Epoxy and polyurethane are two types of topcoats that are often used together. The key distinction between epoxy and polyurethane is that the former includes epoxide groups, whereas the latter contains urethane links. In terms of application, the main distinction between epoxy and polyurethane is that epoxy resins can handle moderate temperatures, whereas polyurethanes can tolerate high temperatures.
Epoxy and polyurethane are both polymer substances. A macromolecule that has a lot of numerous small repeating units (monomers) is known as a polymer. These monomers come together to make a polymer after they are combined. The term epoxy is used to refer to epoxy resins with an organized arrangement of epoxy functional groups. Polyurethane is another kind of polymer material that includes urethane connections.
What is Epoxy?
Epoxy resin, also known as epoxy glue, is a type of polyurethane made from epoxy functional groups. It’s a polyurethane with the addition of urethane groups. These polymers can be low- or high-molecular weight polymers with at least two epoxide groups. Epoxy resin production in industry is mostly fueled by petroleum oil. However, other plant-derived resources exist as well.
Epoxy resins can combine with one another via catalysis-induced homopolymerization, resulting in crosslinks. Alternatively, epoxy resins can react with various substances such as polyurethanes and Nylon 6 to form adhesives.
- Amines
- Acids
- Phenols
- Alcohols
- Thiols
These are referred to as co-reactants. The terms hardeners or cures are other names for these co-reactants. As a result, the crosslinking reactions that epoxy resins undergo with these hardeners connotes “curing”. The crosslinking procedure results in the formation of a thermosetting polymer with desirable chemical and mechanical characteristics.
The specific quantity of epoxy groups in the epoxy resin may be calculated using the following method:
- The amount of epoxide groups in an epoxy resin is determined by the ratio between the number of epoxy groups and the material’s weight.
- “mol/kg” is the unit used to measure this quantity. We occasionally refer to this as the “epoxide number.”
Some Common and Important Forms of Epoxy Resins
Bisphenol A Epoxy Resin
Epoxy resins made from epichlorohydrin and bisphenol A are classified as this sort. bisphenol A diglycidyl ethers are the result of a chemical combination involving epichlorohydrin and bisphenol A. If the amount of bisphenol A is increased (compared to epichlorohydrin), it creates high-molecular-weight polymer materials that are linear in character.
Bisphenol F Epoxy Resin
We use bisphenol F instead of bisphenol A here, but the polymer’s formation mechanism is identical to that of the bisphenol A epoxy resin (as previously said).
Novolac Epoxy Resin
When phenols combine with formaldehyde and are glycosylated with epichlorohydrin, they create Novolac epoxy resins. This polymer has excellent chemical and high-temperature resistance, but it is rather inflexible.
Aliphatic Epoxy Resin
Aliphatic alcohols or polyols are glycosylated to generate these polymers. At room temperature, this polymer has a low viscosity.
Gorilla Two-Part Epoxy
Gorilla takes epoxy to a new level—the Gorilla tough level. With its superior solvent and water resistance, Gorilla epoxy adhesive is incredibly strong and durable for household and automotive repairs alike. The easy-to-use syringe keeps the epoxy resin and hardener separate, so it is easy to dispense and won’t harden over time. The two-part, gap-filling formula easily bonds steel, aluminum, glass, wood, ceramic, tile and most plastics. Plus, it Dries in an ideal, crystal-clear finish that makes projects look spotless. Directions: 1. Prepare your work area and the surface: It is recommended to use Gorilla epoxy In a well-ventilated area. Prepare the surface: to improve adhesion, roughen smooth surfaces before gluing. Then clean and dry all surfaces to be bonded. 2. Mixing Gorilla epoxy: remove the black cap. With tip pointing upward, cut or snap the end from tip of the syringes. With the tip still pointing upward, eliminate air and ensure even dispensing by slowly pushing the plunger until both the resin and the hardener are at the tip. Push the plunger to dispense even amounts of resin and hardener onto a clean, disposable, contained surface. Mix the two parts for about 20 seconds, until the mixture is uniform. 3. Application: after mixing is complete, apply Gorilla epoxy within 5 minutes. The epoxy mixture will continue to thicken and the bond strength will decrease the longer you wait to apply. 4. Clamping: to reach maximum bond strength, clamp project together and leave undisturbed. Important cure times: set: 5 minutes to apply and position handling: allow to cure for 30 minutes undisturbed (no weight or handling) final cure: allow 24 hours for load-bearing weight storage: to close, pull plunger slightly back. Wipe tip clean with dry cloth and align notch on tip and cap. Close tightly.
Loctite Epoxy Five Minute Instant Mix
Easy-to-use self-mixing dispenser and precision applicator. High-strength formula bonds wood, metal, tile, ceramic, glass, plastic and more. Final bond is high strength and weather-, water- and solvent-resistant. Sand able and paintable.
