CN113125310A

CN113125310A - Method for monitoring permeation behavior of photoinitiator-907 in plastic package

Info

Publication number: CN113125310A
Application number: CN202110415634.3A
Authority: CN
Inventors: 蔡荟梅; 彭雲; 侯如燕; 程燕
Original assignee: Anhui Agricultural University AHAU
Current assignee: Anhui Agricultural University AHAU
Priority date: 2021-04-19
Filing date: 2021-04-19
Publication date: 2021-07-16
Anticipated expiration: 2041-04-19
Also published as: CN113125310B

Abstract

The invention discloses a method for monitoring photoinitiator permeation behavior in plastic packaging, and belongs to the technical field of food safety detection. The method comprises the following specific steps: dissolving a photoinitiator in a common printing ink solvent, dripping the photoinitiator on the surface of a plastic package, putting the plastic package into a sealed culture dish wrapped by tin foil paper, after transferring for a period of time, dripping nano gold sol at the same position exposed by the photoinitiator, drying and carrying out Raman spectrum detection. The surface-enhanced Raman spectroscopy established by the invention does not need complex sample pretreatment operation, has the advantages of less sample and reagent dosage, low cost, quick detection and high sensitivity, and is suitable for monitoring the migration behavior of the photoinitiator.

Description

Method for monitoring permeation behavior of photoinitiator-907 in plastic package

Technical Field

The invention belongs to the technical field of rapid detection of food safety hazard components, and particularly relates to a method for monitoring photoinitiator permeation behavior in plastic packaging.

Background

The photoinitiator is a compound which can absorb radiation energy in an ultraviolet light region or a visible light region to generate an active intermediate (free radical or cation) and further initiate polymerization, crosslinking and curing of monomers, is an important component of the ultraviolet curing ink, directly influences the photocuring rate and the curing degree, and is widely applied to the food packaging and printing industry. Among them, 2-methyl-1- (4-methylthiophenyl) -2-morpholinyl-1-acetone (photoinitiator-907 or Irgacure 907) is a high-efficiency photoinitiator, and is commonly used in ultraviolet curing ink due to the advantages of good stability, high curing speed, no yellowing and the like. However, after the ink is cured, the unpolymerized photoinitiator can remain in the ink on the food packaging and under certain conditions can migrate into the food, potentially posing a health hazard to humans. Between 2009 and 2011, 6 events occurred where Irgacure 907 on food contact packaging migrated into the food, resulting in food contamination. These events have led to public safety concerns for photoinitiators.

At present, the toxicity of most photoinitiators has not been fully evaluated and comprehensive toxicological data is lacking, since photoinitiator residue and migration problems are found late and are of a wide variety. Existing toxicology studies have shown that BP and 4-MBP are carcinogenic, reproductive and skin contact toxic, and cause estrogen receptor responses leading to hypospadias. ITX interferes with endocrine function, increases the probability of tumorigenesis and is carcinogenic, and damages cell membranes when contacting cells at low levels for a long time, resulting in loss of some functions of the cells. It can be seen that photoinitiators migrating from the packaging into the food product are potentially hazardous to the health of the consumer.

The photoinitiator-907 (Irgacure-907) can absorb ultraviolet radiation energy to form free radicals or cations in the ink curing process, initiate polymerization, crosslinking and grafting reactions of monomers and oligomers, and cure the ink into a high molecular polymer with a three-dimensional network structure in a short time. Most of the current printing food inks use the photoinitiator-907 during the curing process, so the inventors examined the permeation behavior of the initiator with a solution of the photoinitiator-907 and studied it as a template for studying the permeation of the photoinitiator.

