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Heat stability and migration from silicone baking moulds



Mitt. Lebensm. Hyg. 96, 281– 297 (2005) 281
Heat stability and migration from
silicone baking moulds
Roger Meuwly, Kurt Brunner, Céline Fragnière, Fritz Sager and Vincent Dudler
Swiss Federal Office of Public Health, P.O. Box, 3003 Bern
Received 27 May 2005, accepted 23 August 2005
Flexible silicone baking moulds, available in different forms and colours, have
been marketed for some years as alternatives to traditional metal bakeware. Accord-
ing to the manufacturers, silicone baking moulds offer numerous practical advan-
tages: they are non-stick, can be used in the microwave, are dishwasher-safe and
resistant to a large temperature range.
Silicones constitute a group of polymeric chemical substances containing poly-
siloxanes characterized by Si-O-Si and Si-C bonds. Silicones include a range of
products with a variety of properties and applications: silicone liquids (release
agents, impregnating agents for textiles, additives, etc.), silicone pastes (lubricants,
etc.), silicone resins (heat-resistant and release coatings, etc.) and silicone elastomers
(sealants, baking moulds, etc.).
Silicones, for food contact applications, are not regulated at the EU level but at
the national level for example in Germany (1), France (2), etc. Annex 1 of the Regu-
lation (EC) 1935/2004 includes Silicones within a list of materials and articles which
may be covered in the future by specific measures (3). In Switzerland, there are no
specific regulations for articles in silicones but they must fulfill the general require-
ments of the Swiss Ordinance concerning “Articles of Daily Use” (4) which states,
as in the article 3 of the Regulation (EC) 1935/2004, that articles should not release
to or form in foodstuffs any substance in a quantity that poses a risk to human
health or that adversely affects the organoleptic properties of the food. The Council
of Europe, in which Switzerland actively participates, issued “Resolution AP (2004)
5 on silicones used for food contact applications” which contains some specific
requirements and an inventory list of substances used in the manufacture of the
products (5). One requirement states: “The total of all substances migrating into
food from silicone materials or articles should not exceed 10 mg/dm2of the surface
Original papers
Meuwly 19.10.2005 13:12 Uhr Seite 281
area of the final material or article or 60 mg/kg of food, this being considered as the
overall migration limit”. The same limit is given in the French legislation (2).
Even though silicone elastomers demonstrate a high degree of thermal stability and
excellent resistance to aging, high temperatures lead to depolymerization of the elas-
tomer, with subsequent volatilization and migration of certain substances. The few pub-
lications concerning the suitability of silicones as food contact materials have indeed
shown that a certain quantity of substances migrates from silicone-based articles (6, 7).
The objective of this work was to study the release of chemical substances from
the silicone baking moulds at various temperature, especially around 200220°C,
temperatures attained in an oven when cakes and pastries are baked. Some tests at
higher temperatures up to 280°C were also performed to check the statement of the
manufacturers concerning the heat stability of the moulds. The tests currently spec-
ified for migration for food contact applications involve temperatures not exceeding
175°C. It is thus very important to develop migration procedures that make possi-
ble the investigation in a real temperature range.
The stability of the silicone moulds at high temperature was checked by two
tests: measurement of the loss of volatile components during heating as described
in the German recommendations (1) and the French legislation (2) and overall
migration (OM) studies with modified polyphenylene oxide as a food simulant.
Some indications about the nature of the migrants were also collected during this
Silicone baking moulds of various shapes were received or bought from differ-
ent retail stores (Table 1). These kitchenware are used in food preparation, especially
for baking cakes, pastries, etc., in a microwave or in a conventional oven and for
storage of food in the freezer. According to the manufacturers, the moulds can with-
stand extreme temperatures such as the ones reported in Table 1.
282 Mitt. Lebensm. Hyg. 96 (2005)
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Table 1
Characteristics of silicone baking moulds samples
Sample Nr Type Temperature Thickness Colour
mould size (cm) min/max (°C)1(mm)2
A4 Baking forms –25 to 220 1.97 Red
B12 Mini-Gugelhofs –25 to 250 1.17 Red
C4 Mini-puddings –60 to 260 1.39 Blue
D6 Muffins –40 to 280 0.95 Orange
E24 Minicakes –40 to 280 1.02 Black
F9 Minicakes –40 to 280 0.97 Red
G9 Minicakes –60 to 280 1.20 Red-brown
1according to the manufacturers
2average value, measured at different positions
Chemicals and apparatus
Modified polyphenylene oxide (MPPO, Tenax, temperature stability: Tmax=
350°C) 60 to 80 mesh (Supelco): before the first use MPPO was extracted 6 h with
diethylether, transferred in a Petri dish which was placed in a fume hood to allow the
diethylether to evaporate. The complete evaporation of the solvent was achieved by
placing the Petri dish into an oven at 160°C for 6 h. Dry MPPO was stored into a
closed flask. Diethylether p.a. (Merck) was distilled over 1 g sodium hydride per liter
diethylether. The samples were aged in an oven (Heraeus T 5042 EK) without air cir-
culation. The oven was regulated within the permitted tolerance (±5°C) on the tem-
perature indication given by an additional thermocouple (type K) positioned in the
middle of the oven at the sample location. The temperature profile of each experiment
was recorded by a datenlogger (Ecolog TN4 with an accuracy of ±0.6°C at 200°C).
GC-MS analyses were performed using a Hewlett-Packard GC 5890 equipped
with an HP 5972 MSD detector. The capillary column was a DB-1ht (J & W Scien-
tific) with the dimension 30 m0.25 mm i.d. and a coating film thickness of 0.1 µm.
The GC initial settings were: injector temperature 270°C and column temperature
70°C followed by a temperature program of 20°C/min up to 360°C. The mass spec-
trometer was operated at a transfer line temperature of 280°C with EI at 70eV at a
scan mass-range 50400 amu. For spectra interpretation a Wiley 7 library was used.
MALDI-TOF/MS spectra were obtained from Solvias AG, 4002 Basel, using an
LDI-1700 spectrometer (Linear Scientific, Inc. Reno, USA) equipped with a laser
operating at 337 nm. The matrix used was 2,5-dihydroxybenzoic acid. The mass-
range was 10000 Da (4 calibrating substances from 1300 Da to 7000 Da) with a mass
accuracy of ±0.1%. Single charged ions ([M+Na]+) were detected and analyzed.
Mitt. Lebensm. Hyg. 96 (2005) 283
Meuwly 19.10.2005 13:12 Uhr Seite 283
Overall migration at high temperatures
According to the Resolution of the Council of Europe (5), migration tests
should be conducted according to the EC Plastic Directives. The overall migration
tests of the silicone baking moulds were performed according to the Commission
Directive 97/48/EC laying down the basic rules necessary for testing migration of
the constituents of plastic materials and articles intended to come into contact with
foodstuffs (8). The experimental methods are described in the European Standard
EN 1186-13: “Test methods for the determination of the overall migration at high
temperatures” (9). The determination of the overall migration into fatty food simu-
lants from plastic material articles is performed by total immersion of test specimens
in a fatty food simulant, normally olive oil, at temperatures up to 175°C for selected
times. At high temperature the migration tests with olive oil introduce a number of
analytical difficulties (oxidation of oil, ...). Replacement of olive oil by an appropri-
ate absorbent material is an alternative accepted by the legislation: MPPO is listed
like isooctane and ethanol as a test medium in substitute fat test (8). In this substi-
tute procedure, the mass of the components absorbed on modified polyphenylene
oxide (MPPO) is taken as the measure for the assessment of the overall migration
into a fat simulant. This procedure with MPPO has allowed to test silicone baking
moulds up to 280°C, maximum temperature according to the manufacturers of the
heat stability of some articles.
