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Silicone glazing for solar applications in rural areas
Renewable Energy Vol. 3, No. 2/3, pp. 2 4 5 2 4 8 , 1993 Printed in Great Britain.
0960-1481/93 $6.00+.00 Pergamon Press Ltd
SILICONE GLAZING FOR SOLAR APPLICATIONS IN R U R A L AREAS M. DABBOUR a n d S. ARAFA Science Department, The American University in Cairo, 113 Kasr El-Aini, Cairo, Egypt Abstract--Silicone glazing is a translucent glass fabric reinforced material which was produced by coating silicone resin 1-2577 on an open weave leno fabric in a coating tower constructed in Basaisa village, A1 Sharkiya Governorate, Egypt. The unique feature of the tower used in this work is the utilization of solar energy for both powering its coating mechanism through the use of a photovoltaic module, and also heating its curing chamber. The optical and mechanical properties of siliconeglazing were studied. Silicone glazing is found to have a solar transmission of 90%, an ultraviolet cut-off at 270 nm, and an infrared cutoff at 8.0 ~m. The material has a high tensile strength, particularly along the fill and the wrap directions of the reinforcing fabric. The tensile strength tested at 0.8 strain rate is 50, and 80 pli (pounds per lineal inch) at the fill and the wrap directions, respectively. Silicone glazing was found suitable for many solar applications such as greenhouse screen, space solar heating, solar food driers, and skylights in buildings, especially in rural areas.
INTRODUCTION
In 1986-1987, a solar powered continuous coating tower was first designed and tested as a joint project between the Peoples Alternative Energy Services PEAS, in San Louis, Colorado, and Ghost Ranch Conference Center at Abiquiu, New Mexico. A similar solar tower was constructed in Basiasa village, Egypt, for the purpose of producing the glazing locally, and studying the properties of the produced material. The coating process involves passing the glass fabric slowly through a bath of silicone resin, and then up through a curing chamber in order to cure the resin and bond it to the glass fabric. After the silicone is cured, the coated fabric is then wound on a take up roller. The coating tower utilizes solar energy in two ways. The first is to power up the coating driving mechanism through the use of photovoltaic (PV) modules, and a 12 V deep cycle battery. The second is to heat the curing chamber by utilizing the solar radiation falling directly on its south facing glass cover. Radiation reflected from reflecting surfaces can also be utilized. Figure 1 shows the tower and the coating process. The produced glazing uses a Dow Corning silicone resin 1-2577 conformal coating, and an open weave glass fabric. The resin can be chemically described as monophenyldimethylsiloxane. It is diluted in toluene in its uncured form. The open weave glass fabric is of the aluminoborosilicate type. It is 0.15 mm thick, and has 30 wrap, and 10 fill yarns per inch, hence the fabric has 2.5 by 1.6 mm openings, over which the silicone film is formed. The silicone is cured by heat treatment
in the curing chamber, where the temperature ranges between 80 and 100°C. Upon heat treatment, crosslinking takes place, and methanol evolves as a byproduct. The surface of the glass is chemically compatible with the silicone, thus leading to the formation of a strong siloxane bonding, which results in better adhesion between the resin and the glass without the use of a coupling agent [1].
