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The Secret to Composite Materials: Epoxy Resin

November 6th, 2017 | by Peter Jacobs
The Secret to Composite Materials: Epoxy Resin


Imagine going down to your local sporting goods store to purchase a new mountain bike. The salesperson who helps you talks about bikes made with composite materials. You have no idea what composite materials are, but you like the fact that they are lightweight and durable at the same time. You purchase that new bike and off you go.

Would you be any less impressed by your purchase if you knew that your bike frame consists mainly of carbon fibers? If you do not know what carbon fibers are, you probably wouldn’t care. On the other hand, a basic understanding of carbon fibers may leave you wondering how your bike frame stays together under so much punishment. In short, it is all about epoxy resin.

Composite materials would not be what they are if it were not for epoxy resin and curing additives. It is epoxy resin that binds composite materials together to provide durability, tensile strength, and rigidity. Without it, carbon fiber sheets would be no more valuable to building a bike than sheets of nylon or cotton fabric.

  • Basics of Epoxy and Resin

Epoxy, in and of itself, is not a single material. Rather, it is a cured end product of epoxy resins. That probably doesn’t help you if you don’t understand what resin is. So, first things first.

Resin is a highly viscous substance that is easily converted into polymers. It can be natural or synthetic, and many things in nature produce their own resin in response to injury. Pine sap is a good example. It is a resin produced by pine trees that promotes the healing in the outer surface of trunks and limbs.

The most important aspect of resins is the ability to convert them into polymers. A polymer is a very large molecule composed of long chains of repeated subunits. These large molecules and long chains make polymers invaluable in the production of synthetic plastics, polystyrene, and other such materials. But polymers are not just synthetic. Human DNA is a biopolymer, as are most of the proteins in our bodies.

With all of that explained, epoxy resin is a synthetic resin that contain epoxide groups. By combining base resins with various hardeners and curatives, manufacturers can take advantage of the cross-linking properties of epoxy to cure a resin into an extremely strong and durable material.

  • Epoxy Resin Composites

The large molecules and chains of epoxy resins are ideal for composite fabricating because they add the strength composite materials would otherwise lack. Again, the example of carbon fiber sheets works very well here. No matter how tightly you wrap carbon fiber sheets around a mold, they will not hold the form of that mold once it is removed. Even if they did, they would not be strong enough to withstand any kind of punishment.

Injecting epoxy resin is the solution. Once the resin impregnates the layers of carbon fiber sheeting, the bonding process begins. Sheets can then be run through a compression machine or vacuum bagging to remove excess epoxy, thereby evenly distributing what remains throughout the carbon fiber sheets. Then it’s off to curing.

During the curing process, applied heat activates the hardeners and curatives to induce the cross-linking process that gives composite materials their strength. By the time the curing process is complete, you have a tough but lightweight finished material.

Whether you understand epoxy resin or not, it is the secret to that composite bike frame that is keeping you from tumbling to the ground. It is the secret to almost all composite materials we use today.

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