Polym. Tech.
84
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Transcript of Polym. Tech.
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Introduction to free-radical
polymerization
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Polymerization mechanisms
- Step-growth polymerization
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Polymerization mechanisms
- Chain-growth polymerization
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Advantages of free-radical polymerization
- very robust technique- wide range of vinyl monomers and functionalities- wide range of operating conditions- aqueous media: emulsion polymerization
Disadvantages of free-radical polymerization
- non-selective reaction- non-trivial product control
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Chain reactions
characteristics:
•each polymer chain grows fast. Once growth stops a chain is no longer reactive.
•growth of a polymer chain is caused by a kinetic chain of reactions.
•chain reactions always comprise the addition of monomer to an active center (radical, ion, polymer-catalyst bond).
•the chain reaction is initiated by an external source (energy, reactive compound, or catalyst).examples:
radical polymerizationionic polymerizationcoordination polymerizationgroup transfer polymerization
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Radical polymerization
• initiation (start)• propagation (growth)• chain transfer (stop/start)• termination (stop)
During initiation active centers are being formed.During termination active centers disappear.
Concentration of active centers is very low (10-9 - 10-7 mol/L).
Growth rate of a chain is very high (103 - 104 units/s).
Chains with a degree of polymerization of 103 to 104 are being formed in 0.1 to 10 s.
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Initiation
Most common method of initiation: thermal decomposition of a thermally labile compound, the initiator
These radicals are called primary radicals. Initiation takes place by addition of a monomer unit.
kd is a first order rate constant.Common values of kd are in the range: 10-4 - 10-6 s-
1.The rate of radical production is then given by:
]I[k2dt
]•R[dd
I 2 Rkd
R + M R1
ki
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The actual rate of initiation Ri is expressed in terms of the rate of radical production that leads to actual polymer chains growing!:
]I[fk2R di
where f is the efficiency factor: the fraction of radicals that really leads to initiation.Therefore, in all cases: f 1
The rate constant ki is not used in the mathematical description of the polymerization.
Examples of thermal initiators:
C
O
O O C
O
H3C C
CN
CH3
N N C
CN
CH3
CH3
Ea = 140 – 160 kJ mol-1
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propagation
This reaction is responsible for the growth of the polymer chain. It is the reaction in which monomer is added at the active center:Mi + M
kp Mi+1
The rate of this reaction Rp can be expressed as:
]M][•M[kR pp
Assumption:the reaction rate constant kp is independent on chain length. This appears to be reasonable above chain length i = 5 - 10
Propagation is the most important reaction for monomer consumption.
The reaction rate constant kp typically has a value in the range 102 - 104 L/mol s
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Termination
Chain growth stops by bimolecular reaction of two growing radicals: termination
Traditionally two different reactions are recognized:• termination by combination (ktc)• termination by disproportionation (ktd)
Schematically these reactions can be represented as:
The general kinetic equation reads:2
tt ]•M[k2R
The reaction rate constant kt is in the range 106 - 108 L/mol s
Mi + Mj
ktcMi+j
Mi + Mj
ktdMi Mj+
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Termination
Every reaction consists of two steps:1) approach of both reactants2) chemical reaction
The second step in the termination reaction is very fast. This means that the rate of approach (partially) determines the overall termination rate.
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at 5 % conversion
Termination: which is faster?
1. + or +
2. + or +
in a viscous medium in a non-viscous medium
3. + or +
at 85 % conversion
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Rate of polymerization
The rate of polymerization in a chain growth polymerization is defined as the rate at which monomer is consumed.
