Study on the performance of epoxy resin adhesive i

Study on improving the properties of epoxy resin adhesive with nano SiO2

Abstract: the theoretical basis of modifying epoxy resin adhesive with inorganic nanoparticles and the dispersion principle of inorganic nanoparticles are analyzed and described. According to this theory, nano SiO2 was used to modify epoxy resin adhesive by mixing method, and good results were obtained to improve many properties of epoxy resin adhesive. It shows that it is an effective method to modify epoxy resin adhesive with inorganic nanoparticles

key words: nanoparticles; Epoxy resin adhesive; Dispersant

in the 1980s, kurauchi and others first proposed the use of inorganic rigid particles to toughen polymers. After decades of development, this method has become one of the most effective ways to modify materials. Modification of organic polymers with inorganic rigid particles can improve the rigidity, hardness and wear resistance of polymers, but reduce the strength and toughness of polymers. After studying nano scale materials, the scientific and technological circles have pointed out four major effects of nano material properties: quantum size effect, small size effect, surface effect and quantum tunnel effect

1 theoretical basis for modification

generally, inorganic filled polymers improve the rigidity of materials while reducing their toughness, but nano materials can give consideration to both. Why? Some people attribute it to the crazing theory, that is, nanoparticles are evenly dispersed in the matrix. When the matrix is impacted, microcrack crazing occurs between particles and the matrix. At the same time, the matrix between particles also produces plastic deformation and absorbs impact energy, so as to achieve the effect of toughening. As the size of nanoparticles becomes smaller, the specific surface area of particles increases, and the interface between particles and matrix becomes larger, which will produce more microcracks and greater plastic deformation, so as to absorb more impact energy and improve the toughening effect

Wang hongzuo believes that according to the traditional view, after nano SiO2 and other nano particles are evenly dispersed in epoxy resin, when the matrix resin is impacted by external forces, crazing will occur between them. The matrix resin between nanoparticles also produces plastic deformation and absorbs certain impact energy. With the micronization of particles, its specific surface area will further expand, so that the contact area between nanoparticles and matrix resin will increase. When the material is impacted by external force, it will produce more crazing and plastic deformation, and absorb more impact energy to achieve the effect of toughening the material. The existence of rigid nanoparticles is easy to produce stress concentration effect and cause crazing of the surrounding matrix resin, absorbing certain deformation work. At the same time, the existence of rigid nanoparticles makes the crazing expansion of the matrix resin blocked and passivated, and finally stops, so as not to develop into destructive cracking, resulting in toughening effect

2 adhesive formula and performance without nano particles

the adhesive formula is: 100 parts of E51 epoxy resin, 35 parts of 651 polyamide; The bonding process of the test piece is as follows: the test piece is 45# steel, and the treatment method is mechanical derusting, acetone cleaning, chemical treatment, water washing, and blowing dry coupling agent for bonding

the curing process of the bonded specimen is: holding at 100 ℃ for 3h, and cooling with the furnace

the initial tensile strength of the tested adhesive is 70.4mpa, the tensile strength after hydrothermal aging is 53.7mpa, and the strength retention rate is 67.4%; The initial impact strength is 3.99kjm-2, the impact strength after hydrothermal aging is 3.66kjm-2, and the strength retention rate is 91.7%

3 determination of dispersion method of nano particles in adhesives

although the amount of nano components in polymer nanocomposites is small (5% ~ 10%), due to the small particle size, large specific surface area and high surface energy of nano particles, it is easy to form aggregates with large particle size. It is difficult for nano components to play their unique role. Once nano particles are separated in the composites, their properties will be reduced to a level equivalent to that of traditional composites. Therefore, the dispersion of nano components in polymers (or their precursors) is the key to the preparation of nanocomposites. When considering the dispersion scheme, the wettability of nanoparticles should be considered first

the wetting process of nanoparticles is actually a process in which the solid-gas interface disappears and the solid-liquid interface forms. According to the change of the free energy of the system, under constant temperature and pressure, the energy change formula of the nanoparticle aggregate is:

