The compatibility of insulating glass silicone structural sealant and butyl sealant.

1. The preface

Sealant is a material with adhesiveness and cohesion required for sealing joints in glass construction projects. Silicone structural sealant is a must-use bonding and sealing material for glass curtain walls. It plays the role of bearing and transmitting static and dynamic loads between components, especially for fully hidden frame insulating glass curtain walls. All the loads are borne by the structural adhesive. Butyl sealant is currently one of the four sealants with the largest consumption and the widest application range. It is made of isobutylene polymers and processed by special processes from butyl sealants. It is widely used as the first sealant sealing for insulating glass. When sealants come into contact with other materials, they should not react deleteriously with each other. In actual engineering, in order not to affect the quality and durability of the silicone structural sealant itself, as well as the safety of the insulating glass curtain wall and the life of the assembly system, double-channel sealing, especially the use of automatic insulating glass butyl sealant coating machine equipment for double-channel sealing consistency test must be carried out before sealing. If the structural sealant is in contact with butyl sealant, if it is incompatible, the sealing performance of the insulating glass will be reduced, the molecular migration will produce chemical fog, the butyl sealant will flow, and the insulating glass will fail.

The commonly used test method for the compatibility of butyl sealant is to apply sealant on the butyl sealant film to make the sealant and butyl sealing fully contact. After the sealant is completely cured, separate the interface between the butyl rubber and the sealant, and observe whether the contact parts are sticky, oily, or softened due to molecular migration. This method is relatively simple and practical, but there is no in-depth study of the changes in the physical and chemical properties of the sealant before and after migration.

This experiment mainly investigates whether the insulating glass sealing materials are compatible when they are in contact with each other and refers to the test method of "compatibility with adjacent contact materials without ultraviolet treatment" in the international industry standard "Test Method for Building Sealants for Structural Assembly", Different types of butyl sealants are used for contact materials, and aging treatment is carried out in several ways with good correlation in practical applications, namely: heat treatment (70°C, 28d), ultraviolet treatment (300W, lamp distance 250mm, 28d), high temperature and high-temperature Wet treatment (60°C, relative humidity 95%, 28d), research and analyze the effects of several treatment methods and butyl sealant types on the bond strength and elongation at break of the structural sealant after aging treatment.

2. The experimental part

2.1 Instruments and equipment

High-temperature test chamber: model KTM-HTG30, temperature accuracy ±0.1 ℃; ultraviolet radiation test chamber: model SZW-3, accuracy: U=0.5 ℃; constant temperature and humidity test chamber: model HS-250, temperature accuracy ±0.2 ℃, relative humidity ± 1%; thermogravimetric analyzer: model TGA/DSC1, temperature accuracy ± 0.25 ℃, a heating rate 0.1 ~ 250 ℃/min; infrared spectrometer: model NicoletiSlO.

2.2 Raw materials

1) Structural sealant: silicone structural adhesives(SI, S2, S3).

Silicone structural adhesives S1 and S3 do not contain alkane plasticizers, and S2 contains alkane plasticizers. The spectrum of S2 is shown in Figure 1. Through the analysis of the infrared spectrum, it can be found that there are obvious absorption peaks at wavelengths of 2960cm^-1, 2925cm^-1, 2855cm^-1, 1458cm^-1, and 1378cm^-1, which are the asymmetric stretching vibration peaks of the C—H bond of CH₃, CH₂ C—H bond asymmetric stretching vibration peak, CH₂ C—H bond symmetric stretching vibration peak, CH₂ deformation vibration or CH₃ asymmetric deformation vibration peak, CH₃ CH₃ C—H bond symmetric deformation vibration peak.

^{Figure 1 Infrared Analysis Spectrum of S2 Silicone Structural Adhesive}

2) Butyl sealants (Bi, Bii, Biii). 

Three kinds of butyl sealants from different manufacturers were used in the experiment, and no alkane-flammable plasticizer was detected in the three kinds of butyl sealants. The infrared spectrum of butyl sealant is shown in Figure 2.

^{Figure 2 Infrared analysis spectrum of butyl sealant}

2.3 Test method

Figure 3 is a schematic diagram of the structure of the structural sealant and butyl sealant tensile adhesion test piece, and also the compatibility experiment between the sealant and the contact material butyl rubber. Prepare 20 test pieces according to Figure 3, one side of each test piece is float glass, and the other side is an anodized aluminum plate. Contact material butyl sealant, every 5 specimens as a group, and then under standard conditions, heat treatment (70C), ultraviolet treatment (300W, lamp distance 250mm), and high temperature and high humidity treatment (60℃, relative humidity 95%) After being placed under the same conditions for 28 days, it was stretched at a test speed of (5.5±0.5) mm/min.

^{Figure 3 Schematic diagram of the structure of the tensile bond test piece}

1. - Substrate 1, non-coated float glass with a width of (40±10) mm and a thickness of not less than 5 mm;
2. - Substrate 2, an anodized aluminum plate with a width of (40±10) mm and a thickness of not less than 3 mm;
3. - Structural sealant, width b, value (12±1) mm; thickness dv, value (12±1) mm; length l1, value (50±3) mm;
4. - Contact materials;
5. - Anti-stick material.

3. Test results and discussion

3.1 Properties of silicone structural adhesive

When the three structural sealants are in contact with no butyl sealant, 10 I-shaped test pieces are prepared. The tensile bond strength and elongation at break after being placed for 28 days under standard conditions and high temperature and high humidity conditions are shown in Table 1. It can be seen from Table 1 that after high temperature and high humidity treatment, the strength of S1 structural adhesive decreased by 12.5%, S3 decreased by 9.4%, and the strength of S2 did not change much; while the elongation at break, S1 and S2 both decreased, and S3 increased by 71%.

