Silicones exhibit many useful characteristics, including:
1. Low thermal conductivity.
2. Low chemical reactivity.
3. Low toxicity.
4. Thermal stability (constancy of properties over a wide temperature range of -100 to 250 °C).
5. The ability to repel water and form watertight seals.
6. Does not stick to many substrates, but adheres very well to others, e.g. glass.
7. Does not support microbiological growth.
8. Resistance to oxygen, ozone, and ultraviolet (UV) light. This property has led to widespread use of silicones in the construction industry (e.g. coatings, fire protection, glazing seals) and the automotive industry (external gaskets, external trim).
9. Electrical insulation properties. Because silicone can be formulated to be electrically insulative or conductive, it is suitable for a wide range of electrical applications.
10. High gas permeability: at room temperature (25 °C), the permeability of silicone rubber for such gases as oxygen is approximately 400 times that of butyl rubber, making silicone useful for medical applications in which increased aeration is desired. Consequently, silicone rubbers cannot be used where gas-tight seals are necessary.
Silicones are used in many products. Ullmann's Encyclopedia of Industrial Chemistry lists the following major categories of application: Electrical (e.g., insulation), electronics (e.g., coatings), household (e.g., sealants for cooking apparatus), automobile (e.g., gaskets), office machines (e.g., keyboard pads), medicine/dentistry (e.g., teeth impression molds), textiles/paper (e.g., coatings).
Silicone is used in microfluidics, seals, gaskets, shrouds, and other applications requiring high biocompatibility. Additionally, the gel form is used in bandages and dressings, breast implants, testicle implants, pectoral implants, contact lenses, and a variety of other medical uses.
Scar treatment sheets are often made of medical grade silicone due to its durability and biocompatibility. Polydimethylsiloxane is often used for this purpose, since its specific crosslinking results in a flexible and soft silicone with high durability and tack.
Polyurethanes are used in the manufacture of high-resilience foam seating; rigid foam insulation panels; microcellular foam seals and gaskets; durable elastomeric wheels and tires (such as roller coaster, escalator, shopping cart, elevator, and skateboard wheels); automotive suspension bushings; electrical potting compounds; high performance adhesives; surface coatings and surface sealants; synthetic fibers (e.g., Spandex); carpet underlay; hard-plastic parts (e.g., for electronic instruments); and hoses.
Polyurethane resists corrosion of varieties of acids organic solvents. It is often used in alternative of rubber products in harsh environments alternatives.
Mechanical properties of the polyurethane has great adjustability. By crystallization ratio between of hard segment and soft segment, polyurethane can get different mechanical properties. Therefore, polyurethane products have good wear resistance, heat resistance, sealing, noise, processing, and other excellent performance.
Wide Range of Hardness
The classification of hardness for polyurethane relies on the prepolymer's molecular structure can be manufactured from 20 SHORE A to 85 SHORE D
High Load Bearing Capacity
Polyurethane has a high load capacity in both tension and compression. Polyurethane may undergo a change in shape under a heavy load, but will return to its original shape once the load is removed.
Polyurethanes perform very well when used in high flex fatigue applications. Flexural properties can be isolated allowing for very good elongation and recovery properties.
Abrasion & Impact Resistance
For applications where severe wear prove challenging, polyurethanes are an ideal solution even at low temperatures.
Polyurethanes possess high tear resistance along with high tensile properties.
Resistance to Water, Oil & Grease
Polyurethane's material properties will remain stable (with minimal swelling) in water / oil / grease. Polyether compounds will last many years in subsea applications.
Polyurethanes exhibit good electrical insulating properties.
Strong Bonding Properties
Polyurethane bonds to a wide range of materials during the manufacturing process. These materials include other plastics, metals, and wood. This property makes polyurethane an ideal material for wheels, rollers, and inserts.
Performance in Harsh Environments
Polyurethane is very resistant to temperature extremes, meaning harsh environmental conditions will not cause material degradation.
Mold, Mildew & Fungus Resistance
Most polyether based polyurethanes do not support fungal / mold / mildew growth and are highly suitable for tropical environments and FDA applications. Special additives can also be added to reduce this in polyester materials as well.
Varying color pigments can be added to polyurethane in the manufacturing process. Ultraviolet shielding can be incorporated into the pigment to provide better color stability in outdoor applications.
Economical Manufacturing Process
Polyurethane is often used to manufacture one-off parts, prototypes or high volume production. Size ranges vary from a couple grams to 2000lb parts.
Short Production Lead Times
Compared to conventional thermoplastic materials polyurethane has a relatively short lead time with significantly more economical tooling costs.
Advantages of Polyurethane When Compared to Conventional Materials:
TPE (TPR) Advantages:
TPE materials have the potential to be recyclable since they can be molded, extruded and reused like plastics, but they have typical elastic properties of rubbers which are not recyclable owing to their thermosetting characteristics. TPE also require little or no compounding, with no need to add reinforcing agents, stabilizers or cure systems. Hence, batch-to-batch variations in weighting and metering components are absent, leading to improved consistency in both raw materials and fabricated articles. TPE can be easily colored by most types of dyes. Besides that, it consumes less energy and closer and more economical control of product quality is possible.
TPE (TPR) Processing:
The two most important manufacturing methods with TPE are extrusion and injection molding. Compression molding is seldom, if ever, used. Fabrication via injection molding is extremely rapid and highly economical. Both the equipment and methods normally used for the extrusion or injection molding of a conventional thermoplastic are generally suitable for TPE. TPE can also be processed by blow molding, thermoforming, and heat welding.
TPE (TPR) Applications:
TPE are used where conventional elastomers cannot provide the range of physical properties needed in the product. These materials find large application in the automotive sector and in household appliances sector. For instance copolyester TPEs are used in snowmobile tracks where stiffness and abrasion resistance are at a premium. They are also widely used for catheters where nylon block copolymers offer a range of softness ideal for patients. Thermoplastic silicone and olefin blends are used for extrusion of glass run and dynamic weatherstripping car profiles. Styrene block copolymers are used in shoe soles for their ease of processing, and widely as adhesives. TPE is commonly used to make suspension bushings for automotive performance applications because of its greater resistance to deformation when compared to regular rubber bushings. TPE may also be used in medical devices and sex toys. TPE is also finding more and more uses as an electrical cable jacket and inner insulation. TPE is also used in some headphone cables.