Karak Vegetable Oil-Based Polymers

Properties, Processing and Applications
1. Auflage 2012
ISBN: 978-0-85709-714-9
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 336 Seiten

The growing need to find a sustainable, environmentally-friendly replacement for petroleum-based materials is fuelling the development of bio-based polymers from renewable resources. Amongst the most promising of these are vegetable oil-based polymeric materials. Vegetable oil-based polymers provides a comprehensive review of the research in this important field.After an introduction to classification and polymerization, Vegetable oil-based polymers goes on to review the factors involved in polymer biodegradation. The extraction, purification and application of vegetable oils are then explored, along with vegetable oil-based polyesters and poly(ester amide)s, polyurethanes and epoxies. The book then reviews polyamides, polyolefins and vegetable oil-based hyperbranched polymers. It concludes with an analysis of vegetable oil-based polymer composites and polymer nanocomposites.Vegetable oil-based polymers is an indispensable guide for all those involved in the research and development of biopolymers as well as the wide range of industries looking for more sustainable polymer materials. - Provides a comprehensive review of recent research in the area of vegetable oil-based polymeric materials - Discusses vegetable oils and their derivatives, biodegradable polymers and the fundamentals of polymers - Explores the extraction, purification and application of vegetable oils, along with vegetable oil-based polyesters and poly(ester amide)s, polyurethanes and epoxies

Niranjan Karak is Professor of Polymer Science and Technology and Head of the Chemical Sciences Department at Tezpur University, India. He has published over 87 research papers, two books and two chapters in two edited books, and also regularly acts as a reviewer for many international polymer journals.

Autoren/Hrsg.

