- Email: [email protected]
FTIR investigation of the specific migration of additives from rigid poly(vinyl chloride)
EUROPEAN POLYMER JOURNAL
European Polymer Journal 41 (2005) 707–714
www.elsevier.com/locate/europolj
FTIR investigation of the specific migration of additives from rigid poly(vinyl chloride) D. Atek, N. Belhaneche-Bensemra
*
Laboratoire des Sciences et Techniques de l’Environnement, E´cole Nationale Polytechnique, BP 182, El-Harrach, Alger, Algeria Received 7 February 2004; accepted 27 October 2004 Available online 5 January 2005
Abstract Commercial sunflower oil was epoxidized and used as organic costabiliser for rigid poly (vinyl chloride) (PVC) containing zinc and calcium stearates as primary stabilisers and stearic acid as lubricant. For applications in the packaging of foodstuffs, migration testing must be realised. For that purpose, two food simulants were used (sunflower oil and 15% (v/v) aqueous ethanol). The test conditions were 12 days at 40 °C. Circular samples of rigid PVC were immersed in a well known volume of food simulant. A circular sample and 10 ml of food simulant were taken off every day to be analysed. The specific migrations of the additives were investigated by using Fourier transform infrared spectroscopy. The direct analysis of the food simulants was difficult because overlapping of the bands of the additives. However, the analysis of PVC films obtained by dissolution of the circular samples in tetrahydrofuran and evaporation of the solvent was more conclusive. The specific migrations of the metal carboxylates and epoxidized sunflower oil were evidenced. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Migration; PVC; Epoxidized sunflower oil
1. Introduction Polyvinyl chloride (PVC) is one of the oldest synthetic polymers. Low stability is an inherent property of PVC. It is known that this polymer undergoes severe degradation via zip elimination of HCl at relatively low temperatures. Degraded PVC is characterised by the
*
Corresponding author. Tel.: +213 21 52 53 01; fax: +213 21 52 29 73. E-mail address: [email protected] (N. BelhanecheBensemra).
development of intense discoloration resulting from the formation of conjugated polyene structures [1]. The poor thermal stability of PVC requires the use of heat stabilisers in the processing of the polymer. The most important stabilisers of PVC are different metal soaps like Pb, Cd, Ba, Ca and Zn carboxylates and some diand mono-alkyltin compounds, e.g., maleates, carboxylates, mercaptides [2]. Epoxy compounds are well known as typical non-metallic stabilisers for PVC [3]. Activity is essentially related to the amount of oxirane oxygen, but plasticization, lubrication and cost parameters play a role in their selection and use [4]. They are generally regarded as secondary stabilisers used to enhance the effectiveness of metal soaps.
0014-3057/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2004.10.043
708
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
2.3. Migration testing
In previous studies [5,6], commercial sunflower oil was epoxidized and the effects of epoxidized sunflower oil (ESO) on the thermal degradation and stabilisation of PVC in the presence of metal carboxylates (Ba/Cd and Ca/Zn stearates) were investigated. For applications in the packaging of foodstuffs, migration testing must be realised. The detection and the quantification of contaminants migrating from the polymers into food simulants are essential for the safety assessment of food contact plastic packaging materials. The aim of this study is to investigate the migration of additives from rigid PVC stabilised with ESO in the presence of Zn and Ca stearates. For that purpose two food simulants were used (sunflower oil and 15% (v/v) aqueous ethanol). The specific migrations of the additives were investigated by using Fourier transform infrared spectroscopy.
Migration tests were conducted using two food simulants (sunflower oil and 15% (v/v) aqueous ethanol). These food simulants represent fatty and moist food and beverages. The test conditions were 12 days at 40 °C. Twelve circular samples of rigid PVC were immersed in 120 ml of each food simulant at 40 °C. A circular sample and 10 ml of food simulant were taken off every day to be analysed. Each sample was wiped and weighed. The rate of variation of the mass (s) was determined as a function of time following the relation: s ¼ ðmt m0 =m0 Þ 100 where m0 is the initial mass before immersion and mt is the mass of the sample at the time t. 2.4. Fourier transform infrared spectroscopy
2. Experimental procedures A Philips type PU 9800 FTIR spectrometer was used. The food simulants were placed between two KBR pellets and analysed directly. On the other hand, the PVC circular samples were dissolved in tetrahydrofuran (THF). After evaporation of the solvent, a polymeric film was recuperated and analysed. The resolution was 2 cm1.
2.1. Materials Algerian PVC with K value 65–67 from ENIP SKIKDA, Zn stearate from ALDRICH, Ca stearate from Prolabo and stearic acid from HENKEL were used. Epoxidized sunflower oil was specially prepared as described previously [5]. The level of oxirane oxygen was 6.4%.
3. Results and discussion 2.2. Preparation of PVC films 3.1. FTIR characterisation of sunflower oil and epoxidized sunflower oil
A formulation containing 1% of Zn stearate, 1% of Ca stearate, 5% of ESO and 1% of stearic acid was prepared. PVC and additives were mixed in a two-roll mill at 180 °C during 5 min. The film thickness was about (0.40 ± 0.01) mm. Then circular samples of (18 ± 0.01) mm in diameter were cut.
