Motorsport Composite Fundamentals: Resin Fundamentals Knowledge

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Resin Fundamentals Knowledge

05.54

00:00	Now, that we've discussed the different forms of reinforcement fibres, it makes sense to move on to the matrix material that these fibres are suspended within.
00:08	In almost all high performance composites, or more specifically, the fibre reinforced polymers that are our focus in this course, the matrix is a synthetic resin.
00:18	This resin will initially be in a liquid form and then cure into a solid polymer during construction through a process called polymerisation.
00:27	We aren't going to get too deep into the chemistry because it's not necessary for our practical work, but before we get ahead of ourselves, let's get some of the fundamental knowledge out of the way.
00:37	There are two key types of polymers for our discussions, thermoplastics and thermosets.
00:44	Thermoplastics are the plastic materials most people will be familiar with, like ABS and polypropylene for example.
00:51	These can be melted and reformed, making them great for recycling, but they aren't always heat resistant and strong, meaning they aren't commonly used for high performance composites.
01:02	Instead, we use thermosets, which form chemical bonds when cured, improving their strength and heat resistance, but this also means that they can't be melted down and reformed.
01:13	Instead, if they're exposed to excessive heat, they'll break down and degrade.
01:18	There are a few key thermoset resins we're interested in for the construction of our composites.
01:24	Polyester, vinyl ester, epoxy and polyurethane.
01:28	Each of which we'll cover in the following modules.
01:30	What's important for the construction process is that we have control over when the resin cures, and this ability is engineered into the chemicals.
01:39	While some resins cure from exposure to UV light, heat or pressure, in most cases for our work, another chemical, known as a catalyst or a hardener, will be mixed with the resin just before construction, which starts the reaction, causing the resin to cure.
01:55	This is what's referred to as a two part resin system, where the parts are mixed in varying ratios depending on the formulation.
02:03	It should also be noted that the curing process for the resins we're interested in is exothermic, meaning heat is produced and released.
02:11	This is a very important safety consideration, something that we'll discuss later in the course.
02:16	The term peak exotherm describes the point at which the highest temperature is reached during the reaction.
02:23	This is a key indicator of the curing process and can influence the final properties.
02:28	Too low can mean an incomplete cure, and too high can damage the material, either way leading to reductions in the mechanical properties.
02:36	The time from mixing the catalyst or hardener until the resin is no longer in a usable state in the mixing container is called the pot life.
02:45	What defines the usable state depends on the initial viscosity of the resin.
02:49	Viscosity being the fluid's resistance to flow.
02:52	In simple terms, a high viscosity fluid is thick and flows slowly, whereas a low viscosity fluid is runny and flows quickly.
03:00	For a high viscosity resin, the pot life may be until the viscosity doubles, whereas for a low viscosity resin, the viscosity may quadruple during its pot life.
03:10	Pot life is similar to working time, which is the time the resin remains in a low enough viscosity that it can be easily applied and worked with during the layup.
03:19	In either case, this can be influenced by the ratio of catalyst or hardener to resin, and the ambient temperature, with more catalyst or a higher ambient temperature both speeding up the curing process and therefore reducing the pot life and the working time.
03:34	This is going to be critical to understand for the construction process, and it's also helpful for comparing the curing speeds of different resin offerings.
03:42	Past this, there'll typically be various resin offerings from the supplier that are specially formulated for different construction techniques, such as laminating, infusion, and casting, as well as tool, pattern and mould making, and coatings, all of which we'll be discussing later in the course.
03:59	For example, infusion resin will be of lower viscosity, allowing it to flow through the reinforcement more easily.
04:06	Laminating resin, on the other hand, should be more viscous, allowing the resin to hold its place better during hand layups, and not run too much with gravity and pull in lower areas of the layup.
04:18	The different offerings will also have varying compatibility with different mould types and additives.
04:24	These additives are generally used for a variety of reasons.
04:27	Fillers are used to reduce the cost by replacing some of the more expensive materials with a cheaper option to achieve the same volume.
04:35	For example, tooling resins will often use a filler because the additional weight is no detriment to their performance.
04:42	There's a range of other additives that can be used to improve the manufacturing process, and therefore the final product, but don't worry too much about this for now as we'll be covering these soon.
04:52	It's just important to keep this consideration in mind, and fully understand the supplier's specifications to be sure we're purchasing the right resin for our application, and one that's compatible with the other products that we intend to use.
05:06	Before we move on to discuss specific resin types, let's summarise the key points from this module.
05:12	In high performance composites, we use thermoset resins as our matrix.
05:16	Although they can't be recycled like thermoplastics, their mechanical properties and heat resistance makes them well suited to motorsport applications.
05:24	The resin is mixed with a catalyst or hardener to initiate the curing process which has an influence over the time of the pot life.
05:32	This time varies with different resin types and mixtures while also being influenced by other factors like temperature.
05:39	Resins are available in a wide variety of formulations tailored to different construction techniques and compatible with other products, so we need to be sure to understand the supplier's specifications.