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This study investigates the bonding properties of modified wood by considering three different aspects: water related characteristics, mechanical performance and optical (fluorescence microscopy and X-ray micro-computed tomography) observation of adhesive penetration into modified wood structure. In recent years, the new wood modifications have become more commercially available in the market for both exterior and interior applications due to improved properties that modification can bring to the wood e.g. the improved biological durability, dimensional stability, hardness and weathering resistance of the wood as well as the environmentally friendly nature of the wood modification processes (Militz and Hill 2005). Besides these advantages, modification can affect some technological aspects of the wood such as its bonding performance. For example, it can alter the strength of adhesion as a result of changes in chemical, physical and structural characteristics of the wood. For example, the less polar and less porous modified wood surfaces can result in reduced adhesion due to formation of less free OH groups for bonding leading to poorer adhesive wetting of the wood surface and weaker chemical bonds between the two adherents (Hunt et al. 2007). As modified wood becomes a more demanded material for different applications, there is a need to study its bonding performance where the challenge is to bond different modified materials as their physical and chemical characteristics are substantially changed by modification. In this thesis, measurements of capillary water uptake, contact angle and surface energy were used to determine the water related properties and hydrophobic behavior of furfurylated (FA40 and FA70, which represent 65 and 75 % WPGs) and N-methylol melamine (NMM) (10, 20 and 30%) modified Scots pine and thermally treated Scots pine and beech (modified through an industrial scale vacuum press dewatering method at 195 and 210 °C). The capillary water uptake results indicated a considerable reduction of water uptake for all modifications in all directions both after short (24 h) and long contact times (168, 336 h). Contact angle measurement data revealed an increased hydrophobicity of modified wood. However, some exceptions were observed, mainly for thermally treated wood. Modifications provided radial and tangential surfaces with a non-polar character. Penetration of adhesives into the wood structure plays an important role in the production of glued wood-based panels and products by affecting the bond quality (Frihart 2005, Kamke and Lee 2007). The gross penetration of emulsion polymer isocyanate (EPI), polyurethane (PU) and polyvinyl acetate (PVAc) adhesives into modified wood, both with and without pressure, were determined by using fluorescence microscopy based on measurements of effective (EP) and maximum penetration (MP). Without application of pressure, the EP of EPI adhesive reduced after NMM modification and furfurylation (FA70) and also PU adhesive after NMM modification while the EP of PVAc adhesive increased into furfurylated and NMM modified (10 and 20%) wood. For thermally treated Scots pine, increasing the treatment temperature improved EP of all adhesives. Among used adhesives, PU penetrated much deeper into thermally treated wood for both treatment temperatures. Comparison of penetration of adhesive with and without pressure revealed that with the exception of EP of PU and EPI adhesives into NMM-modified wood and PVAc into thermally treated beech at 195°C, application of pressure led to rather different results as compared to the EP data when no pressure was applied. Visual observation and analysis of fluorescence microscopy photomicrographs provided more detailed information on modality of penetration. Due to the large and deep penetration of PU adhesive into thermally treated Scots pine observed in both studies (with and without pressure), the 3D pattern of penetration of this adhesive was obtained by X-ray micro- computed tomography indicating the pathways which were used by this adhesive for penetration. In another study, the bonding shear strength of the same modified wood materials glued with the same adhesives was also investigated. For all adhesives used, the shear strength significantly reduced after furfurylation and NMM modification of Scots pine samples, mainly due to the brittle nature of the wood after modification rather to the failure of the bondline. Bonding strength of both Scots pine and beech was also negatively affected by thermal modification and the bondline was found to be the weakest link in thermally modified wood. The EP of adhesives and the bondline thickness did not relate to the shear strength of all modified wood materials. It was indicated that the lower shear strength of modified wood could be attributed to other factors, such as the decreased chemical bonding or mechanical interlocking of adhesives, and the reduced strength of brittle modified wood substrate. The effect of two important bonding variables, wood moisture content and open assembly time on penetration of PU adhesive into thermally modified wood (195 and 210 °C) was also studied. The equilibrium moisture content (EMC) level of 8.6% was found to be the optimum for an effective penetration of PU adhesive in thermally modified Scots pine treated at 195°C. In most of the cases, penetration of PU adhesive did not change significantly by increasing the open assembly time, which suggested using a shorter open assembly time of 15 min than 30 min for bonding of thermally modified Scots pine with PU adhesive, in order to save time and reducing the production costs. For samples treated at both treatment temperatures and after shorter open assembly time, the highest MP values observed at moderate EMC levels of 8.6 and 8.2% and the lowest at the higher EMC levels of 13.2 and 12.5%. In another study, the effect of phenol formaldehyde (PF) treatment on bonding performance of beech glued with PVAc and phenol resorcinol formaldehyde (PRF) adhesives was also investigated. The results of both dry and wet conditions indicated higher shear strength for samples bonded with PRF than PVAc. With the exception of 25% PF treated wood bonded with PVAc, the PF modified wood can be glued with both adhesives satisfactorily under dry condition, while under wet condition only the 25% PF modified samples bonded with PRF provided acceptable bonding. For both adhesive systems, PF modification caused a reduction of adhesive penetration into wood structure, especially in the case of higher load treatment. The development of bonding strength of modified birch veneers glued with hot curing phenol formaldehyde (PF) adhesive was investigated in different pressing (20 s , 160s) and open assembly times (20s , 10 min). Generally, the bonding strength improved by extending the pressing time. In 20 s pressing, increasing assembly time did not change the bonding strength in most of the cases while at 160 s pressing, prolongation of assembly time developed a better bonding for controls, NMM modified and thermally treated veneers at 180°C. The combination of 10 min assembly time and 160 s pressing time provided the highest bonding strength for controls, NMM modified and thermally treated veneers at 180°C while furfurylated samples achieved the highest values in 20 s assembly and 160 s pressing times. In general, modification affected negatively the bonding performance of the veneers, especially for furfurylated and NMM modified samples. In General, the overall results obtained in this thesis showed that modified wood has lower bonding ability and performance than unmodified wood as result of the decreased water related properties, less penetration of adhesive into wood structure and decreased bonding strength after modification. However, the increased dimensional stability and low water uptake of modified wood might lead to better performance in long term.
USDA Forest Service, Forest Products Laboratory (Madison, Wisconsin) and the Wood-Based Composites Center of Virginia Tech (Blacksburg, Virginia) co-sponsored a conference, held November 5-6, 2003, in Madison, Wisconsin, on the fundamentals of composite processing. The goals were to assess what we know, define what we need to know, and then establish the state of the art in hot-pressing of wood-based, particulate composites. Academic and industrial professionals from around North America and Europe were invited to participate because of their expertise and interest in this area of research. The workshop covered four critical topics associated with hot-pressing of composites: resin curing and bonding, press control, physics of hotpressing, and computer simulations of the pressing process.‍?This report is the official record of the presentations and discussions that occurred during this workshop.
Adhesive Bonding: Science, Technology and Applications, Second Edition guides the reader through the fundamentals, mechanical properties and applications of adhesive bonding. This thoroughly revised and expanded new edition reflects the many advances that have occurred in recent years. Sections cover the fundamentals of adhesive bonding, explaining how adhesives and sealants work, and how to assess and treat surfaces, how adhesives perform under stress and the factors affecting fatigue and failure, stress analysis, environmental durability, non-destructive testing, impact behavior, fracture mechanics, fatigue, vibration damping, and applications in construction, automotive, marine, footwear, electrical engineering, aerospace, repair, electronics, biomedicine, and bonding of composites. With its distinguished editor and international team of contributors, this book is an essential resource for industrial engineers, R&D, and scientists working with adhesives and their industrial applications, as well as researchers and advanced students in adhesion, joining, polymer science, materials science and mechanical engineering. - Offers detailed, methodical coverage of the fundamentals, mechanical properties and industrial applications of adhesive bonding - Enables the successful preparation of adhesives for a broad range of important load-bearing applications in areas such as automotive and aerospace, construction, electronics and biomedicine - Covers the latest advances in adhesive bonding, including improved repair techniques for metallic and composite structures, cohesive zone modeling, and disassembly and recycling
Biobased Adhesives Unique and comprehensive book edited by acknowledged leaders on biobased adhesives that will replace petroleum-based adhesives. This book contains 23 chapters covering the various ramifications of biobased adhesives. The chapters are written by world-class scientists and technologists actively involved in the arena of biobased adhesives. The book is divided into three parts: Part 1: Fundamental Aspects; Part 2: Classes of Biobased Adhesives; and Part 3: Applications of Biobased Adhesives. Topics covered include: an introduction to biobased adhesives; adhesion theories and adhesion and surface issues with biobased adhesives; chemistry of adhesives; biorefinery products as biobased raw materials for adhesives; naturally aldehyde-based thermosetting resins; natural crosslinkers; curing and adhesive bond strength development in biobased adhesives; mimicking nature; bio-inspired adhesives; protein adhesives; carbohydrates as adhesives; natural polymer-based adhesives; epoxy adhesives from natural materials; biobased polyurethane adhesives; nanocellulose-modified adhesives; debondable, recyclable, and biodegradable biobased adhesives; 5-Hydroxymethylfurfural-based adhesives; adhesive precursors from tree-derived naval stores; and applications in various diverse arenas such as wood bonding, controlled drug delivery, and wearable bioelectronics. Audience This book will interest materials scientists, adhesionists, polymer chemists, marine biologists, food and agriculture scientists, and environmentalists. R&D personnel in a slew of wide-ranging industries such as aviation, shipbuilding, railway, automotive, packaging, construction, wood bonding, and composites should find this book a repository of current and much-needed information.