When an article is intended to come into repeated contact with foodstuffs like
these silicone baking moulds, tests shall be carried out three times (M1, M2 and M3)
on a single sample using a fresh sample of simulant on each test as described in the
European Standard EN 1186-1: “Guide to the selection of conditions and test meth-
ods for overall migration” (10). Its compliance shall be checked on the basis of the
level of the migration found in the third test (M3).
The residue of the migration was analyzed by GC-MS and MALDI-TOF to
investigate the nature of the migrants.
The surface of the sample to be tested was covered with modified polyphenylene
oxide (MPPO) and kept at the selected time/temperature test conditions in an oven.
The MPPO were then extracted with diethylether. The extract was evaporated to
dryness using a nitrogen stream and the residue mass was determined gravimetri-
cally. The residual mass does not contain volatiles.
Sample preparation
The determination of the overall migration of silicone baking moulds was
performed on the flat bottom part of the article in contact with the food. The dust
on the samples was removed with compressed air and the samples were treated with
antistatic cloth.
284 Mitt. Lebensm. Hyg. 96 (2005)
Meuwly 19.10.2005 13:12 Uhr Seite 284
The surface of the sample to be tested was covered with MPPO taking 4 g
MPPO per dm2of surface area. For the blank determination, an empty Petri dish
was taken and the same mass of MPPO was placed on it. The examination of a blank
was carried out in parallel. The test sample was covered with a glass plate and put in
the preheated oven at the required temperature. The sample was left in the oven for
the selected period of time (M1, 1 h in general) as soon as the temperature in the
oven had once again reached a temperature within the permitted tolerance (±5°C)
for the test temperature. The average time for the oven to reach the test temperature
again was 13 min at 175°C, 16 min at 220°C, 23 min at 260°C and 27 min at 280°C.
The sample was removed from the oven and allowed to cool to room temperature
without removing the glass cover. The MPPO was carefully transferred into a
200 ml Erlenmeyer flask and 20 ml of diethylether was added. The solution was
stirred for 1 minute and then allowed to stand for 1 minute without shaking. The
diethylether solution was decanted from the MPPO through a filter into a 200 ml
vial. The extraction procedure of MPPO was repeated twice with each time 30 ml
diethylether. The filter was rinsed with 10 ml diethylether and the combined
diethylether solution was concentrated with a Rotavap to approximately 5 ml. The
residue was transferred to a weighted 15 ml vial and concentrated further to dry-
ness, using a stream of nitrogen until constant weight was obtained. The mass of the
residue was determined by substracting the original mass of the vial from the mass
of vial plus residue.
The second migration test (M2) was performed with the sample used for the first
test via the same procedure as described above. The third migration test (M3) was
performed with the sample used for the first and the second tests via the same pro-
cedure. Prolonged heating time tests were performed on two samples to check
the effect of a repeated use on the overall migration. Again the overall migration
value during a repeated 1 h test at the selected temperature was determined during
100 hours. The sample was heated with MPPO for (x-1) h, MPPO was discarded, a
fresh sample of MPPO was taken and the sample was heated for a further 1 h. The
migrants in the fresh MPPO were determined to give the overall migration value for
1 h at time x.
The precision of the measurements was assessed on different samples at 220°C.
This was shown to be sample dependent. The standard deviation under repeatability
conditions oscillated between 1228% for the first migration test (M1) and
decreased steadily for each additional heating cycle to reach 6–15% for the third
migration test (M3).
The total release of volatile substances was measured by simply weighing the
moulds before and after the heating during 4 hours at 200°C as described in the
German recommendations (1) and the French legislation (2). About 10 g of the sam-
Mitt. Lebensm. Hyg. 96 (2005) 285
Meuwly 19.10.2005 13:12 Uhr Seite 285
ple were cut in pieces of about 12 cm and left for 48 h above calcium chloride in a
desiccator. The pieces were weighed (precision of ±0.1 mg) and then put in the oven
for 4 h at 200°C. After cooling in a desiccator the pieces were weighed again and the
percentage of volatiles was calculated based on the ratio of the weights. The release
of volatiles should not exceed 0.5% (1, 2).
Results and discussion
Overall migration
The determination of the overall migration of the sample A was performed at
different temperatures during repeated 1 h contact cycle with MPPO (Figure 1). Up
to 100°C the sample showed low migration value, especially at the third 1 h expo-
sure. From 150°C, the values increased rapidly for the three exposure time and the
limit of 10 mg/dm2prescribed by the Resolution of the Council of Europe (5) is
reached in most cases. These results confirm the good stability of silicone elastomers
up to 150°C. All experimental points can be fitted with a sigmoidal curve of the
where T is the temperature of observation in degree Celsius, R depicts a degra-
dation rate of the silicone, K and b are two constant factors. The curve in Figure 1
shows the amount of migrants liberated by sample A at the third 1 h exposure test
(M3) used to check the compliance of articles intended to come into repeated con-
tact with foodstuffs.
286 Mitt. Lebensm. Hyg. 96 (2005)
0 50 100 150 2 00 250 30 0
Overall migration during one hour [mg/dm
heating cycle (M1)
heating cycle (M2)
heating cycle (M3)
Fit curve of M3 data
Figure 1 Overall migration of sample A during a repeated one hour test
Meuwly 19.10.2005 13:12 Uhr Seite 286
The thermal stability of the different samples was tested at temperature between
175 and 280°C (Table 2). At 175°C for the first 1 h contact all the investigated sam-
ples showed high overall migration values, between 25.5 mg/dm2and 49.2 mg/dm2.
At the third exposure the values M3 used to check the compliance of articles
intended to come into repeated contact with foodstuffs were slightly lower. Again
no significant difference was observed between the samples. The increase of the test
temperature from 175 to 220, 260 and 280°C showed in parallel a slight increase of
the migration values. The behavior of the various samples at these temperatures was
almost the same. The true values for the overall migration in fatty food simulants are
subject to uncertainty owing to the lack of precision inherent in the method. A
point to consider is that at high temperatures, the more volatile compounds of the
migrate could evaporate without being absorded on the MPPO and consequently
could not contribute to the overall migration value. The values in Table 2 possibly
underestimate the real loss of material during the heating.
