introduction to polymer stabilization
DESCRIPTION
PresentationTRANSCRIPT
RK / ACS ‘01 - 1 -
America Chemical Society MeetingSan Diego CA 2001
“Introduction to Polymer Stabilization”
by
Dr. R.E. King IIISenior Staff Scientist II
Ciba Specialty ChemicalsTarrytown NY 10591
April 1 - 5, 2001
Ciba
RK / ACS ‘01 - 2 -
Outline of Presentationl Auto-Oxidation & Stabilizationl Review of Various StabilizersØAntioxidants¬Primary: Phenols & Arylamines¬Secondary: Phosphites & Thiosynergist¬New Chemistries: Hydroxylamines & Benzofuranones
ØUV Stabilizers¬Excited State Quenchers¬UV Absorbers¬Hindered Amines
l Recent Challenges in the Fieldl Conclusions & Recommendationsl Acknowledgments
RK / ACS ‘01 - 3 -
Polyamides: -CO-NH-CH2-
Polyesters: -CO-O-CH2-
Polyacetal: -O-CH2-O-
Unsaturated Systems: -CH=CH-CH2-
Polyolefins: -CH2-CH-CH2-
Selected Polyethylenes H2C=CH-CH2-
F. Gugumus; Plastics Additives, Gachter & Muller, Ed., 3rd Ed., Ch. 1.
Autoxidation:Sites of Hydrogen Abstraction
R
RK / ACS ‘01 - 4 -
Representative Definition of Polyolefins
R
Polypropylene
Polyethylene
Of Course, It’s Really Not This Simple …..
Ø Catalyst / Co-CatalystØ Polymerization ProcessØ Finishing StepØ Method of StabilizationØ End-Use Application
RK / ACS ‘01 - 5 -
** Goal: Keep Molecular Architecture Intact **
"Fully Formulated Pellets"
V2V1 V3 V4 V5
* * *
* * * Reactor Flash Deactivate Drying Storage
"Dry Blended Fluff"
"Base Stabilized Pellets"
Possible Additive Addition Points =
General Polymerization Scenario
Value Chain
RK / ACS ‘01 - 6 -
Q. Why Do I Need to Use Stabilizers ?
l A. Stabilizers Used to Maintain the Polymer'sOriginal Strength, Flexibility and Toughness.
l Properties Need to be Maintained to Meet EndUse Applications that have Performance Targets
l Useful to Split Performance Targets (Economics)
ØLow End: Non-Durable GoodsØMid-Range: Use it for a WhileØHigh End: Durable Goods
Review: Stabilization of Polyolefins
RK / ACS ‘01 - 7 -
ROO • R •
+ ROOH
RO • + • OH
Oxygen
Cycle II Cycle I
Energy (UV Light, Heat)Catalyst Residues
Path of Degradation
R· Alkyl RadicalRO· Alkoxy RadicalHO· Hydroxy RadicalROO· Peroxy RadicalROOH Hydroperoxide
Scheme 1 - Autoxidation Cycle
Energy; Shear; Melt Processing; Catalyst Residues
Polymer
Polymer
Polymer
RK / ACS ‘01 - 8 -
Products of Melt Processing
l Alkyl Radicalsl Peroxy Radicals Affect Melt Processing and
l Alkoxy Radicals Long Term Thermal Stability
l Hydroxy Radicals
