Is there a good low toxicity / food safety clear casting material?

Question

I need to cast some plastic resin into the wood, such as to make a cutting board, where the resin is minimally toxic.

(For the moment, let's ignore the toxicity of the wood itself.)

I have used the "Castin' Craft" brand catalyzed polyester material. The bulk liquid (according to the MSDS) contains styrene, which is not good for humans. Once the material is catalyzed and has hardened and outgassed for a day or two, I stop smelling the styrene. Nevertheless, I wonder if there is something better.

Is there another clear material I could use as an alternative?

Answer 1

You can find many epoxies and some other resins that are certified food safe. Casting resins are often used for items that will be in contact with the body or food. The US and EU (and I assume other countries), have standards for certifying the materials as safe for these purposes.

There are actually several parts to the answer. Certain kinds of plastics are approved for certain kinds of uses (e.g., incidental or single-use contact vs. storage or repeated use, dry vs. wet, etc.). For a type of plastic that is suitable for a purpose, the manufacturer gets their particular product certified as safe. So a product that is food safe for one purpose may not necessarily be food safe for a different purpose.

I can't recommend a particular product, but search for "food safe" at whatever source you will buy the resin from. Then just verify that the item description says "food safe" (it can't be legally described as food safe if it isn't certified as such). And be aware that you may need to verify whether the food safe rating covers your intended use.

In any case, "food safe" assumes accurate mixing ratios, thorough mixing, and fully cured. If those conditions aren't met, it will still contain materials that aren't good for you.

Be aware that most epoxy resins you find will be designed for one of two kinds of applications--either casting or coating. The casting resins are typically low viscosity and are designed to cure in a thick casting without generating runaway heat. The coating resins are typically higher viscosity and are designed to cure in a thin layer (usually less than 1/4"). If you try to cast something thick with a coating resin, it can generate intense heat, the resin may boil, and you will likely ruin everything involved. Just check the product description for the maximum recommended thickness.

Answer 2

There are other resins (mostly 2 part epoxy resins) that can be food safe. Can be means that :

1. It has to say "food safe" on the packaging, and
2. You have to measure the components and mix them very pecisely.

2 Component resins bring all the chemicals needed to harden, only they are seperated in the 2 components. The components themselves are harmful, even if the resin is food safe. Ideally you'd mix just the right amount of hardener into just the right amount of resin and after the curing time all chemicals bonded together and became inert. If the resin isn't completely hard after curing, there are remains of harmful chemicals left and it isn't food safe.

Here's a datasheet by the FDA listing all categories of materials that are approved for either one-time or repeated contact with food. And here's a guide to understand the FDA sheet that also lists a few food safe casting resins.

Another possible alternative is thermo plastic. Heed the same advice and look for products marketed as "food safe", but you'll find many more food safe thermo plastics than resins. The downside is that none of them are as clear as resin and you might not want to cut a hot roast beef on this board.