Quality control of finished polymer and plastic products

Illustration QC of finished plastic products


High-performance polymers are used in virtually any industry and found in most consumer products. The carefully designed properties of these polymers are achieved through very precise and complex production steps. To ensure that the polymers conform to the specifications, quality control of the finished products is a key aspect in the production chain.

Metrohm offers dedicated solutions for the determination of many parameters, such as:


Regulatory compliance in quality testing


Our instruments are suitable for a variety of analyses in compliance with ASTM, ISO, and DIN standards.

> See how you can comply with international standards using Metrohm instruments


Spectroscopy for polymer testing

Spectroscopic techniques offer several advantages when it comes to analyzing polymer samples. Generally, sample preparation is kept to a minimum or not required at all, and the measurements are nondestructive. As a result, the entire procedure is simple and time-saving – providing accurate results within seconds.

With the NIRS DS2500 Analyzer from Metrohm, you can perform reflectance measurements for polymers in any environment. This compact and robust analyzer allows you to measure multiple parameters simultaneously.

> Learn more about the NIRS DS2500 Analyzer

> See what parameters you can analyze with a NIRS DS2500 Analyzer

Checking additives in finished plastics

Polymer pellets for spectroscopic analysis
Polymer additives are used to modify polymers in various ways: to create a particular color, to make the material easier to process and longer lasting, to change the appearance, or to make it softer and more flexible, to name but a few. Hence, the content of these stabilizers in the finished product must be checked to confirm that it conforms to the requirements.

Using spectroscopy, you can determine low levels of additives directly in intact polymer pellets. Metrohm has developed an exemplary application for the determination of a light stabilizer (Tinuvin 770) and an antioxidant (Irganox 225), illustrating the scope and ease of use of spectroscopy.


Checking copolymer levels in finished plastics

Structural formula of EVA or PEVA

It is almost impossible to overstate the influence of the sequential order of different monomer units in polymers. This order determines the main properties of the end product.

Spectroscopy is capable of determining the copolymer levels in polymer pellets without any sample preparation, thus enabling you to confirm the product quality easily and quickly.


Fast identification of postconsumer plastic with Raman spectroscopy

Identification of postconsumer plastic with Raman spectroscopy

Dealing with plastic waste is one of humanity's biggest tasks for the present and the future. To recycle plastic waste, however, you have to know what material type you're dealing with.

Raman spectroscopy is ideally suited for identifying functional groups in polymers and for revealing details of polymer structures. The techniques that work in R&D and production also work in the plastic recycling industry. Here, it is crucial to sort plastic by material type. Raman can effectively distinguish materials such as ABS, PE, PS, PET, and PMMA in waste, irrespective of color, surface water, deformation, or dirt – and all this within seconds and without any material contact.

> Learn more about the Mira M-1 analyzer



Thermostability testing of PVC

PVC and other chloride-containing polymers are among the most versatile and useful synthetic materials available. However, these materials have a low thermostability. At elevated temperatures, these polymers degrade and release hydrogen chloride (HCl). This so-called PVC dehydrochlorination is a serious drawback, but can be largely eliminated by the addition of thermal stabilizers. The finished product’s thermostability, however, has to be checked as part of quality control.

The determination of HCl is described in the ISO 182 Part 3 standard. The method used for determining the thermostability of polymers involves heating of polymer samples, transferring the HCl gas that forms into a solution, and measuring the conductivity of the solution.

PVC Thermomat system for thermal stability measurement of polyvinyl chloride with software on laptop screen

Metrohm offers a dedicated instrument for this measurement: the 895 Professional PVC Thermomat. With this instrument, you can analyze multiple PVC samples simultaneously and control the entire process on your computer.

> Learn more about the 895 Professional PVC Thermomat

It goes without saying that Metrohm supplies not only the instruments but also the applications for determining the thermostability of PVC and other chloride-containing polymers. Read more in the documents you can download below.



Water determination in plastics

Polymers readily absorb water. The properties of plastics can be compromised by the presence of excessive amounts of moisture. In the pellet molding process, for example, residual moisture reacts with the molten polymer and thus deteriorates its physical and chemical properties. Therefore, the water content of polymers has to be checked to ensure appropriate product quality.

One commonly applied method for water determination in polymers is loss on drying (LOD). However, LOD does not determine the water content, but rather the total content of volatile components. Besides, the determination of the LOD is extremely time-consuming.

The method of choice: Coulometric Karl Fischer titration

Water determination in PVC powder with Karl Fischer titration

As a viable alternative to LOD, Metrohm offers coulometric water determination, a time-tested technique that has proven its worth in countless applications.

Since most polymers are not soluble, the moisture is extracted from the polymer samples by heat and the evaporating moisture is transferred to the coulometric cell by a dry carrier gas stream. The so-called oven technique is a well-established sample preparation technique in Karl Fischer titration and is recommended in various norms (e.g., ASTM D 6869-03 or ISO 15512).

