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Managing fiberglass-reinforced polyester composite wastes
Resources and Conseruation, 15 (1987) 299-308 Elsevier Science Publishers B.V., Amsterdam - Printed
299
in The Netherlands
Short Communication
Managing Fiberglass-Reinforced Polyester Composite Wastes J.M. BOUVIER,
S. ESPEROU
DU TREMBLAY
and M. GELUS
Uniuersitk de Technologie de Compikgne, 60206 Compikgne Ceden (France) (Received
March 24,1987; accepted April 18,1987)
INTRODUCTION
Plastic composite materials are extensively used in industry as replacements for metals because of their light weight and high rigidity. In the course of manufacture of such materials solid wastes are generated, particularly from imperfect molding processes. Relatively large quantities of such wastes are produced in the case of low-unit-value products such as fiberglass-reinforced polyester composites which are popular in the automobile and boat industries ( 11. Typically, such composites consist of polyester resin (30 wt% ) , glass fibers (35 wt% ) , fillers ( 30 wt%, e.g. calcium carbonate) and various additives. Wastes represent about 10 wt% of the composites manufactured and they are characterized by low bulk density (0.2 to 0.25 Mg/m3), low energy content and high mechanical strength. These solid wastes, like other organic wastes, must be managed, preferably by recycling. Figure 1 illustrates conventional techniques for converting organic solid wastes as a function of the type of waste and its value. These techniques are not well adapted to fiberglass-reinforced polyester wastes because of the specific composition and physico-chemical properties of these wastes (high minerals content, presence of thermosetting resin, thermal stability of glass fibers). Thus, thermochemical treatments must be used to remove polyester resin and weaken the composite so as to facilitate separation of glass fibers, for example by grinding. In the literature, very few studies have considered the problem of recycling composite materials. Morel et al. [ 21 and Vuichard and Lafosse [ 31 have studied the recycling of ground polyester composite wastes into both thermoplastic and thermosetting resins. They obtained better results with wastes previously pyrolyzed at 450~550°C in the presence of steam. But the physical properties of the recovered glass fibers were poor because of the severity of the pyrolysis. Pertinent to this discussion, Das et al. [ 4-6 ] investigated degradation mechanisms of styrene-polyester copolymers in inert and oxidative atmospheres
0166-3097/87/$03.50
0 1987 Elsevier Science Publishers
B.V.
300
AW
*
,/ HECWnt non thermoplastics
/_,
FERMENTATION y--~+pl
“’ __
_ _-_
RECYCLING
/--I
Fig. 1. Classical processes for transforming organic solid wastes. AW: aqueous wastes; LECW: lowenergy-content wastes; HECWt: high-energy-content wastes - thermoplastics; HECWnt: highenergy-content wastes - non thermoplastics.
and under isothermal conditions. In the presence of air, there were two firstorder reactions: the first involved the scission of weak crosslinks with liberation of free linear chains; the second corresponded to random scission of the free linear chains into smaller fragments. In an oxygen atmosphere, the degradation showed only one first-order reaction; the activation energy decreased from 50-71 kJ/mol to 8-29 kJ/mol as the oxygen flowrate increased. Experiments used small-size or powdered samples to limit the effect of diffusion on the degradation kinetics. These types of studies do not allow extrapolation to thermochemical degradation of solid wastes of fiberglass-reinforced polyester composites. It is necessary to study larger samples under different thermochemical conditions. Two ways can be examined, depending upon the nature of the pyrolyzing medium, similar to Bouvier et al. [ 731 for the pyrolysis of tire wastes. In gas-solid pyrolysis, the pyrolysis occurs due to gas-solid contact in terms of heat transfer. In liquid-solid pyrolysis, the pyrolysis is due to the liquid-solid contact in which the pyrolyzing liquid ensures heat and mass transfer (solvolysis of partly degraded polymers ) . EXPERIMENTAL
Polyester composites Samples were taken from identical wastes and cut in 40 x 5 x 5 mm pieces. poly [ glycol They were composed mainly of polyester resin (styrene-crosslinked
301
Fig. 2. Experimental apparatus for gas-solid thermolysis. (1) precision balance; (2) electrical heating; (3) sample holder; (4), (4’) oxygen, nitrogen; (5), (5’) flowmeter; (6) recorder; (7) converter; (8) temperature control.
