ACS SYMPOSIUM SERIES 410 Historic Textile and Paper Materials II Conservation and Characterization S. Haig University of California—Davis Howard L. Needles, EDITOR University of California—Davis Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division at the 196th National Meeting of the American Chemical Society, Los Angeles, California, September 25-30, 1988 American Chemical Society, Washington, DC 1989 In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. Library of Congress Cataloging-in-Publication Data Historic textile and paper materials II: conservation and characterization S. Haig Zeronian, editor, Howard L. Needles, editor p. cm.—(ACS Symposium Series, 0097-6156; 410) "Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division at the 196th National Meeting of the American Chemical Society Lo Angeles California, September 25-30, Includes bibliographical references ISBN 0-8412-1683-5 1. Textile fabrics—Conservation and restoration— Congresses. 2. Paper—Preservation—Congresses. I. Zeronian, S. Haig, 1932- . II. Needles, Howard L. III. American Chemical Society. Cellulose, Paper, and Textile Division. IV. American Chemical Society. Meeting (196th: 1988: Los Angeles, Calif.). V. Series TS1449.H57 1989 746—dc20 89-38410 CIP The paper used in this publication meets the minimum requirements of American National Standard for Information Sciences—Permanence of Paper for Printed Library Materials, ANSI Z39.48-1984. _ Copyright © 1989 American Chemical Society All Rights Reserved. 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The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance oT any right or permission to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related there to. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN THE UNITED STATES OF AMERICA In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. ACS Symposium Series M. Joan Comstock, Series Editor 1989 ACS Books Advisory Board Paul S. Anderson Mary A. Kaiser Merck Sharp & Dohme Research E. I. du Pont de Nemours and Laboratories Company Alexis T. Bell University of California—Berkeley John L. Massingill Harvey W. Blanch Dow Chemical Company University of California—Berkeley Daniel M. Quinn Malcolm H. Chisholm University of Iowa Indiana University James C. Randall Alan Elzerman Exxon Chemical Company Clemson University Elsa Reichmanis John W. Finley AT&T Bell Laboratories Nabisco Brands, Inc. C. M. Roland U.S. Naval Research Laboratory Natalie Foster Lehigh University Stephen A. Szabo Conoco Inc. Marye Anne Fox The University of Texas—Austin Wendy A. Warr Imperial Chemical Industries G. Wayne Ivie U.S. Department of Agriculture, Robert A. Weiss Agricultural Research Service University of Connecticut In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. Foreword The ACS SYMPOSIUM SERIES was founded in 1974 to provide a medium for publishing symposia quickly in book form. The 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 submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however verbatim reproductions of previously pub lished papers are no research are acceptable, because symposia may embrace both types of presentation. In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. Preface EXTENSIVE RESEARCH HAS BEEN PUBLISHED on the chemistry and physics of paper and textiles. From the volume of available work, physical scientists must extract the information required by conservators to assist them in the preservation of fibrous materials. To this end, the Cellulose, Paper, and Textile Division of the American Chemical Society has sponsored four symposi paper and textiles of histori provided a forum where conservators and physical scientists could meet and discuss matters of mutual interest Papers presented at the first three meetings have been published as chapters in three volumes of the Advances in Chemistry Series: • Preservation of Paper and Textiles of Historic and Artistic Vabie\ Williams, John C., Ed.; Advances in Chemistry 164; American Chemical Society: Washington, DC, 1977. • Preservation of Paper and Textiles of Historic and Artistic Value II; Williams, John C., Ed.; Advances in Chemistry 193; American Chemical Society: Washington, DC, 1981. • Historic Textile and Paper Materials: Conservation and Characterization; Needles, Howard L.; Zeronian, S. Haig, Eds.; Advances in Chemistry 212; American Chemical Society: Washington, DC, 1986. This volume contains chapters from the fourth symposium. The seriousness of problems related to the conservation of paper is already well recognized. In about 1850, paper became much more susceptible to deterioration because of the acidic nature of the products prepared by the manufacturing processes then being introduced. Today, steps are being taken to correct and prevent problems. The Wall Street Journal of March 6, 1989, reported that the publishing industry estimated vii In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. that in 1990, 50% of all paper used in book publishing would be acid free compared with only 25% in 1989. According to a report in the March 13, 1989, Chemical & Engineering News, acid-free paper is estimated to last 300 years compared with an approximately 30-year lifetime for acidic paper. The change to alkaline—neutral papermaking is laudable and will assist in the preservation of books published in the future. (The production of alkaline-neutral paper is surveyed in Chapter 1 of this volume.) However, the difficulty with books printed since 1850 remains. Methods of deatidifying paper are critically evaluated in Chapter 2, and the potential of graft copolymerization as a