Goodship / Middleton / Cherrington Design and Manufacture of Plastic Components for Multifunctionality

Structural Composites, Injection Molding, and 3D Printing
1. Auflage 2015
ISBN: 978-0-323-35384-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 236 Seiten

Reihe: Plastics Design Library

Design and Manufacture of Plastic Components for Multifunctionality: Structural Composites, Injection Molding, and 3D Printing presents the latest information on how plastics manufacturers are increasingly being driven towards carbon emission reduction, lightweighting, and cost savings through process integration. These technologies have the potential to revolutionize future products with built-in functionality such as sensors, smart packaging, and damage detection technology for everything from milk bottles and salad packaging to automotive bumpers and plane fuselages. This book introduces the three core manufacturing methods for multifunctional materials, composites, injection molding, and 3D printing, all processes facing challenges for the implementation of new technology. Users will find a book that brings together both process and material advances in this area, giving process engineers, designers, and manufacturers the information they need to choose the appropriate material and process for the product they are developing. - Provides an introduction to the latest technologies in the area of multifunctionality, enabling engineers to implement new breakthroughs in their own businesses - Gives an understanding of the processes that need to be considered in both design and manufacture of future devices, while using materials from a broader palette than used in existing manufacturing processes - Includes best practice guidance and flow charts to aid in material and process selection - Covers revolutionary future products with built-in functionality such as sensors, smart packaging, and damage detection technology for everything from milk bottles and salad packaging to automotive bumpers and plane fuselages

Principal Research Fellow at the Warwick Manufacturing Group (WMG), a department at the University of Warwick providing research, education and knowledge transfer in engineering, manufacturing and technology. Her areas of specialism are plastics materials, their processing and recycling, and she has undertaken many research projects in these areas - most recently looking at multifunctional materials. She - like WMG - works at the interface of academia and industry.She has edited two books under the Woodhead imprint:Management, Recycling and Reuse of Waste Composites (2009)Waste Electrical and Electronic Equipment (WEEE) Handbook (2012)

Autoren/Hrsg.

Goodship, Vannessa

Middleton, Bethany

Cherrington, Ruth

Leseproben

2

Materials and Deposition Processes for Multifunctionality

Ruth Cherrington

Jianwang Liang

Abstract

This chapter provides an introduction across a broad scope of materials in multifunctional applications. It will also look at some deposition processes that can be used to design integrated processes and add-on components for the benefit of the bulk processes that are the main focus of this book. Electrical conductivity, thermal conductivity, antimicrobial activity, shape memory, magnetism, and sensing are all introduced.

Keywords

coating

conductivity

reinforcement

deposition

multifunction

process

antimicrobial

sensing

2.1. Materials

2.1.1. Introduction

Multifunctional materials are designed to perform one or more necessary functions. The most common examples are found in composite or hybrid materials that are combined to perform another function beyond that of structural strength (Thomas and Qidwai, 2004; Leigh, 2010). Electrical and thermal conductivity, magnetic, optical, and many more other functionalities can be integrated into structural materials to provide advantages beyond which traditional materials are capable (Nemat-Nasser et al., 2005). A significant amount of research has been conducted into two-phase structural materials, such as fiber composites, laminates, foams, and other porous structures to provide weight or volumetric benefits. This will be discussed in more detail in Chapter 3.

This chapter will provide an introduction across the broad scope of materials in multifunctional applications. It will look at some deposition processes that can be used to design integrated processes and add-on components, for the benefit of the bulk processes that are the main focus of this book.

These sections can be considered as looking into functions of

Electrical conductivity

Thermal conductivity

Antimicrobial

Magnetic materials

Shape memory

There is an introductory section explaining the main uses of another generic material family: the ceramics. This explores ceramic developments in line with polymeric ones.

Finally, there is a brief section looking specifically at how polymers can be used in sensor applications. The chapter now begins looking at electrical conductivity and how it can be used.

2.1.2. Electrical Conductivity

As our world becomes more and more technically advanced and computer technology and electrical devices more prevalent, the ability of materials to conduct electric is a useful property being utilized in a continuing developing range of advanced applications in everything from coatings to embedding function whether as an add-on or within the matrix of a structural component. These are the traditional domains of metals such as copper, but increasingly polymeric-based application solutions are being investigated including applications such as electrostatic discharge, electromagnetic shielding for electronic devices, and even for lightning strike protection.

Electrostatic charges need to be discharged in a controlled way to prevent electrical damage. An uncontrolled electrical discharge may generate high currents that may damage the material or influence the performance of electronic equipment (Cosnier and Karyakin, 2011). For example, static charge that builds up within medical equipment is traditionally discharged by using a metal earthing plate that makes contact with the ground. However, if equipment was encased in a conductive polymer, electric charge could be continually drained away, maintaining a static-free environment (Zhou and Lubineau, 2013). Research into conductive polymers and their development into commercial application has meant demand for materials such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is on the increase. Therefore, this section will introduce some of the better known conductive polymers after first explaining how materials can conduct electricity.