EXPERIMENTAL
The infrared transmission of silicone glazing and other samples was studied using a Perkin-Elmer 1400 series infrared spectrophotometer in the range 4000200 cm -~. The scan time was 3 min for all samples. The test was performed using the KBr powder method, and also performed using standing film samples. The powder samples were: glass fabric reinforcement, heat cured silicone resin, silicone glazing with reinforcement. The standing film samples also included polyester reinforced with polyethylene yarns, 200 #m thick polyethylene film, and 3 mm glass sheet. The same samples were tested in the NIR, visible and UV region using a NIR, UV ACTA spectrophotometer. In addition, an integrating box was designed to test the solar transmission of the glazing at different angles of incidence. The tensile strength of the silicone glazing, and other samples was tested using a tensile machine of the ZDM type. Cross head speeds from 60 to 180 mm per rain can be selected on this machine. The elongation and the ultimate stress in the two principle 245
246
M. DABBOURand S. ARAFA
~e
Solar glazing tower
/f ~1[] ~) Coated fabric " ~
\ I11-'I-Resin '""°" tt //1~f~ curing chambir Reflecting surfaces to direct the solar radiation
q~
//I"~--0---
"~
Uncoatedsla.* cloth
~...]"'" Siliconere.in [1
Fig. 1. A schematic diagram for the coating tower, and the coating tower and process. directions, the fill and the wrap were measured as a function of the strain rate. In addition, the stressstrain relationship was obtained at 10, 30, 45 and 60 ° off the wrap direction. Other glazing specimens such as polyethylene (PE), and reinforced polyester were compared to the silicone glazing. Other tests such as the thermal volatile products, the impact and the tear strength of the material were also performed [2]. RESULTS AND DISCUSSION Figure 2(a) shows the infrared transmission of some of the studied samples. The spectra of the powdered silicone glazing samples containing glass fabric, and that of just silicone resin film are found to be essentially the same. The IR spectrum seems to be unaffected by the presence of the glass fabric in the glazing samples. This is because the absorption bands of the glass fabric overlap with those of the silicone resin. For example, the B-O stretch at 1440 c m - ' , and S i ~ ) stretch of the siloxane bond around 1000 c m of the glass fabric overlap with the C - H bending of the CH3 and the S i ~ ) stretch of the siloxane bond in the silicone resin, respectively. In addition, the strength of the absorption bands of the silicone resin as a result of the ionic character of its major bands ( S i C : 12%, Si-O 51%), and the high per cent weight of the resin (68%) compared to that of the glass (32%), cause the IR spectrum of the silicone glazing to be mainly determined by the silicone resin. When the silicone glazing in a film form is compared to KBr diluted powdered samples, it is found that the region < 1280 cm -~, where the strong Si-O, and Si-CH3 absorption peaks in powdered specimens take place, appears as almost a cut-off in cross-linked samples
[3, 4]. Films such as PE, and reinforced polyester do not have a distinct cut-off in the IR region ; therefore, they exhibit significant transmission losses to the ambient environment when used in solar applications. On the other hand, silicone glazing can block heat radiated at wavelengths greater than 8 #m. Its transmission in the region 7-8 pm is limited. Glass in this regard is greatly superior to all other samples as it is opaque to any wavelengths beyond 5/~m [5, 6]. Figure 2(b) shows that the silicone glazing sample has five distinct peaks at 2440, 2350, 2280, 1720 and 1680 nm, which can be assigned to the overtones of the C - H in the methyl group [7]. Silicone glazing shows a cut-off at 270 nm because most of its UV absorption peaks lie below this wavelength. This shows that it has excellent UV transparency since all the UV radiation reaching the earth lies in a region above the cut-off wavelength. This means that the silicone glazing has exceptional UV resistance. On the other hand, glass and polyester films have their cutoff at 300 nm; PE at 340, and so they are not as superior as silicone glazing [8]. Solar transmission for different glazings can be found by two methods. The first is the integrating box experiment, which gives an averaged value in the range 250-1100 nm within which the solar cell used as a detector can act sensitively. The second method is taking the average of the per cent transmission of the spectrophotometer over the solar spectrum obtained by Thekakera for air mass two (AM 2) [9]. The results show that per cent solar transmission is 91, 85, 90 and 87 for silicone glazing, PE, polyester, and 3 mm glass, respectively. The high solar transmission of the silicone glazing sample is due to the thinness of the material (0.15 mm), and low index of refraction (1.476), which lead to the
Silicone glazing for solar applications in rural areas
247
(a) 2.5 I
Wavelength (p-m) 6 8 12 20
4
,,,,~...~
t
~(1)
t
i
powdered glass
i
(b) -- 100 90 8o
(4)
el 7o .o 60 "~
(3) Silicone glazing film with fiber glass reinforcement
// ~/
polyethylene (2) Polyethylene (3) Silicone resin film (4) 3 mm g l a s s sheet
J V
3500
I 260
2 5 0 0 1800 1400 1000 600
300
t I 340 360 450
Wavelength (cm -I)
50 ." 40 ~ 30 20 to
(1) Polyester reinforced with
I 550
I 650
I 300
I I 1 6 0 0 2400
Wavelength (rim)
Fig. 2. (a) The infrared spectra o f some of the studied samples. (b) The optical spectra for some of the studied samples in the NIR, visible and UV range.
