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Chapter 35
A Diester to Protect Hair
from Color Fade and Sun
Damage
Timothy Gao, PhD, Jung-Mei Tien, Abhijit Bidaye,
Scott Cardinali and Jena Kinney
Croda Inc., Edison, N.J., USA
Key WorDS: diester, colorfade, tryptophan degradation, hair fiber
integrity, broad-spectrum UV filter
ABSTrACT: A new broad-spectrum UV filter to protect hair from
color fading and integrity damage, quaternium-95 (and)
propanediol, has been developed for rinse-off formulations.
Shampoos and conditioners containing this material
protected dyed hair against surface tryptophan degradation
and tensile strength reduction.
Like skin, hair is susceptible to damage from exposure to the sun.
This damage affects its aesthetics and mechanical and physical
properties, resulting in dull, flat hair. Research indicates that both
UVA and UVB radiation are responsible for this damage. Hoting, 1
for example, studied hair tresses dyed red by exposing them to UVA
and UVB radiation, finding that the tresses underwent more fading
after UVA irradiation. Artificial hair color based on pyrazole intermediates
also has shown significant fading after shampoo washing
and UV exposure. 2 Hoting thus concluded that exposure to UVA
radiation resulted in a significant and perceivable change in the dyed
red hair color. According to his research, the red pigment introduced
into the hair fiber by the dyeing process acts as a photoreceptor,
absorbing photons and photochemically degrading after UVA and
visible light irradiation.

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Chapter 35 Gao et al.
The effects of UVB radiation on hair also can be severe, resulting
in the breakdown of disulfide bonds both inside the hair fiber and
on the surface of the cuticle. 3 Such disruptions to the disulfide linkages
of the hair fiber can have a major impact on hair’s mechanical
properties, resulting in the loss of tensile strength and an increase in
porosity and irregularities on the hair surface.
To protect hair from UV damage, UV filters deposited on the
hair surface absorb incident UV light. As noted, since both UVA
and UVB radiation cause severe and perceivable damage, broadspectrum
UV absorbers provide the best protection from fading and
sun damage. In addition to broad spectrum coverage, deposition and
absorption onto the hair surface are crucial factors to consider when
designing materials for rinse-off systems.
Figure 35.1. absorption spectrum of the diester solution
In the present chapter, the authors introduce a quaternized
diester a designed to provide broad-spectrum protection to hair in
rinse-off systems. An absorption spectrum of the diester solution
(20.0 mg/L active in SDA-40), shown in Figure 35.1, ranges from
the UVB region (280–320 nm) to the UVA region (320–400 nm).
The absorption peak, located at 310 nm, falls within the UVA region,
thus researchers concluded the material should provide efficacious
a Chromaveil (INCI: Quaternium-95 (and) propanediol) is a product of Croda Inc.

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A Diester to Protect Hair from Color Fade and Sun Damage
color protection for dyed hair. Additional studies (data not shown)
examined the material’s stability after five days of UV exposure,
showing no change in absorbance or net weight for the diester.
Thus, further studies were warranted to examine its ability
to protect hair fibers from cuticle damage and reduced tensile
strength resulting from degradation of tryptophan and proteins on
the hair surface and inside the hair fiber. The ability of the diester
to protect hair from colorfade in the presence of UV radiation also
was examined.
Materials and Methods
Various protocols were used to evaluate the diester’s ability to
protect hair fibers from UV damage. Bleached European brown
hair tresses were dyed with either a commercially available medium
brown hair color or medium auburn color for 30 min following the
instructions provided in color kits. For testing of UVB damage,
virgin dark brown hair was used. Some tresses were treated with
control and diester-containing shampoos and conditioners (see Formulas
1 and 2). A subset of treated tresses were then irradiated b for
3 hr on each side, totaling 6 hr-equivalent to one day of UV exposure
4 -with UV radiation (200–400 nm) at 50 W/m 1 using a quartz
inner filter and type “s” borosilicate outer filter. At the start of the
study and at intervals equivalent to every five days of UV exposuree.g.,
after every 30 hrs-tresses were treated again with control and
diester-containing shampoos and conditioners. Irradiated tresses
were exposed to the total equivalent of 15 days of UV exposure. Test
conditions were maintained at 40°C and 65% relative humidity.
Different types of tresses were compared, including those that
were dyed and not exposed to treatment or UV exposure; dyed and
treated with the control shampoos and conditioners and exposed
to UV; and dyed and treated with shampoos and conditioners containing
the diester and exposed to UV. Comparative color loss was
determined both objectively and subjectively. The total color loss
(∆E) was calculated by assessing the changes in L*, a*, b* readings
b the atlas Ci300+ Xenon Weather-Ometer is a product of atlas Material testing Solutions,
International hair Importers

