Natural Rubber Materials: Volume 1: Blends and IPNs (Polymer Chemistry Series) - Hardcover

Hardcover

ISBN 10: 1849736103 ISBN 13: 9781849736107

Publisher: Royal Society of Chemistry, 2013

Synopsis

A comprehensive two volume set covering the synthesis, characterization and applications of natural rubber based blends, interpenetrating polymer networks, composites and nanocomposites.

About this title

About the Author

Sabu Thomas is professor at the School of Chemical Sciences, Mahatma Gandhi University, Kottayam, India. He received Ph.D from Indian Institute of Technology, Kharagpur and a B.Tech in Polymer Science and Technology from Cochin University. Prof. Thomas has gained additional experience as a visiting professor at a number of universities around the world. A Fellow of the Royal Society of Chemistry and a member of the American Chemical Society, his research has led to the publication of some 360 articles in international peer-reviewed journals, several book chapters and patents. The co-editor of four books, he has been a visiting professor and lecturer at some of the world's leading polymer research laboratories.

From the Back Cover

The combination of its unique morphology, physical properties, cost effectiveness and environmental friendliness make natural rubber an appealing constituent for many materials and applications. This comprehensive two volume set covers the synthesis, characterization and applications of natural rubber based blends, interpenetrating polymer networks, composites and nanocomposites.

Volume 1 covers different types of natural rubber-based blends and IPNs as well as manufacturing methods, thermo mechanical characterization techniques, life cycle analysis and their applications. Volume 2 focuses on natural rubber-based composites and Nanocomposites including the different types of fillers, the filler-matrix reinforcement mechanisms, manufacturing techniques, and applications.

This is the first book to consolidate the current state of the art information on natural rubber based materials with contributions from established international experts in the field. The book provides a "one stop" reference resource for professionals, researchers, industrial practitioners, graduate students, and senior undergraduates in the fields of polymer science and engineering, materials science, surface science, bioengineering and chemical engineering.

Excerpt. © Reprinted by permission. All rights reserved.

Natural Rubber Materials Volume 1

Blends and IPNs

By Sabu Thomas, Rajisha K. R., Hanna J. Maria, Chin Han Chan, Laly A. Pothen

The Royal Society of Chemistry

Copyright © 2014 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84973-610-7

