This document discusses the optical properties of polymers, including refractive index, gloss, haze, yellowness index, transmittance, and photoelasticity/birefringence. It explains how each property is defined and measured, how it relates to the material composition and structure, and the relevant ASTM standard test methods. The refractive index, gloss, haze, and yellowness index sections provide specific examples of how these properties are affected by materials, additives, and processing.

1. Optical Properties of polymer
Aadrsh Kumar Tiwari
(M.Sc. Polymer chemistry)
Roll no.-131021
Enrollment no.-1750016

2. •Introduction
•Refractive index
•Gloss
•Haze
•Yellowness index
•Transmittance
•Photoelastic or birefringence

3. Introduction
•Polymer optical properties of polymers, such as, gloss,
transparency, clarity, haze, colour, surface aspect and
refractive index , are closely linked to our perception of a
plastic products quality and visual performance.
•Polymer optical properties testing will bring you the insight to
accelerate development and optimise production.
•Optical properties are dependend on the specific polymer or
copolymer material, the formulation (colourants, fillers,
plasticizers and other additives) and the crystallinity of the
materials.
•But also mechanical and chemical degradation or aging
processing influence the optical properties of polymers and
polymer formulations.

4. •The aesthetics(concerned with beauty) of a product
must be maintained throughout product’s packaging,
transport and storage, or in the automotive industry
where a consumer’s perception of ‘glossy’, strong,
surface features are inextricably linked to the 'value'
of the product.
•From our independent perspective(view), we expertly
analyse a range of optical properties, delivering
accurate information which helps to achieve the
desired aesthetics during development, production or
in the end-use application.
•During production, various steps such as colouration,
heat treatment and mechanical processing can affect
optical properties.

5. Refractive index
•The refractive index (n) is an important optical
property of polymers and is widely used in material
science.
•The knowledge of the refractive index is crucial in all
optical applications of transparent polymers.
•Since it is characteristic for each material, it can be
used for identification purposes or for the prediction of
other properties.
•For example, the refractive index undergoes a second-
order transition at the glass transition temperature,
and thus can be used to determine its value.

6. • It is directly related to the polarizability and depends on the
wavelength of light.
•The first law of optical refraction was discoverd by Snellius
(1618) and (independently) by Descartes (1637).
For light passing from air into a denser medium it is given as
n = sin(θi) / sin(θr)
where n is the index of refraction; and θi and θr are the angles
of incident and refracted light.
•A similar law can be applied to light that crosses frome one
material into another material:
ni / nr = sin(θi) / sin(θr)
where ni and nr are the refractive index of the incident and
refractive medium.

7. •A typical polymer has a refractive index of 1.30–1.70, but a higher
refractive index is often required for specific applications.
•The refractive index is related to the molar refractivity,
structure and weight of the monomer.
• In general, high molar refractivity and low molar volumes
increase the refractive index of the polymer.
•Refractive Index ASTM D542

8. • Polymer laboratories use refractive index as a diagnostic tool to
help understand the critical stress in a system or the resulting
impact of additives or heat treatments (such as cross linking, or
annealing) have on the material.
•We also provide ultra-violet and visible (UV/VIS) light absorption
and transmission measurements.
•Refractive index(n) is characterized by the Abbe number (v).
•A high refractive index material will generally have a small Abbe
number, or a high optical dispersion.
• v is obtained from three refractive index measurements at the
wavelengths 656.3, 589.3, and 486.1 nm.
•The capacity to separate the colors of white light increases as v
decreases.

9. Gloss
•Gloss is defined as the ratio of the reflection of the sample to
that of a standard.
•Gloss is an optical property which describes how well a
surface reflects light in specular direction.
•It is of great practical importance for many applications.
• The reflectivity (or reflectance) is defined as the fraction of
incident light intensity reflected at the interface (surface effect).
•Only highly polished metal mirrors have nearly total
reflectance.
•If the reflectance is almost zero, the surface appears totally
matt(dull).
•A material with reflectance in between these two extremes is
called glossy or shiny.
• The gloss is responsible for the lustrous (shiny) appearance
of plastic films.
•Specular Gloss ASTM D2457, ASTM D523.

10. •Gloss is the capacity of the polymer surface to
reflect light in a given direction.
•The gloss of the polymer increases with increasing
refractive index.
•The fraction of the light intensity that neither enters
the material nor follows the pass of mirror reflection
is dispersed or scattered by diffraction.
•The lustrous(shiny) appearance of a plastic is
determined by both the reflection and diffraction,
meaning the shininess of a surface depends on both
the specular reflection and the diffuse light of the
surrounding surface area, which is often called
the contrast gloss or luster.