l Hydroperoxides Affect Melt Processing, LongTerm Thermal & UV Stability
l Alcoholsl Aldehydes Affect Taste & Odor
l Ketones
l "Polymer" “It’s Just Not the Same”
RK / ACS ‘01 - 9 -
Types of Thermal Stabilizer Chemistries
l Melt Processing StabilityPhosphitesHindered Phenols
HydroxylaminesLactonesTocopherols (Vit. E)
l Long-Term Thermal StabilityHindered PhenolsThiosynergist (& Phenol)
Hindered Amines
Traditional
New Stuff
Traditional
New Stuff
RK / ACS ‘01 - 10 -
Parallel Growth & Variety of StabilizersV
olum
e P
olym
er
Melt PhaseHP-LDPE
Solution PhaseSlurry Phase
zn-PPzn-PE
Gas Phasezn-PPzn-PE
AO: BHT; TNPP
UV: Absorbers
AO: HMW & Specialty Phenolics & Phosphites
UV: HMW Absorbers Hindered Amines (HALS)
1935 1955 1975 198519651945
As new polymersfilled more demanding
applications, new additivesneeded to be developed
RK / ACS ‘01 - 11 -
Mechanism of Activity:Phenolic Antioxidants
RK / ACS ‘01 - 12 -
C
O
OOH CH2CH2 CH2
4
C C
O
OH CH2CH2 O C18H37
OH
OH
OH
OH OHCH3H
Ca2+P O
O
CH2OH
OC2H5
2
OH
O
Representative Commercial Phenolic AO’s
N
N
N
O
O
O
OH
OH
OH
OH
S
SC8H17
C8H17
C
O
OH CH2
CH2
O (CH2)2-]2-S-
HO (CH2)2 C NH
O
2
OH
RK / ACS ‘01 - 13 -
Phenolic Free Radical Chemistry
+ RO · - ROH
OH
O
O
Species Attacked Predominantly
O
·
·
·O
·
RK / ACS ‘01 - 14 -
Phenolic Free Radical Chemistry
O
O+ RO · + RO ·
- ROH
OR
O
Disproportionation
O OH
+
Quinonemethide
·
RK / ACS ‘01 - 15 -
Phenolic AO (BHT) Oxidation ChemistryO·
+ RO· + RO·
- ROH - ROH
Coupling
OH
Quinonemethide
O
OHHO CH CH
Stilbenquinone (Yellow)
CH CH OO
+ 2 RO·- 2 ROH
RK / ACS ‘01 - 16 -
Gas Fade / Gas Yellowing Chemistry
+ 2 RO·
- 2 ROH
CH=CHHO HO O CH-CH O
+ ·NO2 HONO +
OH O·
·NO2
O
CH2
O
H3C
O
H3C NO2
H2O + R2NH2NO2
Base(e.g. R2N-H)
Alkalinity(e.g. R2N-H)
- HONO
Stilbenquinone
Quinonemethide
Coupling
·
Bis-Phenol
RK / ACS ‘01 - 17 -
Changing the Reactivity ofQuinone Methide Chemistry
O
COOR
OH
COOR
OCOOR
COORO
H• Transfer ROO•
x 2
ε = 116@ 420 nm
OCOOR
COORO
ε = 34,800@ 440 nm
Klemchuk and Horng: Poly. Degrad. Stab. 1991, 34, 333.
O
COOR
Re-Aromatization
RK / ACS ‘01 - 18 -
Vitamin E (α-tocopherol) Mechanisms{complicated version}
O
OH
CH3CH3
CH3
R CH3
O
O
CH2CH3
CH3
R CH3
O
OH
CH 3
CH 3
R CH3
O
H
O
OH
CH3
CH3
R CH3
O
H
O
OH
CH3
CH3
RCH3
CH2
O
OH
CH2
CH3
CH3
R CH3
Formyl-chroman-3-en (H)
Formyl-γ-Toc (G)
α-Toc
POO
(a)
(h)
(b)
QM
Toc benzyl
(I)+ α-Toc(α-Toc. )
O
OH
CH2CH3
CH3
R CH3
R
(p)
O
OH
CH3
CH3
R CH3
CH2OOH
O
OH
CH3
CH3
R CH3
