Research for adhesion of silicone rubber and fiberglass fabric

Research for adhesion of silicone rubber and fiberglass fabric

Silicone rubber has good resistance of heat, cold, electrical insulation, ozone atmospheric aging, wide range of uses. Meanwhile, compared with other rubber, the strength of silicone rubber is low. Silicone composite fabric, this shortcoming can be improved to meet the needs of some special occasions.

Fiberglass fabric with advantages of high strength, high temperature, low temperature performance. This paper researches the composition of silicone rubber and fiberglass fabric to improve the composite strength, high temperature resistance, low temperature performance.

Silicone rubber is non-polar polymer material, the surface energy is low. If there is no surface modification treatment for fiberglass fabric, the bonding strength of silicone rubber / glass cloth effective composition layer will be not good, so the composition material won’t achieve the desired effect.

Surface modification of fiberglass fabric are coupling method and RFL (resorcinol formaldehyde latex) method. We use different silane coupling agents and resorcinol and other raw materials, optimize the combination of the formation of glue, impregnated glass cloth, silicone rubber vulcanization in the realization of the compound with silicone rubber, and make evaluation of different treatment methods.

Raw materials

Methyl vinyl silicone rubber 110-2; low phenyl silicone rubber 120-1; vinyl triethoxysilane A151, analytical grade; ɣ -aminopropyltriethoxy Base silane, KH-550 industrial products; plain fiberglass fabric, E glass, thickness 2mm .

Surface treatment of fiberglass fabric

First, the fiberglass fabric in the electric oven for high temperature dewaxing, conditions 250 ℃ × 30min; remove the cooling, immersed in the glue, soaked for a certain time out, at 150 ℃ for 10min.

Silicone rubber / fiberglass fabric bonding and composite peel strength determination

Take the surface-treated glass cloth in a hot mold, then put silicone rubber mixing film laying on the fiberglass fabric, in 4.9 Mpa pressure and 165 ± 5 ℃ temperature for 10 mins.

The second-stage vulcanization condition is 150 ℃ ×1h,250℃ × 4h. The 180°peel strength of the silicone rubber and the glass cloth was carried out at a peel speed of 50 mm / min on an electronic tensile tester.

Results and discussion

Determination of surface treatment agent

Fiberglass fabric surface coated with paraffin lubricant in the wiredrawing process, so it will impact the bonding of silicone rubber and fiberglass fabric. Therefore, the fiberglass fabric must be pretreated. Pretreatment methods are chemical treatment such as acetone cleaning and heat treatment. We remove the paraffin lubricant by heating.

Fiberglass fabric surface is easy to absorb moisture and gas, and the action of the surface of the fiberglass fabric with the water molecules can be transmitted through the adsorbed water film, and to form multi-layer adsorption. Water layer thickness is about 100 times the water molecules. The absorption rate of the surface of the fiberglass fabric quickly at a relative humidity of 60% to 70%, only 2 to 3 seconds to complete. So the glass cloth after dewaxing treatment, the further surface modification should be also made.

Experiments show that, the bonding strength between silicone rubber and untreated fiberglass fabric is very low. When the impregnating time was the same, the surface treatment agents A151 and RFL had no obvious effect on the adhesion, while KH550 and A151 and resorcinol coexist with A151, the bonding effect of silicone rubber and glass cloth was good. Different surface treatment agent in Table 1, Table 2.

Table1 The composition of surface treatment agent

Table 2 The composition of RFL

The solid content is 26.9%
Table 3 shows the 180°Peel strength of the glass cloth and the silicone rubber composite treated with different surface treatment agents.
Table 3 The 180°Peel strength of Glass cloth / Vinyl silicone rubber.
It is expected that the A151 hydrolyzate adsorbed on the surface of the glass cloth, and the silanol group can combine with the surface hydroxyl group and the silicone rubber molecule of the white carbon by hydrogen bond or chemical bond, and the vinyl group can participate in the vulcanization of the silicone rubber, so that the peel strength of composite system is increased substantially; but the experiment found that the bonding effect is not obvious. After heat treatment, A151 hydrolyzate is arranged on the surface of glass cloth, forming a multi-molecular layer, while the number of silanol groups favorable for bonding is very little, and due to steric hindrance effect, A151 most of the vinyl of A151 can not participate in the vulcanization of silicone rubber, as shown in Pic 1.
Fiberglass fabric surface
Pic 1 The directional arrangement of A151 Hydrolyzed products
KH550 contains aminopropyl, the glass surface reaction showed greater activity, and amino group can be hydrogen bonded to silicone rubber and black carbon, thereby enhancing the bonding effect. Resorcinol and A151 in aqueous solution in the condensation reaction occurs with oligomers, this oligomer containing phenolic hydroxyl and silanol groups, and act as the “bridge” role between the glass cloth and silicone rubber, so the two materials bonded firmly.

