Determination of Brook field Viscosity on Melted Polymer

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Determination of Brook field Viscosity on Melted Polymer


Scope and Application:


This is the specification method for determining the brookfield  viscosity of Neoprene.
The technique and procedure incorporated here can be applied to any material viscosity in the range of 100,000 to 2,000,000 centipoises.

 Principle:

A small cylinder is rotated at a fixed speed in the test fluid.The force required to overcome the viscosity causes a deflection of a pointer on a spring.The viscosity is read from a dial.

Interference:

Oil on the surface or incorporated in the sample lubricates the spindle and gives low and erratic results.Excess moisture in the sample will also give lower and erratic results.


Sensitivity, Precision, Accuracy:

A  variation in temperature of 1°C makes a difference of 50,000 centipoise in the results;accurate temperature control must therefore be maintained.

The precision at the 95% confidence limits is 85000 at the 1000000 cp level for the average of three readings on one sample.


Apparatus:


1. Synchro lectric Viscometer, Brookfield, RVF model with speed range of 2- 20rpm, mounted on stand with gear and knob for making fine adjustment.
2.Number 7 Spindle.
3. Circulating water bath capable of maintaining a temperature of 50° ± 0.5  C
Thermometer range 25° -75°C
Steel Stirring rod
Flashlight for adjusting spindle depth.

 Procedure:

1. Adjust the temperature of the water in the bath to 50° ± 0.5  C

2.Fill the container whose width is approximately 75 cm to the shoulder with sample and place in the appropriaate circulating water bath, making certain that the water level in the bath is at least 1 cm above the sample level in the jar.

3.Maintain the bath temperature at 50° ± 0.5 C

4.when the sample has been in the bath for two hours remove the lid from the jar and stir the sample slowly and evenly with a stainless steel stirring rod, making certain not to trap air in the sample.

5.Remove the stirring rod and insert a thermometer in the sample so that the bulb of the thermometer is approx 1 cm from the bottom of the jar. The thermometer mist no be closer than 1 cm to the sides of the  jar.

6.Twist the thermometer very slowly (2-3 rpm) until the mercury column is steady.

7.If the temperature is within the specified range remove the thermometer and proceed to run the viscosity in the following manner.

8.Place the No.7 Spindle in viscometer( The spindle must be clean, dry and preheated to the test temperature, 50 degree Celsius.)

9. Adjust the speed control knob to 2 rpm.

10.Center the viscometer over the sample and lower the spindle into the  sample very slowly. Steady the spindle with one hand so that pressure will be applied evenly to prevent damage to the viscometer.


11. Train the flashlight on the top of the sample so the immersion mark on the spindle can be seen clearly.

12.Continue to lower the spindle until the surface so the immersion mark on the spindle can be seen clearly.

13.Wait for the sample to level out as there will be slight indentation made by the spindle.

14. It may be necessary to raise the spindle slightly to prevent covering the immersion mark. It is essential to watch this part of the operation closely and under no circumstance permit the immersion mark to be covered completely.

15.Should the spindle be immersed below the mark do not attempt to continue the test, but remove the spindle and the test over using a clean spindle.

16. When the sample surface has leveled off, adjust the spindle so that the sample covers approx half of the immersion mark.

17. Start the viscometer in the normal manner.

18. After 8 revolution s(4 min) without stopping the viscometer take a reading on the outside scale.

19. Without making any adjustment after 8 additional revolutions take a second reading.

20. If the two reading thus taken agree with in one scale division record the average of the two reaction.

21.If the two readings do not agree, check the slippage reading, viscometer level, depth of spindle and position of the spindle.

22.If all conditions are satisfactory take additional readings as above until two consecutive agree within one scale division.


Calculation:

Brookfield viscosity centipoises = Scale reading Observed X 20,000

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