The spectra of ESO and sunflower oil given in Figs. 1 and 2 are similar as their chemical structures are close. ESO results from a reaction of epoxidation of sunflower oil [5,6]
O CH 2 – O – OC – CH2 – CH2 CH – O – OC –R2 CH 2 – O – OC –R3
O
CH2 – CH – CH Z
CH2 – CH – CH Y2
CH2 – CH3 Y1
R1
R2 and R3 may be identical or different from R1 concerning the number of epoxy groups present. Chemical structure of ESO
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
709
CH 2 – O – OC – R1 CH – O – OC – R2 CH 2 – O – OC – R3 R1 = - CH 2 – CH2
CH2
CH
CH
Z
CH 2
CH
CH
CH2 – CH3
Y1
Y2
R2 and R3 may be identical or different from R1 concerning the number of double bonds. Chemical structure of sunflower oil
Table 1 Characteristic functional groups of ESO [7,8]
3
3.5
5
4
9
No.
Frequency (cm1)
Characteristic group
1 2 3 4 5 6 7 8 9 10
3468 3008 2919 2855 1747 1462 1378 1238 1163 1101
–C@O (ester) –CH epoxy, @C–H (cis) –CH– –CH– –C@O (ester) –CH2– (methylene) –CH3 (methyl) –C–O (epoxy), –CH2– –C–O (ester), –CH2– –C–O
11
726
Absorbance
2.5 6 8
2
1.5
10
7
0.5
11
1
-0.5 4000
3500
3000
2500 2000 1500 Wave number (cm-1)
1000
500
Fig. 1. FTIR spectrum of epoxidized sunflower oil. The band numbers correspond to those indicated in Table 1.
C
C , (CH ) , –HC@CH– (cis) 2 n O
3 4
2.5
5
Table 2 Characteristic functional groups of sunflower oil [8]
9 6
2
Absorbance
2.0 1.5
8 7
10 11
1.0 0.5
1
0.0 4000
3500
3000
2500 2000 1500 Wave number (cm-1)
1000
500
No.
Frequency (cm1)
Characteristic group
1 2 3 4 5 6 7 8 9 10 11
3468 3009 2920 2853 1741 1462 1376 1238 1161 1100 723
–C@O (ester) @C–H (cis) –CH (CH2) –CH (CH2) –C@O (ester) –C–H (CH2, CH3) –C–H (CH3) –C–O, –CH2– –C–O, –CH2– –C–O –(CH2)n–, HC=CH– (cis)
Fig. 2. FTIR spectrum of sunflower oil. The band numbers correspond to those indicated in Table 2.
3.2. FTIR study of migration in food simulants The comparison of the spectra of Figs. 1 and 2 and of the Tables 1 and 2 shows that all the bands present in sunflower oil are also present in ESO but with a shift of 1–3 cm1 for some ones. The most notable difference is the frequency of the ester band: 1747 cm1 in ESO and 1741 cm1 in sunflower oil.
Figs. 3 and 4 show FTIR spectra of the samples of sunflower oil and 15% (v/v) aqueous ethanol after various times of contact with the PVC discs at 40 °C. It is clear that the direct analysis of the spectra of food simulants cannot show the migration of additives because
4000
Absorbance ( arbitrary units )
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
Absorbance (arbitrary units)
710
12 9 1 0
3500
3000
1000 500
2500 2000 1500 Wave number (cm-1)
12 9 1 0
4000 3500
Fig. 3. FTIR spectra of samples of sunflower oil after various times of contact in days with PVC discs at 40 °C.
3000
2500 2000 1500 Wave number (cm-1)
1000
500
Fig. 4. FTIR spectra of samples of aqueous ethanol after various times of contact in days with PVC discs at 40 °C.
1.4 1.0
(b) 1..2
727
723 1.0
0.8
Absorbance
Absorbance
(a)
726
695
0.6 0.4
724
0.8
687
0.6 0.4
0.2
0.2 800
760
720
680
640
800
Wave number (cm-1)
760 720 680 Wave number (cm-1)
640
0.8 724
(d) 723
1.2
722
724
0.6
0.8 683
0.4
Absorbance
Absorbance
(c)
0.4 686 0.2
800
760
720 680 Wave number (cm-1)
640
800
760 720 680 Wave number (cm-1)
640
0.8
(e)
724
Absorbance
725 0.6 692
0.4
0.2 800
760 720 680 Wave number (cm-1)
640
Fig. 5. Deconvolution of the spectra of ESO (a) and of samples of sunflower oil after various times of contact with PVC discs at 40 °C: 0 day (b), 1 day (c), 9 days (d), 12 days (e).
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
Absorbance (arbitrary units)
Absorbance ( arbitrary units)
SO
0. 0553 mg/ml 0. 1382 mg/ml 0. 2767 mg/ml
(a) 3 4 2 1
0. 5530 mg/ml
(b)
ESO 2000
1500 1000 Wave number (cm-1)
711
4000
3500
3000
2500 2000 1500 Wave number (cm-1)
1000
500
500
Fig. 8. FTIR spectra of PVC film (a) and PVC film with additives (b).
