Reference Work Entry

Handbook of Adhesion Technology

pp 1527-1533

Adhesion Technology Recap – Current and Emerging Areas

  • Lucas F. M. da SilvaAffiliated withDepartment of Mechanical Engineering, Faculty of Engineering of the University of Porto Email author 
  • , Andreas ÖchsnerAffiliated withDepartment of Applied Mechanics, Technical University of MalaysiaUniversity Centre for Mass and Thermal Transport in Engineering Materials, School of Engineering, The University of Newcastle
  • , Robert D. AdamsAffiliated withDepartment of Mechanical Engineering, University of BristolDepartment of Engineering Science, University of Oxford

Abstract

This chapter gives a brief description of the subjects and chapters that are included in this handbook. The handbook is organized in ten parts: theory of adhesion, surface treatment, adhesive and sealant materials, testing of adhesive properties, joint design, durability, manufacture, quality control, applications, and emerging areas. A total of 57 chapters are presented covering all aspects of adhesion and adhesives. In addition to the information contained in each chapter, an extensive list of references is given (approximately 4,000 references).

Abstract

This chapter gives a brief description of the subjects and chapters that are included in this handbook. The handbook is organized in ten parts: theory of adhesion, surface treatment, adhesive and sealant materials, testing of adhesive properties, joint design, durability, manufacture, quality control, applications, and emerging areas. A total of 57 chapters are presented covering all aspects of adhesion and adhesives. In addition to the information contained in each chapter, an extensive list of references is given (approximately 4,000 references).

Theory of Adhesion

In the chapter Theories of Fundamental Adhesion by Packham, the historical development and current status of the four classical theories of adhesion (mechanical theory, adsorption theory, electrostatic theory, and diffusion theory) are reviewed. The role of weak boundary layers is also discussed with emphasis on the importance of careful investigation of the locus of failure of an adhesive bond. Next, Brogly, in Forces Involved in Adhesion describes the main forces responsible for adhesion, from strong covalent bonds to weak van der Waals forces, also considering specific interactions such as acid–base or capillary forces. The chapter Wetting of Solidsby Shanahan and Possart considers thermodynamic aspects of wetting, which involves intimate contact between the two phases and the environment. A short overview of the relevant processes and parameters in the spreading of liquids on substrates is presented in the chapter Spreading of Liquids on Substrates by Reiter. In a simplified view, the dynamics of these processes can be understood as being controlled by the balance of driving forces and resistance due to dissipative processes. Finally, in the chapter Thermodynamics of Adhesion, Possart and Shanahan show that wetting data may be used to estimate the thermodynamic, or Dupré, energy of adhesion, provided certain assumptions are made and suitable models constructed for, in particular, interfacial tensions.

Surface Treatments

The use of surface treatments to optimize adhesion has been well-established. In the chapter General Introduction to Surface Treatments, Critchlow considers the main treatment methods for metals and polymers in terms of how such processes are carried out and their influence on surface physical and chemical properties. Consideration has been given to a range of treatments from simple degrease options to the more highly complex multistage processes. Davies, in Surface Treatments of Selected Materials, discusses high-performance surface treatments for several metals and other materials. Surface treatment of aluminum and other metals are used to illustrate how proper surface preparations meet these requirements. The chapter Surface Characterization​ and Its Role in Adhesion Science and Technology by Watts reviews a variety of methods of surface characterization that have been found to be useful in the study of adhesion. The methods considered can conveniently be considered in three groups: surface topography, surface free energy of a material, and surface specific chemical analysis. Next, Watts in the chapter Use of Surface Analysis Methods to Probe the Interfacial Chemistry of Adhesion, explores the manner in which the surface analysis methods of x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) can be used to extract information regarding the interfacial chemistry of adhesion from polymer/metal systems such as adhesive joints. The last chapter of this section, Organosilanes:​ Adhesion Promoters and Primers by Abel, describes organosilanes from their genesis to their chemistry. The necessary interactions that such molecules have to develop on materials in order to fulfill their main role as adhesion promoters are explained. The use of silanes as primers particularly where the user aims to improve adhesion or protect from corrosion is also considered. Some other organic or nonorganic adhesion promoters are also discussed.

