Polymer analysis: what you need to know

Since first coming into widespread use in the 1950s, plastic production has increased at an incredible rate, with over 380 million metric tons of polymer resin and fiber being produced globally, with numbers still increasing. This is because in many ways plastic is an amazing material.

It’s versatile, inert, forms a hermitic seal, cheap to produce, made from an abundance source, lightweight, and easy to form into complex shapes. It helps to keep production and shipping costs down and perishable items fresher for longer. Our lives without plastic would be a lot less convenient.

However, we should bear in mind that the features of plastic that make it such a useful material, such as its longevity, stability and low cost of production are also what is causing it to have a very negative impact on the environment.  Only 16% of plastics produced currently being recycled and as we look to increasingly work with recycled and recyclable polymers thermal analysis plays an important role in ensuring that these new materials meet the high standards required. Learn more about this in our blog on polymer recycling and reuse with thermal analysis.

Thermal analysis is an excellent technique for supporting polymer manufacture and new materials development. Thermal analyzers help to ensure your product always makes the grade your customers expect, and your brand remains one associated with high quality.

If you are new to polymers or polymer analysis, here’s our quick 101 overview.

Polymer analysis: what you need to know

 

Main uses of polymers

Packaging

It comes as no surprise that packaging is the number one use of polymers, with 146 million tons being made every year. This is over 35% of the total polymer production. Plastic makes an excellent packaging material. It can keep freight costs down as it’s lightweight, can be made into purpose shapes to protect delicate goods, and form a hermetical seal, so helps to keep food fresh as it’s shipped around the globe.

Building and construction

65 million tons of plastic is produced purely for the building and construction industry. As well as the low cost, the easily formable aspect makes plastic ideal for window and door profiles and seals. Its longevity makes it great for pipes and floor coverings, and its low thermal conductivity makes it an ideal insulator. It’s also relatively non-flammable compared with more traditional construction materials, such as wood.

Textiles

Coming in at a close third are textiles. 59 million tons of plastic are produced for the textiles industry every year. Most of this is clothing, with polyester and nylon cheaper and thinner than cotton, making clothes lighter and less expensive to produce. These synthetic fibers are also used in soft furnishings, such as rugs and carpets, where they are lightweight, cheap, hard-wearing, and easy to clean.

Consumer and Institutional products

Polymers are found in a huge range of products from toothbrushes to furniture and include fast moving consumer goods (FMCGs) like toiletries. It’s a broad category where plastic is used because of its low cost and, in many cases, such as contact lenses, is the only suitable material for the application. 42 million tons of plastic is produced for this sector every year.

Transportation

The increase of the use of plastics in cars and commercial vehicles has been driven by a need to make cars more efficient to reduce harmful greenhouse emissions. Plastic is an excellent lightweight alternative to traditional automotive materials and complex polymer blends and engineered plastics such as acrylonitrile butadiene styrene (ABS) are now commonplace. The transportation sector alone needs 27 million tons of plastic per year.

Electrical / Electronics

18 million tons of plastic are created per annum to produce electrical and electronic items. Most plastic is electrically insulating, meaning that it’s excellent for producing electrical mounts, circuit board level packaging, insulating material such as cable sheaths and the non-electrical parts of mechanical-electrical components. However, conductive plastics are now available and are used when the conductive part of the component needs to be flexible or a very complex shape.

Industrial machinery

With a relatively low 3 million tons of primary use plastic produced each year, the industrial machinery sector uses plastic in many ways to reduce the weight and cost of plant equipment.

A further 47 million metric tons of plastic are produced each year for a wide range of smaller sectors.

Types of plastic and their uses

Polystyrene (PS)

Accounting for 6.1% of all virgin resin demand in Europe, polystyrene is used for protection and heat insulation for plastic cups, food trays, building insulation and bicycle helmets. It’s also a key component in the packaging of large, delicate items however, it has a relatively low recycling rate.