> Read more about this topic in the press release

> Learn more about automated Karl Fischer coulometric titration


NIR spectroscopy: Rapid and nondestructive

Spectrum of water determination in EtOH (second derivative)

Although coulometric water determination is the gold-standard method for moisture determination in plastics, NIR spectroscopy might be a preferable alternative, as it is nondestructive and rapid. To demonstrate this, we have developed an application to determine water in plastic contact lenses.

> Learn more about Metrohm NIRSystems



Halogens and sulfur in polymers: Combustion Ion Chromatography

When organic materials containing halogens and sulfur undergo combustion, they develop toxic, hazardous gases. To eliminate this risk in case of a fire, some plastics have to be checked in view of their halogen and sulfur content. Determining these parameters should be as reliable, accurate, and – not least – time-saving as possible.

Schematic illustration of pyrohydrolytic combustion ion chromatography analysis for halogen and sulfur determination

Combustion Ion Chromatography (CIC) is a highly suitable method for this purpose. In this inline technique, the sample undergoes pyrohydrolytic combustion and the compounds of interest are turned into gaseous form and directly absorbed by a solution. This solution is then analyzed by ion chromatography. The coupling of the digestion and the analysis instrument allows you to increase sample throughput as well as the precision and correctness of the results.

CIC is highly reliable – testing has shown a recovery rate between 99% and 102.4% (using a certified polyethylene granulate containing known quantities of chlorine, bromine, and sulfur, see TA-049 below).

CIC in quality testing of halogen-free electrical cables and wiring

Nowadays, halogen-free (also known as zero-halogen) electrical cables and wiring are increasingly used. DIN EN 62321-3-2 stipulates CIC for determining total bromine in electric and electronic products. CIC is a helpful tool for determining whether the investigated polymers comply with laws, standards, and requirements (IEC 60502-1, RoHS, etc.).

> Learn more about combustion ion chromatography

> Browse more combustion ion chromatography applications for polymers



Voltammetry: Determination of residuals and impurities

Voltammetry is a versatile technique that determines electrochemically active substances, e.g., inorganic or organic ions but also neutral organic compounds. Users benefit from a wide range of applications and at the same time from comparatively low investment and operation costs, short analysis times, and high precision and sensitivity.

Residual monomers: Styrene in polystyrene

Voltammogram of residual styrene in polystyrene determined with voltammetry

After polymerization of styrene to polystyrene, small amounts of the toxic, carcinogenic styrene may still be present in the finished product. The residual styrene content in polystyrene therefore has to be determined, and this can be easily done using voltammetry.

> Learn more about voltammetry


Metal impurities in plastics

Semiautomated voltammetry system for voltammetric trace analysis

Voltammetry is capable of determining metals in any plastic. For voltammetric analysis, the plastic samples have to be prepared in order to remove the organic components. Typically, this is done via mineralization (microwave digestion), combustion, or, alternatively, via extraction (with a mineral acid). This same procedure can of course also be applied to raw materials (read more here).

Examples of metals that can be voltammetrically determined in PET include:
  • antimony,
  • cobalt, and
  • titanium.

> Learn more about voltammetry



Pushing the limits with conductive polymers

Electrochemistry setup with potentiostat/galvanostat, electrochemical cell, sensors

In general, synthetic polymers are isolators. However, if they possess an extensive π electron system, they can (semi)conduct electricity.

The most common conducting polymer (CP) materials are polyaniline, polypyrrole as well as polythiophene and its derivatives. By incorporating doping ions or substituents, metal-like conductivities and other exceptional properties are obtained – from organic light-emitting diodes (OLEDs) to polymer solar cells or conducting polymer-based supercapacitors devices and electrodes. To investigate the electrochemical properties of the conducting polymers or of polymer electrolytes during electrodeposition, in-situ measurements such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry are required. In these leading-edge technologies, researchers all over the world rely on Metrohm Autolab instruments.

> Learn more about electrochemistry from Metrohm Autolab

Further applications and products

Titration curve for functional groups

End-group titration in polymers and resins

Today’s polymers and resins are produced with tailor-made properties. In the context of structure and property, functional groups play a decisive role, which is why the acid number and the hydroxyl value are often determined.

Read the application Read more about this on the Feedstock QC page
Preparing polymer samples for water content determination with Karl Fischer titration

Webinar: Titration Solutions for Difficult Polymer Samples

If you're interested in moisture as well as hydroxyl and acid number titration of difficult polymer samples, then you should watch this webinar.

Go to the webinar
Enzymatic degradation of bioplastics monitored with titration

Titration for monitoring enzymatic degradation of bioplastic

Bioplastics are either biobased or biodegradable or both. Polyhydroxybutyrate (PHB) is both. The polyester is a polymeric storage substance of bacteria that is enzymatically degraded at a later stage. The enzymatic PHB degradation can be effectively monitored with acid-base titration.

Read more about biosynthetic and biodegradable PHB