Handbook of Plastic Foams

Types, Properties, Manufacture and Applications

Arthur H. Landrock

• Publisher: William Andrew
• Year: 1995
• Print ISBN: 9780815513575
• eBook ISBN: 9780815517658
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

This book is intended to be a source of practical information on all types of plastic foams (cellular plastics) in use, including the new structural plastic foams. Elastomer (rubber-like) foams are also considered. The book is intended primarily for those who require a non-theoretical, authoritative, easy-to-use handbook in the subject area. It should be of value to materials engineers, plastics fabricators, chemists, chemical engineers and students. Recognized authorities have written several chapters and parts of chapters in their fields of expertise. The book is organized in such a way that information on a desired subject can be found rapidly. An unusual feature is a comprehensive listing of all known standardization documents (test methods, practices, and specifications), including some international standards. Each document includes a brief description of its contents.

1

INTRODUCTION TO FOAMS AND FOAM FORMATION

Michael O. Okoroafor and Kurt C. Frisch

INTRODUCTION

Cellular plastics or plastic foams, also referred to as expanded or sponge plastics, generally consist of a minimum of two phases, a solid–polymer matrix and a gaseous phase derived from a blowing agent. The solid–polymer phase may be either inorganic, organic or organometallic. There may be more than one solid phase present, which can be composed of polymer alloys or polymer blends based on two or more polymers, or which can be in the form of interpenetrating polymer networks (IPNs) which consist of at least two crosslinked polymer networks, or a pseudo–or semi–IPN formed from a combination of at least one or more linear polymers with crosslinked polymers not linked by means of covalent bonds.

Other solid phases may be present in the foam in the form of fillers, either fibrous or other–shaped fillers which may be of inorganic origin, e.g. glass, ceramic or metallic, or they may be polymeric in nature. Foams may be flexible or rigid, depending upon whether their glass–transition temperatures are below or above room temperature, which, in turn, depends upon their chemical composition, degree of crystallanity, and degree of crosslinking. Intermediate between flexible and rigid foams are semi–rigid or semi–flexible foams. The cell geometry, i.e. open vs. closed cell, size and shape, greatly affect the foam properties. Thus, closed–cell foams are most suitable for thermal insulation, while open–cell foams are best for acoustical insulation.

Plastic foams can be produced in a great variety of densities, ranging from about 0.1 lb/ft³ (1.6 kg/m³) to over 60 lb/ft³ (960 kg/m³) (1). Since the mechanical–strength properties are generally proportional to the foam densities, the applications of these foams usually determine which range of foam densities should be produced. Thus, for rigid foam, load–bearing applications require high densities and (or) fiber–reinforced foams, while low densities are usually used for thermal insulation.

The production of polymeric–foam materials can be carried out by either mechanical, chemical, or physical means. Some of the most commonly used methods are the following (2):

1. Thermal decomposition of chemical blowing agents generating either nitrogen or carbon dioxide, or both, by application of heat, or as the result of the exothermic heat of reaction during polymerization.

2. Mechanical whipping of gases (frothing) into a polymer system (melt, solution or suspension) which hardens, either by catalytic action or heat, or both, thus entrapping the gas bubbles in the polymer matrix.

3. Volatilization of low–boiling liquids such as fluoro–carbons or methylene chloride within the polymer mass as the result of the exothermic heat of reaction, or by application of heat.

4. Volatilization of gases produced by the exothermic heat of reaction during polymerization such as occurs in the reaction of isocyanate with water to form carbon dioxide.

5. Expansion of dissolved gas in a polymer mass on reduction of pressure in the system.

6. Incorporation of hollow microspheres into a polymer mass. The microspheres may consist of either hollow glass or hollow plastic beads.

7. Expansion of gas–filled beads by application of heat or expansion of these beads in a polymer mass by the heat of reaction, e.g. expansion of polystyrene beads in a polyurethane or epoxy resin system.