At present, the detection method of the photoinitiator mainly adopts a chromatography and chromatography-mass spectrometry combined method, and although the traditional chromatography or chromatography-mass spectrometry combined method has good sensitivity and reproducibility and is a 'gold standard' method for qualitative and quantitative analysis of the photoinitiator, the method needs a complex and time-consuming sample pretreatment process, personnel need to be trained, and the price of instruments and equipment is high. However, these conventional physicochemical analysis methods are time-consuming and complicated for sample pretreatment. Furthermore, monitoring the permeation behavior of the photoinitiator is of great importance for the rational use of the photoinitiator and for reducing the photoinitiator residues in foodstuffs. However, the permeation behavior of photoinitiators in food packaging materials cannot be monitored, since chromatography and mass spectrometry techniques do not allow in situ detection. Therefore, there is a need to develop a fast method to monitor the permeation behavior of photoinitiators in food packaging in situ and in real time.

The Raman spectrum can provide information such as the structure, the components, the functional groups and the like of a substance, is the fingerprint of the substance, but has weak signals and large fluorescence interference. Surface enhanced raman spectroscopy, which combines raman spectroscopy with nanotechnology, can enhance the signal of molecules adsorbed on the surface of metal nanostructures (usually gold or silver), with intensities as high as 104 times and more. In recent years, surface enhanced raman spectroscopy, as a new analysis technology, has the advantages of rapidness, no damage, high sensitivity and the like, and has become an important detection tool in the fields of biology, medicine, chemistry, environment, food and the like.

Surface-enhanced Raman spectroscopy (SERS) combines Raman spectroscopy and nanotechnology to enhance the signal of molecules adsorbed on the surface of metal nanostructures (usually gold or silver), with intensities as high as 104 times and more. Currently, the enhancement mechanism of SERS has two explanations, electromagnetic enhancement and chemical enhancement. Electromagnetic enhancement refers to the enhancement of local electromagnetic field generated by metal surface plasmon resonance, thereby enhancing the signal of sample molecules. The chemical enhancement means that sample molecules adsorbed on the metal surface and atoms or atom clusters on the metal surface are subjected to chemical action, and the change of the polarizability causes the signal enhancement of the sample molecules. The influence factors of the enhancement process are complex, the contribution of two enhancement mechanisms in different systems is different, and the SERS enhancement effect is generally considered to be caused by the combined action of the two enhancement mechanisms. .

Disclosure of Invention

In order to rapidly detect whether the photoinitiator in the plastic food package permeates into food, the invention provides a method for monitoring the permeation behavior of the photoinitiator in the plastic food package. The method for detecting the permeation behavior of the photoinitiator has the advantages of simplicity, rapidness, no damage and the like.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method of monitoring the penetration behavior of photoinitiator-907 in a plastic package, said monitoring method comprising: dissolving a photoinitiator-907 in an organic solvent to obtain an organic solvent solution of the photoinitiator-907, dripping the organic solvent solution on the surface of a plastic package, and adding an AuNPs solution after permeation and migration to obtain to-be-detected permeable plastic; ② irradiating the permeable plastic to be measured with laser with the wavelength of 785nm and the power of 0.3-1 mW, and measuring the permeability plastic to be measured at 1083 +/-1 cm in real time^-1Raman signals in the spectral range and monitor the penetration behavior of photoinitiator-907 by the different raman signals obtained at the penetrated and non-penetrated locations.

Wherein the Raman signal acquisition time is 0.3-1 s, the scanning range is 5 multiplied by 5 mu m, and the step diameter is 20 mu m.

Wherein the organic solvent comprises acetone, acetonitrile, methanol, ethyl acetate and xylene.

Wherein the concentration of the photoinitiator-907 solution is 1-200 mg/L.

Wherein the AuNPs solution is 50nm and 250 mg/L.

Wherein the plastic comprises PP, PE and PET.

Wherein the scanning depth of the Raman spectrum is 0-40 μm.

Wherein, after the front and the back of the Raman spectrum are scanned, the scanning depth is 0-80 μm.

Advantageous effects

According to the invention, through theoretical research on Raman spectra and evaluation of feasibility of SERS detection of seven photoinitiators (Irgacure 907, ITX, EHA, TPO, EDB, MK and CBP), only the Irgacure 907 is found to be more suitable for SERS detection by taking nanogold sol as an enhanced substrate.

