Rheological Tests
Studying the deformation and flow of plastic materials
Rheological tests are essential for understanding the behavior of plastic materials when subjected to deformation or flow. These analyses provide crucial information on viscosity, elasticity, and other rheological properties, allowing for evaluating the workability of materials, optimize transformation processes, and predict the performance of finished products.
Through the application of different techniques and methodologies, rheological tests enable the study of the behavior of plastic materials under different conditions of temperature, pressure, and deformation speed.
Rheological tests performed by Plastanalisi
In our laboratory, we have state-of-the-art equipment and highly qualified personnel to perform a wide range of rheological tests, including:
Melt Flow Index Measurement: Melt Flow Index (MFR) and Melt Volume Rate (MVR) (ISO 1133)
The melt mass flow rate (MFR) is determined through viscosity measurement in the molten state. It represents the quantity of polymer, expressed in grams, that flows out of a capillary of standard dimensions under a standard weight at specific temperature and time conditions, according to ISO 1133.
The melt volume flow rate (MVR) is determined in a similar way to the MFR; in the case of the MVR, the measurement is expressed in cm³ as the quantity of polymer extruded from the standard capillary under a standard weight (ISO 1133). MFR and MVR are therefore two different ways of expressing the same property of the material; this is a characteristic connected to molecular weight, in the sense that an increase in molecular weight leads to an increase in the viscosity of the polymer and therefore a decrease in MFR or MVR.
Given the same structural characteristics, an increase in MFR-MVR improves workability; however, other properties such as impact resistance decrease.
Relative Viscosity Measurement for Polyamides
The viscosity of diluted solutions of polyamides is measured to determine the average molecular weight of the polymer. This analysis is important for evaluating the quality and properties of polyamides, which are widely used materials in various applications. The test is carried out at 25°C in a thermostatic bath.
The time it takes for the solution of known concentration of the polymer takes to travel the fixed distance is divided by the flow time of the solvent, and the result is expressed as a dimensionless number: relative viscosity. The viscosity measurement obtained is inversely proportional to the fluidity of the polymer. A high flow time of the solution corresponds to high viscosity values characteristic of polymers with high molecular weights. This measurement can be used to confirm the data provided in technical data sheets.
The relative viscosity value, when referring to particular moldings, can indicate the degradation that has occurred in the material during its processing.
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