Author: Su Huifang, Zhang Yanhong and Zhang Rongrong
　
Abstract: This paper introduces the current market situation of silicone rubber products in China, tests and characterizes some silicone rubber products, and compares them with white oil rubber. It is found that some silicone rubber products in China have poor thermal stability like white oil filled silicone rubber products, and they will be debonding, cracking and other phenomena after being used for sealing and bonding of hollow glass and building curtain wall It is suggested to select materials carefully.
Key words: silicone rubber products; hydrolysate; thermal stability; service life
Foreword
Condensation silicone rubber products are based on 107 rubber. The traditional production process is to use the intermediate after hydrolysis of dimethyldichlorosilane, such as the mixed ring (DMC) of siloxane separated from the hydrolysate (the term "siloxane" is provided by Encyclopedia of the industry), which is polymerized, degraded, neutralized and debased by over catalyst to obtain 107 silicone rubber meeting the requirements.
In recent years, with the rapid development of the construction industry, 107 rubber, as the raw rubber of silicone rubber products, the demand is also greatly increased, and its market competition is increasingly fierce. In order to reduce the production cost, many manufacturers use dimethyldichlorosilane hydrolysate (hereinafter referred to as hydrolysate) to replace DMC as the raw material to prepare 107 rubber. Compared with the traditional process, the production cost of 107 glue is lower. On the one hand, the price of hydrolysate is relatively low. On the other hand, it reduces the links of cracking and rectification, reduces the cost and energy consumption, so its market price is relatively low. At present, the market competition of silicone rubber products in China is fierce. In order to gain the price advantage in the market competition, some silicone rubber manufacturers choose 107 glue produced by polymerization of this production process as the base glue, and even some manufacturers directly use hydrolysate as the main polymer to prepare silicone rubber products. The production cost is reduced, which makes the price of sealant in the current market drop again.
In this paper, the thermogravimetry and infrared spectrum of silicone rubber products from different manufacturers on the domestic market are tested, and the reasonable suggestions for the selection of silicone rubber products are put forward according to the test results.
1. Current situation of silicone rubber products in China
Two component silica gel samples (labeled as 1 × 3) were prepared from hydrolysate. Several brands of two-component silica hollow glass adhesive and structural adhesive samples (labeled as 2 × 3-5 × 3) were obtained from the market. They were tested and characterized by IR and TGA respectively. IR spectrum analysis: tested by infrared spectrometer of thermo Nicolet company of the United States; TGA: tested by Mettler company of the United States Toledo's thermogravimetric analyzer test.
According to the test method in GB / t31851-2015, a two-component silicone rubber test sample was identified by infrared spectrum and thermogravimetry, and it was found that it contained white oil (marked as white oil filled rubber).
1.1 infrared spectrum analysis of different silicone rubber samples
Carry out infrared test on 1 × 5 × silicone rubber sample, and compare with the infrared spectrum of white oil filled rubber sample, as shown in Figure 1.
Fig. 1 Infrared Spectra of silicone rubber samples and white oil filled rubber samples
It can be seen from Figure 1 that the spectral lines of silicone rubber sample 2 × 5 × and silicone rubber sample 1 × prepared from hydrolysate are very similar, and the main absorption peak patterns are basically the same. At 2962cm-1 is the expansion vibration absorption peak of - CH3, 1259cm-1 is the deformation vibration absorption peak of - CH3, and 1000 ~ 1130cm-1 is the expansion vibration absorption peak of Si-O-Si, indicating that 1 × 5 × silicone rubber sample has a high matching degree It has the same functional group. The infrared spectrum of the white oil filled rubber shows its unique absorption peak. At 2960cm-1, the C-H bond asymmetric stretching vibration peak of CH3, 2924cm-1, 2854cm-1, the C-H bond symmetric stretching vibration peak of CH2, 1466cm-1, the deformation vibration peak of CH2 or the unsymmetrical deformation vibration peak of CH3.
1.2 thermogravimetric analysis of different silicone rubber samples
Take 107 glue and silicone oil produced by traditional domestic process as basic raw materials to produce two-component silicone glue (marked as 0 × 3), conduct thermogravimetric test on 0 × 5 × sample, and the thermogravimetric curve is shown in Figure 2.
It can be seen from Fig. 2 that there is obvious weight loss of 0 × sample above 250 ℃, and the weight loss of phase I will end at about 600 ℃, and the weight loss of phase II will end at about 800 ℃.
Fig. 2 thermal weight loss curve of each silicone adhesive sample
It can be seen from Fig. 2 that the thermal weight loss curve of the sample 2 × 5 × obtained from the commercial silicone rubber is similar to that of the sample 1 × prepared from hydrolysate, which starts to lose weight when the temperature rises to (100-150) ℃, which is far lower than the 250 ℃ of the sample 0 × 0 (the temperature at which the obvious mass loss occurs), indicating that the sample 1 × 5 × contains the substances that are not resistant to temperature, causing it to start to emerge in the low temperature zone of (100-150) ℃ Now the quality loss and thermal stability are poor.
1.3 discussion
From Figure 2, it can be seen that the decomposition temperature of silicone rubber products from some manufacturers on the market is low, which will affect their aging performance, and the mechanical properties will decay too fast in the later stage, resulting in the shortening of the service life of the sealant, which will affect the safety of use in the project.