Table 2
Overall migration during a repeated one hour test at different temperatures
Sample A B C D E F
M1 25.5 25.9 29.1 49.2 33.8 25.8
M2 21.1 25.7 21.6 33.7 26.1 19.7
M3 21.8 21.8 23.9 31.7 23.2 17.7
M1 34.2 44.7 38.2 48.1 41.5 33.7
M2 31.8 41.9 33.4 37.2 36.0 32.1
M3 28.4 35.9 28.9 32.8 41.9 29.0
M1 45.3 42.7 40.9 44.7 50.5 37.7
M2 40.3 45.1 32.6 40.5 48.2 33.7
M3 34.7 31.8 27.2 27.9 34.1 24.9
M1 44.4 40.7 41.5 45.0 44.0 37.2
M2 32.1 33.5 38.4 39.0 37.6 32.3
M3 32.8 31.6 39.6 31.3 34.9 27.3
M1: Sample X heated 1 h (X1)
M2: Sample X1 heated 1 h (X2)
M3: Sample X2 heated 1 h (X3)
The values of the overall migration during a 1 h heating cycle at 220°C based on
the heating time of samples A and D are depicted in Figure 2a. These values give an
indication of the quantity of the migrants liberated each time the mould is heated for
1 h at 220°C. The values of the overall migration decrease rapidly during the first
exposure of the moulds with MPPO. But even after 100 h of heating, a small quan-
tity of substances continue to migrate from the moulds to the MPPO. This certainly
indicates a continual degradation (depolymerization) process which always supplies
Mitt. Lebensm. Hyg. 96 (2005) 287
Meuwly 19.10.2005 13:12 Uhr Seite 287
new substances able to migrate. Mould A is two times thicker than mould D; this
certainly plays a role in the quantity of the products of decomposition and there-
after in the quantity of the migrants. The data were not corrected as regards the
thickness of the samples in order to depict effective migration values. By plotting
the measured values as the sum of the measured migration in function of the square
root of time (Figure 2b) it appears clearly that the loss is not linear. This indicates
that the kinetics of loss is not principally governed by a diffusion process. Other
processes, such as the degradation rate of the silicone backbone or the direct
volatilization of migrants at the sample surface are likely to play a role in this meas-
The results do not take into account the “simulant D reduction factor” used
to correct the results for foodstuffs containing fat as indicated in Directive
85/572/EEC (11). For example a reduction factor of 3 would apply for confec-
tionery products in paste form with fatty substances on the surface and a reduction
factor of 5 for fresh pastry, cakes and other baker’s wares with fatty substances on
the surface. At all temperatures, even at 280°C at the third 1 h exposure contact and
when a reduction factor of 5 is used, all the investigated silicone baking moulds had
an overall migration value below the recommended limit of 10 mg/dm2(5).
288 Mitt. Lebensm. Hyg. 96 (2005)
0 20406080100120
time [ho u
Overall migration [mg/dm
sample A
sample D
Cumula tive loss [mg/dm
Figure 2 Overall migration during one hour test at 220°C after a prolonged heating time
Meuwly 19.10.2005 13:12 Uhr Seite 288
The total release of volatile substances after 4 h at 200°C (Table 3) was measured
by weighing the moulds before and after the heating as described in the German
recommendations (1) and the French legislation (2). During the first heating cycle of
4 h at 200°C, the weight loss of the samples was 0.11–1.78%. As shown in Table 3
the values of the weight loss decrease rapidly after the first heating cycle. Already
during the second and during the whole of the following heating cycle, all the sam-
ples showed a value lower than 0.21%, below to the limit of 0.5% given in the Ger-
man and French recommendations. The high weight loss in the first heating cycle is
most likely due to residual solvents and/or by-products formed during the manu-
facture of the articles or due to the fact that the time for the postcuring of the article
was not sufficient. This process is easy but requires much energy. To avoid addi-
tional expenses, some firms leave out this last stage and ask their customers to heat
the mould at 230°C during 2 h without food before the first use, stating that the
possible development of some smoke is not deleterious.
Table 3
Weight loss of volatiles (%) at 200°C in heating cycles of 4 h
Number of heating cycle
Sample 1235
A 0.11±0.01* 0.04± 0.01 0.02± 0.01 0.01± 0.01
B 0.58±0.01 0.12±0.01 0.08±0.01 0.04 ±0.01
C 0.93±0.01 0.15±0.00 0.07±0.01 0.04 ±0.01
D 1.68±0.02 0.20± 0.02 0.11 ± 0.03 0.06±0.04
E 0.96±0.04 0.21±0.03 0.15±0.02 0.08 ±0.01
F 1.78 ±0.02 0.07±0.03 0.14 ± 0.03 0.12±0.09
G 0.46±0.01 0.12± 0.00 0.06 ± 0.01 0.04±0.01
* average of three measurements with the standard deviation s
By varying the temperature from 200 to 220 and then to 280°C (Tables 35), the
increase of the weight loss is considerable. Table 5 shows that the least stable sample
D lost 4.47% of its weight during the first 4 h of heating at 280°C and even 1.44%
during the 5th heating cycle of 4 h. These results show a strong dependence of the
amount of volatiles on the heating temperature and clearly indicate that these sili-
cone moulds are not as stable at high temperature as advertised by their manufac-
turers. The sample D, supposed to withstand temperature to 280°C, lost during the
first 12 h of heating (34 h heating cycle) 1.99% of its weight at 200°C, 2.38% at
220°C and even 8.58% at 280°C. After these prolonged thermal treatments, some
samples were discolored or brittle.
Mitt. Lebensm. Hyg. 96 (2005) 289
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Table 4
Weight loss of volatiles (%) at 220°C in heating cycles of 4 h
Number of heating cycle
Sample 1235
A 0.15±0.01* 0.06±0.01 0.05± 0.01 0.02±0.01
B 0.74±0.02 0.17±0.01 0.10±0.01 0.02± 0.01
C 1.21±0.03 0.14±0.02 0.10±0.03 0.08 ±0.01
D 2.11±0.06 0.19± 0.01 0.08 ± 0.02 0.08±0.03
E 1.37±0.09 0.19±0.05 0.14±0.03 0.11 ±0.01
F 1.86 ±0.08 0.17±0.03 0.14 ± 0.02 0.16±0.03
G 0.65±0.02 0.13± 0.01 0.08 ± 0.01 0.05±0.01
* average of three measurements with the standard deviation s
Table 5
Weight loss of volatiles (%) at 280°C in heating cycles of 4 h
Number of heating cycle
Sample 1235
A 0.78±0.08* 0.30±0.02 0.28± 0.04 0.25±0.02
B 3.01±0.11 2.24±0.01 2.23±0.21 1.34 ±0.22
C 4.11±0.25 2.87±0.18 1.70±0.21 0.63 ±0.01
D 4.47±0.22 2.25± 0.48 1.86 ± 0.37 1.44±0.38
F 3.27 ±0.07 1.51±0.08 1.40 ± 0.09 1.95±0.07
* average of three measurements with the standard deviation s
Characterisation of the migrants
Silicone baking moulds are silicone elastomers made from crosslinked polydi-
methylsiloxanes. Thermal degradation of silicone elastomers have been described in
many studies (12–15). The decomposition of the polymers occurs in three stages:
1) evaporation of volatile components, 2) thermal decomposition and 3) thermal
oxidation: The second and third processes often overlap. Additives and initial
removal of volatiles by postcuring increase the stability (16).
