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KhamrokulovMakhmud Gafurdjanovich, PhD, the faculty of Management and Professional Education Tashkent Chemical Technological Institute E-mail: khamrakulovtkti@mail.ru Sarimsakov Abdushukur, Doctor of Technical Sciences, Professor Institute of chemistry and physics of polymers of the Academy of sciences of the Republic of Uzbekistan
INFLUENCE OF THE CONTENT OF HARMFUL SUBSTANCES TO THE FOOD SAFETY OF POLYMER PACKAGES
Abstract. The quality of food products is largely dependent on their packaging. Packaging should protect food from external influences as much as possible and not negatively affect the quality of products. At the same time, more and more attention is being paid to the elements of plastic packaging, namely the content of substances harmful to health, such as monomers, harmful low molecular weight compounds, plasticizers, dyes, acids, etc., which are capable of transferring (migrating) from packaging to food products.
The purpose of the study: the aim of this work is to ensure food safety of polymer packaging by determining acetaldehyde by gas chromatography.
Keywords: polyethylene terephthalate, acetaldehyde, thermal degradation, PET bottles, concentration limits, gas chromatography.
Currently, the negative effects on the human body of food products in polymer packaging, in particular from PET, have been unequivocally proven. In developed countries, there is a tendency to replace PET bottles with disposable thin-walled glass containers.
However, in many countries, plastic packaging made from polymers, including PET, is still widely used for food packaging.
The migration of acetaldehyde from PET bottles, despite the potential carcinogenic effect of the substance, can hardly be hazardous to health, since the amount of acetaldehyde migrating from the package is several orders of magnitude less than what is already found in natural foods. However, in drinks that have the least taste of their own, even small proportions of acetaldehyde lead to tangible taste changes. Lowering the level of acetaldehyde migration to val-
ues below the threshold of perception is technically possible, however - apparently, for cost reasons - not all packaging manufacturers go for it. [eleven].
No less important for packaging materials are their barrier properties, in particular, sorption and desorption of acetaldehyde. This effect is associated with the production of containers, the consequence of which is the release of acetaldehyde at high temperatures and its subsequent sorption upon cooling.
Acetaldehyde is a substance released in small quantities during the processing of PET. Acetaldehyde is capable of diffusion from the walls of bottles and affects the taste of drinks, so it is necessary to control its release during the production and processing of PET and the production of preforms. Acetaldehyde is released during the polymerization of PET in the melt and passes into the structure of PET during cooling and granulation. Acetaldehyde is
partially liberated during solid phase polymerization, and up to 1.5 ppm (millionths) of acetaldehyde can remain in the starting granules. The same amount of acetaldehyde is released during PET blowing, and more acetaldehyde is released during injection [2, 100]. The formation of acetaldehyde is not associated with any noticeable loss of internal viscosity, but is a consequence of the transition of acetaldehyde from a solid solution to a gaseous and / or liquid state at high temperatures. This means that the amount of acetaldehyde released can be reduced by choosing the optimal casting conditions, that is, minimizing the temperature, that is, choosing the optimal PET processing mode. Therefore, it is necessary to ensure:
- low cylinder temperature;
- minimize screw speed, back pressure, injection speed - all factors leading to additional dissipative heat generation;
- minimize the melting time (the shorter the time, the better), since the more PET is at elevated temperature, the more acetaldehyde is released [3, 31].
Thus, during thermal degradation, it is possible to release very harmful substances that migrate into the liquid poured into the bottle and poison the drinkers and working people living nearby in the production of preforms. Permissible concentrations of harmful substances released during the production and processing of PET are presented in (table 1).
