We offer various solutions for recycling plastic based on Near Infrared (NIR) spectroscopy. Since we keep getting similar, basic questions about the possibilities, I have written up the essential points around NIR. This article covers, among other things, what NIR is, how it works, what the limitations are (especially with regard to sorting plastic), how trinamiX’s NIR technology helps us gaining more insights and why we need more knowledge about NIRS in recycling industry and further technologies.

Table of contents

Part 1: What is Near Infrared spectroscopy?

Part 2: Why is NIR spectroscopy the dominant technology for sorting plastics in plastics recycling?

Part 3: What are the limitations of NIR?

Part 4: What is an optical reference standard made of white PTFE used for?

Part 5: From theory to practice: how trinamiX’s solution can help understand recycling problems?

Part 6: Conclusion: Why do we need to look for additional technical solutions for sorting?

Let’s start with part 1:

Part 1: What is Near Infrared spectroscopy?

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Near infrared spectroscopy (NIRS) is a spectroscopic technique that uses the near-infrared region of the electromagnetic spectrum to measure the absorbance and scattering of light by samples. This technique is used in a wide range of applications, from pharmaceuticals to food science. In this article, we will discuss the basics of NIR.

What are some common applications of NIR spectroscopy?

Near infrared spectroscopy is used in a variety of industries for a variety of purposes. Some common applications include:

  1. Pharmaceuticals – NIRS can be used to measure the purity of drugs and detect impurities.
  2. Food Science – NIRS can be used to detect the presence of contaminants in food. This technique can be used to ensure the safety of food products and prevent food poisoning.
  3. Plastic Recycling – NIR spectroscopy is used to analyze the quality of plastic and how it can be used in the recycling process. This technique is used by companies that produce plastics because they need to know if the product they are producing will meet certain standards or not

NIR spectroscopy is a technique used to measure the molecular weight distribution of plastic. This can be achieved by measuring the absorption of infrared radiation at different wavelengths. NIR spectroscopy allows for a fast determination of what types of plastic are present, and it has many possible applications in recycling processes.

Part 2: Why is NIR spectroscopy the dominant technology for sorting plastics in plastics recycling?

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There are a number of reasons why NIR spectroscopy is the dominant technology for sorting plastic in plastic recycling.

  • Firstly, it is an extremely fast technique that can provide results in a matter of seconds.
  • Secondly, it is non-destructive, meaning that the plastic can be recycled after being analyzed.
  • Finally, it can be used to identify a wide range of different types of plastic, which is essential for effective recycling.

How is NIR spectroscopy is used in plastic recycling?

NIR spectroscopy is used in two main ways in plastic recycling.

  • Firstly, it can be used to sort plastic waste into different categories. This is achieved by identifying the absorption bands of different plastics and then using this information to separate them.
  • Secondly, NIR spectroscopy can be used to determine the purity of recycled plastic. This is done by measuring the absorption of infrared radiation at different wavelengths and then comparing this to a standard.

Part 3: What are the limitations of NIR?

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NIR spectroscopy can be used to quickly determine which types of plastic are present and offers many possible applications in recycling processes. However, NIR spectroscopy is not without its limitations:

  • One of the main problems is that it can be difficult to get accurate results if the plastic sample is small, transparent, thin or filled with carbon black.
  • Furthermore, NIR spectroscopy can only be used to identify a limited number of different types of plastics. Many sorting solutions are limited to less than 20 plastic types, and in some cases much less, especially the faster sorting is required. (I will explain which basic parameters need to be considered when designing such solutions in a later blog post. Stay tuned!)

Despite these limitations, NIR spectroscopy is still the most effective technique for sorting and recycling plastics. It is important to understand what NIR can do well, rather than focusing on what NIR cannot do. This article is intended to contribute to this and we will be happy to advise you on your individual task.

How well can your task be solved with NIR?

Why can’t material filled with carbon black be detected?

One of the main limitations of NIR spectroscopy is that it cannot detect plastics that are filled with carbon black. This is because soot absorbs infrared radiation very strongly and is therefore difficult to distinguish from other plastics. In fact, you get a “non-signal” that is accordingly very different from all other signals. So you can distinguish black plastics from all others, but not black plastics from each other.

