has done a lot of research in this area, and our country has also achieved certain results in this area, and is now undergoing industrialization.

6． Combustion recovers energy. Since the main components of polystyrene foam are carbon and hydrogen, it can burn and has a total calorific value (about 4600kJ/kg), which is greater than standard coal (about 2600kJ/kg) and fuel oil (about 4400kJ/kg). Therefore, utilizing its combustion heat through incineration is also an effective way. This method is adopted by many developed countries with abundant funds and advanced equipment. For example, a Japanese 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 that uses the heat generated by the incineration of waste plastics to produce steam. The steam can be used for production, which can save energy. . However, judging from the situation in our country, the incineration method is still lagging behind other methods. Plastics generate a lot of heat when burning. Ordinary stoves are easy to burn out and are difficult to burn completely. A specially designed combustion stove requires high equipment maintenance costs. At the same time, the gas generated by combustion can easily cause secondary pollution and must be treated.

7. Graft modification to prepare paint. The coatings are prepared by adding pigments to the base material and then stirring and grinding them. The base material is a film-forming material. Polystyrene foam is composed of organic polymers. After being dissolved in a solvent, it can be used as the base material of the coating. It has good water resistance and insulation. However, the adhesion and film-forming properties of coatings prepared with PS as base material are very poor. As long as they are modified and an appropriate amount of cross-linking agent and plasticizer are added, the film-forming properties and film quality can be improved. Can be made into various types of coatings. For example, Li Liangbo et al. crushed waste polystyrene foam and dissolved it in xylene, added an initiator, and dripped acrylic acid at a certain temperature for graft modification reaction to obtain component A; dissolved petroleum asphalt in xylene, Obtain component B; mix water, emulsifier and auxiliaries evenly to obtain component C; carry out complete emulsification of the above three components in an emulsification kettle to prepare waterproof coating. The grafting of acrylic acid molecules onto the molecular chain of polystyrene not only enhances the adhesion of the coating film, but also improves the stability of the emulsion. The prepared coating has good heat resistance, low temperature flexibility and bonding strength. In addition, grafting flexible butyl acrylate onto rigid polystyrene molecular chains can improve the flexibility and adhesion of polystyrene. With appropriate additives, anti-corrosion coatings with good performance can be made [14 ].

1.3 Progress of polystyrene foam modified adhesives

Adhesives play an important role in various sectors of the national economy. Whether it is aerospace, aviation, construction, or decoration, adhesives are inseparable. The total production of adhesives in the world was close to 5 million tons in the mid-1970s, and has continued to grow at an annual rate of approximately 300,000 tons in recent years. Among all adhesive products, construction adhesives account for about 25%-35%. With the rapid development of my country's national economy, there is a big gap in construction adhesives. Using waste PS to prepare adhesives to meet the market demand for high-quality and low-cost adhesives is a killing two birds with one stone. Our country's scientific researchers began to engage in research in this area in the late 1980s, and achieved some results by 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 non-polar substance. Its molecules contain benzene rings, which are highly rigid and less flexible. Its adhesion to the surface of polar substances is very weak. The adhesive produced directly is not strong enough and the adhesive layer is hard and brittle. Therefore, it is necessary to introduce polar and flexible groups on the styrene chain links to increase flexibility and improve bonding strength, so as to obtain bonding force and adhesion. All good adhesives. The key technology for using waste polystyrene foam to prepare adhesives is the selection of modifiers. According to literature reports [15-35], there are the following modifiers:

1. Phthalate modification. Hu Guangjun used the plasticizer dibutyl phthalate to modify polystyrene foam. The solvent was acetone and magnesium oxide was used as filler. The resulting adhesive can be used to bond speaker circuits, reducing the bonding cost by about 100%. 70; Wang Xiuyan crushed the waste polystyrene foam and added it to the No. 1 innovative solvent to dissolve it and then added dioctyl phthalate and essence to make a self-adhesive. This self-adhesive has a good bonding effect. It can be reused and can be used for bonding various labels, trademarks and paper products.

