 Open Access
 Total Downloads : 114
 Authors : Tarek. M. Fouad, Prof. Dr E. F Abadir, Prof. Dr. S. M. ElMarsafy, Dr. Khaled Shokry
 Paper ID : IJERTV5IS100341
 Volume & Issue : Volume 05, Issue 10 (October 2016)
 Published (First Online): 24102016
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Flammability and Thermal Degradation Properties of Sprayable Polydimethyl Siloxane Coating
Prof. Dr E. F Abadir1, Tarek. M. Fouad3
Prof. Dr. S. M. EL Marsafy1, Dr. Khaled Shokry2 3Phd Student
1,2Chemical Engineering At Chemical Engineering Department Department, Faculty of Engineering Faculty of Engineering, Cairo University
Cairo University Giza – 126 13 (Egypt).
Giza – 126 13 (Egypt).
Abstract Recent years, there has been a large increase in employing polymers in engineering applications. Modified Polysiloxanes are generally recognized as the newest generic class of high performance protective sprayable coating.
This paper introduces a background, which highlights the application of Polydimethylsiloxane as a thermal spray protection coating. The flammability behavior as well as kinetics of the degradation process are discussed. The activation energy for degradation will also be presented.
Where the mixed liquor Polydimethylsiloxane (PDMA) with Mica, flame retardant (ATO, ATH) is adding to withstand higher temperature than silicone rubber pure and to employ this technique as sprayable thermal insulation coating for metallic case of aircraft outer surface.
Key Words: Polydimethylsiloxane; Flammability; Thermal degradation; kinetic approach; Activation Energy

INTRODUCTION Polydimethylsiloxane (PDMS) containing Si OSi
main chain and methyl side groups processes many
excellent properties, such as high exibility, high hydrophobicity and excellent thermal stability. It is widely used in the aerospace, construction, electronics and automotive [1].
The development of silicone resins after World War II resulted in the first major commercial applications for silicone coatings; heatcured, high temperature resistant paints for exhaust stacks, boilers, heat exchangers, mufflers,
engines and aircraft components.
Commercial development of Polysiloxanes occurred during World War II, when the need increased for a new breed of materials that could be suitable for a wide range of applications.
Polysiloxanes were used for waterproofing and sealant greases, as well as instrument damping liquids and thermoset engine gaskets [2].
Silicone rubber exhibits a list of excellent characteristics including biocompatibility, oxidation resistance, thermal stability, climate resistance. Because of the unique structure of Polysiloxanes. Therefore, it is made to high performance
thermal shielding, weather resistance coatings and used widely in plastics industry, automobile industry, mold and die industry, electronic industry. Silicones are greatly acknowledged for their better thermal and thermo oxidative stabilities compared to most carbonbased polymers. This acute resistance against ame has put PDMS in the top list of polymers for applications at high temperature where ame appears [3].
But Polysiloxanes are macromolecules composed of repeating siliconoxygen bonds (SiO) along the backbone.
The strong SiO bond itself aids the thermal and oxidative stability of siloxanes. The bond energy of a SiO bond (~107 kcal) is more than 20 kcal higher than that of CC bonds (83 kcal) and CO bonds (85 kcal). Therefore, the amount of thermal energy needed to break the Polysiloxanes backbone, under neutral pH conditions, is much greater than that of most polymeric materials (silicone rubber) [4].
Therefore, Polysiloxanes are one of the most unique materials available today. As a class of polymers, Polydimethylsiloxane display an unusually wide range of properties [5].
They can be viscous yet lubricating as liquids, while an apparently solid form can be either rigid or elastomeric. They are highly thermally and oxidatively stable, display a high degree of chemical inertness, show high UV, resistance have low surface energies, have good dielectric strength (making them good insulators), and have attractive physical properties over a wide range of temperatures [6].
They have shown the ability to withstand short term exposure to severe conditions > 400Â°C (in inert atmospheres) and extended exposures at200Â°C (in air) without any significant changes in their properties [7].
That is the main aim for using this new technique of thermal protection by sprayable coating to overcome problems using thermal insulation by adhesive technique. We used mixed sprayable liquor Polydimethylsiloxane coating (PDMA) as thermal protection coatings.
Adhesion has all been tried, but none has been found entirely satisfactory. Organic modified polysiloxanes are generally recognized as the newest generic class of high performance protective coating.

