FUNDAMENTAL POLYMERIC MATERIALS

xivPREFACEnatural polymers are included in structures and examples, including starches and polypeptides, to make the important connection that may building blocks of biology are alsopolymers.Some reorganization and combination was done in the third edition, with Chapters 3 and4 from the previous edition combined, and some of the detailed information on polymerrheology and transport was shortened so that students could be introduced to the materialwithout being overwhelmed. Only small sections were removed, and at many instances,new materials were added, such as the addition of techniques for polymer analysis,processing techniques (including three-dimensional prototyping), and the inclusion ofmicroencapsulation with the coatings section. Updates to advanced polymerizationtechniques includes some of the emerging techniques to make well-defined polymers,such as atom-transfer radical polymerization, although these methods are treated in a ratherbrief sense, so that students can understand the basics of the technique improvements andwhat advantages are achieved compared to other techniques. (In most cases, referencesare given for those seeking more detail.)Some of the things that I liked best about this book for teaching an introductorypolymers course have been retained. These areas include the description of processes toformulate different products, along with sketches of the processes, the arrangement of thebook in going from molecular to macromolecular to physical structures, and the generaltone of the book that attempts to connect with the reader through examples that may befamiliar to them.New homework problems have been introduced throughout, primarily those that I havefound useful in teaching.CHRISTOPHER S. BRAZELTuscaloosa, ALAugust 2011

PREFACE TO THE SECOND EDITIONThis work was written to provide an appreciation of those fundamental principles ofpolymer science and engineering that are currently of practical relevance. I hope the readerwill obtain both a broad, unified introduction to the subject matter that will be of immediatepractical value and a foundation for more advanced study.A decade has passed since the publication of the first Wiley edition of this book. Newdevelopments in the polymer area during that decade justify an update. Having used thebook in class during the period, I’ve thought of better ways of explaining some of thematerial, and these have been incorporated in this edition.But the biggest change with this edition is the addition of end-of-chapter problems at thesuggestion of some academic colleagues. This should make the book more suitable as anacademic text. Most of these problems are old homework problems or exam questions. Idon’t know what I’m going to do for new exam questions, but I’ll think of something. Anysuggestions for additional problems will be gratefully accepted.The first Wiley edition of this book in 1982 was preceded by a little paperback intendedprimarily as a self-study guide for practicing engineers and scientists. I sincerely hope thatby adding material aimed at an academic audience I have not made the book less useful tothat original audience. To this end, I have retained the worked-out problems in the chaptersand added some new ones. I have tried to emphasize a qualitative understanding of theunderlying principles before tackling the mathematical details, so that the former may beappreciated independently of the latter (I don’t recommend trying it the other way around,however), and I have tried to include practical illustrations of the material wheneverpossible.In this edition, previous material has been generally updated. In view of commercialdevelopments over the decade, the discussion of extended-chain crystals has beenincreased and a section on liquid-crystal polymers has been added. The discussion ofphase behavior in polymer-solvent systems has been expanded and the Flory–Hugginstheory is introduced. All kinetic expressions are now written in terms of conversion (ratherthan monomer concentration) for greater generality and ease of application. Also, inxv

xviPREFACE TO THE SECOND EDITIONdeference to the ready availability of numerical-solution software, kinetic expressions nowincorporate the possibility of a variable-volume reaction mass, and the effects of variablevolume are illustrated in several examples. A section on group-transfer polymerization hasbeen added and a quantitative treatment of Ziegler–Natta polymerization has beenattempted for the first time, including three new worked-out examples. Processes basedon these catalysts are presented in greater detail. The “modified Cross” model, givingviscosity as a function of both shear rate and temperature, is introduced and its utility isillustrated. A section on scaleup calculations for the laminar flow of non-Newtonian fluidshas been added, including two worked-out examples. The discussion of three-dimensionalstress and strain has been expanded and includes two new worked-out examples.Tobolsky’s “Procedure X” for extracting discrete relaxation times and moduli from datais introduced.Obviously, the choice of material to be covered involves subjective judgment on the partof the author. This, together with space limitations and the rapid expansion of knowledge inthe field, has resulted in the omission or shallow treatment of many interesting subjects. Iapologize to friends and colleagues who have suggested incorporation of their work butdon’t find it here. Generally, it’s fine work, but too specialized for a book of this nature. Theend-of-chapter references are chosen to aid the reader who wishes to pursue a subject ingreater detail.I have used the previous edition to introduce the macromolecular gospel to a variety ofaudiences. Parts 1, 2 and most of 3 were covered in a one-semester course with chemistryand chemical engineering seniors and graduate students at Carnegie-Mellon. At Toledo,Parts 1 and 2 were covered in a one-quarter course with chemists and chemical engineers. Asecond quarter covered Part 3 with additional quantitative material on processing added.The audience for this included chemical and mechanical engineers (we didn’t mentionchemical reactions). Finally, I covered Parts 1 and 3 in one quarter with a diverse audienceof graduate engineers at the NASA–Lewis Research Labs.A word to the student: To derive maximum benefit from the worked-out examples, makean honest effort to answer them before looking at the solutions. If you can’t do one, you’vemissed some important points in the preceding material, and you ought to go back over it.STEPHEN L. ROSENRolla, MissouriNovember 1992