Polyurethane (PUR)

Making up 7.8% of European resin demand in 2020, PUR is used for a huge variety of applications thanks to its ability to be formed into different types of materials. Foamed PUR is used for insulation products and flexible PUR is ideal for seats and handles. Solid PUR has high strength and is used for protective applications.

Polyethylene terephthalate (PET)

Much of our food and drink packaging is made from PET, including plastic bottles of water. It’s particularly useful for this as it’s very good at providing a barrier to gases such as oxygen and carbon dioxide. This helps keep food fresh and carbonated drinks fizzy. In 2020, PET resin accounted for 8.4% of all virgin resin demand in Europe.

Polyvinyl chloride (PVC)

The use of PVC, or vinyl, has reduced over the past decade. It used to be the second most widely used plastic resin, but today PVC only accounts 9.6% of global demand. It’s flexibility and high impact strength mean that it’s still the material of choice for cable insulation and pipes, floor and wall coverings, window frames and inflatable pools.

High density polyethylene (HDPE)

As its name suggests, HDPE has very dense polymer chains and is a strong material. It’s used for toys, shampoo bottles, milk bottles and pipework. It makes up 12.9% of the demand for resin and is easily recyclable.

Low density polyethylene (LDPE)

LDPE has a relatively simple structure, making it easy and low cost to process into products. It’s the plastic used for grocery bags, plastic wraps, food storage containers and wire covering. 17.4% of the demand for plastic resins was for LDPE in 2020, despite some challenges with recycling.

Polypropylene (PP)

Stronger than LDPE but not as dense as HDPE, PP is ideal for microwave-proof containers due to its good heat resistance. It’s also used in bank notes, thermal vests, and diapers. PP has the highest demand of all the plastic types and accounts for almost 20% for all plastic use. Unfortunately, it’s not fully recyclable.

Others

18.1% of virgin plastic resin demand is for a mix of other types. These include important plastic types such as PMMA for touch screens, PTFE for telecommunication cable coatings and ABS in automotive parts.

What are the main purposes of polymer analysis?

1. Quality control

Within a production environment, the main reason for polymer analysis is quality control. Will the finished product look and perform the way it should over the lifetime of the part? If it doesn’t, then will it be scrapped before it leaves the facility? Or, even more costly, will the customer reject it, or will you have to do a product recall? Clearly, with such stringent specifications for polymer-based products, rigorous quality control is essential.

There are two main options for production quality control, inline / online analysis or offline / atline. Let’s look at the advantages and disadvantages of them both.

Inline or online quality control

This is where you have a system that is an integral part of your production line that monitors your products in real time during the production process. It gives you fast feedback and therefore allows you to halt production immediately if there’s a problem. This saves you money and time. But it doesn’t work for every type of sample and these instruments can be inferior to offline ones in terms of detection limits.

Offline or atline quality control

This is where your analysis equipment is in a lab or to the side of production and samples or raw materials are taken out of production for analysis. It’s the most common type of analysis in polymer production. Measurements aren’t done in real-time, but with fast analytical techniques you can still get relatively fast feedback on production runs, plus you have the advantage of choosing equipment with the best detection limits.

Offline quality control consists of the following:

  • Visual inspection. This is the simplest and least expensive way to check if something is right. And it’s fine for basic checks like whether the product is the right color or whether it has any cracks or other visible defects. It is, however, subjective to the operator and often will need to be backed up by other methods.

  • Chemical analysis. This is excellent at determining the composition and to find out which elemental components are present and whether any are missing. Example techniques are chromatography and XRF analysis. Chromatography takes some time, and the sample preparation is relatively complex, however XRF is simpler and faster.

  • Physical property analysis. Thermal and mechanical property analysis gives you direct information on how the component will perform in the field. It includes specific tests like tensile strength analysis and impact testing. There are many options for physical property analysis, but thermal analysis is one of the most versatile as it will also give you information on what the polymer is made from. It can be used for raw materials as a compositional check, as well as for finished goods to ensure in-house processing hasn’t altered the physical characteristics in an unwanted way.

