In this series of posts we’ll examine resin additives. Topics covered will be why use them and applications as well as specific additive and filler filler types and their individual Pros & Cons.
Resins are a unique tool for the composite industry in how they bring other materials together, the glue of composites. Which makes the additives that go into them that much more interesting, because the resins additives that go into the resins solve an endless number of problems in the world today. Additives are commonly used to modify resin systems for thickening purposes and enhancing mechanical, thermal, or even electrical properties. Some additives change the mechanical properties of a resin enhancing its ability to suit tasks such as secondary bonding, vertical application, gap filling, blister repair, fileting, fairing, or injecting. Many of these additives work by manipulating the viscosity of a general laminating resin while some add ranging degrees of reinforcement to the resin for structural application. Basically, like using the additive properties as a composite within the resin itself as short reinforcement. Additive characteristics can be engineered to provide better overall parts dependent on the need.
In most composite applications, viscosity of a resin is manipulated or determined by the ratio of resin to a particular filler placed into a mixture. Less filler and more epoxy will yield a lower “runnier” viscosity product. However, as additional filler is added, the epoxy will become thicker, such as seen by certain thixotropic pastes. All of this is dependent on the additive and the resin used. The importance of mixing these additives is not necessarily a perfect ratio mixture but to achieve a particular viscosity or thickness for a needed job or application. Many products available are simply predetermined mixtures of various types of additives marketed for a specific job. However, it can be much cheaper and more feasible to make some of these products rather than buy them outright.
To make things simple, there are a few various viscosities that can achieved to complete a task at hand. Getting the proper consistency, thickness, or viscosity for a job will make it much easier to apply and achieve optimal bonding performance to various substrates. To make thigs easier to reference, well use comparable product consistencies to describe the viscosity.
Ranch Dressing to Honey Consistency: Achieved in buying a thicker resin or by minimal amount of additive such as Fumed Silica or Microbeads. This consistency achieves an easier rolling ability with application to laminating or to small fill holes.
Ketchup Consistency: Slightly thicker for use in bonding flat, horizontal, or like (close) mating surfaces together. Also used in application to fill holes and great for when needing to inject into specific locations using a syringe.
Plaster Consistency: Much thicker in application for bonding to vertical surfaces, like that of a thixotropic resin. This consistency is best utilized for repairs to composite surfaces along vertical walls where a thinner consistency would simply run out. This is also an option for bonding where a minimal surface gap is evident and for bonding various hardware into place and works well with gap filling
Peanut Butter Consistency: With more thickener added, this consistency will hold to vertical surfaces and is widely used for a filling and fairing compound. This consistency is also highly regarded in its ability to achieve bonds to uneven mating surfaces and works well with gap filling.
While many of the selectable additives available may achieve a desired viscosity when mixed with a resin, certain types of additives and even mixtures of multiple additives can be used for optimal performance. The performance of these additives is determined by their size and molecular makeup. From microns, nanometers, millimeters, and beyond, the end uses are fillers or additives are nearly endless.
Next week we’ll begin to look at specific material additives, starting with Fillers & Resin Reinforcements.