Table 1.- Permissible concentrations of harmful substances released during the processing of polyethylene terephthalate [4]
Harmful substance according to GOST 12.3.030-83 Migration to model environments in finished products, mg/l In the air of the working area, mg/m3 In the atmospheric air of populated areas (maximum one-time), mg/m3 In the atmospheric air of populated areas (daily average), mg/m3
Acetaldehyde 0.2 5 0.01 0.01
Dimethyl terephthalate 0.5 0.1 0.05 0.01
Terephthalic acid — 0.1 0.01 0.001
Acetic acid — 5 0.2 0.06
Carbon oxide - 20 5 3
Table 2.- Sanitary rules norms and hygienic standards of packaging and closures [5]
I. Polymer materials and plastics basec on them **
Name of material Controlled Allowable mi- MPC, in Hazard MPC mg/m3 Hazard
indicators gration, mg/l water, mg/l Class in air Class
Acetaldehyde — 0.200 4 0.010 3
Ethylene glycol - 1.000 3 1.000 —
Terephthalic Acid- Dimethyl terephthalate — 1.500 4 0.010 —
Based Polyethyl- Formaldehyde 0.100 — 2 0.003 2
ene Terephthalate Alcohols:
and Copolymers methyl 0.200 — 2 0.500
butyl 0.500 — 2 0.100 3
isobutyl 0.500 — 2 0.100 4
Acetone 0.100 — 3 0.350 4
The catalyst for thermal degradation of PET is radation, PET must be dried to a moisture content water. It is proved that, in order to avoid thermal deg- of less than 0.003-0.004 wt.%. Such a low moisture
content is unattainable with conventional polymer drying techniques. For this, it is necessary to have special, expensive units and installations for the deep drying of PET granules.
It is known that the technology for the production of PET containers is associated with heating of PET granules and molds, while acetaldehyde is released from under-dried PET granules, which, when solidified, remains locked in microcracks and voids in the polymer. Over time, acetaldehyde is released into the environment and dissolved in food stored in this container. The consequence of this is an increase in the toxicity of the product. This necessitates periodic analytical monitoring of the acetaldehyde content in the PET container. It is no coincidence that GOST 51695 Polyethylene terephthalate. General specifications ", which sets out the method for gas chromatographic determination of acetaldehyde in polyethylene terephthalate (PET). The mass fraction of acetaldehyde in PET according to GOST should not exceed 2 ppm. [6].
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However, a critical examination of the method reveals a number of inaccuracies, not specific, but general provisions that suggest multivariance and irreproducibility of the results of the analysis, there are no clear indications of the implementation of the definitions. In particular, according to the GOST methodology, sampling and injection is carried out using an automatic metering device or syringe. These two methods of sampling and introducing samples are put on an equal footing and, in all likelihood, assume the equality of results. However, knowing the principle of operation and the arrangement of both devices, the opposite can be assumed. According to the GOST method, sampling of sample vapors preheated to 80 °C is carried out. If the experimenter uses a syringe, then in this case condensation of sample vapors on the cold walls of the syringe is possible, which is not observed when using an equilibrium steam dispenser, since the pipelines along which the steam sample is moving are heated above the boiling point of acetaldehyde.
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Figure 1. Chromatogram of acetaldehyde at 80 °C
Thus, the condition for the equality of such a parameter as temperature is not met, not to mention the fact that these are completely different methods of sampling and sampling, characterized by different errors, and equivalent results cannot be obtained.
The work was carried out in a gas chromatograph in accordance with the conditions of the methodology under consideration by GOST. Since the developers of the technique do not offer a specific metering device, in our experimental work we used an automatic dispenser of equilibrium acetaldehyde vapor.
Before comparing the results of analyzes with two variants of sample injection, we conducted an experiment to eliminate errors associated with the preparation and temperature control of the sample at 80 °C (Fig. 1.).