CH2 OOH
(o)
(n)(m) O2
dimerize(i)
(j)
SPD (E)
(e) (d)+2 POO
+2 P (- >C=C<)
DHD (F)
TRI (A,B,C)
O
O
CH2CH3
CH3
R CH3
QM
O
OH
CH3CH3
CH3
R CH3
(k)
via Toc-benzyl
(l ,c)
(c)
(g)
α-Toc ·α-Toc
dimerize
O
OCH3
CH 3
R
CH 3
O
O
CH3
CH3
R
CH3
O
OCH 3
CH3
R
CH 3
O
OCH3
CH3
RCH3
O
O
CH3
CH3
R
CH3
·
O
OH
CH3
CH3
R CH3
CH 2OO ·
·
·
Al-Malaika, Ashley and Issenhuth
O
O
CH3CH3
CH3
R CH 3
·
O
OH
CH2CH3
CH3
R CH3
·R
·
IntramolecularH-abstraction
IntermolecularH-abstraction (+ PH)
·+ α-Toc +POO
RK / ACS ‘01 - 19 -
Mechanism of Activity:Phosphites
RK / ACS ‘01 - 20 -
Decomposition of Hydroperoxides
R-OOH
R-O• + •OH
R-O• + •OH
R-O• + OH + Ti(IV) -
R-OO• + H + Cu(I) +
Heat
Light
Ti(III)
Cu(II)
RK / ACS ‘01 - 21 -
Oxidation of Phosphites to Phosphates
P.P Klemchuk, “Antioxidants” in Ullmann’s Encyclopedia ofIndustrial Chemistry, VCH Publishers, Deerfeild Beach, FL, 91 (1985)
(RO)3 P + R'OOH (RO)3 P=O + R'OHPhosphite Phosphate P(III) P(V)
Relative rates of reaction for various R groups:alkyl > aryl > sterically hindered aryl
(RO)3 P=O + R'OOH No Reaction
RK / ACS ‘01 - 22 -
O P OC2H5
2
P
O
O
O CH2 CH2 N
3
P
O
O
2
P P OO
O
OO
O
O P
O
O
PP
O
O
O
O
O OH37C18C18H37
O ]3-PC9H19
O
P
OO
P
O
OO
POO
F
CH3H
Representative Commercial Phosphites
O P
3
RK / ACS ‘01 - 23 -
Hydrolysis of Phosphites
Relative rates of reaction for various R groups: alkyl > aryl > sterically hindered aryl
(RO)3 P + H2O (RO)2 P
O
H + ROH
(RO)2 P
O
H + H2O (RO) P
O
H
OH
+ ROH
(RO) P
O
H
OH
+ H2O HO P
O
H
OH
+ ROH
Dialkyl Phosphite
Alkyl Phosphorus Acid
Phosphorus Acid
RK / ACS ‘01 - 24 -
Mechanism of Activity:Diarylamines
RK / ACS ‘01 - 25 -
Chemistry of Secondary ArylaminesSynergy with Hindered Phenols
NH
R R+ ROO• + ROOH
OH
NH
R R+ +
Pospisil in Developments in Polymer Stabilization, G. Scott, Ed., Vol. 1, Ch.1.Varlamov et al.: Kinetics and Catalysis 1994, 35, 838.
N
R R
N
R R
O
RK / ACS ‘01 - 26 -
Mechanism of Activity:Thioethers/Thioesters
RK / ACS ‘01 - 27 -
S
O O
OR
OR
S
O O
OR
OR
O
RO
O
SOH
O
ORR
O
O
SOH
O
SS
O
OR
O O
OR
+ ROHROOH
+
heat
ROH +ROOH
x 2
Armstrong et al.: Eur. Poly. J. 1979, 15, 241.
+ H2O
Chemistry of ThiosynergistsReaction with Hydroperoxides
RK / ACS ‘01 - 28 -
Mechanism of Activity:Hydroxylamines
RK / ACS ‘01 - 29 -
R
R
N OH
Hydroxylamine
R
R
N O.H
Nitroxyl Radical
R
R
N+
O
Nitrone
R.
R
R
N OH
R
R
N+
O
Hydroxylamine Nitrone
+ ROOH + ROH + HOH
R
R
N+
O
Nitrone
R
R
N O.*R
*Nitroxyl Radical
H
R
R
N+
O
*Nitrone
*RR.
*R.
R.
