| Epoxy resin (EP) has been widely used as adhesive in aviation, spaceflight and national defence field,etc.for its outstanding advantages on excellent process ability, mechanical, moulding, electric properties, low shrinkage during cure and good chemical resistance as advanced resin matrix Regrettably their high cross-linkdensity, britteleness and substantially non-elastic limited their applications in elastic-bonding and ultro-low-temperature for cryogenic engineering projects. The effective way is to produce a more elastomeric epoxy resin. The essential method is to reduce the elastic modulus or transfer its glass transition temperature (Tg) to low temperature. Successful attempts are flexible crosslinking agent toughening or flexible crosslinking in main-chain of epoxy,and employment of active flexibilizers. In this dissertation, the methods and mechanisms of toughening EP have been reviewed, and a view to prepare a kind of flexible, elastic,transparent epoxy adhesive, having high elongation at break and satisfactory mechaincal properties, by flexible chain structure used polyetheramines. The aim of this study is to prepare a series of high elasticity -high elongation epoxy resin systems with simple formulas design. Main contents and conclusions of this dissertation are as follows:1. Adhesive formulas was prepared by using flexible mixed curing agents---polyetheramines and different kinds of epoxy resin. The results indicated all the systems obtained high elongation at break. Considering the relationship between strength and flexibility- elasticity, Diglycidyl ether of bisphenol A (DGEBA)/ polyetheramine and diglycidyl ether of bisphenol A (DGEBA)/aliphatic flexible epoxy resin/ polyetheramine had high elongation at break and satisfactory mechaincal properties.2. By using DSC, the processing of curing for the diglycidyl ether of bisphenol A (DGEBA)/ polyetheramine system was ascertained to be 80℃/2h+125℃/2h. The curing activation energy Ea of different kinds polyetheramines were DGEBA/D230: 58.924kJ/mol, DGEBA/D400:51.730 kJ/mol, DGEBA/T403:57.062 kJ/mol, DGEBA/D2000:49.881 kJ/mol,and the order of reaction n and the dynamic equations of the curing reaction were DGEBA/D230:dα/dt=1.99E7exp(-7087.68/T)(1-α)0.898; DGEBA/D400: dα/dt=1.28E6exp(-6222.04/T)(1-α)0.883; DGEBA/T403:dα/dt=9.75E6exp(-6863.36/T)(1-α)0.897; DGEBA/D2000:dα/dt=1.20E5exp(-5999.64/T)(1-α)0.867.3. The mechanical properties of diglycidyl ether of bisphenol A (DGEBA)/ polyetheramine system were examined. Polyetheramine (D400) have better synergistic effect on improving the elongation at break of system. The maximum of tensile strength, elongation at the break, impact strength and tensile shear strength get about 21.69Mpa, 53.10%, 156.81kJ/m2, 45Mpa, respectively. The mixing proportion between filling agent, curing condition and other factors are investigated. Meanwhile, the influence of active toughener toughener are tested and analyzed.4. The results of Dynamic mechanical thermal analysis(DMA) indicated that the cured blends clearly display only one maxima on the tand curves. The glass transition temperature(Tg) decreased with the enhancement of polyetheramine (D2000) content, and storage modulus E' elevated. It is the toughening mechanism for the flexible chain modified epoxy. Besides, the chains were wrapped in the three-dimensional network of the epoxy. The impact energy could be held back or delayed due to the existence of the flexible chain. In this case, the dissipation of relatively large part of the impact energy may be attributed to crack bifurcation and crack path alternation. Differential scanning calorimetry (DSC) analysis discuss the relationships between Tg, hardness and crosslink-density of aliphatic flexible epoxy resin/ polyetheramine system. 5. According to the results of DMA, SEM, DSC and mechanical properites, the toughening mechanism of polyetheramine modified epoxy resin was discussed initially. Increasing the molecular weights between crosslinkings could improve tougheness.The impact energy may be attributed to crack bifurcation and crack path alternation by large and flexible chains.
|
PDF Full Text Request