Contents

Chapter 1 Natural Rubber Based Blends and IPNs: State of the Art, New Challenges and Opportunities Gordana Markovic, Milena Marinovic-Cincovic, Vojislav Jovanovic, Suzana Samarzija-Jovanovic and Jaroslava Budinski-Simendic, 1, 
Chapter 2 Natural Rubber: Biosynthesis, Structure, Properties and Application Jitladda Tangpakdee Sakdapipanich and Porntip Rojruthai, 28, 
Chapter 3 Non-Rubbers and Abnormal Groups in Natural Rubber Eng Aik Hwee, 53, 
Chapter 4 The Production of Natural Rubber from Hevea brasiliensis Latex: Colloidal Properties, Preservation, Purification and Processing C. C. Ho, 73, 
Chapter 5 Natural Rubber Blends and Based IPNs: Manufacturing Methods Wanvimon Arayapranee, 107, 
Chapter 6 Filler Migration in Natural Rubber Blends During the Mixing Process Hai Hong Le, Sybill Ilisch, Gert Heinrich and Hans-Joachim Radusch, 132, 
Chapter 7 NR Blends and IPNs: Miscibility and Immiscibility Wiwat Pichayakorn, Jirapornchai Suksaeree and Prapaporn Boonme, 177, 
Chapter 8 Natural Rubber Based Non-Polar Synthetic Rubber Blends Seiichi Kawahara, 195, 
Chapter 9 Natural Rubber Based Polar Synthetic Rubber Blends Konstantinos G. Gatos, 213, 
Chapter 10 Thermoplastic Elastomers from High-Density Polyethylene/Natural Rubber/Thermoplastic Tapioca Starch: Effects of Different Dynamic Vulcanization Mohd Kahar Ab Wahab, Nadras Othman and Hanafi Ismail, 242, 
Chapter 11 Natural Rubber/Engineering Thermoplastic Elastomer Blends E. Purushothaman and Mehar Al Minath, 265, 
Chapter 12 Radiation Processing of Natural Rubber with Vinyl Plastics Chantara Thevy Ratnam, Zurina Mohamad and Mohammad Khalid Siddiqui, 284, 
Chapter 13 Blends and IPNs of Natural Rubber with Acrylic Plastics Wiwat Pichayakorn, Jirapornchai Suksaeree and Prapaporn Boonme, 300, 
Chapter 14 Photoreactive Nanomatrix Structures Formed by Graft Copolymerization of 1,9-Nonanediol Dimethacrylate onto Natural Rubber Oraphin Chaikumpollert, Nanthaporn Pukkate and Seiichi Kawahara, 324, 
Chapter 15 Blends and IPNs of Natural Rubber with Thermosetting Polymers Raju Thomas, Ishak Ahmad, Sahrim Hj. Ahmad and Shinu Koshy, 336, 
Chapter 16 Natural Rubber Blends with Biopolymers Silvia Maria Martelli, Carol Sze Ki Lin, Zheng Sun, Nathalie Berezina, Farayde Matta Fakhouri and Lucia Helena Innocentini-Mei, 349, 
Chapter 17 Clay Reinforcement in Natural Rubber Based Blends: Micro and Nano Length Scales Yamuna Munusamy, Hanafi Ismail and Chantara Thevy Ratnam, 370, 
Chapter 18 Rheological Behaviour of Natural Rubber Based Blends Ploenpit Boochathum, 394, 
Chapter 19 Spectroscopy: Natural Rubber Based Blends and IPNs SA-AD Riyajan, 441, 
Chapter 20 Mechanical and Viscoelastic Properties of Natural Rubber Based Blends and IPNs Wiwat Pichayakorn, Jirapornchai Suksaeree and Prapaporn Boonme, 481, 
Chapter 21 Scattering Studies on Natural Rubber Based Blends and IPNs Valerio Causin, 501, 
Chapter 22 Transport of Penetrant Molecules Through Natural Rubber Based Blends and IPNs Isaac O. Igwe, 530, 
Chapter 23 Life Cycle Analysis, Ageing and Degradation Behaviour of Natural Rubber Based Blends and IPNs Cristina Russi Guimarães Furtado and Márcia Christina Amorim Moreira Leite, 550, 
Chapter 24 Application of Natural Rubber Based Blends and IPNs in Tyre Engineering and other Fields Mir Hamid Reza Ghoreishy and Mohammad Alimardani, 569, 
Subject Index, 600, 

CHAPTER 1

Natural Rubber Based Blends and IPNs: State of the Art, New Challenges and Opportunities

GORDANA MARKOVIC, MILENA MARINOVIC-CINCOVIC, VOJISLAV JOVANOVIC, SUZANA SAMARZIJA-JOVANOVIC AND JAROSLAVA BUDINSKI-SIMENDIC

1.1 Introduction and History

The field of polymer science and technology has undergone an enormous expansion over recent decades primarily as a result of chemical diversity. Dilute solution behaviour, elasticity, tacticity, single crystal formation, viscoelastic behaviour, etc., attained the prime interest from past researchers. The concept of physically blending two or more existing polymers to obtain new products is now attracting widespread interest and commercial utilization.

Investigation of polymer blends is one of the most active areas of research and development in the field of polymers at the present time. Polymer blends provide answers to technological challenges posed by the increasing difficulties of synthesizing new monomers and polymers to meet diverse demands, either domestic or industrial. The wide range of properties attainable with these systems were hitherto either impossible to obtain from an individual polymer or would involve costly development of new polymers. In fact, blending of polymers is one of the easiest and most flexible methods of generating new polymeric materials. It has become an important technique for improving the cost–performance ratio of commercial polymers. Polymer blends also provide a platform for scientific investigations in various fields such as newer characterization techniques, processing, molecular engineering to control the blend structure, structure-property correlation and modelling, etc.

It is important to be able to predict and understand the resultant properties of a blend and its morphology from the properties of the constituent polymers. Predicting the mechanical behaviour of polymer blends and composites with respect to composition, structure (morphology of the blend) and properties of the components covering a wide temperature range are particularly important.