290 Mitt. Lebensm. Hyg. 96 (2005)
OSi Si
Figure 3 Structure of the migrants
Cyclic polydimethylsiloxanes (Cn) Linear polydimethysiloxanes (Ln)
n=5– 35 Si(CH3)2-groups
Meuwly 19.10.2005 13:12 Uhr Seite 290
According to the literature, the degradation products consist primarily of
cyclic polydimethylsiloxane (Cn) and linear polydimethylsiloxane (Ln) oligomers
(Figure 3). It is assumed that linear polydimethylsiloxanes are methyl terminated linear
chain without excluding the fact that some chains are hydroxyl terminated (17, 18).
The distribution of the different siloxanes in the residue of the global migration
at different temperatures were determined from the MALDI-TOF and the GC-MS.
In the MALDI-TOF, the oligomeres have a difference of 74.2 Dalton which is the
mass of the repeated unit Si(CH3)2O-group. The migrating substances mainly con-
Mitt. Lebensm. Hyg. 96 (2005) 291
8 9 10 11 12 13 14 15 16 17 18
Time [min]
Abundance [a.u.]
C8 C9 C10
C14 C15
L8 L9 L10
L11 L12 C24
Figure 4 GC-MS of residue of sample A at the third one hour exposition at 175°C
9 101112131415161718
Time [min]
Abundance [a.u.]
C8 C9
C22 C23
Figure 5 GC-MS of residue of sample B at the third one hour exposition at 175°C
Meuwly 19.10.2005 13:12 Uhr Seite 291
292 Mitt. Lebensm. Hyg. 96 (2005)
Table 6
Composition of residue in % from the overall migration tests
Temp. 175°C 220°C 260°C
Sample A B C D E F A B C D E F A B C D E F
C7 519 1.3
C8 593 2.2 1.0 1.1
C9 667 0.6 3.5 1.7 2.9
C10 742 1.1 1.0 5.5 2.6 1.2 5.6
C11 816 3.6 1.9 8.4 3.8 3.1 8.7 0.4
C12 890 6.2 3.1 11.1 4.5 7.3 11.0 1.0 1.1 1.0
C13 964 11.0 5.1 12.4 5.0 8.8 12.2 1.7 1.3 2.8 2.6 1.7 2.9
C14 1038 15.1 7.6 13.5 5.3 10.4 13.1 4.7 4.3 7.1 5.2 4.5 7.0 0.5 0.5
C15 1112 16.4 9.6 12.9 5.1 11.3 12.7 9.1 8.9 12.8 7.9 8.9 12.0 1.4 0.9 1.4
C16 1186 14.8 9.6 10.6 4.3 10.6 10.7 13.4 12.3 16.3 9.6 12.6 14.7 3.2 1.5 2.1 3.3 0.6 1.0
C17 1261 11.9 8.1 7.9 3.4 8.3 8.2 15.6 12.9 16.1 9.7 13.9 14.7 6.4 3.2 4.3 6.7 1.7 3.0
C18 1335 7.8 5.8 5.1 2.4 5.5 5.8 14.7 11.1 13.3 8.7 13.4 13.0 10.0 6.2 8.2 10.3 4.0 6.7
C19 1409 4.9 4.0 3.1 1.6 3.5 3.8 12.5 8.6 10.3 7.2 10.8 10.5 12.7 10.2 12.4 12.7 8.0 11.7
C20 1483 3.2 2.2 1.8 1.0 2.2 2.3 10.0 6.0 7.7 5.8 8.8 8.2 14.3 14.0 15.3 13.0 12.9 15.2
C21 1557 1.8 1.2 1.0 0.5 1.1 1.3 7.2 4.1 5.5 4.6 6.4 6.2 14.2 14.6 16.1 11.6 15.4 16.1
C22 1632 0.9 0.6 0.5 0.7 5.0 2.6 3.7 3.4 4.8 4.3 12.3 11.9 14.0 9.6 16.6 14.4
C23 1706 3.3 1.9 2.3 2.6 3.2 2.8 10.0 11.6 11.3 7.4 14.3 11.6
C24 1780 1.9 1.1 1.2 1.6 1.9 1.7 7.2 7.5 7.2 5.2 11.5 8.5
C25 1854 0.9 0.7 0.9 0.9 4.4 3.7 4.3 3.2 7.2 5.4
C26 1918 2.4 2.6 2.7 1.6 4.4 3.3
C27 2003 1.2 1.9 1.2 0.9 2.3 1.9
C28 2077 1.3 1.2
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Mitt. Lebensm. Hyg. 96 (2005) 293
Temp. 175°C 220°C 260°C
Sample A B C D E F A B C D E F A B C D E F
L7 533 1.6
L8 607 0.7 4.4
L9 681 2.3 8.5 1.6
L10 756 4.2 11.0 3.3 0.7
L11 830 5.5 10.3 6.8 1.6
L12 904 6.2 8.0 5.5 1.3 3.1 0.7
L13 978 6.3 5.7 3.9 3.3 4.7 1.3
L14 1052 5.4 3.8 2.7 5.2 5.1 1.8 0.5
L15 1126 3.9 2.3 1.7 5.4 4.6 2.0 0.4 1.0
L16 1200 2.6 1.3 0.9 4.1 3.5 1.5 1.1 1.8
L17 1275 1.4 0.6 2.8 2.4 1.0 1.4 2.4
L18 1349 0.7 0.3 1.6 1.6 2.1 2.5
L19 1423 0.5 0.8 1.0 2.1 2.1
L20 1497 0.4 0.6 1.6 1.4
L21 1571 0.3 0.2 1.6 1.0
Cn= cyclic polydimethylsiloxane, Ln= linear polydimethylsiloxane
n= number of Si(CH3)2-groups
Meuwly 19.10.2005 13:12 Uhr Seite 293
sist of siloxane oligomers of molar mass between 500 and 2100 Dalton which corre-
spond to oligomers with 7 to 28 Si(CH3)2O-groups. Figures 4 and 5 represent typi-
cal GC-MS graphs of the residue of the global migration. Figure 4 represents the
GC-MS obtained with sample A, mostly cyclic polydimethylsiloxane oligomers, at
the third one hour exposition (M3) at 175°C whereas Figure 5 represents sample B,
mixture of cyclic and linear polydimethylsiloxane oligomers, at the same condition.
Samples C, F and G show the same pattern as sample A whereas sample D and E, to
some extent, are comparable to sample B.
The composition of the residue at the third one hour exposition (M3) in fonc-
tion of the temperature is given in Table 6. The GC-MS of the residue of the samples
at different temperatures were normalized by considering that the total surface of all
silicone peaks equals 100%. The sum of cyclic (Cn) and linear (Ln) polydimethyl-
siloxane oligomers for some samples differ slightly from 100% due to the fact that
the percentage of each peak is only given to the first decimal.
By increasing the temperature during the test for the global migration, the size
of the siloxane oligomers increases. From 175°C to 220°C and finally to 260°C, the
largest peaks for the sample A increase from n=14–16 to n=16–18 and n=1921
units of Si(CH3)2O-groups. By increasing also the temperature from 175 to 220 and
finally to 260°C, the content of the linear polydimethylsiloxane oligomers in the
residue decreases, for exemple from 39.7% to 25.2 and then 10.3% for sample B.
Compounds with a molecular weight above 1000 Dalton are commonly consid-
ered to be of low toxicological relevance because they can not normally enter the
metabolism. The percentage of the polydimethylsiloxanes lower than 1000 Dalton
varies from 21.9 to 68.1% at 175°C, between 1.7 and 14.2% at 220°C, whereas at
260°C all the polydimethylsiloxanes in the residues are superior to 1000 Dalton.
