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Flame retardant properties of binary blends: a comparison of miscible and immiscible blends
Polymer
Degradation
Printed PII:
ELSEVIER
SO141-3910(96)00231-5
and Stahiltiy 51 (1997) 1X7-189 0 1997 Elsevier Science Limited in Northern Ireland. All rights reserved 0141.3910/97/$17.00
Flame retardant properties of binary blends: a comparison of miscible and immiscible blends P. P. Lizymol*
& Sabu Thomas
School of Chemical Sciences, Mahatma Gandhi University, Priyadarsini Hills PO, Kottayam, Kerala 686560, India (Received
9 October
1996; accepted
26 October
1996)
The flammability and smoke characteristics of poly(viny1 chloride) (PVC)/poly(ethylene-co-vinyl acetate) EVA, (PVC/EVA), poly (vinyl chloride) (PVC)/poly (styrene-co-acrylonitrile) SAN (PVC/SAN) and EVA/SAN blends were investigated. Comparison of these properties for miscible and immiscible blends shows that miscibility has little effect on flame retardancy and smoke production while all other physical and mechanical properties depend on miscibility. 0 1997 Elsevier Science Limited
1 INTRODUCTION
2 EXPERIMENTAL
During the last few decades, flame retardant polymers have shown a tremendous growth due to the specific mandatory regulations in fire protection for a large number of applications, such as in electrical engineering and electronics as insulating materials, in construction and housing materials and as encapsulating and protecting materials. The smoke contribution and level of toxic gases generated during the burning of polymeric materials are receiving increased In many fires, more than half of the attention.‘,2 deaths are caused by smoke inhalation rather than by direct burning. Because of the presence of additives, the smoke evolved from some flame retardant formulations can be more toxic than that from non-flame retardant formulations. PVC has been used extensively to formulate fire-resistant plastics due to its inherent flame resistant properties.’ In the present study, a comparison of the flame retardant and smoke emission characteristics of miscible and immiscible binary blends of PVC, EVA and SAN is made. The effects of the miscibility of the polymer blends on their flame and smoke characteristics are assessed.
Commercially available samples of PVC, EVA and SAN were used. Details regarding the materials and methods of preparation are published elsewhere.4 The limiting oxygen index (LOI) of the samples were determined according to ASTM-D 2863.81. Smoke characteristics of the homopolymers and blends were compared gravimetrically. The static thermal stability of the blends was determined by a previously reported method” as follows. About 100 mg of each sample was placed in a long test tube and heated to a constant temperature of 200°C in an oil bath. Congo red paper was hung from the mouth of the closed tube with cotton. The stability time was taken as the time at which the congo red paper turned brown. The amount of volatile gas evolved at 200°C for the various blends was compared from the weight losses of the samples at 200°C.
* Present
address: Polymer Division, Poojappura, Thiruvananthapuram-12,
3 RESULTS
3.1 PVC/EVA
AND
DISCUSSION
blends
Blends of PVC and EVA (45% vinyl acetate) were found to be partially miscible.4 Among the
BMT wing SCTIMST, Kerala, India. 187
P. P. Lizyn
188
Table 1. Comparison of the flame retardant properties PVC, EVA and PVC/EVA blends Blend PVCIEVA
100/o 70130 50150 30170 0/100
LOI
Volatile gas (% at 200°C)
38 21 18 17 17
32 IO 5 3 0
Smoke density (%)
86 35 22 IY 6
of
Static thermal stability (min) 90 290 355 370 No colour change even after 720 min
various combinations examined the PVC/EVA, 50/50 blend has two glass transition temperatures and a two-phase morphology while all other compositions have a single-phase morphology and a single T, (unpublished results). Table 1 shows the flammability properties of PVC, EVA and PVC/EVA blends. The LOI values of the blends decrease gradually with an increase in EVA content. The percentage of volatile gas evolved at 200°C and smoke density of the blends also decrease with an increase in EVA content. Static thermal stability increases with EVA content. Comparison of the properties of the three compositions show that miscibility has no effect on the flame retardant and smoke suppressant properties of the blends. These properties depend mainly on the blend composition. The PVC/EVA 70/30 blend is found to be a miscible composition with comparatively good flame retardant and smoke characteristics.
SAN increases the static thermal stability at 200°C. The increase in stability may be due to the of the blends. Both the partial miscibility homopolymers and their blends produce a large amount of smoke on burning. The amount of volatile gas evolved at 200°C is slightly improved by blending with SAN compared to pure PVC (see Table 2). blends
3.3 EVA/SAN
The blends of EVA and SAN are completely immiscible in solution and in the solid state.i.” LOI values show that they have very poor flame retardant properties. Even though these blends are completely immiscible, by blending SAN with EVA, the smoke density improves. This may be due to the dilution of SAN content with EVA in these blends. The percentage of volatile gas evolved also decreased with an increase in EVA content (see Table 3).
