Silicone also known as polysiloxane is a polymer made up of siloxane characterized by a flexible, rubbery texture with chains of oxygen and silicon atoms. This unique polymer can be a key component used in:
What Is Silicone Made Of?
Silicone, being a versatile polymer, finds application in various forms:
Silica, a prevalent form of sand, serves as the primary constituent of silicone.
How is Silicone Produced?
Let’s delve into the step-by-step process of silicone production:
Step 1: Isolate Silicon From Silica
Isolating silicon from silica is the first step in producing silicone. To achieve this, a large volume of quartz sand is heated to temperatures as high as 1800 degrees Celsius. Pure silicon is the result. Once it cools, which can be cooled and ground into a fine powder.
Step 2: Combine Powder With Methyl Chloride
The fine silicon powder is combined with methyl chloride. Applying heat triggers a reaction between these components, resulting in the formation of methyl chlorosilane. The methyl chlorosilane mixture comprises various compounds, with dimethyldichlorosilane being the most prominent one. It serves as the primary building block for silicone.
Step 3: Distill the Mixture
To transform dimethyldichlorosilane into silicone, a complex distillation process is employed to separate the different components of methyl chlorosilane. By heating the mixture to specific temperatures, the various chlorosilanes are separated based on their distinct boiling points.
Step 4: Addition of Water
Following the distillation process, the addition of water to dimethyldichlorosilane causes the separation of hydrochloric acid and disilanol. The hydrochloric acid acts as a catalyst, leading to the condensation of disilanol into polydimethylsiloxane.
Step 5: Polymerization of the Silicone
Polydimethylsiloxane contains a siloxane bond, which forms the backbone of silicone. Polymerizing silicone involves different methods depending on the desired properties of the final product
Although the silicone production process may seem complex, it is relatively straightforward and can take place for mass production at a relatively low cost. Therefore, it is unsurprising that versatile silicone has gained popularity as one of the most widely used elastomers in commercial and industrial applications
Silicone Properties
Silicone offers numerous advantages attributed to its polysiloxane composition:
Thermal Stability: Silicone exhibits excellent thermal stability, withstanding temperatures ranging from -80°C to 250°C.
Natural Aging Resistance: It resists natural aging processes such as oxidation and UV degradation.
Fire Resistance: Silicone displays resistance to fire, emitting low levels of smoke and toxic fumes. It possesses self-protective properties and tends to caramelize ashes.
Low Surface Energy: Silicone has a low surface energy, which contributes to its repellent properties.
Good Wetting: It demonstrates good wetting capabilities on various substrates.
Hydrophobia: Silicone exhibits hydrophobic characteristics, resulting in a beading effect when in contact with water.
Release or Adhesion Properties: Silicone can be tailored to provide either release or adhesion properties, depending on the specific requirements.
Exceptional Harmlessness: Silicone is highly safe for a wide range of applications, offering exceptional harmlessness.
Biocompatibility: It is well-suited for food contact and medical applications, demonstrating biocompatibility.
Skin Contact Safety and Comfort: Silicone ensures safe and comfortable contact with the skin.
Flexible Chain: Silicone’s flexible chain structure allows it to maintain lubrication and gas permeability performance even at temperatures as low as -100°C.
Easy Processing: Silicone is easily processed and possesses excellent spreading and coating capabilities.
Versatile Forms: Silicone is available in various forms, including fluids, liquid silicone elastomers (LSR), and high-consistency rubbers (HCR).
Silicone Applications
Silicone materials are highly beneficial for a wide variety of applications. Because of its properties, silicone materials have many advantages, which include the following:
Automotive
Silicone grease finds a common application in the automotive industry as a lubricant for brake components. Its stability at high temperatures is not water-soluble and its low likelihood of fouling makes it an ideal choice
Automotive spark plug wires are insulated by multiple layers of silicone to protect sparks from jumping to adjacent wires, causing misfires, In automotive intake systems, particularly for engines with forced induction, silicone tubing is occasionally employed.
Gaskets in automotive engines, transmissions, and various other applications are manufactured using sheet silicone
However, automotive body manufacturing plants and paint shops steer clear of silicones to avoid trace contamination that may result in the formation of “fish eyes”—small, circular craters that blemish a smooth finish.