m i n i m i z a t i o n o f the a b s o r p t i o n a n d reflection losses [5]. T h e u l t i m a t e s t r e n g t h at r u p t u r e a l o n g the fill a n d the w r a p increases w i t h the i n c r e a s i n g strain rate. This is d u e to t h e visco-elastic n a t u r e o f the silicone m a t r i x [10, 11]. T h e tensile strength is expressed in p o u n d s per lineal inch (pli) b e c a u s e t h e c r o s s - s e c t i o n a l area o f the
silicone glazing is irregular. T h e e l o n g a t i o n s t a y e d b e t w e e n 3 a n d 4 % for b o t h the fill a n d the w r a p . T h e a p p l i e d stress is m a i n l y c a r r i e d by the r e i n f o r c i n g y a r n s in the s a m e d i r e c t i o n o f t h e load. T h e silicone m a t r i x d i s t r i b u t e s t h e load t h r o u g h o u t the specimen. F i g u r e 3(a) s h o w s t h a t the s t r e s s - s t r a i n r e l a t i o n s h i p
(a)
(b) At ¢0 = 1.2
80 70
-
]
At ~0 = 0.8 At 1=° = 0.4
--
60 _ 50
At the wrap
At t* = 1.2
-
At ~o = 0.8
40
At ~o = 0.4
30
]
/
At the fill
36 34
100
30 28 26 24 22 20 18 16
30 ° 60 °
12 1
20 I0
t l
t I I 2 3 4 % elongation
I 5
2 10
20 3o 40 % elongation
50
60
Fig. 3. (a) The stress-strain curves for the fill and the wrap of the (30 × 10) silicone glazing at different strain rates. (b). The stress strain for silicone glazing at different angles.
248
M. DABBOUR and S. ARAFA
exhibits little deviation from Hooke's law, and an absence of any noticeable knee before the ultimate rupture of the specimen as a result of the flexibility of the silicone matrix [12]. Off axis specimens at 10, 30, 45, 60 ° were tested at 0.8 rain- ~ strain rate. When the tensile forces act at an angle to the wrap direction, particularly at 30, 45 and 60 °, the stress-strain relationship shows only a small portion of the curve obeying Hooke's law, as shown in Fig. 3(b). This is followed by a region where the deformation tends to increase more rapidly than the stress, which is carried by the silicone matrix, and then the stress starts to rise again as most of the load.is carried by the glass until ultimate rupture occurs [l 3]. The experimental results show that the maximum value obtained along the fill and the wrap, and the minimum values are around 3060 ° to the wrap. The ultimate strength of the material when the load is applied at any angle to the wrap direction can be obtained by applying the T a s i - H i l l criterion [14]. The thermal volatile products of the silicone glazing were identified after long hours of heating, and were mainly methyl linear or cyclic polysiloxane due to slow degradation of the polymer chains through the molecular interchange of the siloxane linkages. This slow degradation shows itself in the linear behavior of the weight loss of the specimen vs the time of heating [15, 16]. This proves the outstanding heat
Table 1. Properties of the produced silicone glazing Weight of 1 m 2 Per cent weight of the glass Thickness Appearance Per cent solar transmission UV cut-off IR cut-off Refractive index of the silicone resin Tensile strength tested at 0.8 strain rate per minute : at the fill, and wrap directions, respectively. The tear strength by the trousers test method : at the fill and wrap directions, respectively. The impact strength by the falling test method Cost per square meter (1990)
0.22 g 320 0.15 mm Translucent 91 270 nm 8.0 #m 1.476 50 and 80 psi 370 and 430g lmil 1 60 g cm LE 19.0
