INDUSTRIAL USES OF STARCH AND ITS DERIVATIVES INDUSTRIAL USES OF STARCH AND ITS DERIVATIVES Edited by J. A. RADLEY M.Sc., C.Chem., F.S.D.C., F.R.I.C. APPLIED SCIENCE PUBLISHERS LTD LONDON APPLIED SCIENCE PUBLISHERS LTD RIPPLE ROAD, BARKING, ESSEX, ENGLAND ISBN-13: 978-94-010-1331-4 e-ISBN-13: 978-94-010-1329-1 DOl: 10.1 007/978-94-0 10 -1329-1 © APPLIED SCIENCE PUBLISHERS LTD 1976 Softcover reprint of the hardcover 1st edition 1976 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or other wise, without the prior written permission ofthe publisher, Applied Science Publishers Ltd, Ripple Road, Barking, Essex, England Preface The literature of starch has proliferated in the last ten years at an almost geometric rate and a number of important changes and developments in the technology of starch and its derivatives have taken place which makes it highly desirable to review these in some depth. The immensity ofthe subject determined the writer to seek the assistance of a number of prominent workers throughout the world. Where older work contains factual information of present value it has been retained, generally in the form of Additional References. These are brief abstracts which will help specialised searchers in a branch of the subject to complete the information given in the text. Inclusion of dis jointed information can often lead to the loss of coherence and clarity, and the device of the Additional References, whilst allowing smooth presentation, also allows the inclusion of up-to-the-minute material appearing after the main text has been written. Apart from the immense amount of important practical and theoretical detail required to produce and use starch for many applications in a number of important industries, a thorough knowledge is also required of a number of aspects for the successful buying and selling of starch. This book was written and published contemporaneously with two others entitled Starch Production Technology and Examination and Analysis of Starch and Starch Products. The three books together provide a wide coverage of starch technology and chemistry with the self-contained individual volumes providing precise information for specialist readers. The writer feels that starch may well play an increasing role in the global scene. New varieties, e.g. of wheat, maize, sorghum and triticale, with greatly increased yields per unit area, make it possible that Europe alone could become a net exporter of cereals and could attain self-sufficiency in v vi PREFACE total cereal production within the present decade. The extremely large unutilised agricultural capacity of the world provides the potential for greatly increased production. An important part of the attainment of agricultural self-sufficiency will be planned development of existing and novel applications for starch and cellulose. This book reviews the tra ditional uses of starch and its derivatives. The conversion of starch into glucose syrups and isomerised syrups is also reviewed. This will continue to expand the already major outlets for starch derivatives. These markets should all increase at a rate comparable with that of industrial growth in Europe. It appears highly probable that sophisticated starch derivatives will gradually replace non-renewable petrochemical products and that agriculture itself may change in such a way that land will be used not simply for the maximum production of a crop but for the maximum production of carbohydrate. My most sincere thanks are due to the contributors for their most helpful and ready co-operation in getting out a volume that is as up to date as humanly possible, and to my secretary, Mrs R. M. Russell, for her valuable help and care in producing the manuscript. I should also like to record my thanks for the constructive criticism of many practical details through the book in its early stages that were made by Mr Jack Seaman before his tragic and untimely death. Finally, my thanks are also due to the publishers for their part in the production of this book. Contents Preface. v 1. Adhesives from Starch and Dextrin 2. The Food Industry 51 3. The Role of Starch in Bread Staling by E. M. A. WILLHOFT 117 4. The Textile Industry 149 5. The Paper Industry by A. H. ZIJDERVELD and P. G. STOUTJESDIJK 199 6. Miscellaneous Uses of Starch 229 7. Utilisation of the By-products of Starch Manufacture 253 Index 259 vii CHAPTER 1 Adhesives from Starch and Dextrin The field of adhesives is a very wide one, and to cover it completely from all points of view, including the theoretical and the manufacturer's, would be outside the scope of this volume; hence attention will be directed solely to the adhesives made from starch and dextrin. Starch adhesives were