Absorbent Technology Edited By P.K. Chatterjee and B.S. Gupta

Contents

Preface
During the past two decades the disposable absorbent market has grown considerably and become highly competitive. New products appeared in the market with newly developed materials and more sophisticated structural designs. The challenge to remain competitive in this business primarily depends on how well the fundamental science and technology in this field are implemented to attain the product and process innovations. This book will serve the function of providing fundamental scientific and engineering information that are needed to develop and bring into the market place new and innovative absorbent materials and structures. It has all the aspects of absorbency that are essential to understanding the attributes of any absorbent materials or composites and to designing new products with unique characteristics.

The book contains some chapters, thoroughly revised, taken from an earlier edition entitled “Absorbency” published in 1985 by Elsevier Science Publisher and some new chapters that discuss more recent developments on the subject. The chapters are arranged in a sequence that facilitates a reader to advance progressively through fundamental theories of absorbency to more practical aspects of the technology. Each chapter provides the cun’ent status of the technology as well as the future prospects that would stimulate further research in the subject area. The book is intended for both the academic and the industrial scientists and engineers engaged in research and development on absorbency and absorbent products. Our special thanks go to individual authors of the chapters of the current book as well as those who contributed in the previous edition. We would like to express our appreciation to Elsevier Science Publisher for providing us with the opportunity to participate in this publication. One of us (BSG) would like to extend his appreciation to the management of the Department of Textiles Engineering, Chemistry and Science, College of Textiles, North Carolina State University, for its encouragement and support.

Our acknowledgement and appreciation are also due to Dr. Sumedha Gupta Ariely for many helpful suggestions during the review of chapters and the cooperation of Ajit Moghe and Chad Wade in preparing many drawings and photographs and providing assistance all along, as needed. We would like to express our sincere thanks to Mrs. Susan Olsen who assisted us with secretarial help all through the preparation of the present manuscript.

And, finally, we take this opportunity to express our deep appreciation to our families for their understanding and support during the course of this project that required many long hours of activities during evenings and weekends.

Introduction
The current monograph, “Absorbent Technology,” is a thoroughly revised and expanded edition of “Absorbency” published in 1985. As mentioned in that publication, the term “absorbency” is used in many different fields with different connotations. In the biomedical field, for example, absorbency refers to a phenomenon related to the consumption (degradation or decomposition) of a material in a biological or physiological environment. In skin biology, the diffusion of ionic species, gases, vapor or oil, through the epidermis is frequently referred to as absorbency. In this book, the term “absorbency” is described as an interdisciplinary scientific phenomenon that deals with the absorption of aqueous fluids by porous media, or more specifically, by fibrous and polymeric systems. The theoretical aspects of absorbency, as well as the structure, properties and performance of materials, currently being used or considered for use in absorbent structures, have been illustrated in various chapters. The technology related to manufacturing and designing of absorbent products has not been the primary objective of this book, neither has been the business aspect of these materials.

Absorbency criteria are characterized by the mode and the extent of the transport of liquid into an absorbing material. Numerous attempts have been made to define and predict absorbency using many classical theories, dating back to the nineteenth century, as well as those developed more recently, i.e. within the last few decades. Unfortunately, none of those theories can be utilized to effectively elucidate the intricate mechanism that governs fluid absorption in products that are available in the marketplace. None-the-less, many unique absorbent products have been developed over the years, which at least partially fulfill the need of consumers. The development of the majority of those products was not based on a scientific or mechanistic approach, but on trial and error techniques and on the intuitive imagination of innovative technologists. Since the absorbent products field has become more and more competitive, the necessity of more in-depth scientific study has become vitally important.

Product innovation comes through an intimate relationship between the development of fundamental science and technologies related to material characterization and the manufacturing processes. Industries, constrained by high labor costs and low profit margins, are inherently slow in investing in research on fundamental science where the payoff is not immediate but long term. Technology feeds on science and it is the lack of scientific study that has shortchanged the field of fluid absorbency for many decades. This edition of the book, it is hoped, will stimulate industry as well as academia to undertake research activities on more fundamental aspects of absorbency that will lead to technological innovations of the future.

Regarding the materials for absorbent products, cotton cellulose has been utilized since the time of the Egyptian civilization. Not until the end of the nineteenth century was wood pulp, in the form of fluff and then tissue, used as an absorbent material. Shortly thereafter rayon was introduced into the field. The growth of new materials for absorbent products remained status quo until late 1960’s when a new class of materials called “super absorbents” appeared and made a great impact in the field. Its absorption characteristic, particularly liquid retention capacity under pressure, is unique and helped the industry to come up with new and innovative, and more comfortable and hygienic, products. The development of super absorbent materials goes back to 1960’s and since then many different kinds with more efficient absorption properties have been developed and are still being developed.