Conductive materials have a large number of conduction electrons (between one and four electrons per atom). Common examples of high-conductivity materials are metals such as copper, silver, iron, and aluminum. The degree of conductivity is dependent on the number of charge carriers as well as the number of electrons in the material and their mobility. In a metal it is assumed that all the outer electrons are free to carry charge and when a voltage is applied across the metal, the electrons flow from one end of the conductor to the other under the influence of the electric field. Insulating materials such as wood, glass, ceramic, or the vast majority of polymers have tightly bound electrons and thus almost no electron flow activity can be found; as a result, they have high resistance to charge carriers flowing. Their conductivity is very poor. To be a conductor, free electrons need to be present to move. In between metals and insulators, they are materials called semiconductors such as silicon. For these materials, the conductivity can be adjusted by changing temperature or the loading of added charge-carrying agents that are known as dopants. This can be done at a structural or bulk level.

For example, adding charge-carrying materials as dopants (such as metal flakes) to insulating polymers by extrusion a conductive path can be created. There are also additions that can be made at a molecular level that will now be explained in the difference between instrinsically and extrinsically conductive polymers.

2.1.2.1. Intrinsically Conductive Polymers

Conductive polymers are a distinctive group of organic materials that exhibit the electrical and optical properties of both metals and semiconductors (Geoghegan and Hadziioannou, 2013b). They have a wide range of practical applications due to their low cost, conductive ability, and ease of synthesis. More than 25 conductive polymer systems have been reported; however, polyaniline, polyacetylene, polypyrrole, and poly(3,4-ethylenedioxythiophene) (PEDOT) are the most intensively studied.

Polyaniline has been around for hundreds of years and was first reported in 1835 as “aniline black” (Syed and Dinesan, 1991). It is a dark green powder in its conductive form and can be doped to produce high-level conductivities. However, one of the major limitations is that it has poor solubility in commonly known solvents such as sulfuric acid, methane sulfonic acid, formic, and acetic acids. Polyaniline has been successfully used as a coating to prevent the buildup of static energy in electrical components (Aldissi, 1993).

Polyacetylene is a conducting polymer with one of the simplest structures. It was first found to conduct electricity in 1977 and later it was discovered that very heavy doping can produce conductivities similar to that of copper. However, the material was found to be very difficult to work with as it could not be easily dissolved; therefore, other synthesis routes have since been investigated to enable the material to be dissolved into liquid precursors (Townsend et al., 1985). Therefore, uses for bulk plastic materials are unlikely in the near future.

Polypyrrole is a conductive polymer that is commonly used for commercial applications due to its long-term stability. It was first reported in 1916 as “pyrrole black” by the oxidation of pyrrole with hydrogen peroxide to produce an amorphous powder. The applications of polypyrrole were once limited due to its poor solubility; however, recent efforts have enabled the production of soluble polypyrrole formed by graft copolymerization of pyrrole. This has led to applications such as polypyrrole–paint, polypyrrole–polyvinylchloride injection molded composites, and polypyrrole-coated fabrics and fibers (Saville, 2005).

PEDOT was developed by Bayer in the late 1980s as an antistatic coating (Geoghegan and Hadziioannou, 2013b). It has excellent transparency, good electrical conductivity (in excess of 300 s/m) and shows good stability in air and humidity. It has also been found to be stable at relatively high temperatures, with the ability to withstand 125°C for several thousand hours. However, PEDOT is insoluble and therefore very difficult to work with. To enable commercial success PEDOT has been doped with the water-soluble polyelectrolyte, poly (styrenesulfonate) (PSS) resulting in a good conductivity liquid solution known as PEDOT:PSS (Yoshioka and Jabbour, 2006). In addition, it is important to identify the amount of PSS added into PEDOT as it does affect the stability and the quality of the overall dispersion process (Aernouts et al., 2004). With more than 20 years of evolution, PEDOT has become one of the most commercially developed conductive polymers. What is most interesting about the development of PEDOT is it is not the most conducting of the conductive polymers but it is the ability to process it in a variety of ways by doping it that have led to its commercial success. The use of PEDOT-based materials is being heavily researched around the world in a variety of applications from batteries to photovoltaics. It is especially interesting as a replacement for indium tin oxide (ITO) that has wide use as a transparent film-conductive coating in a wide variety of electrical devices but presents manufacturers with supply issues due to its expense.

2.1.2.2. Extrinsically Conductive Polymers

The electrical conductivity of structural...