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FAQ | Application
Questions Answers
Which devices are suitable for sample preparation? For polymer analytics, the plastic samples must be dissolved in suitable solvents. Here, you must observe the applicable standard: For example, polyamide is often measured as per the standard ISO 307, PET as per ISO 1628-5. In all cases, a certain concentration is started, e.g. 0.5 g in 100 ml of solution. In order to precisely start this concentration, you will need a scale for analytic purposes (accuracy ± 0.1 mg) and a volumetric flask (e.g. 50 ml). The starting of the samples can be simplified if the solvent is added (metered) via a flask burette (e.g. Titronic® 500). This allows for variable sample weights, while a certain plastic quantity must be weighed for a process with volumetric flasks - you will only need normal sample bottles for this. In many cases, 100 ml screw bottles have been used here, sometimes, smaller sample bottles of 50 or 40 ml have been sufficient. Magnetic stirrers or shakers are required for the dissolution process. Some samples (e.g. PET) must be dissolved at higher temperatures (100°C - 125°C), so that at least one heatable magnetic stirrer (a heating stirrer block would be better) is required.
How many different solvents can I use with one device? For the AVS®370 and AVS®Pro, you can rinse with a max. of 2 different solvents. In general, the first solvent must be a good solvent for the sample previously measured in the viscosimeter. The second solvent is used for drying and must therefore be volatile (e.g. acetone or dichloromethane): It will rinse out the residue left behind by the first solvent and will be removed during the subsequent drying process by an air stream or a vacuum by evaporation. The second solvent does not need to be a solvent for the measured sample, if the sample residue was already be removed by the first solvent.
How can I avoid the generation of bubbles in Ubbelohde or micro Ubbelohde viscosimeters? The main cause for bubbles with Ubbelohde viscosimeters: At the end of a measurement, a small volume of the sample remains in the capillaries. When the sample is repumped into the measuring sphere, air bubbles may form from this sample residue and the air above the level vessel. With the software-controlled devices AVS®370 and AVS®Pro III, the capillary can be blown out prior to a measurement by a brief puff of air - this will prevent these bubbles from forming.
When does the measurement take place with suction or pressure, respectively? The classic standard measuring mode is the pressure operation. It is still used often today for non-critical samples (non-toxic, not aggressive). In case of a malfunction, the liquid is pressed out of the capillary pipe and then usually flows into the thermostat bath. Therefore, the suctioning operation is recommended for aggressive samples - such as polymer solutions. With this operating mode, the capillary pipe is connected to the ViscoPump via a safety bottle. In case of a malfunction, the sample will enter the safety bottle and will be detected there by a safety sensor. In addition to this safety advantage, only the suctioning operation allows the use of a disposal/cleaning system. Therefore, the work is done in a suctioning mode for all AVS®370 devices with a disposal system and for all AVS®Pro systems.