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© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 20071
Recent Candle Stabilization
Developments at Ciba
Second World Candle Congress
June 2007
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 20072
Overview of Discussion Topics
• Stabilizer Additive Technology
• Historical Developments and Current Needs in the Candle Industry
• Soy Wax Candles Stabilization Study
• The Challenge of Fragrance Oil Stabilization—Some Preliminary
Observations
• Candle Stabilization Refinements—Ideas for Doing It Better
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 20073
Candle Stabilization
• Scented candles are complex chemical systems prone to
degradation when exposed to light and heat.
– Waxes: different types and blends for different candle applications
• Paraffin
• Microcrystalline
• Vegetable> Soy
> Palm
> Cottonseed
– Dyes
– Fragrances: typical functional groups include
• Aromatics and phenolics
• Aldehydes, ketones and esters
• Ethers and alcohols
• Olefins
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 20074
Degradation Mechanism—Free Radicals
• Free radicals—Atomic or molecular species with unpaired
electrons on an otherwise open shell configuration. These
unpaired electrons are usually highly reactive.
• Formation—By exposure of a substance to light energy or by
thermal cleavage of a chemical bond.
© Ciba Specialty Chemicals
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Robert Waldron, June 20075
Bond Cleavage Due to Light Absorption
• Absorption of light is the reaction of light with a material
(chromophore).
• Different functional groups and molecules absorb different
wavelengths (energies) of light.
• Single bonds correlate to very high energy light or shorter overall
wavelengths (less susceptible to cleavage).
• Double (π) bonds are responsible for light absorption (more
susceptible to cleavage).
• Polar groups also give rise to reactivity with light.
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 20076
Bond Cleavage Due to Light Absorption
© Ciba Specialty Chemicals
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Robert Waldron, June 20077
Auto-oxidation Process Induced by Light and Heat
R R* R. (alkyl radical)
R. ROO. (peroxy radical)
ROO. ROOH + R’. (hydroperoxide & alkyl radical)
ROOH RO. + .OH (alkoxy & hydroxyl radicals)
This is a chain-propagating process.
h
O2
R’H
h or
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 20078
Stabilizer Additives to Interrupt the Auto-oxidation Process
• UV Absorbers (UVA)
– Prevent damage caused by free radical formation when a substrate is exposed to light.
– Absorb UV light energy at specific wavelengths and dissipate this energy as heat.
• Hindered Amine Light Stabilizers (HALS)
– Scavenge oxygen-centered and alkyl free radicals.
– Cyclic mechanism with regeneration of active chemical species.
• Antioxidants (AO)
– Scavenge oxygen-centered free radicals.
• Phosphite Process Stabilizers
– Decompose hydroperoxides.
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 20079
Where Stabilizer Additives Act to Disrupt Degradation
R R* R. Counter with UVA
R. ROO. Counter with HALS
ROO. ROOH + R’. Counter with HALS, AO
ROOH RO. + .OH Counter with Phosphite
h
O2
R’H
h or
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200710
UVA Examples
• Benzophenones—Lower photo-permanence, coverage better in short wavelength
range
• Benzotriazoles—Higher photo-permanence, good coverage over broad
wavelength range
O OH
OR
NN
N
OH
R
R
© Ciba Specialty Chemicals
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Robert Waldron, June 200711
UVA Mechanism—Keto-Enol Tautomerism
© Ciba Specialty Chemicals
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Robert Waldron, June 200712
Hindered Amine Light Stabilizers
Substituted Tetramethyl Piperidines
NR1
R2
R1 = “Head Group” R2 = “Backbone”
Activity
Basicity
Compatibility
Solubility/compatibility
Equivalent Wt.
Basicity
© Ciba Specialty Chemicals
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Robert Waldron, June 200713
HALS Examples
• Amine Type—high basicity, pKb= 5.1-5.5
• Amino-ether Type—low basicity, pKb= 9.6, does not interact with acids,
metals
NH3C
H
O.CO.(CH2)8.CO.O
N
H
CH3
NC8H
17.O
H
O.CO.(CH2)8.CO.O
N
H
O.C8H
17
© Ciba Specialty Chemicals
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Robert Waldron, June 200714
HALS Proposed Mechanism—Cyclic Regeneration
N
A
XE C
RH
N
O
X
N
O
X
E
R
E C R
O
H
O
E C R
O
E C R
OH
H
A = H, alkyl, alkoxy, carbonyl
ROO.
Key initiating
step
© Ciba Specialty Chemicals
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Robert Waldron, June 200715
Use of Stabilizer Additives in Candles
• Conventional Technology—adequate for candles made with highly-refined
paraffin wax and with minimal fragrance component
– Benzophenone and/or benzotriazole UVAs (typically in solid form)
– No free radical scavenging
• Advanced Technology—prompted by the destabilizing impact of increased
fragrance oil loadings
– Synergistic blend of benzotriazole UVA and non-interacting HALS in liquid form
– UV absorption and free radical scavenging
• Latest Developments
– Increased cost and decreased availability of paraffin wax
– Widespread substitution of vegetable waxes for petroleum-based waxes
How well will stabilizer packages proven in paraffin wax work in vegetable wax?