ACKNOWLEDGMENTSThe most important person to acknowledge is Dr. Stephen Rosen, who penned the first andsecond editions of this book with a great vision for organizing the wealth of information onpolymers into a textbook covering the fundamentals that provided an excellent tool forclassroom learning. The guinea pigs (or students) who helped do a trial run of this edition inmy polymeric materials classes in 2011 provided corrections and suggestions throughoutthe semester.I greatly appreciate my departmental colleagues and university for allowing me asabbatical from my normal professor duties to expand my research and write several papersas well as updating this book. I am also grateful to the U.S.–U.K. Fulbright Commission,which partially funded my stay in the United Kingdom during which I began writing thisthird edition.xvii

CHAPTER 1INTRODUCTIONAlthough relatively new to the scene of materials science, polymers have becomeubiquitous over the past century. In fact, since the Second World War, polymeric materialsrepresent the fastest growing segment of the U.S.’ chemical industry. It has been estimatedthat more than a third of the chemical research dollar is spent on polymers, with acorrespondingly large proportion of technical personnel working in the area. From thebeginning, the study of polymers was an interdisciplinary science, with chemists, chemicalengineers, mechanical engineers, and materials scientists working to understand thechemical structure and synthesis of polymers, develop methods to scale up and processpolymers, and evaluate the wide range of mechanical properties existing within the realmof polymeric materials. The molecular structure of polymers is far more complex than themolecules you may have studied in a general chemistry course: just compare the molecularweights, H2O is 18, NaCl is about 58, but polymers have molecular weights from 10,000 totens of millions (or possibly much higher for cross-linked polymers). Many of thestructures you might have seen in a general cell biology course are made of polymers––proteins, polysaccharides, and DNA are all notable biological polymers. In amaterial science course, you may have studied crystal structures in metals to understandthe mechanical behavior of different alloys (polymers can form crystals, too, but imaginethe difficulty of trying to line up a huge polymer molecule into a crystal structure).Polymers are a unique class of materials having wide ranging applications.A modern automobile contains over 300 lb (150 kg) of plastics, and this does not includepaints, the rubber in tires, or the fibers in tires and upholstery. Newer aircraft incorporateincreasing amounts of polymers and polymer-based composites. With the need to save fueland therefore weight, polymers will continue to replace traditional materials in theautomotive and aircraft industries. Similarly, the applications of polymers in the buildingconstruction industry (piping, resilient flooring, siding, thermal and electrical insulation,paints, decorative laminates) are already impressive and will become even more so in theFundamental Principles of Polymeric Materials, Third Edition. Christopher S. Brazel and Stephen L. Rosen.Ó 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.1