EXPERIMENTAL
Experiments were carried out in order to determine the optimum formulations and additives for the preparation of PDMS liquor as a thermal insulation coating for coating the metallic surface of an air craft body.

Spray Coating Equipment
Automatic Spraying Equipment with water purification system was used for mixing and spray coating of PDMS coating, an electric oven was used for curing range (80130) Â°C.

Materials and Techniques

PDMS (SILIKPHEN P/80/X) Chemical formula: PDMS Resin CH3[Si(CH3)2O]n Si(CH3)3 Appearance: viscous Liquid.

Mica (Muscovite)
Chemical formula: KAl2 (Al Si3 O10) (FOH)2 Grade V Appearance: Crystal Color Ruby / Green

Antimony trioxide (ATO)
Flame retardant Chemical formula: Sb2O3
Appearance: white powder

Alumina Trihydrate (ATH) Chemical formula: AL2(OH)3 Appearance: white powder


All chemicals supplied by AboZabal company for Special chemicals, Egypt

Techniques

Thermal Gravimetric Analysis (TGA)
The thermal gravimetric analysis was carried out using a Shimadzu instrument Thermogravimetric Analyzer instrument (TGA50) with platinum crucibles [8].
The tests are performed in a dynamic mode, going from room temperature to 1000Â°C. Experiments are carried out under nitrogen, with a flow rate of 20 ml/min in order to remove the evolved corrosive gases rapidly [9]. Heating rates of (5,10, 15and 20) Â°C/min were used for selected samples [10].

Flammability Analysis
Limiting oxygen index and vertical flame test are widely used to evaluate flame retardant properties of materials and to screen flame retardant formulations.

Limiting Oxygen Index Measurements (LOI %)
The LOI test is probably the most wellknown test for flammability. The limiting oxygen index is defined as the minimum percentage of oxygen that is required to maintain flaming combustion of a specimen under specified laboratory conditions. The apparatus applied is the Model HC2 Flammability Unit Oxygen gas, Nitrogen gas, and
precision pressure regulator systems. The applicability of using the oxygen index test (ASTM D 286376) to obtain an indication of the relative flammability of fireretardant treated PDMS mixtures polymer was investigated. The limiting oxygen index apparatus is designed to allow a candle like burning of the specimen in a slowly rising mixture of oxygen and nitrogen. In the test, a specimen is placed in the holder at the center of the base of the test column. The flow valves are adjusted to obtain the desired initial oxygen concentration and total flow rate. The Oxygen Index, in percent, is calculated from the final oxygen concentrations tested [11].
Limit oxygen index (%) = 100 * (Volumetric Flow of Oxygen)
(Total Volumetric Flowof Oxygen and Nitrogen)
2.2.2.2 Vertical lame Test (UL94V)
The apparatus used is the Vertical Testing Model (CZF1), indicating the vertical ratings requirements (V0, V1,
V2). In the mentioned test a specimen is supported in a vertical position and a flame is applied to the bottom of the specimen. The flame is applied for ten seconds and then removed until flaming stops at which time the flame is reapplied for another ten seconds and then removed.
Two sets of five specimens are tested. The two sets are conditioned under different conditions. Test is run with bars one half inch wide and five inches long. These are held vertically and exposed to a laboratory burner flame three quarters of an inch high. Each sample is ignited for ten seconds, the flame allowed to go out, and ignited for a second time often seconds [12].



