Posted in Recycle Silicone

Silicone Coating and Silicone Emulsion Recycling

Silicone emulsions are used in both hair and skin care products. The preparation of
stable emulsions results in a silicone oil in a micelle, having a fine particle size. The
preparation of the emulsion requires the use selection of the proper emulsifier pair and more commonly the use of a homogenizer to obtain a stable emulsion.[ 1 ]

When silicone is delivered from a micelle, the energetics of delivery to the substrate is
complicated by: (a) the presence of emulsifiers, (b) the type of emulsifiers, and (c) the
particle size of the silicone. All must be optimized for best performance of the emulsion in the formulation.

Many of the complications of using emulsions for the delivery of silicone to substrates relate to the fact that the silicone is delivered out of a micelle. When surface-active agents are added to water, the first observable effect is that the surface tension at the air water interface drops. As one continues to add surfactant, the critical micelle concentration is reached. At this point micelles are formed. There is an equilibrium between surfactant in the micelle and the surfactant the interface reducing the surface tension. Additionally, the surfactants used have detergency properties. When an emulsion is applied to the skin or hair, the silicone oil is delivered to the substrate that has been wet out by the surfactant at the air water interface. The emulsion breaks and the oil is deposited.

However, the surfactant having emulsification properties re-emulsifies some of the oil. The net result is that silicone ends up both on the substrate, in the wash water. This complex equilibrium results in inefficiency when one uses emulsions.

In addition, emulsions have some inherent shear instability, and freeze thaw instability.
Finally, there are limitations as to the type of additional surfactant that can be added to an
emulsion containing system. If the formulation is shifted too much, the emulsion will break. Care must be exercised in preparing emulsion-based systems. With the proper selection of emulsion and the proper formulation techniques, silicone emulsions can be used in the creation of many emulsions useful in many applications.

These applications include uses as mold release agents, automotive tire gloss compounds, textile softeners, overspray in web offset printing and antifoam compounds.

Dimethicone and dimethiconol emulsions are used commonly in many industrial and personal care applications. All emulsion products comprise (a) water typically at least 40%, (b)silicone (typically 55%) and the remainder surfactant to make an emulsion. The fact that the silicone is contained in an emulsion by necessity requires that the delivery be from a micelle.

Since there is an equilibrium that exists between the silicone on the substrate, like fabric, fiber, metal, rubber, hair or skin, and the silicone in the emulsion, much of the silicone ends up in the wash water. Not only is this very costly and an inefficient use of expensive raw materials, but there are real environmental concerns since the wash water ends up in the sewer. In order to overcome this limitation, silicone surfactants have been developed that provide non-micellular delivery to the substrate.

In pulping, silicone process aids reduce the amount of heat and harsh chemicals required to “cook” the wood chips, which lowers energy and material costs and reduces fiber damage [ 2 ].

Silicone antifoams control foam and improve pulp drainage, which improves process efficiency and reduces bleaching requirements.

Silicone process aids do not contain dibenzodioxin or dibenzofurans and do not form harmful byproducts; they do not add to biological oxygen demand (BOD) in water systems and have proven safe for water treatment operations.

Silicone release coatings give label and tape makers an almost limitless array of substrate, processing, performance, and application options.

Silicone pressure sensitive adhesives adhere reliably to low-energy surfaces. They also withstand extreme temperatures, chemical attack, and long-term exposure to weather and UV light.

Water-based, solvent less, and solvent-reducing silicone formulations help pulp, paper, and label and tape manufacturers worldwide address cost, safety, and environmental protection issues.

Silicone technology for de-inking and micro-“stickies” control make paper recycling easier and more cost effective.

Silicones perform under conditions that would defeat organic (carbon-based) materials, are more effective at lower levels, and provide unique solutions to difficult problems.

Silicone architectural coatings typically last twice as long as acrylic coatings, and silicone building sealants typically last three times as long as urethane sealants.

High-voltage-insulator silicone coatings perform for 10 years or more, while some other protection methods must be reapplied every 18-36 months. Imagine the long-term cost savings of silicone. Adding as little as 1.1¢ worth of silicone to a typical 300-gram hair-conditioning rinse doubles dry combing benefits and increases shine by 20%.

A single silicone paint additive can provide as many as five different performance benefits.

Silicones have been used safely and successfully in personal care products for more than 30 years.

If an organic sealant needs to be cut out and replaced every seven years, the amount of garbage produced and solvents used will be at least three times greater than if a longer-lasting silicone sealant had been used.

Many silicone fluids and elastomers can be recycled.

Silicones help manufacturers eliminate water-wasting process steps and reduce the use of air-polluting solvents.

Silicones help automakers comply with an entire alphabet of environmental laws and regulations ( i.e. RoHS, EPA, CARB LEV (Low-Emission-Vehicle), WEEE, Euro 4, Euro 5, EU law 1999/13/EC and more ).

Silicone Coating Recycling

Belgian recycling specialist RecuLiner has struck up a partnership with Munksjö Group, a Finnish manufacturer of release papers for the pressure sensitive adhesive industry (PSA). Their goal is to develop and promote the recycling of silicone-coated release liners from PSA label end-users into cellulose fibre insulation.[ 3 ]

The fibre used in the thermal and sound insulation of buildings has typically been produced from old newspapers. But silicone-coated release paper material has proved to be an ‘excellent’ substitute material for this purpose, resulting in an even better performing product.

The partnership with Munksjö will promote this new recycling option as part of a program and as a complementary possibility’ to its existing recycling opportunities in paper production. The program was set up and will now ensure free-of-charge collection from many release liner end-users in Belgium, Luxembourg, the Netherlands, France and Germany.

The collaboration with RecuLiner provides a valuable opportunity to increase the number of available recycling options for paper release liners in Europe. It also further broadens the geographical coverage of the recycling program.

Silicone Emulsions Recycling

In the environment, polydimethylsiloxane fluid breaks down into water, carbon dioxide, and minerals already found in the earth’s crust. Silicone emulsions are basically silicone oil, water and an emulsifier. The silicone oil does the lubrication, the water carries the oil and allows for easy dilution of the oil and the emulsifier binds the two together. However, problems can arise in emulsions, the large array of splitting possibilities are shown perfectly in the diagram below:

Taken from: http://www.particlesciences.com/news/technical-briefs/2011/emulsion-stability-and-testing.html

Though there are many technical terms, the origin of all these kinds of splitting are the same. Like milk, Silicone emulsions can ‘go off’ if left in a hot, moist environment. Like milk, Bacteria and fungi can grow that feed on the emulsifier and cause the separation of an emulsion, leading to a ‘lumpy’ consistency.

There are a few precautionary measures that can be taken to ensure that Silicone emulsion doesn’t split:

• Store the container in a cool, dry area
• Do not store diluted material for long periods of time
• Regularly wash out dilution vessels to stop bacteria/fungi carrying over into fresh batches
• Use Allcosil Stabiliser to increase the lifespan of the Silicone Emulsion
• Allcock&Sons Ltd. Company is producing specially formulated products which are tailored-made for the digestion and removal of silicone emulsion as follows [ 4 ]

References:

1. Basic Silicone Chemistry, Anthony O’Lenick, Silicone Spectator, January 2009
2. www.dowcorning.com
3. www.reculiner.com and www.munksjo.com
4. www.allcocks.co.uk