Moisture content determination of PET
Determining moisture content in PET granulate. An explanation of which analysis technique is most suitable, but also why.
Polyethylene terephthalate (PET) is widely known from the PET bottle. It is a thermoplastic material with many other applications besides the PET bottle. Although it may sound contradictory, PET is sensitive to water, especially during processing at high temperatures and pressures. When the material contains water (> 0.02 %) and is subsequently heated, the water can cause the molecular chains to break down via hydrolysis. This can have a drastic effect on the quality of the material.
For many companies that process PET, it is therefore extremely important to dry PET as much as possible before processing. But how can one check whether this drying process has taken place correctly?
This can be done in two ways, following the weight loss of the material during drying or via Karl Fischer titration.
Monitoring the weight loss of the material during drying seems to be the most obvious method. However, in order to be able to indicate small amounts of water in ppm range (parts per million), one must have a very accurate balance, such as a thermogravimetric analysis (TGA). With this analysis technique, it must be taken into account that not only the decrease in weight of water is monitored, but the decrease of all volatile components (such as used solvents or gaseous degradation products). This can lead to incorrect assumptions about the volatile component present when a small weight decrease is registered.
The most suitable technique for determining the amount of water is by Karl Fischer titration. The PET granulate is heated in a glass vial, so that water is released and blown into a titration liquid by means of a dry nitrogen flow. The liquid only reacts with water and the amount of water can be accurately determined on a ppm scale. An additional advantage is that the granulate can be sampled at various locations or after various time intervals in hermetically sealed bottles in order to determine the course of the drying process.
PTG /e has a wide range of analysis techniques and can therefore choose the most suitable technique or choose to combine techniques.
Interested in the various techniques and what they can be used for?
Download our overview of analysis equipment and techniques.
One of our customers was using a certain grade of plastic for injection molding of their top-selling product. However, they had recently switched supplier and wanted to make sure that the material they ordered was exactly the same as they were used to. Therefore they sent us a sample of the product and asked if we could identify the material.
When identifying an organic material, a technique we use regularly is Infrared (IR) spectroscopy. With IR, the sample is irradiated with a beam of infrared light at different wavelengths. Functional groups interact with the infrared light, creating a unique signal. Combining all these signals yields a spectrum that is characteristic for that specific material, comparable to a fingerprint.
We recorded an initial IR spectrum and it was immediately evident that the sample was some kind of Nylon. However, there are several variations of Nylon that exhibit very similar IR spectra. Therefore, we made a detailed comparison of the IR spectra of the sample (yellow) to several different kinds of Nylon from our database, as shown in the figure below. Based on small differences of characteristic peaks, indicated with the colored arrows, we were able to exclude Nylon 6/6 (blue), Nylon 6/10 (pink) and Nylon 6/12 (green) as possible candidates. The best match was obtained with Nylon 6 (red).
To confirm our IR hit we used Differential Scanning Calorimetry (DSC) and determined the melting point (Tm) to be around 220°C. To finalize the material identification, we performed thermogravimetric analysis (TGA) to determine whether the Nylon contained any filler. The sample was heated to 900°C to remove the organic material, whilst recording the weight loss in weight percentage (wt%). At 900 °C, the residue was 24 wt%, which can be attributed to inorganic filler material (like glass fiber, which is commonly used to reinforce Nylon 6).
So, by a smart selection of three different techniques and with the help of our extensive database, we were able to determine quickly that the material was indeed Nylon 6 containing an inorganic filler. With this crucial information, the customer was fully reassured and could continue production without interruption.
Interested in our IR analysis? Please contact us via email@example.com and we will be happy to discuss the possibilities.
With Easter upon us, many of us enjoy eating the associated chocolate eggs. It’s often easy to overlook the numerous steps between cacao harvesting, transporting, processing, and ultimately enjoying the taste of the final chocolate confection. As PTG/e, we’ve provided support in one of those many steps, related to the manufacturing process of chocolate products.
One of our customers approached us for viscosity measurements on raw cacao, an intermediate product in the chocolate production process. The viscosity data was required for the pump design needed to transport the cacao through pipes from one vessel to another. To correctly size such a pump, it is important to know what the viscosity of the material is, and particularly what the range of viscosities could be at different pumping speeds and temperatures.
Therefore, we used our TA Instruments DHR-2 rheometer, equipped with a Peltier heating system, with a 60 mm parallel plate configuration. We measured the viscosity of the raw cacao over a wide range of shear rates (simulating different pumping speeds), and at different temperatures as well. An example of such a flow sweep measurement performed at 90 °C is shown in the plot below.
While at low shear rates the raw cacao has a more or less constant viscosity, it can clearly be seen that the viscosity decreases dramatically at increased shear rates. This kind of material behavior is usually referred to as ‘shear thinning’, where the viscosity decreases as the flow increases and a certain yield stress is overcome. You could compare this behavior to peanut butter, which does not flow if you tilt the jar upside down, but spreads easily once you start smearing it on a sandwich. Such information on the shear thinning behavior of any material can be very useful in process design, because less energy is needed to pump a lower viscous material of course.
With all the viscosity data we collected under various circumstances, our customer could complete his pump design and thus satisfy their customer needs.
Besides raw cacao, we have had the pleasure of measuring a wide variety of foodstuffs, such as fruit juices, bread paste and pesto. Similarly, we have had the (arguable) pleasure of measuring cattle feed ingredients as well as filtered sewer sludge. Most importantly in all cases, we were able to provide our customers with useful viscosity data in order to aid in their process design.
Interested in viscosity measurements of your fluids? Please contact us at firstname.lastname@example.org, we will be glad to discuss the possibilities.