resistance of D C 1-2577 as a result of its high bond energies. CONCLUSION Table 1 summarizes the properties of the silicone glazing material using the solar glazing tower. The silicone glazing is found to desirable properties for solar applications in rural areas. REFERENCES
1. M. Dabbour, Silicone Glazing for Solar Applications in Rural Areas. M.Sc. Degree Thesis. The Science Department, The American University in Cairo, Cairo, Egypt (1991). 2. R.P. Brown, Handbook of Plastics Test Methods. George Godwin, London, Chs 8, 14 and 17 (1981). 3. L. J. Bellamy, The Infrared Spectra of the Complex Molecules. Chapman and Hall, London, Chs 2, 5 and 20 (1975). 4. J.A. McHard and A. L. Smith, Spectroscopic techniques for identification of organosilicon compounds. Anal),. Chem. 31, 1174-I179 (1959). 5. P. N. Chereinisoff, Solar Energy Technology Handbook. Marcell Dekker, New York, pp. 405-420 (1980). 6. P. Lunde, Solar Thermal Engineering. John Wiley and Sons, New York, pp. 121-133 (1980). 7. J. Henniker, Infrared Spectroscopy of Industrial Polymers. Academic Press, London (1967). 8. C. Bukhard, The ultraviolet absorption spectra of certain organosilicon compounds. Journal of the American Chemical Society, 72, 3256 0952). 9. R. B. Pettit, Hemispherical transmittance properties of solar glazings as a function of averaging procedures, and incident angle. Solar Energy Mat. l, 125 (1979). 10. B. Parkyn, Glass Reinforced Plastics. Iliffe Books, London, Chs 8, 12, 13 and 15 (1970). 1I. O. Sweetings, The Science and Technology of Polymeric Films. V.l. Interscience, New York, Chs l, 12 and 13 (1971). 12. L. Hollaway, Glass Reinforced Plastics in Construction. Surrey University Press, London, Chs 2 and 3, pp. 163168 (1978). 13. E. B. Shand, Glass Engineering Handbook. McGraw Hill Book Company, New York, pp. 411-461 (1958). 14. B. Agarwal and L. Broutman, Analysis and Performance of Fiber Composites. John Wiley and Sons, New York, Chs 4 and 8 (1978). 15. M. A. Mendlesohn, Stability of polymeric materials in solar collector environment. In Polymers in Solar Energy Utilization (ed. C. Gebelein), American Chemical Society Series, Washington DC, (1982). 16. R. M. Luck, The reduction of solar ligh[ transmittance in thermal solar collectors as a function of polymer outgassing. In Polymers in Solar Energy Utilization (ed. G. Gebelien), American Chemical Society Series, Washington DC, (1982).
0960-1481/93 $6.00+.00 Pergamon Press Ltd
SILICONE GLAZING FOR SOLAR APPLICATIONS IN R U R A L AREAS M. DABBOUR a n d S. ARAFA Science Department, The American University in Cairo, 113 Kasr El-Aini, Cairo, Egypt Abstract--Silicone glazing is a translucent glass fabric reinforced material which was produced by coating silicone resin 1-2577 on an open weave leno fabric in a coating tower constructed in Basaisa village, A1 Sharkiya Governorate, Egypt. The unique feature of the tower used in this work is the utilization of solar energy for both powering its coating mechanism through the use of a photovoltaic module, and also heating its curing chamber. The optical and mechanical properties of siliconeglazing were studied. Silicone glazing is found to have a solar transmission of 90%, an ultraviolet cut-off at 270 nm, and an infrared cutoff at 8.0 ~m. The material has a high tensile strength, particularly along the fill and the wrap directions of the reinforcing fabric. The tensile strength tested at 0.8 strain rate is 50, and 80 pli (pounds per lineal inch) at the fill and the wrap directions, respectively. Silicone glazing was found suitable for many solar applications such as greenhouse screen, space solar heating, solar food driers, and skylights in buildings, especially in rural areas.
