Non-Thermal Plasma Technology for Polymeric Materials

Applications in Composites, Nanostructured Materials, and Biomedical Fields

Sabu Thomas, Miran Mozetic, Uros Cvelbar, Petr Spatenka, K.M. Praveen

• Publisher: Elsevier
• Year: 2018
• Print ISBN: 9780128131527
• eBook ISBN: 9780128131534
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Non-Thermal Plasma Technology for Polymeric Materials: Applications in Composites, Nanostructured Materials and Biomedical Fields provides both an introduction and practical guide to plasma synthesis, modification and processing of polymers, their composites, nancomposites, blends, IPNs and gels. It examines the current state-of-the-art and new challenges in the field, including the use of plasma treatment to enhance adhesion, characterization techniques, and the environmental aspects of the process. Particular attention is paid to the effects on the final properties of composites and the characterization of fiber/polymer surface interactions. This book helps demystify the process of plasma polymerization, providing a thorough grounding in the fundamentals of plasma technology as they relate to polymers. It is ideal for materials scientists, polymer chemists, and engineers, acting as a guide to further research into new applications of this technology in the real world. - Enables materials scientists and engineers to deploy plasma technology for surface treatment, characterization and analysis of polymeric materials - Reviews the state-of-the-art in plasma technology for polymer synthesis and processing - Presents detailed coverage of the most advanced applications for plasma polymerization, particularly in medicine and biomedical engineering, areas such as implants, biosensors and tissue engineering

Chapter 1

Relevance of Plasma Processing on Polymeric Materials and Interfaces

K. M Praveen^1,2,3, C.V. Pious⁴, Sabu Thomas¹ and Yves Grohens², ¹International and Inter University Centre for Nanoscience and Nanotechnology (IIUCNN), Mahatma Gandhi University, Kottayam, Kerala, India, ²University of South Brittany, Laboratory IRDL PTR1, Research Center “Christiaan Huygens,” Lorient, France, ³Department of Mechanical Engineering, SAINTGITS College of Engineering, Kottayam, Kerala, India, ⁴School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala, India

Abstract

With the advent of emerging technologies all over the world at the end of 20th century and in the beginning of 21st century, polymers have played a huge role in transforming conceptual ideas into structural integrities useful for mankind. Even though polymers of desired properties can be tailored through a synthesis route, considering the cost aspects it is preferable to modify the existing polymers through surface/interface engineering techniques in order to meet the manufacturing requirements of engineering industries all over the world. The behavior of polymers at the interfaces is of fundamental importance in a wide range of technologies and applications. Adhesion problems exist with the bonding of polymers, the adhesion of coatings to polymer surfaces and interface/interphase problems associated with melt-blended polymers and polymer micro, as well as nano composites, are recurring and challenging areas in polymer-based industries. With a thorough understanding of the surface and interface phenomenon in polymer multiphase systems, one can engineer their interfacial properties by controlling the interface/interphase region leading to the development of advanced materials with multifunctional properties. This chapter discusses most recent developments in the area of surface engineering of polymeric interfaces with special reference to the plasma surface modification technique.

Keywords

Interfaces; surface modification; plasma surface treatment; polymer composites

1.1 Introduction

With the growing global energy crisis and ecological risks, polymers are playing a vital role in five major areas where the needs of society face huge technological challenges. These are: energy, sustainability, health care, security and informatics, and defence and protection [1]. In order to fulfil the aforesaid diverse societal needs, advanced polymeric materials are developed either by synthesizing new polymers or through the modification of existing polymeric materials. In most of the cases, researchers opt for the modification of existing polymers rather than synthesizing new polymers due to the considerable cost aspects. Polymers are a major class of materials and possess a wide range of mechanical, physical, chemical, and optical properties. Polymers have increasingly replaced metallic components in various applications. These substitutions reflect the advantages of polymers in terms of corrosion resistance, low electrical and thermal conductivity, low density, high strength-weight ratio (particularly when reinforced), noise reduction, wide choice of colors and transparencies, ease of manufacturing and complexity of design possibilities, and relatively low cost.

The interface is defined as the boundary between two layers of materials with different chemistries and/or microstructures. The interphase is described as the volume of material affected by the interaction at the interface. The term interphase is considered as a three-dimensional zone which is different from a two-dimensional interface and it is now widely used in the adhesion community to indicate the presence of a chemically or mechanically altered zone between adjacent phases. In the interphase zone, one can observe the gradation of properties from one phase to another, rather than the abrupt change necessitated by the acceptance of a two-dimensional interface [2].

Adhesions of polymeric materials have a direct relationship with surface/interfacial properties. The adhesion at the interface/interphases has prime importance when advanced polymeric materials are developed via surface modification techniques. Adhesion problems exist with the bonding of polymers and the adhesion of coatings to polymer surfaces, while interface problems between different phases of melt-blended polymers and polymer composites are recurring and challenging areas in polymer-based industries. With a thorough understanding of the surface and interface phenomenon in polymer multiphase systems, one can control the interfacial properties by engineering the interface/interphase region leading to the development of advanced materials with multifunctional properties.

The first section of this chapter provides a concise introduction to polymeric materials, followed by a description of their structure, properties, and applications. Then it addresses the salient features of polymer surfaces and interfacial problems with a brief overview of surface phenomena and adhesion phenomena in the bonding of polymers. Finally, the major part of this chapter covers the relevance of plasma processing on polymeric materials and interfaces. This part starts with a basic introduction, continues with discussions on the mechanism of plasma surface modification, effects of plasma treatment on specific polymers, various characterization techniques, and applications of plasma in polymeric materials.