pi RRdt
]M[d
Since for the production of high molar mass material Rp » Ri this equation can be re-written as:
•]M][M[kRdt
]M[dpp
From the beginning of the polymerization:• increasing number of radicals due to decomposition of the
initiator• increasing termination due to increasing radical
concentration (Rt [M·]2)• eventually a steady state in radical concentration:
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2td
ti
•]M[k2]I[fk2
RR
This steady state assumption leads to:
t
d
k
]I[fk=•]M[
From which the differential rate equation is derived:
t
dpp k
]I[fk]M[k=R
At low conversion this means:
log(Rp) vs log[M] yields a slope = 1
log(Rp) vs log[I] yields a slope = 0.5
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When the initiator decomposes slowly compared to the entire polymerization process:
kt0
p
e]M[]M[
dtk]M[
]M[d
]M[kR
When ln([M]0/[M]) is plotted versus time, then the slope should equal k:
t
dp k
]I[fkkk
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Kinetic chain length
i
p
R
R
species initiating
unitsmonomer ofnumber
td
p
2t
p
t
p
i
p
k]I[fk2
]M[k
•]M[2k
•]M][M[k
R
R
R
R
Also =kp [M] , with t time of growth of a polymer chainHere we find at low conversion:log(n) vs log[M] yields a straight line; slope = 1log (n) vs log[I] similar; slope = -0.5thus: increase in [I] leads to an increase in rate of polymerization and a decrease in chain length.
The special case with a slowly decomposing initiator leads here to:
kt0e
wheretd
p
k]I[fk2
kk
td kIfkM
M
][2
1
•][2k
•][2
t
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The number average degree of polymerization Pn of chains formed at a certain moment is dependent on the termination mechanism:* combination: Pn = 2
* disproportionation: Pn = chemistry:
CH2 C
H
+ C
H
CH2 CH2 C
H
C
H
CH2
CH2 C
CH3
C O
OMe
+ C
CH3
C
CH2
O
OMe
CH2 C
CH3
C
H
O
OMe
+ C
CH2
C
CH2
O
OMe
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Initiatie/terminatie via MALDI-ToF MSMethyl acrylaat met benzoine
O
+
O
O
A B
+ CH3
C
1276.0 1310.6 1345.2 1379.8 1414.4 1449.0
Mass (m/z)
0
1248.5
0
10
20
30
40
50
60
70
80
90
100
% I
nte
nsi
ty
1295.98
1312.01
1398.071382.05
1296.991313.01
1383.051399.081352.03
1438.09
1353.04
1439.101314.01
1334.041297.99 1384.06 1400.081420.10
1358.071342.041332.02 1428.101359.07
1429.101418.101343.051294.02 1333.021315.03 1385.08 1401.091360.08 1435.071349.041336.051276.101427.40
1288.0 1296.2 1304.4 1312.6 1320.8 1329.0
Mass (m/z)
0
1248.5
0
10
20
30
40
50
60
70
80
90
100
% In
ten
sity
1295.98
1312.01
1296.991313.01
1314.01
1297.99
1294.02 1315.031298.99
1327.0 1335.4 1343.8 1352.2 1360.6 1369.0
Mass (m/z)
0
662.2
0
10
20
30
40
50
60
70
80
90
100
% In
ten
sity
1352.03
1353.04
1334.04
1358.071354.051342.041332.02
1335.04 1359.071348.031343.051333.02 1350.03
1346.03 1360.081349.041336.05
B-MA12-A
A-MA13(-H)
A-MA13(+H)
B-MA14(-H)
B-MA14(+H)
B-MA13-B
A-MA13-A
16.03 Da
16.03 Da
?
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Trommsdorff effect
In radical polymerization we speak about:1) low conversion, i.e. polymer chains are in dilute solution (no contact among chains)2) “intermediate” conversion, i.e. the area in between low and high conversion3) high conversion, i.e. chains are getting highly entangled; kp decreases.
Somewhere in the “intermediate” conversion regime:* polymer chains loose mobility.* Termination rate decreases* Radical concentration increases* Rate of polymerization increases* Molar mass increases
This effect is called: gel effect, Trommsdorff effect,or auto-acceleration
In the polymerization of MMA this occurs at relatively low conversion.