Stabilization Chemistry of Hydroxylamines
RK / ACS ‘01 - 30 -
Mechanism of Activity:Benzofuranones (Lactones)
RK / ACS ‘01 - 31 -
R-H
Highly Stabilized Radical
RR
OO
OO
ROO
H
R = Carbon or Oxygen Centered Radical
OO
H OO CN
tBu-OO
OO
O
Ph
Ph
Ph
OO
O O
tBu-OO
OO
CN CN
O
Ph
Ph
Ph
O
Ph
Ph
Ph
OO
2
Stabilization Chemistry of Benzofuranones
Benzofuranone (Lactone)chemistry is a powerful radical
trap for R•, RO•, and ROO•
RK / ACS ‘01 - 32 -
Effective Temperatures for Stabilizers
Hindered Amine
Hindered Phenol
Thiosynergist (& Phenol)
PhosphiteHydroxylamine
Lactonealpha-tocopherol (E)
Temperature (°C)
0 50 100 150 200 250 300
Long Term Thermal Stability
Long Term Thermal Stability Melt Processing Stability
Long Term Thermal Stability (No Melt Processing Stability)
Melt Processing Stability
(No Melt Processing Stability)
(No Long Term Thermal Stability)
RK / ACS ‘01 - 33 -
Phenolic AOs react withoxygen centered radicals
Phenolic AOs react withfree radicals to yield inactiveproducts (ROH and H20)
Phosphites react withhydroperoxides to yieldinactive products (ROH)
Path of Degradation Path of Stabilization
Scheme 2 - Inhibited Autoxidation Cycle
ROO • R •
+ ROOH
RO • + • OH
OxygenCycle II Cycle I
Energy; Shear; Melt Processing; Catalyst Residues
PolymerCarbon Centered RadicalTraps Improve Efficiencyof Traditional Stabilizers
RK / ACS ‘01 - 34 -
Melt Processing / Long Term Stability
Heat History: Multiple Extrusion; Oven Aging;
No apparent change
Chain Enlargement Chain Breaking
Incr
easi
ng
D
ecre
asin
g
Molecular Weight
Dec
reas
ing
In
crea
sing
Melt FlowRate
RK / ACS ‘01 - 35 -
Impact of Various Stabilizers Classes in Polypropylene: PO161-95/CR13195Single Pass Extrusion Melt Flow Rate Data (Nominal = 4.5 dg/min)
5
7
9
11
13
15
0 500 1000 1500 2000Stabilizer Loading (ppm)
dg/m
in
I-3114 I-1330 I-168 FS-42 HP-136 CH-944 DSTDP
RK / ACS ‘01 - 36 -
0
15
30
45
60
250°C / 482°F 280°C / 536°F 310°C / 590°F
Melt Flow (230°C/2.16 kg)
0.1% AO-1 / P-1, 1st pass
0.1% AO-1 / P-1, 3rd pass0.1% AO-1 / P-1, 5th pass
0.06% AO-1/P-1 + 0.01 L-1, 1st pass
0.06% AO-1/P-1 + 0.01 L-1, 3rd pass0.06% AO-1/P-1 + 0.01 L-1, 5th pass
Spheripol Polypropylene Homopolymer; 0.075% Calcium Stearate; Extrusion: 20 mm single screw,L/D = 25; Multiple pass extrusion at different temperatures
Melt flow rate controlof binary blends of AO / P
is insufficient at high temps; Addition of 15% Lactonemakes a big difference !
Example #1Enhanced Free Radical Trapping Efficiency
RK / ACS ‘01 - 37 -
Example #2Inhibiting Gas Fading / Gas Yellowing Chemistry
“Gas Fading” is a discoloration phenomenon that is sometimesobserved during storage of fabricated articles….
Selected Variablesl Phenolic Antioxidants (Level and Type)l Phenolic Antioxidant / Phosphite Ratiol Surface Area (Pellet, Part or Fiber)l HALS (Alkalinity and Structure)l Resin (Catalyst Residues)l Spin Finish / Lubricantsl Acid Scavengers
RK / ACS ‘01 - 38 -
Phenol vs. Phenol Free StabilizationPhenol Based Stabilization (Phenol / Phosphite)
l AdvantagesØExcellent Melt Flow ControlØGood Initial ColorØLong Term Thermal Stability (< 150oC)ØRelatively Easy to Analyze