RESULT AND DISCUSSION
3.1 FORMULATIONS
Thermal and flammability properties of various PDMS coating mixtures formulations have been recorded and extensively discussed. Kinetics of thermal degradation has been studied and the activation energies of degradation of the specimens under investigation by using two different kinetic methods (KissingerAKahiraSunose Method, FlynnWallOzawa). The samples of different compositions are illustrated in table (31).
Table (31) Different PDMS Mixtures
MICA% 0 2 2.5 3 3.5 4 5 7 8 22 32 40
ATO % 0.5 1 1.5 1.7 2 2.5 3 4 5 7 10 12
ATH % 0.5 1 1.5 2 2.5 3 4 5 7 10 13 16
3. 2 Thermogravimetric Analysis (TGA)
Thermal analysis for different formula of PPDMS thermal protection coating mixtures was conducted using (TGA –
50) analysis as previously mentioned. The degradation for each sample was measured at three rates (5,10, 15, 20
Â°C/min). Figs. (31) to (37) illustrate the TGA curves for different samples.
PDMS exhibits mainly a 4step degradation behavior, involving different sections It was shown that PDMS thermally decomposes to cyclic oligomers through SiO bond scission in a chainfolded cyclic conformation energetically favored by overlapping of empty silicon
dorbitals with orbitals of oxygen and carbon atoms.
Degradation for PDMS samples starts at 340Â°C and ends at 950Â°C for (PDMSS1 to PDMS S5). gradual improvement was noticed on adding the mixture flame retardant (ATO, ATO) the maximum improvement was noticed by sample (PDMS S6) as observed in Fig. (36).
15 Â°c/min
15 Â°c/min
20 Â°c/min
20 Â°c/min
Weight%
Weight%
remarkable improvement was noticed on adding (Mica) 40 % as indicate by sample (PDMSS7) which has a high thermal stability Fig. (37).
5 Â°c/min 10 Â°c/min
110
100
90
80
70
60
50
5 Â°c/min 10 Â°c/min
110
100
90
80
70
60
50
0 100 200 300 400 500 600 700 800
Temperature Â°c
0 100 200 300 400 500 600 700 800
Temperature Â°c
100
95
90
85
80
75
70
65
60
55
100
95
90
85
80
75
70
65
60
55
5 Â°c/min
5 Â°c/min
10 Â°c/min
10 Â°c/min
15 Â°c/min
15 Â°c/min
20 Â°c/min
0
20 Â°c/min
0
Weight %
Weight %
Fig. (3 1) TG Curves of P PDMS S1 at Different Heating Rates
Temperature Â°c
Temperature Â°c
200
200
400
400
600
600
800
800
Fig. (3 2) TG Curves of PDMSS2 at Different Heating Rates
100
85
5 Â°c/min
10 Â°c/min 15 Â°c/min 20 Â°c/min
100
85
5 Â°c/min
10 Â°c/min 15 Â°c/min 20 Â°c/min
70
55
40
70
55
40
0
200
400
600
800
0
200
400
600
800
Temperature Â°C
Temperature Â°C
10 Â°c/ min
10 Â°c/ min
80
70
60
50
80
70
60
50
Weight %
Weight %
Weight %
Weight %
Fig. (3 3) TG Curves of PDMSS3 at Different Heating Rates
100
5 Â°c / min
100
5 Â°c / min
90
15 Â°c/ min
20 Â°c/min
90
15 Â°c/ min
20 Â°c/min
0
200
400
600
800
0
200
400
600
800
Temperature Â°c
Temperature Â°c
15 Â°c /min
15 Â°c /min
Weight %
Weight %
Fig. (3 4) TG Curves of PDMS S4 at Different Heating Rates
105
5 Â°c /min
10 Â°c /min
105
5 Â°c /min
10 Â°c /min
95
20 Â°c / min
95
20 Â°c / min
85
75
65
55
85
75
65
55
0
200
400
600
800
0
200
400
600
800
Temperature Â°C
Temperature Â°C
Fig. (3 5) TG Curves of PDMS S5 at Different Heating Rate
95
95
5 Â°c /min
10 Â°c /min 15 Â°c /min
20 Â°c /min
5 Â°c /min
10 Â°c /min 15 Â°c /min
20 Â°c /min
f ( ): is a general differential function of degradation, depending on the degradation reaction mechanism.
85
75
65
55
45
85
75
65
55
45
: Conversion (is a dimensionless quantity). d /dt: Rate of Conversion (Sec1).
Weight %
Weight %
k (T): is the temperaturedependent rate constant which often has Arrheniustype dependence:
k(T) = Aexp (Ea) (3.3)
RT
Where:
0
200 400 600 800 1000
0
200 400 600 800 1000
Temperature Â°C
Temperature Â°C
Fig. (3 6) TG Curves of PDMS S6 at Different Heating Rate
A: Is preexponential factor (having a unit of inverse time).
Ea=E: Apparent activation energy (KJ/mole). R: Gas constant.
T: Absolute temperature.
Using equation (3.2) and introducing the linear heating rate
= dT/dt, equation (3.3) can be rewritten as:
105
100
95
90
85
80
75
70
65
60
55
105
100
95
90
85
80
75
70
65
60
55
5 Â°c /min
5 Â°c /min
10 Â°c /min
15 Â°c /min
20 Â°c /min
10 Â°c /min
15 Â°c /min
20 Â°c /min
=
= exp (
) ()
Weight %
Weight %
(3.4)
0
200 400 600 800 1000
0
200 400 600 800 1000
TemperatureÂ°c
TemperatureÂ°c
Fig. (3 7) TG Curves of PDMS S7 at Different Heating Rates

