How to choose resin for making carbon fiber composite materials

Composite materials are composed of reinforcing fibers and a plastic material. The role of resin in composite materials is very important. The choice of resin determines a series of characteristic process parameters, some mechanical properties and functionality (thermal properties, flammability, Environmental resistance, etc.), resin performance is also a key factor in understanding the mechanical properties of composite materials. When the resin is selected, a series of processes and properties of composite materials are determined naturally.

At present, the application and performance of most carbon fibers require the selection of resin as the carrier. The performance of the resin greatly affects the overall performance of the composite material. Different application environments and requirements need to mix resins with different components. The selected resin Can have a significant impact on your finished project. The choice of molding resin can vary depending on fabric compatibility, service conditions and desired properties of the finished part. When making carbon fiber composites, there are generally three types of thermosetting resins to consider: epoxy, vinyl ester, and polyester. Here is a broad overview of all three, including their features, and what they should be used for.

epoxy resin

For composite parts that require ultimate strength, manufacturers will use epoxy resins. In addition to improving strength properties, epoxies are generally preferred over polyesters and vinyl esters for dimensional stability and increased bonding to other materials.

Advantage:

Epoxy resin, high strength properties, suitable for vacuum infusion applications, easy to handle, medium viscosity

Shortcoming:

Cannot be used on chopped strand mat, is not UV stabilized, must be paired with a topcoat when exposed to UV light

  polyester resin

Polyester resins are the most widely used resins in the composites industry. Polyester resins are less expensive, have some corrosion resistance, and are more forgiving than epoxies. The majority of all fiberglass parts are constructed using polyester resins because they are easy to work with, cure quickly, and are resistant to temperature and catalyst extremes. Fiber Glast comes with two different types of polyester resins, each with their own benefits and uses.

Easy handling, fast wet-out, high thixotropic index (product will not run on vertical surfaces)

Shortcoming:

Lower physical properties compared to more expensive resins

Vinyl ester resin

Vinyl ester resins are considered a blend of polyester and epoxy - meaning their handling characteristics, performance and price often fall between the other two. Notably, of the three, vinyl ester resins will provide the highest corrosion resistance, temperature resistance, and elongation (toughness). Therefore, they are generally used when high durability, thermal stability and corrosion resistance are required.

Advantage:

Vinyl ester resin

-very stable, -corrosion-resistant, heat-resistant

Shortcoming:

- Short shelf life (3 months)

Therefore, it is important to understand the differences between the resins and how they affect the properties of the composite. But all composite materials have common advantages: higher strength, stiffness, lighter weight and better environmental resistance. Each of these characteristics can be made more prominent through the use of complementary resins. To select the most suitable resin, it is first necessary to determine what the main properties required for the composite should be.

1. Supplements to existing features

The most cost-effective way to make lightweight composites is to use unsaturated polyester resins. The resin has relatively good mechanical, electrical and chemical properties and can be used in a range of general applications such as transportation, structural and building profiles.

However, if greater stiffness or strength is required, then epoxy is arguably best. The bond between the epoxy resin and the fibers is strong, which means that higher shear loads can be transferred between the fibers, giving the composite material higher strength values. Combined with the higher fiber content permitted by epoxy resins, composites can be made with excellent strength and high stiffness, which can be further modified for high temperature applications if required.

Alternatively, if the composite needs to be resistant to harsh environments in addition to stiffness, vinyl ester resins may be a better choice. The molecular structure of vinyl esters provides chemical resistance, so if the composites are to be used in marine environments or in industrial applications where acids or bases are present, the use of vinyl esters will improve the performance of the composite.

When producing composite profiles that need to be assembled with screws, the composite material must be strong against cracks and breakage. This can be achieved through structural design, but choosing the right resin can simplify the structure, reduce costs and make the composite suitable for a wider range of applications. For example, polyurethanes are extremely tough compared to unsaturated polyesters, making them ideal for such applications.

2. Add new features

Selecting a resin that complements the most valuable characteristics of the composite will enhance the performance and longevity of the composite. However, taking the time to choose your resin will do you much more than improve existing properties.

Resins can also add entirely new properties to composite products. Resin additives can be added to resins to achieve a range of benefits: from simple improvements in surface finish or color, to more complex enhancements such as UV resistance, antimicrobial, or antiviral properties.

For example, since resins naturally decompose when exposed to sunlight, adding UV absorbers to protect against UV radiation can give composites better performance in brightly lit environments that often lead to embrittlement and disintegration of the material.

Likewise, antimicrobial additives can be mixed into the resin to prevent bacterial or fungal contamination. This is useful for any composite product that involves human manipulation, such as machinery, public transportation, and medical equipment.

3. Other external influences

It is worth noting that in some cases, the addition of resin additives can change the properties of the composite. For example, in some extreme cases, large amounts of flame retardant additives are required in order to function effectively. At this point, the number of fibers in the composite must be reduced, with a corresponding reduction in strength and stiffness.

Resin selection is an important part of the overall composite design and should not be overlooked. The best solution can be created by establishing the most desirable characteristics of composite materials, matching them with suitable resins to improve these characteristics, and taking into account the balance between fibers and resins.