Clean plasma modification for recycling waste plastic bags: From improving interfacial adhesion with wood towards fabricating formaldehyde-free plywood

It remains a great challenge to manufacture formaldehyde-free plywood, because of the wide application and cost advantage of formaldehyde-based adhesives. Herein, the waste plastic bag was recycled as an alternative to formaldehyde-based adhesives for manufacturing formaldehyde-free plywood. An industrial atmospheric dielectric-barrier-discharge plasma system was used to treat the plastic bag, in order to enhance the interfacial adhesion of the resultant plywood. The results suggested that plasma modification would excite oxygen and nitrogen into energetic particles and further ruptured the raw chemical bonds of plastic bag. Oxygen- and nitrogen-containing functional groups can be grafted, thus enhancing plastic bags’ surface polarity and wettability. As further supported by nanoindentation, the adhesion energy of plasma-modified plastic bag and poplar cell wall was elevated by 19.13% when compared to the unmodified sample, thus suggesting the improved interfacial adhesion and interfacial compatibility. Benefiting from that, formaldehyde-free plywood with a high bonding strength (0.82 MPa) was successfully fabricated. Shear strain in plywood distributed uniformly after plasma modification, suggesting the even distribution of adhesive and the enhanced bearing-load capacity of interface. This study paves a new way to effectively recycle plastic waste as an alternative to traditional adhesives for formaldehyde-free plywood manufacture.