Experiments show that, KH550 and A151 coexist, resorcinol and A151 coexist because of the surface treatment agent of the fiberglass fabric.

Factors affecting peel strength
(1)The type of silicone rubber: Using low-phenyl silicone rubber and surface treatment agent Ⅱ, Ⅳ treated glass fabric to make the complex, its 180°peeling test also occurred partial stripping, resulting in cohesive failure or breaking phenomenon. Peel strength is similar to the data in Table 3. Visible, the type of silicone rubber has little effect on bonding strength.

(2)Impregnating time: Glass cloth in the surface treatment agent II impregnated for different times, almost no impact on the peel strength, shown as Pic 2.
Pic2 Effect of impregnating time on peel strength (low phenyl silicone rubber, surface treatment agent II)
We believe that the silane coupling agent of glass fabric of occurs firstly in physical adsorption, complete with quick speed in short time

(3)The reaction time of resorcinol and A151
The reaction speed of Trialkoxysilane is very quick in the pH = 3~4 aqueous solution, it is hydrolyzed into alkylsilanetriol in 1~30 min, condensed to disiloxane alcohols, trisiloxane alcohols or higher oligomers. A151 and resorcinol coexist in aqueous solution, the hydrolysis and polymerization reaction, generated to phenolic hydroxyl groups and silanol groups of more complex oligomers. Aqueous solution of resorcinol / A151 was allowed to stand for 7 days, and the insoluble precipitate was formed. The glass cloth was prepared by the reaction of resorcinol and A151 at room temperature for 90 min and the solution was immersed for 7 days. The 180° peel strength of the composite was shown in Table 4.
Table 4 Effect of reaction time on peel strength
From Table 4, the reaction time of resorcinol and A151 had no significant effect on the peel strength of silicone rubber / glass cloth, The surface-treating solution was left in the form of gel-like oligomers after long-term storage. But the solution still has the right amount of resorcinol and polysilanol and its reactants. This shows that for the resorcinol / A151 system, the bonding role of silicone rubber and glass cloth is the reaction product of resorcinol and A151, and the bonding effect is almost independent of solution concentration

(4)Immersion in ethanol: Glass cloth was impregnating with the surface treatment agent, the hydrolyzate of the silane coupling agent covers the surface of the glass fiber to form multi-molecular layer. The deposition of the coupling agent on the fiber surface can be divided into three components, component 1 accounts for about 98% of the total, it’s the physical adsorption of silicone hydrolyzate on the surface of the fiber, it can be washed off with water quickly; Component 2 is a chemically adsorbed coupling agent which can be washed off in boiling water for 3 to 4 hours;Component 3 is a polysiloxane or trimer in the glass fiber surface formed multiple bonding products.The complex was soaked in ethanol for 1 hour, and it was considered that all the components 1 were dissolved in ethanol and disappeared from the silicone rubber / glass cloth interface. The comparison of the peel strength of the composites before and after immersion in ethanol is shown in Table 5.
Table 5 Effect of alcohol immersion of 180°peel strength
* is Peel data for the wet-peeled sample which placed after 8 months.

When the composite was soaked in ethanol for 1 hour, the peel strength decreased by 15% ~20%, while the influence of the medium on the peel strength was larger. This indicates that the surface treatment agent adsorbed on the surface of the fiber by physical condition only accounts for 20% of the adhesion of the silicone rubber / glass cloth, and a small amount of the chemical bonding component plays a decisive role in this bonding process.

(5)Second-stage vulcanizing: KH550 / A151, resorcinol / A151 surface treatment system coupling effect is not affected by second-stage silicone rubber vulcanization (shown in Table 3).

(6)Thermal ageing: the peel strength of the composites was not significantly decreased after aging at 100 ℃ for 8 days, and the cohesive failure or glass cloth breakage occurred in the 180 ° peel test after the composite of the glass cloth impregnated with the surface treatment agents II and IV and the silicone rubber. Indicating that silicone rubber / glass cloth composite anti-aging performance.

We studied the surface treatment of glass cloth to improve the bonding of silicone rubber / glass cloth, and the surface treatment effect was evaluated by the 180° peel strength of silicone rubber / glass cloth composite. The results are summarized as follows:
(1)KH550 / A151, resorcinol / A151 are two effective systems of a silicone rubber / glass cloth surface treatment

(2)For the silicone rubber / glass cloth composite, the surface-treating agent component in the form of a chemical bond at the bonding interface is a decisive factor for the bonding.

(3)The surface treatment effect of KH550 / A151 system on glass cloth was not affected by the immersion time, and the surface treatment effect of resorcinol / A151 system was independent of the reaction time.

(4)The above two surface treatment systems are suitable for bonding of glass cloth with vinyl and low phenyl silicone rubber, and the bonding property is good, and the peel strength does not decrease after heat aging (100℃ · 8d) .

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