2. Research and development

Developing new materials for specific applications requires analysis to make sure that it looks and performs as expected. Sometimes development will be for a brand-new product and techniques such as thermal analysis will be used to check that the product has the right physical properties. Ensuring that the additives used to control the final color will not affect crystallization or strength is an important part of checking new formulations in the lab.

Analysis will also be used when checking potential new materials for introducing into existing production lines. For example, checking that the use of recycled materials will yield the same look and performance as virgin polymers.

Another use of polymer analysis is to analyze a competitor’s product to determine the compositional make up and physical specifications. This is useful to reverse engineer parts when customers need a back-up supplier.

Predicting performance of new materials

One useful application of thermal analysis, particularly for new materials, is the prediction of the performance of the component over its lifetime. We’ll look at specific thermal analysis techniques in more detail later, but it’s possible to predict product lifetime using STA (simultaneous thermal analysis) equipment and then use advanced software techniques to estimate the time taken for the material to degrade under standard use. This kind of analysis can take off literally years of development time.

3. Troubleshooting and tackling customer complaints

This may be for internal troubleshooting as well as returns or complaints for customers. Examples of problems with polymer-based products include:

  • Misshapen or cloudy parts
  • Too stiff or not stiff enough leading to poor damping
  • Raw material not pure

Thermal analysis gives us information on crystallization, material additives, strength, and rigidity among others. We can often use the family of techniques to undertake root cause analysis of production issues, or tackle customer complaints by showing that the material is performing as it should.

 

Thermal analysis for polymer analysis

Thermal analysis (TA) describes a collection of analytical techniques that measures the change in a materials behavior as a function of time and /or temperature, either when heated, cooled or kept at constant temperature. The sample sizes are usually in the mg range and the material changes detected can be extremely small.

Examples of material behaviors that are monitored are sample weight, viscosity, temperature and sample dimensions changes. These measurable changes are plotted on an output graph and the characteristics of these graphs give you precise information on fundamental material properties like melting point, glass transition and crystallization temperature. From this you can determine a material’s fundamental characteristics and composition and predict how the material will behave in each application. A simple example is whether the plastic used in a high-temperature application (like a car engine) will have a melting point high enough to remain solid in use

Advantages of thermal analysis

The main advantage of thermal analysis is that it precisely analyses fundamental bulk material properties. Even for complex materials, you can often tease out the behavior of the constituent polymers to ascertain what’s in the mix. It’s applicable to a wide range of materials and doesn’t need material specific calibration curves, so you can easily investigate novel materials.

There is very little sample preparation, with no harmful chemicals to contend with and, with a little training, the analyzes can be run by anyone, especially with an instrument that has a high degree of automation.

The analysis procedures are relatively short, with many completed in under an hour. The equipment is inexpensive to run, and you don’t have to keep the equipment in standby when not in use, cutting electricity and gas consumption.

X-ray fluorescence for polymer analysis

So, whilst TA delivers excellent baseline performance and sensitivity for materials verification and thermal behavior characterization, X-ray fluorescence (XRF) analyzers are used for elemental and compositional measurements within a polymer matrix.

Examples of what XRF analysis is used for include checking raw polymers as well as finished products for chlorine content, to give an indication of the presence of PVC (and potentially phthalates) in the materials being used. You can also use it to determine bromine content in polystyrene waste. To separate HBCD from other brominated compounds sample preparation is needed. XRF can also easily measure metal content in plastics.

Advantages of XRF

A fast and non-destructive technique, XRF can analyze polymers in solid, powder, liquid and pellet form, and needs very little sample preparation. As it’s completely non-destructive, it can be used on finished components for a final elemental compositional check. It can also be used to measure the thickness and composition of metal coatings, such as metal plating on plastic components.

Want to find out more about polymer analysis?

Our guide on protecting your brand with thermal analysis of polymers sets out to explain and demystify thermal analysis of polymers even further including how to interpret results for some common ASTM method measurements.

 

Download the guide

 

And if you have any questions or want a demo of our instruments to find out what would suit your analysis needs, contact our experts.


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Date: 4 August 2022

Author: Olivier Savard, Product Manager Thermal Analysis

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