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Molar mass
in the ideal case:
n
n
P
2P (termination by combination)
(termination by disproportionation)
However, a growing chain may transfer its activity to a new chain:
This reaction is then followed by re-initiation, the start of a new chain:
Mi + T Mi + Tktr
T + M M1ki'
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Chain transfer
chain transfer to:• monomer• initiator• solvent or chain transfer agent• polymer• allylic transfer
monomer, initiator and chain transfer agent are mathematically treated identically:
•][X]M[k•]M[k2•]M[kdt
]polymer[dX,tr
2td
2tc
As derived beforethis leads to:
]M[k
]I[k
]M[k
]S[k
k
k
]M[k
•]M[k2
]M[k
•]M[k
]M[k
]X[k
]M[k
•]M[k2
]M[k
•]M[k
P
1
p
I,tr
p
S,tr
p
M,tr
p
td
p
tc
p
X,tr
p
td
p
tc
n
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The rate of “polymer formation” is now defined as:
]T][•M[k]•M[k2]•M[kdt
]polymer[dtr
2td
2tc
The rate of polymerization as derived before:
•]M][M[kdt
]M[dp
From the definition of number average degree of polymerization it follows:
dt]polymer[d
dt]M[d
Pn
]M[k
]T[k
]M[k
]•M[k2
]M[k
]•M[k
]•M][M[k
]T][•M[k]•M[k2]•M[k
P
1
p
tr
p
td
p
tc
p
tr2
td2
tc
n
thus:
]M[]T[
CP
1
1P
T0,n
n
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Chain transfer to polymer
• Intermolecular chain transfer
• Intramolecular chain transfer
Traditional approach: intermolecular, strong increase in branching density towards high conversion.
Recent results: • Hardly conversion
dependent
• Dilution results in higher degree of grafting
0 10 20 30 40 501
2
3
4
5
6
7
8
conversion ca. 25% conversion > 80%
mo
l% b
ran
che
s
[BA]0 / %(w/w)
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Ziegler-natta
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Summary
tMkL p ][
]][[ MMkR pp
Chain-length
Rate of polymerization
Initiator decomposition is the reaction step most strongly influenced by temperature.
][
1~
MtTime of chain-growth
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Chain length distribution
Crucial in the derivation of the CLD is the chance on formation of an i-mer chance on propagation:
tp
p
RR
Rp
thus: chance on chain stop: 1-pDuring the growth of a single chain p is constant
disproportionationmol fraction i-mer: p1px 1i
i
mass fraction i-mer: 21i
i
ii p1ip
ix
ixw
which yields:
p1
p1iwP
p1
1ixP
iw
in p1P
PD
n
w
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combination
2i3
i
ii
2i2i
p)1i()p1(i2
1
ix
ixw
p)1i()p1(x
which yields:
p1
p2P
p1
2P
w
n
2
p2D
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111 k
kr
21
222 k
kr
kk1111
kk1212
kk2121
kk2222
Copolymerization
——MM11• + M• + M11 —M—M11••
——MM11• + M• + M22 —M—M22••
——MM22• + M• + M11 —M—M11••
——MM22• + M• + M22 —M—M22••
}}
}}
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Copolymerizationffii:: fraction of monomer fraction of monomer ii in reaction mixture in reaction mixture
ff11 = [M = [M11] / ([M] / ([M11] + [M] + [M22])])
FFii:: fraction of monomer fraction of monomer ii built into polymer built into polymer
FF11 = d[M = d[M11] / (d[M] / (d[M11] + d[M] + d[M22])])
22221
211
212
111
2 frfffr
fffrF
Long chain assumption (Long chain assumption (kkii, , kkdd ignored; ignored; kkpp, , kktt not ~ chain not ~ chain length)length)
Reactivity ratios independent of environmental factorsReactivity ratios independent of environmental factors
22221111
22221
211
p2
kfrkfr
frfffrk
Average copolymerisation rate: Average copolymerisation rate:
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0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1f 1
F 1
MMA / BAEthene / VAcVDC / VC
Ideal copolymerisation
Composition driftComposition drift
If If ff11 ≠ F≠ F11
→ → ff11 changes changes
→ → FF11 changes changes
What does composition What does composition drift mean for the polymer drift mean for the polymer that is formed?that is formed?
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Polymerization techniques
• Kinetic / mechanistic factors related to chain length, chain composition
• Technological factors e.g. heat removal, reaction rate, viscosity of the reaction mixture, morphology of the product
• Economic factors; production costs, enviromental aspects, purification steps etc.