Modeling of degradation kinetics

Kinetics of Thermal Degradation of PDMS Samples In this section, the activation energies of degradation of PDMS samples were evaluated using FlynnWallOzawa and KissingerAKahiraSunose Method. At first, a brief introduction to the kinetic methods is given hereinafter to
define the degree of degradation (Conversion) ().
Equation (3.4) assumes that the three parameters (Ea, A, f() describe a chemical or physical change, irrespective
of its complexity. Starting from equation (3.4) various kinetic evaluation methods have been developed [14].
If the activation energy depends on , the use of various isoconversional methods could lead to various activation energies for a given degree of degradation. In this study, two isoconventional methods were used to evaluate the activation energy, namely FlynnWallOzawa and KissingerAKahiraSunose.
FlynnWallOzawa method, Plots of log versus 1/T in this method were used to calculate the activation energy by measuring the slope of a straight line [15].
Result illustrated in table (33) ad fig (38) to fig. (313).
A plot of ln versus 1/T the straight line of slope
(1.052Ea/R) obtained from thermograms for several heating rates. The slope can be used to evaluate the apparent activation energy, as shown by equation (3.5).
Where () is given by equation (3.1) [13].
ln = ln AE
( )
( )
R g x
5.331 1.052 E
RT
(3.5)
x =
…. (3.1)
KissingerAKahiraSunose method, the Eq. (1) can be shown as follows:
() = exp ( ) . (3.6)
()
Where W0, W, and Wf are the initial, instantaneous, and final weight of the sample during the degradation process, respectively.
Which is integrated with the initial condition of x =0 At T = to
Following expression:
g(x) = x dx A T exp ( E ) dT = AE P ( E )
0 f(x) T
RT R RT
For nonisothermal degradation, the degradation rate (d /dt), can be generally described as:
= () () …. (3.2)
. (3.7) Since, essentially the technique assumes that the A, f (x) and E are independent of T, while A and E are independent
of x. Result illustrated in table (34) and fig (314) to fig. (318).
The KAS method is based on the CoatsRedfern approximation [16].
Table (32): Value of PreExponential Factor for Different Samples
2
2
ln
= ln
( )
( )
(3.8)
Conversion x 0.1 0.2 0.3 0.4 Ea
Aapp
Thus, the plot Ln / T2 vs.
1/ T for a constant value of x
(s1)
Temp Â°C Kj/mole
should be a Straight line whose slope can be used to evaluate the apparent activation Energy [17].