The invention firstly monitors the permeation behavior of Irgacure 907 in plastic through Raman spectrum. The conditions for monitoring the permeation behavior of the Irgacure 907 in the plastic through the Raman spectrum are harsh, and the wavelength, the emitted light power and the time have great influence on the result.

By the method provided by the invention, the permeation behavior of Irgacure 907 in the plastic can be easily seen to be related to the common solvent of the ink and the plastic material. Irgacure 907 penetrated PE (thickness 80 μm) at 3h exposure, whereas exposure 20d penetrated 40 μm in PP (thickness 80 μm) and PET (thickness 80 μm) with acetone, acetonitrile and methanol as solvents. Irgacure 907 penetrated through PE at 6h exposure and only 40 μm of PP and PET at 20d exposure, using ethyl acetate as solvent. Irgacure 907, in xylene as solvent, penetrates PE at 12h exposure, but only 40 μm for PP and 20 μm for PET at 20d exposure. Combining the speed of Irgacure 907 penetration and the characteristic peak intensity of Irgacure 907 at different depths under the same exposure time, the Irgacure 907 penetration ability in different solvents in three plastics is in the order of acetone > acetonitrile > methanol > ethyl acetate > xylene. The capability of the plastic material PET and PP for obstructing the permeation of Irgacure 907 is stronger than that of PE.

Drawings

FIG. 1 SERS spectra of seven photoinitiators.

FIG. 2 shows that Irgacure 907 with different concentrations has a characteristic peak (1083 cm)^-1) Second derivative maps of (a).

FIG. 3 PCA diagram of Irgacure 907 on gold plate

FIG. 4 optical image, two-dimensional SERS image and SERS spectrum of Irgacure 907 on plastic surface.

FIG. 5 SERS spectra of Irgacure 907 at various concentrations on PP (A), PE (B) and PET (C).

FIG. 6 PCA of Irgacure 907 on PP (A), PE (B) and PET (C) surfaces

FIG. 7 Raman spectra of Irgacure 907(0.1mg/L) at different laser wavelengths and laser powers.

FIG. 8 Raman spectra of Irgacure 907(0.1mg/L) at different acquisition times.

Figure 9 is the permeation of Irgacure 907 in PE in acetone and its distribution profile.

Figure 10 is the permeation of Irgacure 907 in acetonitrile in PET and its distribution profile.

Detailed Description

The present invention will be further described with reference to the following examples for better understanding of the technical features, objects and advantages of the present invention, but the present invention is not limited to the examples.

In this example, photoinitiator standards: 2-Isopropylthioxanthone (ITX, ≧ 99%), 2,4, 6-trimethylbenzoyl-diphenylphosphine oxide (TPO, ≧ 99%), ethyl p-N, N-dimethylaminobenzoate (EDB, ≧ 99%), isooctyl p-N, N-dimethylaminobenzoate (EHA, ≧ 99%), 2-methyl-1- (4-methylthiophenyl) -2-morpholinyl-1-propanone (Irgacure 907, ≧ 99%), 4' -bis (dimethylamino) benzophenone (MK, ≧ 99%) and 4-chlorobenzophenone (CBP, ≧ 99%) are commercially available from Sigma-Aldrich, USA.

The food plastic packages PE, PP and PET are not printed on the surfaces and are all 80 μm thick.

AuNPs are nanogold sol solutions.

High resolution Raman spectrometer, LabRAM HR Evolution, from HORIBA Jobin Yvon S.A.S. of France.

Example 1

In this embodiment, seven common photoinitiators, i.e., ITX, TPO, EDB, EHA, Irgacure 907, MK, and CBP, are selected and the raman spectra thereof are collected.

2 mul of 7 photoinitiator standard solutions (ITX, TPO, EDB, EHA, Irgacure 907, MK and CBP) with the concentration of 10mg/L are respectively sucked and transferred onto a sealing film, blank acetonitrile is used as a reference, 2 mul of AuNPs (50nm, 250mg/L) are added, a pipetting gun is used for blowing and mixing for 20s, 2 mul of mixed solution is dripped onto a gold plate, and Raman spectroscopy measurement is carried out after drying in a dark place at room temperature.