means of strengthening paper is described in Chapter 3. Another problem conservators face is the deterioration of paper by exposure to light; it is discussed in Chapter 4 Paper is hydrophilic and may turn yellow over time atmosphere in which books are stored is brought out in Chapter 5, and yellowing is discussed in Chapter 6. Unlike paper, textiles are made from a wide range of fibers formed from different types of polymers. Textiles are usually colored, and the type of dye used depends on the fiber. Thus, each fiber has its own unique set of problems. For example, synthetic fibers are less susceptible to insects than are natural fibers, whose potential for damage depends on the fiber and on the insect. Also, the rate at which fibers deteriorate when exposed to sunlight varies, depending on how they have been dyed and which type of dye has been used. Again, a fiber's susceptibility to a reagent depends on its organochemical nature. Different dyes are susceptible to different reagents as well. Thus, whereas some general rules can be applied to textile conservation, knowledge of the individual fiber, dye, and finish is important Currently, the vast majority of textiles being collected by museums are made from natural fibers, and attention is focused on these products in this volume. Silk is discussed in Chapters 7-9, and cellulosics in Chapters 10 and 11. Techniques that may be useful for the characterization of textiles to be preserved are described in Chapters 13-15. One of the fascinations of studying textiles is that in addition to being manufactured from conventional fibers, they can be formed from other materials. Problems related to conservation of a particularly sensitive material, tapa cloth, are discussed in Chapter 12. The authors wish to thank Sandy Brito for her valuable and prompt assistance with respect to the correspondence generated in the viii In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. organization of the symposium and of this volume. We would also like to acknowledge the help we received from Cheryl Shanks and Donna Lucas of the ACS Books Department in the preparation of this book. S. HAIG ZERONIAN University of California Davis, CA 95616 HOWARD L. NEEDLES University of California Davis, CA 95616 August 3, 1989 ix In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. Chapter 1 Permanence and Alkaline—Neutral Papermaking D. J. Priest Department of Paper Science, University of Manchester Institute of Science and Technology, Manchester, P.O. Box 88, Sackville Street, Manchester M60 1QD, United Kingdom The papermaking proces i increasingl bein modified that the sheet is forme environment, rathe Pape this way is normally longer lasting because acid hydrolysis of the cellulose can no longer occur. However, the reasons for introducing the modified process are largely economic, and the product may not necessarily meet specifications for permanence and durability. This review describes the technicalities of the economic advantages (including easier fibre refining, increased filler content, the use of calcium carbonate fillers, and the availability of cost-efficient neutral sizes), the factors involved in making a change to neutral/alkaline papermaking, and how all this impinges on producing a satisfactory permanent paper. Paper is essentially a bonded mat or felt of relatively small fibres to which can be added, if required, fillers, wet strengtheners, coatings and so on. Although a paper-like material can be produced from many different polymeric fibres, paper itself is nearly always made using fibres from natural sources, usually, but not exclusively of course, from wood. These natural fibres all comprise polysaccharides of one sort or another, predominantly cellulose, which are very hydrophilic because they contain many accessible hydroxyl groups. The essential adhesion between fibres is a consequence of hydrogen bonds formed through these hydroxyl groups, as is the sensitivity of unmodified paper to disintegration when wetted by water. In many of its uses, paper needs to have resistance to penetration by aqueous fluids such as writing inks or the damping solutions used in lithographic printing. The treatment given to the surfaces of fibres to make them hydrophobic, which is usually done as the sheet is being formed, pressed and dried on the papermaking machine, is known as "internal sizing", to distinguish i t from "surface size" applied on a size press part way down the drying section of the machine. 0097-6156/89A)410-0002$06.00A) o 1989 American Chemical Society In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. 1. PRIEST Alkaline-Neutral Papermaking 3 Since the early days of machine made paper in the first half of the nineteenth century, the most widely applied method of internal sizing has been the use of naturally occurring resinous materials ("rosins") in conjunction with an aluminium salt, usually aluminium sulphate (called "alum" by papermakers). Various forms of rosin sizes (rosin soaps, rosin emulsions, fortified rosins) have been developed over the years to improve the process, but these variants still involve the use of alum as a means of ensuring that fibres retain a layer of size. Aluminium sulphate hydrolyses in aqueous solution to yield complex hydrated aluminium ions plus hydroxonium ions (Jj 2), and hence a low pH. Papers made using alum/rosin sizing are often said to be "acidic", although this is rather imprecise terminology. A complete definition, following the related TAPPI standard method (3), is that paper acidity is the extent to which water-soluble materials in the paper alter the