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Polyurethane Resin vs Polyesther Resin
Polyester and polyurethane resins are the most commonly used casting material available. Polyester resin is most commonly used in the construction of molded reinforced fiber and composite products, so its mechanical properties are reinforced with the fiberglass itself. The polyester resin used in the molding application is a viscous liquid (like honey) requiring the addition of catalysts and accelerators to complete the curing process. Polyester resins are contact products which require no pressure to cure and can be cured from a fluid or solid state.
The advantage of polyester resin is that it is easy to use and is the lowest cost resin among resin products. However, there are a number of critical disadvantages in that the resin without the addition of fiberglass has poor mechanical properties, it’s emission during use in open molds is considered carcinogenic and it has a high and unpredictable shrinkage rate.
Most of us are familiar with polyester resin as it is the binder in fiberglass products – it is the polyester resin that produces the distinct and often oft putting odor of fiberglass.
Polyester resins also lack the same mechanical properties and are less water resistant than polyurethane resins. The flash off of styrene during the curing process causes a fairly large degree of volumetric shrinkage, the full extent of which is often difficult to predict. Styrene emissions are also harmful and may necessitate the institution of specific, often expensive, environmental safety measures balance off ease of use, low cost, and positive physical characteristics.
Polyurethane resin is used in an extremely wide range of production products, such as rubbers to medicines. To understand this material, it is best to have a basic understanding of how polyurethanes are made. Polyurethane resin is considered versatile because it can be used to produce an array of items, from inks to plastics. This is possible because the material can be manipulated to great extremes, which can change its properties from a soft pliable rubber to a very hard and rigid plastic.
In many cases, polyurethane resin is produced in a liquid form and can be poured into molds. When used for this purpose, the material is highly impressionable, which means that the slightest detail, such as a small crack, can be seen in the finished product.
There are many advantages to polyurethane resins. They are commonly noted for their chemical, oil, and grease resistance, and they are typically very good at resisting abrasion and, as such, are not easily torn. This can explain why they are often used to produce synthetic rubbers. Additionally, they can be used to create strong adhesives as well as highly detailed rigid casts.
Polyurethane resins can be formulated to create pliable rubber molds such EnvironMolds MoldQuik and then be made into a hard plastic casting material such as KastEZ Resin or a water clear casting material such as AquaClear Resin. Though polyurethane costs a bit more to manufacture, they have significantly better mechanical properties (stronger and more tear resistant), more importantly the emissions are extremely low when curing, and thus far safer to be around.
In summary, it is recommended that polyester resins be used in fiberglass fabrication and that polyurethane resins be used for general mold making and casting.