For the experiment, a solution of acetaldehyde was prepared so that its vapor concentration did not change over time. The chromatographic conditions in the experiment corresponded to the GOST methodology. Sampling and injection were carried out using a syringe, and without pre-heating the sample. The sample thus prepared was repeatedly analyzed. To determine the magnitude of the random error, the mean square deviations (S) were calculated from the retention time, height and peak area. S by retention time, which was 0.22%, by peak height - 2.35%, by peak area - 2.36%. Thus, in this experiment, we excluded errors associated with sample preparation and temperature control of samples, which are part of the total error. A random error consisted only of the error of the experimenter and the device. Next, we changed the experimental conditions and conducted it with preliminary heating of the sample at 80 °C. In this experiment, sampling and injection were carried out with a syringe: a) without heating, b) with preliminary heating of the syringe. According to the results of the experiment, the mean square deviation was calculated. When using a cold syringe, S was 5.37% in peak height and 5.35% in peak area. When using a heated syringe, S was 4.39% in peak height and 4.10% in peak area. On average, according
to the results of the experiment, thermostating of the sample increased the value of the random error by 1.5 times. The greater scatter of the analysis results is associated, in our opinion, with the instability of the thermostat, as well as with the condensation of the sample on the colder walls of the vessel and the nodes of the syringe, which also leads to a change in the composition of the gaseous phase. Preheating the syringe leads to some improvement in the convergence of the analysis results, which, in our opinion, indicates a decrease in the contribution of the condensation factor of the sample on the walls of the syringe (the syringe was also thermostated at 80 °C). The magnitude of the random error consisted of the errors of the experimenter, instrument, and thermostating of the sample [7, 30-33].
In the next experiment, sampling and injection were carried out using an equilibrium steam dispenser. The root mean square deviation was calculated from the height and peak area. S by peak height, which amounted to 3.54%, by peak area - 3.53%. Comparing these data with the results obtained in the previous experiment, we can conclude that the random error decreased by an average of 1.5 times, which is very obvious if we take into account that when using an equilibrium steam meter, condensation of the sample does not occur on cold walls, since pipelines along which the steam sample is moving are warming up.
Thus, the results of the studies showed that these methods of sampling are unequal, and this, in our opinion, is one of the oversights of the GOST methodology. The methodology as amended by the aforementioned GOST cannot provide reliable analytical control over the content of acetaldehyde as a toxicant. In addition, the GOST methodology contains a number of other inaccurate and nonspecific guidelines for analysis. So, in the technique two methods of sample preparation are equalized: "grinding the sample in a special mill or manually using any cutting tool." At this stage, an error may occur, associated in particular with a different de-
gree of grinding of the material. In addition, the use of the mill as a more "aggressive" way of influencing the sample can lead to various mechanochemical side processes caused by the action of shear deformations. This can also affect the results of gas chromatographic analysis, since according to GOST, mechanical and manual grinding of the samples are placed in one row, and it is understood that they are equivalent [8, 34-36].
In our opinion, the process of grinding the sample must be carried out in a liquid nitrogen environment, eliminating the evaporation of acetaldehyde.
The approach to the number ofparallel measurements is unclear; according to the methodology, it is enough to draw two parallels. Based on such data, it is impossible to obtain the necessary metrological characteristics of the results and conduct competent statistical processing (to evaluate reproducibility and correctness).
The presence of such oversights made by the developers of the methodology reduces its practical value, and requires additional review and introduction of appropriate adjustments to the existing methodology.
References:
1. Elmar Schwartzr Mullerdi (VHC) Harald Brugger - Aspects of the impact of beverage packaging on health. Environmental Policy Information, - Vienna, AK Österreich. 2011.
2. Khamrakulov M., Negmatova M.- Research of the effect of different factors on the allocation of acetaldehyde from polyethylene polyethylene terephthalate. The 4th International youth conference "Perspectives of science and education" (December 10, 2018) SLOVO \ WORD, New York, USA. 2018.
3. Pogodina Elena - PET: subtleties of processing. Plastics Journal № 10 (104) 2011.
4. GOST 12.3.030-83. SSBT. Processing of plastics. Safety requirements.
5. Resolution of the Cabinet of Ministers of the Republic of Uzbekistan dated July 7, 2017.- No. 476 On approval of the General Technical Regulation on the safety of packaging in contact with food.
6. GOST R51695-2000 - Polyethylene terephthalate: General specifications.
7. Sayfullaeva Z. S., Khamrakulov M. G., Khasanova D. Yu., Askarov I. R. Identification examination of polymer products.- Standart scientific and technical journal "Uzstandard" - No. 1. 2019.- P. 30-33.
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