ANC Bulletin

United States. Munitions Board. Aircraft Committee. Subcommittee on Air Force, Navy, Civil Aircraft Design Criteria

Published: 1951

Total Pages: 144


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"Long Term Durability of Structural Materials" features proceedings of the workshop held at Berkeley, CA in October, 2000. It brought together engineers and scientists, who have received grants from the initiative NSF 98-42, to share their results on the study of long-term durability of materials and structures. The major objective was to develop new methods for accelerated short-term laboratory or in-situ tests which allow accurate, reliable, predictions of the long-term performance of materials, machines and structures. To achieve this goal it was important to understand the fundamental nature of the deterioration and damage processes in materials and to develop innovative ways to model the behavior of these processes as they affect the life and long-term performance of components, machines and structures. The researchers discussed their approach to include size effects in scaling up from laboratory specimens to actual structures. Accelerated testing and durability modeling techniques developed were validated by comparing their results with performance under actual operating conditions. The main mechanism of the deterioration discussed included environmental effects and/or exposure to loads, speeds and other operating conditions that are not fully anticipated in the original design. A broad range of deterioration damage, such as fatigue, overload, ultraviolet damage, corrosion, and wear was presented. A broad range of materials of interest was also discussed, including the full spectrum of construction materials, metals, ceramics, polymers, composites, and coatings. Emphasis was placed on scale-dependence and history of fabrication on resulting mechanical behavior of materials.