With the fierce market competition in keto rubber industry, some silicone rubber manufacturers, in order to reduce costs, start with 107 rubber and silicone oil, use 107 rubber prepared from hydrolysate as raw material as the raw rubber of silicone rubber products, and even some manufacturers directly use hydrolysate as the base rubber. The price of the hydrolysate is low. The 107 glue produced with the hydrolysate as raw material is less than the 107 glue produced by the traditional process because of the less equipment loss and the less market price. However, the hydrolysate is a mixture of linear and DMC, and DMC is a mixture of D3, D4, D5, D6 and other cyclosomes. The quality of the hydrolysate is uncontrollable, and the quality of 107 rubber batches prepared with DMC as raw material is quite different. Combined with the thermogravimetric curve of 1 × sample in Figure 2, the temperature range at which it begins to have significant mass loss is (100-150) ℃, far lower than 250 ℃ of 0 × sample. The infrared spectrum of Fig. 1 shows that the spectral lines of the two samples are very similar, and the functional groups are the same. Although the functional group structure of 0 ා and 1 ා samples is the same, the thermal stability of 1 ා sample is obviously poor, just like the milk added with "melamine". Although it is milk in appearance, it is very harmful.
2 Comparison of different silicone rubber samples and white oil filled rubber samples
The thermal weight loss curve of the white oil filled rubber sample measured according to the test method in GB / t31851-2015 is compared with that of the 1 × 5 × sample, as shown in Figure 3.
Fig. 3 thermogravimetric curves of silicone rubber samples and white oil filled rubber samples
From Figure 3, it can be seen that the obvious weight loss of 1 × 3-5 × 3 sample and the white oil filled rubber sample starts to appear when the temperature rises to about 100 ℃, and the mass loss curve in the low temperature area is very similar. The weight loss rate of 1 × 5-5 × samples and white oil filled rubber samples began to increase gradually at about 100 ℃, indicating that their thermal stability is very poor.
With the rapid development of building doors, windows and curtain walls, and the gradual increase of new and super high-rise building doors, windows and curtain walls, the quality requirements of sealant products are higher and higher. For example, the European standard Etag 002 "EU Technical Certification Guide for structural sealant assembly system" clearly points out that the service life of silicone structure is not less than 25 years; The new standard of domestic construction industry, g / t475-2015 silicone structural sealant for building curtain wall and g / t471-2015 insulating glass elastic sealant for building doors and windows curtain wall, clearly put forward 25-year quality assurance requirements; the newly revised gb16776 silicone structural sealant for building also put forward 25-year quality assurance requirements for silicone structural sealant, which will be fully implemented in 2021; GB / t11944 insulating glass puts forward that "the expected service life of insulating glass shall be at least 15 years". However, the thermogravimetric results in Figure 3 show that the decomposition temperature of the sample 2 × 3-5 × 5 is low, which is similar to that of the white oil glue. When it is used, it has the illusion of good extrudability, softness and elasticity. However, their aging resistance is poor. With the passage of time, irreversible volume shrinkage, hardening and cracking will occur, and even debonding will occur. For the sealant and the substrate, the Bonding has a great impact. The service life of these products can not be guaranteed, and can not meet the quality requirements of the current construction industry, which will bring serious quality problems and security risks.
3 conclusion
At present, although the price of some silicone rubber products on the market is low, there is a phenomenon of low thermal decomposition temperature and poor thermal stability like white oil rubber. In the later stage, a series of problems will be exposed, such as hardening, cracking, debonding, etc., poor aging resistance, leading to the early failure of silicone rubber products, unable to guarantee the service life of products, resulting in the leakage of hollow glass Gas, water leakage and other phenomena, the glass plate on the curtain wall of high-rise buildings falling off, bring great security risks. We need to be careful in material selection. Silicone rubber manufacturers should not blindly pursue profit maximization, ignore product quality problems, and bring serious security risks to the society.
References
[1] Ge Qiang, sun Xiaoquan, Lu Ming, Zhu Wenying. The effect of hydrolytic material pretreatment (the term "pretreatment" is provided by the industry Encyclopedia) on the viscosity of 107 silicone rubber [J]. Silicone material, 2015,29 (06): 479-482
[2] Zhao Yanqin. Overview of hydrolysis process of dimethyldichlorosilane [J]. Cleaning world, 2019,35 (06): 74-76 + 78
[3] Ni Zhiyuan. Factors influencing the synthesis of 107 silicone rubber from hydrolysate [J]. Chemical management, 2013 (18): 117
[4] Zheng ruibing, song Xinfeng, Zhu Xiaoying, Li peiguo. Factors influencing the synthesis of 107 silicone rubber from hydrolysate [J]. Silicone material, 2008 (05): 309-310
[5] GB / t31851-2015, test method for alkane plasticizer in silicone structural sealant [S]
*Part of the data in this paper is provided by Zhengzhou Zhongyuan siland Hi Tech Co., Ltd.
[Zhengzhou Zhongyuan silande High Tech Co., Ltd.] recommendation of mainstream products in 2020: · mf895 silicone waterproof sealant · mf889-25 silicone weather sealant · mf889f silicone fire retardant and weather resistant sealant · mf899-25 silicone structural sealant · mf882 silicone hollow glass sealant more products [Zhengzhou Zhongyuan silande High Tech Co., Ltd.] project selection by 2020: · Shenzhen Shenzhen International Convention and Exhibition Center, innovation and scientific research demonstration center of China Architectural Design and Research Institute, R & D building of Zhuhai Xingye new energy industrial park, Changsha meixihu international culture and Art Center, more projects of fortune zone [Zhengzhou Zhongyuan siland Hi Tech Co., Ltd.] recent hot spot: · time bomb?! The application status and selection mistakes of MS glue in China. Products + services + "silande" will create a better future with you! 2020 to build a "quality year" for enterprises, another world first! Zhongyuan silande has helped the world-class aviation hub, the "silande" in Beijing and Shenzhen win the "first choice brand" award! Appear in 2019 Shanghai Exhibition
[purchase the company's products now]
·Online shopping mall: zzzy.51mqw.com
Source: China curtain wall net, please click below to read the original!