Development of the hottest polyurethane modified e

2022-08-03
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Development of polyurethane modified epoxy resin adhesive II

2.2 mechanical properties of polyurethane modified epoxy resin

after the modified epoxy resin was cured at 100 ℃ for 3 hours, the mechanical properties were tested. The results are as follows:

it can be seen from Figure 5 that the tensile strength and Young's modulus decreased with the increase of the amount of polyurethane prepolymer; The tensile strength and Young's modulus decreased sharply after the addition amount reached a certain degree (30 phr); With the increase of the addition amount (after 50 phr), the tensile strength and Young's modulus decreased gradually, but the decrease was significantly slower than that in the previous stage

with the increase of flexible segments in the polymer, the flexibility of the polymer increases and the rigidity decreases, so the tensile strength and Young's modulus decrease all the time. At the same time, micro phase separation occurred after the curing of the system, and polyurethane rubber particles were dispersed in the continuous phase of epoxy resin. The effect of rubber phase is also different at different stages. When the addition amount is small, the rubber phase plays the role of stress concentration that causes crazing and prevents the further development of crazing when impacted, and absorbs energy. In general, it still shows the nature of continuous phase of epoxy resin. Therefore, although the tensile strength and Young's modulus decrease due to the introduction of flexible links, the decrease range is relatively small; After the addition amount reaches a certain degree (30 phr), due to the aggregation of polyurethane rubber particles, the particle size gradually increases, the degree of phase separation deepens, and the rubber phase is similar to the defects of the system. The dominant role of the system is that the continuous phase of the epoxy resin is destroyed, so the tensile strength and Young's modulus decrease significantly; With the continuous increase of the addition amount, polyurethane gradually gathered to form a continuous phase, and the system gradually showed the properties of polyurethane. Although the tensile strength and Young's modulus decreased, the decreasing material was not the same as that of the previous stage

For example, the selection of experimental speed

it can be seen from Figure 6 that the elongation at break increases with the increase of the amount of polyurethane prepolymer added. After the addition amount reached a certain degree (70 phr), the elongation at break increased rapidly. With the increase of the amount of prepolymer, the impact strength increased continuously, and the first peak appeared when the amount of prepolymer was 10 phr, and then the impact strength began to decrease with the increase of the amount of prepolymer; After the addition amount reached 50 phr, the impact strength began to increase, and the second peak appeared when the addition amount was 70 phr, and then the impact strength began to decrease

with the increase of flexible segments in the polymer, the flexibility of the polymer increases and the rigidity decreases, so the elongation at break increases all the time; The elongation at break increased rapidly after the performance of the system changed to that of polyurethane

due to the increase of the flexibility of the system and the different role of the rubber phase in different stages, there are two peaks in the change of impact strength. When the rubber phase is mainly toughened, the impact strength increases; When the rubber phase mainly destroys the main curing system, the impact strength decreases; The impact strength of polyurethane increased after continuous phase was formed; When the addition amount is too high, the impact strength decreases again because the system becomes soft. At 100 phr, the strength is even higher than that of pure epoxy resin. Therefore, when we use this equipment. In addition, at 70 and 100 parts, the impact test piece is in the shape of tough rubber, which is bent and beaten continuously when impacted

it can be seen from Fig. 7 that when the content of polyurethane rubber phase is small (20 phr), the failure mode is brittle fracture; When the phase content of polyurethane rubber reaches a certain degree (50 phr), the yield point appears on the stress-strain curve, and the failure mode is ductile fracture; When the content of polyurethane rubber phase is high (100 phr), the failure mode is ductile fracture. In fact, although the failure mode is ductile fracture when the amount of rubber is 50 phr, the tensile strength is already very low

it can be seen from Fig. 8 that with the increase of the amount of polyurethane prepolymer, the bending strength and bending modulus have been decreased, which is also the result of the decrease of the rigidity of the system. In addition, when the polyurethane prepolymer was added to 50 phr, the cured resin was too soft, and the bending strength and bending Young's modulus could not be measured

(to be continued)

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