I. significance of polyester melt viscosity measurement
Polyester processing such as spinning and injection molding is carried out in the molten state, melt viscosity is one of the most important parameters in its rheological properties, and is also the key to ensure product quality.
In the spinning process, if the viscosity of polyester melt is low, the spinneret is easy to stick to the spinneret, which will lead to a series of problems such as reduced success rate of switching, decreased strength of finished silk and poor dyeing performance.The melt viscosity is high, easy to cause melt rupture, as well as wool broken head increase, elongation decline, improve the irregularity, color absorption performance become poor and other consequences.Therefore, accurate measurement of melt viscosity is very important for polyester spinning and injection molding.
In the traditional viscosity test of polymer melts, capillary rheometer is widely used. Its advantage lies in its simple structure, the ability to adjust the melt rate and temperature in a wide range, and the rheological physical quantity is very close to the processing conditions.As a product that can also be used for polymer melt viscosity test, melt index meter has the advantages of cheap price and simple test method, which can better meet the needs of small and medium-sized enterprises for polyester melt viscosity test.Reply "check" to see more related articles
The testing principle of melt index instrument
The testing principle of the melt index instrument is to make the measured polymer (hereinafter referred to as "the measured object") reach the melting state through a high temperature heating furnace under the specified temperature conditions, and to conduct extrusion test through a hole with a certain diameter under the specified load gravity, and to measure the viscosity of the polymer by melt flow rate.Generally, melt flow velocity is inversely proportional to viscosity, and the flow resistance of materials with high viscosity is greater. Under the same condition, the flow velocity of materials with low viscosity is slower than that of materials with low viscosity, which is the basic basis for the determination of melt index meter.
It is worth mentioning that in daily work and research, melt flow rate (MFR) is usually used to represent the fluidity, viscosity and other physical properties of polymer in molten state.
Basic test method of melt index instrument
1. A method
Method A is A very simple method, and the calculation formula is as follows:
MFR (g/10min) = M 600/T
Where, T= collection time (s), M= mass of collected material (g).
2. The B method
Different from method A, which measures the mass of extruded material according to time, method B is based on the volume displacement of polymer melt to measure its flow characteristics. This method does not need to cut and weigh the extruded material.The calculation formula is as follows:
MVR rho = MFR = PI R L rho 600/ T
Where R= piston radius (cm),
T= time (s) required for extrusion of polymer with L length,
L= denoted length (mm),
Rho = apparent density of the melt (g/cm).
3. A/B method
The A/B method is the set of A and B methods for testing the same material -- with the melt flow rate obtained from method A, measuring the apparent density of the melt (rho) on the condition that the same result can be obtained using method B.The value of this test is that the effective apparent density of the melt can be obtained, and this result can be used to obtain the test results of method A through the calculation formula of method B (without manual cutting or weight) (the operator must use manual cutting or weight).
The calculation formula is as follows:
MFR (B method) = PI R L rho 600/tB
MFR(method A) = M 600/tA
Where R= piston radius (cm),
TB = time (s) required for method B to move L,
TA = the interval time (s) of each cutting material in method A,
L= length (mm) indicated by method B,
M= mass of materials collected by method A within tA time (g),
Rho equals MtB(apparent density, g/cm).
The Dynisco analyzer recommends the average of at least five values derived from the A/B method as the test result.The average apparent density of the melt obtained by this method can be used for method B, and then the relevant values of method A can be obtained without cutting (the flow rate of method B must be the same as that of method A).It is called the apparent density of a melt because it is actually a correlation coefficient.If, in the A/B test, there is no leakage between the cartridge and the piston, no air bubbles in the extrusion expansion, and no other secondary influence factors occur, the test results may be used to assess the true melt density.