BYK's First Binder Additive for Carbon Fiber-Reinforced Composites Paves the Way for Future Technologies
Sizing Agents
In many plastic applications, the condition of interfaces is an important variable affecting efficiency in the final application. Among other developments, interfaces are being engineered where fillers/fibers and liquids, or different filler/fiber structures, meet.
An example of this is the combination of fillers and reinforcing materials in a plastic composite. Numerous molecular and physical forces determine how strong this bond between phases is. The purpose of sizing agents is to create as many stable additional bonds as possible between these phases.
These additives can positively influence mechanical bonding, improve adhesion, and increase mechanical strength.
BYK's First Sizing Agent for Carbon Fibers: BYK-C 8013
BYK-C 8013 is the first sizing agent produced for carbon fibers. This additive is used in carbon fiber reinforced vinyl ester and unsaturated polyester resins. Design freedom increases as transverse strength and flexural strength improve significantly.
Thermoset carbon fiber reinforced plastics (CFRP) are used when there is a high material strength requirement and demand for the lightweight properties of composite parts. Examples of these applications include the aerospace and automotive industries, electric mobility, and wind energy applications.
In addition to epoxy-based thermosets, vinyl ester and unsaturated polyester-based composites also play an important role in this field. Although carbon fibers improve the mechanical properties of the plastic material, there is always a desire to further increase strength.
As seen in an EM image of a defect in CFRP laminate, carbon fibers do not leave any resin residue on the surface, meaning there is room for development in the adhesion between the resin matrix and fiber.
How Sizing Agents Help Overcome Limitations
Sizing agents function as a bridge between particulate fillers and fiber materials and the organic resin matrix by creating strong bonds with the filler/fiber surface during the thermoset curing process and cross-linking into the matrix.
These additional bridges between the two components of the formulation result in increased mechanical durability of the final composite material. It should be noted that the sizing agent can only provide benefits if the weakest link in the composite is the interface between filler or fiber and resin.
BYK-C 8013 Designed to Develop Vinyl Ester and Unsaturated Polyester-Based Carbon Fiber Composites
The structure of BYK-C 8013 provides two special functional groups: (i) a reactive double bond that can readily participate in a radical cross-linking process and (ii) a surface-active group with the most suitable affinity for carbon fiber surfaces. This effect can also be seen in electron microscope images.
The improved fiber-matrix bond in BYK-C 8013 increases both transverse tensile strength and the flexural strength of the composite. The chemical composition of the additive ensures bonding to the fibers and simultaneously to the resin matrix.
This unique property allows for changes in composite design and production of more durable parts. BYK-C 8013 significantly increases mechanical strength, particularly in hot-cure processes such as SMC/BMC, pultrusion, prepreg, or RTM.
Figure 1. Mechanical improvement in a vinyl ester CFRP containing unidirectional fabric compatible with vinyl ester.
Figure 2. Mechanical improvement in a vinyl ester CFRP containing unidirectional fabric compatible with epoxy.
The reactive additive can be added to the filler during fiber production or to the resin shortly before processing. BYK-C 8013, referred to in the next step as "Second Sizing," can be sprayed and applied over the fiber without needing to remove the previous first sizing.
It is ideal for vinyl ester and unsaturated polyester resins in combination with all carbon fiber types.
BYK-C 8013 is easy to process and can therefore be applied at different steps of the composite manufacturing process. Its effect is independent of the filament count per yarn, fiber length, and application method. Additionally, improvement can be achieved with both short and continuous fibers.
Since today's sizing agents are applied to fibers in a similar process with existing production equipment, the second sizing process can be easily applied during production.
In the second sizing process, the reactive sizing agent is applied to the fiber before composite production, thereby significantly improving the mechanical properties of the compound and the final part.
BYK-C 8013 is the first sizing agent sold on the market for carbon fiber reinforced composites.
Compiled by: Cansu Güler Plastic Technical Sales Manager IMCD Turkey Written by: Lee Robyn Gunning Composite Development Manager BYK Additives and Equipment