Standard solutions (10mg/L) of these 7 photoinitiators were each added dropwise to goldSERS detection was performed on the plate. The SERS spectra of the seven photoinitiators are shown in figure 1, where the photoinitiators with raman signal include Irgacure 907, TPO, MK and ITX, whereas EDB, EHA and CBP have no raman signal, compared to the control. The characteristic peak of Irgacure 907 is at 1083cm^-1The characteristic peak of TPO is 998cm^-1Where the characteristic peak of MK is at 775cm^-1At this point, the characteristic peak of ITX is 681cm^-1And 1031cm^-1To (3). This is probably due to the fact that the four photoinitiators Irgacure 907, TPO, MK and ITX bind to AuNPs more strongly than the other three photoinitiators, and although TPO, MK and ITX have raman signals, the raman signal intensity is significantly weaker than that of Irgacure 907. In the practical process, only Irgacure 907 can be used for monitoring the permeation of the Irgacure 907 by using Raman spectroscopy, and other photoinitiators are not available.

After the mixed solution of Irgacure 907 and AuNPs dropped on the gold plate is dried, the AuNPs are clearly observed to be unevenly distributed on the gold plate under a Raman microscope lens, and an obvious concentrated AuNPs ring is formed around the edge of the sample, which is called as a coffee ring effect. This phenomenon is also observed in SERS detection of other compounds, such as food colorants, pesticides, urea, ammonium sulfate, and the like. The 'coffee ring' region shows that Irgacure 907 interacts with AuNPs and has stable and consistent good signals, so that points in the region are selected and detected by an optimized SERS method. As can be seen from FIG. 2a, Irgacure 907 does not detect Raman signal when AuNPs are not added, and after AuNPs are added, it is 1083cm^-1The Raman signal (figure 2b) appears, the peak is attributed to the stretching vibration of C-S in Irgacure 907, and the result shows that when AuNPs is used as an enhancing substrate, the SERS signal of Irgacure 907 is greatly enhanced, and the feasibility of detecting Irgacure 907 by SERS technology is fully proved.

FIG. 3 shows that Irgacure 907 with different concentrations has a characteristic peak of 1083cm^-1The second derivative average spectrum of (1) shows the concentration of Irgacure 907 to 1083cm^-1The SERS signal intensity is positively correlated. Therefore, 1083cm^-1The peak is suitable as a quantitative characteristic peak of Irgacure 907.

When added to plasticsAfter drying of AuNPs in the same location as Irgacure 907(10mg/L), the sample also formed a "coffee ring" on the plastic surface as on the gold plate, the "coffee ring" region being evident from the optical image in FIG. 4A. Two-dimensional raman spectroscopic imaging scans of different regions on the sample were performed. Point "a" in FIG. 4B was selected on a ring with substantial aggregation of AuNPs, with spectra at 1083cm^-1A characteristic peak of Irgacure 907 appears (fig. 4C), indicating that an interaction between Irgacure 907 and AuNPs occurs. Point "b" was selected in a region located slightly further away from the "coffee ring" where the AuNPs are less concentrated, and the spectrum of point "b" was at 1083cm^-1The intensity of the peak is weaker than "a" (FIG. 4C). Point "C" is chosen outside the "coffee ring", and the spectrum of point "C" shows no AuNPs and no raman signal (fig. 4C). Overall, the "coffee ring" region has a consistent and stronger signal than the rest of the sample, and spots within this region are also selected for detection on the plastic.

FIGS. 5A, B and C show SERS average spectra of Irgacure 907 at different concentrations on PP, PE and PET surfaces, respectively. The results show that the characteristic peak of Irgacure 907 appears at 1083cm on the surfaces of PP, PE and PET plastics^-1No offset occurred and no significant background interference of the plastic was observed. On plastics, Irgacure 907 at 1083cm^-1The SERS signal intensity is positively correlated with the concentration. However, at the concentration of 0.05mg/L, the SERS signals of Irgacure 907 on three plastics are not very clear, so the PCA analysis is carried out on the SERS spectra of different concentrations of Irgacure 907 to determine the LOD value of the Irgacure 907 on the plastics.