Fig. 6. FTIR spectra of ESO, SO and solutions of various concentrations of ESO in SO.
they are all identical. Furthermore the characteristic bands are overlapped and the amounts of migrated additives are very low. However a more deep investigation of the domain 640–800 cm1 (epoxy group) of the spectra of sunflower oil after various times of contact with
(a) 723
0.5
0.4
(b) 0.5
723
686
Absorbance
Absorbance
0.6
PVC discs by using the software GRAMS 386 as shown in Fig. 5 evidenced the migration of ESO. So the analysis of the bands of Fig. 5(a–e) shows the shift of the band at 723 cm1 of sunflower oil (b) to 724 cm1 (c–e) which is close to the position of the corresponding band in ESO at 726 cm1. In the same manner, simulated bands in sunflower oil at 687 and
723
0.4 713
0.3
0.2
0.2 800 780 760 740 720 700 680 660 640 Wave number (cm-1)
800 780 760 740 720 700 680 660 640 Wave number (cm-1) 0.6
0.6
(c) 0.5
724
713
0.4
(d)
0.5
723
725
Absorbance
Absorbance
725
0.3
725
0.3
0.3
0.2
0.2
800 780 760 740 720 700 680 660 640 Wave number (cm-1)
713
0.4
800 780 760 740 720 700 680 660 640 Wave number (cm-1)
Fig. 7. Deconvolution of the spectra of solutions of ESO in SO at various concentrations: 0.0553 mg/ml (a), 0.1382 mg/ml (b), 0.2767 mg/ml (c) and 0. 5530 mg/ml (d).
712
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
Table 3 Characteristic bands of the used additives present in PVC film [7–10] No.
Wave number (cm1)
Functional group
Mode of vibration
Additive
1 2 3 4
1740 1577 1539 1461
C@O (ester) CO 2 (carboxylic acid salt) CO 2 (carboxylic acid salt) CH2 (methyl, methylene)
Streching Streching Streching bending
ESO Ca stearate Zn stearate ESO, Zn stearate
0.30
(a)
0.40
0.20 A1577 / A1432
A1740 / A1432
0.30
(b)
0.20 0.10 0.00
0.10
0.00 0
50
100 150 200 Time (hours)
250
0
300
50
100 150 200 Time (hours)
250
300
0.40
(c)
0.35
(d)
A1461 / A1432
A1539 / A1432
0.30 0.25
0.15
0.05
0.20 0.10 0.00
0
50
100 150 200 Time (hours)
250
300
0
50
100 150 200 Time (hours)
250
300
Fig. 9. Variation of absorbances ratios as a function of time of contact with sunflower oil.
724 cm1 (b) are shifted to 692 and 725 cm1 (e) which are close to the corresponding bands in ESO at 695 and 727 cm1 (a). On the other hand, solutions containing various concentrations (0.0553, 0.1382, 0.2767 and 0.5530 mg/ml) of ESO in sunflower oil (SO) were prepared and analysed by FTIR. The maximal concentration of 0.5530 mg/ml was chosen according to the hypothesis that all the initial amount of ESO in the PVC disc migrated in the fatty simulant. The other lower concentrations were chosen arbitrary. The spectra of these solutions are given in Fig. 6. It can be noted that the bands at 726, 1378, 1465 and 1747 cm1 which are indicated by arrows in Fig. 6 shifted from their initial position in sunflower oil. This feature may be due to an interaction of hydrogen bonding type involving epoxidized sunflower oil, sunflower
oil and the free fatty acids present [7]. Furthermore, the deconvolution of the domain 640–800 cm1 (epoxy group) was carried out. The results are shown in Fig. 7. For the lowest concentration 0.0553 mg/ml (Fig. 7a), the shape of the band is similar to those of ESO and SO (Fig. 5a and b respectively). The increasing of the concentration of ESO leads to the broadening of the band (Fig. 7b–d). Furthermore, the simulated bands shifted from 687 and 724 cm1 (Fig. 5b) to 713 and 725 cm1, respectively (Fig. 7b–d). These modifications may be due to the higher amount of ESO present in SO and to an interaction between ESO and SO. On the other hand, the comparison of Figs. 5 and 7 shows that the broadening of the band as observed in Fig. 7 has not occurred in Fig. 5. This feature can be related to the migrated amount of ESO which is very low.
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714 0.30
0.42
(a)
(b) 0.28 A1577 / A1432
0.38 A1740 / A1432
713
0.34 0.30
0.26 0.24 0.22
0.26
0.20 0
50
100 150 200 Time (hours)
250
0
300
50
100 150 200 Time (hours)
250
300
0.40
(c)
A1539 / A1432
0.35
0.30
0.25 0
50
100 150 200 Time (hours)
250
300
Fig. 10. Variation of absorbances ratios as a function of time of contact with aqueous ethanol.
0.5
done. For that purpose the following absorbances ratios were calculated:
Sunflower oil 15% (v/v) aqueous ethanol
τ (%)
0.4
A A A A
0.3 0.2 0.1 0.0 0
50
100
150 200 Time (hours)
250
300
Fig. 11. Effect of the nature of the food simulant on the rate of mass variation at 40 °C.