J-B Weld 8265S Original Cold-Weld Steel Reinforced Epoxy
J-B Weld is The Original Cold Weld two-part epoxy system that provides strong, lasting repairs to metal and multiple surfaces. Mixed at a ratio of 1:1, it forms a permanent bond with tensile strength of 5020 PSI after curing. At room temperature, J-B Weld sets in 4-6 hours to a dark grey color and fully cures in 15-24 hours. Use On: Household, Automotive, Marine, Plumbing, Crafts, Outdoor Equipment, Agricultural Equipment, Motorcycle, Toys, Boats, Personal Watercraft, In/Outboard Engines and Deck & Hull Accessories.
What is Polyurethane?
Polyurethane, also known as polycarbonate urethane, is a polymer composed of urethane links (carbamate linkages). Polymerization converts isocyanates and polyols to form a polyurethane. Although the term “polyurethane” implies that the polymer consists of urethane monomers, it actually contains urethane linkages instead.
The isocyanates must contain at least two functional groups that enable them to polymerize in order for polyurethanes made from the monomers to have excellent properties. Furthermore, polyols containing at least two hydroxyl groups per molecule are required. The exothermic reaction occurs when the isocyanate (-N=C=O) group combines with the alcohol (-OH) groups to form a urethane linkage ( -NH-C(=O)-O).
Gorilla Original Gorilla Glue, Waterproof Polyurethane Glue
The product that started it all. Original Gorilla Glue built a name for itself with its incredible, industrial holding power and versatility. The water activated polyurethane formula expands into materials to form an incredibly strong bond to virtually anything. Gorilla Glue is a 100% waterproof glue, safe for indoor and outdoor use and strong enough to stand up to the elements. Gorilla Glue’s your solution for almost any project or repair. Sand it, paint it, stain it. Simply stated, it’s the Toughest Glue on Planet Earth. Directions: 1. Prepare and Dampen the Surfaces: All surfaces must be clean, dust free and tight fitting. For shiny surfaces, such as metals, glass and some plastics, roughen up the material to give the glue something to bite into. Lightly dampen one surface with water. We recommend using a damp cloth or spraying with water. Do not saturate the surface. For dense hardwoods, lightly dampen both surfaces prior to gluing. 2. Evenly Apply Gorilla Glue Onto the Dry Surface. Carefully apply onto the dry surface. Do not over apply. We recommend wearing gloves or spreading the glue with a disposable brush. 3. Clamp the Two Surfaces Together Tightly. Make sure the clamping pressure is distributed evenly across the surface. Or, if you don’t have a clamp, use heavy objects or Gorilla Tape to achieve the appropriate clamping pressure. Clamp objects for 1–2 hours. For best results, allow 24 hours to cure.
Franklin 2303 Titebond Polyurethane Glue
Superior waterproof wood glue is ideal for exterior and interior woodworking! Available in five sizes. Stronger, safer, easier to clean up and less expensive than polyurethane glues. Allows eight minutes of open time and has an application temperature as low as 47° F. One hour clamp time! Cleans up with water. Does not foam. Innovative Rockler Gluing Accessories (Sold Separately): Rockler Glue Applicator Set: All your gluing needs in one versatile, easy-to-clean kit! Includes 8 oz. Glue Bottle with Standard Spout, Silicone Brush Applicator, Glue Roller, Mortise Applicator, Funnel, and Centering Attachment. All attachments thread onto Titebond 16 oz. (pint) and 32 oz. (quart) bottles. Rockler Silicone Glue Brush: Finally, a glue brush that you'll never have to throw away! This brush features silicone bristles that are easy to wash with water, and quickly shed dried glue for long-lasting service. Rockler Silicone Mini Glue Brush: Same convenient features as the larger brush, but is easier to use in tight spaces and even features a dropper tip to dispense glue into dowel holes.
Loctite PL Premium Polyurethane Construction Adhesive
Loctite PL Premium Polyurethane Construction Adhesive is a one component, polyurethane based, moisture-curing adhesive. It is VOC compliant and contains no chlorinated solvents or water. Loctite PL Premium provides superior adhesion to most common construction materials. It can be used for interior or exterior projects and is 3X as strong as ordinary construction adhesives. It is also waterproof, paintable and cures even in cold temperatures. Ideal for sub floor installations.
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Pros Of Using Polyurethane In Your Woodworking Projects
There are several advantages to utilizing polyurethane in your projects, including the fact that it provides a non-slip surface. It is also waterproof, so you won’t have to worry about water ruining it.
The flexibility of polyurethane.
Epoxy, while technically tougher and more durable, has proven to last longer because it flexes with an impact and abrades less than polyurethane. Of course, this isn’t always essential, but in some cases (particularly flooring), it is a significant issue.
