New lightweight materials: Balsa wood‐polymer composites based on ethyl α‐(hydroxymethyl)acrylate

It is clearly demonstrated here that ethyl α‐(hydroxymethyl)acrylate (EHMA) is a unique monomer for increasing the dimensional stability and physical properties of balsa wood. Copolymers containing EHMA, and especially EHMA‐styrene mixtures, were shown to improve the dimensional stability (water soak test) and the absolute mechanical properties of balsa wood. Improvements in specific modulus and specific toughness (absolute properties divided by specific gravity) were achieved using an EHMA‐styrene monomer mixture with polybutadiene diacrylate as cross‐linker and toughening agent, with the best results obtained at low (10–40%) weight gain. This is the first report that we are aware of describing specific property improvement greater than expected based on density increase. These improvements in modulus and toughness were ascribed to efficient penetration of monomers into the cell walls. Solid‐state NMR and scanning electron microscopy confirmed strong interaction of the copolymers generated in situ with wood cell wall components, consistent with the property improvements obtained. The combination of a light‐weight, renewable wood precursor with synergistic reinforcement by this combination of monomers offers unique opportunities for increased use of wood‐polymer composites in a wide variety of structural and insulating applications.