Page 25 - Plastics News April 2019

FeAtures

Testing Polystyrene: Why The Weakness?

There are numerous ways in which a plastic utensil can fail and there are a range of factors that impact
physical properties of a product like plastic utensils be it a fork ,cup or a plate

e’re going to discuss a hypothetical situation, similar are many reasons why that might be happening: improper
Wto the ones we might receive with a product across copolymer ratio, exposure, contamination, or degradation.
the many industries we work with here at SGS PSI. Let’s A range of factors can impact physical properties of a
assume that a new client has an issue with plastic utensils– product like plastic utensils. If the mix of polymers used in
the kind you might buy for a picnic–that keep breaking the product are not correct, the resulting utensil might be
during normal use. They’re going to work with us while too brittle and end up snapping in half. Nuclear Magnetic
we perform failure analysis using various techniques to Resonance Spectroscopy (NMR) analysis may be used to
determine the exact cause of the failure.
determine the ratio of copolymers.
Throughout our discussion, we will examine some of the We use size exclusion chromatography (SEC) to determine
ways a plastic utensil–or any polystyrene-based product– the molar mass of the polymer. If the broken spoon’s
might fail. By examining first exactly what polystyrene polymers have a smaller molar mass than a spoon that
is and then looking at some of the ways it is known to is able to successfully scoop ice cream, then we have
fail, we can walk you through, briefly, and explain what reason to suspect that something is causing degradation.
working with an independent testing lab might look like From there, we can perform other analyses to determine
for you or your company. causation.

UV-degradation is one such example. If the plastic utensil
polymer is missing key additives, extended sunlight or
oxygen exposure can make the utensils brittle or discolor
them. To determine if that has happened, we use High-
Performance Liquid Chromatography (HPLC), Liquid
Chromatography–Mass Spectrometry (LC-MS), and Gas
Chromatography–Mass Spectrometry (GC-MS), all of which
separate compounds in polymers and provide identity of
individual components. Through those testing methods,
we’ll be able to determine which additive is missing. These
same tests can be used to determine if the utensil failure
Before we dive into testing, it’s important to understand was caused by contaminants or solvents.
the polymer in question. Fortunately, we have decades of
experience in polymer science and independent testing Another test for that cause is Scanning Electron Microscopy
(SEM): An analysis in which a beam of electrons generate
to help inform us.
signals at the surface of a solid object that can be used to
Polystyrene is a synthetic hydrocarbon composed of determine texture, chemical composition, and crystalline
styrene. It is usually a thermoplastic polymer and is a structure. This analysis can be used as well to look for signs
common plastic for many applications due to its low of environmental or physical contaminants, manufacturing
cost and durable properties. Polystyrene is incredibly defects, or use stresses.
widespread and is used in many modern manufacturing This hypothetical situation is not far-fetched at all. As you
processes.
learned from this one test case, the reasons for failure
There are numerous ways in which a plastic utensil can be incredibly varied. Everything from production and
can fail: snapping in half, lacking rigidity, unattractive physical composition to outside factors like UV degradation
discoloration, etc. Let’s say your spoons keep breaking can influence a material–and often there is more than one
in your ice cream: an endlessly annoying problem. There cause involved at a time.

25 April 2019 Plastics News