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PA6 test methods

This article is going to elaborate on the following topics:

Determination of extractable content in Polyamide-6 by the gravimetric method
Determination of chips moisture content
Determination of Polyamide-6 relative viscosity

Determination of extractable content in Polyamide-6 by the gravimetric method

The essence of the method is extraction of low molecular compounds with boiling water. Extractables content  is determined by means of weighing dried chips before and after  extraction. 
Extractables (low molecular compounds) are monomer (caprolactam) and oligomer (cyclic dimer, trimer etc.) soluble  in water.

Sample preparation and analysis fulfillment

For analysis two simultaneous samples are selected. The weighed sample 4.5 grams with accuracy 0.00001 gram is put into round-bottom flask 250 ml, 200 ml of water is added and magnet agitator is used. Filled flasks are put at the flask heater and connected to the return cooler, joined with the circulation cooler   (t =10-15 0C). Mixing speed of magnetic agitators is set by means of the last left switch. Under each plate the heating temperature regulator is installed. It’s necessary to pay attention to air tightness of the unit.
The samples are extracted within 5 hours and then cooled. After that with the help of a vacuum flask, water jet and funnel with a porous filter the sample is separated from extraction water. The sample shall be flushed with distilled water several times, then put into a glass and dried at the drying cabinet at T = 125 0? within 3 hours. Then the sample is cooled at an exicator within 30-60 minutes and weighed on the analytical balance.
Extractables content is determined according to the following formula:
 
 
                                    m1   -    m2
%  Extractables = ---------------------- ? 100%
                                          m1
 
 
m1- sample weight before extraction, g
 
m2 - sample weight after extraction, g
 
 

Determination of chips moisture content

Moisture content is determined by the method of Coulonometric titration at Karl-   Fischer titrator   “AQUA 40.00” with a heating unit.
Applied chemical agent: HYDRANAL-Coulomat AG manufactured by Riedel-
de Ha,n  (Germany).
Test parameters:
Heating unit temperature: 1900?
Sample weight:      50-80 mg
Time of test duration:      15 min.
The measurement procedure conforms to the device operation manual.

Determination of Polyamide-6 relative viscosity

Relative viscosity is determined at the automatic viscosimeter AVS-361 by means of WINVISCO program (manufacturer SCHOTT, Germany).

Tests parameters:
Before test performance wet chips shall be dried at the vacuum drying cabinet at  90 ??   within 1-2 hours.
Solvent – ?2S?4 , concentration 95.6%±0.2%
Measurement temperature -  20 ??
Polymer solution concentration in water – 0.01 g/ml
Temperature of polymer dissolving in sulfuric  acid - 60 ??
Time of dissolving – 3-4 hours (up to complete dissolving)
 
Polymer solution is prepared with help of the automatic burette “TITRONIC” connected to electronic analytic “SARTORIUS”. Dissolving is carried out at the thermal unit  “VARIOMAG”. The procedure of polymer solution preparation and relative viscosity  measurement conforms to the device operation manual.
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