Modifying elastic modulus of two-component polyurethane adhesive for structural hardwood bonding

Abstract

Subject to this study is the modification of an experimental two-component polyurethane (2C PUR) as an alternative adhesive for structural hardwood bonding. The 2C PUR has been adapted by calcium carbonate as filler to increase its modulus of elasticity with the aim of increasing the modulus analogue to the ones typically observed for classic amino- and phenol based adhesives. The 2C PUR system was compared with a commercial one-component polyurethane (1C PUR) and a phenol resorcinol formaldehyde (PRF) adhesive. The wetting properties of the adhesives were tested in terms of surface tension, polar and dispersive part and contact angle on European beech wood (Fagus sylvatica L.). In addition, adhesive polymer films of 2C PUR were tested for tensile strength and modulus of elasticity (E-Modulus) following ISO 527-1. The adhesives bond performance on beech wood was determined by lap-joints according to EN 302-1 in various climate conditions. The results show that 2C PUR has proper wettability properties on beech wood. Adding 60% wt filler to the polyol component increased the E-Modulus from 2.3 GPa (0%) to 4.4 GPa. The tensile strength of the modified 2C PUR polymer films was comparable with the industrial 1C PUR. Tensile shear strength and wood failure percentage of 2C PUR lap-joints were increased by adding filler and met requirements in dry and re-dried conditions according to EN 302-1. However, the addition of filler didn’t result in an improvement in wet conditions. The present study shows sufficient performance for bonding hardwood with 2C PUR in dry conditions, while the system still needs to be improvement regarding its performance in humid conditions.

Feasibility of Bonding High-Moisture-Content Wood Using Nothofagus chilean Species

“…This property plays a crucial role in the ability of liquid sealants to spread and infiltrate wood cells, ultimately impacting the bonding strength between the two surfaces [27]. In this step, the adhesive molecules interact with the wood surface through molecular forces such as Van der Waals, hydrogen bonding, and dipole-dipole interactions [32]. After that, the adhesive penetrates the wood surface's pores, filling up the voids and crevices.…”

Challenges Facing the Development and Market Introduction of Hardwood Cross-Laminated Timbers

“…In another study (Bockel et al 2020), a 2C PUR adhesive was used to determine the tensile strength of lap joints made of European beech (Fagus sylvatica). Calcium carbonate as filler was added to the adhesive in an effort to increase the modulus of elasticity.…”

Research of Potential Catalysts for Two-Component Silyl-Terminated Prepolymer/Epoxy Resin Adhesives

“…The system studied in the work belongs to the elastomeric adhesives, the largest members of this segment are polyurethane and silyl-terminated polymers [ 2 , 3 ], which are available in one-component or two-component formulations. They are widely used because of the ability to ensure a broad property envelope, high reactivity at low temperatures and adhesion to various substrates [ 4 , 5 , 6 , 7 , 8 , 9 ]. Adhesion and material mechanical properties are largely dependent on the polymers, plasticizers, fillers and adhesion promoters present in the system, but it is very important to choose specific and effective catalyst systems to achieve good adhesion, workability time and the best possible mechanical properties ensuring the formation of a polymer network [ 10 , 11 , 12 ].…”