synthetic silica in silicone rubber for improved clarity.

by:Keyuan     2020-07-02
Silicon is the most abundant mineral on Earth, and silicon accounts for 25.
7% of the Earth\'s crust is the second most stable atom after oxygen.
The structure of these naturally occurring materials has been shown to enhance the various properties of silica gel (polysiloxane)
But within a very limited range.
In order to provide specific benefits for formulators using uniform morphology, synthetic silicon has been developed.
Precipitated hydrated silicon and smoky silicon are two types of synthetic materials, both of which are composed of Evonik Degussa (Evonik).
Synthetic gas phase silica has been used in silicone rubber composites since at least 1951 to improve various properties. Earl L.
Warrickof Dow first cited the use of silicon, \"produced by a filling process known to have a defined hole volume and heat\" to improve the mechanical properties of silicone rubber (ref. 1).
Due to its unique particle morphology, the gas phase method silica is especially used to control the properties of the flow and improve the properties of tensile strength, tear and wear resistance.
Gas phase silica can also produce translucent or even transparent silicone rubber films due to its fine particle size.
This paper discusses the improvement of the transparency of these silicone rubber films when using specially prepared structures
Modified products such as Aerosil 200 SPfumed silicone for Aerosil 300 SP do not sacrifice performance.
The precipitated hydrated silicon is produced through a solution process and then dried.
Further processing can produce products with specific properties that can be added as powder.
The morphology of these particles is typical of colloidal silicon, and more discrete particles are formed in colloidal silicon.
This limits the enhanced and Rheo-benefit compared to fumed silica.
In 1942, chemistHarry Kloepfer first obtained a gas phase silica process patent in Degussa (ref. 2).
In 1944, the first gas phase method silicone was produced in Rheinland ferden, Germany.
Gas phase method silica is prepared by combustion hydrolysis process, where chlorine Silicon, hydrogen and oxygen are combined in a flame of more than 1,000 [degrees]C.
This creates a very uniform primary silica particle: Si [Cl. sub. 4]+ 2[H. sub. 2]+ [O. sub. 2][right arrow]Si[O. sub. 2]
The 4HCl Evonik engineer is able to control the process to achieve the desired average primary granularity ([PS. sub. 50])
, Usually from 7 nm to 40 nm.
Particle size distribution of silica with high surface area gas phase method, low [PS. sub. 50]
, Narrower than the range of low surface area gas phase method silica.
Primary particles of gas phase silica only exist for a very short period of time, perhaps only in the first meter outside the flame.
At the same time as very pure, the reaction also forms silicon alcohol, Silicon
Oh, on the surface of the particle.
These surface silicone alcohol are critical to the final performance of the gas phase method silica.
The density and structure of these Silicon alcohol determine many properties of the gas phase method silica.
Silanols may exist in the form of free silicon alcohol, silicone group or bridge Silicon alcohol group (figure 1).
After the formation, these primary particles will soon encounter other particles and begin to form a complex network known as Tron (figure 2).
This is due to the chemical and physical interaction of the silicon alcohol on the surface of the particle, as well as the simple fusion when the particle cools.
These aggregated particles determine the morphology of silica and affect its final properties and the properties seen in various applications.
Over time, through the silicon alcohol structure on the surface of the particles, the aggregate of the reunion begins to form.
This can be enhanced through the packaging and storage process.
Even under a small amount of shear, the gathering of these reunions began to break.
Proper dispersion of the gas phase method silica leads to particles closer to the aggregation structure initially formed in the flame tube.
Through surface Silicon alcohol chemistry, various chemical treatments can be applied to affect the performance of gas phase method silica.
The most typical is to give the particles a certain degree of hydrophobic silicon and silicone materials.
This surface chemical learning then affects the final properties of the gas phase method silica to obtain dispersion, drainage, flow and enhancement. [
Figure 1 slightly][
Figure 2:
Since there is no discrete primary particles in the gas phase silica, it is more common to classify these materials by surface area.
Bruna, emit and Taylor developed a common method of measuring this property in 1938, usually the abbreviated BET surface area (ref. 3).
For the gas phase method silicone, which is usually used in the silicone rubber industry, the BETsurface is usually 130 [m. sup. 2]/g to 400 [m. sup. 2]/g.
Fumsil 200 is a commonly used grade of gas phase silica with 200 [m. sup. 2]/G surface area.
Various tests have been determined that there are usually 2. 5 Si-OH groups per [nm. sup. 2]of surface (ref. 4).
This seems to be correct in the typical surface area range.
Figure 3 shows the molecular model of Aerosil 200 where white represents silanol. [
Figure 3 slightly][
Figure 4 slightly]
In this process, it is also possible to produce other metal oxides that burn.
