Abstract : Calcium sulfate whiskers are new non-metallic materials made from gypsum. The calcium sulphate whiskers were used as fillers to prepare epoxy adhesives. The effect of calcium sulfate whiskers on the properties of epoxy adhesives was investigated and compared with several currently used fillers. The comparison shows that the tensile strength can be increased by 50% to 120%, and the shear strength can be increased by 40% to 140%. The effect is obvious. Calcium sulfate whiskers are very good fillers for adhesives.
Key words: calcium sulfate whiskers; fillers; adhesives
The calcium sulfate whisker is a calcium sulfate fibrous single crystal synthesized from raw gypsum by a specific process and formula. It has a uniform cross section, a complete shape and a highly sophisticated internal structure. It is a non-metallic material with many special properties. Calcium sulfate whiskers used in polymer materials can not only enhance, toughen, but also play a role in thickening, heat resistance, abrasion resistance, and oil resistance. In this study, calcium sulfate whiskers were used as fillers to conduct experimental studies on preparation of epoxy adhesives in the laboratory. The study focused on the effect of calcium sulfate whiskers on the strength, toughness, heat resistance and thixotropy of epoxy adhesives. The results show that the epoxy adhesive formulated with calcium sulfate whiskers as a filler has not only obvious enhancement, toughness, thickening, heat resistance, abrasion resistance, oil resistance, high thixotropy, etc., compared with commonly used fillers. The overall cost of formulating adhesives does not increase. It can be said that the application of calcium sulfate whiskers in adhesives has a very broad prospect.
1 test materials and equipment
Calcium sulfate whiskers, developed by Northeastern University. The main properties of calcium sulfate whiskers are shown in Table 1. In order to facilitate comparison, the most commonly used fillers currently used in the preparation of epoxy adhesives were also selected in the test: quartz powder (industrial grade), alumina powder (produced by Shenyang Reagent Plant II), and ultra-fine aluminum silicate (Hebei Langfangjin Co., Ltd. Factory production) and precipitated white carbon (produced by Shenyang Northeast Chemical Plant). The test resin was E-44 epoxy resin produced by Jiangsu Sanmu Group. KH-550 silane coupling agent, produced by Gaizhou Chemical Co., Ltd., whose chemical composition is H2NCH2CH2CH2Si-(OC2H5)3.
The epoxy adhesives formulated for various fillers were made into tensile specimens and tensile shear specimens according to the national standards GB6329-86 and GB7124-86 respectively, and the tensile strength and shear strength were measured by a material tensile tester. strength. The amount of filler added is expressed as parts phr of filler added per 100 parts of E-44 epoxy resin.
2 test content and results
2.1 Comparison of Epoxy Adhesives Formulated with Different Fillers
Calcium sulphate whisker, quartz powder, alumina powder, precipitated silica and ultra-fine silicon in the same amount (20 phr each, ie 20 parts, the same below) under the same conditions Aluminium is a filler and an epoxy adhesive is formulated. Then, the tensile strength and shear strength of these adhesives are measured according to standards. The test results are shown in Table 2.
As can be seen from Table 2, the epoxy adhesive formulated with calcium sulfate whiskers has the highest strength.
2.2 The effect of calcium sulfate whisker dosage on the strength of epoxy adhesive
Figures 1 and 2 show the relationship between the amount of calcium sulfate whiskers and the tensile strength and shear strength of the formulated adhesive. As can be seen from FIGS. 1 and 2 , when the amount of calcium sulfate whiskers is 10 to 30 phr, the strength of the epoxy adhesive has little effect, but the highest is 20 phr.
2.3 The effect of the coupling agent on the adhesive strength
Because the calcium sulfate whisker surface is very complete and smooth, the bond with the resin is often not ideal. Therefore, in the preparation of epoxy adhesive with calcium sulfate whiskers, an appropriate amount of silane coupling agent is added at the same time to increase the binding force between the calcium sulfate whiskers and the epoxy resin matrix. Table 3 shows the test results when the amount of KH-550 silane coupling agent was 1% of the amount of calcium sulfate whiskers.
As can be seen from Table 3, the strength of the adhesive was significantly improved after the addition of the KH-550 silane coupling agent.
2.4 The effect of calcium sulfate whiskers mixed with other fillers on adhesive bond strength
Whiskers fibers and many particle fillers have the effect of reinforcing the resin, but the reinforcing mechanism of the two is not the same. The reinforcing effect of whisker fiber is that the fiber itself plays a load-bearing role, and the particle itself does not play a load-bearing role, and its reinforcing effect is to prevent the dislocation ability of the base molecule. Therefore, if the fibers and particles are mixed in an appropriate ratio as a resin filler, the reinforcing effects of the two are often combined to achieve more satisfactory results. Table 4 shows the bond strength of epoxy adhesives formulated with calcium sulfate whiskers and quartz powder. Comparing the results in Table 4 with the test results in the preceding tables, it can be seen that the tensile strength and shear strength of the epoxy adhesive formulated with the mixed fillers are significantly improved. And after the modification of the coupling agent, the increase is greater.
2.5 Apparent properties of epoxy adhesives formulated with calcium sulfate whiskers
In the test process of using various fillers to prepare epoxy adhesives, it can be clearly observed that epoxy adhesives prepared with calcium sulfate whiskers as a filler have good dispersibility, high thixotropy, no flow, and a cured surface. Smooth, no white flowers appear. In addition, due to the high temperature performance of the calcium sulfate whiskers, the temperature resistance of the epoxy adhesives formulated therewith is also correspondingly improved.
3 conclusions
(1) Compared with currently used fillers, epoxy adhesives formulated with calcium sulphate whiskers modified with silane coupling agents can increase the tensile strength by 50% to 120%, and the shear strength can be relatively increased. 40% to 140%, the effect is very obvious.
(2) Mixing calcium sulfate whiskers with other particle fillers for the preparation of epoxy adhesives is more effective. If the modified calcium sulfate whisker and quartz powder are mixed as a filler, the tensile strength and shear strength of the formulated epoxy adhesive can be increased by 17% compared to using only a single modified calcium sulfate whisker as a filler. 7%.
(3) The epoxy adhesive formulated with calcium sulfate whiskers has good appearance characteristics and high cost performance.
(4) Calcium sulphate whisker is an excellent filler with enhanced, toughened, heat-resistant and high thixotropic properties. The use of calcium sulfate whiskers to formulate epoxy adhesives can greatly improve the performance of the adhesives and have broad application prospects. At the same time, it has opened up new ways for deep processing of gypsum mines.