Although lipids is below 5% (w/w) of the
hair, the lipids play an important role in keeping hair healthy, such as shining
and texture. The goal of this study is to elucidate the effect of lipids in
hair on exposure to surfactant and to clarify how much their loss impacts
hair strength. The experimental approach was to obtain physical properties of
the hair lost lipids or the hair conserved lipids; dual modification was
treated to hair in washing. The results show hair in which lipids are conserved
over time by washing, maintains their physical properties. It was confirmed
that hair with lost lipids decreases its strength in structure and elasticity.
Keywords: Hair, Structure, Lipid, DSC
INTRODUCTION
According to
the mechanism of lipid loss in our previous study, lipids are clearly
classified into two groups [1]. The first group consists of highly hydrophobic
lipids that are removed from the inside of hair by direct emulsification. The
second group, on the other hand, comprises relatively less hydrophobic lipids
that diffuse to the outermost layer of hair and are lost by a roll-up process.
The lipids in the first group are prevented by filling inside hair with
amine-coupling materials in carbodiimide chemistry [2] named internal
modification, and the lipids in the second group are prevented by coating polar
film, named surface modification. Gas chromatography/mass spectrometry (GC/MS)
study proved that the dual modification consists of internal and surface
modification perfectively prevents lipid loss against surfactant in wash.
This study
handles the change of physical property upon alteration of lipid in hair. The
lipid decomposition studies have led to the development of a simple method for
the extraction and analysis of lipids from tissues. The entire procedure can be
carried out in approximately a few days; it is efficient, reproducible and free
from deleterious manipulations. Lipid-based residue reports require correct
understanding of both the total amount of lipid decomposition and their role.
Today, the first demand is well-established by the study in detail [3-5] but
the second is, however, more questionable. Numerous studies have shown that
very complicated methods currently used in their research provide lipid
extraction under complicated process. The lab considered it to be advantageous
if the chloroform solvent is used in multiple times. Further, exploration of
the roles of the lipid in hair may provide clues for understanding the
mechanism of hair conditioning.
In this paper,
we report the change of physical property for the hair from human hair
conserved lipids because of dual mechanisms, greatly facilitates the
measurement of increased amounts of labile lipid components, such as fatty
acids, squalene, cholesterol and wax esters. These experiments use differential
scanning calorimetry (DSC), bending tester, tensile strength tester and GC/MS
to determine physical property by conserved lipids. The results from these
evaluations have been confirmed based on determining the quantities of lipids.
We used hair as a representative model of tissue and systematically
demonstrated how lipids in tissues are lost by surfactant use. It has been
demonstrated that the mechanism by which physical properties are enhanced from
lipids depends on the type of shampoo.
MATERIALS AND METHODS
DSC
Dry-DSC
experiments were performed with a DSC-400 (Perkin Elmer, US). Each sample was
subjected to heating and cooling treatments at a scanning rate of 10°C/min
under
Pendulum test
The
vibrational mechanical tests based on pendulum motion were performed with a
home-built system analyzer (Hanagiyeon, Korea). Test specimens were taken from
the middle section of the start point bar and were vibrated up to a side height
position with a support vibration of 30 mm. The length of hair tress was 150
mm. Measurements were conducted over a temperature range of 25°C with 30 cycles
under a constant frequency of 75.0Hz.
Tensile strength
Experiments
were performed by preparing and testing the properties of 20 individual hair
fibers per each sample. The properties were evaluated to convenient method
using a Diastron (UK) testing machine model MTT175.
Bending rigidity
The bending
rigidity of hairs was measured with KES‐FB
instruments (Kato Tech, Japan). Testing samples were cut into 30 × 50 mm2
in size.
Analysis of lipid concentrations
Hair samples
were analyzed on an Agilent (7890A GC System, US) gas chromatograph coupled to
an Agilent detector (5975C MSD System, US). The mass spectrometer was operated
in the electron impact mode at ionization voltage of 70 eV. Mass spectra in the
full scan mode were recorded in the mass range of 50-500 amu. Selected ion
monitoring (SIM) was carried out by monitoring m/z 228 for myristic acid, m/z
256 for palmitic acid, m/z 69 for oleic acid, m/z 284 for stearic acid, m/z 85
for docosane, m/z 85 for tetracosane, m/z 74 for 18-MEA, m/z 121 for squalene, m/z
386 for cholesterol and m/z 257 for myristyl palmitate, palmityl palmitate and
stearyl palmitate. Peak identification was based on comparison with standards
for retention times and mass spectra fragmentation. M/z 230 for o-Terphenyl as
the internal standard was added to the lipid solution. 100 mg of each reference
substance was dissolved in 10 mL of the 2:1 mixture of chloroform and methanol.
The concentration of all mixture of reference substances was 1000 mg/L. 10μL of
the internal standard, o-Terphenyl (2000 mg/L) was added to 1 mL of the
extractable lipids.