Polymer blends and interpenetrating polymer networks (IPNs) form part of the composite materials system. Composite materials may be defined as materials made up of two or more phases. They may be grouped into:

(i) particulate filled: consisting of a continuous matrix phase and a discontinuous filler phase made up of discrete particles;

(ii) fibre filled;

(iii) skeletal IPNs: both as continuous phases.

The factors that influence the properties of composite materials are: properties of the components, shape of the filler phase, morphology of the system, and the nature of the interface between the phases. The mechanical behaviour of composites is greatly affected by the interfacial adhesive bond between the phases. The morphology in polymer blends is indicative of the phase or phases and interrelationships existing in the blend. It reflects the domain size of the dispersed phase, state of aggregation, nature of the interface between the phases, etc. phase is nothing but a structurally homogeneous part of a material system. There may be a single continuous phase with one or more disperse phases, or two or more continuous phases which may contain one or more disperse phases. Blends are defined as simply a mixture of two or more polymers or copolymers. They may be miscible (domain size of the order of 0.5 nm) or immiscible (domain size of the order of 100 nm), depending on thermodynamic requirements. Miscible blends are thermodynamically stable, molecular level mixtures. Immiscible blends are separated into microscopic phases with very minimum interfacial adhesion and unstable morphology. Polymer alloy blends (PABs) are a class of polymer blends, heterogeneous in nature, with controlled morphology and properties, achieved by compatibilization and dynamic vulcanization. Compatibilized blends are also macro phase separated (domain phases are between those of miscible and immiscible systems), but the presence of interfacial agents or chemical bonds stabilizes the morphology and increases interfacial adhesion. Domain size is also controlled and reduced, giving a fine dispersion. An IPN, another rapidly growing development in the area of polymer science and technology, is a typical polymer blend in which two or more polymers exist in network form and are synthesized in juxtaposition. When one of the polymers is crosslinked, the product is called a semi-IPN. A general scheme is shown in Figure 1.1.

We can represent the system definition as (Table 1.1).

The advantageous properties of IPNs come from co-continuity and excellent compatibilization (obtained by co-reactions) that result in fine dispersions. Often IPNs do not possess co-continuity of networks; rather one phase forms fine droplets (10–100 nm diameter) dispersed in another phase. IPNs with specific topological network structure provide smaller domains of phase-separated materials. Their miscibility level gives rise to a multiphase polymer system with ordered variety of domain structure ranging from a nanometre to micrometre scale. In this respect PABs and IPNs are similar. However there is a difference in the dispersion of the domains. PABs with domain diameter < 100 nm are difficult to prepare, due to the difference in the method of preparation of the multiphase systems. PABs are prepared by melt blending whereas IPNs are obtained by polymerization and crosslinking.

In the preparation of PABs morphological control and stabilization by in situ compatibilization and dynamic vulcanization is gaining importance. The introduction of crosslinks into IPNs restricts the domain size to very small phases and enhances the degree of formulation of micro-heterogeneous structure which results in broad glass transition regions, making them very effective as damping materials over a broad temperature range.

Polymer blends may be either homogeneous or phase separated or a combination of both. The factors determining homogeneity or otherwise are mainly: the method of mixing, the kinetics of the mixing process, the processing temperature, and the presence of solvent or other additives, etc. However the miscibility of two or more polymers is primarily determined by thermodynamic criteria governed by Gibbs free energy considerations. The relationship between change in Gibbs free energy due to mixing (ΔGm) and the enthalpy (ΔHm) and entropy (ΔSm of mixing for a reversible system is:

ΔGm = ΔHm - ΔSm

If ΔGm is positive over the whole composition range at a given temperature, the two polymers in the blend will separate into phases comprising either of the pure components, providing that a state of thermodynamic equilibrium has been reached. For complete miscibility, two conditions are necessary:

[MATHEMATICAL OMITTED] (1.2)

ΔGm must be positive and the second derivative of ΔGm, also with respect to the volume fraction of component 2 (φ22) over the whole composition range.

