Study on accelerated aging test method of the hott

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Research on accelerated aging test method of building curtain wall sealant

Research on accelerated aging test method of building curtain wall sealant

January 1, 2019


in the past 20 years, the sealant industry has experienced rapid development and technological change. On the one hand, there are many sealant products based on new polymers, new curing systems and new formulas; On the other hand, fierce business competition has forced manufacturers to greatly shorten the product development cycle. Some well-known sealant products with the same formula have been sold for more than 20 years, while many new products have not yet withstood the test of Chinese coatings for enough time. Now, if you want to establish a reliable performance evaluation of a new product, you still need to obtain it through long-term outdoor testing and performance evaluation on the project site

in order to shorten the evaluation time, different short-term laboratory aging test methods can be used. These test methods have been successful, but they are also questioned by building regulators due to the lack of direct correlation with the actual service life of products. [1] Therefore, the sealant industry urgently needs a convincing test method to quickly evaluate the performance of products. Laboratory accelerated aging test is the method to evaluate the long-term performance of products in the shortest possible time; However, it is still necessary to integrate these test methods and improve the accuracy of these test methods. People are aware of the importance of improving the long-term use of sealant products. Abroad, RILEM tc139-dbs studied the aging test method of building sealant from 1991 to 2000. This paper will introduce the research and aging test methods

2 development of test method for aging resistance of sealant

during the whole service life of sealant, it is necessary to continuously withstand the mechanical tensile changes of the interface and the impact of environmental aging. The main reasons for the failure of the sealant interface include the cyclic displacement of the interface, sunlight, temperature changes (cold and hot) and the influence of water vapor (water). Of course, sealant also needs to bear the influence of many other factors in the use process, such as dust accumulation, acid rain, cleaning solvent, microbial breeding and compatibility with other building materials. [2] When researching and developing the aging resistance test method of sealant, we must focus on the most important factors that affect the aging of sealant. Therefore, we choose the most important aging influencing factors to test: sunlight radiation, water vapor, latitude and interface displacement. Interface displacement is a major factor affecting the aging of sealant, which affects both during and after the sealant is fully cured

according to different sealant interface types, the sealant should bear different degrees of displacement. And usually it will bear the influence of different displacement forces at the same time, and even there may be forces in three different directions, such as the simultaneous action of shear force, tensile force and compressive force; For different substrate interfaces, the displacement force rate may be different; Therefore, considering the actual operability of the test and the most common force on the sealant interface, the study decided to narrow the scope of the test, and only carry out displacement cyclic tensile test, and this test is only for elastic sealant. The aging resistance test method is: apply the tested sealant between two substrates placed in parallel to make a sample, and the sample curing can choose Static curing (no displacement) or dynamic curing (displacement); Then test the samples according to the set repeated aging cycle test procedure (light, heat and water vapor) and cyclic tensile test procedure

aging test includes 8 weeks of accelerated aging with artificial climate aging instrument. You can choose to add rapid mechanical aging cycle (default: 200 cycles), and then carry out thermal displacement cycle test on the sample according to a certain displacement according to the requirements of is09047[3] (Section 8, week 1), as shown in figure 1. After completing each aging procedure, extend the sample to the required proportion, check the appearance and adhesion of the sample, and record it according to the requirements of IS0/dis11600. The above aging resistance test procedures can be repeated continuously, and the specific test process is shown in Figure 2

the default test parameters and procedures are as follows:

· the default anodic aluminum oxide of the substrate, see is013640 (is01996) [4]

· substrate size - default 75mm × 2mm × 6mm please refer to is08339 (is01984) to report the development of this discipline [5]

· curing condition (a, borc) - default: a see is011600

· artificial light source (xenon arc, fluorescent uva-340lamp) - default: Xenon lamp, see iso4892 -1 -3 (is01998a) [6]

· aging procedure: durability accelerated climate aging, water vapor conditions (spraying or soaking), light source temperature, water vapor temperature, illumination time and water vapor cycle. The default values are xenon lamp/water spray, xenon lamp/water immersion and fluorescent lamp UVA-340/water spray

· rapid aging cycle (optional): including fatigue cycle, mechanical stretching and aging resistance cycle, default: 200 cycles - see JIS and save wood recyclable a l439 (jiscl997); [7]。

· thermomechanical cycle (is09047): mechanical tension and aging resistance cycle - the default value is set in the test program

