Visakh / Liang Poly(Ethylene Terephthalate) Based Blends, Composites and Nanocomposites

1. Auflage 2015
ISBN: 978-0-12-801274-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 252 Seiten

Reihe: Plastics Design Library

Poly(Ethylene Terephthalate) (PET) is an industrially important material which is not treated specifically in any other book. Poly(Ethylene Terephthalate) Based Blends, Composites and Nanocomposites fills this gap and systematically guides the reader through all aspects of PET and its blends, composites and nanocomposites. It covers theoretical fundamentals, nanocomposites preparation, modification techniques, structure-property relationships, characterisation of the different blends and composites, and material choice for specific applications. Consisting of contributions from experts in the field this book is a useful reference for the researchers and engineers working on the development and characterization of PET materials as well as on implementing them in real-world products. It can also be used as a standard reference for deeper insight in the mechanical, thermal, thermo-mechanical and visco-elastic aspects in product design decisions. - Provides a systematic overview on all types of poly(ethylene) terephthalate (PET) based blends, composites and nanocomposites - Informs about characterization, structure-property relationships and types of modifications - Links material properties to specific applications, enabling engineers to make the best material choice to increase product performance and cost efficiency, in industries ranging from aerospace to energy

Autoren/Hrsg.

Visakh, P. M.

Liang, Mong

Leseproben

2

Modification of Polyethylene Terephthalate

Magdalena Aflori1

Mioara Drobota1,2
1    Physical Characterization of Polymers Department, Petru Poni Institute of Macromolecular Chemistry, Iasi, Romania
2    Department of Applied Chemistry and Materials Science, University Politehnica of Bucharest, Bucharest, Romania

Abstract

Nowadays, polymers find wide applications in modern industry, but finishing and bonding of almost all polymers present low hydrophilicity of their surfaces, which affects printability, wettability, biocompatibility, and adhesion. Therefore, polymer films need additional surface treatments to modify the surface properties, for better wettability and adhesion activities. There are different methods to modify the surface properties of the polymer films such as chemical or plasma treatments, ultraviolet (UV) or laser irradiation. Chemical surface modification may produce toxic compounds and physical alterations in the composition of the surface. From the polymer class, the polyesters have been frequently used to improve protein and cell adhesion.

Keywords

polymers

ultraviolet light

collagen

plasma

polyethylene terephthalate

polyesters

Outline

2.1 Introduction 15

2.2 Radio-Frequency Plasma 16

2.2.1 Principle of the Techniques 16

2.2.2 Effects of RF Treatments on Polyethylene Terephthalate 18

2.2.2.1 Characteristics of the Treated Surface 18

2.2.2.2 Degradation Behavior 22

2.2.3 Stabilization of Treated Polyethylene Terephthalate 23

2.3 Ultraviolet Technique 23

2.3.1 Principle of the Technique 23

2.3.2 Study of Functional Groups Created on Treated Surfaces 24

2.3.3 Effects of the UV Radiation on Polyethylene Terephthalate 25

2.4 Protein Immobilization on Treated Surfaces 26

2.4.1 Principle of the Technique 26

2.4.1.1 Collagen Immobilization After UV Treatments 32

2.4.2 Biocompatible Character of the Surface 34

2.5 Conclusions 35

Acknowledgments 35

References 36

2.1. Introduction

Nowadays polymers find wide applications in modern industry, but finishing and bonding of almost all polymers present low hydrophilicity of their surfaces, which affects printability, wettability, biocompatibility, and adhesion. Therefore, polymer films need additional surface treatments to modify the surface properties, for better wettability and adhesion activities [1–5]. There are different methods to modify the surface properties of the polymer films such as chemical or plasma treatments, ultraviolet (UV) or laser irradiation. Chemical surface modification may produce toxic compounds and physical alterations in the composition of the surface [6–9]. From the polymer class, the polyesters have been frequently used to improve protein and cell adhesion [10–12].

The aim of this study was to examine whether the surfaces of polyesters need to be modified to improve protein adhesion. Polyethylene terephthalate (PET) was selected for the study on the basis of the reactivity of its ester group. This polymer was studied in order that good protein adsorption could achieved onto the polymer surface [13–16] by utilizing the methods discussed hereinafter. Therefore, we have decided to focus in this chapter on nonconventional methods like plasmas and UV radiation that generate surfaces with chemically reactive groups that can subsequently be used for the covalent immobilization of biologically active molecules. Here we will review work that is focused on surfaces containing carboxy, hydroxy, amine, and aldehyde groups, which are the main chemically reactive groups amenable for the covalent immobilization of biologically active molecules.