used by the ancient Egyptians whilst the use of flour for making papyrus was mentioned by Pliny and ninth-century 112 writing papers of Chinese origin were sized with starch. Decorative wall hangings appeared in France prior to 1630 and wallpapers stuck on with flour pastes were a natural development from these. Starch sizes and adhesives became much more common in the Industrial Revolution and in the USA John Biddis was granted a patent in 1802 for the manufacture of starch from potatoes.113 The introduction of postage stamps in 1840 and the subsequent invention of gummed envelopes gave a fillip to the demand for adhesives whilst, later, further impetus was given by the development of photography and the introduction of matches. The pro duction of the tubular cartridge not only accelerated the development of the shotgun from the muzzle-loader but also laid the foundation of the cardboard tube industry. The paper bag and high-speed sealing by machines have developed into the vast packaging industry of today. Until 40 years ago animal glue was by far the most widely used industrial adhesive. It has been replaced by vegetable adhesives, nowadays, for many purposes and these also have special fields of use of their own. They are especially suitable for labelling and sealing by high-speed, automatic machinery for manufacturing corrugated boxwood, plywood, envelopes, stamps and gummed tapes. They possess the advantages of low price and can be applied cold or at moderately low temperatures, being reasonably lacking in odour and taste. 1 2 INDUSTRIAL USES OF STARCH AND ITS DERIVATIVES The latter point makes them especially useful in the food packaging industry or for any use where the adhesive may make contact with the tongue, e.g. envelopes and stamps etc. 1.1 PURPOSE AND APPLICABILITyl One of the most important considerations affecting the manufacture of adhesives is the particular purpose for which they are intended. It might appear, for example, that if a starch paste affixes paper to glass firmly, it would serve in most trades which require to label bottles containing their products, but more mature consideration will show that it is not so. Labels may be applied by hand or by machinery, and an adhesive which works well for the first purpose would not be suited to the latter, e.g. a tapioca starch paste will work quite well for hand labelling, but on a machine, although it contains a lot of water, would not feed correctly, as it is too viscous and does not possess enough 'stick' or 'tack'. If it were to be thinned down to the required viscosity the large amount of water present would saturate the label and cause it to pucker on drying, and what 'stick' or tackiness the paste did possess previously would be seriously impaired. A very tacky paste is not required in hand labelling, although in the machine it may be an important point, especially in a pick-up gum machine. Again, although the adhesive in this case must be tacky, it must not at the same time 'fibre' or 'spin', i.e. form long fine threads when two surfaces between which a portion of adhesive has been pressed are pulled apart. When an adhesive on a fast-working machine starts to spin, thousands of fine threads are very soon fiying all over the place, which means that time is lost in stopping and cleaning the machine and replacing the poor batch of adhesive by a good one. In this connection the following observation is of interest. A tapioca dextrin, fairly well converted, or a yellow potato dextrin, will give solutions in water which can be made to fibre, but if potato and tapioca starches are mixed in the correct proportions and together converted to dextrin, the product gives solutions which will not spin. R. Takahashi and co-workers 157 have examined the spinnability of starch pastes and have devised an apparatus for its measurement. They obtained the following results: 1. The length of the threads spun in various unmodified starch pastes of the same viscosity decreased in order: potato > tapioca > waxy com > wheat> maize starch. ADHESIVES FROM STARCH AND DEXTRIN 3 2. The degree of spinnability was related to the relaxation time, expressed as z' /G' where z' = dynamic viscosity, poise; G' = dynamic modulus, dyne/cm2 and structural viscosity. 