Aluminum, titanium, zinc and zirconium are just a few base metals that may be used.
Each creates a unique attribute enhancement to the formula.
Further treatment of particles may include surface modification with dynaylan silicone products (Evonik)
Or silicone.
The introduction of one of the materials leads to more hydrophobic particles.
Change the way surface chemistry learns to change how particles interact with fluid media that disperse them.
The flow and enhancement performance can then be adjusted depending on the specific fluid properties.
The most commonly used silicone in silicone rubber applications is dynasylan HMDS (
Hexamethyldisilizane).
Another synthetic silica commonly used is made by a solution precipitation process.
Mix sodium \"water glass\" with sulfuric acid to produce silica. [Na. sub. 2]O x 3. 3Si[O. sub. 2]+ [H. sub. 2]S[O. sub. 4][right arrow]Si[O. sub. 2]+ [Na. sub. 2]S[O. sub. 4]+ [H. sub. 2]
O precipitated silica is cleaned and filtered before further processing.
This may be as simple as separating particles by size, or it may include grinding, granulation, or pre-burning.
The PS50 value of the product produced by this method is as high as 7mm down to 3 [micro]m;
BET surface area is 30 [m. sup. 2]/g to 800[m. sup. 2]/g.
This also produces more discrete particles with feweraggregated particles than the gas phase method silica.
The result of this method is that it is easier to disperse the product, but for the gas phase method silica, the viscosity increases and the enhancement performance decreases.
Another synthetic silicone that is commonly used is a plastic silicone.
Similar to precipitated silica, it is also produced by viaa solution method.
\"Grow\" silicate particles by several methods (ref. 5).
Since these particles are formed together, the size distribution of the particles is very narrow.
The shape of a particle is usually spherical with discrete particles.
Since these particles are discrete, they provide less stickiness and less enhancement.
Any change in performance is achieved by the normal filling effect.
The application of gas phase method silica and other gas phase method metal oxides in silicone rubber will affect the performance of gas phase method (
Flow Control)
Enhanced, transparent, electrical insulation and thermal stability.
Proper dispersion of the gas phase method silica includes crushing the reunion into a gathering particle close to uniform.
This will usually maximize the expected benefits of gas-phase silicon.
As mentioned above, silicon with higher specific surface area has more granular distribution of products with lower specific surface area that are more difficult to disperse.
Due to higher surface area and the ability to build networks, these smaller particles are also more effective in many desired properties.
In order to concentrate, the untreated gas phase method silica [m. sup. 2]
/G surface area can significantly improve the collapse (sag)resistance.
This is especially important for RTV.
1 Construction sealant with flow characteristic can be specified.
Figure 4 shows the difference in flow properties (
Anti-collapse or depression)
When 8% w/wAerosil 150 gas phase method silica is added to the formula.
It is also possible to use surface treatment structures-
The modified gas phase method silica can achieve a high load of mechanical enhancement without sacrificing the important flow performance in the molding product.
Figure 5 shows the liquid silicone rubber (LSR)
Formula for treating structures using Aerosil R 8200 fumedsilica, HMDS-
Modified gas phase silica gel.
This combination allows extremely high loads up to 30% w/wfumed silica in some cases.
Most gas phase silicone can be used to enhance silicone rubber products.
The degree of improvement of each type of gas phase method silica is different from the effect on other properties.
This property is affected by surface area, surface treatment, and loading level.
Due to the high purity and low moisture absorption of some surface-treated fumed Silicon, these are excellent options for modifying the electrical insulation properties of silicon cable compounds.
Titanium dioxide by air oxide Ti [Isophase method]O. sub. 2]
In order to improve the thermal stability and high temperature performance of silicone rubber, P25 can be added to silicone rubber.
This is particularly valuable for bakeware products, automotive and aerospace applications.
Finally, a wide range of silicone rubber applications for healthcare, home, sporting goods and food applications require high transparency.
A typical application is baby-
Bottle nipples (figure 6).
High transparency allows to monitor the flow of liquids, especially when it is difficult to see transparent liquids, and to ensure a clean and hygienic surface before use. [
Figure 5 Slightly]Structure-
Evonik has developed a new grade of gas phase silica to enhance the transparent properties of silicone rubber.
As mentioned above, the typical structure of gas phase method silica is random aggregates/aggregates.
Through proprietary processes, Evonik is able to modify the particle morphology and structure to provide a narrower particle size distribution without affecting the average particle size.
These changes allow for easier dispersion of particles, but also slightly lower the thickening effect in the liquid system.
When replacing the gas phase method silica with equal surface area, the final flow properties should be monitored.
This structural modification method provides for the synthesis of silica, where the morphology appears to be between the standard gas phase method silica and the gas phase method silica produced by the sol gel process.