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Chapter 35 Gao et al.
on the treated tresses using a spectrocolorimeter c . The equation
used to calculate the total color loss was:
∆E = [(∆L) 2 + (∆a) 2 + (∆b) 2 ] 1/2
Formula 1. Shampoo test formulations
Ingredient Control Diester Shampoo
Sodium laureth sulfate 35.00% w/w 35.00% w/w
Cocamidopropyl betaine 10.00 10.00
Quaternium-95 (and) propanediol, 75%
active (ChromaVeil, Croda) --- 2.00
peG-150 pentaerythrityl tetrastearate
(and) peG-6 caprylic/capric glycerides
(and) water (aqua) --- 2.80
Water (aqua) 55.00 50.20
100.00 100.00
Formula 2. Conditioner test formulations
Ingredient Control Diester
Conditioner Conditioner
Quaternium-91 (and) cetrimonium
methosulfate (and) cetearyl alcohol 2.14% w/w 2.14% w/w
Cetearyl alcohol 3.86 3.86
Quaternium-95 (and) propanediol, 75% active
(ChromaVeil, Croda) --- 2.00
phenoxyethanol (and) methylparaben
(and) ethylparaben (and) butylparaben
(and) propylparaben (and)
isobutylparaben (phenonip, Clariant) 1.00 1.00
Water (aqua) 93.00 91.00
100.00 100.00
The changes in hair color indexes were calculated using the
respective values after the shampoo and conditioner treatments
and before UV exposure; and after the equivalent of 15 days of UV
c LabScan Xe Spectrocolorimeter is a product of hunterLab.

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A Diester to Protect Hair from Color Fade and Sun Damage
exposure. The results of the instrumental evaluations were confirmed
via subjective testing. The swatches were photographed and compared
to dyed but untreated swatches, which represent the initial dye
color, to allow for visual comparisons. Panelists were also asked to
rate the color protection effects in simple comparisons of the control
and the diester swatches to the untreated control.
To determine the amount of damage on the hair fiber due to the
UVB irradiation, several parameters of the hair fiber were measured.
As noted, UV exposure to hair can break down the disulfide bonds
in the hair fiber. Tryptophan is a key amino acid found on the hair
surface and it decomposes under UVB irradiation. 2
Surface tryptophan degradation is thus an indicator of damage
to the disulfide bonds and it can be quantified through comparative
fluorescence intensities of hair tresses using a spectrofluorometer d .
The excitation wavelength was set at 295 nm and the tryptophan
emission intensity was measured at 340 nm. The emission intensity
was assumed to be directly proportional to the surface tryptophan
concentration.
Using surface tryptophan intensities of the hair sample before
UV exposure as the baseline, the tryptophan protection factors of
hair samples treated with diester shampoo or the control shampoo
after UV exposure can be calculated using the equation:
F (Tr) = [I f / I o ] X 100%
In this equation, F(Tr) is the tryptophan protection factor,
calculated as a percentage; I f is the surface tryptophan fluorescence
intensity of the hair sample after UV exposure; and I o is the surface
tryptophan fluorescence intensity of the same hair sample before
UV exposure.
UVB rays not only decompose the surface tryptophan but also
penetrate the hair cuticle and cause damage inside the cortex. This
damage affects hair’s mechanical properties and can be measured in
terms of its tensile strength (stress-to-break). Using a tensile tester e ,
the tensile strength of single fibers from the treated tresses was
measured before and after UV exposure.
d Spex FluoroLog-3 is a instrument manufactured by horiba Jobin Yvon.
e Miniature tensile tester (Mtt) 670 is a product of Dia-Stron Ltd.

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Chapter 35 Gao et al.
To test the ability of the diester to protect hair fibers in rinse-off
systems, a shampoo and conditioner were formulated with and without
the diester (see Formulas 1 and 2).
UV Protection with Diester
UVA protection in shampoo: Auburn-colored tresses were treated
with the control and diester shampoo and exposed to 15 equivalent
days of UV exposure (see Figure 35.2). The treated tresses were
visually compared to one another and to a dyed tress that was not
exposed to UV irradiation (Figure 35.2a). The tresses treated with
the control shampoo (Figure 35.2b-c) lost a significant amount of
color while the hair tresses washed with the shampoo containing the
diester (Figure 35.2d-e) showed less color fade. The total color loss
(∆E) of the tresses treated with the shampoos was also assessed after
15 days of UV exposure. Tresses that demonstrated better color protection
had a smaller ∆E. The quantitative color loss data confirms
what the visual assessment illustrates—that the shampoo containing
the diester had a significantly smaller ∆E, and the diester-treated
tress maintained more color. The diester thus demonstrates color
protection with a ∆E of 10.5, compared to the control shampoo
with a ∆E of 12.4, a difference of almost 2 units (see Figure 35.3).
To confirm the correlation between visual inspection of images,
color index measurement and consumer perception, 17 panelists
selected the tresses they thought had the most and least change in
color after tresses were exposed to 15 days of UV. Subjective evaluation
results indicated that 100% of the panelists perceived that
the diester shampoo gave superior color protection on the medium
auburn treated hair (data not shown).
A similar study was performed with the shampoos on hair dyed
with medium brown color. The tresses shown in Figure 35.4 were
treated with the control and diester shampoo. Hair tresses washed
with the diester shampoo (Figure 35.4e-f) showed less color fade
than the control shampoo (Figure 35.4c-d). The left two tresses
were dyed and not exposed to UV (Figure 35.4a-b), to serve as a
reference.
Figure 35.5 shows the quantitative ∆E total color changes of
hair tresses colored medium brown that were treated with both
shampoos and exposed to 15 days of UV exposure. Hair tresses