3. The degree of spinnability increased with increasing degree of gelatinisation and with decrease of gelatinising temperature by introduction of hydroxy-ethyl, hydroxy-propyl and acryl-amide groups, etc. 4. They conclude that the spinnability increases with increasing dis persion of the starch granules. Sometimes the product has to resist water, as when used for affixing labels on champagne or wine bottles. For this purpose the glues made by the cold dispersion of starches in alkali (Perkin glues) at high concentration (generally 18-25 %) and afterwards neutralised with a mineral acid such as nitric or sulphuric acid are suitably water resistant. Other methods of imparting water resistance to starch, e.g. urea formaldehyde resins, glyoxal, etc. have also been tried with effect. In other cases the addition of calcium or barium hydroxide confers some water-resisting power, but the effect is slight. If a firm will accept returned empty bottles, the labels must be easily detachable when immersed in warm water or in the cleaning liquid of the washing machine; straight starch pastes serve very well here. Similarly with biscuit-tin labels. So far we have only mentioned adhesives for use between a non absorbing and polished body and one that absorbs some of the adhesive, but when we come to deal with rough surfaces, such as a wood-to-wood joint, different requirements are met. In ajoint between two rough surfaces all interspaces must be filled with adhesive, which must also firmly unite those portions that are in contact, the area of which is very much less than the surface area of the interspaces. Thus the efficiency of an adhesive to bind together two rough surfaces will depend very largely on its viscosity; it must be sufficiently fluid to penetrate the interspaces, and yet have enough body to give a thin but strong layer of adhesive when the joint is dry. With a comparatively rough surface the adhesive can 'key' itself into the material, and a rough parallel ism between the strength of the joint and the strength of a thin film of the adhesive should exist as long as the adhesive is not stronger than the material it is joining. When other factors, such as rate of loading and relative humidity, elasticity, deformability, flexibility, stress and strain relations, are taken into account the determination of the tensile strength 4 INDUSTRIAL USES OF STARCH AND ITS DERIVATIVES of a thin film of adhesive does give a good indication of its value in practice.2 F. Camps-Campins106 has measured the pore size of a number of papers, and he points out that paper adhesives have to be formulated so that the penetrative properties have to counterbalance the pore size of the paper. Thus papers with small pore size require penetrative adhesives but those with large pores require a filming type of adhesive. Further, according to this worker, the pore size affects the rate at which the glue sets and also the behaviour of the wet glue films under pressure. The adhesive must be formulated, therefore, so that its properties compensate for these factors and for unequal porosities in the surfaces to be glued. Singleterry's114 observations are of interest in this respect as this worker has found that the adhesive is keyed to the paper by filling the undercut regions about the surface fibres giving mechanical keying. The term 'deformability' is used to define the property of an adhesive to adapt itself readily to stresses and strains, slow or sharp, which may be set up in a joint after it has been made. While the adhesive is drying and setting, strains are set up in the joint by swelling, shrinking, warping, alteration either in humidity or temperature, and it is the deformability of a good adhesive which allows it to accommodate itself to new conditions as they occur and yet maintain a firm bond between the surfaces joined. In some adhesives the internal strains set up on drying are so great that the film flies to pieces; an example of this kind is gum-arabic or gum senegal. If, however, glycerine, glucose or some similar agent is added to the gum it acts as a plasticiser and confers deformability on the film, which then dries without disintegrating. So important is this property that when measuring the tensile strength of an adhesive film it is quite as necessary to note its deformability as its strength, if the figures are to be of value in the practical evaluation of the substance as an adhesive. Colloids in general show this property to a greater extent than pure substances and are generally superior to them as adhesives. The following figures illustrate this point: Isinglass, tensile strength, 13 000 Ib/in2 (90 N/mm2) tough; starch, 7000 Ib/in2 (48 N/mm2), ductile; sodium silicate, 600 Ib/in2 (4 N/mm2), very brittle; gum-arabic, no value obtainable, very brittle. Gum-arabic cracks spontaneously on drying and dextrin pastes which crack on the surface should not be used to make adhesives for first-class work. If gum-arabic is plasticised, how ever, its strength immediately increases. Rate of loading and humidity are important, and it has been found that long-continued stress on a joint, made between metals with recognised