INTRODUCTION
In 1986-1987, a solar powered continuous coating tower was first designed and tested as a joint project between the Peoples Alternative Energy Services PEAS, in San Louis, Colorado, and Ghost Ranch Conference Center at Abiquiu, New Mexico. A similar solar tower was constructed in Basiasa village, Egypt, for the purpose of producing the glazing locally, and studying the properties of the produced material. The coating process involves passing the glass fabric slowly through a bath of silicone resin, and then up through a curing chamber in order to cure the resin and bond it to the glass fabric. After the silicone is cured, the coated fabric is then wound on a take up roller. The coating tower utilizes solar energy in two ways. The first is to power up the coating driving mechanism through the use of photovoltaic (PV) modules, and a 12 V deep cycle battery. The second is to heat the curing chamber by utilizing the solar radiation falling directly on its south facing glass cover. Radiation reflected from reflecting surfaces can also be utilized. Figure 1 shows the tower and the coating process. The produced glazing uses a Dow Corning silicone resin 1-2577 conformal coating, and an open weave glass fabric. The resin can be chemically described as monophenyldimethylsiloxane. It is diluted in toluene in its uncured form. The open weave glass fabric is of the aluminoborosilicate type. It is 0.15 mm thick, and has 30 wrap, and 10 fill yarns per inch, hence the fabric has 2.5 by 1.6 mm openings, over which the silicone film is formed. The silicone is cured by heat treatment
in the curing chamber, where the temperature ranges between 80 and 100°C. Upon heat treatment, crosslinking takes place, and methanol evolves as a byproduct. The surface of the glass is chemically compatible with the silicone, thus leading to the formation of a strong siloxane bonding, which results in better adhesion between the resin and the glass without the use of a coupling agent [1].
EXPERIMENTAL
The infrared transmission of silicone glazing and other samples was studied using a Perkin-Elmer 1400 series infrared spectrophotometer in the range 4000200 cm -~. The scan time was 3 min for all samples. The test was performed using the KBr powder method, and also performed using standing film samples. The powder samples were: glass fabric reinforcement, heat cured silicone resin, silicone glazing with reinforcement. The standing film samples also included polyester reinforced with polyethylene yarns, 200 #m thick polyethylene film, and 3 mm glass sheet. The same samples were tested in the NIR, visible and UV region using a NIR, UV ACTA spectrophotometer. In addition, an integrating box was designed to test the solar transmission of the glazing at different angles of incidence. The tensile strength of the silicone glazing, and other samples was tested using a tensile machine of the ZDM type. Cross head speeds from 60 to 180 mm per rain can be selected on this machine. The elongation and the ultimate stress in the two principle 245
246
M. DABBOURand S. ARAFA
~e
Solar glazing tower
/f ~1[] ~) Coated fabric " ~
\ I11-'I-Resin '""°" tt //1~f~ curing chambir Reflecting surfaces to direct the solar radiation
q~
//I"~--0---
"~
Uncoatedsla.* cloth
~...]"'" Siliconere.in [1
Fig. 1. A schematic diagram for the coating tower, and the coating tower and process. directions, the fill and the wrap were measured as a function of the strain rate. In addition, the stressstrain relationship was obtained at 10, 30, 45 and 60 ° off the wrap direction. Other glazing specimens such as polyethylene (PE), and reinforced polyester were compared to the silicone glazing. Other tests such as the thermal volatile products, the impact and the tear strength of the material were also performed [2]. RESULTS AND DISCUSSION Figure 2(a) shows the infrared transmission of some of the studied samples. The spectra of the powdered silicone glazing samples containing glass fabric, and that of just silicone resin film are found to be essentially the same. The IR spectrum seems to be unaffected by the presence of the glass fabric in the glazing samples. This is because the absorption bands of the glass fabric overlap with those of the silicone resin. For example, the B-O stretch at 1440 c m - ' , and S i ~ ) stretch of the siloxane bond around 1000 c m of the glass fabric overlap with the C - H bending of the CH3 and the S i ~ ) stretch of the siloxane bond in the silicone resin, respectively. In addition, the strength of the absorption bands of the silicone resin as a result of the ionic character of its major bands ( S i C : 12%, Si-O 51%), and the high per cent weight of the resin (68%) compared to that of the glass (32%), cause the IR spectrum of the silicone glazing to be mainly determined by the silicone resin. When the silicone glazing in a film form is compared to KBr diluted powdered samples, it is found that the region < 1280 cm -~, where the strong Si-O, and Si-CH3 absorption peaks in powdered specimens take place, appears as almost a cut-off in cross-linked samples
