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Thermoplastics Composites - The Sustainable Alternative

Since 2013, CompositeTechs has been enhancing the workforce of dozens of companies in the plastics and composites industry by providing part time experts for technical, sales and market development, market analyses and M&A activities.

Recently our support for the development of thermoplastic composites to replace thermosets and metallic components has been increasing. We have performed part analysis and design, defined manufacturing processes, made prototypes for qualification, driven parts into production, established greenfield facilities and enhanced in-house capabilities. We have performed detailed market analyses and supported numerous M&A activities for thermoplastic composites and green composites to the point where the majority of our current programs are thermoplastic. I’m not sure if this trend is a snapshot of the entire industry, but I’d like to think so.

Why would the industry lean towards thermoplastic instead of the well-established thermoset composites? The thermoset industry began just about a hundred years ago, and as a result there is a well-established database and a low technical risk. Most composite companies own substantial capital equipment that is used for thermosets, and the entire workforce, from the design engineers to the shop labor to the sales force, are trained and comfortable with their products.

Thermoplastic composites are new and, therefore, alien and many companies have had limited preliminary trials that, for various reasons, didn’t end up so well. Autoclaved PEEK components didn’t seem to offer promised price advantages and there was that crystallinity issue... Baking an Ultem laminate for a half-hour in a press results in a crispy, oxidized, and useless part (oxidation wreaks havoc when you’re processing above 600F). Thermosets are in the comfort zone, and it’s harder to justify the jump to thermoplastics.

Of course, that comfort zone is dissolving, as our customers can testify. Thermoplastics offer improved properties, including improved toughness, damage tolerance, increased energy absorption, impact resistance, corrosion resistance, higher temperature performance, and others. Thermoplastic composites offer lower manufacturing costs and much lower cycle times. High volume composite applications in many industries are converting to thermoplastics. Thermoplastics are easier on the manufacturing floor as they are fully automatable, and they can be joined with no adhesives or fasteners, i.e., they allow for ‘dustless joining’. With all these improvements in mind, our customers are still interested in another advantage: thermoplastics are the sustainable alternative.

Sustainability is defined in general terms as maintaining a balanced environment, such as a fully recycled manufacturing facility. In broader terms it means a fully balanced community or world, where waste is fully integrated back into the system in a productive means. Sustainability is not just a green solution however; it involves providing balance to the community as a whole, i.e., the workforce, the neighborhood, the industry.

Many aspects of thermoplastic composites are sustainable lending towards a model of green composites. First, the material is, for the most part, fully recyclable. When a molded thermoplastic composite part completes its life cycle, e.g., when a next-generation Gulfstream airplane fuselage reaches its life limit, it can be chopped up, put into a hopper and injection molded into something else with little loss of properties. In contrast, with thermoset composite recycling, you end up with a chemical mess after fiber extraction and loss of the matrix in reuse. Thermoplastic prepregs have the added advantage of no shelf life, and trim can be chopped and molded into something else. In a properly designed part, there will be no prepreg scrap. Most thermoset production lines project a 30 to 50% prepreg scrap factor. In comparison, both thermoplastic and thermoset prepregs can be recycled, but the former is fully recyclable, uses less energy to recycle, and has the potential for no scrap.

Thermoplastic prepreg has another advantage in that it does not require refrigeration. It is not unusual for a moderate sized thermoset prepreg manufacturing facility to maintain large freezers, with capital equipment costs approaching $500KUS, plus long term power usage costs. All of this cost goes away with thermoplastics; just store them in a bag and they will last until you need them. Thermoset prepregs typically have a shelf life of six months to one year, so for small production orders with minimum prepreg order sizes much of the prepreg may end up in a landfill.

Processing of thermoplastics is also more sustainable than thermosets. One of the largest composite manufacturing industries globally is marine, and there are boatbuilding shops up and down every coast. You can usually find them by following your nose, as the smell of styrene monomer and other volatile organic compounds (VOC’s) waft for quite a distance. Styrene monomer is a main component in polyester resin which is used quite extensively in boatbuilding. Other thermosets including epoxies each carry their own brands of VOC’s. VOC’s can be carcinogenic and can offer other health hazards to not only the manufacturing personnel but to the entire community. Since thermoplastics are already polymers, their processing does not involve use of monomers, and there are no VOC’s to worry about.

The use of thermoplastic polymers also results in big energy savings. Thermosets start as monomers which must be held at temperature and pressure for extended periods (typically an hour) in order for them to polymerize while being constrained to final shape. Thermoplastics, in contrast, are heated to be softened and then formed to final shape. Consequently, the time to process a thermoplastic composite is typically less than ten minutes, resulting in much less energy per part to manufacture.

Thermoplastics can also be welded together, and when properly designed, adhesives, fasteners, and energy consuming machining operations can be avoided. Since holes are not being drilled for fasteners, and attachment areas can be formed and not machined, the term ‘dustless processing’ is mentioned by Airbus and others as a major advantage of thermoplastics in the shop floor environment.

Are thermoplastics composites the final solution for a sustainable environment? Of course not. Just because a part is recyclable doesn’t mean it will be recycled. Think of the island of floating plastic in the Pacific as an example. Recycling will not happen unless there is enough motivation, including financial rationale and government regulations, and of course, societal mindset. Thermoplastics composites offer major sustainability advantages over thermoset composites, and they are the best method I can see for getting to where we need to be. It’s great to see that others think so too.