The results of PCA analysis of solutions of Irgacure 907 at different concentrations on PP, PE and PET are shown in FIGS. 6A, B and C, respectively. The data cluster of Irgacure 907 with the surface concentration of PP of 0.1mg/L can be separated from the data cluster of 0mg/L, while the data cluster of 0.05mg/L cannot be separated from the control, which indicates that the LOD value of the concentration of Irgacure 907 on PP is 0.1 mg/L. Similarly, the LOD values for the concentrations of Irgacure 907 on PE and PET were 0.1 mg/L. The areas formed by adding Irgacure 907 solution with a volume of 2 μ L to the surfaces of PP, PE and PET were different and 3.80X 10^-4、4.90×10^-4、 6.15×10^-4dm². The LOD values of Irgacure 907 on PP, PE and PET were 0.53, 0.41 and 0.33. mu.g/dm, respectively, converted into the content per unit area²。

As shown in FIG. 7, which is a Raman spectrum of Irgacure 907(0.1mg/L) at different laser wavelengths and laser powers, it can be seen that under the excitation of 785nm and 532nm lasers, the Raman signal intensity of Irgacure 907 solution (0.1mg/L) at the same concentration on plastics is different, and the Raman signal intensity is weaker under the excitation of 532nm lasers (1.5 mW) but is relatively stronger under the excitation of 785nm lasers (0.3mW, 0.5mW and 1 mW). At a power of 0.3mW, the raman signal of Irgacure 907 is not significant, the peak shape is not very clear, and the signal intensity increases as the laser power increases to 0.5 mW. But when the power was increased to 1mW, the signal intensity became weaker and the samples at and around the sampling point were seen to be burned out from the microscope image, so a laser wavelength of 785nm, a laser power of 0.5 ± 0.1mW, was chosen to obtain a good signal-to-noise ratio without damaging the sample.

Fig. 8 is a raman spectrum of Irgacure 907(0.1mg/L) at different collection times, and raman spectra of Irgacure 907 collected at 3s, 5s and 10s are set respectively. The raman response signal strength of Irgacure 907 increases with the extension of the acquisition time. When the acquisition time is 3s, the Irgacure 907 signal is weaker, the peak shape is not very clear, when the acquisition time is 5s, the peak shape is clear, and when the acquisition time is 10s, the Raman signal intensity is slightly enhanced. Therefore, to obtain a better signal in a shorter time, the acquisition time is chosen to be 5 ± 1 s.

Example 2

Based on the theoretical results of example 1, this example provides a method for permeation behavior of photoinitiator-907 in PE, which specifically operates as follows:

preparing 200mg/L Irgacure 907 acetone solution, dripping 2 mu L of Irgacure 907 acetone solution on the front surface of PE, drying in a sealed culture dish wrapped by tinfoil paper at room temperature, and taking out at the time points of exposure time of 0h, 1h, 3h, 6h and 12h respectively.

Preparing a 250mg/LAuNPs solution, dripping 50nm of the solution on the same position of PE plastic, and scanning the solution to a depth of 0-40 mu m; and (3) dripping AuNPs at the position where the photoinitiator on the back surface of the plastic is exposed, wherein the scanning depth is 40-80 mu m. The parameters of the Raman instrument are set to be that the laser emission power is 0.5mW, the acquisition time is 0.5s, the scanning range is 5 multiplied by 5 mu m, the number of plane scanning points is 9, and the step diameter is 20 mu m.

The scanning result is shown in FIG. 9, and it can be seen from FIG. 9 that under this condition, the permeation of the photoinitiator-907 can be clearly observed by Raman spectroscopy. Similarly, the acetone can be replaced by acetonitrile, methanol, ethyl acetate and xylene by scanning for 1083cm^-1The penetration was obtained by Raman spectroscopy, and the penetration depth is shown in Table 1. However, under other conditions, the penetration of the photoinitiator-907 was difficult to see.