3.3. FTIR study of migration in PVC films Fig. 8 represents the spectra of PVC alone (a) and with all the used additives (b). The comparison of the two spectra allowed the identification of some characteristic bands which are related to the additives present in the formulation as shown in Table 3. The spectra of PVC films after various times of contact with sunflower oil and 15% (v/v) aqueous ethanol were recorded. A semi-quantitative estimation of the migration of additives (ESO, Zn and Ca stearates) was
1740/A 1577/A 1539/A 1461/A
1432: 1432: 1432: 1432:
ESO migration. Ca stearate migration. Zn stearate migration. ESO and Zn stearate migration.
The band at 1432 is due to the vibration of CH2 of PVC [11] and was taken as a reference band. The variations of these four ratios of absorbances as a function of time of contact with sunflower oil and 15% (v/v) aqueous ethanol, respectively, are given in Figs. 9 and 10. It can be noted that all these curves decreased with time of contact. This can be directly related to a phenomenon of migration of ESO, Zn and Ca stearates in the two food simulants used. Furthermore, the higher values of absorbances ratios were obtained for the films which were in contact with sunflower oil. This feature indicates the influence of the nature of the food simulant on the phenomenon of migration. 3.4. Rates of mass variation The rates of mass variation (s) as a function of time gives informationÕs about the phenomenon which occurred between the samples of PVC and the food simulants used. An increase means that the food simulant
714
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
penetrated the sample while a decrease means that some additives migrated in the food simulant. Hence s gives informationÕs about the overall migration that occurred. According to current legislation (Directive 90/128/EEC and its amendments; EEC 1990), the overall migration to a foodstuff from food contact plastics must be less than 10 mg of plastic compounds per dm2 of surface area. The mass variation data are shown in Fig. 11. It can be noted that the relatively highest values of s were obtained in sunflower oil. Furthermore, an increase in s was first observed for the two food simulants indicating their penetration in the PVC discs. It was followed by a decrease in s indicating the migration of some additives in the food simulants. It seems that the penetration of the food simulants in the discs favored the mobility of the additives and then their migration. The values of the overall migration estimated were 2.457 mg/dm2 in sunflower oil and 0.786 mg/dm2 in 15% (v/v) aqueous ethanol. So, the results obtained by the mass variations of the PVC discs are in accordance with those of FTIR investigation. The migration of some additives present in the PVC discs occurred. The phenomenon is influenced by the nature of food simulant and the time of contact. However, the overall migration in the two food simulants considered is lower than the maximum allowable migration: 10 mg/dm2. On the other hand, the EEC legislation is based on a system of positive lists where compounds intended to be used as monomers or additives for food contact plastics are individually evaluated by the EEC Scientific Committee for Food (SCF). Compounds which are necessary for the production of plastics but which may be harmful to human health are restricted in their use by assigning specific migration limits (SMLs) or maximum allowed concentrations in the plastics (QMs). Concerning the additives used in this study, Zn and Ca stearates and stearic acid are included in the positive list of additives allowed for use in plastics (Directive 90/ 128/EEC). Hence there is clearly a need for further work to evaluate the specific migration of ESO. Although similar stabilisers like epoxidized soya bean oil are accepted as additives for food contact plastics, toxicological tests
are required to assess the safety of this new stabiliser. The migration levels measured in food simulants will determine the extent of the toxicological data required.
Acknowledgments The authors are indebted to Dr M. T. Benaniba who kindly prepared the epoxidized sunflower oil for us.
References [1] Starnes Jr WH. Structural and mechanistic aspects of the thermal degradation of poly (vinyl chloride). Prog Polym Sci 2002;27:2133–70. [2] Minagawa M. New developments in polymer stabilization. Polym Degrad Stab 1989;25:121–41. [3] Stepeck J, Daoust H. Additives for plastics. New York: Springer; 1983. [4] Dworkin RD. PVC stabilizers of the past, present and future. J Vinyl Technol 1989;11(1):15–22. [5] Benaniba MT, Belhaneche-Bensemra N, Gelbard G. Stabilizing effect of epoxidized sunflower oil on the thermal degradation of poly (vinyl chloride). Polym Degrad Stab 2001;74:501–5. [6] Benaniba MT, Belhaneche-Bensemra N, Gelbard G. Stabilization of PVC by epoxidized sunflower oil in the presence of zinc and calcium stearates. Polym Degrad Stab 2003;82(3):245–9. [7] Socrates G. Infrared characteristic group frequencies. New York: John Wiley & Sons; 1980. [8] Guillen MD, Cabo N. Infrared spectroscopy in the study of edible oils and fats. J Sci Food Agric 1997;75: 1–11. [9] Beltran M, Marcilla A. Fourier transform infrared spectroscopy applied to the study of PVC decomposition. Eur Polym J 1997;33(7):1135–42. [10] Benavides R, Edge M, Allen NS, Mellor M, Harvey H, Schmets G. The evaluation of an innovative costabilizer for poly (vinyl chloride)—II. Interactions between metal stearates and the costabiliser. Polym Degrad Stab 1996; 53:319–27. [11] Krimm S, Folt VL, Shipman JJ, Berens AR. Infrared spectra and assignments for PVC and deuterated analogs. J Polym Sci 1963(Part A1):2621–50.