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200716
Soy Wax Candles Stabilization Study
• Wax—NatureWax™ Container Candle Blend C-3 from Cargill
– Hydrogenated vegetable glycerides
• Mettler dropping point = 125 - 130 F
• Iodine value = 50 - 56
• Three representative candle formulations:
– Vanilla fragrance with no dye,
– Hydrangea fragrance with blue dye,
– Cinnamon fragrance with red dye.
• Three light stabilizer (LS) options:
– No light stabilizer,
– 0.3% w/w of conventional LS package (1:1 blend of benzophenone and
benzotriazole UVAs)
– 0.3% w/w of advanced LS package (1:1 blend of benzotriazole UVA and non-
interacting HALS)
© Ciba Specialty Chemicals
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Robert Waldron, June 200717
Soy Wax Candles Stabilization Study—Additives Tested
• BP1 (solid benzophenone UVA)
• BZT1 (solid benzotriazole UVA)
© Ciba Specialty Chemicals
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Robert Waldron, June 200718
Soy Wax Candles Stabilization Study—Additives Tested
• BZT2 (liquid benzotriazole UVA)
• HALS1 (liquid, non-interacting hindered amine light stabilizer)
© Ciba Specialty Chemicals
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Robert Waldron, June 200719
Accelerated Light Exposure Tests
• Pre-exposure and post-exposure color measurements of all candle
samples were made with an X-Rite® SP 64 spectrophotometer
(D65 illuminant, 10 degree observer).
• Control samples were stored in the dark inside sealed plastic bags.
• Test samples were placed in a light box:
– Open upper level equipped with 3 double banks of cool-white
fluorescent tubes (34 Watts each)
– Enclosed, ventilated lower level equipped with 3 double banks of
―black light‖ (UV) tubes (40 Watts each)
© Ciba Specialty Chemicals
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Robert Waldron, June 200720
Equipment for Accelerated Light Stability Testing
© Ciba Specialty Chemicals
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Robert Waldron, June 200721
Quantifying Color Stability
• CIELAB color scale system
– L* signifies lightness/darkness
– a* signifies red/green color axis
– b* signifies yellow/blue color axis
– ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2
© Ciba Specialty Chemicals
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Robert Waldron, June 200722
Soy Wax Candles Light Stability Test—3 Weeks UV Light Exposure
No LS
0.3% BTZ2/HALS1
0.3% BP1/BTZ1
Vanilla, no dye
Hydrangea, blue dye
Cinnamon, red dye
0
5
10
15
20
25
30
35
40
delta E*
© Ciba Specialty Chemicals
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Robert Waldron, June 200723
Soy Wax Candles Light Stability Test—5 Weeks Fluorescent Light Exposure
No LS
0.3% BTZ2/HALS1
0.3% BP1/BTZ1
Vanilla, no dye
Hydrangea, blue dye
Cinnamon, red dye
0
5
10
15
20
25
30
35
40
delta E*
© Ciba Specialty Chemicals
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Robert Waldron, June 200724
Fragrance Oil Impact
• Impact of 330 hours UV light exposure on paraffin wax candle with blue dye in the
absence of fragrance, no LS—ΔE* = 3
© Ciba Specialty Chemicals
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Robert Waldron, June 200725
Fragrance Oil Impact
• Impact of 330 hours UV light exposure on paraffin wax candle with blue dye and
fragrance oil, no LS—ΔE* = 29
© Ciba Specialty Chemicals
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Robert Waldron, June 200726
Countering Fragrance Oil Impact with LS/AO
• Much reduced color change after 330 hours UV light exposure when optimum
LS/AO package is used to offset the impact of the fragrance oil—ΔE* = 4
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200727
Examples of Fragrances
O
Jasmone
OH
OH
OMe
Vanillin
O
Camphor
© Ciba Specialty Chemicals
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Robert Waldron, June 200728
Typical Fragrance Functional Groups
Aromatics
R H
O
Aldehydes
R R'
O
Ketones
RO
H
Alcohols
Olefins
RO
R'
Ethers
R O
O
R'
Esters
OH
Phenolics
© Ciba Specialty Chemicals
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Robert Waldron, June 200729
Stabilization of Neat Fragrance Oil
• Concept: ―Pre-stabilization‖ of neat fragrance oil.
– May inhibit dye/fragrance degradation reactions under elevated
temperature processing conditions before they progress to the
point of causing major candle color stability problems.