What possibilities are there to distinguish black plastics?

I will also write a separate blog post on this later, which will show possible alternatives. So for now, just a few ideas:

Basically, recognising and sorting black plastics is THE big problem in plastics recycling. However, there are a few approaches:

  • MIR: NIR works approximately in the range of 1,000 nm to 2,500 nm. Black becomes “visible” the further you move into the mid-infrared (MIR, from approx. 3,000 nm). However, technical solutions here are not yet really suitable for recycling solutions in the industrial sector (more on this in a separate post). Manufacturers include Innospec and Specim.
  • Electrostatic charging: Black PE and PP can be separated quite well via electrostatic charging. One plastic can be electrostatically charged, the other not. In the fall, a magnet is used to separate the charged particles. A well-known manufacturer of such solutions is Hamos.

Part 4: What is an optical reference standard made of white PTFE used for?

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An optical reference standard made of white PTFE is good for calibrating NIR spectroscopy equipment. This is because PTFE has a very low absorption of infrared radiation, meaning that it can be used to accurately measure the absorption of other plastics. As a result, using a PTFE reference standard helps to ensure that the results of NIR spectroscopy are accurate. Material filled with carbon black has very high absorption and is therefore the opposite of the white PTFE.

What is an optical reference standard used for in plastic recycling?

Due to the low absorption of the NIR signal, or the high reflection, the reflection standard is ideally suited to reflect the NIR signal. A reflective standard virtually “mirrors” the signal. This accessory is therefore ideal for measuring thin plastics, e.g. foils. With the reflection standard, the NIR signal passes through the material twice. Otherwise, the signal would hardly be reflected by the material itself and there would only be a very, very weak NIR signal. This would make the identification of thin and/or transparent materials, such as foils, virtually impossible.

What is a diffuse reflection?

When light reflects off a surface, it can be reflected in numerous ways. Diffuse reflection occurs when the light is reflected in all directions. When sunlight shines on a rough surface, such as sand or gravel, this form of reflection is frequent. Optical PTFE (the material used for Reference standard) is a diffuse reflector.

Part 5: From theory to practice: how trinamiX’s solution can help understand recycling problems?

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trinamiX developed a NIR spectroscopy solution that can be used to accurately sort plastic waste. The solution is based on patented technology, which allows to measure the absorption of infrared radiation at different wavelengths with great accuracy. The solution has been proven to be more effective than other techniques, and it can be used to identify a wide range of different types of plastic.

In addition to these basic technical advantages, trinamiX’s NIR solution is particularly convincing due to its very simple handling, compact size, modern user interface and fair price. This means that even non-professionals can generate knowledge quickly and easily.

trinamiX’s NIR spectroscopy solution is already being used by a number of companies and organizations, and it has helped to improve the efficiency of their recycling processes.

This article was intended to provide some theoretical background on NIR. The NIR solution from trinamiX is ideally suited for gaining practical experience with NIR and confirming the statements made in this article. The intuitive user guidance enables even non-experts to use the technology. Only when there is a comprehensive understanding of NIR can new recycling methods be established. A tool like this can thus transfer knowledge in non-profit organisations, schools, companies, engineering offices and universities and contribute a significant part to the success of the EU Green Deal.

Conclusion: Why do we need to look for additional technical solutions for sorting?

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NIR is a cost-effective, fast and therefore an established sorting technique. However, it cannot distinguish carbon black-filled plastics and films are also a challenge. According to Plastics Europe, 29 million tonnes of post consumer waste were collected in the EU in 2018, of which over 42% was thermally recycled. Much of this was certainly sorted out because NIR cannot detect all plastics. As long as there are no reliable technical solutions, we need to better understand NIR technology, question planned applications and use NIR where it can show its advantages, e.g. in very small and handy solutions for mobile detection of plastics.

Gain more knowledge about plastics with the help of simple NIR tools

A small contribution on how to exploit the full potential of NIR – and thus already make a difference with available solutions today – is what this blog post series aims to do. Let me know what topics are driving you. I will be happy to help you with my expertise!

Technical solutions like NIR are essential to implement the EU Green Deal. Let’s get started and discuss their applications in detail. I look forward to hearing from you!

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