Furthermore, silicone compounds like silicone rubber serve as coatings and sealants for airbags. The high strength of silicone rubber makes it an excellent adhesive and sealant for high-impact airbags. The combination of silicones with thermoplastics yields improvements in scratch and mar resistance, as well as a reduced coefficient of friction.
Aerospace
Silicone plays a vital role in the aerospace industry due to its excellent sealing properties, stability in extreme temperature conditions, durability, sound-dampening capabilities, anti-vibration qualities, and inherent flame-retardant properties. Ensuring the utmost functionality is crucial for passenger safety in the aerospace sector, necessitating the use of high-performance materials in every aircraft component.
Specifically engineered silicone grades designed for aerospace applications remain stable within a temperature range of -70 to 220 °C. These grades are employed in constructing gaskets for windows and cabin doors. Aircraft experience significant temperature variations in relatively short periods, transitioning from freezing temperatures at high altitudes to ambient temperatures on the ground, especially in hot countries. Silicone rubber can be molded with precision, ensuring gaskets form airtight seals both in flight, where atmospheric pressure decreases and on the ground.
The heat-resistant properties of silicone rubber make it suitable for gaskets in aircraft engines, surpassing the longevity of other rubber types. This not only enhances aircraft safety but also reduces maintenance costs. Silicone is used to seal instrument panels and electrical systems in the cockpit, safeguarding printed circuit boards from the effects of extreme altitude, such as moisture and extremely low temperatures. Additionally, silicone can be utilized as a protective sheath for wires and electrical components, preventing the infiltration of dust or ice into the inner workings of the aircraft.
Due to the inherent noise and vibration associated with air travel, it is crucial to consider powerful engines, landings, and high speeds to ensure passenger comfort and the safe operation of the aircraft. Silicone rubber, with its exceptional noise reduction and anti-vibration properties, can be formed into small components and fitted into narrow gaps, effectively shielding various equipment from undesirable vibrations. This includes overhead lockers, vent ducts, hatches, entertainment system seals, and LED lighting systems.
Building Construction
Silicone is highly regarded for its strength and reliability in the construction industry. One-part silicone sealants and caulks are commonly utilized to seal gaps, joints, and crevices in buildings. These one-part silicones cure by absorbing moisture from the atmosphere, making installation straightforward. In plumbing, silicone grease is typically applied to O-rings in brass taps and valves to prevent lime from adhering to the metal.
Since 1974, structural silicone has been employed in curtain wall building façades. The Art Institute of Chicago was the first building to utilize this material exclusively for fixing exterior glass, relying solely on silicone. This innovation revolutionized the construction industry. Silicone membranes have also found application in covering and restoring industrial roofs due to their exceptional resistance to UV radiation. These membranes maintain their waterproof performance for decades, making them highly durable.
Coatings
Silicone films have the capability to be applied onto silica-based substrates like glass, creating a covalently bonded hydrophobic coating. These coatings were originally developed for aircraft windshields to repel water and maintain visibility, eliminating the need for mechanical windshield wipers, which are impractical at supersonic speeds. Over time, similar treatments were adapted for the automotive market, with products marketed by Rain-X and other companies.
Silicone can also be used to coat or impregnate many types of fabrics, resulting in a robust and waterproof composite material, such as silnylon.
By utilizing stabilizing surfactants, a silicone polymer can be suspended in water. This property enables the use of water-based formulations to deliver various ingredients that would otherwise require stronger solvents or be too viscous to use effectively. For instance, a waterborne formulation can combine the reactivity and penetration ability of a silane into a mineral-based surface with the water-repellent properties of a siloxane, resulting in a more versatile surface protection product.
Cookware
Silicone, known for its low-taint and non-toxic properties, finds extensive use in applications requiring contact with food. It has become an important material in the cookware industry, particularly in the production of bakeware and kitchen utensils. Silicone serves as an insulator in heat-resistant potholders and similar items, although it conducts heat more effectively than fiber-based products with lower density. Silicone oven mitts, capable of withstanding temperatures up to 260 °C (500 °F), enable safe handling of boiling water and hot surfaces.
