Development of Waste Styrofoam Modified Emulsion Adhesive II

2.1 Solvent Selection

Polystyrene is a linear polymer of Division E crystals, which can be dissolved in solvents such as aromatic hydrocarbons, halogenated hydrocarbons, ketones, and esters. The strength of dissolving force can be determined by the difference of the solubility parameter of polystyrene foam and solvent. The smaller the difference between the solubility parameters of solvent and polystyrene, the stronger the dissolving power. The polystyrene solubility parameter is 9.1 cal0.5/cm11.5. In addition, it is also necessary to consider the influence of the boiling point and polarity of the solvent on the adhesive force. Therefore, the choice of the ideal solvent should be: strong dissolving power, moderate volatility, easy mixing with other solvents, and better fillers, auxiliaries, etc. The dispersion, but also has a good wetting of the adherend, while requiring economical, non-toxic. Table 1 below lists the physical properties of several solvents with similar polystyrene solubility parameters.

As can be seen from Table 1, the polarity size was acetone> ethyl acetate> toluene; the dissolving power was acetone> ethyl acetate> toluene. The polarity of the solvent is large, and the binding ability of the binder is greater, but the most polar ethyl acetate cannot be used as a solvent because ethyl acetate has a low boiling point, volatilizes too fast, and is fast drying, which is not conducive to sizing. . Select the better solubility of ethyl acetate and toluene to form the main solvent, with a small amount of acetone to form a mixed solvent, the addition of acetone helps to increase the polarity of the solvent and control the volatilization rate. Taking into account the higher price of acetone, it is advisable to use less. Some of the solvents were removed during the experiment and recycled after recycling, which greatly reduced costs.

Pure solvent solubility parameters.

The dissolving power of the mixed solvent composed of ethyl acetate, toluene, and acetone can reach 50% of the polystyrene foam. The optimum ratio is: m (ethyl acetate): m (toluene): m (acetone) II 3:2:0.5.

2.2 Selection of Modifiers

2.2.1 Graft Modifiers

Maleic anhydride was used to graft-modified polystyrene. On the one hand, the polarity of polystyrene was increased and the affinity of the adhesive with the material was improved. On the other hand, maleic anhydride and polystyrene undergo a small amount of cross-linking reaction, improving the toughness of the adhesive. When the amount of maleic anhydride was 1.0%, the shear strength was the highest. When the amount of maleic anhydride is <1.0%, the more carboxyl groups are introduced, the stronger the adhesiveness is, as the amount of maleic anhydride increases. When the amount of maleic anhydride is more than 1.0%, the effect with styrene is reduced as the maleic anhydride increases, causing a decrease in the adhesive strength. Unsaturated double bond end groups in polystyrene can be graft copolymerized with acrylic acid under the action of benzoyl peroxide (BPO) to increase flexibility, and its amount is about 10%

2.2.2 Plasticizers

The main role of plasticizers is to weaken the secondary bonds between polymers, that is, van der Waals forces, thereby increasing the mobility of polymer chains, reducing the crystallinity of polymer chains, and increasing the plasticity of polymers as polymer. Hardness, film amount, softening temperature, and embrittlement temperature are reduced, while elongation, flexibility, and flexibility are improved. It improves elasticity and improves cold resistance in adhesives. Since dibutyl phthalate has good compatibility with polystyrene, it can be used as an external plasticizer, and the amount thereof is preferably 8.0% to 10% of the weight of the polystyrene.

2.2.3 Toughener

Tougheners are monofunctional or polyfunctional compounds that react with the host polymer as part of the curing system. The active group of the toughener directly participates in the main polymer reaction and can improve the shear strength, peel strength, low temperature performance and flexibility of the adhesive. The commonly used toughening agents for adhesives include unsaturated polyester resins, rubbers, polyamide resins, acetal resins, polysulfone resins, and polyurethane resins. The performance of modified polystyrene obtained by adding different modifiers for modification is also different. The results are shown in Table 2.

From Table 2, it can be seen that adhesives modified with rosin-modified phenolic resin and petroleum resin have the best adhesive effect on wood and the best hardness and toughness. It is because rosin-modified phenolic resin has strong polar hydroxyl (-OH) and hydroxymethyl-group (-CH20H), which makes the adhesive and adherend interact with each other with stronger intermolecular forces and chemical bonds. On the surface, organic long-chain molecular layers are generated due to chemical or physical effects and have strong adhesion to adherends. At the same time, the petroleum resin contains a C=C- and its chain segments contain styrene, methyl styrene and other groups, which crosslink with rosin-modified phenolic resin to form a wear network, and the bonding strength is greatly improved. The use of stone alone; adhesives made of resin as a modifier are not as effective as Adhesive III for wood adhesion. This is because there is only one C=C- and styrene, methylstyrene and other groups in the petroleum resin, and there is no strong polar OH, a CH20H group, etc., and the adhesive and the adherend cannot crosslink to form a long chain. Molecular layer. Adhesives made of phenolic resin with rosin modifier as modifier alone have good adhesive effect on wood board, but the adhesive layer is softer and each performance is inferior to Adhesive III. Under the same reaction conditions, adhesives using SBS resin and rosin-modified phenolic resin as modifiers V and maleic anhydride and rosin modifier IV have weaker adhesive bonding effect and drying time. The long shortcomings are detrimental to the application.

(to be continued)