ISO 1133-2 Testing Moisture-Sensitive and Quick Degrading Plastics
Special precautions must be taken for tests performed on these materials (for example, PBT, PET, or PA). First, these materials must be sufficiently dried and must be dry when poured into the extrusion barrel. An optional nitrogen blanket at the extrusion barrel prevents direct contact by the material with the ambient air. The test is run in defined time sequences and they are recorded by the software. The extrusion plastometers must meet specific conditions for this purpose in terms of spatial and temporal temperature distribution in the extrusion barrel.
Correlation of IV measurements for the MFR value for linear PET
The molecular weight of polyethylene terephthalate (PET) is usually described in terms of intrinsic viscosity. This is the IV value in dl/g. The longer the polymer chains, the higher this characteristic value. This makes it possible to demonstrate molecular chains and how they can occur when moisture that is too high during the melting process.
The disadvantages of this method are that recyclers of PET in particular, are often not equipped to handle corrosive or toxic solvents. Furthermore, the fact that the test lasts a long time poses a practical problem. Therefore, measurement of the melt mass flow rate (MFR) has been used since the early 1990s in this area as well.
Using testXpert III to control the Mflow and Aflow extrusion plastometers makes it possible to determine the correlation between IV values and the MFR by means of premeasurements, which can then be applied to other measurements.
Videos showing the determination of MFR and MVR to ISO 1133
Next Generation Xflows: Aflow Extrusion Plastometer
Test/test equipment requirements
The flow property of a thermoplastic material is characterize by its melt flow index. Depending on the test method, either the mass per unit time (MFR measurement) or volume per unit time (MVR measurement) is determined. ZwickRoell offers various melt flow index testers for the determination of melt flow rates. Our portfolio includes the manually operated, compact Cflow instrument, the modular Mflow with traditional weights, and the Aflow, a fully automated all around testing solution with electromechanical force control. The latter was developed for particularly high specimen volumes and is designed for the determination of volume and mass flow rates according to methods A, B, C and D. The instruments support all common standards and methods, including ISO 1133, ASTM D1238 and ASTM D3364,
One of the key functions of the Mflow and Aflow is the detection of possible air pockets in the plastic melted mass, which temporarily increase the piston speed and lead to incorrect flow rates. With high-resolution travel and time measurement of the ZwickRoell instruments, changes in piston speed are automatically detected. This gives you the option to exclude certain measuring sections to avoid errors in the flow rate calculation. The user is also supported by the APC (adaptive process control) function, which measures the speed of the piston shortly before the actual measurement begins. Based on this data, the system then selects the best control options—travel distance or time based control—and thus sets the optimal measuring interval for the MVR value to be expected.
The intuitive and workflow oriented touch operation allows the user to easily switch between the instrument and the PC. The melting process and the material behavior during the measurement can be observed live directly on the instrument and through the ZwickRoell testing software.