Karak, Niranjan

Leseproben

1 Fundamentals of polymers
Abstract:
This chapter discusses the fundamentals of polymers. It deals with the concept and importance, definition, classification, raw materials, polymerisation processes and techniques, modification and structure– property relationships of polymers. It also describes the basic properties of different additives used and the processing of polymers. Building on our basic knowledge of polymers and their properties allows the details of different vegetable oil-based polymers to be discussed, making the importance of this chapter undeniable. Finally, a journey of discovery into vegetable oil-based polymers follows from considering the potential, different applications and challenges of existing polymers. Key words polymer definition classification structure–property relationship application 1.1 Introduction
Polymers are composed of large molecules with a high molecular weight, unlike fine chemicals or small molecular compounds. These macromolecules are formed by covalent links of large numbers of simple repeating units with identical constituents, where the addition or subtraction of a few such units does not change the properties. The term ‘polymer’ is a combination of two Greek words: ‘poly’ meaning ‘many’ and ‘meros’ meaning ‘parts’ or ‘units’. A polymer is thus the sum of many parts or units. ‘Polymerisation’ is the process of forming polymers from their respective reactive units. The small molecules which form repeating units are known as monomers. Monomers typically react in the presence of a catalyst or initiator to form a polymer. The number of repeating units present in each polymer chain is known as the ‘degree of polymerisation’ (DP) and is used to determine the molecular weight of the polymer by the following formula: molecular weight = molecular mass of repeating unit X ‘DP’ The high molecular weight of polymers is a result of the high DP, given the number of monomers in each chain. In a polymerisation process, different polymer molecules may have different numbers of repeating units in their chains and hence the chain lengths are different, even under the same set of reaction conditions in the same batch. This is because the number of reactions involved in the formation of each polymer molecule is very high, so controlling the number of repeating units in different molecules is extremely difficult. The chain length of one molecule will differ from other molecules in the same polymer. Thus the number of repeating units varies from chain to chain, even within the same batch of polymers, so only the average number is taken and the molecular weight is expressed as the average molecular weight. Biopolymers are found in animal and plant sources. Natural polymers include protein-based fibres such as wool and silk (mainly polyamide), carbohydrate fibres such as flax and cotton (mainly cellulose) as well as in tree saps which produce amber and latex (mainly hydrocarbon). The term ‘polymer’ was first coined by Berzelius in 1833. However, it was only in the 1920s that the concept of a polymer as a long sequence of repeating units linked by covalent bonds, was presented by H. Staudinger. (Nobel prize winner for chemistry, 1953).1 At the same time, Carothers also rationally synthesised polymers from their respective monomers by means of different polymerisation processes. In addition to the above, knowledge about the structures (i.e. composition, arrangement and spatial disposition of the repeating units of the polymer chains) became a part of scientific knowledge, enabling their use in different applications. Since then, a large number of useful polymers have been developed, offering a large variety of properties and applications. This is made possible by the unique properties and structural versatility of polymers compared to other categories of materials such as ceramics and metals. The significance and utility of polymers is illustrated by the following facts.2 • They are versatile with respect to their feed stock resources. The same monomer or starting material of a polymer can be obtained from petroleum, forestry or agricultural products. • They exhibit versatility in structure and hence in their properties. For example, polyurethanes may be obtained as foam, thermoplastic, elastomeric, resin, adhesive or sealant material, depending on the composition of their constituents and the conditions of polymerisation. • The amount of energy required for processing is small. This is because of the low melting and softening points of polymers and their ease of solubility in a variety of solvents. • Polymers can be modified easily because of their organic nature and the presence of a large numbers of modifiable active sites in their structures. • Polymers are light in weight because of their low density and large volume. This is due to their long, coiled and entangled chain structure. • Polymers may be mass produced within a short timescale. They are also versatile in relation to polymerisation and processing techniques. • Because the long chain and organic nature of polymers enables a large number of secondary interactions, they can be easily decorated. • Polymers can be manufactured at a low overall cost. 1.2 Classification
Polymers are generally classified into categories based on their source, mode of formation, main chemical linkages, structure, thermal response, type of repeating unit, physical properties and bio-degradation characteristics, and so on.3 1.2.1 Source
There are three different classes based on polymer source. 1. Natural polymers: These are obtained from natural sources, that is flora and fauna. Examples are natural rubber (NR), wool, cellulose and silk. These are also known as biopolymers. 2. Semi-synthetic polymers: Chemically modified natural polymers are classified as semi-synthetic polymers. Some examples are epoxidised natural rubber (ENR), chlorinated natural rubber (Chlororub), nitrocellulose, carboxy methyl cellulose (CMC) and cellulose acetate. 3. Synthetic polymers: Synthetic polymers are obtained from their respective monomer(s) or reactants by chemical reactions in the laboratory. Most polymers fall into this category. Some examples are polyethylene, polypropylene, phenol-formaldehyde resin and styrene-butadiene rubber. Polymers obtained from natural resources such as vegetable oils, animal fats and insects are known as bio-based polymers. They are natural derivatives of synthetic polymers rather than completely natural or completely synthetic polymers. 1.2.2 Mode of formation
Polymers can be classified into three categories: addition, condensation and rearrangement, based on their mode of formation. Addition polymers Addition or chain growth polymers are formed by the direct addition of monomer molecules held together by a covalent bond without loss of any by-product during the polymerisation process. Thus the molecular mass of a monomer molecule and a repeating unit is the same. Examples of this class of polymers are vinyl polymers such as polystyrene, polybutadiene and poly(vinyl chloride), and diene polymers such as polybutadiene, and poly-isoprene, polychloroprene. Condensation polymers Condensation or step growth polymers are formed by the incremental growth of monomer(s) or condensed product(s) of the reactant molecules through covalent bonds after the elimination of by-products such as H2O, NH3, HCl, HCHO, phenol, and so on. The molecular mass of a repeating unit is less than the molecular mass of a monomer(s) or reactant(s). Examples of this class of polymer are nylons, polyesters, polyimides and polycarbonates. Rearrangement polymers These polymers are formed by rearrangement of the monomer(s) or reactant(s) in an incremental manner, without elimination of any byproducts. Though they do not fall into either of the previous two classes, they exhibit some characteristics of both; for example, polyurethane, which is formed by a step growth polymerisation mechanism. It is not formed by condensation (as no by-product is formed), nor is it an addition polymer, as it is not formed by chain growth mechanism. Although the terms addition or chain growth, and condensation or step growth are often used synonymously, they are not exactly the same. The classification of addition and condensation is based on the composition of the repeating unit and monomers or reactants used, whereas the classification of chain growth and step growth is based on the mechanism of the formation of the polymers.3 1.2.3 Main chemical linkages
Polymers are classified according to the main chemical...