2. Isocyanate modification. Lei Yanying et al. studied the adhesive made of isocyanate-modified PS: PS is dissolved in a mixed solvent of toluene, acetone and ethyl acetate. After the dissolution is complete, isocyanate is added to react for a period of time, and then the filler zinc oxide is added to obtain a solid content of about 30%. The adhesive has a viscosity of 0.5-1 Pa. s, shear strength is 3.4MPa, and uneven peel strength is 1.2 KN/m. This glue can be used for bonding wood, paper products, daily 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 into a mixed solvent of toluene, ethyl acetate, acetone and chloroform, stirred it thoroughly and then added phenolic resin for reaction to obtain a milky white PS modified adhesive. The adhesive has a shear strength of 3.47MPa and an uneven peel strength of 14.8KN/m. It can be used for bonding wood and daily necessities. Research by Shang Jinming and others shows that when the amounts of phenolic resin and polystyrene foam are equal, its bonding strength is close to that of 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 polymer cross-linking agent can be added as a modifier, so that a network molecular layer is formed on the surface of the adherend after the adhesive is cured. Li Jian et al. selected two modifiers containing strong polar groups, isocyanate and phenolic resin, to modify waste polystyrene foam and achieved good results. Dissolve waste polystyrene foam in a mixed solvent of toluene, acetone, chloroform, and ethyl acetate. After complete dissolution, separate mechanical impurities, add an appropriate proportion of cross-linking agent toluene diisocyanate and phenolic resin, and then add fillers to make a sticky product. Thick red adhesive, the shear strength of this adhesive can reach 3.72 MPa, and the uneven tear strength is 17.10KN/m. This adhesive can replace milky glue for wood bonding with good effect. It also has good bonding performance to plastics and porous materials.

4. Rosin resin modification. Qu Junjie et al. studied the preparation of adhesives by modifying waste polystyrene foam with rosin resin. Using xylene as the solvent, the adhesive produced can bond porcelain plates, mosaics, plastic floors, etc.

Chen Zhen et al. studied the effect of rosin dosage on the performance of PS modified adhesive, and also examined the effect of various solvents on the bonding strength of PS modified adhesive. Research results show that adding a small amount of rosin is beneficial to improving the bonding strength. However, since the phenanthrene ring in rosin is easy to dissociate, as the amount of rosin increases, the bonding strength decreases; in all solvents, polystyrene is mixed with ethyl acetate for modification The bonding strength is maximum after.

5. Styrene-butadiene-styrene (SBS) block polymer modification. The styrene block in the styrene-butadiene-styrene block polymer has a similar structure to polystyrene and has good compatibility, so SBS block polymer is used as the PS modifier. , can improve the peel strength of the adhesive and reduce the hardness and brittleness of the adhesive layer. Bao Qifu selected ethyl acetate, No. 120 gasoline, toluene, and turpentine as mixed solvents, SBS block polymer as modifier, and rosin resin as tackifier, and the shear strength of the obtained adhesive reached 4.43 MPa, uneven peel strength is 1.4KN/m. The adhesive can be used for bonding wood, ceramic tiles and other materials. It can replace polyvinyl acetate emulsion glue for bonding furniture and toys, and can also replace neoprene for edge sealing of wood.

6. Modified with maleic anhydride. Meng Yuezhong dissolved waste polystyrene foam in an organic solvent, added an initiator and maleic anhydride to perform a grafting reaction, and then emulsified it with an aqueous solution of polyvinyl alcohol in an emulsification device to prepare PS modified white glue. , the shear strength is above 3.92MPa, the cost is only one-third of that of 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 a mixed solvent. After dissolving the waste polystyrene foam, he added polyvinyl acetal for modification to obtain a white thick adhesive. The biggest feature of this adhesive is its wide operating temperature. It can be used at -40℃-40℃, and the shear strength has always been maintained at 8.7 MPa, while commercially available white latex can only maintain a strength of 9.0MPa between 0-40℃.

8. Polyvinyl alcohol modification. Chen Ende used xylene to completely dissolve the polystyrene foam and then added polyvinyl alcohol for modification to obtain a medical sealant. This medical sealant does not react with formalin and is heat-resistant, cold-resistant, and non-toxic. water leakage.

