Study on the improvement of comprehensive mechanic

Under the research of flexible modifier improving the comprehensive mechanical properties of epoxy resin,

Koizumi said: "now I'm still learning how to tell a story well. 2. results and discussion

2.1. the effect of feeding ratio on the molecular weight and water absorption of amino terminated polyurethane

isocyanate group (-nco) is particularly active, and its reaction with hexanediol or ethylenediamine can be carried out almost quantitatively. Control toluene 2,4-diisocyanate (TDI) in the reactant." Amino terminated polyurethane (ATPU) with different molecular weight can be prepared with the relative amount of hexanediol (q= -nco/-oh), see synthesis route map 1. Table 1 shows the relationship between Q and the molecular weight (MC) and water absorption of the synthesized ATPU. It can be seen that as Q decreases from 2.0 to 1.1, MC gradually increases and its water absorption decreases, indicating that with the increase of MC, its polarity decreases. When mc=600, the RW of ATPU is 1.7%, which is far lower than the water absorption of other commonly used epoxy resin curing agent aliphatic amine system, but it still shows that it has certain water absorption. Therefore, in order to reduce the influence of moisture on the properties of adhesive, attention should also be paid to prevent water absorption when storing ATPU. Comparing the theoretical value of the molecular weight of ATPU with the experimental value, we know that the relationship between the molecular weight of ATPU MC and Q can well conform to the linear stepwise polymerization theory, which meets the test (2):

mc=1/(Q-1) × M + MTDI + 2meda (2)

where m is the molecular weight of the repeating unit: MTDI is the molecular weight of TDI; MEDA is the molecular weight of ethylenediamine

Table 1 reactant feeding Q based on the influence of ATPU molecular weight and water absorption

Product Name unit price (yuan/t) construction consumption (g/m2) material cost

(yuan/m2)

dry film thickness（ μ m) Polyurethane coating of this project ~100022.65~27.20 35090% ceramic epoxy coating (USA).% Polyurethane paint (USA) 501000 chlorinated polypropylene coating (domestic) 50150~180

* (MC) theory is calculated according to formula (2); (MC) the measured value is calculated according to formula (1)

2.2. Effect of molecular weight of amino terminated polyurethane on the mechanical properties of adhesive

Figure 2 Effect of molecular weight of ATPU on the peel strength of adhesive a is the equivalent ratio of ATPU and epoxy resin, the same below

the mechanical properties of adhesive are closely related to the molecular structure of curing agent. As can be seen from Figure 1, ATPU molecule contains a large number of carbamate group -nhcoo- and flexible hydrocarbon fatty chain - (CH2) 6-, and has fatty amine group with high reactivity. Therefore, the adhesive prepared with it and epoxy resin can not only cure at room temperature, but also is expected to have impact resistance, good flexibility, high peel strength, high adhesion, and the extruded household board directly has patterns and good high and low temperature resistance. Figure 2 shows the effect of molecular weight (MC) of ATPU on the peel strength of adhesives with different proportions. It can be seen that with the increase of (MC), the peel strength of the adhesive reaches the maximum. This is because with the increase of the molecular weight of ATPU, on the one hand, the crosslinking density and cohesive energy density in the adhesive decrease; At the same time, the fluidity and wettability of the adhesive will also deteriorate, thereby reducing the adhesion of the adhesive to aluminum alloy metal (see Figure 3); On the other hand, the flexible chain segment between the crosslinking points becomes longer, which improves the flexibility of the adhesive (see Figure 4). Figure 2 also shows that when MC is small and the equivalent ratio of flexible curing agent to epoxy resin is 1.0, the moderate peeling of adhesive is the largest. When ATPU or crosslinking density decreases, the mechanical strength decreases. However, with the increase of MC, the influence of the amount of flexible curing agent on the peel strength of the adhesive becomes less

Fig. 3 Effect of molecular weight of ATPU on adhesive adhesion

Fig. 4 Effect of molecular weight of ATPU on flexibility of adhesive

the test also shows that there is a positive relationship between displacement change and resistance change. The 0.6 mm thick adhesive coating made of amino terminated polyurethane with molecular weight of about 880 and bisphenol a glycidyl ether epoxy resin has a surface drying time of less than 24 hours when cured at room temperature (℃), After 72 hours, its comprehensive mechanical properties reach the performance of curing at 80 ℃ for 6 hours, that is, its peel strength ≥ 58n/cm, adhesion ≥ 14.6 MPa, while flexibility 11, fixture 12 mm. This shows that the flexibility of epoxy resin can be significantly improved by molecular design and synthesis of flexible curing agent with appropriate structure, and the comprehensive mechanical properties can be further improved with the further extension of curing time. At the same time, it has room temperature curing and strong bonding ability to aluminum alloy metal, so it is expected to realize the engineering application of bisphenol a glycidyl ether epoxy resin adhesive in the microwave absorbing coating of supersonic aircraft. (article/Guan Jianguo, Wang Wei, Gong Rongzhou)