Toughened epoxy oligomers are mainly liquid polysulfide rubbers, liquid nitrile rubbers, low molecular polyamides, isocyanate prepolymers, and the like. It is characterized by a low molecular weight polymer that is inherently flexible and mostly contains reactive groups with epoxy resins. Flexible segments that become cured epoxy after curing. Mainly used for the preparation of room temperature or medium temperature curing, with medium strength and toughness, heat resistance is not very high solvent-free epoxy structural adhesive.
1. Polysulfide Rubber Toughened Epoxy Structural Adhesives Liquid polysulfide rubber is a viscous liquid with a relatively low relative molecular mass M, including two types of M=500 to 1000 low viscosity and M=3000 to 4000 high viscosity. The polysulfide rubber reacts with the epoxy group through the thiol group at the end of the molecule to form a soft segment in the molecular structure of the epoxy cured product, so that the adhesive has high shear strength and peel strength, chemical resistance and salt spray Function and heat resistance. In the absence of a catalyst, the thiol group reacts very slowly with the epoxy group. Organic amines such as DMP-30, diethylenetriamine, triethylenetetramine, hexahydropyridine, etc. have a significant catalytic effect on it, with DMP-30 being the most effective. With the increase of the amount of polysulfide rubber, the elongation and impact toughness of the castables of bisphenol A epoxy resin and DMP-30 system increased, and the tensile strength of the bisphenol A epoxy resin and DMP-30 system showed a maximum value when the amount of polysulfide rubber was 30-50 PHR. The shear strength of cementation shows a maximum around 40PHR. The use temperature does not exceed 80°C. If aromatic amine or dicyandiamide is used as a curing agent, the use temperature can reach 100-120°C.
Application examples are as follows:
(1) Polysulfide modified epoxy adhesive formulation (parts by mass):
Bisphenol A epoxy (epoxy value 0.48 to 0.57) Polysulfide rubber (M=1000) CaCO3 DMP-30
A: 100 — 179 One B: One 100 71 15
A: B = 1.5:1
Curing conditions: 121°C/1h.
Performance: (aluminum alloy-aluminum alloy) shear strength, MPa: room temperature 30.9, 82°C 10.3, -49°C 17.2; flexural strength 62.2 MPa; peel strength 3.14 kN/m.
(2) 210 Adhesive Formula (parts by mass):
Epoxy E-51 Liquid Polysulfide Rubber (M=980) Hexahydropyridine 100 50 8
Curing conditions: 100°C/3h. The pressure is 0.02 to 0.03 MPa.
(3) Aircraft structural adhesive formulation (parts by mass):
Epoxy Resin E-44 Polysulfide Rubber (M=1000) CaCO3(400 mesh) DMP-30
100 55 50 15
Curing conditions: 120°C/2h.
Properties: (Al-Al) shear strength: room temperature 31.5 MPa, 80°C 10.5 MPa; flexural strength (room temperature) 6.3 MPa.
Source: 21st Century Fine Chemicals Network
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