[3, 4]. Films such as PE, and reinforced polyester do not have a distinct cut-off in the IR region ; therefore, they exhibit significant transmission losses to the ambient environment when used in solar applications. On the other hand, silicone glazing can block heat radiated at wavelengths greater than 8 #m. Its transmission in the region 7-8 pm is limited. Glass in this regard is greatly superior to all other samples as it is opaque to any wavelengths beyond 5/~m [5, 6]. Figure 2(b) shows that the silicone glazing sample has five distinct peaks at 2440, 2350, 2280, 1720 and 1680 nm, which can be assigned to the overtones of the C - H in the methyl group [7]. Silicone glazing shows a cut-off at 270 nm because most of its UV absorption peaks lie below this wavelength. This shows that it has excellent UV transparency since all the UV radiation reaching the earth lies in a region above the cut-off wavelength. This means that the silicone glazing has exceptional UV resistance. On the other hand, glass and polyester films have their cutoff at 300 nm; PE at 340, and so they are not as superior as silicone glazing [8]. Solar transmission for different glazings can be found by two methods. The first is the integrating box experiment, which gives an averaged value in the range 250-1100 nm within which the solar cell used as a detector can act sensitively. The second method is taking the average of the per cent transmission of the spectrophotometer over the solar spectrum obtained by Thekakera for air mass two (AM 2) [9]. The results show that per cent solar transmission is 91, 85, 90 and 87 for silicone glazing, PE, polyester, and 3 mm glass, respectively. The high solar transmission of the silicone glazing sample is due to the thinness of the material (0.15 mm), and low index of refraction (1.476), which lead to the
Silicone glazing for solar applications in rural areas
247
(a) 2.5 I
Wavelength (p-m) 6 8 12 20
4
,,,,~...~
t
~(1)
t
i
powdered glass
i
(b) -- 100 90 8o
(4)
el 7o .o 60 "~
(3) Silicone glazing film with fiber glass reinforcement
// ~/
polyethylene (2) Polyethylene (3) Silicone resin film (4) 3 mm g l a s s sheet
J V
3500
I 260
2 5 0 0 1800 1400 1000 600
300
t I 340 360 450
Wavelength (cm -I)
50 ." 40 ~ 30 20 to
(1) Polyester reinforced with
I 550
I 650
I 300
I I 1 6 0 0 2400
Wavelength (rim)
Fig. 2. (a) The infrared spectra o f some of the studied samples. (b) The optical spectra for some of the studied samples in the NIR, visible and UV range.
m i n i m i z a t i o n o f the a b s o r p t i o n a n d reflection losses [5]. T h e u l t i m a t e s t r e n g t h at r u p t u r e a l o n g the fill a n d the w r a p increases w i t h the i n c r e a s i n g strain rate. This is d u e to t h e visco-elastic n a t u r e o f the silicone m a t r i x [10, 11]. T h e tensile strength is expressed in p o u n d s per lineal inch (pli) b e c a u s e t h e c r o s s - s e c t i o n a l area o f the
silicone glazing is irregular. T h e e l o n g a t i o n s t a y e d b e t w e e n 3 a n d 4 % for b o t h the fill a n d the w r a p . T h e a p p l i e d stress is m a i n l y c a r r i e d by the r e i n f o r c i n g y a r n s in the s a m e d i r e c t i o n o f t h e load. T h e silicone m a t r i x d i s t r i b u t e s t h e load t h r o u g h o u t the specimen. F i g u r e 3(a) s h o w s t h a t the s t r e s s - s t r a i n r e l a t i o n s h i p
(a)
(b) At ¢0 = 1.2
80 70
-
]
At ~0 = 0.8 At 1=° = 0.4
--
60 _ 50
At the wrap
At t* = 1.2
-
At ~o = 0.8
40
At ~o = 0.4
30
]
/
At the fill
36 34
100
30 28 26 24 22 20 18 16
30 ° 60 °
12 1
20 I0
t l
t I I 2 3 4 % elongation
I 5
2 10
20 3o 40 % elongation
50
60
Fig. 3. (a) The stress-strain curves for the fill and the wrap of the (30 × 10) silicone glazing at different strain rates. (b). The stress strain for silicone glazing at different angles.