9． Reactive monomer graft modification. Waste polystyrene is grafted and polymerized with reactive monomers, and reactive groups can be grafted on the styrene chain links to produce adhesives with good performance from waste polystyrene foam. There are patent reports that 100 parts of PS are dissolved in a mixed solvent of aromatic hydrocarbons and chlorinated hydrocarbons to form a glue. Add the activator cuprous chloride and the initiator butyl peroxybenzoate. Heat the temperature to 90-120°C and add 20-30 parts. Acrylonitrile and propylene alcohol monomers are grafted for 2 hours to graft polar groups on polystyrene to change the properties of PS. Then asbestos powder or calcium silicate is added to form a kind of polystyrene with good water resistance and good adhesion. Strong white thick adhesive. Its water resistance and shear strength are more than 10 times and 3 times that of polyvinyl acetate emulsion glue respectively. This PS adhesive can be used as glue for wood, furniture and daily life, and can also be used to bond cement products, floors, wallpapers and various other products. kind of fabric. Grafting acrylonitrile and acrylic alcohol on polystyrene macromolecules can significantly improve its adhesion, but the proportion of monomers added is very high, so the cost is high, and the acrylonitrile monomer is also very toxic. It brings certain difficulties to production. Therefore, it is difficult to promote the application. Chen Kailai et al. studied the grafting of carboxylate monomers onto styrene links and successfully produced a water-resistant adhesive for building interior decoration. Waste polystyrene foam is dissolved in two organic solvents, A and B, to make a glue. Under the action of the initiator, a graft polymerization reaction occurs with the unsaturated monomer, and the polystyrene macromolecule chain is grafted. By adding polar groups on the branches and adding tackifying resin, a brown glue can be produced with a shear strength of 4.4-4.7MPa, and its fire resistance is far superior to similar products. The strength can reach 4.0 after being immersed in water. 5 MPa, the water-resistant glue prepared in this way can be used for bonding wallpaper, ceramic tiles, parquet, and floors. Mixed into cement at a ratio of 1:1, the construction performance is better and does not affect the performance of bonding floors and ceramic tiles.

Among the above-mentioned modifiers, there are no reports of using epoxy resin as a modifier. Epoxy resin is often called "universal glue" and has good adhesion to various metals and most non-metallic materials. Performance, it is widely used in industrial sectors such as aircraft, missiles, automobiles, construction, electronic appliances, and wood processing. Moreover, epoxy resin glue has good process performance, high bonding strength, small shrinkage, excellent dielectric resistance, and good electrical insulation properties. and other advantages [43]. Its molecules also contain polar groups. If you can use it to modify PS glue, you should get a modified PS glue with excellent performance. On the other hand, epoxy resin adhesives are generally relatively brittle, so adding a toughener that can improve both the PS brittleness and the epoxy resin brittleness can solve this problem. I ended up choosing isocyanates with satisfactory results. It not only improves the bonding strength and shortens the curing time, but also saves solvents and reduces costs. In addition, I also tried to significantly reduce the amount of monomers in the formula based on the milky white glue formula, use PS to replace the polymerized monomers, and add plasticizers to produce a wood adhesive with better performance than milky white glue. The cost of commercially available emulsion rubber is greatly reduced, and the purpose of waste utilization is achieved at the same time.

2 Development of PS modified adhesive

2.1 Development of solvent-based PS modified adhesive

2.1.1 Instruments and pharmaceuticals: constant temperature Water bath; electric stirrer; NDJ-1 rotational viscometer; Instron 4467, 4505 general material testing machine; blast oven; SC-7 gas chromatograph (hydrogen flame identifier). Drugs: polystyrene foam; epoxy resin (E-51); toluene diisocyanate; azobisisobutyl cyanide; ethyl acetate; toluene; talc; amine curing agent.

2.1.2 Experimental Principle

Polystyrene is an amorphous linear non-polar substance. Its molecule contains benzene rings and is highly rigid but less flexible. The adhesive force on the surface of polar substances is very weak, the adhesive made directly from polystyrene is not strong enough and the adhesive layer is brittle and hard. Therefore, it is necessary to add a modifier to the PS glue solution for modification treatment, and introduce polar groups on the styrene chain links to increase flexibility and improve bonding strength. I chose epoxy resin (E-51) and toluene diisocyanate as modifiers. Under the action of the initiator azobisisobutyl cyanide, toluene diisocyanate first reacts with polystyrene. The reaction formula is as follows:

(2) Cross-linking reaction between chain free radicals and toluene 2, 4-diisocyanate

(R represents benzyl)

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

In this way, isocyanate successively converts PS, The epoxy resin is modified and partially cross-linked.