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A Diester to Protect Hair from Color Fade and Sun Damage
treated with the diester shampoo showed less total color change,
almost 3 units, than the control shampoo, indicating the diester
shampoo provided better color protection.
Figure 35.2. effects of the diester vs. control shampoo on medium auburn hair
Figure 35.3. total color changes of medium auburn-colored hair treated with different
shampoos after 15 days of UV exposure

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Chapter 35 Gao et al.
Again, the panel evaluation demonstrated a strong correlation
between the visual results and the instrumental results. On medium
brown hair, 94.1% of panelists chose the tresses treated with the
diester shampoo as having retained the most color.
Figure 35.4. effects of the diester vs. control shampoo on medium brown hair
Figure 35.5. total color change of medium brown-colored hair treated with different
shampoos after 15 days of UV exposure

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A Diester to Protect Hair from Color Fade and Sun Damage
UVA protection from a conditioner: Another set of auburn-colored
tresses was treated with a rinse-off conditioner containing the
diester (Formula 2) and the same conditioner without the UV filter
to serve as a control. Figure 35.6 shows that hair tresses washed
with the diester conditioner (Figure 35.6d-e) showed less colorfade
on auburn-colored hair than the control conditioner (Figure 35.6bc).
The left tress was dyed but not exposed to UV radiation (Figure
35.6a) to serve as a reference.
Figure 35.6. effects of the diester vs. control conditioner for medium auburn color
Although not as definitive as the shampoo studies, 64.7% of the
panelists preferred the diester conditioner on auburn-colored hair.
UVB protection from a shampoo: To assess for surface tryptophan
damage, the surface fluorescence intensities of virgin brown tresses
treated with either the control or diester shampoo were determined
after 15 equivalent days of UV irradiation (see Figure 35.7) and
compared to the fluorescence intensities of the hair before UV
exposure.
The shampoo containing the diester showed 97.48% tryptophan
protection after the 15 equivalent days of exposure, while the control

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Chapter 35 Gao et al.
shampoo showed 91.42% tryptophan protection. The addition of the
diester to the shampoo improved the protection against degradation
of amino acids in the hair fiber. The tryptophan degradation testing
was not performed on the conditioner series; however, researchers
anticipate similar results would be seen.
Figure 35.7. Change in tryptophan intensity after UV exposure and treatment with diester
shampoo
Testing UVB Protection with Tensile Strength
Fibers showing a decrease in stress-to-break forces after UV exposure
have undergone a loss in mechanical strength primarily due to
the breaking of disulfide bonds inside the hair cortex. A comparison
of the tensile strength of virgin brown hair treated with the diester
shampoo was made to hair similarly treated with the control rinseoff
product. Note that disulfide bonds inside the cortex have been
broken in the tresses treated with the control shampoo, while tresses
treated with the diester have no disulfide bond breakage (see Figure
35.8). The diester shampoo protected the hair from UVB damage
and preserved the hair’s natural strength.
Using the same methodology, virgin brown hair tresses were
treated with the control and diester conditioner, respectively, for
tensile strength measurements. The diester conditioner also provided
protection against damage to the fiber (see Figure 35.9).

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A Diester to Protect Hair from Color Fade and Sun Damage
Figure 35.8. Change in tensile strength after UV exposure and treatment with shampoos
Figure 35.9. Change in tensile strength after UV exposure and treatment with conditioners
Conclusions
While protection of hair from the sun is not a new concept, technology
continues to improve to offer consumers better protection as
part of their daily regimen. As shown, the diester is substantive to

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Chapter 35 Gao et al.
the hair and offers broad-spectrum protection in rinse-off systems.
Although the diester has not yet been tested in leave-in systems, the
authors expect the diester to provide good hair protection.
The addition of the diester in wash-off systems provides protection
against UVA-induced colorfade as well as protection from
UVB-induced disulfide bond breakage that manifests as a loss of
hair strength. The diester also protects from the degradation of
amino acids on the hair surface. This broad-spectrum protection
gives consumers the freedom to enjoy the sun without the concern
for hair damage. In addition, it offers protection for artificial hair
color and fiber integrity.
Published May 2009 Cosmetics & Toiletries magazine
references
1. E Hoting, Sunlight-induced modifications in bleached, permed, or dyed human hair, J Soc
Cosmet Chem, 48 79–91 (Mar/Apr 1997)
2. B Locke and J Jachowicz, Fading of artificial hair color and its prevention by photofilters,
J Cosmet Sci, 56 407–425 (2005)
3. T Gao and A Bedell, UV damage on natural gray hair and its photoprotection, J Soc
Cosmet Chem, 52 103–118 (Mar/Apr 2001)
4. M Jeanmougin and J Civatte, Dosimetrtrie du rayonnement UV solaire, Ann Dermatol
Venerol, 114 671–676 (1987)