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I want to make bamboo bike like Craig Calfee and so many others have made, but if possible, I would rather not use epoxy, which is not biodegradable.

A bamboo bike has a frame made of bamboo, held together at joints by hemp-epoxy (or fiberglass-epoxy / carbon fiber-epoxy) composite lay up by hand. Is there any natural/DIY alternative to epoxy which can be used with hemp fibers in a similar fashion to hold the joints strongly?

I want to use a truly biodegradable polymer, even if synthetic. Even better if it can be IDY homemade concoction. What did woodworkers use other than hide glue before PVA and epoxy became so prevalent?

I'm looking for a plant based or synthetic non-animal sourced biodegradable polymer. Isn't there something one can make from plant proteins similar to hide glue?

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    "What did woodworkers use other than hide glue before PVA and Epoxy became so prevalent?" Possibly the simplest answer is they just didn't make things in the same ways that epoxy and other resin systems allow. There are some natural resins, which cooked together with oils can make polymers but strength-wise they're nowhere in the same realm as epoxy, polyester and urethane resins. The predecessor to PVAs is easy, that's protein glues of a few kinds (fish glue, hide glue and hoof glue) and casein.
    – Graphus
    Jan 12, 2019 at 19:27
  • "Isn't there something one can make from plant proteins similar to hide glue?" There may be, but nothing you can make at home using regular kitchen equipment, and for certain historical formulas it wouldn't be safe to try (fire and explosion hazard) and anyway some of the key ingredients are now unobtainium or restricted due to health concerns and no longer available for sale to the general public (mercury, lead and arsenic compounds).
    – Graphus
    Jan 12, 2019 at 19:29
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    If it is "truly biodegradable", what will keep it from degrading as soon as it's finished?
    – WhatRoughBeast
    Jan 13, 2019 at 0:58
  • @WhatRoughBeast, cardboard and paper are truly biodegradable, what stops a paperback from degrading as soon as it's published? ;-)
    – Graphus
    Jan 13, 2019 at 6:51
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    @Graphus - Cardboard and paper are indeed biodegradable, and will start deteriorating as soon as exposed to weather - even simply high humidity. How useful would a bicycle be which cannot be ridden in rain, fog, or even exposed to high humidity?
    – WhatRoughBeast
    Jan 13, 2019 at 6:57

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Is there any natural/diy alternative to epoxy which can be used with hemp fibers in a similar fashion to hold the joints strongly?

You might like to look into what I think is generically called bio-epoxy. The only one I'm familiar with (from reading about it some years ago) is EcoPoxy, but a quick Google search reveals there are now others. These are not all-natural products, but they may be the closest you can get with the strength you require.

Caveat emptor
I have no idea how seriously we can take the claims of these products being 'natural' or 'green', but I would recommend skepticism. There are already plenty of distortions, exaggerations and even outright lies in the conventional adhesives and coatings industry (because lack of regulatory control allows them) and I'd expect at least as much if not more in this sub-sector!

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What did woodworkers use other than hide glue before PVA and Epoxy became so prevalent?

You might be thinking of casein glue, which is made from milk protein. Casein glues were common in aircraft manufacturing until the start of World War II. This March 2018 newsletter from the Vintage Glider's Club has an excellent overview and cites further reference documents. See also this summary from Science Direct.

Casein glues are strong and tend to be stable under heat, but they're not fond of long-term humidity. My guess, based on Water-Resistant Casein-Based Adhesives for Veneer Bonding in Biodegradable Ski Cores, is that riding in the rain would be fine, but you'd want to store the bike where it'll be dry between rides. (Naturally: you wouldn't want the components to rust, either.) Also, if you layer reinforcing fibers on the joints, give the glue plenty of time to dry between layers so you don't trap moisture. And maybe consider a waterproof finish--beeswax, perhaps, to keep everything biodegradable?

Bad news: I had a hard time finding suppliers of powdered casein glue. Clarion Casein or National Casein (in a listing for Chemical Supermarket) might be possibilities.

Good news: the Internet abounds with recipes. I can't speak to the strength of the vinegar/baking soda formulations, but U.S. Dept. of Agriculture's Tech Bulletin No. 205, Gluing Wood in Aircraft Manufacture (1930) includes a couple formulas, Casein Glues: Their Manufacture, Preparation, and Application (1967) has one, and the plywood ski study above discusses the formulation they tested.

I landed here because I was also wondering about biodegradable bike frames. Best of luck to you and everyone else experimenting with this idea!

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  • Hi, welcome to WW. Casein glue is an obvious thought with this sort of thing, and it can be made at home from scratch if needed, which the OP indicated would be desirable. The reason I didn't mention it as an option is from all I've read and seen firsthand casein glues are a thin-bond adhesive, requiring close-fitting joints and clamp pressure to form reliably strong joints. Correct me if I'm wrong but the glues used in bamboo bikes must bridge gaps, and even be used for form 'fillets' similar to how welds and brazing are sometimes built up, in essence becoming external reinforcement.
    – Graphus
    Sep 6, 2021 at 7:31
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    (@Graphus) on all the handful of bamboo bikes I've seen, the joints are indeed built up, but out of composites rather than just glue. I've heard of fibreglass cast tape (interesting as it sets with water/humidity but I don't know the chemistry) being used as well as epoxy-impregnated hemp/fibreglass/carbon fibre. For the thinner tubes (chainstays/seatstays) metal joint plates are fairly common as they're need for the dropouts/derailleur hanger/disc brake mounts etc. anyway. I've actually designed a couple of these plates
    – Chris H
    Oct 5, 2021 at 14:14
  • Some of the sources like the Vintage Gliders Club article suggest casein has fair gap filling qualities, and I suspect a casein/sawdust mix would fill gaps, but I agree, bonding to end-grain on some of those joints is dicey at best. I wonder if casein would bond to uni carbon fiber, or if wrapping with cotton cord or glue-soaked strips of muslin would be strong enough. I may run some experiments if I ever get the time.
    – jtc
    Oct 7, 2021 at 0:10

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