hydrogen-hydroxyl ion equilibrium of pure water causing an excess of hydroge under specified conditions The important point is that the cellulose in these alum/rosin sized papers is susceptible to acid hydrolysis, which results in a lowering of the degree of polymerisation and, eventually, to a serious reduction in the strength of fibres and to complete embrittlement of the paper. Some recent work in the writer's laboratory suggests that when alum/rosin papers are made, the hydroxonium ions which lead to the degradation are adsorbed independently of aluminium ionic species W. In recent years, increasing attention is being paid by the paper industry to systems in which sizing is accomplished without the need to have the wet end of the machine running at acidic pH values. In these newer systems the pH may be around the neutral point, or be slightly alkaline due usually to the use of calcium carbonate filler (see below), so they are known as "neutral/alkaline". Papers made in this way do not yield acidic aqueous extracts and hence degrade more slowly (5, 6). Clearly, this is of great significance to those concerned with ensuring that important books and archival documents use paper expected to have a long life, and which will not lead in 30-150 years time to the enormous problems now being experienced in libraries and archives with paper made 30-150 years ago (7). However, it must be recognised that the reasons for introducing neutral/alkaline papermaking were not primarily associated with permanence; papers made in this way do not necessarily meet all the requirements for permanence and durability. Also, the alum/rosin acidic sizing method has been such a dominant force in papermaking that many other features of the process have been designed around it and adapted to it; the often used term "alum/rosin sizing system" is entirely appropriate. Making the change to neutral/alkaline papermaking nearly always involves, as we shall see, much more than throwing a switch or opening a valve. In a previous publication in this series (8), Hagemeyer set alkaline papermaking in the context of future demand for paper, and dealt briefly with some of the technical consequences. Since then, more mills have converted to the new method, and the aim of this chapter is to inform the reader in some detail about the reasons for changing to neutral/alkaline papermaking, some of the consequences for the production and properties of paper, and how the change impinges on In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. 4 HISTORIC TEXTILE AND PAPER MATERIALS U permanence and durability. It is important for those concerned with conservation and permanence to be able to communicate with papermakers and others with an awareness of relevant problems. Where possible, literature is cited, but a complete review is not intended, and some of the comments arise from the writer's past involvement in some of the industrial aspects of neutral/alkaline papermaking. REASONS FOR CHANGING TO NEUTRAL/ALKALINE PAPERMAKING. As in most industrial change, the chief Incentive is economic, and we need to look at ways in which the neutral/alkaline process gives rise to savings in the cost of production. Four main areas are involved: the fibre furnish, mineral fillers, the sizing system and the papermaking process itself. Although for convenience these will be discussed in turn, it should be noted at the outset that there is a great deal of interaction between the various aspects. FIBRE FURNISH. It is wel or refined at a neutral process is greater than at the acidic pH of around 4.5 common in alum/rosin systems. (When running an alum/rosin system it is inevitable that much of the stock preparation part of the mill operates at low pH because most of the water used is recycled from the wet-end of the paper machine). The increase in refining efficiency means, for example, that a given level of strength in the paper can be obtained for a lower expenditure of energy. This is a major fundamental economic incentive for converting to neutral/alkaline papermaking, because large amounts of expensive energy are consued in refining fibres (_10)* This basic advantage can be exploited in different ways, depending on the particular product being made and market requirements (£)• For example: a) The composition of the fibre furnish can be altered. The proportion of hardwood pulp might be increased, for instance, to give a product with the same strength as before, but with improved formation and opacity. Some cheap, relatively weak, bleached mechanical pulp might be introduced, or the proportion already used increased, again giving better uniformity and opacity, and a lower apparent density, but without loss of strength. This latter trend, of course, would not be acceptable in a permanent grade of paper. b) The potentially improved strength can be offset by increasing the amount of mineral filler in the paper, and this is a common route to follow, because fillers are usually much less expensive than the fibrous raw materials they replace, whilst at the same time properties such as brightness and opacity are improved. This important aspect is discussed more fully in the next section. c) A product of similar composition can be made but simply using less energy in refining. In fact, these three approaches are not mutually exclusive, and a mill would need to consider how to combine changes to optimise financial savings whilst producing a paper acceptable in quality to the particular market being served. In Historic Textile and Paper Materials II; Zeronian, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.