diethylene-isophthalic calcium carbonate.
acid-maleic
anhydride]
) , glass fibers (5 mm long) and
Experimental apparatus for gas-solid thermolysis
A thermogravimetry technique was adapted for investigating thermolysis of the polyester composites under inert and oxidative conditions. The apparatus, described in Fig. 2, consisted of a vertical tubular furnace with electrical heating (2) and temperature control system (8)) a metal tube (6 cm diameter) and a precision balance (1)attached to a sample holder ( 3 ) . The lower part of the metal tube contained glass packing to preheat the thermolyzing gas. The gas, either nitrogen or a nitrogen-oxygen mixture, was supplied through flowmeters (5) and (5’). The sample holder was designed as a flat plate so as not to modify heat transfer. The signal from the precision balance was converted ( 7)) amplified and recorded for analysis ( 6).
Fig. 3. Reactor for liquid-solidthermolysis. (1) cover; (2) body; (3) composite sample; (4) solvent; (5) thermocouple; (6) rupture disc; (7) manometer.
Experimental methodology for gas-solid thermolysis The furnace (2) was steady-state heated and the thermolyzing gas was delivered at a flow rate of 2-5 L/min. Thus, the sample holder was taken out, loaded with polyester composite sample, and then placed in the heated zone. The weight of the sample was recorded versus time. Thermolysis curves were obtained and transformed into dimensionless form using a conversion ratio defined as:
where mi, m, and mf are respectively mass of the sample.
the initial mass, mass at time t, and final
Experimental methodology for liquid-solid thermolysis Experiments were carried out in a 350 cm” stainless steel retort ( Fig. 3 ) . The reactor consisted of a cover (1) and a body (2)) a manometer ( 7)) a thermocouple ( 5) and a rupture disk ( 6). A graphite seal was used. The retort was
303 TABLE 1 Gas-solid thermolysis of fiberglass-reinforced polyester composites in inert atmosphere Temperature, ’C
Weight loss at infinite time, %
370 362 355 348 345 344 338 329
25.1 25.3 21.8 24.8 24.4 24.4 24.2 23.5
externally heated by immersion in a fluidized sand bed; the reactor was agitated by a shaker. Experimental methodology consisted of preheating the fluidized bed to the desired temperature, putting the reaction medium (polyester composite sample and solvent with a liquid/solid mass ratio of about 10) into the reactor, closing the reactor and placing it on the shaking system into the fluidized bed. After the reaction, the retort was removed and immersed in cold water for 15 min, opened, and the reaction mixture analyzed. The operation was repeated for different times and temperatures. Dibutyl phthalate was used as the liquid because of its thermal stability, low vapor pressure and high boiling point. RESULTS AND DISCUSSION
Kinetics of gas-solid thermolysis in an inert atmosphere The mass loss of organic materials varies between 22 and 26 wt% and tends to rise as the temperature is increased (Table 1) , The conversion curves, expressed by the conversion ratio x versus time, are shown in Fig. 4 for various temperatures ( 338,348,362, and 370” C) . These are sigmoidal showing a short non-isothermal period. As for many pyrolysis reactions in inert gas, the thermolysis of the copolymer behaves like a first-order reaction ( d.r/dt = /+,[ 1 -xl ) from the inflection point. The rate constant 12,was numerically computed from 320 to 370°C (Table 2). It is characterized by an activation energy of 179 kJ/mol and a frequency factor of 2.22 x lOi min-‘. Kinetics of gas-solid thermolysis in an oxidizing atmosphere Organic materials are completely eliminated 35 wt%. Conversion curves are presented
up to a total mass loss of about versus temperature (Fig. 5,
time, Fig. 4. Gas-solid temperature.
thermolysis
mln
in an inert atmosphere.