European Polymer Journal 41 (2005) 707–714
www.elsevier.com/locate/europolj
FTIR investigation of the specific migration of additives from rigid poly(vinyl chloride) D. Atek, N. Belhaneche-Bensemra
*
Laboratoire des Sciences et Techniques de l’Environnement, E´cole Nationale Polytechnique, BP 182, El-Harrach, Alger, Algeria Received 7 February 2004; accepted 27 October 2004 Available online 5 January 2005
Abstract Commercial sunflower oil was epoxidized and used as organic costabiliser for rigid poly (vinyl chloride) (PVC) containing zinc and calcium stearates as primary stabilisers and stearic acid as lubricant. For applications in the packaging of foodstuffs, migration testing must be realised. For that purpose, two food simulants were used (sunflower oil and 15% (v/v) aqueous ethanol). The test conditions were 12 days at 40 °C. Circular samples of rigid PVC were immersed in a well known volume of food simulant. A circular sample and 10 ml of food simulant were taken off every day to be analysed. The specific migrations of the additives were investigated by using Fourier transform infrared spectroscopy. The direct analysis of the food simulants was difficult because overlapping of the bands of the additives. However, the analysis of PVC films obtained by dissolution of the circular samples in tetrahydrofuran and evaporation of the solvent was more conclusive. The specific migrations of the metal carboxylates and epoxidized sunflower oil were evidenced. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Migration; PVC; Epoxidized sunflower oil
1. Introduction Polyvinyl chloride (PVC) is one of the oldest synthetic polymers. Low stability is an inherent property of PVC. It is known that this polymer undergoes severe degradation via zip elimination of HCl at relatively low temperatures. Degraded PVC is characterised by the
*
Corresponding author. Tel.: +213 21 52 53 01; fax: +213 21 52 29 73. E-mail address: [email protected] (N. BelhanecheBensemra).
development of intense discoloration resulting from the formation of conjugated polyene structures [1]. The poor thermal stability of PVC requires the use of heat stabilisers in the processing of the polymer. The most important stabilisers of PVC are different metal soaps like Pb, Cd, Ba, Ca and Zn carboxylates and some diand mono-alkyltin compounds, e.g., maleates, carboxylates, mercaptides [2]. Epoxy compounds are well known as typical non-metallic stabilisers for PVC [3]. Activity is essentially related to the amount of oxirane oxygen, but plasticization, lubrication and cost parameters play a role in their selection and use [4]. They are generally regarded as secondary stabilisers used to enhance the effectiveness of metal soaps.
0014-3057/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2004.10.043
708
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
2.3. Migration testing
In previous studies [5,6], commercial sunflower oil was epoxidized and the effects of epoxidized sunflower oil (ESO) on the thermal degradation and stabilisation of PVC in the presence of metal carboxylates (Ba/Cd and Ca/Zn stearates) were investigated. For applications in the packaging of foodstuffs, migration testing must be realised. The detection and the quantification of contaminants migrating from the polymers into food simulants are essential for the safety assessment of food contact plastic packaging materials. The aim of this study is to investigate the migration of additives from rigid PVC stabilised with ESO in the presence of Zn and Ca stearates. For that purpose two food simulants were used (sunflower oil and 15% (v/v) aqueous ethanol). The specific migrations of the additives were investigated by using Fourier transform infrared spectroscopy.
Migration tests were conducted using two food simulants (sunflower oil and 15% (v/v) aqueous ethanol). These food simulants represent fatty and moist food and beverages. The test conditions were 12 days at 40 °C. Twelve circular samples of rigid PVC were immersed in 120 ml of each food simulant at 40 °C. A circular sample and 10 ml of food simulant were taken off every day to be analysed. Each sample was wiped and weighed. The rate of variation of the mass (s) was determined as a function of time following the relation: s ¼ ðmt m0 =m0 Þ 100 where m0 is the initial mass before immersion and mt is the mass of the sample at the time t. 2.4. Fourier transform infrared spectroscopy
2. Experimental procedures A Philips type PU 9800 FTIR spectrometer was used. The food simulants were placed between two KBR pellets and analysed directly. On the other hand, the PVC circular samples were dissolved in tetrahydrofuran (THF). After evaporation of the solvent, a polymeric film was recuperated and analysed. The resolution was 2 cm1.
2.1. Materials Algerian PVC with K value 65–67 from ENIP SKIKDA, Zn stearate from ALDRICH, Ca stearate from Prolabo and stearic acid from HENKEL were used. Epoxidized sunflower oil was specially prepared as described previously [5]. The level of oxirane oxygen was 6.4%.
3. Results and discussion 2.2. Preparation of PVC films 3.1. FTIR characterisation of sunflower oil and epoxidized sunflower oil
A formulation containing 1% of Zn stearate, 1% of Ca stearate, 5% of ESO and 1% of stearic acid was prepared. PVC and additives were mixed in a two-roll mill at 180 °C during 5 min. The film thickness was about (0.40 ± 0.01) mm. Then circular samples of (18 ± 0.01) mm in diameter were cut.