3 durability aging test results

3.1 research of Oxford Brooke University ()

the initial research was completed by Oxford Brooke University, [8] selected 15 high-performance sealant products from 12 manufacturers, including 5 silicone adhesives, 4 polyurethane adhesives, 3 silicone modified polyether adhesives, 2 polysulfide adhesives and a solvent silicone modified acrylic adhesive. The test base material adopts anodized aluminum oxide specified in is0-disl3640. All samples have been tested for 4 aging cycles. Each aging cycle includes 8 weeks of fluorescent lamp/condensation artificial aging test and 2 is09047 displacement cycles (4 days); After four aging cycle tests, the expected aging effect was not achieved. Therefore, after the fourth aging cycle, it was decided to add 1000 mechanical fatigue tensile cycles (± 25% tensile amplitude, 5 cycles/min). The test results show that it is possible to increase the mechanical fatigue tensile cycle in the future test methods. Figure 3 shows the appearance of the sample after testing

after the first three anti-aging cycles, the surface of silicone adhesive basically has no change. After the fourth anti-aging cycle, some silicone adhesives have a small amount of bonding failure, mainly in the corner of the interface with the highest stress. These silicone adhesives deepened some bond failure in the additional mechanical fatigue test, and different adhesives showed different degrees of damage. Generally speaking, except that the colloid of the dynamically cured sample has slight deformation, there is basically no difference in the performance between the statically cured and dynamically cured samples. The aging resistance test has no obvious effect on the properties of silicone adhesive, and there are no cracks, fine cracks and obvious discoloration

after testing, polyurethane sealant showed great differences. In addition to different compression deformation, a single component polyurethane adhesive showed obvious degradation; Another one component polyurethane adhesive interface has bond failure, discoloration and fine cracks on the surface. The other two-component polyurethane adhesives showed serious discoloration after the first aging cycle, and blisters and cracks appeared after the second cycle. Colloidal cracks eventually led to the complete fracture of the sealant after mechanical aging

silicone modified polyether sealant has not changed much in the first two anti-aging cycles. One sealant has surface cracks after the second cycle, and the other two sealants withstand the test of four anti-aging cycles, with no or only minor bond damage. All silicone modified polyether adhesives failed to bond after mechanical fatigue test. The curing of one component polysulfide adhesive is very slow. After three aging cycles, some parts of the adhesive are still not fully cured. Because these adhesives were not completely cured, these uncured parts evolved into colloidal cracks and completely broke in the second and third cycles

it is obvious that these adhesives cure too slowly to withstand the large and rapid displacement of the curtain wall assembly interface. The two-component polysulfide adhesive performed relatively better, although colloidal cracks also appeared in the second cycle and deepened in the subsequent cycle. Silicone modified acrylic sealant performs better than other modified adhesives. There was no obvious degradation in the first three cycles, and after the fourth cycle, some bonding failure occurred at the edge of the sealant interface; The mechanical fatigue cycle enlarges the bond failure area

in general, the research of Oxford Brooke University confirmed that RILEM's aging cycle test has a significant environmental benefit of 10 points, and the method can distinguish the weather aging resistance and mechanical aging performance of products. The damage type and colloidal surface change in the test process are similar to those in the actual application process. This study confirms that the initial elastic modulus of sealant cannot well represent the long-term performance of sealant. Obviously, it is more important to change the performance after aging (hardening, reverse reaction, etc.). Dynamic curing reduces the aging performance of some products, but improves other properties. The aging degradation effect of aging cycle test on most sealants is slower than expected, and the mechanical fatigue aging performance is significantly increased to meet the requirements of creep endurance (or stress relaxation) test, which deepens the degradation of sealants. Therefore, rilemtcl39.dbs added mechanical fatigue aging as an optional test item to each aging cycle in the final technical recommendation document

3.2 research of Tokyo Institute of Technology (2001)

after RILEM's aging resistance test method research, Japan sealant Industry Association conducted further research. This study was organized by the Tokyo Institute of technology in Yokohama (takana Miyauchi 2002). [9] In this study, 11 kinds of sealants were selected, including 2 kinds of silicone adhesives, 2 kinds of silicone modified polyether adhesives, 2 kinds of polysulfide adhesives, and 2 kinds of polyurethane adhesives - all of which are one-component adhesives and one two-component adhesives; A silicone modified polybutyl adhesive, a two-component cured acrylic adhesive and a one component aqueous acrylic adhesive

the two-component polysulfide adhesive adopts a new isocyanate curing system of polyether/polysulfide copolymer. The sample base material is anodized aluminum oxide according to is0-disl3640, and all samples are primed with primer according to the sealant manufacturer's recommendations. The surfaces of two-component polyurethane adhesive, two-component cured acrylic adhesive and one-component waterborne acrylic adhesive samples were also sprayed with high elastic coatings. All sealant samples shall be cured according to method a[5]. The climate aging test is carried out with the automatic aging instrument of xenon lamp light source, and the anti-aging cycle includes (or does not include) 200 cycles of mechanical fatigue aging

silicone sealant samples have no obvious degradation in the first two aging cycles. The two Silicone Modified Sealants had a certain degree of pulverization in the first anti-aging cycle, but they finally passed three anti-aging cycles. The single component polysulfide adhesive has passed three aging cycles despite moderate chalking and cracking; Without mechanical fatigue cycle test, although there was serious pulverization and cracking, the two-component polysulfide adhesive passed the first two cycles and failed in the third cycle; When the mechanical fatigue cycle test is included, it fails in the second cycle. Whether or not mechanical fatigue cycle test is included, single component

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