2.1.3 Preparation of adhesive

Place the reaction vessel in a constant temperature water bath, install the stirring rod, and add 100 parts of mixed solvent (ethyl acetate: toluene = 4: 1), add 50 parts of washed and dried waste polystyrene foam scraps in batches, and stir while adding. After all is dissolved, gradually raise the temperature to 70°C, and add 0.5 parts of initiator. Azobisisobutyronitrile, 3 parts of toluene 2,4-diisocyanate, react under medium speed stirring for about 1-1.5 hours, then add 0.5

parts of toluene 2,4-diisocyanate Isocyanate, cool to 50°C, add 10 parts of epoxy resin (6101), continue the reaction for 1 hour, add 10 parts of filler after cooling, and obtain a slightly yellow viscous glue. A curing agent needs to be added when using this glue.

2.1.4 Testing methods for various indicators of adhesives

The non-volatile content is measured according to the GB/T2793-95 method, and the viscosity is measured according to the GB/T2794-95 method. , the tensile shear strength is measured according to the GB7124 method, and the limit of harmful substances in the adhesive is measured according to the GB18583-2001 method.

2.2 Development of emulsion-type PS modified adhesive

2.2.1 Instruments and drugs

Instruments: electric mixer; electric heating mantle; four-necked flask; Spherical reflux condenser; thermometer; dropping funnel; Instron 4467, 4505 general material testing machine; blast oven; SC-7 gas chromatograph; infrared spectrometer.

Drug: polystyrene foam; butyl acrylate; vinyl acetate; dioctyl phthalate; ethyl acetate; toluene; initiator ammonium persulfate; mixed emulsifier (dodecane Sodium sulfate: OP-10＝

1:2)

2.2.2 Preparation of aqueous PS modified glue

in a four-necked flask Add 50 parts of mixed solvent (ethyl acetate: toluene: 4:1), add 40 parts of washed, dried and crushed waste polystyrene foam in batches with stirring, gradually raise the temperature to 40°C, and wait until it is completely dissolved into a transparent sticky After the liquid becomes thick, add 1 part of compound emulsifier, 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 acetate = 1:1), and heat to 60 ℃, increase the stirring speed, re-emulsify for 30-40 minutes, and drop part of the initiator (ammonium persulfate 10% solution); during the reaction, heat is released and the temperature begins to rise automatically. At this time, heat the temperature to reach 75°C. Add a solution consisting of 12 parts of mixed monomer and 80 parts of water drop by drop. During the process of adding the mixed monomer aqueous solution, add a part of the initiator at regular intervals (the total amount of initiator is 1 part). The reaction temperature should be controlled at 75 Between -85℃, after all the additions are completed (it takes about 1.5-2h), add all the remaining initiators, raise the temperature to 90℃ and keep it warm. Stop heating when the recovered solvent reaches 80-85% of the added amount, and then , cool to 50°C, add two parts of the plasticizer dioctyl phthalate, stir evenly, adjust the pH value to about 7, cool to room temperature, and obtain a white viscous liquid.

2.2.3 Test methods for various performance indicators of PS modified emulsion adhesive

The non-volatile content of the adhesive is measured according to the GB/T2793-95 method, and the rotational viscosity of the adhesive is measured according to The compressive shear strength is measured according to the HG/T2727 Appendix B method, the ash content and PH value are measured according to the GB11175 method, and the limit of harmful substances in the adhesive is measured according to the GB18583-2001 method.

3 Results and discussion

3.1 Results and discussion of solvent-based PS modified adhesive

3.1.1 The obtained PS modified adhesive The technical properties of polystyrene foam are shown in Table 1

3.1.2 Selection of solvents

Polystyrene foam is dissolved in aromatic hydrocarbons (such as benzene, toluene, xylene, etc.), chlorine Most organic solvents include hydrocarbons (such as chloroform, trichloroethylene), carboxylic acid esters (such as ethyl acetate, butyl acetate), ketones (such as acetone, butanone). Choosing a suitable solvent to dissolve foam plastics should mainly consider the following aspects: First, the selected solvent must have good dissolving ability for polystyrene and newly added modifiers, and good dispersion properties for additives; secondly, , the properties of the solvent should have a certain improvement effect on the properties of the adhesive; third, the solvent selected should be low-toxic, cheap, easy to obtain, and safe. Considering the above factors, it is more suitable to use ethyl acetate or toluene as the solvent. However, considering that the solubility of mixed solvents is better than that of a single solvent, and due to different boiling points, volatilities, and polarities, by changing the mixing ratio, the drying time of the adhesive can be adjusted to meet the needs of different occasions. Therefore, a mixture of ethyl acetate and toluene was selected as the solvent for polystyrene foam. The physical and chemical parameters of these two solvents are shown in Table 2.

