Chapter6_poly (2)

Chapter6_poly (2) - Chapter 6 Polymeric Materials for Aero...

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Chapter 6 Polymeric Materials for Aero Applications
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Reading Material • Callister, p. 489 - 565
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tructure and Properties of Polymers Structure and Properties of Polymers • Major aerospace uses of polymers are in composites, dhesives and nonstructural applications such as adhesives and nonstructural applications such as seats and canopies • Compared to metals, polymers have low density, low tiffness and strength and low conductivities stiffness and strength, and low conductivities. • Service temperature is limited to about 300°C • Dimensional stability over time is still uncertain Polymers are typically amorphous but can partially crystallize with slow cooling • E: 7 MPa -4 GPa (for metals: 50-400 GPa) UTS: up to 100 MPa (metals: 4000MPa)
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Classification • Basic classification is according to the response to rising temperature: thermoplastics, thermosets and elastomers – Of course there are also: thermoplastic elastomers (TPE) and thermosetting elastomers (TSE) and even thermoplastic elastomers.
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Mer and Polymer Microstructure - Review Poly mer = many mers (mer is a structural entity repeated along the chain) H H H H H H mer H H H H H H H H H H H H C C C C C C H H H H H H Polyethylene (PE) Cl C C C C C C H H H Polyvinyl chloride (PVC) Polypropylene (PP) CH 3 C C C C C C H H H 3 3 Covalent hain onfigurations and strength: chain configurations and strength: secondary onding Branched Cross-Linked Network Linear bonding Direction of increasing strength
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g and Tm Tg and Tm the presence of bulky side groups, polar side group,s double chain bond, and aromatic groups all increase Tg higher M (molecular weight) increases Tg branching and crosslinking increase Tg ermal treatment history can thermal treatment history can affect Tg
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Molecular Structures of Polymers - Review • There are four types f molecular of molecular structures: linear (a), branched (b), cross linked (c) and network (d) 3-D framework
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olymerization - eview Polymerization Review •T w o processes: addition polymerization or condensation polymerization • Addition: ifunctional monomer units are attached on one at a – Bifunctional monomer units are attached on one at a time in chain-like fashions to form a linear macromolucule itiator/catalyst + monomers – Initiator/catalyst + monomers • Condensation (with byproduct typically H 2 O) – The formation of polymer by stepwise intermolecular chemical reaction – trifunctional monomer cross linked or network polymers Note polymer alloys can be created; e.g. polyimide-sulphones
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hermoplastic Polymers Thermoplastic Polymers – Soften when heated (and eventually liquify) and harden when cooled. The process is totally reversible and can be repeated a number of times (pop bottles become carpets etc) – With the increase of temperature, secondary bonding rces diminishes due to molecular motion relative forces diminishes due to molecular motion, relative movement of adjacent chains is made easy.
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This note was uploaded on 11/13/2011 for the course CIVE 2*** taught by Professor - during the Spring '11 term at Carleton CA.

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Chapter6_poly (2) - Chapter 6 Polymeric Materials for Aero...

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