Two points could play an important role in this topic; at high temperatures: a) the
thermal degradation of silicone elastomers favours the formation of larger
oligomers and/or b) the lower oligomers are not absorbed by MPPO.
Up to 100°C, silicone elastomeres can be considered as inert as shown by low
overall migration values. Around 150°C, silicone elastomers start to degrade at such
a rate that the limit of 10 mg/dm2prescribed in the Resolution of the Council of
Europe is reached in most cases. To keep the value within the limit, it is necessary to
take into account the “simulant D reduction factor”. Due to analytical uncertainty,
there is no significant difference in the overall migration results of the various sili-
cone baking samples. A study has shown that MPPO generally overestimates the
contamination of the foods from packaging (19). The release of volatiles is high dur-
ing the first use and then decreases rapidly.
Neither the determination of the overall migration, nor that of the volatiles gives
a complete view of the behaviour at high temperature of the silicone moulds. Each
one brings some part of the response to the thermal stability of silicone elastomers.
294 Mitt. Lebensm. Hyg. 96 (2005)
Meuwly 19.10.2005 13:12 Uhr Seite 294
Some questions concerning the reality of the high temperature migration test-
ings are still open. What is the real temperature at the food-silicone baking moulds
interface especially in the case of food containing a certain quantity of water? What
is the temperature of the paste or the cake in a normal or a microwave oven? These
questions are very significant due to the fact that increasing the temperature acceler-
ates the rate of the degradation process of the moulds. The migration levels in foods
compared to MPPO is another critical point. It is therefore intended to investigate
further the migration study with real foods instead of simulants.
We would like to thank Awilo Ochieng Pernet for carefully reading the manus-
Heat stability of silicone baking moulds used in bakery has been evaluated with
different standard methods. The results of the migration tests using modified
polyphenylene oxide (MPPO, Tenax) as a food simulant indicate that these materi-
als are stable up to 150°C. Above this temperature the limit of 10 mg/dm2pre-
scribed by the Resolution of the Council of Europe is reached in most cases. The
migration residue is essentially composed of cyclic oligomeric polydimethylsilox-
anes, however, some samples contain cyclic and linear oligomeric polydimethyl-
siloxanes. The mass of these oligomeres is between 500 and 2100 Dalton whereas the
maximum varies from 1000–1500 Dalton depending on the test temperature. The
loss of volatiles at 200°C completes the migration values and shows that some
moulds lose more than 0.5% of their weight during a 4 hour heating process.
Although the loss of the mould weight decreases rapidly with the number of uses,
all the observations indicate that silicone baking moulds are not inert enough for use
in all the range of temperature indicated by the manufacturers.
Die Temperaturbeständigkeit von Silikonbackformen wurde mit verschiedenen
genormten Methoden überprüft. Die Ergebnisse der Globalmigrationsprüfung mit
modifiziertem Polyphenylenoxid (MPPO, Tenax) als Lebensmittelsimulanz hat
ergeben, dass das Material bis 150°C stabil bleibt. Ab dieser Temperatur überschrei-
ten fast alle geprüften Muster den Globalmigrationsgrenzwert von 10 mg/dm2, der
von dem Europarat empfohlen wird. Der Hauptanteil des Migrationsrückstandes
besteht aus zyklischen oligomeren Polydimethylsiloxanen, und in einigen Mustern
sind auch lineare vorhanden. Diese Oligomere haben Molekularegewichte zwischen
500 und 2100 Dalton, wobei der Hauptanteil je nach Testtempereratur zwischen
1000–1500 Dalton variiert. Die Bestimmung der flüchtigen Anteile bei 200°C ver-
vollständigen die Globalmigrationresultate, teilweise betragen die Gewichtsverluste
während des Erhitzens nach 4 Stunden mehr als 0.5%. Obschon der Gewichts-
Mitt. Lebensm. Hyg. 96 (2005) 295
Meuwly 19.10.2005 13:12 Uhr Seite 295
verlust der Silikonbackformen mit zunehmenden Gebrauch exponentiell abnimmt,
zeigen alle Experimente, dass, entgegen den Angaben der Hersteller, die Silikon-
backformen über den ganzen Temperaturbereich nicht genügend inert sind.
La stabilité thermique des moules en silicone utilisés en pâtisserie a été étudiée à
l’aide de diverses méthodes types. Les résultats des essais de migration utilisant de
l’oxide de polyphénylène modifié (MPPO, Tenax) comme simulant alimentaire
indiquent que ces matériaux sont stables jusqu’à 150°C. Au-dessus de cette tem-
pérature, la valeur de 10 mg/dm2recommandée par la Résolution du Conseil de
l’Europe est atteinte dans la plupart des cas. Le résidu de migration est composé
principalement d’oligomères de polydiméthylsiloxane cycliques mais également
linéaires pour certains moules. Ces oligomères ont une masse comprise entre 500 et
2100 Dalton avec un maximum qui varie de 1000–1500 Dalton avec la température
de test. La mesure de perte des substances volatiles à 200°C complète les résultats de
migration et montre que certains moules perdent plus de 0.5% de leur poids durant
un chauffage de 4 heures. Bien que la perte de masse des moules diminue rapidement
avec le nombre d’utilisation, toutes les observations indiquent que les moules de
cuissons en silicone ne sont pas assez inertes pour une utilisation dans tout le
domaine des températures annoncées par les fabricants.
Key words
Silicones, baking moulds, heat stability, migration, volatiles
1Franck R. und Wieczorek H. (Eds): Kunststoffe im Lebensmittelverkehr, Empfehlungen des
Bundesinstitutes für Risikobewertung, XV. Silicone, 53. Lieferung, Carl Heymanns Verlag,
Köln, Januar 2004. (
2 Matériaux au contact des denrées alimentaires, Produits de nettoyage de ces matériaux: Arrêté du
25 novembre 1992. Les éditions des Journaux officiels français brochure N° 1227, 15 juillet 2002
3 Regulation (EC) No 1935/2004 of the European Parliament and of the Council of 27 October
2004 on materials and articles intended to come into contact with food and repealing
Directives 80/590/EEC and 89/109/EEC. Official Journal of the European Communities
13.11.2004 L 338
4 Verordnung vom 1. März 1995 über Gebrauchsgegenstände (GebrV, SR 817.04). EDMZ,
3000 Bern. (
5 Council of Europe, Resolution AP (2004) 5 on Silicones used for food contact applications
(replacing Resolution AP (99) 3). Council of Europe, Strasbourg
6Piringer O. and Bürcherl T.: Extraction and Migration Measurements of Silicone Articles and
Materials coming into Contact with Foodstuffs. Document RD-6/26 from Committee of Experts
on Materials coming into Contact with Food. Council of Europe, Strasbourg, November 1994
7Lund K.H. and Petersen J.H.: Safety of food contact silicone rubber: Liberation of volatile
compounds from soothers and teats. Eur Food Res Technol 214, 429–434 (2002)
296 Mitt. Lebensm. Hyg. 96 (2005)
Meuwly 19.10.2005 13:12 Uhr Seite 296
8 Commission Directive 97/48/EC of 29 July 1997 amending for the second time Council
Directive 82/711/EEC laying down the basic rules necessary for testing migration of the
constituents of plastic materials and articles intended to come into contact with foodstuffs.
