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 TRI/Princeton
is internationally recognized as a premier center for human
hair research. For more than five decades, TRI has served
as "the other lab" for the industry, solving some
of its immediate problems and pioneering many inventive approaches
to the study of hair fibers and hair damage. A fundamental
understanding of the science behind hair grooming processes
is a prerequisite to developing successful and innovative
formulations. TRI continuously devises methodology and testing
capabilities that keep hair care on the cutting edge. Through
reproducible experiments, TRI provides quantifiable answers
to industry's questions and product claims about the many
cosmetic attributes desired by consumers.
Instrumentation
For years, TRI scientists
have developed and modified a number of unique instruments
in order to study the often unquantifiable attributes of human
hair. An example is TRI’s Single Fiber Torsion Pendulum,
which was designed to study damage done to hair as a result
of twisting and setting processes. This method utilizes an
oscillating motion to study hair damage by imitating the movement
of hair when it is twisted by hand, braided, or curled with
a hot iron. The instrument measures the fiber's resistance
to twisting, as well as how much energy is dissipated from
the fiber, to ascertain damage. The less energy dissipated
from the fiber, the more resilient the hair is.
Methodology
Original methodologies have been a staple of TRI’s hair
research from the onset. For instance, TRI researchers use
a Goniophotometer to record light scattering curves, which
allows them to evaluate luster, or hair shine. In addition
to quantifying luster, this method can determine changes in
hair shine as a result of product deposits, surface damage
caused by cosmetic treatments, and damage as a result of mechanical
processes, such as combing, blow-drying, and curling. TRI
scientists further examine how differences in morphology and
composition affect hair’s luster. With a fundamental
understanding of what factors contribute to a customer’s
perception of luster, TRI researchers can identify hair-care
formulations that increase shine.
Microscopy
Product
Build-up
TRI has used Microspectrofluorometry (by flourescently labeling
colorless products) and Scanning Electron Microscope (SEM)
analysis to identify product buildup. Figures Below.
Examples of these two techniques, untreated hair on the left,
and hair displaying product buildup on the right.
Diffusion
of Chemicals into Hair
At TRI, we are modeling
and quantifying the diffusion of chemicals into hair for development
of chemical treatments (perming, dying) that minimize damage
to the hair. Figure Below. Microfluorometry is used
to demonstrate the progressive (left to right) diffusion of
a chemical (fluorescent red dye, in this case) into the hair
shaft.
UV
Degradation of Hair
The photo-damage
caused by the long wavelength UV component of sunlight is
an inevitable consequence of enjoying life in the outdoors.
Researchers at TRI have mapped sunscreens as they diffuse
into hair fibers and also established the mode of their protective
action. Figure Below. SEM image of the unique fracture
pattern of severely UV damaged hair: from left to right, fractured
cuticular sheath and cortex, the cuticular sheath, and magnification
of the later showing fusion of the cellular structures.
Mechanical
Properties of Hair
Innovations at TRI
have been instrumental in determining the effect of a proposed
treatment on the hair's mechanical properties. Many chemical
processes involve the breaking and remaking of the hair's
disulfide bonds which leads to weakening of hair and untimely
hair loss. Hence the study of these properties is crucial
to the final acceptance of any formulation for hair.
Figures
Above.
Using microfluorometry, to detect, highlight, and quantify,
physical damage to the hair fiber by standard grooming practices
and weathering. Fluorescent intensity is directly proportional
to increased damage.
The
following facilities at TRI/Princeton are used in this research:
- TRI/Automated
Hair Comber™
- Combs hair in a consistent, reproducible manner, providing
insight into types and degrees of combing damage
- TRI/Fatigue
Tester™
- Measures strength and fatigue resistance by subjecting
hair fibers to repeated tensile deformation
- TRI/SCAN™
Surface Force Analyzer - Three-dimensionally maps the
surface energy of single hair fibers
- Diastron
- Generates stress-strain curves for wet or dry hair and
calculates parameters that characterize the mechanical properties
of hair
- Dynamic
Vapor Sorption -
Analyzes the sorption/desorption behavior of hair to evaluate
the moisturizing ability of formulations
- Fourier
Transform Infrared (FTIR) Spectrometer (Attached to Advantage
Microscope) - Studies hair damage and presence of formulation
compounds on surfaces
- Goniophotometer
- Measures luster values of single hair fibers and tresses
- Image
Analysis Techniques
- Measures hair tress volume and product deposition and
coating uniformity
- Instron
Tensile Tester
- Measures tress compression energies to study the ability
of formulation to give body and softness to hair tresses
as well as combing force and interfiber friction
- Microfluorometer
-
Models and quantifies the diffusion of chemicals into hair;
detects and quantifies physical damage to hair fibers; and
measures surface deposits, build-up and dye diffusion
- Microspectrophotometer
(VIS and UV) - Examines the effect of UV exposure on
hair
- Scanning
Electron Microscope (FESEM)
- Maps fiber surfaces, cross-sections, and fracture behavior
- Single
Fiber Torsional Pendulum - Measures a hair fiber's resistance
to twisting and how much energy is dissipated from the fiber
- UltraScan
XE (Colorimeter) - Evaluates depth and intensity of
hair dyes and dye fading
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