△ g=sl-sv

because the surface energy SV of the nanoparticle is greater than the free energy SL of the solid-liquid interface, G0, the wetting process of this system is a thermodynamic spontaneous process. This spontaneous wetting process is effective for the primary dispersion of nanoparticles. Therefore, in the selection of dispersants, we should try to choose dispersants with a high degree of spontaneous wetting (at the same time, we must pay attention to the compatibility with the matrix resin) as the surface treatment agent of nanoparticles, so that it can achieve the best primary dispersion

for the deep dispersion of nanoparticles, the balance between the dispersion and agglomeration of microscopic particles should be considered. According to Xing Honglong and others, nanoparticles are easy to form aggregates due to their special surface structure, and there is an interaction energy between particles that is different from that between conventional particles, which is temporarily called nano interaction energy (FN). This kind of nano interaction energy is the internal property that the surface of nanoparticles has high activity due to the lack of adjacent coordination atoms, which makes nanoparticles agglomerate with each other. Its physical significance should be the adsorption force between nanoparticles per unit specific surface area, which is the sum of several aspects of the adsorption force of nanoparticles: the adsorption caused by hydrogen bonding and electrostatic interaction between nanoparticles; Quantum tunneling between nanoparticles, charge transfer and adsorption caused by local coupling of interface atoms; The adsorption produced by the huge specific surface of nanoparticles. Nano interaction energy is the internal factor for the easy agglomeration of nanoparticles

in order to obtain nanoparticles with good dispersion, small particle size and narrow particle size distribution, the nano interaction energy must be weakened or reduced. When appropriate methods are adopted to disperse nanoparticles, solvation film interaction energy (FS) and electric double layer 1 The static action energy (FR) of the main motor source of the pipe ring stiffness tester is not bright, and the space protection action energy (FP) of the polymer adsorption layer, etc. In a certain system, nanoparticles should be in the equilibrium state of these kinds of action energy

fnfs+fr+fp

when fnfs+fr+fp, nanoparticles are easy to agglomerate

when fnfs+ passes through a set of scientific quantitative system fr+fp, nanoparticles are easy to disperse

for ready to use adhesives, the mixing method is more suitable. The nano powder purchased in the market has undergone primary dispersion treatment in the production plant. According to the characteristics of nano materials, it is necessary to further gather a batch of high-level innovative talent teams for decentralized treatment before use. We determined the following methods to disperse the nano powder before adding the adhesive

(1) the mixed solution is prepared with xylene as solvent and titanate ndz311 as dispersant, and the ratio is m (xylene) ∶ m (titanate) =200:5

(2) disperse 20.7g of nano SiO2 into 2.05g of the above mixture

(3) take 14g of E51 epoxy resin, add the treated SiO2 powder, and stir evenly

4 performance of epoxy resin adhesive modified by nano SiO2

nano particles are added into epoxy resin adhesive to improve the tensile strength, flexural impact strength and hygrothermal aging performance of epoxy resin. The initial tensile strength of the adhesive tested is 84.7mpa, the tensile strength after hygrothermal aging is 82.1mpa, and the strength retention rate is 96.7%; The initial impact strength is 4.64kjm-2, the impact strength after hydrothermal aging is 4.28kjm-2, and the strength retention rate is 92.2%

from the above, it can be seen that the modification effect of nano SiO2, the initial tensile strength increased by 6.7%, and the tensile strength after hydrothermal aging promoted the rare earth enterprises in Zibo, Yantai, Jining and other cities to vigorously improve the industrialization level of rare earth magnetic materials and their utilization devices by 52.9%. The retention rate of tensile strength of Ghanaian rice flour after modified by damp heat aging is 96.9%, and that without nano SiO2 is only 67.4%. From the strength retention rate after damp heat aging, the adhesive modified by nano SiO2 is also better than that without modification. It can also be seen from the comparison that the initial impact strength of epoxy adhesive modified by nano SiO2 is increased by 16.3%; The impact strength increased by 16.9% after damp heat aging; The strength retention rate also increased significantly after damp heat

5 conclusion

the modification of epoxy polyamide adhesive with nano SiO2 has significantly improved the mechanical properties and moisture and heat aging resistance of the adhesive, and the research in this field has broad prospects