l Potential DisadvantagesØ Tendency to Discolor:¬ After Prolonged Melt Processing¬ Exposure to Oxides of Nitrogen¬ Exposure to Gamma Irradiation¬ Sensitive to Catalyst Residues
l Industry Standard (Entrenched ~ last 20 Years)
RK / ACS ‘01 - 39 -
“Triangles” of Polymer Discoloration
l Polymers stabilized with phenolic AO’s can besusceptible to discoloration if the system is “abused”
Thermally Induced
Discoloration
>Heat>Shear
Phenol Oxygen
“Gas Fade”Induced
Discoloration
SurfaceArea
PhenolNxOy
RK / ACS ‘01 - 40 -
Gas Fade / Gas Yellowing Chemistry
+ 2 RO·
- 2 ROH
CH=CHHO HO O CH-CH O
+ ·NO2 HONO +
OH O·
·NO2
O
CH2
O
H3C
O
H3C NO2
H2O + R2NH2NO2
2
Base(e.g. R2N-H)
Alkalinity(e.g. R2N-H)
- HONO
Stilbenquinone
Quinonemethide
Coupling
·
Bis-Phenol
RK / ACS ‘01 - 41 -
Effective Temperatures for Stabilizers
Hindered Amine
Hindered Phenol
Thiosynergist (& Phenol)
PhosphiteHydroxylamine
Lactonealpha-tocopherol (E)
Temperature (°C)
0 50 100 150 200 250 300
Long Term Thermal Stability
Long Term Thermal Stability Melt Processing Stability
Long Term Thermal Stability (No Melt Processing Stability)
Melt Processing Stability
(No Melt Processing Stability)
(No Long Term Thermal Stability)
* Traditional approach is to use an AO/P blend;
Yet the tendency to discolor was notacceptable for color sensitive applications
* Need new stabilizer system (w/o phenolic AO)
RK / ACS ‘01 - 42 -
Phenol vs. Phenol Free Stabilization
Phenol Free Systems (HALS / “Hyperactive” / Phosphite)
l AdvantagesØGood Melt Flow ControlØExcellent Initial Color and Color MaintenanceØExcellent Gas Fade ResistanceØExcellent Discoloration Resistance / Gamma RadiationØLong Term Thermal Stability ( < 120oC)
l Potential DisadvantagesØ “It’s Different” (vs. Phenol / Phosphite)ØDifferent Method of Analysis (vs. Phenol / Phosphite)
l Becoming Industry Standard (~ last 3- 5 Years)
RK / ACS ‘01 - 43 -
Example #2: Color StabilityGas Fade Resistance / Color Maintenance
Phosphite Hydroxylamine Lactone
N
OH
C18H37H37C18
Hindered AminesProvide UV / Long Term Thermal Stability
N
O
O
OO
n
N
N
N
N
NNN
N
H
H H
(CH2)6
n
Provide Melt Processing Stability
O P
3
OO
HCH3
CH3
RK / ACS ‘01 - 44 -
Graph 3A - YI Color Maintenance; Gas Fade Exposure @ 60°C; Knit Socks
0 5 10 15 20 25
1500 ppm AO-1/ P-1(AO Standard "A")
2000 ppm AO-2/ P-1(AO Standard "B")
1800 ppm HA-1/ P-1(no-AO "1st Generation")
1200 ppm HA-1/ NOH(no-AO "State of the Art")
1200 ppm HA-1/ NOH/ P-1(no-AO "New / Improved")
1200 ppm HA-2/ NOH/ P-1(no-AO "New / Improved")
1200 ppm HA-2/ L-1/ P-1(non-AO "New / Improved")
YI Color
4 Wks3 Wks2 Wks1 Wks0 Wks
Compared to phenol based systems, the phenol free systems offer excellent gas fade resistance….
RK / ACS ‘01 - 45 -
Types of UV Stabilizer Chemistries
l UV AbsorbersØHydroxyphenylbenzophenonesØHydroxyphenylbenzotriazolesØHydroxyphenyltriazines
l Excited State QuenchersØNickel based complexes
l Free Radical TrapsØHindered Amines
RK / ACS ‘01 - 46 -
Mechanism of Activity:UV Absorbers
RK / ACS ‘01 - 47 -
Representative UV Absorbers
NNN O
CH3
H
NNN
+O
CH3
H
light
Calvert and Pitts: Photochemistry, Wiley, New York, 1967, p.534.Heller and Blattmann: Pur. Appl. Chem. 1973, 36, 141.Kramer: Angew. Makromol. Chem. 1990, 183, 67.
