In polymer industry, while setting a new lab, the first instrument which is likely to be considered by the plastics moulders is the Melt flow index testing machine. Also known as an extrusion plastometer in more technical language, this apparatus is utilized to calculate the melt-flow rate or mass-flow rate (MFR) of pure and compounded thermoplastic resins.
With the rising competition comes the constant pressure on plastics manufacturers to comply with required quality standards. Thus, the use of polymer testing instruments has been increased to evaluate incoming material and test finished products.
The melt-flow index test calculates one point on the viscosity curve under the standard conditions. Keeping the base technique as the same, melt indexers have evolved gradually with time. Computerization and automation have reduced operator-to-operator differences, yielding highly accurate results with repeatability facility.
How does it work?
This polymer tester consists of a heated barrel and piston assembled to take a sample of resin within. A specified load (weight) is applied to the piston, and the melted polymer is extruded through a capillary die of specific dimensions. The mass of resin which is extruded within a time period of 10 minutes is defined as the MFR, expressed in units of g/10 min. It is also commonly termed as the melt index, MI, or melt-flow index, MFI.
Also, there is a strong correlation between MVR, MFI, Molecular weight and other properties of the polymer. All these factors need strong consideration when used in the extrusion process.
The main polymer property investigated is the melt viscosity of the polymer at a particular load and temperature. A thermoplastic resin with an MFR value of 50 g/10 min specifies a lower molecular weight compared to an MFR of 10 g/10 min.
Mass Flow Rate (MFR) and Quality Control
MFR is usually considered as a material-acceptance scale by polymer manufacturers and also as a path for comparing resins from different vendors. It also holds a major place in quality control. Not only can distinct results in polymerization and compounding affect MFR of incoming raw material, but it also acts as a valuable indicator of resin degradation caused due to transit or storage environment. MFR testing on daily basis post moulding or extrusion can help detect improper processing conditions.