Example 3

The embodiment provides a method for permeation behavior of photoinitiator-907 in PET, which comprises the following specific operations:

dissolving 200mg/L photoinitiator-907 (Irgacure 907) solution in acetonitrile, then dripping 2 mu L of solution on the front surface of PET, drying in a sealed culture dish wrapped by tin foil paper at room temperature, taking out after different exposure times (1d, 5d, 10d, 15d and 20d), dripping AuNPs (50nm, 250mg/L) on the front surface of plastic to the same position, and scanning to the depth of 0-40 mu m; and (3) dripping AuNPs at the exposed position of the photo initiator-907 on the back surface of the plastic at the same time, wherein the scanning depth is 40-80 μm. The Raman instrument parameters are set to 0.5mW power, 0.5s acquisition time, 5 multiplied by 5 μm scanning range, 9 planar scanning points and 20 μm step diameter.

The scanning result is shown in FIG. 10, and it can be seen from FIG. 10 that under this condition, the permeation of the photoinitiator-907 can be clearly observed by Raman spectroscopy. Similarly, the acetone can be replaced by acetonitrile, methanol, ethyl acetate and xylene by scanning for 1083cm^-1The penetration depth of the obtained Raman spectrum is shown in Table 2, while the penetration of the photoinitiator-907 is difficult to see under other conditions.

Table 1 peak areas of Irgacure 907 at different depths in PE for different exposure periods

Table 3-2 The average peak area of Irgacure 907 at different depths in PE at different exposure times

Note: "-" indicates no detection

Table 2 peak areas at different depths in PET for different exposure periods Irgacure 907

Table 3-4 The average peak area of Irgacure 907 at different depths in PET at different exposure times

Note: "-" indicates no detection.

Claims

1. A method of monitoring the penetration behavior of photoinitiator-907 in a plastic package, characterized by: the monitoring method comprises the following steps:

dissolving a photoinitiator-907 in an organic solvent to obtain an organic solvent solution of the photoinitiator-907, dripping the organic solvent solution on the surface of a plastic package, and adding an AuNPs solution after permeation and migration to obtain to-be-detected permeable plastic;

irradiating the to-be-measured permeable plastic by using laser with the wavelength of 785nm and the power of 0.3-1 mW, and measuring the to-be-measured permeable plastic within 1083 +/-1 cm in real time^-1Raman signals in the spectral range and monitor the penetration behavior of photoinitiator-907 by the different raman signals obtained at the penetrated and non-penetrated locations.

2. The method of monitoring the penetration behavior of photoinitiator-907 in a plastic package according to claim 1, characterized in that: the Raman signal acquisition time is 0.3-1 s, the scanning range is 5 multiplied by 5 mu m, and the step size is 20 mu m.

3. The method of monitoring the penetration behavior of photoinitiator-907 in a plastic package according to claim 1, characterized in that: the organic solvent comprises acetone, acetonitrile, methanol, ethyl acetate and xylene.

4. The method of monitoring the penetration behavior of photoinitiator-907 in a plastic package according to claim 1, characterized in that: the concentration of the photoinitiator-907 solution is 1-200 mg/L.

5. The method of monitoring the penetration behavior of photoinitiator-907 in a plastic package according to claim 1, characterized in that: the AuNPs solution is 50nm and 250 mg/L.

6. The method of monitoring the penetration behavior of photoinitiator-907 in a plastic package according to claim 1, characterized in that: the plastics include PP, PE and PET.

7. The method of monitoring the penetration behavior of photoinitiator-907 in a plastic package according to claim 1, characterized in that: the scanning depth of the Raman spectrum is 0-40 [ mu ] m.

8. The method of monitoring the penetration behavior of photoinitiator-907 in a plastic package according to claim 1, characterized in that: and after the front and the back of the Raman spectrum are scanned, the scanning depth is 0-80 mu m.