40207_03EPOXY RESINS - EPOXY RESINS L .S. Penn and 3. Wang...

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EPOXY RESINS 3 L.S. Penn and €3. Wang 3.1 INTRODUCTION Epoxy resin systems have achieved acceptance as adhesives, potting compounds, molding compounds and as matrices for continuous fil- ament composites used in structural applications. In this chapter, we discuss epoxy resins in their role as matrices in fiber compos- ites. In this role, they possess several advantages over other types of polymers. The main advantages are: 0 inherently polar nature that confers excel- lent adhesion to a wide variety of fibers; 0 relatively low cure shrinkage that makes dimensional accuracy of fabricated struc- tures easier to obtain; 0 no volatile by-products of the curing reac- tion to cause undesired bubble or void formation; 0 crossIinked structure that confers excellent resistance to hostile environments, both aqueous and nonaqueous. In addition to these advantages, epoxy resins have tremendous versatility because they can be formulated to meet a broad range of specific processing and performance requirements. To know how to take advantage of the formula- tion options, the engineer needs to have an elementary understanding of epoxy resin chemistry and structure-property relation- ships. This chapter attempts to provide that by presenting information about the resin system constituents, how they react together to form a Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 crossllnked network and how they lead to dif- ferent processing parameters and final properties in the formulated system. The chapter also describes the role of cure moni- toring and property evaluation in epoxy resin system technology. 3.2 GENERAL DESCRIPTION OF THERMOSETTING SYSTEMS 3.2.1 DEFINITIONS According to common chemical practice, mol- ecules can be classified by the functional groups they contain. Thus, a molecule contain- ing the epoxide group (shown below) as part of its structure is called an epoxide, regardless of the remaining details of the molecule. /O\ -c-c- I I In practice, other types of molecules are added to the epoxide to formulate a thermosetting system, i.e. one that will undergo a curing reaction to harden into a rigid form. The con- fusing practice has been followed of referring to both the epoxide alone and the formulated system as 'epoxy resin'. One must determine which is truly intended by the context in which it is used. For the purposes of clarity in this chapter, we will use epoxide when refer- ring to the epoxide constituent alone and will
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General descripfion of thermoseffing systems 49 use the term epoxy resin when referring to the uncured or cured formulated system. 3.2.2 THE THERMOSETTING (CURING) REACTION The thermosetting reaction is the joining of many small molecules by chemical reaction to produce an extended network structure.
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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40207_03EPOXY RESINS - EPOXY RESINS L .S. Penn and 3. Wang...

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