The solubility parameter of polystyrene is 9.11

3.1.3 Selection of solvent ratio

Ethyl acetate and toluene are used as mixed solvents. Ester contains polar groups, which is very helpful in improving the performance of adhesives. It has a low boiling point and evaporates quickly; toluene is a non-polar substance with a high boiling point and evaporates slowly. Different ratios of the two will cause Affects the drying speed and adhesion of modified PS glue, so it is necessary to choose a more appropriate solvent ratio.

It can be seen from the figure that as the solvent ratio increases, that is, when the ratio of ethyl acetate increases, the shear strength of the modified liquid increases until the solvent ratio reaches 4:1. , dropped again. The reason may be that

ethyl acetate has a relatively large polarity. On the one hand, it has a modifying effect on the adhesive, and on the other hand, it can form an intermolecular interaction force with the surface of the adhered material. Therefore, , improves the shear strength; and it evaporates quickly, which perfectly meets the requirement of less residual solvent after the epoxy resin is cured and improved shear strength. Therefore, its proportion increases and the glue strength increases. However, when the proportion of ethyl acetate is too large, because it has a low boiling point and evaporates quickly, after the glued edge is solidified, the internal solvent may remain in a liquid or semi-solid state for a long time, affecting the bonding effect and causing shearing. The shear strength is slightly reduced.

3.1.4 Effect of the amount of modifier toluene diisocyanate on the shear strength of the adhesive

Toluene diisocyanate is a highly polar substance, and its modification effect is extremely obvious , only a very small amount can significantly improve the performance of the adhesive. It not only has a good modification effect on polystyrene, but also has a good modification effect on epoxy resin. In the modification reaction of waste polystyrene, the modifier TDI has two functions: one is to introduce polar groups into the polystyrene macromolecules to cross-link the polystyrene macromolecule chains, and the other is to interact with the epoxy The resin reacts to modify the epoxy resin and partially cross-link the epoxy resin and polystyrene. The amount of modifier TDI directly affects the properties of the modified PS glue. If the amount of modifier is small, the polystyrene molecular chain will contain less polar groups, the degree of cross-linking will be insufficient, the toughness will be insufficient, and the epoxy resin will be damaged. It cannot be modified well, and the glue layer is brittle; if too much is used, the material will be over-cross-linked and even form a network structure, reducing the shear strength. Experiments show that the modifier dosage is 2.0 %, the modification effect is better. As shown in Figure 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 "universal glue". It has good bonding properties to various metals and most non-metallic materials, and is widely used in industrial sectors such as aircraft, missiles, automobiles, construction, electronic appliances, and wood processing. Moreover, epoxy resin glue has good process performance and is easy to bond. It has the advantages of high strength, small shrinkage, excellent dielectric resistance, and good electrical insulation properties. Among the PS glue modifiers, there are phenolic resin, rosin resin, phthalate, etc., but no one has tried epoxy resin to modify PS. Because there are also polar groups in epoxy resin, it should have a good modification effect on PS. Therefore, I tried modifying PS with epoxy resin. However, the effect of using epoxy modified PS alone is not good. The adhesive layer is easy to peel off, the bonding strength is not very strong, and the adhesive layer is brittle. This may be due to the factors that both are relatively rigid. I added a third modifier to both, choosing isocyanate and had success. The amount of epoxy resin also affects the properties of the glue. If the amount is too small, the strength will not be high, but when the amount is slightly larger, the shear strength will decrease. This may be because the PS modified adhesive is a solvent-based adhesive, and the epoxy resin is cured. Afterwards, a part of the solvent still remains in the adhesive layer, affecting the performance of the adhesive. This effect becomes more obvious as the amount of epoxy resin increases. Moreover, the cost is also high if the amount is too large. The relationship between epoxy resin dosage and adhesive performance is shown in Table 3