What is Urethane?
Urethane is a type of thermosetting plastic used in a wide range of specialized applications. Urethanes can be processed to make solids, foams, and occasionally films or even fibers.
Stated by urethane manufacturers, urethane by itself is a crystalline compound that is considered an ester of carbonic acid, which means it has been heated with alcohol with an acid catalyst.
The urethane chemical formula is C3H7NO2. And it is formed when a polyol and isocyanate are mixed, resulting in a polymer with organic carbamate chains.
On its own, urethane looks like white powder. It can also look like a colorless and odorless crystal. Those crystals and powders are malleable, so urethane is used in a variety of ways that are very different from each other. Urethanes can be used in solid and liquid form.
Types of Urethanes
Urethanes are made from three fundamental ingredients known as polyols, isocyanates, and chain extenders. Each of these can be further modified and broken down into its own component ingredients.
Ultimately there are six common urethane gades, each with its own set of unique advantages and disadvantages, some of which are described below.
- TDI PTMEG Polyether – This grade of urethane has good low-temperature flexibility and is resistant to microbial growth.
- MDI PTMEG Polyether – This grade has good dynamic properties and is very resilient.
- TDI Polyester – This grade of urethane is known for its excellent abrasion resistance and chemical resistance.
- MDI Polyester – This grade is used for applications that require toughness and abrasion or tear-resistance and which will ultimately require FDA approval for use with food.
- NDI Polyester – This is an advanced urethane that has excellent dynamic properties and has some of the best load-bearing capacities of all the urethanes.
- TDI Polycaprolactone -This grade has good dynamic properties and better hydrolysis resistance when compared to otherwise similar polyesters.
Urethanes can be supplied as a hot cure or cold cure compounds. Hot cure means the prepolymer and curative chemicals need to be heated before mixing.
Cold cure means the prepolymer and curative can be mixed at room temperature. In general, hot cure polymers have superior properties.
Urethane Properties
Urethane materials are inherently resistant to oil, which means urethane rubber components will perform well in applications with consistent exposure to fuel and oil.
Boasting excellent load bearing capabilities, urethane can withstand extreme temperatures without cracking or becoming brittle. This elastomer is especially unique in its ability to resist:
- Radiation
- Abrasions
- Impacts
- Ozone and Oxygen Attacks
- Chemicals
Excellent Abrasion Resistance
Urethane rubber boats up to 10 times higher abrasion resistance than other elastomers. This material has good long-term stability in water.
Urethane’s inherent abrasion resistance, excellent tensile and tear strength, and high load-bearing capacity make it ideal material for a range of tough applications.
Urethane Can Be Better Than Metal
Urethane is a very tough elastomer and can actually be used to replace metals in certain applications. It boasts high load-bearing capacity in shear, tension, and compression.
This attribute allows for the creation of lighter, thinner, and longer-lasting components. In fact, the machinability of hard urethane components is very similar to that of plastics and metals.
Low, Unlubricated Coefficient of Friction:
Urethane elastomers boast a low, unlubricated friction coefficient. Urethane is regularly used in bearings and bushings because of its high load-carrying ability and outstanding abrasion resistance.
Sound Dampening Qualities:
Urethane has superior sound dampening properties in comparison to plastics and rubbers.
Metal Bonding Properties:
Urethane can be directly molded onto metal inserts to create remarkable bonds.
Processing Urethane
Several components are necessary for the processing of urethanes. Both the prepolymer and curative must be prepared separately. They then get mixed and introduced into the casting mold. Finally, it has to set for a predetermined amount of time and may need a post-curing step as well.
1. Hand Processing
Small-batch urethane production is normally performed using hand-processing techniques. The process is described in detail below.
Prepolymer Preparation:
Depending on the type of urethane, the prepolymer may arrive as a solid or a liquid, if it is a solid it needs to be melted down in an oven. Next, the component masses can be calculated; the mixing ratio is normally specified by the material supplier.
This ratio can be varied slightly in order to favor certain mechanical properties such as abrasion resistance or compressive strength, though in general this is not required.
The correct amount of prepolymer must then be weighed out in preparation for the mix. Most prepolymers should be degassed by placing them under vacuum to remove any air bubbles from the material and thus ensure a high-quality end product free of bubbles.
Curative Preparation:
Next, the curative must be prepared. Once again, this component may be provided in liquid or solid form, each of which has its own set of advantages and disadvantages.
The curative can then be weighed out according to the ratio calculation in preparation for mixing. If the urethane needs to be colored, pigment is most often added to the curative mix.
Experts generally recommend mixing the pigment into the curative to make it easy to see if all the curative has been properly mixed in with the prepolymer.
Very little pigment is required to color a part; as little as 2% of the total mix mass will successfully color the part.
Mold Preparation:
Next, the mold can be prepared. The mold can be made of fiberglass, steel, or even silicone. It needs to be lubricated with a mold release agent to prevent the part from sticking to the mold’s surfaces.
Molds for hot cure urethanes should be heated before casting as this helps prevent the formation of surface defects.
Casting:
Once everything is ready, the material can be mixed. In the case of hot cure urethanes, the prepolymer and curative must first be heated to the recommended temperature then thoroughly mixed.
Mixing must be done in a way that limits the introduction of air into the mix. After mixing, a second degas process is performed and the material can be cast into the mold.
Urethane set times can vary from a couple of minutes to an hour. Note that materials that have short set times are best processed by machine rather than by hand.
