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    Home > Coatings News > Paints and Coatings Market > Study on the accelerated anti-aging test method of building curtain wall sealant

    Study on the accelerated anti-aging test method of building curtain wall sealant

    • Last Update: 2020-11-28
    • Source: Internet
    • Author: User
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    1 Introduction:
    the sealant industry has experienced rapid development and technological change over the past two decades. On the one hand, there are many sealant products based on new polymers, new curing systems and new formulations, and on the other hand, fierce commercial competition has forced manufacturers to shorten the product development cycle significantly. Some well-known sealants, the same formula of products have been sold for more than two decades, and many new products have not been tested enough time
    China
    . Establishing reliable performance evaluations for a new product now requires long-term outdoor testing and project site performance evaluations.
    In order to shorten the evaluation time, different short-term laboratory aging testing methods have been used, which have been staically successful, but have been challenged by building coders due to a lack of direct correlation with the actual life of the product. As a result, the sealant industry urgently needs a convincing test method to quickly measure the performance of the product. Laboratory accelerated aging tests are the most likely way to evaluate the long-term performance of a product in the shortest possible time; People are aware of the importance of improving the long-term use of sealant products. Abroad, RILEM TC139-DBS studied the aging testing methods of building sealants between 1991 and 2000. This paper will introduce this research and aging testing methods.
    2 Development of an aging performance test method for sealants
    to continuously withstand mechanical stretching changes in the interface and environmental aging throughout the sealant's life. The main causes of the failure of the sealant interface include the circulation displacement of the interface, sunlight, temperature changes (cold, hot) and the effects of water vapor (water). Of course, sealants also have to withstand many other factors during use, such as dust accumulation, acid rain, cleaning solvents, microbial growth and cellaring with other building materials. In researching and developing sealant aging performance testing methods, we must focus on the most important factors affecting sealant aging, so select the factors considered to be the most important aging factors for testing: sunlight radiation, moisture vapor, latitude and interface displacement. Interface displacement is a major factor affecting sealant aging, both during sealant curing and after complete curing.
    depending on the type of sealant interface, the sealant has to withstand varying degrees of displacement. And usually bear the influence of different displacement forces at the same time, and may even appear three different directions of force, such as shear force, stretch force and compression force at the same time, and for different substrate interfaces, may bear different displacement force rate; This anti-aging test method is: the test sealant will be cast in the middle of two parallelly placed substrates to make a sample, sample maintenance can choose static maintenance (no displacement) or dynamic maintenance (displacement), and then the sample in accordance with the set repeated aging cycle test procedures (light, heat and water vapor) and cycle stretch test procedures for testing.the
    aging test includes 8 weeks of accelerated aging with an artificial climate aging instrument, with the option of a fast mechanical aging cycle (default: 200 cycles), and then a thermal displacement cycle test of the sample according to a certain displacement amount, as required by IS09047 (Section 8, Week 1). After completing each aging procedure, extend the sample to the desired proportion, view the sample appearance, adhesion, and record as required by IS0/DIS11600. The above anti-aging test procedures can be repeated over and over again, and the specific testing process is Shown in Figure 2.
    default test parameters and procedures are as follows:
    . Substrate default anode alumina, see IS013640 (IS01996).
    substrate size - default 75mm×2mm ×6mm see IS08339 (IS01984).
    Maintenance Conditions (A, BorC) - Default: A see IS011600.
    artificial light source (xenon-arc, fluorescent UVA-340lamp) - Default: Xenon lamp, see ISO4892 -1 -3 (IS01998a).
    Aging Program: Durability accelerates climate aging, moisture conditions (spraying or soaking), light source temperature, moisture temperature, light time and water vapor cycle default values are xenon lamp / spray, xenon lamp / water immersion and fluorescent lamp UVA-340 / spray water.
    fast aging cycle (optional): includes fatigue cycle, mechanical stretching and anti-aging cycle, default: 200 cycles - see JIS A l439 (JISCl997);
    Thermal Mechanical Cycle (IS09047): Mechanical stretching and anti-aging cycle - default values as determined by the test program.
    3 Durability Aging Test Results
    3.1 Oxford Brook University Study (1999-2000)
    The original study was conducted by Oxford Brook University, and 12 manufacturers were selected. 15 high-performance sealant products, including 5 silicone gels, 4 polychlorides, 3 silicone modified polyethers, 2 polysulfur gels and a solvent-based silicone modified acrylic gel. The test substrate uses anode alumina as specified by IS0-DISl3640. All samples are tested for 4 aging cycles. Each aging cycle consists of an 8-week fluorescent lamp/condensation artificial aging test and 2 IS09047 displacement cycles (4 days); Therefore, after the 4th aging cycle, it was decided to add 1000 mechanical fatigue stretch cycles (±25% stretch amplitude, 5 cycles per minute). The test results show that the possibility of increasing the
    the machine fatigue stretch cycle in future test methods. Figure 3 shows the appearance of the sample after it has been tested.