Table 1 Test results of structural adhesive strength and elongation at the break without butyl sealant

The thermogravimetric spectra of the three silicone structural adhesives are shown in Figure 4. 

Through thermogravimetric analysis, it can be seen that the quality of S1 and S3 silicone structural adhesives hardly changes before 400°C; while the S2 adhesive with alkane plasticizer detected has a thermal weight loss of 3.6% between 120 and 210°C. According to the international industry standard "Detection method of alkane plasticizer in silicone structural sealant" and the interpretation of its standard, it can be known that alkane plasticizer can be tested by thermogravimetric analysis (heated to 200°C, kept for 5min) and thermal weight loss Method (heating to 250°C) to measure its content, it is speculated that the small molecule alkane plasticizer can be completely volatilized between 200°C and 250°C. This thermogravimetric analysis is based on the test method in the international industry standard "Insulating Glass Elastic Sealant for Building Doors, Windows and Curtain Walls", and the heating rate is 10C/min (when the content of alkane-flammable plasticizer in the sealant is greater than 3%, whether the This thermogravimetric analysis method to estimate the plasticizer content needs to be further verified).

^{Figure 4 Thermogravimetric analysis spectrum of silicone structural adhesive}

3.2 The effect of butyl sealant Bi on the performance of silicone structural adhesive 

In addition to its factors, the tensile bond strength of silicone structural sealants is also affected by many factors, such as temperature, humidity, and ultraviolet light. To accurately reflect the guiding significance of the test results for actual production, the experiments were conducted under standard conditions, heat treatment (70°C), ultraviolet light treatment (300W, lamp distance 250mm), high temperature and high humidity treatment (60°C, relative humidity 95%) and other conditions. Curing, to study the effects of several treatment conditions and contact material butyl sealant types on the bond strength and elongation at break of structural sealants. Butyl sealant Bi was selected as the contact material for the test, and the test results are shown in Table 2.

Table 2 The effect of butyl sealant Bi on the performance of silicone structural adhesive

It can be seen from Table 2 that under standard conditions, the contact material butyl sealant has little effect on the bond strength and elongation at the break of the textured sealant; when heat treatment, the strength is improved; when ultraviolet treatment, the strength is the elongation at break varies with the type of sealant; however, high temperature and high humidity treatment directly leads to a decrease in bond strength. For example, the bond strength of the S1 sealant is L14MPa, which is 11% lower than that of the blank test.

3.3 The effect of butyl sealant Bii on the performance of silicone structural adhesive

Butyl sealant Bii was selected as the contact material for the test, and the test results are shown in Table 3.

Table 3 Effect of butyl sealant Bii on the performance of silicone structural adhesive

Table 3 The effect of butyl sealant Bii on the performance of silicone structural adhesive
From the data in Table 3, it can be clearly seen that the S1 structural sealant, under the standard conditions, the finite strength and the fracture strength were 14% lower than those of the blank test, and the elongation at break was 14% lower than that of the blank test. down 13%. S2 structural sealant is covered with butyl sealant as the contact material under standard conditions. The strength and elongation at break do not change much, but after high temperature and high humidity treatment, the elongation at break drops from 29% to 7%. S3 structural sealant, after high temperature and high humidity treatment, the elongation at break increased by 65%.

3.4 The effect of butyl sealant Biii on the performance of silicone structural adhesive

Butyl sealant Biii was selected as the contact material for the test, and the test results are shown in Table 4.

Table 4 Effect of butyl sealant Bi ii on the performance of silicone structural adhesive

It can be seen from Table 4 that for S1 and S3 sealants, under standard conditions, the strength is almost unchanged; when heat treatment and ultraviolet treatment, the strength increases; when high temperature and high humidity treatment, the strength decreases. However, the white color sealant with alkane plasticizer detected, after heat treatment, ultraviolet treatment, high temperature, and high humidity treatment, the strength increased and the elongation decreased.

3.5 Result Analysis

White oil is a kind of mineral oil, also known as liquid paraffin oil, the main component is a mixture of C16 and C31 alkanes, and the molecular chain is mainly composed of C—C bonds; butyl sealant is mainly polyisobutylene (and/or butyl sealant), the molecular chain is dominated by C—C bonds. According to the principle of similar compatibility, white oil has strong solubility to polyisobutylene (and/or butyl sealant). When butyl sealant encounters white oil solvent, it will be swollen and dissolved by white oil. That is to say, structural sealants containing alkane plasticizers will affect the performance of butyl rubber due to molecular migration, and appear sticky, threading, and other phenomena. However, due to the low strength of the butyl sealant itself, it cannot be easily It directly affects the strength of the structural sealant; after high temperature and high humidity treatment, the elongation at break drops sharply. The mechanical properties of structural adhesives containing alkane plasticizers, especially the weather resistance, are very poor. The reason for the sharp drop in elongation of S2 silicone structural adhesives containing alkane plasticizers may be due to the alkane being burnt by high temperature and high humidity. Plasticizer small molecules overflow.

4. The conclusion

1) Different types of butyl sealants have little effect on the strength and elongation at the break of silicone structural sealants.

2) Different treatment methods affect the strength and elongation of structural sealants, but for different silicone adhesives, the effects are also different.

3) Although the silicone structural adhesive S2 contains an alkane plasticizer, this method of adjacent contact with materials cannot fully reflect the migration of small molecules, and needs to be analyzed in conjunction with traditional compatibility test methods.

4) After high-temperature and high-humidity treatment, the strengths of the three structural adhesives all decreased; in terms of elongation at break, both S1 and S2 decreased, while S3 increased significantly.

5) Containing alkane plasticizer silicone structural adhesive S2, after high temperature and high humidity treatment, the elongation at break drops sharply.

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