The cradle-to-cradle philosophy is desirable for semi-structural cellulose biocomposites. Selective chemical recycling of a thermoset matrix back to reusable monomers was realized while avoiding cellulose fiber degradation. A fully biosourced, PLA-based (polylactic acid) thermoset polymer was molecularly designed for chemical recycling and for curing in chemically heterogeneous plant fiber networks. Curing was by stepwise polymerization of 4-arm functional prepolymers of PLA in a cellulosic wood fiber network of high fiber content. FT-IR data supported covalent fiber/matrix interface bonding. These eco-friendly biocomposites showed high modulus (24 GPa) and high optical transmittance. The matrix was selectively degraded back to the initial building block, lactic acid monomer, under alkali conditions. This progressed without apparent damage to the cellulosic fibers. The green metrics of the synthesis showed strong potential for this material concept in a circular economy.