CS245178B1 - Method for determining the content of shielded amine stabilizers - Google Patents

Abstract

The invention relates to the determination of the content of stabilizers based on shielded amines in plastics by extraction of plastics with chlorinated hydrocarbons by forming a complex with iodine by spectrometrically measuring the absorption of the complex of the sample with iodine at a wavelength of 260 to 300 nm compared to a comparative iodine solution, subtracting the background value and calculating the stabilizer content according to the formula £a + b /A1 - Ap/JlO-6 from V X = --------------------------------------------- 100, n where the symbols have the meaning given in the description. The invention can be used in the chemical industry.

Description

(54) Method for determining the content of shielded amine stabilizers

The invention relates to the determination of the content of stabilizers based on shielded amines in plastics by extraction of plastics with chlorinated hydrocarbons by forming a complex with iodine by spectrometrically measuring the absorption of the complex of the sample with iodine at a wavelength of 260 to 300 nm compared to a comparative iodine solution, subtracting the background value and calculating the stabilizer content according to the formula £a + b /A ¹ - Ap/JlO ^-6 from VX = 100, where the symbols have the meaning given in the description. The invention can be used in the chemical industry.

The invention relates to a method for determining the content of shielded amine stabilizers (HALS) in plastics by spectrophotometry.

It is known that nitrogen with a free electron pair in a suitable solvent forms a complex with iodine /V. Holba: Physical and chemical properties of atoms and molecules, SPN, Bratislava 1979, p. 240/. This is a spectral band that arises from charge transfer. It has a high absorption coefficient /of the order of 10^ to 10 ⁴ mol ^-1 / allowing the determination of low contents of stabilizers in plastics.

It is also known (J. H. Karchner: The Analytical Chemistry of Sulfur and its Compounds, Part II, p. 52) that iodine forms a complex with sulfur and nitrogen in the environment of carbon tetrachloride, the absorption spectrum of which lies in the region of 260 to 300 nm with a maximum in the region of 270 nm.

The methodologies used so far require the use of an expensive device for determining so-called free radicals (Electron Paramagnetic Resonance) or the preparation of thin films of a given plastic, where the absorbance is measured in the range of 1,600 to 1,700 cm ¹ corresponding to the absorbance of “θ groups.

However, this method is not entirely suitable for determining the content of stabilizers in the side chain and increases the content by the increase in absorbance of carbonyl groups formed during thermal stress - it does not determine the basic light-stabilizing skeleton of the molecule. In the case of the presence of carbonyl groups from other components of the stabilization system /plasticizers/, this method of determination cannot be used.

The above-mentioned shortcomings are largely eliminated by the method of determining the content of stabilizers based on shielded amines in plastics by extracting the plastic with chlorinated hydrocarbons by forming a complex with iodine spectrometrically according to the invention.

The essence of the invention lies in the fact that the absorbance of the complex of the sample with iodine as well as the absorbance of the sample without iodine (background) is measured at a wavelength of 260 to 300 nm compared to a reference iodine solution and the stabilizer content is calculated according to the formula £a + b /A ¹ - Ap/^10 ^-6 from V

X = - . 100, n

in which X is the stabilizer content /%/, a, b are the coefficients of the regression line calculated by the least squares method, A ¹ is the absorbance of the sample complex with iodine, A ¹ is the absorbance of the sample without iodine /background/ z is the dilution, V is the volume of the extract /ml/ and n is the weight of the plastic sample /g/.

The advantage of the determination method according to the invention lies primarily in its simplicity, economic simplicity, as well as in the possibility of determining with high accuracy low contents of stabilizers in plastics.

The determination is interfered by all other nitrogen compounds with a free electron pair - however, their presence is quite unlikely, as well as sulfur compounds with a free electron pair. However, the presence of sulfur in the stabilization system for plastics is excluded due to its negative effects on the stabilization system.

The absorption spectra of some stabilizers are shown in the attached figures, where in Fig. 1 curves lb, 2a, 3a, 4a illustrate the absorption spectra of solutions of Tinuvin 622 /0.2 mg/ml/, Chimasorb 944 /0.008 mg/ml, Dastib 845 /0.02 mg/ml/ and Tinuvin 770 /0.008 mg/ml/ in carbon tetrachloride with the addition of iodine solution and curves la,

2b, 3b, 4b illustrate the course of the absorption spectra of solutions of Tinuvin 622 /0.4 mg/l/,

Chymosorb 944 /0.016 mg/ml/, Dastib /0.02 mg/ml/ and Tinuvin 770 /0.016 mg/ml/ in carbon tetrachloride without iodine.

