Polymeric Foams Structure-Property-Performance

A Design Guide

Bernard Obi

• Publisher: William Andrew
• Year: 2017
• Print ISBN: 9781455777556
• eBook ISBN: 9781455777563
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería química y bioquímica

Polymeric Foams Structure–Property–Performance: A Design Guide is a response to the design challenges faced by engineers in a growing market with evolving standards, new regulations, and an ever-increasing variety of application types for polymeric foam. Bernard Obi, an author with wide experience in testing, characterizing, and applying polymer foams, approaches this emerging complexity with a practical design methodology that focuses on understanding the relationship between structure–properties of polymeric foams and their performance attributes. The book not only introduces the fundamentals of polymer and foam science and engineering, but also goes more in-depth, covering foam processing, properties, and uses for a variety of applications.By connecting the diverse technologies of polymer science to those from foam science, and by linking both micro- and macrostructure–property relationships to key performance attributes, the book gives engineers the information required to solve pressing design problems involving the use of polymeric foams and to optimize foam performance. With a focus on applications in the automotive and transportation industries, as well as uses of foams in structural composites for lightweight applications, the author provides numerous case studies and design examples of real-life industrial problems from various industries and their solutions.- Provides the science and engineering fundamentals relevant for solving polymer foam application problems- Offers an exceptionally practical methodology to tackle the increasing complexity of real-world design challenges faced by engineers working with foams- Discusses numerous case studies and design examples, with a focus on automotive and transportation- Utilizes a practical design methodology focused on understanding the relationship between structure-properties of polymeric foams and their performance attributes

Part I

Introduction

Outline

1 Overview of Applications of Polymeric Foams

1

Overview of Applications of Polymeric Foams

Abstract

It is hard to look around our modern world without encountering various types of polymeric materials, since they are used in such a wide variety of applications and functions. A closer examination reveals that many of these polymers are used as foamed articles. Their wide range of cellular morphological and functional characteristics allows them to be used in numerous applications where their lightweight and many other attributes can follow from the cellular nature of these foams. A potential classification and potential end-use applications of polymeric foams include structural foams, flexible foams, and specialty foams.

Keywords

Polymeric foams; blowing agents; structure–property–performance relationship; structural foams; insulation foams; flexible foams; bedding and seating foams; specialty foams; water-repellent membranes

1.1 Introduction

1.1.1 Background

It is hard to look around our modern world without encountering various types of polymeric materials, since they are used in such a wide variety of applications and functions. A closer examination reveals that many of these polymers are used as foamed articles. Their wide range of cellular morphological and functional characteristics allows them to be used in numerous applications where their lightweight and many other attributes can follow from the cellular nature of these foams. A potential classification and potential end-use applications of polymeric foams include:

1. Structural foams: appliances, building and construction, transportation, marine, tanks, pipes and floatation, furniture, packaging, food and drink containers.

2. Flexible foams: bedding and furniture, packaging, carpet underlay, absorbents, footwear and sports applications, toys and novelties, transportation, and textiles.

3. Specialty foams:

a. Biomedical applications: bones and cartilage, lightweight casts, orthopedic equipment, tissue engineering, and synthetic organs.

b. Space application: insulation, coatings, advanced sensors and actuators, structural components, space suits, and expanded structures.

The major foamed products by polymer types used in the various applications described earlier include polyurethane (PU) foams, polyolefin (PO) foams, polystyrene (PS) foams, and polyvinyl chloride (PVC) foams. More specialty polymeric foams include phenolic foams and fluoropolymer foams.

Polymeric foams comprise a small proportion of the total global plastic market [1]. It was estimated to be about 7% of the total polymer consumption in 2007. The foam industry is expected to witness steady growth, since cellular materials offer unique advantages over traditional materials. High-density cellular plastics are widely used in furniture, transportation, and building products, while low-density foams find use in shock absorption, insulation, and rigid packaging. The global polymeric foams market is projected to reach 30 million metric tons by 2020, at an average compounded annual growth rate (CAGR) of more than 3.5% [1]. The Asia-Pacific region is by far the largest and the fastest growing foam market which is projected to exceed 10 million tons by 2020, at a CAGR of more than 4.5% [1]. Although there has been a subdued demand in the recent past, future growth is expected due to various initiatives in polyurethane foams, as well as new and evolving applications, e.g., using foamed PVC for windows, doors, and house sidings; use of cross-linked polyolefin foams in sports and leisure goods [1,2]. It is expected that the resurgence in the polymeric foams market would be sustained from the emerging and continued demand from particularly the Asian-Pacific economies, as well as the Latin American regions [1,2]. Also the construction industry’s renewed focus on sustainable and green construction products particularly in Europe as well as in other developed geographies will continue to drive growth in polymeric foams in the future. The US foamed plastics industry is valued at US$22.5 billion, and demand was expected to reach 10.5 billion pounds in 2015 as key construction and motor vehicle markets recover [1–3]. Foamed urethane will remain the largest segment, while foamed low-density polyethylene (LDPE) will grow the fastest [1–3]. Construction will provide the best opportunities based on growth in insulation and carpet underlay applications [1–3].

