Table Of ContentMaterials Science
of Synthetic Membranes
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
ACS SYMPOSIUM SERIES 269
Materials Science
of Synthetic Membranes
Douglas R. Lloyd, EDITOR
The University of Texas at Austin
Based on a symposium sponsored by
the Division of Polymeric Materials
Science and Engineering
at the 187th Meeting
of the American Chemical Society,
St. Louis, Missouri, April 9-11, 1984
American Chemical Society, Washington, D.C. 1985
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
Library of Congress Cataloging in Publication Data
Materials science of synthetic membranes.
(ACS symposium series, ISSN 0097-6156; 269)
Includes bibliographies and indexes.
I. Membranes (Technology)—Congresses.
I. Lloyd, Douglas R., 1948- . II. American
Chemical Society. Division of Polymeric Materials
Science and Engineering. III. American Chemical
Society. Meeting (187th: 1984: St
IV. Series.
TP159.M4M38 1985 660.2'84245 84-21652
ISBN 0-8412-0887-5
Copyright © 1985
American Chemical Society
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In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
ACS Symposium Series
M. Joan Comstock, Series Editor
Advisory Board
Robert Baker
U.S. Geological Survey USDA, Southern Regional
Research Center
Martin L. Gorbaty
Geoffrey D. Parfitt
Exxon Research and Engineering Co.
Carnegie-Mellon University
Roland F. Hirsch
James C. Randall
U.S. Department of Energy
Phillips Petroleum Company
Herbert D. Kaesz Charles N. Satterfield
University of California—Los Angeles Massachusetts Institute of Technology
Rudolph J. Marcus W. D. Schultz
Office of Naval Research Oak Ridge National Laboratory
Charles S. Tuesday
Vincent D. McGinniss
General Motors Research Laboratory
Battelle Columbus Laboratories
Douglas B. Walters
Donald E. Moreland
National Institute of
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In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
FOREWORD
The ACS SYMPOSIU founded i t provid
a medium for publishin
format of the Series parallels that of the continuing ADVANCES
IN CHEMISTRY SERIES except that in order to save time the
papers are not typeset but are reproduced as they are sub
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embrace both types of presentation.
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
PREFACE
^N^EMBRANE SCIENCE has recently received considerable attention. Mem
branes for industrial separations, therapeutic medical applications, and
controlled release, as well as membrane barriers for packaging, have all
moved from the laborator
for additional application
for membranes to proceed beyond the present level of success, further
advances must be made in the materials science of membranes. The objective
of this book is to compile state-of-the-art reviews of several aspects of the
materials science of synthetic membranes. It is hoped that this compilation
will serve as a useful reference regarding past and present developments, and
that it will provide the impetus for future advances in membrane materials
science.
The 21 chapters that comprise this volume were contributed upon the
invitation of the editor. Prior to publication, the manuscripts were subjected
to peer review and revised accordingly. This volume is the product of
considerable effort on the part of the authors, the reviewers, my editorial
assistant Robert Fabrize, Robin Giroux of the American Chemical Society
Books Department, and Betty Friedrich who typed six chapters. To each of
these people I express my deepest gratitude. I also wish to thank Eric Lee for
his assistance in organizing the symposium and for chairing two of the four
sessions.
This book is dedicated to my past, present, and future graduate
students; it is my pleasure to be associated with these fine people. Finally,
but above all, this book is dedicated to my wife Linda, in appreciation of her
patience and encouragement.
DOUGLAS R. LLOYD
The University of Texas at Austin
Austin, TX 78712
August 1984
ix
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
1
Membrane Materials Science
An Overview
DOUGLAS R. LLOYD
Department of Chemical Engineering, Separations Research Program, Center for Polymer
Research, The University of Texas at Austin, Austin, TX 78712
Material science
membranes are presente
objective is to place each of the subsequent chapters
of this volume into proper perspective. Therefore,
frequent reference is made to the accompanying
chapters and, where necessary, to alternative
information sources. By way of introduction, this
chapter considers in turn: material selection,
material characterization and evaluation, membrane
preparation, membrane characterization and membrane
evaluation. Membrane module design and manufacture,
transport phenomena and process performance are
introduced in the discussion only as they pertain to
membrane materials science. Following this
introduction, the various chapters of this volume are
previewed.
Membrane science is a phrase that encompasses a vast array of
topics (1). The common thread that ties together the various
aspects of membrane science is that each one deals to some extent
with the study of permeation and permeable media. More
specifically, the permeable medium or membrane is a phase between
two phases. The role of the membrane may be either to change the
composition of a solution on the basis of relative permeation rates
(membrane separation processes), to physically or chemically modify
the permeating species (ion-exchange membranes and biofunctional
membranes), to conduct electric current, to prevent permeation
(packaging and coating) or to regulate the rate of permeation
(controlled release). Functionally, membranes may be either
passive or reactive depending upon the membrane's ability to
alter the chemical nature of the permeating species. Membranes can
also be categorized as being either neutral or charged according to
their ionic nature. Structurally, membranes can be categorized as
being either non-porous (that is, membranes in which the membrane
phase is continuous, such as dense polymeric films and liquid
0097-6156/ 85/0269-0001 $06.50/ 0
© 1985 American Chemical Society
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
2 MATERIALS SCIENCE OF SYNTHETIC MEMBRANES
membranes) or porous to various extents (for example, porous
polymeric films in which both the polymer matrix and the void
spaces are continuous. Further categorization according to the
porous structure of these co-continuous membranes is discussed
below under the heading "Membrane Preparation"). The various
chapters in this book discuss the materials science of synthetic
polymeric membranes for separations, conductive membranes and
reactive membranes.
