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Standard Test Method For Melt flow rate
2019/08/22
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Melt flow rate is a commonly used property by the manufacturers in order to compare the quality of the resins that they get from different vendors. This test not only helps to determine the variation in polymers but also a valuable indicator of the resin degradation that usually caused at the time of storage conditions or transportation.The method is described in the similar standards ASTM D1238 and ISO 1133.
These methods are in principle also applicable to thermoplastics for which the rheological behaviour is affected during the measurement by phenomena such as hydrolysis, condensation or crosslinking, but only if the effect is limited in extent and only if the repeatability and reproducibility are within an acceptable range. For materials which show significantly affected rheological behaviour during testing, these methods are not appropriate. In such cases, the use of the viscosity number in dilute solution, determined in accordance with the relevant part of ISO 1628, is recommended for characterization purposes.
ASTM 1238 is particularly useful for quality control tests on thermoplastics.This test method covers the determination of the rate of extrusion of molten thermoplastic resins using an extrusion plastometer. After a specified preheating time, resin is extruded through a die with a specified length and orifice diameter under prescribed conditions of temperature, load, and piston position in the barrel.
ISO 1133 and ASTM 1238 standard test method sounds equivalent, but there are some minor differences that different manufacturers follows to manufacture high-quality of melt flow index tester. The test which is performed from both the standards is different which provides different test results as well. Some of the differences are mentioned below:
Difference in Load Ranges:The load (weight) ranges from 1.2 kg to 21.6 kg to measure the materials with low viscosity rate and high viscosity rate. The temperature and load are determined according to the standard conditions.
Similarities:ISO 1133 and ASTM D1238 have more similarities than differences. Manufacturers consider these standards “technically equivalent,” as both detail similar standards for using an extrusion plastometer, which is commonly known as a melt indexer. Both standards present tests that measure one point on the viscosity curve under controlled conditions and both express MFI in units of grams per 10 minutes. Each standard specifies orifice length and diameter, barrel temperature and piston load ratings.
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