PLATech overview -radiation-heat tailored VOC-free, bio-renewable polylactic acid polymer formulations & methods for multiple industrial adhesion applications

This paper presents an overview of research and results about tailoring crystalline and amorphous form polylactic acid (PLA) polymer resin for use as an adhesive for joining a range of substrates, production of wood-based composites plywood and particle wood-based composites, and, for potential use for elevated temperature applications as for wood structures when subject to fires. The range of substrates successfully joined (with and without bio-plasticizer) ranges from metals, woods, glasses, ceramics, stones, and bricks to synthetic fluoro-polymers. Tensile bond strength for steel-to-steel bonding ranged towards 40+ MPa; superior (over 100%) bonding strength was obtained compared with EVA and other standard adhesives for wood and metal surfaces. Three successful industrial product arenas are described: 3-ply composite plywood panels meeting water soak and shear strength industry metrics; particle boards meeting-exceeding rupture strength, elasticity, and water resistance metrics similar to those expected from urea-formaldehyde based adhesive but without VOC release limitation, PVC-free luxury flooring tiles which meet strict requirements for wear cycles, distortion-free adhesion peel strength; and, production of renewable particle boards with elastic modulus and internal bond strengths comparable with boards made with urea formaldehyde. Thermal and gamma ionizing radiation research results are discussed to tailor key adhesive-relation properties: adhesion strength, viscosity, flow rate, molecular weight, hardness, flexibility, and friability. Scoping studies on radiation-based tailoring with a cross-linking agent were found to permit up to 30% improvements in bond strength as well as for enabling application as an adhesive for elevated (100 °C+) temperature applications with ∼30–50% higher operating temperatures compared with commonly used adhesives. A discussion is included about the remaining challenges and recommendations for further research.