recent candle stabilization developments at...

© Ciba Specialty Chemicals

Business Line Coatings

Robert Waldron, June 20071

Recent Candle Stabilization

Developments at Ciba

Second World Candle Congress

June 2007




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




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




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.




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.




Bond Cleavage Due to Light Absorption




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




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.




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




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




UVA Mechanism—Keto-Enol Tautomerism




Hindered Amine Light Stabilizers

Substituted Tetramethyl Piperidines

NR1

R2

R1 = “Head Group” R2 = “Backbone”

Activity

Basicity

Compatibility

Solubility/compatibility

Equivalent Wt.

Basicity




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




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




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?




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)




Soy Wax Candles Stabilization Study—Additives Tested

• BP1 (solid benzophenone UVA)

• BZT1 (solid benzotriazole UVA)




Soy Wax Candles Stabilization Study—Additives Tested

• BZT2 (liquid benzotriazole UVA)

• HALS1 (liquid, non-interacting hindered amine light stabilizer)




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)




Equipment for Accelerated Light Stability Testing




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




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*




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*




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




Fragrance Oil Impact

• Impact of 330 hours UV light exposure on paraffin wax candle with blue dye and

fragrance oil, no LS—ΔE* = 29




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




Examples of Fragrances

O

Jasmone

OH

OH

OMe

Vanillin

O

Camphor




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




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




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.




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





• 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





• 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





• Yellow transformation products of hindered-phenol antioxidants

– ―Over-oxidation‖ of phenolic AOs:





• 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.‖





• Yellow transformation products of hindered-phenol antioxidants

– Gas Fading—Reaction with NOx





• 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.)




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.




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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strict liability, tort or contract arising in connection with the product(s). Buyer’s sole remedy and Ciba Specialty Chemicals’ sole liability for any claims

shall be Buyer’s purchase price. Data and results are based on controlled or lab work and must be confirmed by Buyer by testing for its intended

conditions of use. The product(s) has not been tested for, and is therefore not recommended for, uses for which prolonged contact with mucous

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