As clearly stated by name, composites is a composition, one of resin and fibre reinforcements. In a very simplified description the resin is the glue that holds the fibres together, creating the panel. There is a vast variation of the possible combinations, types of resins and types of fibres out there, as well as methods of manufacturing these panels. Yet for our purposes we will limit the consideration in carbon fibres, which is the preferred option for larger and more advanced structures due to its strength qualities and heat resistance, and vinyl ester for its water and heat resistance. As a combination they give a larger range of possible applications.
Starting with vinyl ester, it is a product originating from either ethoxylated or proxylated Bisphenol A, Novolac or epoxy resin, reacting with acrylic or methacrylic acid in the esterification process. The chemical reaction involved is slow, requires considerable time and moderate temperatures, producing a waste water that is corrosive and has toxic properties that requires treatment before releasing. In very simple terms, vinyl ester is derived from petroleum products and has some hazardous by-products. Luckily presently there are hybrid formats and are in development pure plant-based forms from cardanol of cashew nuts, so possibly in the future we can referred to an agricultural, environmentally friendlier product.
Carbon fibres are strands made of carbon. The vast majority is made of polyacrylonitrile in the PAN process. Despite that we refer it to it in general as the PAN process, there is no single procedure making the carbon fibres, it is versatile and complex and kept a secret from its proprietors.
The ore products are propylene, which is a product of oil refinery and natural gas, and ammonia, sourced from methane, stem forming or liquified petrol gas (LPG). They react to form the acrylonitrile that is further polymerised, with the contribution of comonomers and catalyst, creating the polyacrylonitrile. Through the process of wet spinning (or lately the dry jet/ wet spinning) the external shape and cross sections of the filament are formed. From the next step of oxidation, the crosslinking of the polymer occurs. Then follows carbonisation, that practically burns the fibres in high temperatures in an oxygen free environment, giving the nice black coloraturas that it so distinctive of the product. Lastly there is the surface treatment and sizing, a critical and safely guarded stage.
I realise that all the designations, chemical reactions and process names can be overwhelming, but for those of you that wish to learn a bit more for this fascinating process, you can start from the following, VinylEster Resins, AOC Resins, Zoltek Resin and Composites World.
For the purpose of my evaluation review, the following stand out.
- The main source of both resin and carbon fibres is petroleum, namely we are still attached to the fuel fossil industry. There are development for plant-based for vinyl ester, which is a source for optimism;
- The acrylonitrile, precursor for the PAN process, is a harmful substance for the aquatic life and need to be stored with caution;
- During the formation of the acrylonitrile, we also get acetonitrile and hydrogen cyanide, also marketed, thus less material waste;
- Through carbonisation, the product is shrink in a ration of 2:1, basically only half of the material coming in, is going out;
- The whole PAN process requires between 183-286kJ/ kg that is 4x to 5x times the energy consumed for aluminium;
- The space and investment requirements to build a facility of this type is gigantic;
- The outcome depends heavily on the organic precursor’s quality and exact procedure, there is no homogeneity in the panels one can get;
Carbon fibres are 5x stiffer and 10x stronger than steel at half its weight. Their overall qualities in heat resistance, weight and water resistance give them such advantages that for advanced application need to be considered. Yet there is no recycling method and we are still depended on fossil fuel for creating them. That reality needs to be altered with different sources and methods that make their existence more environmentally friendly.