Effect of silanol fluid (hydroxyl silicone oil) on the peroxide vulcanized silicone rubber

Abstract:silanol fluid (hydroxyl silicone oil) can effectively improve the structure of the compound. With the increase of silanol fluid (hydroxyl silicone oil) dosage, the positive curing time of peroxide curing system increases gradually, the chemical crosslinking density of vulcanizate decreased gradually, the tensile strength first increased and then decreased, the compression permanent distortion first decreased and then increased.The elongation rate and tear strength showed an upward trend，while the hardness showed a downward trend.

Keyword:silanol fluid，hydroxyl silicone oil,silicone rubber,crosslinking density，mechanical properties

The tensile strength of HTV silicone rubber without reinforcing filler is low, only about 0.35 MPa, poor practicability.It is necessary to add reinforcing filler to improve the mechanical properties of silicone rubber. White carbon black has obvious reinforcing effect on silicone rubber. But, hydrophobic type silica is expensive, while hydrophilic type silica exists a large amount of SS & OH on its surface, that causes the silica easy to agglomerate and hard to disperse,the mechanical properties of silicone rubber are affected and the structural effect is produced,the compound hardens and the processing is difficult.

Low viscosity silanol fluid (hydroxyl silicone oil) (hydroxy silicone oil) is used as structural control agent in silicone rubber process.

After the reaction of silanol fluid (hydroxyl silicone oil) and SI & OH on the surface of silica,the non-polar siloxane was grafted on the surface of silica to reduce the polarity of silica surface. According to the principle of similarity compatibility, it can increase the compatibility between silica and non-polar raw rubber,meanwhile it can solve the problem of the silica easy to agglomerate and hard to disperse.

Therefore, the performance of silanol fluid (hydroxyl silicone oil) used in the silicone rubber processing and molding is being widely studied.

The research result show:

With the increase of the amount of silanol fluid (hydroxyl silicone oil),the hardness and tensile strength of silicone rubber decreased gradually,the elongation rate increased;

Characterization by X-ray photoelectron spectroscopy:It is found that the optimal dosage of silanol fuild (hydroxyl silicone oil) is the most effective to eliminate the structural factors of silicone rubber.At this dosage, the compatibility of silica and silicone rubber,the mechanical properties are all good. When the dosage exceeds the optimum value, the silanol fluid (hydroxyl silicone oil) has no positive effect on the silicone rubber compounds,and the mechanical properties is worse;

With the dosage of silanol fluid (hydroxyl silicone oil),the tensile strength and elongation rate of silicone rubber foam are all improved;

The silanol fluid (hydroxyl silicone oil) can delay producing the carboxyl radicals peroxide sulfurizer;

The mixed use of different modifiers has no significant synergistic effect on the dispersion of silica,while silanol fluid (hydroxyl silicone oil) can make silica obtain good dispersion.

High sulfurization activity of peroxide can meet the requirement of the processing of hot air sulfur extrusion,the chemical processing has high curing efficiency and low curing temperature.Therefore, the research and development of high performance peroxide vulcanization silicone rubber, will facilitate the preparation by extrusion of hot air vulcanization and expand the application field.

Experiment:

1.Material:

Methyl vinyl silicone raw rubber: gum 751, molar mass 630000 g/mol, the vinyl group mass fraction 0.21b.

Methyl vinyl silicone raw rubber: gum 759, molar mass 620000 g/mol,  vinyl mass fraction 0.03B.

Fumed silica

Silanol fluid (hydroxyl silicone oil): hydroxyl mass fraction 8%.

Di (2,4-dichlorobenzoyl) peroxide (bis (24): purity 50%

2.Preparation of silicone rubber compound.

3.Sample preparation.

4.Performance test.

5.Result:

Tab 1, Effect of silanol fluid (hydroxyl silicone oil) on the structuralization of silicone rubber compounds

Dosage of silanol fluid/unit	Structuralization times
0	Compound Failded
3	Compound Failded
5	113
7	56
9	3
11	0

Conclusion: The rubber compounds has excellent processing performance as the silanol fluid dosage 9 units and 11 units.

Tab2. Effect of silanol fluid dosage on vulcanization and crosslinking structure of silicone rubber

Item	Silanol fluid dosage/unit
	5	7	9	11
ML/N.m	2.59	1.71	1.53	1.32
MH/N.m	12.98	10.96	9.38	8.85
Tc10 /s	19	20	20	21
Tc90 /s	63	67	77	83
Average molar mass between crosslinking points / g.mol-1	2 609	2 995	3 543	4 106

Conclusion:Low viscosity silanol fluid (low molecular weight hydroxyl silicone oil) can be used as a structure control agent to prevent the structure of the compound, and at the same time, it can also act as a plasticizer.

Silanol fluid (Hydroxyl silicone oil) can effectively adjust the vulcanization and crosslinking structure of silicone rubber.

The average molar mass between the crosslinking points increased with the silanol fluid dosage increasement, indicating that the chemical crosslinking density of silicone rubber decreased. It can be seen that silanol fluid has an inhibitory effect on the general type of Di (2,4-dichlorobenzoyl) peroxide (bis (24).

Tab 3. Effect of silanol fluid (hydroxyl silicone oil) on basic physical properties of silicone rubber.

Item	Silanol fluid dosage/unit
	5	7	9	11
Tensile strength/MPa	8.7	9.5	10.1	8.8
Elongation rate/%	367.5	423.4	483.5	590.6
Tear strength/kN.m—1	10.9	17.3	19.2	22.3
Shore A	67	65	63	60
Compression permanent distortion/%	49.8	44.7	35.6	45.3

Conclusion:Silanol fluid (Hydroxyl silicone oil) can effectively improve the structure of silicone rubber compound, but it can inhibit the curing system of Di (2,4-dichlorobenzoyl) peroxide (bis (24). With the increase of silanol fluid dosage, the tensile strength first increases and then decreases, the compression permanent distortion first decreases and then increases, the elongation rate and the notched tear strength increase, and the hardness presents a downward trend.