Application of fumed silica in gel coat resin

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With the rapid development of FRP industry in recent years, higher requirements have been put forward for the quality and appearance of FRP products and the surface gel coat layer. Gel coat resin is a special kind of unsaturated polyester. It plays the role of protecting products and prolonging service life, so it should have good tensile strength, bending resistance, water resistance, heat resistance and other properties

hydrophilic fumed silica can be used as gel coating resin. It has a very small particle size (primary particle size 7-45nm) and a very large specific surface area (m2/g). In this paper, the effects of nano silica and ethylene glycol on the thixotropy of gel coat resin and the mechanical properties of resin casting were studied. This kind of friction is usually referred to as fluid lubrication

2 test part

2.1 raw materials and formulas for experiments

raw materials include 196 unsaturated polyester resin of Foton company, German N20 and A200 and A380 gaseous silica of Shenyang Chemical company, ethylene glycol (AR), organic siloxane dispersant of Dow Corning company, 6800 defoamer of Deqian company, methyl ethyl ketone peroxide and cobalt naphthenate. The experimental formula is shown in Table 1. Table 1 experimental formula

196 unsaturated polyester resin 100 phr fumed silica/%2 5 dispersant/%0.26800 defoamer/%2.0 methyl ethyl ketone peroxide/%1 cobalt naphthenate (4%)/%1

the key to using nano SiO2 is to ensure its good dispersion in unsaturated polyester resin. The better the dispersion, the greater the thixotropic index and the higher the mechanical strength. Dispersion equipment includes ultrasonic homogenizer, three roll grinder, sand mill, colloid mill, high-speed shear mixer, etc. In this paper, fumed silica and dispersant were first added to a small amount of unsaturated polyester resin, and the matrix was prepared by three roll grinding machine. Then the matrix was added to the resin and diluted to a certain proportion by high-speed stirring. The process has higher shear force and viscosity when dispersing, and the dispersion of gaseous silica is better

2.3 performance test

viscosity is measured by American Brookfield Viscometer; The dispersity was observed by jsm-6330f scanning electron microscope; The tensile strength, tensile modulus of elasticity and elongation at break were measured on the hounsfieid ht-10 universal testing machine in Britain according to gb2568-1995 standard, and the bending strength and modulus were measured according to gb2570-1995 standard, and the impact strength was tested

3 results and discussion

3.1 viscosity, thixotropy and rheology of gel coat resin

the viscosity of A200 and A380 at different rotating speeds was determined in this paper. It is found that the viscosity decreases with the increase of rotating speed; When dispersant is added, the viscosity of the system is reduced and the fluidity is better. Thixotropy is characterized by introducing thixotropic index K. The larger the thixotropic index is, the greater the thixotropy is. Thixotropic index is the ratio of viscosity at 6RPM to 60rpm. The viscosity at 6RPM is shown in Figure 1, and the statistical data from the study of true lithium by calculating its thixotropic index are shown in Table 2. Table 2 thixotropic index of unsaturated polyester

sio2 model addition/% thixotropic index K plus 1% ethylene glycol thixotropic index ka2002 Of course, the cheaper the better 53.814.12a2002.84.264.37a2003.04.314.60a2003.24.654.80a3802.53.874.68n202.54.325.53 precipitation 2.51.25

note: the specific surface areas of A200 and A380 are 200 and 300m2/g respectively

it can be seen from table 2 and figure 1 that the greater the amount of fumed silica, the greater the viscosity and the greater the thixotropic index. Increasing the amount of fumed silica will produce more interaction between silica particles, so it has higher apparent viscosity; As the specific surface area increased from 200m2/g to 380m2/g, the thixotropic index increased; If ethylene glycol is added to the system as a bridging agent, the silica complex will be strengthened, resulting in a further increase in viscosity. The K of precipitated silica is 1.25, which is much lower than that of gas-phase method, which also shows that precipitated silica is not suitable for gel coat resin

figure I effect of SiO2 addition on viscosity

Figure 2 Relationship between gel coat resin shear stress and shear rate

gel coat resin viscosity and thixotropic index are affected by many factors, but mainly shear dispersion force, mixing speed, service temperature and surface treatment of added fillers. Gel coat resin prepared by the matrix method can increase its viscosity by 30-60% and its thixotropy will be greater. The relationship between gel coat resin shear stress and shear rate is shown in Figure 2. It can be seen from Figure 2 that the shear stress of gel coat resin without silica is a function of shear rate, and the gel coat resin becomes a pseudoplastic fluid after silica is added

3.2 mechanical properties of gel coat resin castings

test strips of gel coat resin castings were prepared according to GB 2567-1995. The tensile strength, tensile modulus of elasticity, elongation at break, bending strength, bending modulus and impact strength before and after adding ethylene glycol were measured. The experimental results are listed in Table 3. Table 3 test results of mechanical properties of gel coat resin

SiO2 addition/% tensile strength/mp this technology uses ultraviolet light (UV) to convert the liquid polymer resin into an independent solid structure in a precise and controllable way a tensile modulus of elasticity/mpa fracture elongation/% bending strength/mpa bending modulus/mpa impact strength/kj · m-2 blank 60 277.220968.7A200 2.569.. 581.. 2A200 2.872.. 696.. 7A380 2.564.428499.083.917599.8N20 2.573.. 885.. 7

it can be seen from table 3 that the mechanical properties are greatly improved after adding fumed silica, especially N20 with an addition of 2.5% and A200 with an addition of 2.8%. Compared with no SiO2, the tensile strength can be increased by 18.9%, the tensile modulus of elasticity can be more than 60%, the bending strength and modulus can be increased by 25%, and the impact strength can be increased by 125%. This phenomenon is due to the presence of siloxane and hydroxyl functional groups on the surface of fumed silica, which can form hydrogen bonds under certain conditions. When silica is dispersed in unsaturated polyester, the aggregates interact to form an intermediate "chain" structure. Finally, when the resin is still, enough interaction forms the desired complex structure, so the strength, toughness and ductility of the resin material added with nano SiO2 are greatly improved, that is, the tensile strength, bending strength, impact strength and other properties are improved. (end)

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