Adhesive and Sealant Materials

The first chapter Classification of Adhesive and Sealant Materials by Sancaktar, classifies adhesive and sealant materials. For this purpose, various categories are considered depending on the polymer base, functionality in the polymer “backbone,” physical forms, chemical families, functional types, and methods of application. Next, in the chapter Composition of Adhesives, Kim et al. give information about various ingredients that may appear in an adhesive or sealant: primary resins, hardeners, solvents, fillers, plasticizers, reinforcements, and various additives. In the third chapter of this section, Papon (Adhesive Families) classifies adhesives and sealants in three broad groups. First, there are adhesives where the polymer is preexisting (and must be placed beforehand in fluid form: solution, emulsion, or “melt” state). Second, there are adhesives where the polymer is formed during the course of a reactive process (polymerization). Third, Papon describes the particular category of pressure-sensitive adhesives where the polymer exhibits viscoelastic properties able to develop adhesion during the bonding step. The basic concepts, formulations, and test methods for pressure-sensitive adhesives are presented in the chapter Pressure Sensitive Adhesives by Paul, stressing the importance of interfacial interactions, viscous loss, and extensibility. Selection of the correct adhesive for an application can be a daunting task due to the many types commercially available ranging from different chemistries through different forms to an almost continuum of material properties. Kellar in chapter Selection of Adhesives gives a logical approach to this task and selection criteria.

Testing of Adhesive Properties

The first chapter by Dillard Physical Properties of Adhesives addresses several relevant physical properties of adhesives, including viscosity, density, and stress–strain behavior, quantities that are often thought to be intrinsic properties of a material. The thermal properties of adhesives are described next by Comyn. Consideration is given to the shelf-life, the hardening process, the glass transition temperature, the thermal conductivity and thermal expansion, and the thermal breakdown of adhesives. In the chapter Failure Strength Tests, da Silva describes the major failure strength tests used to determine the intrinsic adhesive properties. Tensile, compressive, and shear tests are described with reference to the major international standards. Bulk and in situ (adhesive in a joint) tests are discussed and related. The chapter on Fracture Tests by Blackman considers first the fracture in a bulk adhesive specimen under mode I, that is, tensile opening loading conditions. Mode II (in plane shear) and mixed-mode I/II testing of adhesive joints are also considered. There is often the need to measure the resistance to fracture in a joint with flexible substrates. One such test is the peel test and some variants of the peel test are considered in that chapter. Goglio, in the chapter on Impact Tests, describes the main tests used to assess the impact strength of adhesives and joints. The main tests used in the experiments are pendulum, falling weight and Hopkinson bar loading conditions, or evolutions of these. The last chapter of this section by Yamaguchi and Dillard deals with Special Tests. This chapter gives a brief description of special mechanical tests for various types of material and sample geometries, such as blister tests, tensile tests, and shear tests for sealants/foam adhesives, indentation tests, scratch tests, tack tests, and tests for the evaluation of residual stresses.

Joint Design

This section starts with the chapter Constitutive Adhesive and Sealant Models by Sancaktar. The chapter includes deformation theories and viscoelasticity with linearity and nonlinearity considerations, rubber elasticity, singularity methods, bulk adhesive as composite material, damage models, the effects of cure and processing conditions on the mechanical behavior, and the concept of the “interphase.” The chapter Analytical Approach to Joint Design by Tong and Luo presents an analytical approach for determining stress and strength of adhesively bonded joints. Various closed-form solutions for adhesive stresses and edge bending moment for balanced single lap joints are presented and compared. In the chapter Numerical Approach:​ Finite Element Analysis, Ashcroft provides first a general background to the development and application of the finite element (FE) method. Then, he discusses some of the practical aspects of FE modeling and gives applications of the FE method to adhesively bonded joints. FE analysis is currently the only technique that can comprehensively address the challenges of modeling bonded joints under realistic operating conditions. However, a reliable and robust method of using FE analysis to model failure in bonded joints is still to be developed. Öchsner, in the chapter Special Numerical Techniques to Joint Design, introduces special numerical techniques to analyze adhesive joints. The first part covers special FE techniques which reduce the size of the computational models. The second part of this chapter introduces alternative approximation methods, the boundary element method, and the finite difference method. In the chapter Design Rules and Methods to Improve Joint Strength, da Silva describes the main factors influencing joint strength. Methods are then proposed to improve the joint strength by using fillets, adherend profiling and other geometric solutions, and hybrid joining. Repair designs are also discussed. Finally, configurations are recommended for several types of joint. The chapter Design with Sealants by Anderson describes the many factors that go into the design of reliable sealant joints. The various joint types are discussed and illustrated, and their critical dimensions and materials are described. Sato, in the chapter Design for Impact Loads, discusses design methods for adhesively bonded joints subjected to impact loading. Methodologies to treat the dynamic responses of structures are shown. Some examples of stress analysis are shown, where closed-form approaches and dynamic FE analyses are explained. The last chapter of this section Vibration Damping of Adhesively Bonded Joints by Adams et al. discusses the general concept of vibration damping in vibrating structures and how it can be used to limit vibration amplitudes. Simple equations for calculating the damping of a lap joint in tension and bending have been developed. As there is very little experimental data available, the damping of a variety of adhesively bonded single lap joints has been measured by the authors.