2.2. Radio-Frequency Plasma

2.2.1. Principle of the Techniques

A quickly developing area of applied physics and chemistry is plasma processing of materials, but in spite of intense experimental work, plasma-aided manufacturing is not yet fully considered as a viable technology in industrial processes, mainly because of the difficulties arising in achieving permanent surface modification and in controlling the effective plasma–surface interactions and their role in the modification of surface properties [17–20]. A particular case is represented by radio-frequency (RF) discharges, which work well at low pressure, but are also used at atmospheric pressure in suitable gases [21–24]. One advantage of RF discharges is that the electrodes can be kept outside of the discharge volume, thus avoiding electrode erosion and contamination of the plasma with metal vapor. Since the wavelength of the electric field is much larger than the vessel dimensions, reasonably homogeneous plasmas can be generated. Low-pressure RF discharges for etching purposes have found widespread applications in semiconductor manufacturing [25–27], but nowadays, surface modification of polymers for biomedical applications have gained a lot of interest [28–30]. In comparison to DC discharges, RF discharges have few advantages: (1) they are more uniform spatially, (2) their ionization mechanism is more efficient (the electrons can gain energy during the whole cycle), (3) they can also be sustained in depositing (e.g., dielectric layers) discharge environments, and (4) they can operate at lower pressures (the impedance of the discharge decreases with the increase of the frequency).

The RF field is the power supplier for electrons that transmit the power through elastic and inelastic collisions, changing their direction. The electrons will gain additional energy if the changing of direction coincides with the direction of the electric field. Therefore, the electrons from RF discharge can gain sufficient energy to generate ionization processes. The mean power absorbed by an electron is given by

¯=e2E022meveve2+?2

(2.1)

where ve is the term representing the elastic collision frequency of an electron with an atom, ? the frequency of the field, and E0 the amplitude of the electric field. The absorbed power is independent of the sign of the electric field and the electrons predominantly move in the direction of the field to make them move, gaining energy. Contrary to what happens in DC plasmas, the electrons that follow the low-frequency field oscillation (13.56 MHz) can gain sufficient energy for producing ionizations and sustain the discharge, even in the absence of wall- and electrode-originated secondary electrons. RF discharges can also be operated at much lower pressures because the field-induced electron oscillations make inelastic collision processes more efficient. Usually, a matching network is used to connect the RF power supplies to the discharge chamber, in order to increase the power dissipation in the discharge and to protect the generator by matching the impedance of the plasma reactor to that of the power supply.

To describe the electron household of a nonequilibrium volume discharge, generally four reactions are of importance. In a stationary situation, electron losses by attachment and recombination have to be balanced by ionization and detachment processes. For the treatment of the whole system, powerful computer codes are needed to solve the Boltzmann equation and to handle systems of stiff differential equations describing the many reactions.

1. Electron/molecular reactions

:e+A2?A2*+eDissociation:e+A2?2A+e?Attachment:e+A2?A2-Dissociative attachment:e+A2?A-+A?Ionization:e+A2?A2++2eDissociative ionization:e+A2?A++A+eRecombination:e+A2+?A2Detachment:e+A2-?A2+2e

2. Atomic/molecular reactions

?dissociation:M*+A2?2A+MPenning?ionization:M*+A2?A2++M+eCharge?transfer:A±+B?B±+AIon?recombination:A-+B+?ABNeutral?recombination:A+B+M?AB+M

3. Decomposition

:e+AB?A+B+eAtomic:A*+B2?AB+B

4. Synthesis

:e+A?A*+eElectronic:A*+B?ABAtomic:A+B?AB

At low-pressure plasmas the electron energy distribution can be described by a Druyvesteyn approximation, where the energy of electrons is considered much higher than that of the ions, and when it is assumed that the only “energy losses” are by elastic collisions [31,32]. In this approximation, a small number of electrons have relatively high energies (5–15 eV) while the bulk of the electrons belong to the low-energy electron range (0.5–5 eV). Since the ionization potentials of the atoms of common organic structures belong to the tail region of the electron energy distribution, the low degrees of ionization of cold plasmas...