It can be seen that the Coking Gas phase method silica has a more complex aggregation/reunion structure (figure 7).
This is very beneficial when the flow performance is most important.
This also allows to build a higher level of structure after the decentralized step is completed;
This is achieved through the interaction of the silicon alcohol group on the surface. [
Figure 6 slightly][
Figure 7 Slightly]
This kind of structure may also hinder the development of \"water and white\" transparent films.
This forces formulators to choose fumedsilica with high BET surface area, 300 [1 [m. sup. 2]
/G and higher to maximize clarity.
More energy is needed to properly disperse the particles, and it is often necessary to do Silicon treatment, usually heximyl dithiane, to further improve mechanical properties and dispersion.
Colloidal silica produces particles with uniform properties (figure 8).
Since there are no lumps or aggregates, this type of silica does not produce a highly Rheo modification similar to the gas phase method silica, but is more similar to the \"ordinary\" filler.
The lack of aggregate/reunion structure does not provide an enhancement seen with silica in the gas phase method.
The Aerosil SP phase method silica grade has the properties of pyrotechnics and colloidal silicon.
Still manufactured by pyrotechnics, the aggregate/agglomeration structure is changed and the particle size distribution is narrower than the standard grade of similar surface areas (figure 9).
This process also results in a clustered structure that requires less shear force to be applied to achieve an average dispersion.
Since this force is usually fixed, compared to similar surface area materials, this will reduce the time to properly disperse the gas phase method silica of this grade. [
Figure 8:[
Figure 9 omitted
The effect on silicone rubber application the transparency of silicone rubber application can be directly related to the surface area of the gas phase method silica.
Higher surface areas produce better clarity.
This can be seen in Figure 10 as a graphical representation of transparency.
Although better clarity can be obtained with higher surface area particles, dispersion is more difficult.
When the surface area of silica exceeds about 400 [m. sup. 2]
/G, the first-order particles are no longer smooth and are usually inconsistent with the smaller first-order particle size.
In the development of the Aerosil SPfumed silica grade, the goal is to improve clarity without increasing the surface area.
While clarity is the main driver, researchers do not want to sacrifice the mechanical properties of silicone rubber.
With this in mind, the Aerosil 200 SP and Aerosil 300 SP grades have been developed.
In order to get the best definition, choose the gas phase silica with higher specific surface area.
Mechanical properties were not significantly affected when Composite to silicone rubber formulation.
Figure 11 shows changes in tensile strength, tear resistance or hardness. [
Figure 10 slightly][
Figure 11 omitted][
Figure 12:
The improvement in transparency was tested as a reference to the change in the overall color measured using the cie l * a * B * color measurement system.
When the test is defined, a comparison is made with the standard reference ,[DELTA][E. sub. ab]
Records, with higher values, indicate that transparency is better.
When using Aerosil 300 ,[DELTA][E. sub. ab]
To fully improve the six units, the Aerosil 300 SP was identified as 37, while the Aerosil SP was identified as 43.
For most observers, even a change in a unit is sufficient to discern an increase in clarity without visual assistance of this size.
Figure 12 shows a graphical representation of the transparency improvement.
Surface treatment structure
Through structural modification, Silicon alcohol base still exists on the surface.
This allows for chemical surface modification of particles with the usual silicon or polysilicone modification.
It is well known in art that such modifications can improve clarity without the need for compounder for on-site processing.
Aerosil R 812 S fumedsilica begins at 300 [m. sup. 2]
/G specific surface area gas phase method silica and separation with Dynasylan HMDS silicone.
This product is specially developed for the silicone rubber industry.
Based on Aerosil 300 SP gas phase method silica gel, treated with dynaylan HMDS silicone, from [DELTA][E. sub. ab]of 42 to 53.
Conclusion The use of Aerosil SP gas phase method silicone grade can improve the transparency of silicone rubber without sacrificing mechanical properties.
The formulator can use untreated silica, such as aerosil 300 SP, or can choose a surface treatment product based on this new gas phase method silica.
In addition, using this new silicone with Evonik\'s Dynasylan silicon products can improve the transparency of silicone rubber, whether pre-treated or in-situ treated.
This article is based on a paper published at the Rapra technical conference Silicone elasts2016 ,(www. rapra.
Network/conference). References (1. )Earl L. Warrick, U. S.
Patent 2,541,137 in February. 13, 1951. (2. )
Ussa AG (762,723)1942). (3. )S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc. , 60,309 (1938). (4. )
Technical announcement pigment number
The implementation of the \"Basiccharacteristics micro-beads\" win the solid race Company. (5. )R. K.
Iler, silicone Chemistry, John Willie & Sons, New York (1979).
Win the record by Rodney Conn, kaisumah, Jurgen Meyer and Mario Scholz (www. evonik. com)
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