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Analysis for Melt flow rate test results influencing factors
- Nov 29, 2017 -

Analysis for Melt flow rate test results influencing factors

 

The melt flow rate can characterize the viscous flow characteristics of the thermoplastic in the molten state. It is an important index for the molecular weight and flowability of the polymer. It has important guiding significance to ensure the quality of the thermoplastic and its products and to adjust the production process. In the plastic products and intermediate control process, the control of melt flow rate is particularly important, so the factors that affect the determination of the results have become our concern.

 

Melt flow rate(melt flow index) test method

1. Melt Flow Rate Definition: The melt flow rate refers to the mass of a thermoplastic that passes through a standard die every 10 minutes at a certain temperature and load.

 2. Test Method The test method is to cut the section at set time intervals by cutting device and finally calculate the melt mass flow rate by weighing the section quality. The quality of the measurement range: (1-100) g / 10min, with the increase of the flow rate of the cut section of the time interval will continue to shorten. The test shall meet the following conditions:

A. the length of each extruded material between 10-20mm

B.  l cutting time interval should not exceed 240s

C.  total test time should not exceed 25minl measurement results unit: g / 10min

 

Influencing Factors and Analysis of Melt Flow Rate

1. The test results of the factors

(1) elastic factor

In ISO1133 of 6.2-6.3, the operation is to avoid the impact of this factor. According to the pre-estimated flow rate, 3-8g samples were loaded into the cartridge. When charging, compaction sample is loaded with loading rod, and for the material which is sensitive to oxidative degradation, the contact with air should be avoided as much as possible and the loading process should be completed in 1min. Depending on the material flow rate, a loaded or unloaded piston is placed in the cartridge.

 

(2) During the measurement of the volumetric effect, the melt flow rate gradually increases, which indicates that the extrusion rate is related to the melt height in the barrel. The melt has an adhesive force with the barrel, which hinders the downward movement of the piston rod. To avoid this effect, splines should be cut at the same height. ISO1133 in the 3.1.3 in the piston rod should be engraved with two 30mm away from the annular fine reference mark, when the bottom of the piston head and die at a distance of 20mm, the superscript line and the mouth of the cylinder, which The two markers serve as the reference point for the measurement.

(3) Vertical furnace body to maintain vertical furnace test is to ensure that the accuracy of an important factor. Install and maintain the cartridge vertical by holding the cartridge vertical by adjusting a two-way bubble level and adjustable instrument foot mounted perpendicular to the cartridge axis. This will prevent the piston rod tends to cause excessive friction or bending under heavy load

(4) Temperature Gradient The temperature in the middle of the barrel is higher than that in the upper and lower parts. There is a certain temperature gradient, which affects the viscosity of the melt. High temperature, low viscosity, fast extrusion rate. To avoid the effect of this factor, the spline is cut at the same piston height.

In the melt flow rate test conditions, the temperature is the most critical factor, according to different test samples or test requirements to select the test temperature, and indicate the test temperature. The melt flow rate meter is constantly improving to improve temperature control.

In order to overcome the problem of heat dissipation at the bottom of the furnace, the power of the lower heater is increased, and the whole device is contained in the heater, the die is in the central position of the lower heater, which effectively ensures the temperature of the die position;

Lengthen the top of the heater, to ensure that the die from the top 40mm above the temperature uniformity;

If the upper end of the barrel temperature is low, when the high melt refers to the rapid flow of sample material, the upper part of the sample temperature too late to rise, the flow rate slowed down, the test data will be significantly lower

(5) temperature fluctuations

high temperature, high measurement results; low temperature, low measurement results. To avoid this effect, the temperature fluctuates as little as possible (± 0.2 ° C). The effect of temperature is of paramount importance, and therefore, testing is performed strictly in accordance with the temperatures specified in the standard.

(6) Test environment

The test environment did not give any specific requirements in the standard. It should be beneficial to the temperature control of the furnace under the conditions of small temperature fluctuations

7) Thermal degradation

Polymers are thermally degraded in the barrel, and in particular, the oxygen in the air accelerates the thermal degradation more rapidly, lowering the melt viscosity and thus increasing the flow rate. In order to avoid the influence of this factor, try to compact the sample in the cylinder and reduce the air. You can also add some antioxidants, or through the protection of nitrogen, so that thermal degradation can be minimized. For different polymers, the test sample should be stabilized accordingly. For example, for HDPE powders: The polymer powder should be stabilized to prevent degradation prior to analysis. Using a test balance, weigh 0.2 grams of B225 and add 99.8 grams of sample powder to a suitable container. Mix with mixer for 30 seconds

8) Sample moisture or volatile components

Samples that are hygroscopic or contain volatile components generate bubbles at high temperatures and at the same time act as a plasticizer, making the spline contain bubbles that can not be sampled and the melt flow faster. At the same time will affect the reproducibility of the measurement results. To avoid the effect of this factor, dry it before testing to remove moisture and volatile components. There are no specific standards, according to the specific requirements of the material

9) Die size Die diameter:

2.095 ± 0.005mm, height 8.000 ± 0.025mm. Under standard load, if die size is not correct, it will lead to change of shear stress, which will affect the test results. The use of plug gauge to measure the die is qualified, that gauge can pass one end of 2.090mm, 2.l00mm one end of the mold can not be used

10) barrel, piston and die surface roughness barrel, piston and die surface roughness of less than 0.25μm. The piston rod, the inner wall of the barrel and the die wall roughness greater than 0.25μm, the piston rod under the action of the load, the downward resistance of the movement increases; and use a period of time, the piston rod surface and the guide sleeve will deposit a layer of the inner wall Coke, if not cleaned in time, will lead to tight fit between the piston rod and the guide sleeve, resulting in greater friction; die cavity wall deposition of cokes; will affect the test results. Therefore, after each test, the gauze must be wiped clean with standard die, piston and barrel, the die hole diameter with a suitable diameter of the needle after the hot top of the wipe clean

 

 the melt flow rate test points

 1. Familiar with and correctly set the test parameters

2 barrel, piston rod, die to be cleaned

The melt flow rate meter is thermostatted at the stated temperature

4. Melt flow rate meter adjustment level

5. In strict accordance with the operation instructions, to ensure that the test parameters are implemented according to regulations

6. In order to get more accurate test results, should be strictly in accordance with the provisions of the standard test, regular testing with standard samples, and timely detection of problems and solve the test