AN INVESTIGATION OF THE KINETICS ON STATIC ELECTRICITY BUILD UP AND DECAY ON CARPET r A THESIS Presented to The Faculty of the Graduate Division by William Charles Desatta In Partial Fulfillment of the Requirements for the Degree Master of Science in The A, French Textile School Georgia Institute of Technology March, 1967 In presenting the dissertation as a partial fulfillment of • the requirements for an advanced degree from the Georgia Institute of Technology, I agree that the Library of the Institute shall make it available for inspection and circulation in accordance vith its regulations governing materials of this type. I agree that permission to copy from, or to publish from, this dissertation may be granted by the professor under vhose direction it was written, or, in his absence, by the Dean of the Graduate Division when such copying or publication is solely for scholarly purposes and does not involve potential financial gain. It is under­ stood that any copying from, or publication of, this dis­ sertation which involves potential financial gain will not . be allowed without written permission. -£1. 3/IT/65 b AN IHYgSTIGATION OF THE . STIC?^ OF STATIC ELECTHICITI BUILD IT? AND ^SCAX .*N CARPET 'in a d -.ri'^a Approvedt J >r Bate approved "by Chairman? '^/; <'/^ 11 ACKNOWLEDGMENTS The author wishes to express his appreciation to the following persons and manufacturers: Mr. Winston Boteler, thesis advisor, 'vho contributed i valuable aid with this thesis. Mr. R. K. Flege and Mr. R. B. Belser for their aid on the read­ ing committee. Dr. James L. Taylor for providing a graduate assists at"hip. Mr. Howard G. Adams, build"^ .^meer, who contributed his skills and advice toward the construction of the author's apparatus for generating static electricity. E. T. Barwick Company, Chemstrand Company, and Callaway Mills for providing the carpet samples for these experiments. Ill TABLE OF CONTENTS Page ACKNOWLEDGMENTS ii LIST OF TABLES iv LIST OF ILLUSTRATIONS V SUMMARY vii Chapter I. INTRODUCTION AND HISTORY 1 II. GENERATION AND NATURE OF STATIC i+ Theories of Generation Substances in Contact Static Decay Electrostatic Series Dielectric Constant III. INSTRUMENTATION AND PROCEDURE 22 IV. RATE OF STATIC BUILD UP AND DECAY 28 Build Up of Static Dielectric Constant Static Decay V. CONCLUSIONS AND RECOMMENDATIONS 45 Conclusions Recommendations APPENDIX 48 BIBLIOGRAPHY 57 IV LIST OF TABLES Table ' Page 1. Electrostatic Series 18 2. Index of Carpet Samples 29 3. Comparison of Static Build Up on Looped Pile and Cut Looped Pile Carpets 33 4. Dielectric Constants 35 5. Maximum Static Charge Set Up on Carpets 37 6. Rate of Static Build Up on Carpet Samples 38 7. Rate of Static Decay on Carpet Samples at 3 RPM 41 8. Rate of Static Decay on Carpet Samples at 10 RPM 42 9. Summary of Experimental Data on Static Electricity on Carpets 49 LIST OF ILLUSTRATIONS Figure Page 1. Electrical Double Layer 4 2. Energy Levels of a Metal 6 3. Fermi-Dirac Distribution 7 4. Energy Levels of an Insulator 8 5. Excess on n-type Insulator 9 6. Defect or p-type Insulator 9 7. Metal-Metal Contact, Energy Levels at the Surface Before and After Contact 10 8. Insulator-Insulator Contact, Energy Levels at the Surface Before and After Contact 12 9. Metal-Insulator Contact, Energy Levels at the Surface Before and After Contact 13 10. Effect of Normal Forces on Static 15 11. Effect of Velocity on Static 16 12. Electroscope 22 13. Field Mill 24 14. Diagram of Instrument Used to Measure Static Build Up and Decay on Carpets 26 15. Static Build Up Produced with a Teflon Generator at 3 RPM . 30 16. Static Build Up Produced with a Rubber Generator at 3 RPM 31 17. Static Build Up Produced with a Leather Generator at 3 RPM 32 18. Decay of Static Produced with a Rubber Generator at 3 RPM 51 VI Figure Page 19. Decay of Static Produced with a Leather Generator at 3 RPM 52 20. Decay of Static Produced with a Teflon Generator at 3 RPM 53 21. Decay of Static Produced with a Rubber Generator at 10 RPM 54 22. Decay of Static Produced with a Leather Generator at 10 RPM 55 23. Decay of Static Produced with a Teflon Generator at 10 RPM 56 Vll SUMMARY Several samples of carpet from different fibers were studied in this investigation. These included nylon, acrylic, polyester, wool, and polypropylene. The carpet samples included looped pile and cut looped pile. These carpets were tested to determine the rate of static build up, the rate of static decay, and the maximum static charge generated by three different generating materials. The generators were constructed using leather, rubber, and Teflon. These tests were carried out by using a static measuring instru­ ment, called a field mi-lt, and an apparatus of the author's design. The apparatus