Conversion
ratio versus time; effect of
333-353” C) and molar fraction of oxygen (Fig. 6,0.0625-0.5). Compared with thermolysis in an inert gas, the reaction rate is much more rapid and hence the thermolysis time much shorter. The conversion curves are complex in shape showing three distinct domains based on the value of X: (1) Low n values (O
k, and k,,, at various temperatures
T, “C
k; lo’, min
320 329 332 337 338 344 348 355 356 362 377
-
’
k,,,, min _ 1
0.74
0.21 -
1.03 1.95
0.42 0.54 -
2.63 4.29
1.45 -
4.78 5.84
2.72 -
305
10 time,
20
mln
Fig. 5. Gas-solid oxydative thermolysis. gen content: l/8). Fig. 6. Gas-solid oxydative (temperature: 348 ’C ) .
thermolysis.
time Conversion
Conversion
, mln
ratio versus time; effect of temperature
(oxy-
ratio versus time: effect of oxygen content
splits or cracks whose propagation weakens the sample and increases the gas-solid contact area. Thus it causes a self acceleration of the phenomena, leading to an infinite contact area of the highly cracked sample. The linear part of the profile is shorter when the thermolysis conditions are more drastic. The intermediate domain ends at the inflection point of the conversion curves. (3 ) High x values ( 0.7 < n:< 1) : Here, thermolysis is governed by the chemical conversion of polyester copolymer which obeys the following model: dx/dt=k,,Y,,(l-n)“+k,(l-x) where: k,, is the rate constant of oxidative thermolysis, YoZ the molar fraction of oxygen, and (Ythe reaction order. As the thermolyzing gas is flowing, Yo, is constant and so is the product ( Yo, Iz,, ) ; a is close to unity. The values of k,, are reported in Table 2 from 320 to 356°C. The activation energy and frequency factor are 204 kJ/mol and 1.84 X 1017min-1, respectively. Liquid-solid thermolysis Acid hydrolysis of the polyester composite material is unrealistic as a treatment method because of diffusional limitations, so thermolysis was carried out in an organic solvent. Two specific steps were identified: (1) The composite material swells due to the diffusion of the solvent and the sample achieves a rubber-like texture. (2) Due to thermolysis, the polyester copolymer is partly degraded and the resultant oligomers dissolve in the solvent. Figure 7 shows t.he temperature-time relation for completely dissolving the
1
1
2
3
4
J
tlme,hr
Fig. 7. Temperature-time
relationship
for complete dissolution
of polyester copolymer in solvent.
samples. Note that it is possible to degrade massive samples at relatively low ( T z 320-330’ C ) and short residence times ( ca. 1 h ) , which are temperatures milder conditions than for gas-solid thermolysis. EFFECT
OF
THERMOLYSIS
ON
MECHANICAL
STRENGTH
OF
COMPOSITE
MATERIALS
An advantage of the gas-solid thermolysis is the weakening of the composite’s structure, thus facilitating subsequent grinding of the waste. A weakened state can be characterized by measuring the mechanical strength as a function of thermolysis conditions. This was done by determining the rupture energy of samples. Table 3 presents values of Es, the rupture energy ratio, which expresses the.ratio between rupture energy of thermolyzed samples and rupture energy of non-thermolyzed samples. ER slightly increases at short thermolysis times, probably because of additional crosslinking, then decreases slowly due to developing splits in the sample. An extremely weakened state is found at high TABLE 3 Rupture energy ratio, ER, as a function of oxydative thermolysis Thermolysis min
time,
ER
5 I
1.08 1.03
9
0.96
11 17
0.88 0.84
30
0.30
time ( T=348’C,
Yc,, =0.125)
307
conversion ratios (X > 0.9). The effect of molar oxygen fraction important than thermolysis time. Thus, gas-solid thermolysis grinding of the composite wastes at low energy.
