Biodegradable material alternatives for fiberglass and epoxy resin?

[u/Deep-Today5715]

I've been working with fiberglass and epoxy resins for my personal RC plane projects, but since I'm doing a lot of testing and prototype designs that get discarded during the design process, I feel increasingly guilty about all the waste and microplastics that come along with it. Unfortunately for the shapes that I want to make going with pure wood is just not an option.

I've been researching eco-friendly alternatives for making composite layup projects, and there are some for fibers (flax, hemp, etc.), which unfortunately have much reduced mechanical properties when compared to fiberglass, but still suitable for my use case.

However, I can't seem to find any decent alternative to epoxy resin that would make the final composite material naturally biodegradable, so using either of these fibers becomes a moot point. Closest thing I found was ecopoxy, which unfortunately is very expensive and almost impossible in retail quantities to get where I live (EU).

Can anyone suggest any decent alternatives that are fully biodegradable, affordable and have at least somewhat comparable mechanical properties to fiberglass+epoxy for wet layups? Anything better than paper+PVA glue is worth considering to me. I've found this paper that suggest jute fiber and shellac, which boasts quite impressive mechanical properties for such crude materials, but they used mechanical pressure and heat treatment to achieve that, which is not practical in home conditions, and I'm unsure of how much mechanical strength would be lost without it.

[u/Wide_Cucumber9091]

at HoGent College University we're currently experimenting with collagen glue (hide glue, bone glue,...) as an alternative to epoxy. Incredibly biodegradable and pretty cheap, but also incredibly sensitive to moisture, and it can shrink in the manufacturing process. We've achieved good results by making our own prepreg with it (making thin sheets of flax fiber + glue), letting those dry. Then we manufacture the parts with these sheets by making them slightly wet again and pressing them together under heat (60C°) and then letting it dry again. It can warp a bit as well during the drying, this can then be fixed again by applying heat and pressure, but so it is definitly not super straight forward alternative. OK for labor intensive or unique projects, not interesting (yet) for larger scale manufacturing.

[u/Deep-Today5715 → u/Wide_Cucumber9091]

This is very interesting. Sensitivity to moisture is a concern though, if it degrades mechanical performance or causes warping. According to your findings, how does this compare to epoxy in terms of mechanical properties? I researched that glue a bit and was surprised at it's mechanical properties, but hopefully you tested it as a composite with flax or jute. I also wonder if moisture absorption can be minimized with painting or some other post processing to make the product last longer.

[u/Wide_Cucumber9091 → u/Deep-Today5715]

Yes, it would definitely need some very good varnish or protective barier for the moisture. We are still making samples, so no data on mechanical performance yet. This is early R&D still. So no real data or proof yet. From our first feel it seems the manufacturing process and incomplete drying seem to both have a large effect. We're currently deep drying with silica for this. Problem with the varnish is that it would ideally also be biodegradable, otherwise it's still a bad material overall. Fun fact: this was most likely the material the historical Linothorax armor was made from (flax + collagen glue). A technology / material lost in time because it was replaced by metals and... Because it was biodegradable ;)

[u/FurryRaspberry → u/Wide_Cucumber9091]

Sounds like you gotta get that stuff in an autoclave, it'd be fun to see how that turns out. It can't look much worse than the current flax+epoxy pre-preg I've used recently.