Testing Polystyrene: Why The Weakness?

plastic-fork-and-knifeWe’re going to discuss a hypothetical situation, similar to the ones we might receive with a product across the many industries we work with here at SGS PSI. Let’s assume that a new client has an issue with plastic utensils–the kind you might buy for a picnic–that keep breaking during normal use. They’re going to work with us while we perform failure analysis using various techniques to determine the exact cause of the failure.

Throughout our discussion, we will examine some of the ways a plastic utensil–or any polystyrene-based product–might fail. By examining first exactly what polystyrene is and then looking at some of the ways it is known to fail, we can walk you through, briefly, and explain what working with an independent testing lab might look like for you or your company.

Before we dive into testing, it’s important to understand the polymer in question. Fortunately, we have decades of experience in polymer science and independent testing to help inform us.

Polystyrene is a synthetic hydrocarbon composed of styrene. It is usually a thermoplastic polymer and is a common plastic for many applications due to its low cost and durable properties. Polystyrene is incredibly widespread and is used in many modern manufacturing processes.

There are numerous ways in which a plastic utensil can fail: snapping in half, lacking rigidity, unattractive discoloration, etc. Let’s say your spoons keep breaking in your ice cream: an endlessly annoying problem. There are many reasons why that might be happening: improper copolymer ratio, exposure, contamination, or degradation.

A range of factors can impact physical properties of a product like plastic utensils. If the mix of polymers used in the product are not correct, the resulting utensil might be too brittle and end up snapping in half. Nuclear Magnetic Resonance Spectroscopy (NMR) analysis may be used to determine the ratio of copolymers.

We use size exclusion chromatography (SEC) to determine the molar mass of the polymer. If the broken spoon’s polymers have a smaller molar mass than a spoon that is able to successfully scoop ice cream, then we have reason to suspect that something is causing degradation. From there, we can perform other analyses to determine 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 was caused by contaminants or solvents.

Another test for that cause is Scanning Electron Microscopy (SEM): An analysis in which a beam of electrons generate signals at the surface of a solid object that can be used to determine texture, chemical composition, and crystalline structure. This analysis can be used as well to look for signs of environmental or physical contaminants, manufacturing defects, or use stresses.

This hypothetical situation is not far-fetched at all. We’ve tested a wide range of materials over the years and are no stranger to custom, complex testing environments when they’re needed. As you learned from this one test case, the reasons for failure can be incredibly varied. Everything from production and physical composition to outside factors like UV degradation can influence a material–and often there is more than one cause involved at a time.

If you’re looking for help with analytical testing, failure analysis, or just have a question, get in touch today! Our scientists are experienced and well-equipped to tackle a diverse array of questions related to failure analysis. We’re always up for a challenge when it comes to independent, analytical tests.

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