Is Marine Plywood better than plastic for the environment?

Biodegradeable glues are an area of active research right now (example, and woodwork forums thread), but I haven't been able to find a plywood that uses one. The good news is that glue is only 5-10% of the plywood by weight, and the glue is not entirely fossil based (often has urea which at least can be natuarlly produced).

In terms of reuse, one obvious option is to clean the back surface and label that the second time you use them. It would be better in many ways if you could make them double sided in the first place (you're not transporting, cleaning and re-distributing them. Which is a hassle=mental cost as well as a monetary and environmental cost).

Obviously almost all plastics are 100% fossil, and generally can't be re-used, only downcycled. But since your plaques are decorative you should be able to use non-food-grade, recycled plastic for them. If you can that might be better environmentally than plywood because the plastic ones are thinner and lighter, as well as possibly more durable (which may not matter if you replace them regularly for branding reasons).

You would need to do that anyalysis for the exact products you're comparing, in your exact location. This is where we all would like the sustainability equivalent of an MSDS or food tracking label. Something that tells you exactly what you're buying.

My gut feeling is that this isn't really a sustainability question, it's a marketing one. These things are a branding exercise, and an important part of the branding is sustainability. Plywood says to the consumer "natural", with all those associations. It might also be a differentiating factor (for a while) since the industry standard is plastic. That's not a bad thing, but it does influence whoever makes the decisions in your company more than some random employee turning up with "I found it on the internet".

I've tried to give you links and keywords so you can reverse engineer the environmental justification you need from this answer.

Does marine plywood actually have a smaller environmental footprint than PVC as it contains many glues

The glues might outgas volatile compounds, but unless used in an area where volatile compounds are a genuine problem, my opinion is that those glues are not any kind of a problem. In areas where smog is formed by those volatile compounds, you might want to avoid all products outgassing volatile compounds. Anyway, the glues are a very small part of the plywood. Most of the plywood is after all wood.

Other than that, both plastics and plywood store carbon, i.e. they are good for the environment. In the case of plastics, this carbon comes from petroleum. However, the petroleum that was created to produce this plastic would otherwise be burned for its energy, so you can argue that plastics offset carbon dioxide emissions, much like wood stores sequestered carbon.

If there will be a high carbon dioxide emission price, it may mean some petroleum reserves have to be left under the ground for economical reasons. In this kind of environment, plastic no longer offsets carbon dioxide emissions. However, plywood does store sequestered carbon. So, with a high carbon dioxide emissions price, plywood is better than plastic. (I hope the politicians realize someday that it makes sense to have a subsidy for carbon captured by wood -- such a subsidy would make plywood and other wood products more competitive and thous would encourage storage of carbon away from the atmosphere.)

Not sure what will happen to plywood clips at end of use - but hope to use them many times over (definitely not single use).

I think you'll find that plywood can be only reused as-is. If the plywood is of the correct shape, you can reuse it. If not, well then, the only practical solution is to burn it to energy, as plywood cannot be recycled to new plywood of different dimensions.

Plastics, on the other hand, are somewhat easier to recycle. Old plastic products can be used to create new plastic products. Of course plastic can be reused too if it is of the correct dimension.

In general, plastics are more stable than plywood. Plywood can biodegrade, plastics not so much. This is a good thing (plastic stores the carbon for a very long time if not burned) and also a bad thing (microplastics problem in the oceans).