consisted of a variable speed motor connected to a gear reduction box, which in turn was connected to a 19-inch wheel. On this wheel the carpet samples were mounted. The static-generating material was placed on the carpet, the static charge was set up by revolving the wheel, and was measured by the field mill. Polyester cut looped pile carpet proved to have the highest rate of static build up. Nylon 6,6 cut looped pile carpet had the lowest rate of build up. Nylon 6 looped pile carpet and polypropylene looped pile carpet had the lowest rates of decay. The sample with the highest rate of decay was acrylic looped pile carpet. Nylon 6,6 looped pile carpet set up the greatest static charge while acrylic looped pile carpet set up the least charge. Also, cut looped pile carpets proved to have a slower rate of build up and a faster rate of decay than their looped pile counterparts. In terms of static build up and decay, acrylic Vlll carpets proved to be the most desirable carpets while nylon proved to be the least desirable. This is a study providing a method to measure the rate of static build up, the rate of static decay, and the quantity of static charge set up on the carpet samples, and pointing out several possibilities for further study. CHAPTER I INTRODUCTION AND HISTORY Static electricity was first recorded in about 600 B.C. by a Greek scientist, Thales of Milet, who noted that amber, after being rubbed with silk, attracted small particles of various materials. From the Greek word for amber, elektvon^ came the word electricity. It is known from earlier investigators that there is only one kind of electricity or charge, and the distinction between positive and negative electricity is purely a quantitative one. A negative charge is an excess of electrons and a positive charge is a shortage of electrons o From accepted atomic theory one may say that atoms are made up of neutral as well as positively and negatively charged particles. The neutral particles are called neutrons, the positive particles protons, and the negative particles electrons. Electrons surround the nucleus which is made up of protons and neutrons. The normal atom has the same number of electrons and protons, thus having a neutral over-all charge. In a conductor some of these electrons are sufficiently mobile to move freely, and in doing so produce electric currents. However, charges on nonconductors or insulators are immobile. Under certain conditions an atom may lose or acquire one or more electrons and is then called a positively or negatively charged ion, respectively. An example of the presence of static electricity or of an unbalanced charge of two bodies is the spark produced when a person walking on a nylon carpet touches a metal objects However, perhaps the most common and certainly the most dramatic example of the presence of static electricity is lightning. Here the accumulated small charges on water droplets give a cloud a tremendous potential. The discharge of lightning may be between two clouds, which have accumulated opposite charges , or from a cloud to earth. A third example of static electricity is the attraction of very light particles by a charged body, such as Thales of Milet observed. This attraction accounts for the dirt which clings to clothing, furniture covers, and carpets that have been previously rubbed in some manner. 3 Coulomb (1736-1805) and other early experimenters did much to clarify the phenomenum of static. It is known that like charges repel and unlike charges attract each other. Coulomb established a quantitative law about these forces. It states that the electrostatic attraction between two charged bodies is directly proportional to the product of the charges and inversely proportional to the square of Lj. the distance between them. Helmholtz (1821-1894) introduced the contact potential theory of electrification of insulators. Moreover, 5 P. Ec Shaw showed the important influence of chemical and physical conditions of surfaces involved in static generation. In the past two decades, research on static gained in impor­ tance due to the problems arising in the textile and paper industries. These problems arose from the introduction of excellent insulating materials as well as higher processing speeds CHAPTER II GENERATION AND NATURE OF STATIC Theories of Generation The basic concept of static electrification, usually attributed to Helmholtz, assumes that when two materials come into contact a charge is transferred from one to the other. This transfer forms an eZeotv-iQdl double layer consisting of two layers, each with an oppo­ site charge, on or near the surface separated by a few angstrom units. See Figure 1. These two bodies with the small separation between them act as a capacitor.