    After the first three anti-aging cycles, the surface surface of silicone adhesive is basically unchanged, after the fourth anti-aging cycle, some silicone adhesives appear a small amount of bonding damage, mainly in the highest stress interface corner position. These silicone gums, in the additional mechanical fatigue test to deepen some bonding damage, different glues show different degrees of damage. Generally speaking, with the exception of the dynamic maintenance of the sample collosome has a slight deformation, static maintenance and dynamic maintenance of the sample performance is basically no difference. The anti-aging test had no obvious effect on the performance of silicone gel, and no cracking, fine cracks and obvious color change appeared.
    tested polyurethane sealants make a huge difference. In addition to the different compression deformations, one single component of polyurethane glue has significant degradation, and the other single component polyurethane interface has bonding damage, color changes and fine cracks in the surface. The other two two two-part polyurethanes undergo severe color changes after the first aging cycle, and blisters and cracks appear in the collage after the second cycle. The collage crack eventually caused the sealant to break completely after mechanical aging.
    Silicone modified polyether sealants did not change much in the first two aging cycles, one sealant had surface cracks after the second cycle, and the other two sealants were tested by four aging-resistant cycles with little or no bonding damage. All silicone-modified polyethers failed mechanical fatigue tests. Single-component polysulfurization is very slow, after three anti-aging cycles, there are still some parts of the glue is not fully cured. Since the glue is not fully cured, these un cured parts evolve into colloidal cracks that break completely during the second and third cycles.
    it is clear that these glues are cured too slowly to withstand the large displacement and fast displacement of the curtain wall assembly interface. The two-part polysulfur gel performs relatively well, although collosal cracks also appear in the second cycle and deepen in subsequent cycles. Silicone-modified acrylic sealants perform better than other modified gels. There is no significant degradation in the first three cycles, after the fourth cycle, there is some bonding damage at the edge of the sealant interface, and the mechanical fatigue cycle increases the bonding damage area.
    overall, research from Oxford Brook University confirms that RILEM's anti-aging cycle testing methods distinguish between the product's climate-resistant and mechanical aging properties. The type of damage and collage surface changes in the test process are similar to between the actual application process. This study confirms that the initial elastic mod of the sealant does not represent the long-term performance of the sealant well, and apparently, more importantly, the change in performance after aging (hardening, inverting reaction, etc.). Dynamic maintenance reduces the aging performance of some products, but improves others. Aging-resistant cycle testing produces slower-than-expected aging degradation for most sealants, while mechanical fatigue aging significantly deepens sealant degradation. Therefore, RILEMTCl39. The addition of mechanical fatigue aging as an optional test item in the DBS final technical recommendation document is added to each aging cycle.
    3.2 Tokyo Institute of Technology (2001)
    Further research was carried out by the Japan Sealant Industry Association following the study of RILEM's anti-aging testing methods. The study was conducted by the Tokyo Institute of Technology in Yokohama (Takana and Miyauchi 2002). The study selected 11 sealants, including 2 silicone-modified polyethers, 2 silicone-modified polyethers, 2 polyurethanes - all single-component glues and one two-component glue;
    two-part polysulfur adhesive is a new isocyanate curing system of polyether/polysulfur co-property. The sample substrate is made of anode alumina according to IS0-DISl3640, and all samples are applied with a base coating solution according to the recommendation of the sealant manufacturer. Highly elastic coatings are also sprayed on the surface of two-part polyurethane glue, two-part cured acrylic and single-group water-based acrylic samples. All sealant samples are maintained in accordance with Method A. Climate aging testing is performed with an automatic aging instrument from a xenon light source, and the anti-aging cycle contains (or does not contain) 200 cycles of mechanical fatigue aging.
    silicone sealant samples did not degrade significantly in the first two anti-aging cycles. Both silicone-modified sealants showed a certain degree of powdering in the first anti-aging cycle, but eventually passed through three anti-aging cycles. Despite moderate powdering and cracking, the single-component polysulfurization gel also passed three anti-aging cycles, and when not doing mechanical fatigue cycle testing, despite severe powdering and cracking, the two-component polysulfurization gel passed the first two cycles and failed in the third cycle; and failed in the second cycle when mechanical fatigue cycle testing was included. Whether or not mechanical fatigue cycle testing is included, single-component polyurethane glue passes through three aging-resistant cycles, some powdered, but not significantly cracked, while two-component polyurethane gels are severely powdered and cracked during the first anti-aging cycle, and can pass the first cycle if the surface is coated with paint, but not through the second cycle. Two-component cured acrylics pass three anti-aging cycles, regardless of whether the surface is protected by paint, and water-based acrylics can only pass the second anti-aging cycle without mechanical fatigue testing, regardless of paint protection.
    based on the above test results, the feasibility of this aging-resistant assessment method has been verified, and future studies will focus on verifying the comparative reference between aging-resistant testing and actual outdoor aging.
    4 Summary
    Both studies have validated that THELEM anti-aging testing method can distinguish the anti-aging performance of the product, and the failure and appearance of the test sample are similar to the aging conditions that occur during the actual use of the product, so it is a trusted building sealant accelerated anti-aging evaluation method. In addition, although the sealant products in the two studies are different and difficult to compare directly, it can be seen that the aging effect of using xenon lamp source is significant than that of using fluorescent lamp source aging, and mechanical fatigue cycle can accelerate sealant aging in both studies. Finally, dynamic maintenance can be used to simulate displacement at the beginning of sealant curing.
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