4 CONCLUSION The present investigation shows that the flame retardancy and smoke characteristics are not really related to the miscibility of component polymers in the blend. The flame retardancy and smoke characteristics of the major component in the blend is the controlling factor. Hence, as far as flame retardancy is concerned it is easy to select the components of the blend.
ACKNOWLEDGEMENT 3.2 PVC/SAN
blends
The static thermal stability, LOI, volatile gas evolution and smoke density of the polymers and blends show that, on blending PVC with SAN, Table 2. Comparison of the flame retardant properties PVC, SAN and PVC/SAN blends Blend PVC/SAN
100/o 70130 5060 30170 01100
LO1
38 19 18 17 17
Volatile gas (% at 200°C)
32 26 12 20 20
Smoke density (%)
X6 84 82 80 7x
We gratefully acknowledge the financial support from the Council of Scientific and Industrial Research, New Delhi. Table 3. Comparison of the flame retardant properties EVA, SAN and EVA/SAN blends
of Blend EVA/SAN
LOI
Volatile gas (% at 200°C)
Smoke density (%)
Static thermal stability (min)
100/o
17
0
6
YO 360 320 340 No colour change
70130 50150 30170 Oil 00
17 17 17 17
x 14 16 26
36 SO 78 78
Static thermal stability (min) No colour change even after 540 min
of
Flame
retardant properties
REFERENCES 1. Geoffrey, A. Makromol. Chem. Macromol. Symp. 1993, 74, 117 2. Wang, J. Makromol. Chem. Macromol. Symp. 1993, 74, 101 3. Sen, A. K., Mukherjee, B., Bhattacharya, A. S., Sanghi, L.
of binary blends
189
K., De, I? P. and Bhowmik, A. K. Journal of Applied Polymer Science 1991,43, 1673 4. Lizimol, F! I? and Thomas, S. Polymer Degradation and Stability 1993, 41, 59 5. Lizymol, P I? and Thomas, S. Journal of Applied Polymer Science 1994, 51,635 6. Lizymol, I? F? and Thomas, S. European Polymer Journal 1994, 30,1135
Degradation
Printed PII:
ELSEVIER
SO141-3910(96)00231-5
and Stahiltiy 51 (1997) 1X7-189 0 1997 Elsevier Science Limited in Northern Ireland. All rights reserved 0141.3910/97/$17.00
Flame retardant properties of binary blends: a comparison of miscible and immiscible blends P. P. Lizymol*
& Sabu Thomas
School of Chemical Sciences, Mahatma Gandhi University, Priyadarsini Hills PO, Kottayam, Kerala 686560, India (Received
9 October
1996; accepted
26 October
1996)
The flammability and smoke characteristics of poly(viny1 chloride) (PVC)/poly(ethylene-co-vinyl acetate) EVA, (PVC/EVA), poly (vinyl chloride) (PVC)/poly (styrene-co-acrylonitrile) SAN (PVC/SAN) and EVA/SAN blends were investigated. Comparison of these properties for miscible and immiscible blends shows that miscibility has little effect on flame retardancy and smoke production while all other physical and mechanical properties depend on miscibility. 0 1997 Elsevier Science Limited
1 INTRODUCTION
2 EXPERIMENTAL
During the last few decades, flame retardant polymers have shown a tremendous growth due to the specific mandatory regulations in fire protection for a large number of applications, such as in electrical engineering and electronics as insulating materials, in construction and housing materials and as encapsulating and protecting materials. The smoke contribution and level of toxic gases generated during the burning of polymeric materials are receiving increased In many fires, more than half of the attention.‘,2 deaths are caused by smoke inhalation rather than by direct burning. Because of the presence of additives, the smoke evolved from some flame retardant formulations can be more toxic than that from non-flame retardant formulations. PVC has been used extensively to formulate fire-resistant plastics due to its inherent flame resistant properties.’ In the present study, a comparison of the flame retardant and smoke emission characteristics of miscible and immiscible binary blends of PVC, EVA and SAN is made. The effects of the miscibility of the polymer blends on their flame and smoke characteristics are assessed.