This ensures stability again phase separation. Figure 1.2(c) shows the free energy–composition dependence at three temperatures. At T1, Equations (1.1) and (1.2) hold good and miscible single-phase mixtures occur at all compositions at this temperature. At T2 Equation (1.2) is not satisfied for all composition and mix between the points B and B separates into two phases resulting in a total free energy falling on the dashed line, which is lower than the homogeneous phase (solid line). The curve at intermediate temperature Tc showed the critical point at C. In Figure 1.2(a) T1 >T2 and Tc is an upper critical solution temperature (UCST), i.e. the temperature above which a homogeneous phase is possible for a particular composition, whereas in Figure 1.2(b) T2< T1 and Tc is the lower critical solution temperature (LCST), i.e. the temperature below which a homogeneous single phase is possible for a particular composition. In this case miscibility of the component improves with declining temperature. Mixtures that have positive (endothermic) heats and entropies of mixing usually tend to exhibit a UCST whereas mixtures that have negative (exothermic) heats and entropies of mixing usually exhibit a LCST. The area dividing the single phase and two-phase region, i.e. the locus of all points B-B' is called the binodal curve. The inflection points S and S' are the free energy curve for T2 define the spinodal curve, structure and dated line on T-t plane. The critical point at which the binodal and spinodal curve touch may not always lie at the extreme limit of the binodal. In a mix, binodal indicates the boundary between stable and meta-stable compositions whereas spinodal indicates the boundary between meta-stable and unstable compositions. The binodal defines the equilibrium phase behaviour, whereas spinodal is significant with respect to mechanism for kinetic of phase separation processes.

Nucleation is an active process of generating within a meta-stable mother phase the initial fragments, called the nucleus, of a new of more stable phase. Once the nuclei (the critical rate-determining intermediates) are formed, the system decomposes with a decrease in free energy and the nuclei grow. The spinodal decomposition is a kinetic process of generating within an unstable mother phase a spontaneous and continuous growth of another phase. The growth originates not from nuclei but from small-amplitude compositional fluctuations.

The polymer–polymer miscibility is dependent upon a delicate balance of enthalpic (ΔHm) and entropic (ΔSm) forces. These are significantly smaller than those observed in the case of mixing of smaller molecules. The combinatorial entropy term is negligibly small because of the very high molecular weight long-chain structure. The heat of mixing is generally endothermic, resulting in positive free energy of mixing (ΔGm). The polymer–polymer miscibility is primarily due to negative heat of mixing. This can be achieved through specific interactions between the constituent macromolecules comprising the blend.

The morphology of the heterogeneous polymer blends is characterized by two distinct phases and in general depends on thermodynamics and rheology of blend composition, interfacial tension between the component polymers, viscosity ratio and processing conditions and history. In immiscible blends, performance depends upon the interface as well as on the size and shape of the dispersed phase. At equilibrium at low volume fractions of dispersed phase φd< φm = 0.16 droplets are expected, with fibres and lamellae usually at higher values. When the dispersed phase concentration increases to the value corresponding to phase inversion (φ) a co-continuous morphology results. Ravati has shown that for blends with the same processing history, the melt viscosity ratio and composition determine the morphology. Generally, the least viscous component forms the continuous phase over a large composition range. The size of the dispersed phase will depend upon mixing variables and to an extent on the thermodynamics of mixing, which will also determine the sharpness of the boundary between the dispersed phase and the matrix, for example.

In the case of blending of immiscible polymers (which is generally the case), two structural characteristics have to be met to avoid gross phase separation and ensure consistent good properties. These are proper interfacial tension providing a small phase size (below the micron level) and good interface adhesion providing a strong interface to resist the effects of stress and strain. To be compatible, interfacial tension must be zero or negative.

Morphology of the immiscible polymer blends can be controlled by using compatibilization or dynamic vulcanization, or both.

A schematic representation of non-compatibilized and compatibilized blends is given in Figure 1.3.

Mixing, in general, is accompanied by entropy gain and heat absorption (endothermic). Entropy change depends on the number of molecules/unit volume whereas heat of mixing/unit volume is a function of the number of molecules in contact, which remains the same with increasing molecular size. Hence, in the case of polymers, entropy changes/unit volume being exceedingly small, heat of mixing will determine the homogeneity of the mix. Endothermic mixing results when the energy of association in the mix is greater than the mean of the energies of association in the pure components. Specific interactions such as H-bonding or stereoisomerism provide favourable association energy in the mix, resulting in homogeneous blends. Interfaces of blend types are presented in Figure 1.4.

Polymer blends are generally made by mechanical as well as chemical methods, as depicted in Table 1.2.

