Development of Polyurethane Modified Epoxy Resin Adhesive

Abstract : In this paper, the reaction of diol M2 with MDI (-NCO:-OH=2:1) ​​is used to synthesize the end-NCO-based prepolymer; then the prepolymer is reacted with epoxy resin E-51 to synthesize the modified polyurethane. Epoxy resin. The FTIR study showed that the modified epoxy groups did not change; SEM studies showed that with the increase in the amount of urethane rubber gradually gathers, there are three different changes in the microstructure of the modified system. Affected by the microscopic morphology, the mechanical properties and adhesive properties of the modified system have also changed. In this paper, the bonding properties of different curing systems are also discussed. The results show that the modified system has excellent adhesive properties.

Keywords: epoxy resin;polyurethane;modification;microscopic morphology,mechanical properties

Foreword

Epoxy resin is a kind of thermosetting resin. It is widely used in adhesives, coatings, composite materials, etc. due to its excellent adhesion, mechanical strength, electrical insulation, and good processability. Due to the high crosslinked structure of pure epoxy resin, there are shortcomings such as brittleness, fatigue resistance, heat resistance, and poor impact toughness. It is difficult to meet the requirements of engineering technology, and its application is subject to certain restrictions. The modification of epoxy resin has always been a hot topic in Chinese and foreign research, and the toughening of epoxy resin is an important field in the modification work [1-5].

There are many toughening methods for epoxy resins. Although research has been conducted for several decades, some toughening methods have been very mature, but new toughening methods and new toughening agents have recently emerged. At present, research at home and abroad mainly focuses on two aspects. On the one hand, with the continuous development of technology, how to obtain high-performance polymer materials to meet the requirements of many special occasions, and can make it more widely used; On the other hand, with the continuous development of the market, how can we obtain more low-cost polymer materials to meet the needs of the market? CTBN is a very mature and tough epoxy resin, but because of its expensive price and high viscosity, it can only be used in a few places, limiting its application. How to solve the contradiction between performance and cost is always the focus of research at home and abroad.
Polyurethane is a kind of high-performance polymer material, especially with high elasticity and high adhesive strength. It is one of the rapidly developing polymer materials in recent years. It can be combined with epoxy resin in a variety of ways and exhibits its own advantages. Polyurethane products are cheap, if they can be modified epoxy resin, get excellent performance, and can have good process performance, then the market has a very wide application prospects [6-14].

1 Experimental section

1.1 Experimental raw materials

Combination of polyether M2 (molecular weight 2000, functionality 2), self-made; Epoxy resin E-51, industrial products, Wuxi Resin Factory; 4,4'-Diaminodiphenylmethane (MDA), Analytical Pure, Shanghai Reagent No. 1 Room temperature curing temperature curing agent A, synthesized in the laboratory; diphenylmethane-4,4'-diisocyanate (MDI), industrial products, Yantai Wanhua.

1.2 Experimental methods

Shear test strips: Chemical oxidation strip test specimens: Phosphoric acid anodized tensile, impact test specimens: homemade shear strength according to GB 2567-81: GB 7124-86
Peel strength: GB 7122-86
Bending impact strength (adhesive): General method for the impact strength of adhesives Tensile strength, tensile Young's modulus, elongation at break: GB 2568-81
Bending strength, bending Young's modulus: G B2570-81

Impact strength (resin casting body): GB 2571-81
Infrared spectra determined by Nicolet 50X scanning electron microscope determined by JSM-840

1.3 Synthesis of Polyurethane Modified Epoxy Resin

The M2 is heated to 100-140° C. in advance and vacuumed. The degree of vacuum is maintained at 10 to 100 mmHg, and dehydration under reduced pressure is performed for 2-4 hours. The MDI was added to a three-necked flask, protected by N2 gas, and warmed to 80° C. with stirring. The pre-heated polyol (-NCO:-OH 2:1, -NCO excess 5%) was added in proportion, and after 2 hours of reaction, the pre-heated E-51 was added proportionally to continue the reaction. After 2 hours of reaction, 1% of dibutyl tin dilaurate was added and the reaction was stopped after 0.5 hours, and the product was poured out.

2 Results and Discussion

2.1 Characterization of Polyurethane Modified Epoxy Resins

As can be seen from Figure 1, the γ (OH) absorption peak of -OH group at 3480cm-1; the γas absorption peak of NCO group at 2270cm-1 is very obvious; the γc of ester group appears at 1730cm-1. In the absorption peak, a weak γNH absorption peak of the -NH group also appeared at 3280 cm-1. This shows that the activity of the -NCO group is very high, and there has been a small amount of reaction. It can be seen from Fig. 2 that the absorption peak of -OH group is almost invisible at this time, the absorption peak of -NH group and the absorption peak of carbonyl group have become strong peaks, and the absorption peak of -NCO group is slightly weakened, indicating the -OH group of M2. The -NCO group reaction with MDI is almost complete. By comparing the spectra, no significant changes were observed in the other peaks before and after the reaction, indicating that no other reaction occurred.

As can be seen from Figure 3, the γOH absorption peak of -OH group at 3480 cm-1 and the γNH absorption peak of -NH group at 3280 cm-1 coexist; the γas absorption peak of NCO group at 2270 cm-1 is still strong; 920 cm-1 At the place is the characteristic absorption peak of the epoxy group. It can be seen from Figure 4 that the absorption peak of -OH group is already very weak, and the absorption peak of -NCO group is no longer visible, indicating that the reaction between -NCO group and -OH is already complete, and there is still a partial excess in the system - The OH group is not reacted. By comparing the spectra, there was no significant change in the other peaks before and after the reaction, indicating that no other reaction occurred. In particular, the characteristic absorption peak of the epoxide group at 920 cm −1 did not change, indicating that the epoxy group did not react with the —NCO group and did not react with the generated —NH group, and the main structure of the reaction product was still epoxy resin.

(to be continued)