The spectra of ESO and sunflower oil given in Figs. 1 and 2 are similar as their chemical structures are close. ESO results from a reaction of epoxidation of sunflower oil [5,6]
O CH 2 – O – OC – CH2 – CH2 CH – O – OC –R2 CH 2 – O – OC –R3
O
CH2 – CH – CH Z
CH2 – CH – CH Y2
CH2 – CH3 Y1
R1
R2 and R3 may be identical or different from R1 concerning the number of epoxy groups present. Chemical structure of ESO
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
709
CH 2 – O – OC – R1 CH – O – OC – R2 CH 2 – O – OC – R3 R1 = - CH 2 – CH2
CH2
CH
CH
Z
CH 2
CH
CH
CH2 – CH3
Y1
Y2
R2 and R3 may be identical or different from R1 concerning the number of double bonds. Chemical structure of sunflower oil
Table 1 Characteristic functional groups of ESO [7,8]
3
3.5
5
4
9
No.
Frequency (cm1)
Characteristic group
1 2 3 4 5 6 7 8 9 10
3468 3008 2919 2855 1747 1462 1378 1238 1163 1101
–C@O (ester) –CH epoxy, @C–H (cis) –CH– –CH– –C@O (ester) –CH2– (methylene) –CH3 (methyl) –C–O (epoxy), –CH2– –C–O (ester), –CH2– –C–O
11
726
Absorbance
2.5 6 8
2
1.5
10
7
0.5
11
1
-0.5 4000
3500
3000
2500 2000 1500 Wave number (cm-1)
1000
500
Fig. 1. FTIR spectrum of epoxidized sunflower oil. The band numbers correspond to those indicated in Table 1.
C
C , (CH ) , –HC@CH– (cis) 2 n O
3 4
2.5
5
Table 2 Characteristic functional groups of sunflower oil [8]
9 6
2
Absorbance
2.0 1.5
8 7
10 11
1.0 0.5
1
0.0 4000
3500
3000
2500 2000 1500 Wave number (cm-1)
1000
500
No.
Frequency (cm1)
Characteristic group
1 2 3 4 5 6 7 8 9 10 11
3468 3009 2920 2853 1741 1462 1376 1238 1161 1100 723
–C@O (ester) @C–H (cis) –CH (CH2) –CH (CH2) –C@O (ester) –C–H (CH2, CH3) –C–H (CH3) –C–O, –CH2– –C–O, –CH2– –C–O –(CH2)n–, HC=CH– (cis)
Fig. 2. FTIR spectrum of sunflower oil. The band numbers correspond to those indicated in Table 2.
3.2. FTIR study of migration in food simulants The comparison of the spectra of Figs. 1 and 2 and of the Tables 1 and 2 shows that all the bands present in sunflower oil are also present in ESO but with a shift of 1–3 cm1 for some ones. The most notable difference is the frequency of the ester band: 1747 cm1 in ESO and 1741 cm1 in sunflower oil.
Figs. 3 and 4 show FTIR spectra of the samples of sunflower oil and 15% (v/v) aqueous ethanol after various times of contact with the PVC discs at 40 °C. It is clear that the direct analysis of the spectra of food simulants cannot show the migration of additives because
4000
Absorbance ( arbitrary units )
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
Absorbance (arbitrary units)
710
12 9 1 0
3500
3000
1000 500
2500 2000 1500 Wave number (cm-1)
12 9 1 0
4000 3500
Fig. 3. FTIR spectra of samples of sunflower oil after various times of contact in days with PVC discs at 40 °C.
3000
2500 2000 1500 Wave number (cm-1)
1000
500
Fig. 4. FTIR spectra of samples of aqueous ethanol after various times of contact in days with PVC discs at 40 °C.
1.4 1.0
(b) 1..2
727
723 1.0
0.8
Absorbance
Absorbance
(a)
726
695
0.6 0.4
724
0.8
687
0.6 0.4
0.2
0.2 800
760
720
680
640
800
Wave number (cm-1)
760 720 680 Wave number (cm-1)
640
0.8 724
(d) 723
1.2
722
724
0.6
0.8 683
0.4
Absorbance
Absorbance
(c)
0.4 686 0.2
800
760
720 680 Wave number (cm-1)
640
800
760 720 680 Wave number (cm-1)
640
0.8
(e)
724
Absorbance
725 0.6 692
0.4
0.2 800
760 720 680 Wave number (cm-1)
640
Fig. 5. Deconvolution of the spectra of ESO (a) and of samples of sunflower oil after various times of contact with PVC discs at 40 °C: 0 day (b), 1 day (c), 9 days (d), 12 days (e).
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
Absorbance (arbitrary units)
Absorbance ( arbitrary units)
SO
0. 0553 mg/ml 0. 1382 mg/ml 0. 2767 mg/ml
(a) 3 4 2 1
0. 5530 mg/ml
(b)
ESO 2000
1500 1000 Wave number (cm-1)
711
4000
3500
3000
2500 2000 1500 Wave number (cm-1)
1000
500
500
Fig. 8. FTIR spectra of PVC film (a) and PVC film with additives (b).