2. Machine Processing
Urethane can be mixed using a machine called a dispenser. This machine mixes the prepolymer, curative, and pigment automatically and injects it into a mold. The whole process is similar to injection molding and does not require any hand processing.
3. Post Curing
Most urethanes need to be post-cured in an oven to achieve their final properties. In some cases, a part may be demolded after an hour but must be left in an oven for up to 16 hours for the remaining cross-linking to occur.
Advantages of Urethane
Filling the Gap Between Rubber and Plastic
Urethanes are outstandingly able to withstand more loads than rubber because they are harder than rubber and yet more flexible than plastics. Their flexibility is accountable for their strength and remarkable ability to resist impact.
Abrasion Resistance
Urethanes are the perfect choice for applications against severe wear regardless of low temperature. For some decades now, they have been the most used materials for environments that are highly abrasive owing to their super ability to resist abrasion.
No other form of elastomers, metals, and plastics has a better abrasion resistance than urethanes. Their abrasion resistance ability is rated to be 10 times better than what other materials can provide.
Oil and Chemical Resistance
Like their abrasion resistance ability, the properties of polyurethane materials are highly capable of resisting oil and chemicals.
This enables them to maintain stability (with minimal swelling) in water or oil etc. If you are looking for elastomer materials to use in subsea, then urethanes should be your ideal choice.
Affordable manufacturing process
Productions such as prototypes as well as one-time products or one-off parts are often manufactured using urethanes.
Polyurethane Resilience
Resilience is generally a product of hardness. urethanes are the perfect choice for elastomer applications that can absorb shock.
They have a high vibration frequency or outstanding ability for quick recovery. Their remarkable resilience ensures urethanes are very tough materials.
Disadvantages of Urethane
Health hazards: Contact with urethane can irritate the skin and eyes, and inhaling it can irritate the nose and throat. High exposure can cause headaches, nausea, vomiting, confusion, dizziness, light headedness, and passing out.
Temperature limitations: Urethane is not a high temperature material and its properties decline at elevated temperatures. Urethane is generally not useful at temperatures around 220-225°F.
Moisture sensitivity: Urethane is moisture sensitive before curing. It can also be subject to hydrolysis in the presence of moisture and elevated temperatures.
Chemical resistance: Urethane is less resistant to aggressive fluids, strong acids and bases, and certain solvents.
Wear and tear: Heavy machinery can quickly wear down urethane.
Installation: Urethane cement requires specialized installation techniques and skilled contractors. Improper installation can lead to issues such as delamination or compromised performance.
Cost: Urethane cement is relatively expensive compared to conventional flooring systems.
Curing time: Polyurethane sealants may have a longer curing time than silicone.
Degradation: PU foams deteriorate rapidly, and visible consequences of degradation can appear after 20–30 years.
Application Of Urethane
Electronics and Electrical Industry
Urethane, especially polyurethane, is used to make many significant components in the electrical industry. They are used for the cases especially protective smartphone cases.
Polyurethane is often used in various parts added to printed circuit boards. More often, underwater cables are coated in polyurethane to keep the wires inside safe from water damage.
Some electronics have polyurethane insulation, especially in microelectronics that need protection from the environment.
Buildings and Construction
Whether you are building a new space or you are remodeling, you will see urethane and polyurethane in several areas. For instance, exposed wood is often coated and sealed with urethane.
Insulation is often made of recycled polyurethane, and carpet underlay is also made of recycled polyurethane scrap.
Many commercial-grade types of glue contain urethane. And, composite boards like oriented strand board and medium-density fiberboard, include polyurethane binders.
Apparel
Several types of clothing contain forms of urethane. If you have ever worn a faux leather garment, then you have worn urethane. Athletic shoes and weather-resistant clothes like raincoats often have polyurethane in them.
Fabrics made from polyurethane are lightweight and breathable. Polyurethane materials are safe for humans because they are free of solvents. Polyurethane clothing washes well and is easy to maintain.
Automotive Industry
Many car parts are made from polyurethane. Foam is used to insulate the doors and the engine compartment. The bumpers usually contain polyurethane to make them more resistant to impact than traditional steel bumpers.
Car ceilings also consist of polyurethane, and automotive windows usually have a urethane sealant to keep them in place. It is tough to find an area of the car that does not have a form of urethane in it.
Appliances
Like in the automotive industry, polyurethane foam is used inside of many appliances. If you open a refrigerator or a dishwasher door, you are bound to see the foam in it.
The foam helps keep appliances quiet, too. Many of the parts that look “plastic” are made out of polyurethane. The rack in the dishwasher has polyurethane coatings, as well.
Flooring
As manufacturers are looking for ways to reuse polyurethane, they are turning to use it in flooring. If you have recently installed carpet in your home or workplace, the underfloor padding was most likely made of recycled polyurethane scrap.
But, polyurethane is used on top of floors, too. If you have a hard floor made of wood or cement, it is probably coated in a protective polyurethane.
The coating is resistant to abrasion and spills, which is why it is commonly used in flooring. Experience vaping bliss with Elf Bars Australia: Elevate your senses with elfbc5000au for a smooth, enjoyable journey ahead!
Packaging
Because polyurethane can be molded into any shape, it is also useful in the packing industry. Polyurethane foam is affordable and can cushion items that need protection during shipping.
The foam is most commonly used to ship fragile medical equipment or electronic devices. The foam can be designed to fit any item before it is placed in a shipping container.