Influence of Cure Conditions on the Properties of a One-Component Moisture-Cured Polyurethane Adhesive in the Context of Green Gluing of Wood Magdalena Sterley, 1,2 Stacy Trey, 1 A ˚ sa Lundevall, 3 Sara Olsson 1 1 SP Technical Research Institute of Sweden, SP Wood Technology, Drottning Kristinas v€ ag 67, SE-114 86 Stockholm, Sweden 2 Linnæus University, School of Engineering, 351 95 V€ axj€ o, Sweden 3 Swerea IVF, Process development, Argonga ˚tan 30, 43153 M€ olndal, Sweden Received 6 October 2011; accepted 25 January 2012 DOI 10.1002/app.36895 Published online in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: A commercial one-component moisture- cured polyurethane-urea wood adhesive was investigated under different curing environments to simulate parame- ters during green gluing, that is, gluing of freshly sawn and undried timber. This process is an eco-efficient and waste eliminating process in which only the finished wood product properties have been tested; however, not the adhesive itself. Therefore, the effect of moisture and postcuring heat treatment on the adhesive properties such as cure, chemical, and physical characteristics, and adhe- sion to wood were studied. It was determined by rheome- try that the water content was proportional to the time to gel point, with moisture content of 2.6–5.6 wt % water, resulting in a higher initial storage modulus of the adhe- sive. Additionally, it was found that the strength of the wet glued bonds was significantly higher after the heat treatment, corresponding to the increase in ordered biden- tate groups (Fourier transform infrared spectroscopy), higher storage modulus (rheometry), and higher T g (dynamic mechanical thermal analysis). V C 2012 Wiley Period- icals, Inc. J Appl Polym Sci 000: 000–000, 2012 Key words: moisture curing adhesives; polyurethane adhesive; wood adhesive; green gluing; wet gluing INTRODUCTION One-component moisture-cured polyurethane-ureas (MCPU), 1 made up of isocyanate-terminated prepol- ymers, were widely patented in the mid-1980s 2 and have become widespread in wood applications, both for nonstructural use and as certified structural adhe- sives. 3 MCPU wood adhesives for structural use are often based on prepolymerized methylene diphenyl diisocyanate (MDI) combined with polyols. The uncured adhesive contains free isocyanate groups and polyurethane groups. Curing of a one-compo- nent MCPU adhesive occurs when the isocyanate is able to react with available water (in air and/or in contact with a substrate such as wood) to form car- bamic acid. Carbamic acid dissociates into an amine that can form a urea bond after reacting further with an isocyanate group. Carbon dioxide, which is emit- ted during this reaction, can cause foaming of the ad- hesive, risking the creation of cavities in the adhe- sive. 4 Polyols used in MCPUs can also be terminated with different reactive groups to obtain the desired properties in the cured adhesive. 5,6 Thus, in cured MCPU adhesives, different interactions, mainly hydrogen bonding (H-bonding) and crosslinking are created between polyols, urethane, and urea groups. In wood applications, MCPU-containing polymeric MDI has been used for its ability to bond with the water and lignocellulose hydroxyl groups contained in wood, creating both a mechanical and a chemical bond that is tough, has high strength, and is water re- sistant. 7,8 Further, the final mechanical properties, for example strength, and excess residual isocyanate con- tent in the final bond, are dependent on the cure con- ditions such as temperature and relative humidity. These cure conditions can significantly affect the phys- ical properties and the adhesion, owing to microscopic phase separation resulting in differences between intra- and intersegment interactions such as hydrogen bonding, mixing of soft (SS) and hard (HS) segments, and the degree of crystallinity of these segments. 9–12 Based on the conventional technology, timber is usually glued at a moisture content (MC) far below the fibre saturation point, preferably at a MC between 6 and 15 wt %. 5 The chosen level of MC depends on the end use climate conditions of the Correspondence to: M. Sterley (magdalena.sterley@sp.se). Contract grant sponsors: Centre for Building and Living with Wood (CBBT), Wallenberg Wood Science Center, Swerea IVF (Ola Lyckfelt), Swerea SICOMP (Erik Marklund). Journal of Applied Polymer Science, Vol. 000, 000–000 (2012) V C 2012 Wiley Periodicals, Inc.