Fig. 6. FTIR spectra of ESO, SO and solutions of various concentrations of ESO in SO.
they are all identical. Furthermore the characteristic bands are overlapped and the amounts of migrated additives are very low. However a more deep investigation of the domain 640–800 cm1 (epoxy group) of the spectra of sunflower oil after various times of contact with
(a) 723
0.5
0.4
(b) 0.5
723
686
Absorbance
Absorbance
0.6
PVC discs by using the software GRAMS 386 as shown in Fig. 5 evidenced the migration of ESO. So the analysis of the bands of Fig. 5(a–e) shows the shift of the band at 723 cm1 of sunflower oil (b) to 724 cm1 (c–e) which is close to the position of the corresponding band in ESO at 726 cm1. In the same manner, simulated bands in sunflower oil at 687 and
723
0.4 713
0.3
0.2
0.2 800 780 760 740 720 700 680 660 640 Wave number (cm-1)
800 780 760 740 720 700 680 660 640 Wave number (cm-1) 0.6
0.6
(c) 0.5
724
713
0.4
(d)
0.5
723
725
Absorbance
Absorbance
725
0.3
725
0.3
0.3
0.2
0.2
800 780 760 740 720 700 680 660 640 Wave number (cm-1)
713
0.4
800 780 760 740 720 700 680 660 640 Wave number (cm-1)
Fig. 7. Deconvolution of the spectra of solutions of ESO in SO at various concentrations: 0.0553 mg/ml (a), 0.1382 mg/ml (b), 0.2767 mg/ml (c) and 0. 5530 mg/ml (d).
712
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
Table 3 Characteristic bands of the used additives present in PVC film [7–10] No.
Wave number (cm1)
Functional group
Mode of vibration
Additive
1 2 3 4
1740 1577 1539 1461
C@O (ester) CO 2 (carboxylic acid salt) CO 2 (carboxylic acid salt) CH2 (methyl, methylene)
Streching Streching Streching bending
ESO Ca stearate Zn stearate ESO, Zn stearate
0.30
(a)
0.40
0.20 A1577 / A1432
A1740 / A1432
0.30
(b)
0.20 0.10 0.00
0.10
0.00 0
50
100 150 200 Time (hours)
250
0
300
50
100 150 200 Time (hours)
250
300
0.40
(c)
0.35
(d)
A1461 / A1432
A1539 / A1432
0.30 0.25
0.15
0.05
0.20 0.10 0.00
0
50
100 150 200 Time (hours)
250
300
0
50
100 150 200 Time (hours)
250
300
Fig. 9. Variation of absorbances ratios as a function of time of contact with sunflower oil.
724 cm1 (b) are shifted to 692 and 725 cm1 (e) which are close to the corresponding bands in ESO at 695 and 727 cm1 (a). On the other hand, solutions containing various concentrations (0.0553, 0.1382, 0.2767 and 0.5530 mg/ml) of ESO in sunflower oil (SO) were prepared and analysed by FTIR. The maximal concentration of 0.5530 mg/ml was chosen according to the hypothesis that all the initial amount of ESO in the PVC disc migrated in the fatty simulant. The other lower concentrations were chosen arbitrary. The spectra of these solutions are given in Fig. 6. It can be noted that the bands at 726, 1378, 1465 and 1747 cm1 which are indicated by arrows in Fig. 6 shifted from their initial position in sunflower oil. This feature may be due to an interaction of hydrogen bonding type involving epoxidized sunflower oil, sunflower
oil and the free fatty acids present [7]. Furthermore, the deconvolution of the domain 640–800 cm1 (epoxy group) was carried out. The results are shown in Fig. 7. For the lowest concentration 0.0553 mg/ml (Fig. 7a), the shape of the band is similar to those of ESO and SO (Fig. 5a and b respectively). The increasing of the concentration of ESO leads to the broadening of the band (Fig. 7b–d). Furthermore, the simulated bands shifted from 687 and 724 cm1 (Fig. 5b) to 713 and 725 cm1, respectively (Fig. 7b–d). These modifications may be due to the higher amount of ESO present in SO and to an interaction between ESO and SO. On the other hand, the comparison of Figs. 5 and 7 shows that the broadening of the band as observed in Fig. 7 has not occurred in Fig. 5. This feature can be related to the migrated amount of ESO which is very low.
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714 0.30
0.42
(a)
(b) 0.28 A1577 / A1432
0.38 A1740 / A1432
713
0.34 0.30
0.26 0.24 0.22
0.26
0.20 0
50
100 150 200 Time (hours)
250
0
300
50
100 150 200 Time (hours)
250
300
0.40
(c)
A1539 / A1432
0.35
0.30
0.25 0
50
100 150 200 Time (hours)
250
300
Fig. 10. Variation of absorbances ratios as a function of time of contact with aqueous ethanol.
0.5
done. For that purpose the following absorbances ratios were calculated:
Sunflower oil 15% (v/v) aqueous ethanol
τ (%)
0.4
A A A A
0.3 0.2 0.1 0.0 0
50
100
150 200 Time (hours)
250
300
Fig. 11. Effect of the nature of the food simulant on the rate of mass variation at 40 °C.