Official Journal of the European Communities 12.08.1997 L 222
9 EN 1186-13: European Standard, Materials and articles in contact with foodstuffs – Plastics –
Part 13: Test methods for overall migration at high temperatures, September 2002
10 EN 1186-1: European Standard, Materials and articles in contact with foodstuffs – Plastics –
Part 1: Guide to the selection of conditions and test methods for overall migration, April 2002
11 Commission Directive 85/572/EEC of 19 December 1985 laying down the list of simulants to
be used for testing migration of constituents of plastic materials and articles intended to come
into contact with foodstuffs. Official Journal of the European Communities 31.12.1987 L 372
12 Hilborg H., Karlsson S. and Gedde U.W.: Characterisation of low molar mass siloxanes
extracted from crosslinked polydimethylsiloxanes exposed to corona discharges. Polymer 42,
8883–8889 (2001)
13 Homma H., Kuroyagi T., Izumi K., Mirley C.L., Ronzella J. and Boggs S.A.: Evaluation of
surface degradation of silicone rubber using gas chromatography/mass spectroscopy: IEEE
Transactions on power delivery 15 (2), 796–803 (2000)
14 Radhakrishnan T.S.: New method for evaluation of kinetic parameters and mechanism of
degradation from pyrolysis-GC studies: thermal degradation of polydimethylsiloxanes.
Journal of Applied Polymer Science 73, 441–450 (1999)
15 Patel M., Soames M., Skinner A.R. and Stephens T.S.: Stress relaxation and thermogravimetric
studies on room temperature vulcanised polysiloxane rubbers. Polymer Degradation and
Stability 83, 111–116 (2004)
16 Fateh-Alavi K., Gällstedt M. and Gedde U.W.: The effect of antioxidants on the surface oxi-
dation and surface craking of crosslinked polydimethylsiloxane. Polymer Degradation and
Stability 74, 49–57 (2001)
17 Hunt S.M. and George G.A.: Characterization of siloxane residues from polydimethylsilox-
ane elastomers by MALDI-TOF-MS. Polym. Int. 49, 633–635 (2000)
18 Krivda A., Hunt S.M., Cash G.A. and George G.A.: MALDI-TOF/MS Characterization of
LMW PDMS in high voltage HTV silicone rubber insulators. IEEE CEIDP, Victoria BC
Canada 703–708 (2000)
19 Mountfort K., Kelly J., Jickels S.M. and Castle L.: A critical comparison of four test methods
for determining overall and specific migration from Microwave susceptor packaging. J. Food
Prot. 59 (5), 534–540 (1996)
Corresponding author: Dr. Roger Meuwly, Swiss Federal Office of Public Health,
Food Science Division, Food Chemistry Section, P.O. Box, 3003 Bern, Switzerland,
Mitt. Lebensm. Hyg. 96 (2005) 297
Meuwly 19.10.2005 13:12 Uhr Seite 297
... C-VMS and l-VMS are potential migrants of silicone products. Few publications have investigated the migration behavior of silicone elastomers to food simulants or food (Meuwly et al., 2005;Helling et al., 2009;Helling et al., 2010;Helling et al., 2012;Zhang et al., 2012). Migration strongly depends on the food or food simulants used. ...
... In Germany, a representative National Food Consumption Study was conducted in 2005-2006(NFCS, 2008. Because the intake in this study was only assessed for all baking products as a group (including for example, pizza), the 95th percentile intake of 140 g was used and it was assumed that cake represents 50% of this intake. ...
Linear and cyclic volatile methylsiloxanes (l-VMS and c-VMS) are man-made chemicals with no natural source. They have been widely used in cosmetics, personal care products, coatings and many other products. As a consequence of their wide use, VMS can be found in different environmental media, as well as in humans. We bought 14 new silicone baking moulds and 3 metallic moulds from the market and used them in different baking experiments. Four of the silicone baking moulds were produced in Germany, two in Italy, four in China, and for the other moulds were no information available. The metal forms were all produced in Germany. VMS were measured in the indoor air throughout the baking process and at the edge and in the center of the finished cakes using a GC/MS system. Additionally, the particle number concentration (PNC) and particle size distribution were measured in the indoor air. The highest median concentrations of VMS were observed immediately following baking: 301 μg/m³ of D7, 212 μg/m³ of D6, and 130 μg/m³ of D8. The silicone moulds containing the highest concentrations of c-VMS corresponded with distinctly higher concentrations of the compounds in indoor air. Using a mould for more than one baking cycle reduced the indoor air concentrations substantially. Samples collected from the edge of the cake had higher concentrations relative to samples from the center, with a mean initial concentration of 6.6 mg/kg of D15, 3.9 mg/kg of D9, 3.7 mg/kg of D12, and 4.8 mg/kg of D18. D3 to D5 were measured only at very low concentrations. Before starting the experiment, an average PNC of 7300 particles/cm³ was observed in the room's air, while a PNC of 140,000 particles/cm³ was observed around the electric stove while it was baking, but this PNC slowly decreased after the oven was switched off. Baking with 4 of the moulds exceeded the German indoor precaution guide value for c-VMS, but the health hazard guide value was not reached during every experiment. Compared to other exposure routes, c-VMS contamination of cake from silicone moulds seems to be low, as demonstrated by the low concentrations of D4 and D6 measured. For less volatile c-VMS > D6 the results of the study indicate that food might play a more important role for daily intake. As a general rule, silicone moulds should be used only after precleaning and while strictly following the temperature suggestions of the producers.
... Similar results were also observed in other studies carried out with silicone molds, by Helling et al. (2010), whose results showed that 18% of all silicone samples analysed contained more than 0.5% (w/w) of volatile substances, including siloxane oligomers. Studies carried out by Meuwly et al. (2005) showed a strong dependence of the amount of volatiles on the heating temperature and clearly indicated that the silicone molds are not as stable at high temperature as advertised by their manufacturers. More recently, studies carried out by Liu et al. (2021) showed initial values of total VOC concentration 2.53% higher than those recommended by the BfR Recommendations on food contact materials. ...
Full-text available
Four commercially available silicone cupcake molds have been studied. An evaluation of the post-cure treatment applied to the silicone molds was carried out and the loss of volatile organic compounds after cure treatment was quantified. The two higher quality molds showed losses at the 0.5% (w/w) (recommended by BfR standard), while the two lower quality molds exceeded this limit. The migration studies were carried out using Tenax® as a solid food simulant. The volatile compounds that migrate were identified and quantified using SPME-GC-MS. Up to fourteen silicone oligomers were quantified. When the molds were subjected to post-cure treatment, none of them exceeded the global migration of 10 mg/dm²; while those lower quality molds showed migrations higher than 10 mg/dm², so their use in contact with food is not recommended.
... Previous studies have demonstrated that low molecular weight siloxanes (MW < 1500 amu) are present (Meuwly et al. 2005) and could migrate into foods via direct food contact. In particular, the migration studies at high temperatures (Meuwly et al. 2007;Helling et al. 2009Helling et al. , 2010 show siloxanes do enter tested foods. ...
