Influence of Test Temperature on Polyester Chips Viscosity
Abstract: Testing result indicates that polyester chips viscosity are very sensitive to the test temperature. So it requires to control the temperature precision range strictly . Therefore, an ideal constant temperature water bath is necessary to get the reliable result of the viscosity.
Polyester resin in the field of polymer occupy a leading position, it is not only high strength, good heat resistance, non-toxic, and good insulation. By different processing means, it can be made in the film, in the audio and video tapes, lighting film, food packaging, for high-strength composite film, and can be processed into different types of beverage bottles and electrical parts. Polyester chips are also important raw materials for the chemical fiber industry. Spinning polyester chips must maintain a high purity. So the inspection department to each batch of products to conduct a series of performance indicators to ensure the quality of the batch. The viscosity index indirectly represents the size of the molecular weight, which directly affects the quality of the finished polyester yarn, and the test temperature is particularly sensitive to the viscosity, so the required test temperature range must be strictly controlled.
Polyester chips are specified in the relevant standard method by dissolving one or two mixed solvents at a certain temperature to a certain concentration and then measuring the solvent at a specified test temperature by an Ubbelohde viscometer (having a defined capillary diameter) And the time the solution flows, converted into relative viscosity and intrinsic viscosity. ASTMD2857 specified test temperature accuracy of ± 0.01 ~ 0.02 ℃, ISO12228 specified test temperature accuracy of ± 0.05 ℃, China is the national standard in principle to the ISO closer to the set, also set to ± 0.05 ℃
Select the Taiwan polyester chips (contract, the intrinsic viscosity IV0.645 ± 0.015) set the temperature of the thermostat different temperature for the test to observe the changes in viscosity:
1. Test conditions
Solvent: mixed solvent, weight ratio of phenol: tetrachloroethane = 3: 2
Solution concentration: 0.5%
Test temperature: 25.00 ~ 25.08 ℃
2. Accuracy measurement at different temperatures
Table 1 Effect of temperature on the determination of PET slice adhesion
The same time as
Test temperature ° C Relative viscosity Viscosity
25.00 1.363 0.645
25.01 1.363 0.645
25.02 1.360 0.641
25.05 1.355 0.634
25.08 1.350 0.625
From the data of Table 1, the intrinsic viscosity value decreases with increasing temperature, the temperature rises by 0.01 ℃ Viscosity is not affected; the temperature rises 0.02 ℃, the intrinsic viscosity decreases 0.004; when the temperature rises to 0.05 ℃, the intrinsic viscosity decreases 0.011; To 0.08 ℃, the intrinsic viscosity dropped to 0.021, has been outside the scope of the contract. This shows that the temperature parameters directly affect the size of the viscosity, it is necessary to strictly control the temperature accuracy range, the determination of the results can be a reliable guarantee.
3. Need to pay attention to the problem
Determination of viscosity method is not complicated, but in order to ensure the correctness of the test results must be strictly to the various test links, try to avoid errors. This is mainly: ① weighing; ② solution preparation; ③ viscometer cleaning; ④ viscosity determination of the viscosity of the vertical degree; ⑤ visual line when the level of the situation; ⑥ timer press speed; ⑦ constant temperature water bath temperature The
Among them, the constant temperature water bath temperature control accuracy is determined by the thermostat, and the visual line of the error is also determined by the thermostat, especially those observation window for the arc when the marking line blurred, the greater the error. In addition, it is almost entirely determined by the quality of the inspectors. Therefore, the configuration of an ideal precision constant temperature water bath is a guarantee of an important device for viscosity determination.
The same time as
At present, the domestic production of the thermostat groove accuracy is rarely higher than ± 0.05 ℃, roughly, seems to meet some of the international standards and the implementation of the new national standard, but in fact, due to uneven temperature distribution throughout the tank, With the temperature control temperature fluctuations, the overall control accuracy is clearly inferior to 0.05 ℃, especially in the factory application, a number of viscometer placed in different locations, this phenomenon even more directly affect the test data, while , The thermostatic bath with the refrigeration system is far from being extended, and the viscosity test also brings a lot of trouble (generally, there is no cooling system of the thermostat, only when the room temperature is lower than the test temperature of 5 ℃, to ensure that the temperature control Precision).
What is the true 0.01 ° C temperature control accuracy?
The same time as after adjusting the temperature of the thermostat, from today to tomorrow, the temperature changes, not more than 0.01 ℃, and the temperature inside the thermostat tank temperature distribution is poor, not more than 0.01 ℃.
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