Hair shampooing
We used
commercial shampoo, named as P and C. The washing section involved rubbing the
hair by hand. To wash hair with SLES, a 1 g hair swatch was pre-wetted with 1
mL of water and then covered evenly with 0.1 mL of the surfactant. The
surfactant was lathered well by hand for 15 s. Subsequently, the hair was
gently rubbed for the shampoo ingredients to be absorbed into each hair shaft
for 45 s and the hair swatch was rinsed with water for 2 min. The tap water
used in the foaming for washing and rinsing flowed at a speed of 40 mL/s from a
faucet. After removing excess water, the hair swatch was gently dried with a
paper towel. These steps, with exception of the pre-wetting step, were repeated
several times for experiments. After the rubbing wash, the samples were
thoroughly blow-dried.
RESULTS AND DISCUSSION
The behavior of
surfactant is very complicated due to its amphiphilic structure [6]. The
washing mechanism is not simple and the activity of surfactant exhibits that
lipids are lost over time by washing, exposure to the surfactant. However, it
was shown that prevention of these lipids is possible by dual modification for surface
and internal hair [1]. Dual modification produces an increase in the lipid
concentration (Figure 1). The
percentage change in the lipid concentration of the hair is defined as:
100
× (Lipid concentration from virgin - Lipid concentration after washing) / Lipid
concentration from virgin
The lipid
level reaches a maximum of 90% after 10 times of washing by the modification.
The hair washing without the modification decreases the lipid concentration,
and most of this decrease is accounted by a penetration of surfactant inside
hair or roll up mechanism at the hair surface. On the assumption that the
lipids influence physical properties in hair, further experiments for the
physical properties were carried out.
The tensile strength results of
virgin, shampoo control and dual modified hair in wash were demonstrated and
compared in Figure 2. These results
show that the control composites’ tensile properties were significantly lower
when compared to the treated hairs by the dual modification. In all cases, the
control composites of other general shampoos had worse tensile properties than
the human hair reinforced composites (data not shown). It is proved that when
the loading stuff increases for the dual modifications, physical property keeps
due to the prevented lipid amounts. A comparison with the lipid contents
indicates the lipids are responsible for the strength.
Oscillating motion with hair tress makes
movement of a mass for the tress. The elastic force of the hair tress is
responsible for the oscillating motion. Although vibrations frequency does not
depend on the movement distance in physics, hair elasticity reflects height of
hair tress at the ending point as shown with arrows in Figure 3. The height from bottom reaches up to 2.7 cm and 3.4 cm,
for the untreated hair lipid lost and the dual modified hair lipid conserved.
The bending strength results are demonstrated.
The bending rigidity increases with the increase in the lipids content as shown
in Figure 4. The bending rigidity
values are reduced from 1.38 to 0.49 gf due to a defeat of lipid inside the
hair. The bending rigidity of human hair reinforced composite increases up to
almost value of virgin hair when the hair is treated by the dual modification.
We have compared the bending rigidity of virgin and dual modified hair. No
significant difference between them was observed.
The DSC characterizations of all the samples
were subjected to one heating process. The results from the heating are
displayed and taken into consideration in Figure
5. Typical DSC peak in water stands a peak of around 160°C responsible
for α-helix [7]. The keratin
fiber loses their ordered regions at this heating region.
Dry-DSC thermo grams show the presence of two
peaks for all scans of the composites. The origins of the peaks are under debate
[8]. The lower one indicates α-helix structural distribution [9]. The second
temperature appears to be due to cysteine decomposition [10]. The first one
ranges from 230°C to 234.5°C. The peak for the curve was consistent,
independent of hair origin in a three times repeated measurement. Using a
combined approach of lipid concentration and lipid loss for hairs treated with
various shampoos, DSC thermo grams show that the presence of structural
degradation under lipid loss. The lipid loss has significant effect on the
first temperature of the α-helix.
The ΔH is an important parameter since its
magnitude is directly proportional to the overall level of structural rigidity
for releasement of the α-helix. The ΔH of hairs was estimated around 4.5 J/g;
these values were similar in all samples. However, the temperature of the
maximum peak for the α-helix was decreased down to 230°C. This shift of the
peaking temperature indicates that the structure for the α-helix was weakening
due to a loss of lipids.
A cell
membrane complex (CMC) is filled with lipids [11]. The membrane may be unstable
as the lipids lost after washing with surfactant. This may cause destruction of
the entire structure of hair. Our interpretation is not sufficient to explain
the enhancement of hair strength, thus, in order to understand a structural
analysis, it is necessary first to distinguish several levels of description
about strength level and to place these levels within a lipid concentration perspective
in future.
CONCLUSION
On the basis
of the evidence presented above, we suggest that the hair lipids support
strength which is responsible for most physical properties in hair. Human tissues such as skin and hair have the potential to accumulate
lipids, such as glycerides that contain fatty acids important for high value
fatty acids. Although lipid extraction methods for the human hair are well
established, there is currently no explanation for the role of lipids,
especially in hair. This has caused a few problems in lipid research due to
absent goal of the prevention of lipids for hair in entire lipid study and
industry. This experimental study presents the effects of human hair lipids in
compressive strength of conserved lipids. This study conserved lipids against
washing with surfactants, as the experimental group and lost lipids as standard
group being the control groups. Finally, all results prove that the lipids
greatly increase the strength of the hair. Conserving lipids improve the health
of the hair.
COMPETING INTERESTS
All authors are
employed by LG Household & Health Care Ltd.
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