Sometimes for one monomer several techniques of polymerizing are available. Choice of a specific technique depends on a number of factors:
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Homogeneous systems• Bulk polymerization• Solution polymerization
Heterogeneous systems• Suspension polymerization• Emulsion polymerization• Precipitation polymerization• Polymerization in solid state• Polymerization in the gas phase
Polymerization techniques
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Bulk polymerization Polymerization of the undiluted monomer.
Viscosity increases dramatically during conversion. Heat removal and hot spots
Advantages Disadvantages * Pure products * heat control * Simple equipment * dangerous
* No organic solvents * molecular weights very disperse
Applications Polymers through step reactions (nylon 6) PMMA-plates
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Solution polymerizationMonomer dissolved in solvent, formed polymer stays dissolved. Depending on concentration of monomer the solution does not increase in viscosity.Advantages Disadvantages* Product sometimes * Contamination
directly usable with solvent* Controlled heat * Chain transfer to release solvent
* Recycling solvent Applications Acrylic coating, fibrespinning, film casting
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Suspension polymerization• Water insoluble monomers are dispersed in
water.• Initiator dissolved in monomer.• Stabilization of droplets/polymer particles with
non-micelle forming emulsifiers like polyvinylalcohol or Na-carboxymethylcellulose.
• Equivalent to bulk polymerization, small droplets dispersed in water.• Product can easily be separated, particles 0.01-1mm.• Pore sizes can be controlled by adding a
combination of solvent (swelling agent) and non-solvent.
• Viscosity does not change much.
Qu
alita
tive d
escri
pti
on
of
em
uls
ion
poly
meri
zati
on
kin
eti
cs
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Advantages Disadvantages * Heat control simple * Contamination with * Product directly stabilizing agent
usable * Coagulation possible * Easy handling
ApplicationsIon-exchange resins, polystyrene foam, PVC
Suspension PolymerizationQ
ualita
tive d
escri
pti
on
of
em
uls
ion
poly
meri
zati
on
kin
eti
cs
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Emulsion Polymerization
• A micelle forming emulsifier is used.• Initiator is water soluble.• The formed latex particles are much
smaller than suspension particles (0.05-2 µm).• Kinetics differ considerable from other
techniques.• Polymer is formed within the micelles and not in the monomer droplets.
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Antonio de Herrera Tordesillas described an application of natural latex in 1601. A ball game as part of a religious rite.
Qu
alita
tive d
escri
pti
on
of
em
uls
ion
poly
meri
zati
on
kin
eti
cs
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Emulsion Polymerization
Advantages Disadvantages* Low viscosity even * Contamination of at high solid contents products with additives
* Independent control * More complicated of rate and in case of water molecular-weight soluble monomers * Direct application of
complete reactor contents
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Applications of laticesPaints-Construction
* Paints / rough casting / heat insulation* Elastomeric coatings / primers* Additives for cement and concrete* Anti corrosives / wood coatings* Industrial coatings* Rheology modifiers* Roof coatings
* Fillers and levelling powders
Glues-Adhesives* Wood glues / adhesives for furniture laminates* Adhesives for floor-, wall- and
ceiling materials* Packaging- and lamination glues* Adhesion- and contact glues* Leather fibres* Glues in powder form
Textiles* Carpet backside coatings* Fleece binder* Spunbond / textile coating* Equipment of technical textiles* Pressure binder /flocculating glue
Paper
* Boxes and wallpaper* Binders for rubbed paper
* Structural Adhesives* Contact Adhesives
* Varnishes
Source: Clariant
Other* Teflon* Elastomers
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Objective
Properties
Process
Molecular Microstructure & Morphology
How
to in
fluen
ce ?
What is the relation ?