PreExponential Factor Calculation
S1 Rate =10 Â°C\min S2 Rate =10 Â°C\min S3 Rate
325 430 565 650 29.25 0.3898
5
5
x10
4
4
330 455 570 — 55.65 0.2802
x10
From equation (3.2) by putting f (x)=(1x) we get: –
=10 Â°C\min 325 428 620 720 63.56 0.5714 x106
( )
( )
() = A e
E
RT (1 X) . (3.9)
S4 Rate
5
5
=10 Â°C\min 315 422 577 675 71.03 0.2082 x10
S5 Rate
Where: (1x) is the dimensionless amount of reactive
=10 Â°C\min 230 395 450 615 72.54 0.4543 x106
polysiloxanes remaining.
S6 Rate
325 375 410 510 73.12 0.7143 x105
d(x)
(1x)
= AeE/RT d(t) d(T)
( )
( )
d T
dt
(3.10)
=10 Â°C\min S7 Rate =10 Â°C\min
305 380 450 725 73.66 0.2351 x105
Where: – dT = 6 for =10 Â°c/min
S8 Rate
5
5
=10 Â°C\min 256 375 422 475 85.49 0.6157 x10
S9 Rate
Then Equation (3.10)
=10 Â°C\min 275 399 550 650 98.25 0.6242 x105
= 6A eE/RTdT … (3.11)
S10 Rate =10 Â°C\min S11 Rate
240 375 475 658 99.14 0.4851 x105
285 345 424 610 103.74 0.4343 x105
()
By integration both sides of equation (3.10) we get: –
=10 Â°C\min
Table (33): Activation Energy for Thermal Degradation
.
= 6A T1 eE/RTdT (3.12)
of different PDMS Samples as Calculated by FlynnWall
() T0
we repeated the integration for conversion (0.1,0.2,0.3,0.4,) and different T. we can get the value of PreExponential Factor (A) [18].
For different PDMS coating samples by using MATLAB program and the results are illustrated in table (32).
MATLAB program shown as follows: Clc
T = [283 325 430 565 650]; % Put values of T0, T1, T2,
T3 and T4
X = [0 0.1 0.2 0.3 0.4]; % Put values of X E = 29.25; % Put value of E
R = 8.314;
m = length(T) – 1; for i = 1:m
fun1 = @(x) exp(E./(R*x));
P(i) = integral (fun1, T(i), T(i+1)); fun2 = @(x) 1. /(1x);
Q(i) = integral (fun2, X(i), X(i+1)); End
S = ([m sum(P); sum(P) sum(P.*P)]) \[sum(Q); sum(P.*Q)];
plot (P, Q); A = S (2)/6
Ozawa Method
Conv S1 S2
0.1
33.93
0.9093
76.28
0.9561
0.2
26.37
0.9869
67.30
0.9751
0.3
19.16
0.9001
40.655
0.9761
0.35
22.74
0.9442
38.37
0.9623
0.4
33.23
0.9909
—–
——
0.45
40.10
0.9781
——
——
0.1
33.93
0.9093
76.28
0.9561
0.2
26.37
0.9869
67.30
0.9751
0.3
19.16
0.9001
40.655
0.9761
0.35
22.74
0.9442
38.37
0.9623
0.4
33.23
0.9909
—–
——
0.45
40.10
0.9781
——
——
X Ea R2 Ea R2
Eatotal 29.25 55.65 (KJ/mole) Conv S3 S4
X Ea R2 Ea R2
0.1
61.09
0.9503
117.28
0.8043
0.2
71.68
0.854
64.86
0.991
0.3
77.27
0.9446
61.94
0.9049
0.35
88.34
0.991
71.59
0.9807
0.4
69.96
0.8457
40.08
0.9408
0.45
——
——
157.19
0.677
Eatotal 73.66 85.49 (KJ/mole)
Conv
S5
S6
X Ea
R2
Ea R2
0.1
111.86
0.8058
136.83
0.9968
0.2
44.52
0.9957
132.12
0.9995
0.3
89.15
0.940
215.56
0.9408
0.35
40.12
0.8827
67.33
0.8797
0.4
310.36
0.7875
43.54
0.945
0.45
26.42
0.9633
Eatotal 103.74 119.08 (KJ/mole)
3.5
3
3.5
3
2.5
3.5
3
3.5
3
2.5
1.5
1.5
1.5
1.5
1
0.0009
0.0014
0.0019
0.0024
1
0.0009 0.0011 0.0013 0.0015 0.0017 0.0019 0.0021
1/T(kÂ¹)
1
0.0009
0.0014
0.0019
0.0024
1
0.0009 0.0011 0.0013 0.0015 0.0017 0.0019 0.0021
1/T(kÂ¹)
1/T(kÂ¹)
1/T(kÂ¹)
x=0.1
x=0.2 x=0.3 x=0.35 x=0.4 x=0.45 x=0.5
x=0.1
x=0.2 x=0.3 x=0.35 x=0.4 x=0.45 x=0.5
2
2
x=0.1
x=0.2 x=0.3 x=0.35 x=0.4 x=0.45
x=0.1
x=0.2 x=0.3 x=0.35 x=0.4 x=0.45
2.5
2.5
2
2
3
3
X=0.1
X=0.2
X=0.3 X=0.35
X=0.1X=0.2
X=0.3 X=0.35
2.5
2.5
2
2
ln(mg/min)
ln(mg/min)
ln(mg/min)
ln(mg/min)
ln(mg/min)
ln(mg/min)
Fig. (38) Plot of ln versus 1/T for PDMS S1 (FWO)
3.5
3.5
1
0.0008
0.0013
0.0018
0.0023
1
0.0008
0.0013
0.0018
0.0023
1/T (KÂ¹)
1/T (KÂ¹)
1.5
1.5
3.5
3
3.5
3
X=0.1
X=0.2 X=0.3 X=0.35 X=0.4
X=0.1
X=0.2 X=0.3 X=0.35 X=0.4
2.5
2.5
2
2
ln(mg/min)
ln(mg/min)
Fig. (39) Plot of ln versus 1/T for PDMS S2 (FWO)
1.5
1.5
1
0.0008 0.001 0.0012 0.0014 0.0016 0.0018 0.002
1/T(kÂ¹)
1
0.0008 0.001 0.0012 0.0014 0.0016 0.0018 0.002
1/T(kÂ¹)
Fig. (310) Plot of ln versus 1/T for PDMS S3 (FWO)
Fig. (311) Plot of ln versus 1/T for PDMS S4 (FWO)
3.5
3
2.5
x=0.1
x=0.2 x=0.3 x=0.35 x=0.4
x=0.45
3.5
3
2.5
x=0.1
x=0.2 x=0.3 x=0.35 x=0.4
x=0.45
1.5
1.5
1
0.0009
0.0014
1/T (kÂ¹)
0.0019
0.0024
1
0.0009
0.0014
1/T (kÂ¹)
0.0019
0.0024
2
2
3.5
3
3.5
3
X=0.1
X=0.2 X=0.3 X=0.35
X=0.4
X=0.1
X=0.2 X=0.3 X=0.35
X=0.4
2.5
2.5
2
2
ln(mg/min)
ln(mg/min)
ln(mg/min)
ln(mg/min)
Fig. (312) Plot of ln versus 1/T for PDMS S5 (FWO)
1
0.0009
0.0014
0.0019
0.0024
1
0.0009
0.0014
0.0019
0.0024
1/T (kÂ¹)
1/T (kÂ¹)
1.5
1.5
Fig. (313) Plot of ln versus 1/T for PDMS S6 (FWO)
8.5
p=0.05
9
p=0.15
9.5 p=0.4
10
10.5
11
11.5
12
12.5
0.0006
8.5
p=0.05
9
p=0.15
9.5 p=0.4