1.2 Structure, Properties, and Applications of Polymers

Polymers are defined as macromolecules, which are formed by the joining of repeatable structural units. The repeatable structural units are derived from monomers and are linked to each other by covalent bonds. The properties of a polymer depend on the chemical structures of monomeric units, molecular weight, molecular weight distribution, and its architecture. The processes of the formation of polymers from respective monomers is known as polymerization. Two major classifications of polymerization processes are condensation (step-growth or step-reaction polymerization) and addition polymerization (chain-growth or chain-reaction polymerization). In the former, the bonding takes place by condensation reaction resulting in the loss of small molecules which are often water. In the later, bonding takes place by the reaction of unsaturated monomers without reaction by-products. The final properties of the product made from polymers depends highly on the inherent properties of the polymer/s and the additives used for modification. The influence of molecular weight, structure (linear, branched, cross-linked, or network), degrees of polymerization and crystallinity, glass transition temperature, and additives are briefed below.

The molecular weight and molecular weight distribution of polymers strongly influence the final properties of the end products. The mechanical properties such as the tensile and the impact strength, the resistance to cracking, and rheological measurements such as viscosity (in the molten state) of the polymer etc., increases with increase in molecular weight. Summing up of individual molecular weights of the monomeric units in a given chain gives the molecular weight of the polymer. It is important to keep in mind that the average chain length is proportional to the molecular weight of the given polymer. That is, higher the molecular weight of a given polymer, the greater the average chain length. The size of a polymer chain can be expressed in terms of the degree of polymerization which is defined as the ratio of the molecular weight of the polymer to the molecular weight of the repeating unit. The covalent bonds which link the monomeric units together are called primary bonds and the polymer chains are held together by secondary bonding. In a given polymeric material, the increase in strength and viscosity of the polymer with molecular weight is attributed to the fact that, as the length of the polymer chain increases, the greater is the energy needed to overcome the combined strength of the secondary bonding with primary bonding (covalent). Depending upon the type of chains, the polymers are classified into linear polymers, branched polymers, cross-linked polymers, and network polymers. If the repeating units in a polymer chain are all of the same type, the molecule is called a homopolymer. Copolymers contain two types of polymers and terpolymers contain three types.

Crystallinity plays a critical role in delivering enhanced property to polymeric materials and their products. By controlling the rate of solidification during cooling and the chain structure, it is possible to achieve desired degrees of crystallinity to polymers. The improved hardness, stiffness, and low ductility values of polymeric materials are outcomes of increased crystallinity. The optical properties of polymers are also influenced by the degree of crystallinity. At low temperatures, the amorphous polymers are hard, rigid, brittle, and glassy while at high temperatures they are rubbery or leathery. The temperature at which a transition occurs is called the glass-transition temperature (T_g). The information on T_g can predict the nature of the polymer at its service temperature—that is, whether it rigid and glassy, or flexible and rubbery.

The two major classes of polymers are thermoplastics and thermosets. When the temperature of a certain polymer is raised above the T_g, or melting point, T_m, they can be easily molded into desired shapes. The increase in temperature weakens the secondary bonding via the thermal vibration of the long molecules which, in turn, enables more free movement of adjacent chains particularly when subjected to external shaping forces. These types of polymers are referred as thermoplastics. If the temperature of a thermoplastic polymer is raised above its T_g, it becomes leathery and on increasing the temperature further, it turns rubbery. At higher temperatures, say above T_m for crystalline thermoplastics, it becomes a molten fluid and its viscosity decreases with increasing temperature. At this stage, it can be molded into different shapes. When thermoplastics are stretched, the long-chain molecules tend to align in the general direction of the elongation. This process is known as orientation. Due to the viscoelastic behavior, thermoplastics are particularly susceptible to creep and stress relaxation. When subjected to tensile or bending stresses, some thermoplastics may develop localized wedge-shaped and/or narrow regions of highly deformed material. This process is known as crazing. It typically contains about 50% voids. With increasing tensile load on the specimen, these voids coalesce to form a crack, which eventually can lead to a fracture of the polymer. The environmental factors such as the presence of solvents, lubricants, or water vapor, residual stresses in the material, radiation, etc., can increase the crazing behavior in certain polymers. An important feature of certain thermoplastics is their ability to absorb water (hygroscopic nature). With increasing moisture absorption, the T_g, the yield stress, and the elastic modulus of the polymer are lowered severely. Compared to metals, plastics generally are characterized by low thermal and electrical conductivity, low specific gravity, and a high coefficient of thermal expansion. Certain polymers can be stretched or compressed to very large strains, and then, wh...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Chapter 1. Relevance of Plasma Processing on Polymeric Materials and Interfaces
• Chapter 2. Introduction to Plasma and Plasma Diagnostics
• Chapter 3. Plasma Assisted Polymer Synthesis and Processing
• Chapter 4. Plasma Assisted Polymer Modifications
• Chapter 5. Plasma-Induced Polymeric Coatings
• Chapter 6. Application of Plasma in Printed Surfaces and Print Quality
• Chapter 7. Plasma Treatment of Powders and Fibers
• Chapter 8. Plasma Treatment of Polymeric Membranes
• Chapter 9. Selective Plasma Etching of Polymers and Polymer Matrix Composites
• Chapter 10. Wettability Analysis and Water Absorption Studies of Plasma Activated Polymeric Materials
• Chapter 11. Microscopic Analysis of Plasma-Activated Polymeric Materials
• Chapter 12. Spectroscopic and Mass Spectrometry Analyses of Plasma-Activated Polymeric Materials
• Chapter 13. Plasma Treatment of High-Performance Fibrous Materials
• Chapter 14. Plasma Modified Polymeric Materials for Implant Applications
• Chapter 15. Plasma Modified Polymeric Materials for Biosensors/Biodevice Applications
• Chapter 16. Plasma Modified Polymeric Materials for Scaffolding of Bone Tissue Engineering
• Index