on ER is less would allow
Separation of glass fibers In liquid-solid thermolysis, organic material is totally dissolved and the minerals (glass fibers and fillers) are separated. Glass fibers can be recovered by filtration and washing (acetone). After drying, the glass fibers appear to be of good quality and suitable for recycling. In gas-solid thermolysis, the lower the thermolysis temperature, the more difficult is the separation of the glass fibers without breaking them. Samples can be split easily at high temperature and long residence times. In this case, glass fibers are separated by washing over a filter with dilute acid to remove fillers attached to the fibers. But the glass fibers are breakable and their quality is not as good as those from liquid-solid thermolysis. MANAGEMENT
OF POLYESTER
COMPOSITE WASTES
Fiberglass-reinforced polyester wastes are at present landfilled, which is relatively expensive due to the low bulk density. Based on the experimental results reported here, alternative waste management methods may be proposed, The wastes can be densified before landfilling. This would consist of thermolyzing wastes in the presence of an oxidizing gas at 340-370°C. The weakened composite waste can be ground to powder to increase its bulk density by a factor of 4 or 5. The powder contains fillers and short glass fibers and the mixture could be recycled for low-grade uses (embanking, filling for thermoplastic and thermosetting resins, reinforcing fillers for concrete). The glass fibers from the waste can be recycled. This is technically feasible, notably after liquid-solid thermolysis. However, it is necessary to recycle the spoiled liquid used in the thermolysis process. Also, a surface treatment is necessary for the recycled fibers if they are to be used in resin composites. Considering the prices of new glass fibers, the recycling of fibers from wastes does not seem economically feasible.
REFERENCES 1 M. Backman and K. Lidgren, 1986. Recovery of old plastic small craft. Resources and Conservation, 12: 215-224. 2 E. Morel, G. Richet and C. Martin, 1979. Examen des possibilit& de reutilisation des dechets thermodurcissables d’origine industrielle. Final Report, Contract No. CEE-IRCHA 222-77 EEF. 3 R. Vuichard and J.P. Lafosse, 1980. Recuperation de fibres de verre dans les dechets de produits thermodurcissables. Internal Report. No. 381, IRCHA, Vert-le-Petit, France.
308 4 5 6 7 8
SK. Baijal and A.N. Das, 1978. Thermal and oxidative degradation of crosslinked styrene-polyester copolymers. Ind. J. Chem., 16A: 1036-1038. A.N. Das, 1981. Degradation mechanism under isothermal conditions of crosslinked polymer by I.R. spectroscopy. Combust. Flame, 40: 1-5. A.N. Das and S.K. Baijal, 1982. Degradation mechanism of styrene-polyester copolymer. J. Appl. Polym. Sci., 27: 211-223. J.M. Bouvier and M. Gelus, 1986. Pyrolysis of rubber wastes in heavy oils and use of the products. Resources and Conservation, 12: 77-93. J.M. Bouvier, F. Charbel and M. Gelus, 1987. Gas-solid pyrolysis of tire wastes. Kinetics and materials balances of batch pyrolysis of used tires. Resources and Conservation, 15: 205-214.
299
in The Netherlands
Short Communication
Managing Fiberglass-Reinforced Polyester Composite Wastes J.M. BOUVIER,
S. ESPEROU
DU TREMBLAY
and M. GELUS
Uniuersitk de Technologie de Compikgne, 60206 Compikgne Ceden (France) (Received
March 24,1987; accepted April 18,1987)
INTRODUCTION
Plastic composite materials are extensively used in industry as replacements for metals because of their light weight and high rigidity. In the course of manufacture of such materials solid wastes are generated, particularly from imperfect molding processes. Relatively large quantities of such wastes are produced in the case of low-unit-value products such as fiberglass-reinforced polyester composites which are popular in the automobile and boat industries ( 11. Typically, such composites consist of polyester resin (30 wt% ) , glass fibers (35 wt% ) , fillers ( 30 wt%, e.g. calcium carbonate) and various additives. Wastes represent about 10 wt% of the composites manufactured and they are characterized by low bulk density (0.2 to 0.25 Mg/m3), low energy content and high mechanical strength. These solid wastes, like other organic wastes, must be managed, preferably by recycling. Figure 1 illustrates conventional techniques for converting organic solid wastes as a function of the type of waste and its value. These techniques are not well adapted to fiberglass-reinforced polyester wastes because of the specific composition and physico-chemical properties of these wastes (high minerals content, presence of thermosetting resin, thermal stability of glass fibers). Thus, thermochemical treatments must be used to remove polyester resin and weaken the composite so as to facilitate separation of glass fibers, for example by grinding. In the literature, very few studies have considered the problem of recycling composite materials. Morel et al. [ 21 and Vuichard and Lafosse [ 31 have studied the recycling of ground polyester composite wastes into both thermoplastic and thermosetting resins. They obtained better results with wastes previously pyrolyzed at 450~550°C in the presence of steam. But the physical properties of the recovered glass fibers were poor because of the severity of the pyrolysis. Pertinent to this discussion, Das et al. [ 4-6 ] investigated degradation mechanisms of styrene-polyester copolymers in inert and oxidative atmospheres
0166-3097/87/$03.50
0 1987 Elsevier Science Publishers
B.V.
