Posted in Recycle Silicone

Silicone Fluids Recycling

Silicones are the “missing link” between organic and inorganic chemistry and have unique properties that other polymers can not match. By changing the size or structure of the silicone molecule or by adding different compounds to it, one can enhance or change the way it behaves. The secret to silicone’s amazing capabilities lies in its flexible Si-O-Si backbone.

Silicones enable the development of electronic devices that are more powerful, more versatile, more cost effective, and easier to use. They make the cars safer, more reliable, and less costly to maintain.
Household appliances manufactured with silicones are more dependable and require less maintenance.
Silicones protect power transmission equipment from environmental damage and help keep the electricity flowing .They enable also address labels to peel off easily and industrial tapes to stick tightly to difficult surfaces [1].

Silicone fluids, also called silicone oils, or simple silicone are sold by their viscosity and range from 0.65 centistokes to 1,000,000 centistokes. If the product is not made by blending two different viscosity fluids the viscosity is related to molecular weight. The viscosity allows for an approximate calculation of the value of “n” in the formula below [2].

Silicone may be adhered to substrate, including fiber, fabric, metal surface, hair and skin by virtue of one or more of the following mechanisms:

(a) Hydrophobicity – When oil is placed into water, it disrupts the hydrogen bonding between the water molecules in the water solution. This disruption is accomplished only
when the energy of mixing is sufficient to break the hydrogen bonds. When the mixing is stopped, the oil is forced out of the water by the re-formation of the hydrogen bonds between water molecules. This phenomenon can be used to deliver of oil to a surface. Silicone fluids are delivered this way.

(b) Ionic Interactions – The charge on the molecule will also have an effect upon the delivery of the oil to the hair or skin. For example, if the oil has a cationic charge on the
molecule, it will form ionic bonds with substrates that contain negative surface charges. The two opposite charges together forms a so-called pair bond.

(c) General Adhesion – If an oil is delivered to the skin or hair penetrates and then polymerizes, there will be an interlocking network of polymer developed. Although not bonded directly to the substrate, this polymer network will adhere to the substrate.

(d) Specific Adhesion – If an oil is delivered to the skin or hair penetrates and then reacts with groups on the hair or skin, there will be a chemical bond between the polymer and
the substrate. This is the strongest and most permanent of the adhesion mechanisms.

Silicone fluids react almost exclusively by mechanism (a). To the extent the other mechanisms may be introduced, the more strongly and efficiently the conditioner can be
delivered to substrate. Organo-functional silicone seek in large part to capitalize on these additional mechanisms to provide through and efficient conditioning for hair and skin.

An Amazing Range of Capabilities

Silicones are a huge group of products that show some very useful traits like stability at high temperatures and resistance to age, sunlight, moisture, temperature extremes, and chemicals. Silicones can take many different forms and perform hundreds of different jobs. They can be hard and brittle, or soft and flexible.

Silicones can be liquids or solids, durable or temporary, can adhere or release. These polymers can be hydrophobic (repel water) or hydrophilic (absorb water).Silicones can make things soft, smooth, and silky or hard, rough, and tacky. They can destroy foam or stabilize it.

Proven Performance

Structural silicone sealants installed in buildings around the world in the 1980s are still performing today.

Approximately half of all makeup, hair and skin care, and underarm products introduced today contain silicone.

Silicone finishes are widely recognized as the best materials for increasing the softness of fabrics and enhancing the way they feel.

Silicone defoamers have been used extensively in pulp washing operations worldwide since the early 1990s.

Virtually any electronic device that is powered by batteries or electric current relies on silicones.

Silicone Fluids Recycling

2.1.A method is provided for recycling and treating the silicon wafer, cutting and polishing processes as follows [3 ] : a dewatered filter cake is mixed with water so that the filter cake is diluted to form a working fluid. The water reacts with silicon in the filter cake to produce silicon dioxide and hydrogen. After the hydrogen is extracted for storage, specific gravity separation takes place via water so that silicon carbide and silicon particles are separated for sorting. Then, solid-liquid separation is performed on the remaining working fluid to separate silicon dioxide (solid) from water and polyetyleneglycole (PEG, liquid), before PEG is separated from water. Thus, the useful silicon particles, silicon carbide, silicon dioxide, and PEG are recycled from the filter cake to reduce the total amount of materials. Moreover, as the side product, hydrogen, is of high commercial value, the method also adds value to recycling.

2.2 Recycling silicon wire-saw slurries: separation of silicon and silicon carbide in a ramp settling tank under an applied electrical field:

The growing demand for silicon solar cells in the global market has greatly increased the amount of silicon sawing produced each year. Recycling Si and SiC from sawing is an economical method to reduce this material. A study [ 4 ] reports the separation of Si and SiC using a ramp settling tank. As they settle in an electrical field, small Si particles with higher negative charges have a longer horizontal displacement than SiC particles in a solution of pH 7, resulting in the separation of Si and SiC. The agreement between experimental results and predicted results shows that the particles traveled a short distance to reach the collection port in the ramp tank. Consequently, the time required for tiny particles to hit the tank bottom decreased, and the interference caused by the dispersion between particles and the fluid motion during settling decreased. In the ramp tank, the highest purities of the collected SiC and Si powders were 95.2 and 7.01 wt%, respectively. Using a ramp tank, the recycling fraction of Si-rich powders (SiC < 15 wt%) reached 22.67% (based on the whole). This fraction is greater than that achieved using rectangular tanks. Implications: Recycling Si and SiC abrasives from the silicon sawing is regarded as an economical solution to reduce the sawing materials. However, the separation of Si and SiC is difficult. Compared with the rectangular tanks, the recycling fraction of Si-rich powders using a ramp tank is greater, and the proposed ramp settling tank is more suitable for industrial applications.

References

1. www.dowcorning.com
2. Basic Silicone Chemistry, Anthony O’Lenick, Silicone Spectator, January 2009
3. Patent application number: 2012031274, Jr-Jung Iang (Changhua City, TW) ,2012-12-13
4. Air Manag Assoc., Tsai TH1, Shih YP, Wu YF. 2013 May;63(5):521-7