... In two studies by Meuwly, et al, different silicone baking moulds (37 samples) were investigated. 10,41 1 H-NMR, RP-HPLC-UV/ELSD and GC techniques have been used to assess migration of silicone in food. It was observed that, in all cases, cyclic organosiloxane oligomers were found (formula [Si(CH3)2-O] n with n = 6…50). ...
Silicone rubber (SR) is widely used in the food processing industry due to its excellent physical and chemical properties. However, due to the differences in SR product production formulas and processes, the quality of commercially available SR products varies greatly, with chemical and biological hazard potentials. Residual chemicals in SR, such as siloxane oligomers and 2,4-dichlorobenzoic acid, are non-intentionally added substances, which may migrate into food during processing so the safe use of SR must be guaranteed. Simultaneously, SR in contact with food is susceptible to pathogenic bacteria growing and biofilm formation, like Cronobacter sakazakii, Staphylococcus aureus, Salmonella enteritidis, and Listeria monocytogenes, posing a food safety risk. Under severe usage scenarios such as high-temperature, high-pressure, microwave, and freezing environments with long-term use, SR products are more prone to aging, and their degradation products may pose potential food safety hazards. Based on the goal of ensuring food quality and safety to the greatest extent possible, this review suggests that enterprises need to prepare high-quality food-contact SR products by optimizing the manufacturing formula and production process, and developing products with antibacterial and antiaging properties. The government departments should establish quality standards for food-contact SR products and conduct effective supervision. Besides, the reusable SR products should be cleaned by consumers immediately after use, and the deteriorated products should be replaced as soon as possible.
Silicone-based consumer products may contain volatile compounds, predominantly residual siloxane oligomers from production processes. To avoid unwanted release of these volatiles into food, postproduction removal by a tempering process is necessary and might be mandatory for consumer products – especially food contact materials (FCM). According to BfR recommendation XV tempering is assumed to be sufficient if the remaining volatile organic compounds (VOCs) represent less than 0.5 % of the total product weight, a value chosen 60 years ago indicating good manufacturing practice (GMP). However, the reproducibility and comparability of the respective gravimetric method results may be affected by several parameters including sample conditioning, ventilation in the oven and speed of sample handling. Based on the investigations reported in this work, a method evaluation study with an optimized and in-house validated procedure was conducted to assess its inter-laboratory reproducibility. According to the results, the gravimetric determination of the loss of volatile compounds is feasible with an expanded measurement uncertainty of 25 %.
The migration behavior of silicone molecules including octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and dodecamethylcyclohexasiloxane (denoted as D4, D5, D6, respectively) for silicone rubber baking mold (SRBM) under two different baking methods into food simulants and to cakes were investigated. Meantime, different daily used oils including corn, peanut, sunflower and butter were used to investigate the effects of oil property on migration of D4, D5 and D6, respectively where cakes were baked using SRMB at 175 °C for 30 min. Results showed that for olive oil, the migration of D4, D5 and D6 reached maximum in 240 min at 175°C under electric baking condition and reached maximum in 20 min at 800 W under microwaving baking. Unlike olive oil, the migration rate of D4, D5 and D6 into Tanex® decreased significantly with used times under both electric baking and microwaving methods. Importantly, results also showed that the amounts of D4, D5 and D6 in cakes baked with peanut oil and corn oil were significantly higher (p < 0.05) than olive oil, suggesting that olive oil is not a suitable oily food simulant for evaluating the safeness of SRBM and oil properties could also greatly alter the migration of silicones during baking. Moreover, we also observed that the addition of dairy products including milk and milk power could significantly decrease the amount of D4, D5 and D6 in cakes, especially for that of D4. Overall, the current study suggests that choosing a suitable baking oil and/or adding dairy products could significantly reduce the contents of D4, D5 and D6 migrating from SRMB to cakes.
Gut health is determined by an intact epithelial barrier and balanced gut microbiota, both involved in the regulation of immune responses in the gut. Disruption of this system contributes to the etiology of various non-communicable diseases, including intestinal, metabolic, and autoimmune disorders. Studies suggest that some direct food additives, but also some food contaminants, such as pesticide residues and substances migrating from food contact materials (FCMs), may adversely affect the gut barrier or gut microbiota. Here, we focus on gut-related effects of FCM-relevant substances (e.g. surfactants, N-ring containing substances, nanoparticles, and antimicrobials) and show that gut health is an underappreciated target in the toxicity assessment of FCMs. Understanding FCMs' impact on gut health requires more attention to ensure safety and prevent gut-related chronic diseases. Our review further points to the existence of large population subgroups with an increased intestinal permeability; this may lead to higher uptake of compounds of not only low (<1000 Da) but also high (>1000 Da) molecular weight. We discuss the potential toxicological relevance of high molecular weight compounds in the gut and suggest that the scientific justification for the application of a molecular weight-based cut-off in risk assessment of FCMs should be reevaluated.
Packaging materials and migration are closely related issues. As migrants are of different structures and physical state, different separation and detection methods have to be applied, which are presented in the first part of this chapter. For compliance testing certain solvents are used as simulants. Nevertheless, migration experiments into real food are obviously closer to reality and the basis for identification of reasonable simulants. In the second part of this chapter, several published results concerning migration of substances of special interest into simulants and/or food and applied analytics are presented.
Full-text available
Migration in foodstuffs like pizza dough and a high fat lemon cake from silicone baking moulds has been evaluated by GC-MS with a variety of moulds available in the stores. The migration values in a high fat lemon cake (26.6% fat) for the various silicone moulds at the third repeated exposition, 40 min at 175°C, varied from 1.39 mg/kg to 37.80 mg/kg or expressed in mg/dm 2 from 0.15 to 3.10 mg/dm2. The migration values followed a linear relationship with the fat content of the foodstuffs. All the investigated silicone moulds had a migration value below the legal value of 60 mg/kg or 10 mg/dm2. The migrating substances consist principally of cyclic oligomeric polydimethylsiloxanes; however some samples contain a mixture of cyclic and linear oligomeric polydimethylsiloxanes. The mass of these oligomers is between 450 and 1500 Daltons and the percentage of these polydimethylsiloxane oligomers lower than 1000 Daltons varies from 19.8% to 90.9%. In normal conditions of baking temperature and with usual foodstuffs, the silicone moulds are suitable as food contact materials.
Full-text available
Four approaches for testing for overall migration and specific chemical migration from microwave susceptors were evaluated. The methods used olive oil as a conventional liquid food simulant, a semisolid simulant of olive oil and water absorbed onto diatomaceous earth, Tenax™ as a dry simulant, and compositional analysis of the susceptor by ASTM methods. The different methods were tested on five susceptor types used for the packaging of pizza, potato chips (French fries), pasty, popcorn, and a curry. For the comparison, the susceptor materials were impregnated with model substances as migration markers covering a range of molecular weight, volatility and polarity. Levels of specific migration (SM) and overall migration (OM) were determined using the four test methods, which were then evaluated on the basis of their ease and reproducibility of use along with the agreement between specific migration levels into simulants compared with migration into foods. There were severe problems with olive oil as a conventional liquid simulant as it was absorbed by the susceptor and made SM and OM measurements difficult. Humidity conditioning the susceptor for OM was a further difficulty with olive oil. Oil absorption was also a problem using the semisolid simulant, with OM being untried using this approach. The ASTM methods were found to be time-consuming, although the results for SM were similar to those obtained for foods. Overall, however, using Tenax was the preferred method for migration testing of susceptors. It allowed easy measurement of both OM and SM. SM values were generally much higher than for foods, however, and a reduction factor would be required for control of regulated ingredients. For other substances, such as thermal degradation products, a threshold of regulation approach applied to the Tenax extract would be a simple and effective control measure.