O
OC8H17
OH
OC8H17
OOH
light
RK / ACS ‘01 - 48 -
UV Spectra
20 mg/L in EtOAc
0
0.5
1
1.5
250 275 300 325 350 375 400 425
λ (nm)
Abs
TINUVIN 234TINUVIN 328TINUVIN 326TINUVIN 327TINUVIN P
RK / ACS ‘01 - 49 -
Mechanism of Activity:Excited State Quenchers
RK / ACS ‘01 - 50 -
UV Energy Quenchers
* QuencherQuencher
+ UV Light
- Energy dissipated aslower frequency light
R-C-R
O*
R-C-R
O
(Some Chemistries Withdrawn due to Issues with Nickel in the Environment)
RK / ACS ‘01 - 51 -
Mechanism of Activity:Hindered Amines(as free radical scavengers)
RK / ACS ‘01 - 52 -
N
N
N
N
NNN
N
H
H H
(CH2)6
n
N
N N
N
N
N
NN
R R
H
R
R ]2-
NN CH3
C4H9
R =
N
O
O
OO
n
N
N
O
O
O
O
H
H
N
N
N
N
NN N
N
OH H
(CH2)6
n
N NC CO O
OO
(C H2)8 OC8H17H17C8O
Representative Hindered Amine Stabilizers
N
N
N
NN
NN
OO
R =
C4H9C4H9
NHN NH
N
R R
H R
NN
NN
N
NH
N N
N
N
NH
N
NH
N NH
NN
N
N
N
H
NN
N
n
RK / ACS ‘01 - 53 -
R* H
ROO·R=O + ROH
R·
[Oxid]
R
NO R
NO·
RR
NR*
[H+]
R
N+
XNOTE: An acidified hindered amine cannot easilyenter into the free radical scavenging cycle
R* = - H - CH3 - OR”
Hindered AminesUV Stabilization via Free Radical Scavenging
Ø N-H and N-R Hindered Amine Stabilizers (HAS) fit mostneeds regarding light stability, but can be alkaline (basic)
Ø N-OR type HAS enter the UV stabilization cycle quickly,and are not alkaline, in comparison to N-H & N-R type HAS
RK / ACS ‘01 - 54 -
Example #3Interactions with Other Co-Additives ( + , = , - )
HALS-3 (N-H)
HALS-3B (N-H)
HALS-5 (N-H)
HALS-2 (N-CH3)
HALS-2B (N-CH3)
HALS-1 (N-R)
HALS-4 (N-OR)
HALS-8 (N-OR)
0 2 4 6 8 10
pKa (as measured by titration of Conjugate Acid)
HALS-3 (N-H)
HALS-3B (N-H)
HALS-5 (N-H)
HALS-2 (N-CH3)
HALS-2B (N-CH3)
HALS-1 (N-R)
HALS-4 (N-OR)
HALS-8 (N-OR)
Dominant pKa's of Various Hindered Amines (Piperidinyl Group)
RK / ACS ‘01 - 55 -
Example #3Interactions with Other Co-Additives ( + , = , - )
Light Stability of Flame Retardant Fiber
Stabilized PP homopolymer; 15 dpf; Carbon Arc Exposure
0.05% HALS 0.05% HALS 0.50% HALS0
100
200
300
400
500
Hours to 50% Tenacity
HAS-1 HAS-5
No Flame Retardant 5% Brominated Flame Retardant
RK / ACS ‘01 - 56 -
ConclusionsImportance of New Stabilizer Chemistries
l Stabilizers should be used as tools to obtain thebest products with the most value
l Fine tuning accomplished with the physical aswell as the aesthetic and ancillary properties
Ø Better melt flow rate retention (MW; MWD)Ø Lower initial YI color and color maintenanceØ Inhibition of “gas fade” discolorationØ Enhanced additive compatibilityØ Reduced taste and odor (organoleptics)Ø Resistance to “ion” or “irradiation” induced oxidationØ Suppression of “gels” and other imperfections
RK / ACS ‘01 - 57 -
Impact of Performance vs. Concentration
Additive Loading
Per
form
ance
DiminishingReturns
“The Zone”
InsufficientAmount
Unstable PolymerWeaker Additives
Difficult ProcessingHigher Temperatures
Long Residence TimesHigh Shear
Stable PolymerPowerful Additives
Easy ProcessingLower Temperatures
Brief Residence TimesLess Shear
RK / ACS ‘01 - 58 -
Parallel Growth & Variety of Stabilizers
1935 1955 1975 1995
Vol
ume
Pol
ymer
Melt PhaseHP-LDPE
Solution PhaseSlurry Phase
zn-PPzn-PE
Gas Phasezn-PPzn-PE
All Process Typesm-PPm-PE
AO: BHT; TNPP
UV: Absorbers
AO: HMW & Specialty Phenolics & Phosphites
UV: HMW Absorbers Hindered Amines (HALS)
AO: “Hyperactives”
UV: “N-OR” HALS”
RK / ACS ‘01 - 59 -
Hans Zweifel - in Memorial (1939-2001)lDr. Hans Zweifel was a friend as well as
a scientific leader. He helped me tomaintain a balance between businesssupport vs. the science of additives
lHans was also:
Ø Lecturer for Polymer Additives atthe Swiss Federal Institute ofTechnology (ETH) Zürich.
Ø Head of New Product Managementat Ciba Specialty Chemicals
Ø Author of numerous publications &textbooks as well as editor of thenew Plastic Additives Handbook
Ø Excellent guide in our “off hours”adventures in Switzerland