3.3. FTIR study of migration in PVC films Fig. 8 represents the spectra of PVC alone (a) and with all the used additives (b). The comparison of the two spectra allowed the identification of some characteristic bands which are related to the additives present in the formulation as shown in Table 3. The spectra of PVC films after various times of contact with sunflower oil and 15% (v/v) aqueous ethanol were recorded. A semi-quantitative estimation of the migration of additives (ESO, Zn and Ca stearates) was
1740/A 1577/A 1539/A 1461/A
1432: 1432: 1432: 1432:
ESO migration. Ca stearate migration. Zn stearate migration. ESO and Zn stearate migration.
The band at 1432 is due to the vibration of CH2 of PVC [11] and was taken as a reference band. The variations of these four ratios of absorbances as a function of time of contact with sunflower oil and 15% (v/v) aqueous ethanol, respectively, are given in Figs. 9 and 10. It can be noted that all these curves decreased with time of contact. This can be directly related to a phenomenon of migration of ESO, Zn and Ca stearates in the two food simulants used. Furthermore, the higher values of absorbances ratios were obtained for the films which were in contact with sunflower oil. This feature indicates the influence of the nature of the food simulant on the phenomenon of migration. 3.4. Rates of mass variation The rates of mass variation (s) as a function of time gives informationÕs about the phenomenon which occurred between the samples of PVC and the food simulants used. An increase means that the food simulant
714
D. Atek, N. Belhaneche-Bensemra / European Polymer Journal 41 (2005) 707–714
penetrated the sample while a decrease means that some additives migrated in the food simulant. Hence s gives informationÕs about the overall migration that occurred. According to current legislation (Directive 90/128/EEC and its amendments; EEC 1990), the overall migration to a foodstuff from food contact plastics must be less than 10 mg of plastic compounds per dm2 of surface area. The mass variation data are shown in Fig. 11. It can be noted that the relatively highest values of s were obtained in sunflower oil. Furthermore, an increase in s was first observed for the two food simulants indicating their penetration in the PVC discs. It was followed by a decrease in s indicating the migration of some additives in the food simulants. It seems that the penetration of the food simulants in the discs favored the mobility of the additives and then their migration. The values of the overall migration estimated were 2.457 mg/dm2 in sunflower oil and 0.786 mg/dm2 in 15% (v/v) aqueous ethanol. So, the results obtained by the mass variations of the PVC discs are in accordance with those of FTIR investigation. The migration of some additives present in the PVC discs occurred. The phenomenon is influenced by the nature of food simulant and the time of contact. However, the overall migration in the two food simulants considered is lower than the maximum allowable migration: 10 mg/dm2. On the other hand, the EEC legislation is based on a system of positive lists where compounds intended to be used as monomers or additives for food contact plastics are individually evaluated by the EEC Scientific Committee for Food (SCF). Compounds which are necessary for the production of plastics but which may be harmful to human health are restricted in their use by assigning specific migration limits (SMLs) or maximum allowed concentrations in the plastics (QMs). Concerning the additives used in this study, Zn and Ca stearates and stearic acid are included in the positive list of additives allowed for use in plastics (Directive 90/ 128/EEC). Hence there is clearly a need for further work to evaluate the specific migration of ESO. Although similar stabilisers like epoxidized soya bean oil are accepted as additives for food contact plastics, toxicological tests
are required to assess the safety of this new stabiliser. The migration levels measured in food simulants will determine the extent of the toxicological data required.
Acknowledgments The authors are indebted to Dr M. T. Benaniba who kindly prepared the epoxidized sunflower oil for us.
References [1] Starnes Jr WH. Structural and mechanistic aspects of the thermal degradation of poly (vinyl chloride). Prog Polym Sci 2002;27:2133–70. [2] Minagawa M. New developments in polymer stabilization. Polym Degrad Stab 1989;25:121–41. [3] Stepeck J, Daoust H. Additives for plastics. New York: Springer; 1983. [4] Dworkin RD. PVC stabilizers of the past, present and future. J Vinyl Technol 1989;11(1):15–22. [5] Benaniba MT, Belhaneche-Bensemra N, Gelbard G. Stabilizing effect of epoxidized sunflower oil on the thermal degradation of poly (vinyl chloride). Polym Degrad Stab 2001;74:501–5. [6] Benaniba MT, Belhaneche-Bensemra N, Gelbard G. Stabilization of PVC by epoxidized sunflower oil in the presence of zinc and calcium stearates. Polym Degrad Stab 2003;82(3):245–9. [7] Socrates G. Infrared characteristic group frequencies. New York: John Wiley & Sons; 1980. [8] Guillen MD, Cabo N. Infrared spectroscopy in the study of edible oils and fats. J Sci Food Agric 1997;75: 1–11. [9] Beltran M, Marcilla A. Fourier transform infrared spectroscopy applied to the study of PVC decomposition. Eur Polym J 1997;33(7):1135–42. [10] Benavides R, Edge M, Allen NS, Mellor M, Harvey H, Schmets G. The evaluation of an innovative costabilizer for poly (vinyl chloride)—II. Interactions between metal stearates and the costabiliser. Polym Degrad Stab 1996; 53:319–27. [11] Krimm S, Folt VL, Shipman JJ, Berens AR. Infrared spectra and assignments for PVC and deuterated analogs. J Polym Sci 1963(Part A1):2621–50.