Melt rate of flow take a look ating will be characterised because the Rodney Dangerfield of fabric test methods—it gets no respect. folks from all elements of the business downplay the worth of the take a look at or denigrate its utility outright. those that instruct business professionals on process ar fast to signifies that the soften rate of flow (MFR) worth for a fabric could be a single purpose on a curve that characterizes consistence as a operate of shear rate. Since plastics ar non-Newtonian, their consistence varies with shear rate.
The soften rate of flow take a look at moves the melted material at one rate of flow, thus one shear rate, and fails to capture the total vary of the behavior of a fabric as a operate of fixing shear rate. to form matters worse, the shear rate isn't even controlled. whereas the load on the fabric, or the shear stress, is constant throughout the course of the take a look at, the shear rate is AN output of the take a look at. The MFR itself could be a reflection of the shear rate used throughout the course of the take a look at, however it's a results of the take a look at and not a controlled input.
In fact, soften rate of flow testing could be a poor tool for gauging processability, for reasons that we'll justify thoroughly later during this series. however it had been ne'er supposed to be a mensuration of processability; this is often AN interpretation that has been applied by some within the process community. The notion that a soften rate of flow tester is a few sort of poor man’s capillary rheometer is essentially incorrect. additionally, the connection between MFR and average relative molecular mass could be a relative one. There ar a great deal of things which will skew this relationship and create interpretation tough.
For example, adding ingredients to a compound like glass fibers, impact modifiers, and sure additives will alter the MFR of a fabric while not dynamical the typical relative molecular mass of the chemical compound one bit.