The resistance to solvents and alkalis
There are also certain chemical reactions that have a lesser effect on polyurethane goods than epoxy ones. Once more, this doesn’t make one superior to the other; rather, it demonstrates that if you want the product to be exposed to solvents and alkalis on a regular basis – such as in an industrial kitchen – you should choose polyurethane.
The speed of curing
In most cases, polyurethane cures faster than epoxy.However, if you’re in a situation where the resin is required for a mission-critical application or you’re on a time constraint, consider the advantages of utilizing polyurethane to get the show back on the road as quickly as possible.
The resistance to temperature extremes
The resorcinol in polyurethane protects it against moisture, UV radiation, and insect damage. It also has the advantage of being more flexible when exposed to temperatures that vary rapidly (or vice versa). This may be particularly crucial for certain applications.
The resistance to scratching
The polyurethane finish is less scratchable than the epoxy finish, to a small degree. It might not be much of an issue in most cases, but it can be.
Pros Of Using Epoxy In Your Woodworking Projects
The advantages of epoxy resin for your projects are numerous, and they include the following:
The price of epoxy.
Epoxy is often somewhat less expensive than polyurethane. We don’t think that price should be the first thing you consider when working on a project, but if everything else is even, you’d be better off choosing something cheaper than something more pricey. However, we must admit that certain brands have pricing tags that are out of line with the overall market trend, so it’s worth double-checking to ensure you’re not overpaying for either type of resin.
The durability of epoxy.
Epoxy bonds are generally considered to be more durable and robust than polyurethane connections. They can also withstand the most amount of compression pressure. This is particularly crucial if you’re using epoxy resin to finish a floor or a surface where you expect large weights to be placed on it on a frequent basis.
The chemical resistance is different.
Epoxy is not better than polyurethane; rather, they are two distinct things. Some chemicals, like sulfuric acid, for example, react less with epoxy than with polyurethane. The resin surface’s intended location – whether or not it is significant depends on the position.
It adheres to a wider range of surfaces.
Epoxy is more willing to attach to a wider range of surfaces than polyurethane. This may or may not be beneficial to epoxy – it all depends on the context.
It resists humidity and moisture.
Epoxy is also immune to most chemicals and UV rays, making it more secure than polyurethane. If the surface is continuously exposed to water, epoxy will last longer than polyurethane.
Cons Of Using Epoxy In Your Woodworking Projects
We’ve seen the advantages of epoxy and polyurethane, so now it’s time to look at the disadvantages. We think there are four things that can go wrong with your projects if you use epoxy.
The longevity of epoxy
Epoxy has a greater resistance to abrasion and UV light than polyurethane, so it is less prone to wear and tear. However, because polyurethane is more flexible, you’ll have to replace an epoxy surface somewhat more frequently than a polyurethane surface. When employing epoxy, this may result in a significant increase in maintenance expenses. This should be taken into account when determining the project budget.
The problems in the food industry
There are numerous food-industry chemicals that aren’t compatible with epoxy resin. In the dairy business, lactic acid (the acid found in milk) reacts badly with epoxy resin. You may avoid difficulties like these by thoroughly investigating the application of an area where epoxy resin will be used before beginning the project. If it’s not appropriate, you can always use polyurethane instead.
The curing time
It’s also worth noting that epoxy takes twice as long to cure as polyurethane on larger jobs. That may be fine if you can lay down the epoxy on a Friday night and there is no activity around the job until Monday morning, but in some cases, the curing time will severely limit productivity. When budgeting for the project, it’s something you should think about.
UV susceptibility
When exposed to UV light, epoxy surfaces tend to deteriorate. This causes the surface to become yellowish. Now, if this is a concern for you – you may purchase UV-resistant epoxy resin, which is slightly more expensive than the resin you would typically use on your projects.
Cons Of Using Polyurethane In Your Woodworking Projects
This isn’t to suggest that polyurethane is without flaws, either. We believe there are four major problems you may encounter when using polyurethane resin on a project:
Higher upfront costs
The most significant disadvantage of working with polyurethane is that it will cost a lot more initially. This does not imply that epoxy needs to be replaced much more frequently, and polyurethane is actually cheaper over extended periods of time, but the initial investment is far greater, which can be a major problem on big jobs.
Humidity resistance
While polyurethane is water-resistant, it isn’t as good at keeping water off as epoxy resin is and, in the long run, if your finished product will spend a lot of time in the rain – you might wish to avoid polyurethane.
Fast set up times
Polyurethane has a short gel time, and working with it is crucial. It’s not a forgiving material to work with.
Experience required
Polyurethane is a relatively easy material to work with, especially on small projects. However, if you want to do anything significant, like refinishing an entire room or building a new wall, you’ll need experience working with the material. It’s difficult to reverse errors on a big scale and they can be quite costly. You may also wish to get help until you’re more comfortable working with polyurethane.
