Page 41 - Plastics Nuews October 2017

Why is Plastic Clear?

any plastics are very safe, durable, and inexpensive birefringence. Remember how quantifying plastic clarity
Mto produce. That makes it an amazing material in relates to refractive index? Optical birefringence testing
itself. When it’s clear, though, that’s when plastic really looks at how a material refracts light, and it can help us
shines as a material for many different applications. determine whether stress factors have caused a plastic
Sure, there are a few other substances that are clear–like sample to experience whitening–and lose its clarity. If
glass–or at least translucent–like wax paper. Plastic is stress factors were a cause for the whitening it can also
different though and the science behind clarity of plastics indicate from where the stress originated.
is rooted in the littlest details, the monomers. We’ve explored how to quantify clarity, an option for
Remember, polymers are monomers (small molecules) determining why clarity was compromised but we have
that join to form long, and sometimes complex, chains. yet to answer the fundamental question, why do clear
Most polymers contain both crystalline (neatly ordered) plastics matter?
and amorphous (unordered) molecular chains. The Clear plastic is important for a number of reasons. Perhaps
crystallinity of a polymer can impact the clarity of the it’s just simple marketing: companies want to make sure
plastic material. you can see their products through the container. In other
It might seem obvious to you what is applications, though, clarity can be much more important.
clear and what isn’t: if you can see Many materials in medicine
through something, then it’s a clear and laboratory science are
substance, right? But as scientists, we’re clear so that professionals can
often faced with a way to quantify these accurately measure and make
sorts of things. Just how clear is it? decisions without doubt–with
the information before their
That’s where some measurements very eyes. In many applications,
come into play. According to Craftech that’s vital.
Industries, there are two ways that we
can determine the clarity of a material. When you’re designing a product
First is the ‘refractive index’, which is a that needs to be clear, though,
measure of how much light is refracted, one type of plastic reigns
or bent, through a substance. When light supreme: polycarbonate. PC
passes through a clear substance, the light isn’t bent is a strong, clear, and recyclable plastic that’s used in
very much at all. The less light has to bend through a everything from water bottles to lab equipment. PC is
substance, the clearer it is. recyclable because it belongs to a family of thermoplastic
materials, meaning that it will return to a liquid state
The other test of clarity is transparency. How easily when heated. This is unlike thermoset plastics, which
can light penetrate a substance? That’s determined by only decompose when reheated to high temperatures.
something called the “Standard Test Method for Haze and From a renewability standpoint, a thermoplastic material
Luminous Transmittance of Transparent Plastics”. This is preferred.
ASTM test measures the amount of light that can make
its way through a substance. The higher the value, the With continued innovation in the world of plastics every
more light can get through and the clearer a substance is. day, plastic materials are just going to get better thanks
to curious minds and the use of great science. From
It is one thing to determine clarity–but what do you do higher durability to better clarity, we expect to see the
when a plastic that is supposed to be clear becomes applications where clear plastics are used to evolve and
cloudy or white? While discoloration or whitening can improve.
have a number of causes, we have multiple analytical
approaches that can help determine the root cause of What are some other ways that you use plastics and their
the clarity issue. unique ability for clarity every day?

One analytical option for assessing lack of clarity is optical Polymer Solutions News

41 Octob er 2017 | Plastics News