Adhesives and Adhesion. ENGK49 Materiais de Origem Vegetal Aplicados a Construção

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1 Adhesives and Adhesion ENGK49 Materiais de Origem Vegetal Aplicados a Construção

2 Contents Surface Properties of Wood for Bonding Physical Properties of Wood for Bonding Adhesives Bonding Process Bonded Joints Testing and Performance Standards

3 WOOD ADHESIVE USES Lumber Laminates Glue-laminated timbers, Overlayed materials Laminated wood nonwood composites; Multiwood composites (COM-PLYc) Veneer-based material Plywood, LVL, PSL Composite material Fiberboard (low-, medium-, or high-density) Oriented strandboard (OSB); Laminated strand lumber (LSL); Oriented strand lumber (OSL) Cellulosic fiberboard; Hardboard; Particleboard; Waferboard; Flakeboard

4 Wood Bonding Variables

5 THEORIES OF ADHESION

7 International Journal of Adhesion & Adhesives 29 (2009) doi: /j.ijadhadh A REVIEW OF FACTORS INFLUENCING THE DURABILITY OF STRUCTURAL BONDED TIMBER JOINTS

8 Abstract Uses: Rehabilitation and repair of timber structures. Advantages: to maintain satisfactory performance, in severe environments be able to support design loads, for the planned life time. factors determining the durability of adhesive environment, materials and stresses Problem Since this subject in relation to timber bonding is very disperse within the literature Aim:, this paper will focus briefly on each of the aforementioned factors, thus providing a general understanding on the factors that influence the durability of bonded timber joints.

9 Structure of Article Introduction Environment Moisture content Temperature Materials Surface preparation Age of surface Influence of wood species Treated wood Stress Influence of material stiffness on stress Influence of joint geometry on stress Single lap joint Co-axial joint Peel joint Modified butt joint (pulloff test) Joint selection for the assessment of bond performance Summary

10 Introduction Uses: Rehabilitation and repairing techniques of timber structures involving adhesive joints instead of mechanical joints. Advantages Can distribute the applied load More uniform distribution of stress, Little or no damage to the adherends, Adds very little weight has a superior fatigue resistance to other joining methods, joining dissimilar materials, Reduce manufacturing costs. Limitations Careful surface preparation of the adherends, Designed to eliminate peel and cleavage stresses, Some adhesives have a limited high-temperature resistance, Affected by service environments Difficult to disassemble for inspection and repair

11 Introduction

12 Introduction Mechanisms of adhesion bond energies kj/mol for instance Van der Waals forces 20 urea formaldehyde (UF), isocyanates from the polyurethane (PU), epoxies (EP), vinyl adhesives. Hydrogen bonds 60 Phenolics, EP, UF or some PU True chemical bonds PU, EP or isocyanates

13 Introduction Scientific fields (support to literature review) Macromolecular science, physical chemistry of surfaces and interfaces, materials science, rheology, mechanics and micromechanics of fracture. Theoretical models of adhesion mechanical interlocking; electronic theory; theory of boundary layers and inter-phases; adsorption (thermodynamic) theory; diffusion theory chemical bond theory Pocius AV. Adhesion and adhesives technology: an introduction. 2nd ed. Hanser Gardner Publications; Pizzi A, Mittal KL. Handbook of adhesive technology. 2nd ed.crcpressllc; 2003.

14 Environment Moisture content May affect the properties of an epoxy adhesive and the interface between it and the adherend. [12 14] Wheeler and Hutchinson [12] carried out a test programme to investigate the adhesion Broughton and Hutchinson [13] conducted a research study to evaluate the effect of moisture content on the pull-out Temperature Temperature is also an important factor in the durability of structural adhesive joints Cruz et al. [27,28] [29] performed several experiments to assess the influence of the temperature in the behaviour of epoxy adhesives.

15 Materials Surface preparation Thequality of the surface varies with the type of machining process as well as with how carefully the process is controlled. Age of surface The severity and rate of this inactivation depends on wood species, wood moisture content (MC), temperature level and time of temperature exposure.influence of wood species Treated wood Several studies concerning the influence of different preservative treatments, including oil-borne preservatives Influence of wood species hardwoods contain more extractives than softwoods

16 Influence of wood species Materials

17 Stress Influence of material stiffness on stress The stiffness of the various materials involved is a key factor in the development and magnitude of resultant stress concentrations. Influence of joint geometry Single lap joint Co-axial joint Peel joint Fracture tests

18 Stress

19 Modified butt joint (pull-off test) Materials

20 Fracture tests Materials

Wood Products Taxonomy

Then 1 Now 2 Wood Products Taxonomy WOOD Composites Solid Wood Panels Engineered Lumber Composites (ELC) Softwood Lumber Glued Treated Hardwood Lumber Wood/ Non-wood Wood Based LVL Boards Finger joined