Membrane performance is often measured by the ability of the
membrane to prevent, regulate or facilitate permeation. The rate
of permeation and the mechanism of transport depend upon the
magnitude of the driving force, the size of the permeating molecule
relative to the size of the available permanent or dynamic
transport corridor and the chemical nature (dispersive, polar,
ionic, etc.) of both the permeant and the polymeric membrane
material.
Membrane science ca
intimately related categories
characterization and evaluation, membrane preparation, membrane
characterization and evaluation, transport phenomena, membrane
module design and process performance. This chapter and those to
follow emphasize the materials science aspects of synthetic
polymeric membranes; that is, the selection, characterization and
evaluation of membrane materials as well as the preparation,
characterization and evaluation of membranes. Transport phenomena,
membrane module design and process performance enter the discussion
only as these topics pertain to materials science.
Material Selection. In designing a membrane, one must first
determine the physicochemical nature of the permeants (gas, vapor,
liquid, solid; dispersive, polar, ionic; reactive, inert; physical
size and shape). The membrane scientist then has two
materials science controls over permeation: membrane material
selection and membrane preparation procedures. Membrane material
selection allows control over the nature and magnitude of the
permeant-membrane physicochemical interactions. Choice of membrane
material also determines the packing density and segment mobility
of the polymer chains which comprise the solid regions of the
membrane. Membrane preparation procedures determine membrane
morphology and the extent to which physical considerations, such as
steric hindrance, influence the rate of permeation. Together,
material selection and membrane preparation procedures influence
the mechanism of transport, membrane stability and membrane
performance.
In the past, membrane material selection for gas separations
(2) and liquid separations has often followed either an Edisonian
or a common sense approach. For example, almost every polymer that
can be formed into a film has been characterized in terms of gas
permeability (at least for a few common gases). In this volume,
Chern et al. (3) and Lloyd and Meluch (4) discuss membrane material
selection in terms of physicochemical interactions for gas mixture
separations and liquid mixture separations, respectively. Hoehn
(5) presents similar arguments for membrane material selection in
general. In comparison to the wide variety of polymers investigated
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
1. LLOYD Membrane Materials Science 3
for their gas transport properties, the number of polymers studied
for their liquid transport properties is somewhat limited. However,
a survey of recent literature and patents (4) indicates that an
ever-increasing number of polymers, copolymers and blends are being
considered as potential membrane materials for liquid mixture
separations. It is interesting to compare the number of materials
which have reached commercialization for liquid separations and gas
separations. Lloyd and Meluch (4) list in excess of twenty-seven
polymers, copolymers and blends currently being used for liquid
separation membranes. However, only polysulfone and a variety of
cellulose acetates and silicone based polymers have attained
commercial success for gas mixture separations (6).
In addition to the guidelines suggested by Chern et al. (3)
and by Lloyd and Meluch (A), Ward et al. (7) point out that
biocompatibility and sterilizability need to be considered when
selecting membrane materials for therapeutic applications.
Each of these chapter
demonstrates that one ca
structures to obtain membrane materials which theoretically can
achieve the desired control over permeability. Alternatively,
the ideas developed (3-5) can simply serve as criteria by which one
can select, from a list of available polymers, those membrane
materials with the greatest potential for achieving the desired
control over permeability.
Material Characterization and Evaluation. Physicochemical
considerations can be useful in membrane material selection.
However, it would be beneficial if one could experimentally verify
that the proper choice has been made prior to undertaking the often
difficult tasks of membrane preparation and characterization. In
addition, it is frequently beneficial to have fully characterized
the polymer prior to forming the membrane.
In this context, material characterization refers to obtaining
information related to the intrinsic properties of the polymer
rather than structural or physical properties of the membrane which
is to be subsequently formed from the polymer. It is often useful
to characterize the polymer in terms of the following: molecular
architecture or bulk properties (molecular weight characteristics,
degree of branching, chemical functionality and, if necessary,
copolymer or blend composition), polymer solution properties
(polymer swellability, polymer solubility and solution viscosities),
thermal properties (glass transition temperature and crystal melting
temperature), chemical stability and, if appropriate,
biocompatibility. Physical properties of the polymers, such as
mechanical strength and extent of crystallization, often depend
upon sample preparation procedures and are ultimately reflected in
the properties of the membrane. As such, they are discussed below
under the heading of Membrane Characterization and Evaluation.
Lloyd and Meluch (4) summarize several methods of evaluating
potential membrane materials for liquid separations without
actually preparing membranes. They point out that once a membrane
or film has been formed, it is often difficult to distinguish the
intrinsic properties of the polymer from the structural
characteristics of the membrane, which are themselves dependent
In Materials Science of Synthetic Membranes; Lloyd, D.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1985.