The stress relaxation properties of foamed polysiloxane rubbers are important as they can influence the useful life of components made from such a polymer system. Of particular interest is understanding the changes in properties with time and temperature and whether the mechanisms responsible for stress relaxation are able to induce other material property changes. The stress relaxation properties of Dow Corning S5370 polysiloxane samples, aged under controlled conditions, have been measured using a Thermomechanical analyser (TMA) at a number of different temperatures. The results were assessed using the principle of Time-Temperature Superposition. Derived acceleration factors showed good adherence to the Arrhenius relationship and showed two regions where processes with different activation energies dominate. A transition region where there is a change in the predominant degradation process is evident at around 120 °C. Thermogravimetric analysis (TGA) studies were used to provide an improved understanding of the degradation at elevated temperatures (>120 °C). Time-temperature superposition and Arrhenius treatment of the TGA results reveal an activation energy (75±6 kJ/mol) which correlates closely to that derived from stress relaxation (65±5 kJ/mol). Overall, these observations suggest that the degradation processes at elevated temperatures which influence stress relaxation also induce significant weight loss. The dominant degradation process at elevated temperatures(>120 °C) is most probably silicone head to tail unzipping reactions resulting in the production of volatile cyclic species.
Thermal degradation of polydimethylsiloxane (PDMS) polymers having hydroxyl (PS) and vinyl (PS-V) terminals was studied by pyrolysis-gas chromatography (PGC) in the temperature range from 550 to 950°C. The degradation products were primarily cyclic oligomers ranging from trimer (D3) to cyclomer D11 and minor amounts of linear products and methane. The product composition varied significantly with pyrolysis temperature and extent of degradation. A new method was developed to derive a mass loss-temperature curve (pyrothermogram, PTG) and to determine the kinetic parameters of decomposition (k, n, and Ea) from sequential pyrolysis studies. It was shown that isothermal rate constants can be derived from repeated pyrolysis data. Good agreement between the rate constants derived from the two methods validates the methodology adopted. This was further confirmed from thermogravimetric studies. The Ea values for the decomposition of PS and PS-V derived from sequential pyrolysis were 40 ± 2 and 46 ± 2 kcal mol−1, respectively. Various mechanisms for the degradation of PDMS were reviewed and discussed in relation to the PGC results. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 441–450, 1999
The hydophobic recovery properties of polydimethylsiloxane (PDMS) elastomers after environmental degradation arises from the migration of low molecular weight siloxanes from the bulk to the surface. MALDI-TOF-MS analysis of the isotopic distribution of oligomers from the surface of vulcanized PDMS has enabled unambiguous assignment of these as predominantly cyclic siloxanes ranging from 13 to 47 repeat units with smaller proportions of methyl and hydroxyl terminated linear chains ranging from 12 to 24 repeat units.© 2000 Society of Chemical Industry.
Crosslinked polydimethylsiloxanes were exposed to corona discharges in dry air at normal pressure. Short-time solvent extraction and subsequent analysis of the extractables, by gas chromatography, mass spectrometry and size exclusion chromatography showed that, oligomers consisting mainly of cyclics with 4–9 repeating units were formed during corona exposure. The size distribution of the oligomers was independent of the crosslink density and corona exposure time. The amount of oligomers located at the surface increased, with increasing storage time, after the corona exposure in qualitative agreement with the ongoing hydrophobic recovery process. Longer extractions penetrated deeper into the samples, and, in addition to the cyclic oligomers, higher molar mass species (∼50,000 g mol−1 for unexposed samples) were detected. Samples exposed to corona, treated in this way, showed a broadening of the high molar mass peak towards lower molar masses.
The release of volatile compounds from soothers and teats made from silicone rubber has been investigated. Firstly, measurements of the total release of volatiles were performed according to the method in the draft European standard (CEN). Weight losses of 0.17-0.80% after four hours at 200 C were observed using gravimetric measurements. One product had a weight loss above the proposed CEN limit of 0.5%. Secondly, the volatile compounds were identified using a thermal desorption/cold trap injector on a gas chromatograph equipped with infrared spectroscopic (IR) and mass spectrometric (MS) detectors. The main compounds were siloxane oligomers and aliphatic hydrocarbons. One teat released about 0.1 mg diethyl phthalate (DEP), which is considered to be quite a high quantity. Limited amounts of the antioxidant 3,5-di-t-butyl-4-hydroxytoluene (BHT) were found in most samples.
Crosslinked polydimethylsiloxanes with three different chain-breaking antioxidants (Irganox 1076, Irganox 565 and Tinuvin 770) were exposed to air plasma (GHz), and the surface structures of the exposed samples were assessed by contact angle measurements, X-ray photoelectron spectroscopy, optical and scanning electron microscopy, and surface profilometry before and after uniaxial stretching. It was found that samples containing antioxidants oxidized more slowly than the reference sample with no antioxidant. Higher doses of air plasma were required to form a brittle silica-like layer in the samples with antioxidant than in the reference sample with no antioxidant. Tinuvin 770 showed the strongest antioxidative effect whereas Irganox 1076 and Irganox 565 were similar in efficiency.
Conference Paper
This paper reports the results of the characterisation of low molecular weight polydimethylsiloxane (LMW PDMS) extracted from four different brands of high temperature vulcanised (HTV) silicone rubber insulators designed for high voltage applications. LMW PDMS material was obtained from the insulators by sequential soxhlet extractions and mass changes were recorded for each extraction. The insulator extracts were thoroughly characterised using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS), which provides identification of individual molecular species allowing differences in molecular structure to be identified. The extracts were found to contain both linear and cyclic species. Some variations in end groups of the linear species were also noted. These spectra were used to calculate the relative proportions of these species as well as the average molecular weights of the extracts. Significant differences were observed in molecular composition and the speed of recovery of the insulators studied
Analysis using gas chromatography/mass spectroscopy (GC/MS) was performed for evaluation of surface degradation of silicone insulating materials. Silicones are used as coatings for porcelain insulators and shed material for high voltage composite insulators. A comparison between virgin silicone rubber and aged silicone rubber samples, which were aged either on actual power lines or during a field exposure test, was made by GC/MS analysis. The GC/MS spectrum of siloxane in silicone rubber has a series of peaks which corresponds to the number of dimethylsiloxane units in the molecule. We found that the aged samples had a larger concentration of low molecular weight siloxane species than the virgin samples. The top shed surfaces generated more low molecular weight siloxane species than the bottom shed surfaces. Since GC/MS analysis can determine the molecular weight distribution of polymer insulating materials, evaluation of the degree of surface degradation and estimation of the remaining life of insulators may be possible