There are several characterization techniques for polymer blend systems in respect of mechanical behaviour, structure–property relationships, phase morphology characteristics and their interaction vs. miscibility or compatibility, and so on. These may be categorized as: (i) microscopic techniques; (ii) study of glass transition; (iii) spectroscopic techniques; (iv) scattering methods; and (v) viscosity measurements.

1.1.1 Interpenetrating Polymer Networks

IPNs are chemically homogeneous (on a scientific large scale binary systems) which could be conveniently prepared by first swelling the loosely crosslinked component in a suitably chosen monomer and subsequently crosslinking the latter. This procedure of chemical blending offered a way of avoiding the hazards of imminent phase separation present in the physical blending of linear polymers, due to topological constraints (permanently entangled, chemically different macrocycles) on IPN unmixing. IPN materials have been studied extensively on polymer alloys with synergistic physical properties of technological interest. The polyurethane (PU) with epoxy resin was the first reported simultaneous IPN.

1.1.2 History of IPN Development

It is difficult to pinpoint the origin of IPNs. Goodyear's work on vulcanization, and the development of polymer blends, grafts and blocks, all led to the development of IPNs. The first known IPN was invented by Aylsworth in 1914. This was a mixture of natural rubber, sulfur and partly reacted phenol formaldehyde resins. The term 'interpenetrating polymer network' was coined by Millar in 1960, who carried out a series of scientific studies of PS/PS IPNs, which were used as ion exchange resin matrices. Frisch and coworkers conceived of IPNs as the macromolecular analogue of catanenanes. Sperling and Thomas investigated finely divided polyblends using electron microscopy to understand the phase structure and correlated the mechanical and viscoelastic behaviour with the phase structure. Lastumaki et al. considered the use of semi-IPNs as adhesives. The IPN field is not widely explored and it inspires yet more research. The history and development of IPNs and related materials are shown in Table 1.3. Schematic representation of different types of blends is given by Figure 1.5.

Since most IPNs involve the polymerization of one monomer in the immediate presence of the other, they are also called graft copolymers. They form a special class due to the crosslinking of one or both the polymers. The interesting and unique properties of IPNs emerge when the deliberately introduced crosslinks outnumber the accidentally introduced grafts. Some amounts of grafts are still present in IPNs and usually contribute to the IPN behaviour in a favourable manner. The IPNs and graft IPNs are schematically shown in Figure 1.6.

The two characteristic features of IPNs that distinguish them from other polymeric mixtures are that (i) IPNs swell but do not dissolve in solvents and (ii) creep and flow are suppressed.

According to the mode of synthesis, IPNs are distinguished into five different types: (i) sequential IPNs, (ii) simultaneous IPNs, (iii) interpenetrating elasto-meric networks, (iv) thermoplastic IPNs and (v) gradient IPNs:

(i) Sequential IPNs, where polymer I is crosslinked initially followed by the swelling of polymer network I with monomer II plus crosslinker and initiator and subsequent polymerization of monomer II, in situ.

(ii) Simultaneous IPNs (SINs), where a mutual solution of monomer I, monomer II, crosslinker I, crosslinker II are taken together and then polymerized simultaneously by non-interfering modes. The above two types of synthesis are represented diagrammatically in Figure 1.7.

(iii) There is a third mode of synthesis where two lattices of linear polymers are mixed and coagulated and both the polymers are crosslinked simultaneously. They are called interpenetrating elastomer networks (IENs).

(iv) In the case of thermoplastic IPNs, physical crosslinks are present rather than chemical covalent crosslinks. Frequently, the polymers exhibit some degree of phase continuity. In all such cases, the thermoplastic IPNs behave as thermosets at ambient temperature and as thermo-plastics at elevated temperature.

(v) In gradient IPNs the composition is varied within the sample at the macroscopic level. This is carried out by swelling the network in monomer for the required time and polymerizing rapidly, before equilibrium sets in.

(Continues...)

Excerpted from Natural Rubber Materials Volume 1 by Sabu Thomas, Rajisha K. R., Hanna J. Maria, Chin Han Chan, Laly A. Pothen. Copyright © 2014 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2013
• Language: English
• ISBN 10: 1849736103
• ISBN 13: 9781849736107
• Binding: Hardcover
• Number of pages: 634
• Editor: Sabu Thomas