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Differential Scanning Calorimetry
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GlasovergangstemperaturenTg [°C]
Polyvinylacetaat + 29
Polyvinylpropionaat + 7
Poly(VeoVa 10) - 2
Polyvinylidenchloride + 80
Polyacrylonitril + 100
Polyethyleen (-125)
Polystyreen + 100
Polymethylmethacrylaat +105
Poly 2-ethyl-hexylacrylaat -85
Poly n-butylacrylaat -54
Polyacrylzuur (kristallijn) + 166
Poly methacrylzuur + 185Poly acrylamide (kristallijn) + 153
Polyhydroxy-ethyl-methacrylaat + 55
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Monomer: Tg [°C] Methyl - Acrylaat + 8
Ethyl - Acrylaat - 22 n-Butyl - Acrylaat - 54 2-Ethylhexyl - Acrylaat - 85
Methyl - Methacrylaat + 105 Ethyl - Methacrylaat + 65 n-Butyl - Methacrylaat + 20 2-Ethylhexyl - Methacrylaat - 10 Decyl - Methacrylaat - 70 n-Butyl - Acrylaat - 54 iso-Butyl - Acrylaat - 43 sek.-Butyl - Acrylaat - 20 tert.-Butyl - Acrylaat + 41 n-Butyl - Methacrylaat + 20 iso-Butyl - Methacrylaat + 48 sek.-Butyl - Methacrylaat + 60 tert.-Butyl - Methacrylaat + 107
Glasovergangstemperaturen
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Monomeer – Indeling in groepen
Harde monomeren
Styreen
Methylmethacrylaat
Vinylchloride
(Vinylacetaat)
(Vinylpropionaat)
Acrylonitril
Zachte monomeren
Acrylzuuresters
Butadieen
Ethyleen
Versaticsäurevinylester
Malein- und Fumaarzuur-esters met C > 4
Geladen monomerenAcrylzuur
Methacrylzuur
Maleinezuur
Fumaarzuur
Natrium-Etheensulfonaat
Natrium-Etheenphosphaat
Vernettende monomeren
Polyvinyl- und Polyallyl- verbindingen
N-Methylol-verbindingen
Aktieve halogeenhoudendeverbindingen
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Spherulieten in de microstructuur van een polymeer.
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De 3M aspecten van de PE proef. Links de toepassing, een beker (macro), met in het midden de morfologie van dit polymeer (meso). Rechts de atomaire ketens zoals die in het polymeer voorkomen (micro).
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Copolymeren
Block-Copolymeer
Graft polymeer
Statistisch Copolymeer
Alternerend Copolymeer
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Naast een molmassaverdeling bezit een copolymeer ook Naast een molmassaverdeling bezit een copolymeer ook een samenstellingsverdelingeen samenstellingsverdeling
FFmonomer 1monomer 1
ww11
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Approach : Raman spectroscopy as on-line sensor
lasermodel
Properties CopolymerCompositionDistributionMonomer
Composition
Reactivity
Monomer Partitioning
Kinetics
In-situ Raman spectroscopy gives
on-line information on concentrations
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0.0
0.2
0.4
0.6
0.8
1.0
1.2
Eb
0
50
100
150
200
Yo
un
g’s
mo
du
lus
(G
pa)
Elo
ng
ation
at break
(%)
C
B
A
Mechanical properties
Example: 25% styrene - 75% methyl acrylate
0 0.5 1
Fsty
0 0.5 1
Fsty
D
0 0.5 1
Fsty
0 0.5 1
Fsty
DCBA
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Polymeerveroudering
• Plafondtemperatuur• Degradatie• Stabilisatie
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Polymeerveroudering
-Ketenbreuk
-Depolymerisatie
-Crosslinking
-Bindingsverandering
-Zijgroepverandering
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Plafondtemperatuur
• Temperatuur waarbij in evenwicht– 1 mol/l monomeer aanwezig is– Of [M]= concentratie zuiver monomeer
Methylmethacrylaat Tc=220 CAlpha-methyl styreen Tc= 61 C
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65
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67
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Degradatie
• Thermische degradatie– Willekeurige ketenbreuk– Keteneind depolymerisatie (unzipping)
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Degradatie
• Oxidatieve degradatie– Radicaalvorming door reacties met zuurstof
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Degradatie
• Stralingsdegradatie– Fotolyse (UV)– Radiolyse
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Degradatie
• Chemische degradatie– NO2
- SO2
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Degradatie
• Mechanochemische degradatie– Kogelmolen– Spuitgieten– Vermalen
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Degradatie
• Biologische degradatie– Controlled drug release
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Composieten
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80
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Nanotubes for conductive coatings
Encapsulated pigment
Armoured latex particle
Encapsulated clay platelet
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