12. Haze
•Haze is an optical effect caused by light scattering within a
transparent polymer resulting in a cloudy or milky appearance.
•Our polymer scientists use spectrophotometer techniques to
investigate a range of issues which result in haze as a symptom
such as weathering, during product and process development.
•Haze is measured as the percentage of incident light scattered
by more than 2.5° through the plastic specimen.
• Haze is caused by impurities contained in the plastic material
or its level of crystallinity.
•The lower the Haze value, the higher the clarity.
•Haze has no specific unit. It is expressed in %.
•Haze of plastic materials is usually measured by ASTM
D1003.

13. •Figure 2: Haze measurements for all 16 material/additive combinations.
The standard deviations are in the range 1–2 percentage
points.

14. •Figure 2 shows how the haze varies with material
and additive type.
•The three pure materials NM, BM and NZ have roughly
the same haze values, while BZ has a higher value.
•The addition of the low MW PE (C) has a minor effect on
the haze, whereas the clarifying agents A and B affect
the haze of some materials.
•The addition of 0.25% of A reduces the haze for NM,
but the opposite effect is observed for NZ.
Additive B reduces the haze for both NM and BM; but again
The effect is adverse for NZ.
•There are two different types of haze that can occur in materials:
Reflection haze occurs when light is reflected from the surface
of a material.
Transmission haze occurs when light passes through a
material.

15. Yellowness Index
•Yellowness Index ASTM E313.
•Yellowness Index is a number calculated from spectro-
photometric data that describes the change in color of a test
sample from clear or white to yellow.
•This test is most commonly used to evaluate color changes in a
material caused by real or simulated outdoor exposure.
•Yellowness is a property important in many industries, for several
reasons.
•First, processing of various materials may cause yellowing.
•Next, the purity of some products may be determined based on
the amount of yellowness present.
• Also, some products degrade and yellow with exposure to
sunlight, temperature, or other environmental factors during use.
•Thus, yellowness has become an important variable to measure
in industries such as textiles, paints, and plastics.

16. •There are different types of yellowness indices available,
depending on the type of product being measured.
•Two of the most common are:
-ASTM Designation E313-73 Standard Test Method for Indexes
of Whiteness and Yellowness of Near-White, Opaque Materials
-ASTM Designation D1925-70 Standard Test Method for
Yellowness Index of Plastics.
•ASTM D1925 has recently been withdrawn, but its yellowness
index is still used in many industries.
•The yellowness index YI is calculated from the following
equations:
for E313-73 yellowness index

17. for D1925 yellowness index
where X, Y and Z are the tristimulus values.
Tristimulus values
Tristimulus values X, Y and Z are the amounts of
the three primary colors (red, green and blue) of
the visible spectrum of light from 380-780 nm that
specify a color stimulus. They will be derived from
the following equations:

18. Legend:

19. X, Y, Z tristimulus values
h Normalisation factor such that Y = 100 for a sample that
reflects 100% at all wavelengths. Thus
Sl
represents reflectance values of an energy spectrum
measured with a UV/VIS spectrometer for surround of
wave l in given white light - from illuminant.
Pl
represents the relative spectral energy distributions of
the illuminant
xl, yl, zl
standard observer functions

20. •The transmittance of a material is defined as the
ratio of light intensity passing through the material to
the intensity of light received by the specimen.
•It is determined
by reflection, absorption and scattering.
•If both absorption and scattering are negligible, the
material is called transparent.
•In contrast, an opaque material has practically zero
transmittance due to its high scattering power
whereas a materials with negligible absorption but
with appreciable transmittance but lower than 90% is
called translucent.
Transmittance
•ASTM E1348 - 15e1

21. An ASTM designation number
identifies a unique version of an
ASTM standard.
E1348 - 15e1
E = miscellaneous subjects;
1348 = assigned sequential
number
15 = year of original adoption (or,
in the case of revision, the year
of last revision)
e1 = indicates editorial change

22. Photoelastic/Birefringence
•Photo-elastic materials are birefringent , that is,
they act as temporary wave plates, refracting light
differently for different light-amplitude orientations,
depending upon the state of stress in the material.
•Photo-elasticity is a nondestructive, whole-field, graphic stress-
analysis technique based on an opto-mechanical property called
birefringence, possessed by many transparent polymers.
• Combined with other optical elements and illuminated with an
ordinary light source.
• A loaded photo-elastic specimen (or photo-elastic coating
applied to an ordinary specimen) exhibits fringe patterns that are
related to the difference between the principal stresses in a
plane normal to the light propagation direction.
• ASTM D4093 - 95

23. •The method is used primarily for analyzing two
dimensional plane problems, which is the
emphasis in these notes.
•A method called stress freezing allows the
method to be extended to three dimensional
problems.
•Photo-elastic coatings are used to analyze
surface stresses in bodies of complex geometry.