10
10.5
11
11.5
12
12.5
0.0006
Table (34): Activation Energy for Thermal Degradation of different PDMS Samples as Calculated by Kissinger AKahiraSunose method
ln/TÂ²(mg/min KÂ²)
ln/TÂ²(mg/min KÂ²)
samples Activation Energy (Ea) (KJ/mole)
S1
85.43
50.21
———
54.06
S2
112.96
76.55
62.65
61.85
S3
76.97
58.17
98.58
142.62
S4
93.57
112.82
———
260.76
S5
123.38
168.26
———
194.28
S6
136.0
140.65
———
241.75
0.0019
0.00255
0.0019
0.00255
Table (35): Peak Temperature for Thermogravimetric Analysis (TGA) PDMS Mixture as Calculated by
KissingerAKahiraSunose Method
0.00125
1/T (K1)
0.00125
1/T (K1)
Fig. (314) Plot of ln/T2 versus 1/T for PDMS S1 (KAS)
samples
Peak Temperature (0k)
ln/TÂ²(mg/min KÂ²)
ln/TÂ²(mg/min KÂ²)
P1 P2
P3 P4 9
ln/TÂ²(mg/min KÂ²)
ln/TÂ²(mg/min KÂ²)
S1/5
459.36
609.1
——
843.53
P=0.05
S1/10
467.68
623.47
——
873.8
9.5 P=0.15
S1/15
480.14
669.56
——
925.96
10
P=0.3
P=0.4
S1/20
485.14
671.11
——
973.4
10.5
S2/5
487.35
609.43
818.16
926.99 11
S2/10
505.48
631.36
869.32
931.39
S2/15
520.91
633.43
——–
956.23
11.5
S2/20
528.7
664.82
——–
974.91
12
S3/5
494.33
603.97
837.47
923.76
12.5
S3/10
501.23
623.05
852.89
933.52
0.0007
0.0011
0.0015
0.0019
0.0023
S3/15
519.11
631.03
——
939.8 1/T(K1 )
S3/20
525.16
668.84
908.2
978.9
S4/5
493.39
641.62
——–
928.98
Fig. (315) Plot of ln/T2 versus 1/T for PDMS S2 (KAS)
S4/10
498.45
649.93
——–
946.38
S4/15
508.52
656.55
——–
967.22
S4/20
513.81
668.84
——–
976.63
9
S5/5
470.03
643.9
——–
916.21
9.5 p=0.15
S5/10
475.25
662.8
——–
949.4
p=0.3
10 p=0.4
S5/15
482.05
663.55
——–
950.16
S5/20
488.9
676.4
——–
952.43
10.5
S6/5
490.37
649.18
——–
904.8
11
S6/10
509.74
656.26
——–
907.7
S6/15
523.92
662.87
——–
908.65
11.5
S6/20
517.59
678.32
——–
914.41
12
S1/5
459.36
609.1
——
843.53
P=0.05
S1/10
467.68
623.47
——
873.8
9.5 P=0.15
S1/15
480.14
669.56
——
925.96
10
P=0.3
P=0.4
S1/20
485.14
671.11
——
973.4
10.5
S2/5
487.35
609.43
818.16
926.99 11
S2/10
505.48
631.36
869.32
931.39
S2/15
520.91
633.43
——–
956.23
11.5
S2/20
528.7
664.82
——–
974.91
12
S3/5
494.33
603.97
837.47
923.76
12.5
S3/10
501.23
623.05
852.89
933.52
0.0007
0.0011
0.0015
0.0019
0.0023
S3/15
519.11
631.03
——
939.8 1/T(K1 )
S3/20
525.16
668.84
908.2
978.9
S4/5
493.39
641.62
——–
928.98
Fig. (315) Plot of ln/T2 versus 1/T for PDMS S2 (KAS)
S4/10
498.45
649.93
——–
946.38
S4/15
508.52
656.55
——–
967.22
S4/20
513.81
668.84
——–
976.63
9
S5/5
470.03
643.9
——–
916.21
9.5 p=0.15
S5/10
475.25
662.8
——–
949.4
p=0.3
10 p=0.4
S5/15
482.05
663.55
——–
950.16
S5/20
488.9
676.4
——–
952.43
10.5
S6/5
490.37
649.18
——–
904.8
11
S6/10
509.74
656.26
——–
907.7
S6/15
523.92
662.87
——–
908.65
11.5
S6/20
517.59
678.32
——–
914.41
12
p=0.05
12.5
0.0008 0.0013 0.0018 0.0023
1/T(KÂ¹)
Fig. (315) Plot of ln/T2 versus 1/T for PDMS S3(KAS)
p=0.05 p=0.15 p=0.4
p=0.05 p=0.15 p=0.4
9
9.5
10
10.5
11
11.5
12
12.5
0.0008
9
9.5
10
10.5
11
11.5
12
12.5
0.0008
respectively of (40) %, illustrated by Fig. (319). The results are tabulated in Table (36).
ln/TÂ²(mg/min KÂ²)
ln/TÂ²(mg/min KÂ²)
Table (36): Limiting Oxygen Index (LOI %) of PDMS
Sample
code 1
2
3
4
5
6
7
9
LOI% 40
Burning
38.2
36.4
34.3
28.6
27.7
25.4
22.9
Period 10
14
18
20
29
31
33
35
0.0016
1/T(KÂ¹)
0.0024
0.0016
1/T(KÂ¹)
0.0024
Fig. (316) Plot of ln/T2 versus 1/T for PDMS S4(KAS)
(mm) Length Burnt (mm) Response
+ or –
21 22 23 25 37 40 43 46
+ + + + + + + +
p=0.05 p=0.15 p=0.4
p=0.05 p=0.15 p=0.4
9
9.5
10
10.5
11
11.5
12
12.5
0.0007
9
9.5
10
10.5
11
11.5
12
12.5
0.0007
45
40
35
30
25
20
45
40
35
30
25
20
ln/TÂ²(mg/min KÂ²)
ln/TÂ²(mg/min KÂ²)
Mica% 2 2.5 3.5 7 8 22 32 40
0.0016
1/T(KÂ¹)
0.0025
0.0016
1/T(KÂ¹)
0.0025
LOI%
LOI%
Fig. (317) Plot of ln/T2 versus 1/T for PDMS S5(KAS)
0
10
20
Mica%
30
40
50
0
10
20
Mica%
30
40
50
p=0.05 p=0.15 p=0.4
p=0.05 p=0.15 p=0.4
9
9.5
10
10.5
11
11.5
12
12.5
0.0008
9
9.5
10
10.5
11
11.5
12
12.5
0.0008
ln/TÂ²(mg/min KÂ²)
ln/TÂ²(mg/min KÂ²)
Fig (3 – 19) Limiting Oxygen Index (LOI %)
3.4.2 UL94V Test of PDMS
It observed that the value of UL94V test vary from V1 to V0, which indicate that the flammability properties of PDMS samples increased by addition of flame retardant mixture (ATO+ATH) and the results tabulated in
0.0015
1/T(KÂ¹)
0.0015
1/T(KÂ¹)
Table (37).
0.0022
0.0022
Table (37): UL94V of PDMS Samples
Fig. (318) Plot of ln/T2 versus 1/T for PDMS S6(KAS)
Sample code
Rating UL94V
Flame Dropping
Thickness (mm)
Total Flaming
Maximal Flaming