• Preliminary Lab Work in 2006
– Stability criterion—color stability under elevated temperature
exposure conditions (100 C)
– Additives—2 HALS, 2 hindered-phenol antioxidants, 2
phosphites (each evaluated separately)
– Fragrance oils—4 products currently used in the candle
industry
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200730
Stabilization of Neat Fragrance Oil
• Observations/conclusions:
– The most effective stabilizer additive varies from one fragrance oil to
another.
• No universally-applicable ―magic bullet‖ was identified.
– No systematic analysis of stabilizer additive performance is possible
absent detailed knowledge of the composition/chemistry of each
specific fragrance oil.
– Color stability may not be the best criterion for use in fragrance oil
stabilization studies.
• Relative fragrance intensity as measured by GC-headspace analyses of
sealed samples stored at elevated temperature is also of interest.
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200731
Candle Stabilization Refinements
• Stabilizer Additive Handling Characteristics
– Advanced technology liquid blend of benzotriazole UVA and non-
interacting HALS versus conventional solid UVAs
• Advantages
> No dust generation
> Less likely to be exuded from candles
• Potential disadvantage—viscosity
> Technician may find it less convenient to weigh out viscous liquid than powdered solid
> Residual material may be difficult to fully recover from containers (waste)
– Refinement—reduce the viscosity of the liquid light stabilizer blend by
cutting with Isopar solvent
• Blending of 2 parts solvent with 8 parts light stabilizer gives an order-of-
magnitude viscosity reduction
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200732
Candle Stabilization Refinements
• Stabilizer Additive Handling Characteristics, continued
– Some characteristics of Isopar solvents (ExxonMobil Chemical Co.) which
make them suitable for use in candles
• Isoparaffinic hydrocarbon fluid
• High purity, low odor
• Low photochemical reactivity
• Low order of toxicity
• Low potential for skin irritation
• Meet the requirements of many European and U.S. food-contact
directives and regulations
© Ciba Specialty Chemicals
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Robert Waldron, June 200733
Candle Stabilization Refinements
• Stabilizer Additive Handling Characteristics, continued
– Experimental viscosity measurement data for blends of Isopar M and
Isopar V with Tinuvin® 5060
1
10
100
1000
10000
100000
405060708090100
Weight Percent Tinuvin 5060
Vis
co
sit
y, cP
@ 2
0 r
pm
, 20 C
Isopar M
Isopar V
© Ciba Specialty Chemicals
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Robert Waldron, June 200734
Candle Stabilization Refinements
• Yellow transformation products of hindered-phenol antioxidants
– ―Over-oxidation‖ of phenolic AOs:
© Ciba Specialty Chemicals
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Robert Waldron, June 200735
Candle Stabilization Refinements
• Preventing ―over-oxidation‖ of phenolic AOs
– Some phenolic AOs may be more susceptible to forming yellow color
bodies than others.
• The formation of chromophores depends on the structure of the phenol
involved.
• Consider substitution if a yellowing problem occurs with a given structure.
– Use a phosphite process stabilizer in conjuction with the phenolic AO.
• The phosphite functions in a sacrificial mode, alleviating the load on the
phenolic AO, thereby preventing its ―over-oxidation.‖
© Ciba Specialty Chemicals
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Robert Waldron, June 200736
Candle Stabilization Refinements
• Yellow transformation products of hindered-phenol antioxidants
– Gas Fading—Reaction with NOx
© Ciba Specialty Chemicals
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Robert Waldron, June 200737
Candle Stabilization Refinements
• Gas Fading Characteristics
– Can occur at very low NOx concentrations (ppm) in the atmosphere.
– Discoloration (yellowing or pinking) increases with exposure time and
hindered-phenol AO concentration.
– Normally occurs in the absence of light. Exposure to UV light tends
to fade the color.
• Gas Fading Prevention
– Minimize NOx exposure during processing, storage, and
transportation.
– If the hindered phenol AO is used in combination with a HALS, use
low basicity, non-interacting HALS type. (High pH additives favor
color formation.)
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200738
Conclusions
• Soy Wax—The same synergistic combination of benzotriazole
UVA and non-interacting HALS previously proven effective in
petroleum-based candles provides superior color stability in soy-
based candles as well.
• Fragrance Oil—Further development of strategies to stabilize neat
fragrance oils will require more intimate collaboration between
fragrance houses and stabilizer additive manufacturers.
• Optimization—Judicious use of hindered-phenol antioxidants,
especially in combination with a phosphite process stabilizer, can
make a critical difference in candles with especially problematic
dye/fragrance combinations.
© Ciba Specialty Chemicals
Business Line Coatings
Robert Waldron, June 200739
Acknowledgements
• Thanks are due to the following organizations for supplying raw
materials for use in candle stabilization studies at Ciba:
– Arylessence, Inc.
– Candle-Lite, Inc.
– Cargill, Inc.
– ExxonMobil Chemical Co.
– Hanna’s Candle Co.
– Manheimer Fragrances
– Old Williamsburgh Candle
– The International Group, Inc.
– Yankee Candle Co.
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