Furthermore, silicone is utilized in the creation of molds for chocolate, ice, cookies, muffins, and various other food items. It is also used to make non-stick bakeware and reusable mats for baking sheets. In addition, silicone finds application in steamers, egg boilers or poachers, cookware lids, pot holders, trivets, and kitchen mats, showcasing its versatility in the culinary realm.
Defoaming
Silicones are employed as active ingredients in defoamers, primarily because of their excellent spreading properties and low solubility in water.
Electronics
Silicone is employed in the electronic industry for the encapsulation process known as “potting,” which involves encasing electronic components to enhance their stability against mechanical and electrical shock, radiation, and vibration. This technique is particularly crucial in demanding environmental conditions, such as space technology utilized in satellites. When a wide operating temperature range (-65 to 315 °C) is required, silicones are chosen over polyurethane or epoxy encapsulation. Silicones offer several advantages, including little exothermic heat generation during curing, low toxicity, excellent electrical properties, and high purity.
Silicones are frequently incorporated into thermal pastes, which are used to improve heat transfer from power-dissipating electronic components to heat sinks, enhancing overall thermal management.
However, the use of silicones in electronics does come with certain challenges. They can be relatively expensive and susceptible to attack by certain solvents. Silicone has the tendency to migrate onto other components either as a liquid or vapor. This migration can lead to issues such as silicone contamination of electrical switch contacts, causing an increase in contact resistance and potentially leading to failures, often occurring later in the life of the contract after testing has been completed. It’s important to note that the use of silicone-based spray products during maintenance or repairs of electronic devices can contribute to future failures.
Jewelry
Silicone has gained popularity as a modern alternative to traditional metals, particularly in the form of rings. Silicone rings are commonly favored in professions where wearing metal rings can pose risks such as electrical conduction and ring avulsions, which can cause severe injuries. In the mid-2010s, the trend of wearing silicone rings as an alternative gained traction among professional athletes, who began sporting them during games as a practical and safer option.
Lubricants
Silicone greases serve numerous purposes, including lubricating bicycle chains, airsoft gun parts, and various other mechanisms. Usually, a dry-set lubricant is applied with a solvent carrier to penetrate the mechanism. The solvent subsequently evaporates, leaving behind a clear film that provides lubrication while minimizing the accumulation of dirt and grit compared to oil-based or other conventional “wet” lubricants.
Additionally, silicone personal lubricants are available for use in medical procedures or sexual activities
Medicine and cosmetic surgery
Silicone finds extensive use in various applications requiring high biocompatibility, such as microfluidics, seals, gaskets, and shrouds. In the medical field, the gel form is used in, bandages, dressings, breast implants, testicle implants, pectoral implants, contact lenses, and other medical devices.
Scar treatment sheets often employ medical-grade silicone due to its exceptional durability and biocompatibility. Specifically, polydimethylsiloxane (PDMS) is commonly used for this purpose. Its unique crosslinking properties result in a flexible, soft silicone material that exhibits high durability and adhesive properties. PDMS has also been utilized as the hydrophobic component in synthetic block copolymers, forming the vesicle membrane of polymersomes.
In ophthalmology, various silicone-based products are utilized. Silicone oil is used as a replacement for the vitreous humor following vitrectomy. Silicone intraocular lenses are employed after cataract extraction. Silicone tubes are used to maintain an open nasolacrimal passage after dacryocystorhinostomy. Canalicular stents are used for canalicular stenosis. Punctual plugs are utilized for punctual occlusion in cases of dry eyes.
Molding
Two-part silicone systems are commonly utilized as rubber molds for casting resins, foams, rubber, and low-temperature alloys. Silicone molds generally require minimal or no mold release or surface preparation, as most materials do not stick to silicone. In experimental applications, regular one-part silicone can be used to create molds or shape objects. If necessary, common vegetable cooking oils or petroleum jelly can be applied to mating surfaces as mold-release agents.
Silicone cooking molds, commonly used as bakeware, do not need to be coated with cooking oil. Additionally, the flexibility of the rubber allows for easy removal of the baked food from the mold after cooking.
Silicones are suitable for a wide range of applications due to their unmatched flexibility and thermal and environmental stability. For more information, contact A1 Silicones