Flammability properties of PDMS samples
time time
Flammability properties such as Limiting Oxygen index
2
V2
Yes
3.2
252.5
28.3
(LOI %) as well as UL94V Test are measured.
3
V1
No
3.2
120
18.5
4
V0
No
3.2
52.2
11.8
3. 4.1 Limiting Oxygen Index (LOI %) 5
V0
No
3.2
50.4
11.1
6
V0
No
3.2
31.5
10.2
We obviously found that (LOI %) decreased by the 7
V0
No
3.2
30.2
9.3
addition of mixture of (mica) %, up to a maximum 8
V0
No
3.2
28.1
8.4
Flammability properties such as Limiting Oxygen index
2
V2
Yes
3.2
252.5
28.3
(LOI %) as well as UL94V Test are measured.
3
V1
No
3.2
120
18.5
4
V0
No
3.2
52.2
11.8
3. 41 Limiting Oxygen Index (LOI %) 5
V0
No
3.2
50.4
11.1
6
V0
No
3.2
31.5
10.2
We obviously found that (LOI %) decreased by the 7
V0
No
3.2
30.2
9.3
addition of mixture of (mica) %, up to a maximum 8
V0
No
3.2
28.1
8.4
1 V2 Yes 3.2 254.4 56.5
9 V0 No 3.2 25.2 7.5