In Fig. 2, curve a represents the absorption spectrum of an extract of polypropylene granulate stabilized with Dastib 845 in combination with AO 4 K in carbon tetrachloride with the addition of iodine, and curve b represents the absorption spectrum without iodine.

The examples given illustrate, but do not limit, the subject matter of the invention.

Example 1

Determination of Dastib 845 content in polyethylene film.

Devices and aids:

Varian Techtron 635 D spectrophotometer 1 pc analytical balances 1 pc Soxhlet extractor 70 ml 1 Is extraction flask 100 ml 1 pc heating nest 1 pc thermostat 1 pc Temperature-adjustable cuvette holders 2 pcs 100 ml volumetric flask 1 pc 10 ml volumetric flask 3 pcs 1 ml pipette 2 pcs

Chemicals:

carbon tetrachloride p.a.

solution of resublimed iodine /5 mg/ml/ in CCl^ standard sample Dastibu 845

Procedure:

The foil is cut into equal squares of about 2x2 mm, about 0.9 g is accurately weighed and placed in an extraction cartridge. 70 ml of carbon tetrachloride is poured into a 100 ml extraction flask. The flask is placed in a heating nest, the extraction attachment with the cartridge is placed on it and the apparatus is terminated with a condenser. Extraction is carried out for 2 hours. After cooling, the extract is quantitatively transferred to a 100 ml volumetric flask, made up to the mark with carbon tetrachloride and brought to a temperature of 20 °C.

Prepare an iodine reference solution by pipetting 1 ml of iodine solution into a 10 ml volumetric flask and making up to the mark with carbon tetrachloride. Pipette 1 ml of iodine solution into another 10 ml volumetric flask, make up to the mark with the sample solution and measure the absorbance.

280 of the obtained solution /A/ against the reference solution in tempered 1 cm cuvettes /20 °C/ at a wavelength of 280 nm for 5 minutes of tempering the solutions in a closed cuvette space. The preparation time of the measured sample solution with iodine should be about 2 minutes.

Pipette 1 ml of carbon tetrachloride into a 10 ml volumetric flask and make up to the mark with the sample solution 28 0. The absorbance of this solution against carbon tetrachloride is measured (Ap - background absorbance).

280 280

For the difference A - A, the concentration of Dastib 845 in the sample solution is calculated according to the calibration equation obtained as follows:

From the standard solution of Dastib 845 /1.10 g/ml/, calibration solutions are prepared in ten 25 ml volumetric flasks in concentrations of 4, 8, 12, 16, 20, 24, 28, 32, 36 µg/ml. From the corresponding values of the differences /A -A / of these solutions, measured in the same way as for the sample solution, the calibration dependence equation in the form o»a + b /A ²⁸⁸ - A ²⁸⁸ / is calculated by the method of least squares. In our case c /µg/ml/ -0.2816 + 42.3652 /A ²⁸⁸ - A ²⁸⁸ /.

Results from two parallel determination n g J 0.9491 A ²⁸⁰ 0.284 280 A P 0.284 A280 - A ²⁸⁰ 0.214 P c pg/ml_ 8.78 from 1 V, ml 100 x % ‘ 0.093

are summarized in the following table:

0.8204

0.238

0.238

0.188

7.68

100

0.094

Example 2

Determination of the content of Dastib - 845 in polypropylene granulate PF 411/D with 0.1% antioxidant AO - 4 k.

Devices, aids and chemicals: as in example no. 1.

Procedure: Weigh out exactly about 0.70 g of the granulated sample without additional treatment. Proceed as in Example No. 1.

The results from two parallel determinations are summarized in the following table:

n / g 0.7106 0.6977 A ²⁸⁰ 0.630 0.605 A ²⁸⁰ 0.136 0.133 P A ²⁸⁰ - A ²⁸⁰ 0.494 0.472 P c jug/ml 20.65 19.71 From 1 1 In ml 100 100 X% 0.291 0.282

Claims (1)

5 245178 SUBJECT MATTERS A method for determining the content of shaded arain-based stabilizers in plastics by chlorinated hydrocarbon extractions by forming a complex with iodine spectrometric, characterized by measuring the absorbance of the sample complex with iodine to equally diluted iodine as well as the iodine-free absorbance of the sample at 260 to 30 nm to the solvent and the stabilizer content is calculated according to the formula wherein X is the stabillator content (%), a, b is the least squares regression line coefficients, A is the iodine complex absorbance of the sample, i is the iodine-free absorbance, P z is the dilution, V is the extract volume / ml / an is the sample weight (g /). 2 drawings