Commercially available samples of PVC, EVA and SAN were used. Details regarding the materials and methods of preparation are published elsewhere.4 The limiting oxygen index (LOI) of the samples were determined according to ASTM-D 2863.81. Smoke characteristics of the homopolymers and blends were compared gravimetrically. The static thermal stability of the blends was determined by a previously reported method” as follows. About 100 mg of each sample was placed in a long test tube and heated to a constant temperature of 200°C in an oil bath. Congo red paper was hung from the mouth of the closed tube with cotton. The stability time was taken as the time at which the congo red paper turned brown. The amount of volatile gas evolved at 200°C for the various blends was compared from the weight losses of the samples at 200°C.
* Present
address: Polymer Division, Poojappura, Thiruvananthapuram-12,
3 RESULTS
3.1 PVC/EVA
AND
DISCUSSION
blends
Blends of PVC and EVA (45% vinyl acetate) were found to be partially miscible.4 Among the
BMT wing SCTIMST, Kerala, India. 187
P. P. Lizyn
188
Table 1. Comparison of the flame retardant properties PVC, EVA and PVC/EVA blends Blend PVCIEVA
100/o 70130 50150 30170 0/100
LOI
Volatile gas (% at 200°C)
38 21 18 17 17
32 IO 5 3 0
Smoke density (%)
86 35 22 IY 6
of
Static thermal stability (min) 90 290 355 370 No colour change even after 720 min
various combinations examined the PVC/EVA, 50/50 blend has two glass transition temperatures and a two-phase morphology while all other compositions have a single-phase morphology and a single T, (unpublished results). Table 1 shows the flammability properties of PVC, EVA and PVC/EVA blends. The LOI values of the blends decrease gradually with an increase in EVA content. The percentage of volatile gas evolved at 200°C and smoke density of the blends also decrease with an increase in EVA content. Static thermal stability increases with EVA content. Comparison of the properties of the three compositions show that miscibility has no effect on the flame retardant and smoke suppressant properties of the blends. These properties depend mainly on the blend composition. The PVC/EVA 70/30 blend is found to be a miscible composition with comparatively good flame retardant and smoke characteristics.
SAN increases the static thermal stability at 200°C. The increase in stability may be due to the of the blends. Both the partial miscibility homopolymers and their blends produce a large amount of smoke on burning. The amount of volatile gas evolved at 200°C is slightly improved by blending with SAN compared to pure PVC (see Table 2). blends
3.3 EVA/SAN
The blends of EVA and SAN are completely immiscible in solution and in the solid state.i.” LOI values show that they have very poor flame retardant properties. Even though these blends are completely immiscible, by blending SAN with EVA, the smoke density improves. This may be due to the dilution of SAN content with EVA in these blends. The percentage of volatile gas evolved also decreased with an increase in EVA content (see Table 3).
4 CONCLUSION The present investigation shows that the flame retardancy and smoke characteristics are not really related to the miscibility of component polymers in the blend. The flame retardancy and smoke characteristics of the major component in the blend is the controlling factor. Hence, as far as flame retardancy is concerned it is easy to select the components of the blend.
ACKNOWLEDGEMENT 3.2 PVC/SAN
blends
The static thermal stability, LOI, volatile gas evolution and smoke density of the polymers and blends show that, on blending PVC with SAN, Table 2. Comparison of the flame retardant properties PVC, SAN and PVC/SAN blends Blend PVC/SAN
100/o 70130 5060 30170 01100
LO1
38 19 18 17 17
Volatile gas (% at 200°C)
32 26 12 20 20
Smoke density (%)
X6 84 82 80 7x
We gratefully acknowledge the financial support from the Council of Scientific and Industrial Research, New Delhi. Table 3. Comparison of the flame retardant properties EVA, SAN and EVA/SAN blends
of Blend EVA/SAN
LOI
Volatile gas (% at 200°C)
Smoke density (%)
Static thermal stability (min)
100/o
17
0
6
YO 360 320 340 No colour change
70130 50150 30170 Oil 00
17 17 17 17
x 14 16 26
36 SO 78 78
Static thermal stability (min) No colour change even after 540 min
of
Flame
retardant properties
REFERENCES 1. Geoffrey, A. Makromol. Chem. Macromol. Symp. 1993, 74, 117 2. Wang, J. Makromol. Chem. Macromol. Symp. 1993, 74, 101 3. Sen, A. K., Mukherjee, B., Bhattacharya, A. S., Sanghi, L.
of binary blends
189
K., De, I? P. and Bhowmik, A. K. Journal of Applied Polymer Science 1991,43, 1673 4. Lizimol, F! I? and Thomas, S. Polymer Degradation and Stability 1993, 41, 59 5. Lizymol, P I? and Thomas, S. Journal of Applied Polymer Science 1994, 51,635 6. Lizymol, I? F? and Thomas, S. European Polymer Journal 1994, 30,1135