If you follow the link from the article [1], then there's an abstract that describes the process. It sounds like they boil the wood with sodium hydroxide and sodium sulphite, then heat and compress the wood, which somehow leads to better alignment (and/or linking?) of the cellulose polymers.

I don't know what the implications are for recyclability, but there's no mention of injecting other materials so perhaps it decomposes in a similar way to ordinary wood?

[1] https://www.nature.com/articles/nature25476