The global polymer foam industry has shown steady progress in the past few years due to innovations in technology and applications. The inherent foam characteristics include insulation, energy conservation, sound attenuation and absorption, shock absorption, and light-weighting resulting in material savings. Cellular materials can offer a wide range of properties. Foam technology covers a wide range of techniques including those useful for microcellular foaming. These techniques include injection molding and extrusion foaming, bead foaming, and cross-linked polyolefin foaming. These techniques continue to evolve as new designs of screw, mold, die, and blowing agent (BAs) continue to improve. As a result, uniform fine-celled polymeric foam products have been produced to meet demanding performance requirements. Protective packaging is a large, constantly developing market for foams. Nova Chemicals Corporation has manufactured food grade microwaveable foams from styrene maleic anhydride (SMA) copolymers [4]. Huntsman has new expanded polystyrene technology with 0.4–1.6 mm beads developed with a low rate of pentane BA inclusion (3%–7%) [5]. Molders expand the beads for applications ranging from packaging to roofing insulation. All industries are concerned with reducing environmental impact. Efforts are being made to reduce volatile organic compound (VOC) emissions in foaming. Alternatively there are environmentally friendly BAs such as those newly developed by Adeka Palmarole for food packaging, and many types of foam are now water-blown. Foams have been produced using the latest polymeric materials including nano-composites, wood composites, and biodegradable polymers such as polylactic acid (PLA).

1.1.1.1 Polymeric Foaming Systems and Processes

Polymeric foams represent a class of composites in which a gas phase is dispersed in a solid polymer matrix. The polymeric foam is typically achieved by processes that combine the two phases in such a way to lock in the metastable gas dispersion in a polymer liquid matrix via solidification during the foam expansion process. Solidification can be achieved in two types of foaming systems, namely (1) reactive foaming systems and (2) nonreactive foaming systems. In reactive foaming systems, solidification is predominantly achieved by a sol-gel process due to cross-linking network reactions involving multifunctional reactive low viscosity monomeric or prepolymer species. In nonreactive foaming systems, foaming involves fully polymerized species which is heated to a liquid state, and then mixed with the blowing gases prior to the expansion process. In the nonreactive foaming processes, solidification can be accomplished by either vitrification, as in glassy polymers or by crystallization as in semicrystalline polymers.

In both foaming processes, both physical blowing agents (PBAs) and chemical blowing agents (CBAs) may be used, either individually or in combination. PBAs are typically gases or low boiling liquids that are not generated by reaction but are released either by depressurization or increasing temperatures due to active heating or exothermic heat released during the reactive foaming process. On the other hand, CBAs typically release gases via a decomposition reaction during the foaming process. The decomposition reaction is typically thermally activated by active heating or exothermic heat released during the reactive foaming process.

In reactive foaming processes, both PBAs and CBAs may be used. However, PBAs are predominantly used in reactive foaming systems. In reactive foaming involving simultaneous polymerization and foaming processes, the polymerization of monomeric species is usually exothermic, providing a large heat release required for boiling the liquid blowing agent and expanding the gases during the blowing or foam expansion process. CBAs may be used in reactive foaming as well, in as much as the heat released during the polymerization reaction will cause the decomposition of the CBAs, releasing the gas for foam expansion.

In nonreactive foaming processes, the predominant practice is the equilibrium saturation/dissolution of gaseous and/or liquid BAs in the polymer “melt” under high temperature and pressure in the processing equipment. Exiting the processing equipment is normally accompanied by large pressure drops which drive the gas expansion foaming process. The gas expansion process creates cooling effect which leads to solidification by either vitrification at temperatures below the glass transition temperature (T_g) for amorphous polymers or by crystallization below the crystallization temperatures (T_c) for semicrystalline polymers. In nonreactive foaming processes, both PBAs and CBAs are used, either individually or in combination to achieve the product design and performance objectives.

The resulting foam has a polymer matrix with either encapsulated gas/air bubbles or air tunnels incorporated in it. When the foam is a composite of polymer matrix encapsulating gas/air bubbles, the foam is described as closed cell foam structure. On the other hand, when the foam is a composite of polymer matrix with air tunnels running through it, the foam is described as open celled foam structure. Closed cell foams are generally more rigid, while open celled foams are usually more flexible.

Polymeric foams are produced in a number of different ways [6–13]. Examples are through slab-stock foams formed by pouring, extrusion, and different forms ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• About the Author
• Preface
• Acknowledgments
• Part I: Introduction
• Part II: Polymer Science and Engineering
• Part III: Science and Engineering of Polymeric Foams
• Part IV: Design and Uses of Polymeric Foams
• Index