The production of foams can take place by many different techniques. These may include (3):

1. Continuous slab–stock production by pouring or impingement, using multi–component foam machines.

2. Compression molding of foams.

3. Reaction–injection molding (RIM), usually by impingement.

4. Foaming–in–place by pouring from a dual– or multi– component head.

5. Spraying of foams.

6. Extrusion of foams using expandable beads or pellets.

7. Injection molding of expandable beads or pellets.

8. Rotational casting of foams.

9. Frothing of foams, either by introduction of air or of a low–boiling volatile solvent (e.g. dichlorodifluoro–methane, F–12).

10. Lamination of foams (foam–board production).

11. Production of foam composites.

12. Precipitation foam processes where a polymer phase is formed by polymerization or precipitation from a liquid which is later allowed to escape.

It should be recognized that almost every thermoplastic and thermoset resin may be produced today in cellular form by means of the mechanisms and processes cited above. The physical properties of the foams reflect in many ways those of the neat polymers, taking into account the effects of density and cell geometry.

There are numerous books, chapters in books, and reviews published on foams, covering a wide spectrum of cellular plastics. Some of these are listed in references 1–15.

In addition, two journals (in English) deal exclusively with plastic foams. These are the “Journal of Cellular Plastics” (Technomic Publishing Co.) and “Cellular Polymers” (RAPRA Technology Ltd.). A valuable source of information for foamed plastics has been the annual proceedings of various technical organizations such as the Society of the Plastics Industry (SPI); the German FSK and others.

CFC EFFECTS AND ALTERNATIVES

A search for alternate blowing agents for urethane foams became necessary in 1987 following the Montreal Protocol, which mandated the development of foams with substantially reduced CFC content by 1995. CFC’s or chlorofluorocarbons are chemicals that cause ozone depletion in the stratosphere as well as the “Greenhouse Effect”. They have been typically employed as blowing agent in foams. Since the initial proclamation, the mandate has been revised several times to accelerate the CFC phaseout schedule, with the latest revision resulting from the Copenhagen agreement in November 1992 where 87 nations resolved to move up total CFC phaseout by four years in January 1996. The recent Copenhagen revision induced major CFC manufacturers to accelerate their phaseout time table. DuPont announced recently that it plans to stop CFC production by 1994, almost 2 years ahead of plan.

Some countries have independently banned CFC use. For example, Sweden banned the use of CFC’s in 1991, followed by Switzerland in 1992. In Europe Rigid Foam manufacturers are using hydrocarbon blowing agents, such as cyclopentane as an alternative to CFC.

The U.S. Environmental Protection Agency issued a final rule banning the use of CFC’s in flexible plastics and packaging foams, among other uses, after February 15, 1993. Exceptions are CFC–11 and CFC–13 which can be used, temporarily, in mold release agents and the production of plastic and elastomeric materials. However, in 1994, no CFC’s will be allowed in flexible foams in the U.S., and a tax will be levied on other C...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• PREFACE
• CONTRIBUTORS
• Notice
• Chapter 1: INTRODUCTION TO FOAMS AND FOAM FORMATION
• Chapter 2: THERMOSETTING FOAMS
• Chapter 3: THERMOPLASTIC FOAMS
• Chapter 4: ELASTOMERIC FOAMS
• Chapter 5: MISCELLANEOUS AND SPECIALTY FOAMS: (Epoxy Foams, Polyester Foams, Silicone Foams, Urea–Formaldehyde Foams, Polybenzimidazole, Foams, Polyimide Foams, Polyphosphazene Foams, and Syntactic Foams)
• Chapter 6: SOLVENT CEMENTING AND ADHESIVE BONDING OF FOAMS
• Chapter 7: ADDITIVES, FILLERS AND REINFORCEMENTS
• Chapter 8: METHODS OF MANUFACTURE
• Chapter 9: SOURCES OF INFORMATION
• Chapter 10: TEST METHODS
• Chapter 11: STANDARDIZATION DOCUMENTS
• GLOSSARY
• INDEX