CONLUSION
In this study the conclusion can be summarized as follows:

The degradation of PDMS takes place in 4steps.

Degradation for PDMS samples starts at 340Â°C and ends at 950Â°C for (PDMSS1 to PDMS S5). improvement gradually noticed on adding the mixture flame retardant (ATO, ATO) %, for samples (PDMSS6).

The highest resistance to thermal degradation is notice on adding (Mica) 40 % for (PDMSS7) indicate a high thermal stability at high temperature.

An increasing in activation energy from (29.25 to 119.08) Kj/mole was noticed on adding (Mica%) using FlynnWallOzawa method.

The thermal stability of the PDMS samples, were enhanced by addition of flame retardant mixture (ATO+ATH) % as revealed by UL94V to V0.

Flammability improvement achieved by addition of flame retardant mixture (Mica) % which decreased the value of Limiting Oxygen Index (LOI %) of PDMS from (40 to 22.9) %.

PDMS as a sprayable thermal insulation for metallic case of aircrafts is become a simpler coating application than using adhesive thermal insulation application, because of it is high thermal, flammability stability and can applied in difficult surfaces.


LIST OF ABRIVIATION
KAS: KissingerAKahiraSunose method Clc: MATLAB calculating symbol PDMS: Polydimethyl siloxane
FWO: FlynnWallOzawa kinetic method ATO: Antimony trioxide
ATH: Aluminum trihydrate
ASTM: American Society of Testing and

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M. Trautz and Z. Anorg, Evaluation of Arrhenius Frequency Factor (A) by SimpleCollision Theory, Chemistry, Vol. 96, No. 1,1916.
Materials
AZC:AboZabal Company for Specialty
Chemicals
LOI %: Limiting Oxygen Index TGA: Thermal Gravimetric Analysis UL94V: Vertical flame test
R2: Root mean square S: Sample number UV: Ultraviolet