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NANO MTL Lc2 (primary bond (ceramics
ionic n covalent (large bond energy
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NANO MTL Lc2
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molecular structure
linear
secondary bond (chain to chain) ; vdW hydrog dipole
extensive van der Waals n hydrogen bonding between chains
PP PVC PS polymethyl methcrylate (PMMA) fluorocarbon (PTFE)
branched
branch obstacle no bond between chain
branches resulted from side reations that occur during synthesis of the polymer
chain packing efficiency reduced w formation of side branches :arrow_right: lowering polymer density (LDPE)
cross linked
covalent bond all around
achieved during synthesis / by non reversible chem reaction @ elevated temp
accomplished by additive (sulphur) tht covalently bonded to chains
rubber elastic materials - vulcanization
network
tri-functional mer units - having three active covalent bonds ; form 3D network
distinctive mechanical n thermal properties
epoxies n phenolics
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processing
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thermoset
when heated forms a molecular network (chem reaction)
degrades (doesnt melt) when heated
can be molded / processed into desired shape then chem reaction occurs
polymer crystallinity
as packing of molecular chain to produce an ordered atomic ray
state where in a periodic n repeating atomic arrangement is achieved by molecular chain alignment
rarely 100% crystalline
difficult for all regions of all chains to become aligned
heat treating cause crystalline regions to grow n % crystallinity to increase
crystalline n amorphous
bonding within chain = covalent
long coiled chains held by one another by weak 2nd bond n by entanglement
when stress applied weak bonding can be overcome n chain can rotate n slide relative to one another
temp n structure dependent
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degradation
Td very high temp covalent bonds between atoms in linear chain destroyed n polymer burned
exposure to oxygen UV radiation bateria attack = degrade @ low temp
PE PP PVC susceptible to degradation due to their molecular structure n low strength of C-H bonds
fluoropolymers hv high stability to degradation
PTFE high strength of C-F bond in the backbone structure
molecular weight : mass of a mole of chains
longer chain higher weight
degree of polymerization DP = avg # of repeat units / chain