Durability

In the chapter Effect of Water and Mechanical Stress on Durability, Ashcroft and Comyn discuss the effect that absorbed water has on the strength of adhesively bonded joints. The influence of adherend surface treatment, applied stress, and adhesive type on the environmental degradation of bonded joints is demonstrated. Methods of modeling the environmental degradation of adhesively bonded joints using coupled hygro-mechanical finite element (FE) analysis are then described. Bhowmik, in the chapter Effect of Radiation and Vacuum, describes basic understanding of high-energy radiation as well as space vacuum and the properties of high-performance polymers and adhesives when exposed to high-energy radiation in vacuum. As a case study, performance of space durable polymers, such as polybenzimidazole (PBI), modified by low-pressure plasma and atmospheric pressure plasma and fabrication of the polymer by ultrahigh-temperature-resistant epoxy adhesive is reported. The chapter Fatigue Load Conditions by Ashcroft discusses some of the main factors when considering fatigue, with particular reference to issues applicable to bonded joint. The main methods of characterizing and predicting the response of bonded joints to fatigue loading are described. Finally, there are sections on the special cases of creep-fatigue and impact fatigue. In the chapter Creep Load Conditions, Geiss considers viscoelastic models, superposition principles, experimental testing procedures, and predictive methods. In the last chapter of this section, Durability of Nonstructural Adhesives by Palmer, methods evaluating durability and test regimes, including exposure to elevated and reduced temperatures, UV radiation, moisture, saline solutions, stress and fatigue, both individually and combined in cycles are considered.

Manufacture

The first subject in this section is Storage of Adhesives by Engeldinger and Lim. A major part of this chapter focuses on the shelf life and safety aspects. Adhesives are divided into four categories, solvent-based, water-based, hot-melt, and reactive adhesives. In the chapter Preparation for Bonding, Lutz discusses each item of the process chain: the storage of adhesives, transfer to the application area, different metering and dispensing technologies, mixing equipment used, substrate preparation, and quality control. Proposals are made regarding education of personnel and how to create a safe working environment. In Equipment for Adhesive Bonding, Peschka describes the equipment required for manual adhesive bonding processes. Automation and robotics are outlined with a special emphasis on parameters affecting accuracy. Accelerated curing using such devices as UV radiation and inductive heating are also done. The last chapter of this section, Environment and Safety by van Halteren, deals with the different aspects of consumer, work, and environmental protection, including health and safety information, related to the use of adhesives in industrial and domestic areas.

Quality Control

This section starts with the chapter Quality Control of Raw Materials by Wakabayashi. The main components of adhesives are first described and then quality control procedures are discussed such as chemistry, impurity content, molecular weight, viscosity, density, and quality control of raw materials in storage. Next, in the chapter Processing Quality Control by Haraga, the processing quality control of adhesively bonded joints in actual production lines is discussed. Topics such as control of environmental conditions and materials, inspection of surface treatment of adherends, adhesive selection for easy process control, and education and training of operators are treated. In the chapter Nondestructive Testing by Adams, the types of defect encountered in adhesive joints and the nondestructive testing techniques available to detect them are reviewed. Several techniques are available for void detection, the most commonly used being ultrasonics and different types of bond tester. The detection of poor cohesive properties is more difficult, but can be achieved with ultrasonic or dielectric measurements. The last chapter of this section, Techniques for Postfracture Analysis by Suárez, describes the latest forensic engineering techniques used in the investigation of failed joints. An overview of the examination and analysis methodology is given.