248
M. DABBOUR and S. ARAFA
exhibits little deviation from Hooke's law, and an absence of any noticeable knee before the ultimate rupture of the specimen as a result of the flexibility of the silicone matrix [12]. Off axis specimens at 10, 30, 45, 60 ° were tested at 0.8 rain- ~ strain rate. When the tensile forces act at an angle to the wrap direction, particularly at 30, 45 and 60 °, the stress-strain relationship shows only a small portion of the curve obeying Hooke's law, as shown in Fig. 3(b). This is followed by a region where the deformation tends to increase more rapidly than the stress, which is carried by the silicone matrix, and then the stress starts to rise again as most of the load.is carried by the glass until ultimate rupture occurs [l 3]. The experimental results show that the maximum value obtained along the fill and the wrap, and the minimum values are around 3060 ° to the wrap. The ultimate strength of the material when the load is applied at any angle to the wrap direction can be obtained by applying the T a s i - H i l l criterion [14]. The thermal volatile products of the silicone glazing were identified after long hours of heating, and were mainly methyl linear or cyclic polysiloxane due to slow degradation of the polymer chains through the molecular interchange of the siloxane linkages. This slow degradation shows itself in the linear behavior of the weight loss of the specimen vs the time of heating [15, 16]. This proves the outstanding heat
Table 1. Properties of the produced silicone glazing Weight of 1 m 2 Per cent weight of the glass Thickness Appearance Per cent solar transmission UV cut-off IR cut-off Refractive index of the silicone resin Tensile strength tested at 0.8 strain rate per minute : at the fill, and wrap directions, respectively. The tear strength by the trousers test method : at the fill and wrap directions, respectively. The impact strength by the falling test method Cost per square meter (1990)
0.22 g 320 0.15 mm Translucent 91 270 nm 8.0 #m 1.476 50 and 80 psi 370 and 430g lmil 1 60 g cm LE 19.0
resistance of D C 1-2577 as a result of its high bond energies. CONCLUSION Table 1 summarizes the properties of the silicone glazing material using the solar glazing tower. The silicone glazing is found to desirable properties for solar applications in rural areas. REFERENCES
1. M. Dabbour, Silicone Glazing for Solar Applications in Rural Areas. M.Sc. Degree Thesis. The Science Department, The American University in Cairo, Cairo, Egypt (1991). 2. R.P. Brown, Handbook of Plastics Test Methods. George Godwin, London, Chs 8, 14 and 17 (1981). 3. L. J. Bellamy, The Infrared Spectra of the Complex Molecules. Chapman and Hall, London, Chs 2, 5 and 20 (1975). 4. J.A. McHard and A. L. Smith, Spectroscopic techniques for identification of organosilicon compounds. Anal),. Chem. 31, 1174-I179 (1959). 5. P. N. Chereinisoff, Solar Energy Technology Handbook. Marcell Dekker, New York, pp. 405-420 (1980). 6. P. Lunde, Solar Thermal Engineering. John Wiley and Sons, New York, pp. 121-133 (1980). 7. J. Henniker, Infrared Spectroscopy of Industrial Polymers. Academic Press, London (1967). 8. C. Bukhard, The ultraviolet absorption spectra of certain organosilicon compounds. Journal of the American Chemical Society, 72, 3256 0952). 9. R. B. Pettit, Hemispherical transmittance properties of solar glazings as a function of averaging procedures, and incident angle. Solar Energy Mat. l, 125 (1979). 10. B. Parkyn, Glass Reinforced Plastics. Iliffe Books, London, Chs 8, 12, 13 and 15 (1970). 1I. O. Sweetings, The Science and Technology of Polymeric Films. V.l. Interscience, New York, Chs l, 12 and 13 (1971). 12. L. Hollaway, Glass Reinforced Plastics in Construction. Surrey University Press, London, Chs 2 and 3, pp. 163168 (1978). 13. E. B. Shand, Glass Engineering Handbook. McGraw Hill Book Company, New York, pp. 411-461 (1958). 14. B. Agarwal and L. Broutman, Analysis and Performance of Fiber Composites. John Wiley and Sons, New York, Chs 4 and 8 (1978). 15. M. A. Mendlesohn, Stability of polymeric materials in solar collector environment. In Polymers in Solar Energy Utilization (ed. C. Gebelein), American Chemical Society Series, Washington DC, (1982). 16. R. M. Luck, The reduction of solar ligh[ transmittance in thermal solar collectors as a function of polymer outgassing. In Polymers in Solar Energy Utilization (ed. G. Gebelien), American Chemical Society Series, Washington DC, (1982).