2INTRODUCTIONfuture. A trip through your local supercenter will quickly convince anyone of theimportance of polymers in the packaging (bottles, films, trays), clothing (even cotton isa polymer), and electronics industries. Many other examples from pharmaceutical coatingsto playground equipment could be cited, but to make a long story short, the use of polymersnow outstrips that of metals not just on a volume basis but also on a mass basis.People have objected to synthetic polymers because they are not “natural.” Well,botulism is natural, but it is not particularly desirable. Seriously, if all the polyester andnylon fibers in use today were to be replaced by cotton and wool, their closest naturalcounterparts, calculations show that there would not be enough arable land left to feed thepopulace, and we would be overrun by sheep. The fact is that there simply are no practicalnatural substitutes for many of the synthetic polymers used in modern society.Since most modern polymers have their origins in petroleum, it has been argued that thisincreased reliance on polymers constitutes an unnecessary drain on energy resources.However, the raw materials for polymers account for less than 2% of total petroleum andnatural gas consumption, so even the total elimination of synthetic polymers would notcontribute significantly to the conservation of hydrocarbon resources. Furthermore, whentotal energy costs (raw materials plus energy to manufacture and ship) are compared, thepolymeric item often comes out well ahead of its traditional counterpart, for example, glassversus plastic beverage bottles. In addition, the manufacturing processes used to producepolymers often generate considerably less environmental pollution than the processes usedto produce the traditional counterparts, for example, polyethylene film versus brown kraftpaper for packaging.Ironically, one of the most valuable properties of polymers, their chemical inertness,causes problems because polymers do not normally degrade in the environment. As aresult, they increasingly contribute to litter and the consumption of scarce landfill space.One of the challenges in using polymers in materials is developing suitable methods forrecycle or effective methods to improve the degradation of disposable items.Environmentally degradable polymers are being developed, although this is basically awasteful approach and we are not yet sure of the impact of the degradation products.Burning polymer waste for its fuel value makes more sense, because the polymers retainessentially the same heating value as the raw hydrocarbons from which they were made.Still, the polymers must be collected and this approach wastes the value added inmanufacturing the polymers.This ultimate solution is recycling. If waste polymers are to be recycled, they must first becollected. Unfortunately, there are literally dozens (maybe hundreds) of different polymers inthe waste mix, and mixed polymers have mechanical properties similar to Cheddar cheese.Thus, for anything but the least- demanding applications (e.g., parking bumpers, flower pots),the waste mix must be separated prior to recycling. To this end, several automobilemanufacturers have standardized plastics used in cars that can be easily removed, remolded,and reused in newer models. Another identifier helpful in recycling plastics is obvious if youhave ever looked at the bottom of a plastic soda bottle; there are molded-in numbers on mostof the large volume commodity plastics, allowing hand sorting of different materials.Processes have been developed to separate the mixed plastics in the waste. The simplestof these is a sink–float scheme that takes advantage of density differences among variousplastics. Unfortunately, many plastic items are foamed, plated, or filled (mixed withnonpolymer components), which complicates density-based separations. Other separationprocesses are based on solubility differences between various polymers. An intermediateapproach chemically degrades the waste polymer to the starting materials from which new

INTRODUCTION3polymer can be made. Other efforts related to polymeric waste have focused on reducingthe seemingly infinite lifetime of many plastics in the environment by developingbiodegradable commodity polymers.There are five major areas of application for polymers: (1) plastics, (2) rubbers orelastomers, (3) fibers, (4) surface finishes and protective coatings, and (5) adhesives.Despite the fact that all five applications are based on polymers, and in many cases the samepolymer is used in two or more, the industries pretty much grew up separately. It was onlyafter Dr. Harmann Staudinger [1,2] proposed the “macromolecular hypothesis” in the1920s explaining the common molecular makeup of these materials (for which he won the1953 Nobel Prize in chemistry in belated recognition of the importance of his work) thatpolymer science began to evolve from the independent technologies. Thus, a soundfundamental basis was established for continued technological advances. The history ofpolymer science is treated in detail elsewhere [3,4].Economic considerations alone would be sufficient to justify the impressive scientificand technological efforts expended on polymers in the past several decades. In addition,however, this class of materials possesses many interesting and useful properties completely different from those of the more traditional engineering materials and that cannot beexplained or handled in design situations by the traditional approaches. A description ofthree simple experiments should make this obvious.1. Silly putty, a silicone polymer, bounces like rubber when rolled into a ball anddropped. On the other hand, if the ball is placed on a table, it will gradually spread toa puddle. The material behaves as an elastic solid under certain conditions and as aviscous liquid under others.2. If a weight is suspended from a rubber band, and the band is then heated (taking carenot to burn it), the rubber band will contract appreciably. All materials other thanpolymers will undergo thermal expansion upon heating (assuming that no phasetransformation has occurred over the temperature range).3. When a rotating rod is immersed in a molten polymer or a fairly concentratedpolymer solution, the liquid will actually climb up the rod. This phenomenon, theWeissenberg effect, is contrary to what is observed in nonpolymer liquids, whichdevelop a curved surface profile with a lowest point at the rod, as the material is flungoutward by centrifugal force.Although such behavior is unusual in terms of the more familiar materials, it is a perfectlylogical consequence of the molecular structure of polymers. This molecular structure is thekey to an understanding of the science and technology of polymers and will underlie thechapters to follow.Figure 1.1 illustrates the followings questions to be considered:1. How is the desired molecular structure obtained?2. How do the polymer’s processing (i.e., formability) properties depend on itsmolecular structure?3. How do its material properties (mechanical, chemical, optical, etc.) depend onmolecular structure?4. How do material properties depend on a polymer’s processing history?5. How do its applications depend on its material properties?

4INTRODUCTIONFIGURE 1.1The key role of molecular structure in polymer science and technology.N– O–Cl–F–H–– –– –– C––– –The word polymer come

Fundamental principles of polymeric materials / Christopher S. Brazel, Stephen L. Rosen. --3rd ed. pages cm Revised edition of: Fundamental principles of polymeric materials / Stephen L. Rosen. 2nd ed. c1993. Includes bibliographical references and index. ISBN 978-0-470-50542-7 1. Polymers. I. Rosen, Stephen L., 1937- II. Rosen, Stephen L .