Applications

The first application treated is the Aeronautical Industry by Hart-Smith. The following topics are treated: basic needs, adhesive characteristics, surface preparation, design of adhesive joints, durability, defects, thermal effects, quality control, composite structures, repairs, and examples of use. In the chapter Aerospace Industry, Desagulier introduces some of the specific bonding-related issues that face those responsible for bonding operations in space applications such as extremely high mechanical loads over a short time, with the launcher and its payloads subjected to gravity magnified by about 20, followed by exposure to extremely high temperatures over a very long period, with the observation and telecom satellites under zero gravity. Burchardt, in the chapter Automotive Industry, presents the general requirements for adhesives in automotive production. The key properties of the various structural adhesives are described as are elements for the evaluation of adhesives with the optimum properties. The Rail Industry is next treated by Suzuki. It is shown that adhesives are an indispensable joining technology for railway industries. Adhesives are used for the fabrication of almost all rail cars. For example, in the steel main structure of conventional rolling stock, adhesives are applied for bonding decorated aluminum sheets of wall and ceiling to frames, bonding of floor covering to the floor plate, and fixing heat insulating material to the inside of the carriages. The chapter Marine Industry by Davies describes the use of adhesive bonding to assemble structures in the marine industry. The marine environment is extremely aggressive, and this has resulted in widespread use of fiber-reinforced composite materials. Adhesive bonding is a lightweight and corrosion-resistant means of joining these materials. Three industrial applications are used to illustrate the use of adhesive bonding, small pleasure boats, high-performance racing yachts, and bonded structures in the offshore industry. In the chapter Civil Industry, Böhm describes adhesive bonding applications in the civil construction sector, specific requirements, and adherends. The execution of bonding and properties of adhesive-bonded civil constructions are also treated. Jung and Kim, in the chapter Electrical Industry, explain the mechanisms underlying the electrical conduction in adhesive joints, and the thermal and mechanical parameters that should be measured are introduced. In terms of the evaluation of the reliability of adhesives in electronics, the basic test procedures, including several specific test methods and analysis techniques, are explained. The last chapter of this section, Shoe Industry by Martín-Martínez, constitutes one of the very few reviews in the existing literature on shoe bonding and gives an updated overview of the upper to sole bonding by means of adhesives. The surface preparation of rubber soles and both the formulations of polyurethane and polychloroprene adhesives are described. The preparation of adhesive joints and adhesion tests are also revised.

Emerging Areas

In the chapter Molecular Dynamics Simulation and Molecular Orbital Method by Zhao et al., various simulation methods pertaining to adhesion technology are introduced, such as molecular dynamics, quantum mechanics, the molecular orbital method, and the density functional theory. Some examples are proposed investigating adhesion issues using various simulation methods. In the chapter Bioadhesives, Suárez describes the adhesives used by living organisms in nature or substances that are formulated from substantially or totally bio-based raw materials. It also includes natural or synthetic adhesives that are compatible with living tissues and biological fluids, biomimetic and bioinspired adhesives designed and manufactured to use the exceptional properties of biological adhesives, and self-healing polymeric adhesives. Gorb, in Biological Fibrillar Adhesives:​ Functional Principles and Biomimetic Applications, reviews functional principles of biological systems in various animal groups such as insects, spiders, and geckos with an emphasis on insects and discuss their biomimetic potential. Data on ultrastructure and mechanics of materials of adhesive pads, movements during contact formation and breakage, and the role of the fluid in the contact between the pad and substrate are presented. Adhesives with Nanoparticles are discussed by Taylor. This chapter outlines the principal types of nanoparticles, and the methods that may be used to disperse the particles in a polymer matrix. It discusses how nanoparticles can alter the mechanical properties (stiffness and fracture), electrical properties (conductivity), and the functional properties (permeability, glass transition temperature) of thermoset polymers. In the chapter Adhesive Dentistry, Nicholson describes the principal uses of adhesives in clinical dentistry, covering both the materials and the clinical techniques involved. The two types of tooth-colored material, namely, the composite resin and the glass-ionomer cement, are described, together with their current variations. Surface pretreatment is critical for the success of these systems and the current state of the understanding of this aspect of the subject is described. Adhesion in Medicine is covered by Chivers. Adhesives technology has two main applications in medicine as considered in this chapter, for internal fixation of tissues usually after surgery, and for use on the skin, primarily to hold dressings in place. The last chapter by Sato concerns Recycling and Environmental Aspects. Adhesively bonded adherends should be often separated before they can be recycled. For this purpose, dismantlable adhesives, which can be separated with stimulations (softening of adhesive, expansion force due to blowing agents or thermally expandable microcapsules, chemical degradation, and electrochemical reaction), have been developed recently. These adhesives can be applied to adherend recycling or product reworking.

Conclusions

The preparation of this handbook has been an interesting experience for the editors. The review process gave a deeper insight into the various aspects of adhesion from basics to applications and the chance to discuss in detail the chapters directly with the authors. Authors come from every background (chemistry, physics, mechanics) and work in either academia or industry, proving that adhesion is a truly multidisciplinary and widely applied subject. The editors would like to thank the authors for their patience in the preparation of this handbook. Finally, the editors especially thank Dr. Christoph Baumann and Ms. Tina Shelton, Springer editors, who helped enormously toward the success of this handbook.

Copyright information

© Springer-Verlag Berlin Heidelberg 2011
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