300
AW
*
,/ HECWnt non thermoplastics
/_,
FERMENTATION y--~+pl
“’ __
_ _-_
RECYCLING
/--I
Fig. 1. Classical processes for transforming organic solid wastes. AW: aqueous wastes; LECW: lowenergy-content wastes; HECWt: high-energy-content wastes - thermoplastics; HECWnt: highenergy-content wastes - non thermoplastics.
and under isothermal conditions. In the presence of air, there were two firstorder reactions: the first involved the scission of weak crosslinks with liberation of free linear chains; the second corresponded to random scission of the free linear chains into smaller fragments. In an oxygen atmosphere, the degradation showed only one first-order reaction; the activation energy decreased from 50-71 kJ/mol to 8-29 kJ/mol as the oxygen flowrate increased. Experiments used small-size or powdered samples to limit the effect of diffusion on the degradation kinetics. These types of studies do not allow extrapolation to thermochemical degradation of solid wastes of fiberglass-reinforced polyester composites. It is necessary to study larger samples under different thermochemical conditions. Two ways can be examined, depending upon the nature of the pyrolyzing medium, similar to Bouvier et al. [ 731 for the pyrolysis of tire wastes. In gas-solid pyrolysis, the pyrolysis occurs due to gas-solid contact in terms of heat transfer. In liquid-solid pyrolysis, the pyrolysis is due to the liquid-solid contact in which the pyrolyzing liquid ensures heat and mass transfer (solvolysis of partly degraded polymers ) . EXPERIMENTAL
Polyester composites Samples were taken from identical wastes and cut in 40 x 5 x 5 mm pieces. poly [ glycol They were composed mainly of polyester resin (styrene-crosslinked
301
Fig. 2. Experimental apparatus for gas-solid thermolysis. (1) precision balance; (2) electrical heating; (3) sample holder; (4), (4’) oxygen, nitrogen; (5), (5’) flowmeter; (6) recorder; (7) converter; (8) temperature control.
diethylene-isophthalic calcium carbonate.
acid-maleic
anhydride]
) , glass fibers (5 mm long) and
Experimental apparatus for gas-solid thermolysis
A thermogravimetry technique was adapted for investigating thermolysis of the polyester composites under inert and oxidative conditions. The apparatus, described in Fig. 2, consisted of a vertical tubular furnace with electrical heating (2) and temperature control system (8)) a metal tube (6 cm diameter) and a precision balance (1)attached to a sample holder ( 3 ) . The lower part of the metal tube contained glass packing to preheat the thermolyzing gas. The gas, either nitrogen or a nitrogen-oxygen mixture, was supplied through flowmeters (5) and (5’). The sample holder was designed as a flat plate so as not to modify heat transfer. The signal from the precision balance was converted ( 7)) amplified and recorded for analysis ( 6).
Fig. 3. Reactor for liquid-solidthermolysis. (1) cover; (2) body; (3) composite sample; (4) solvent; (5) thermocouple; (6) rupture disc; (7) manometer.
Experimental methodology for gas-solid thermolysis The furnace (2) was steady-state heated and the thermolyzing gas was delivered at a flow rate of 2-5 L/min. Thus, the sample holder was taken out, loaded with polyester composite sample, and then placed in the heated zone. The weight of the sample was recorded versus time. Thermolysis curves were obtained and transformed into dimensionless form using a conversion ratio defined as:
where mi, m, and mf are respectively mass of the sample.
the initial mass, mass at time t, and final
Experimental methodology for liquid-solid thermolysis Experiments were carried out in a 350 cm” stainless steel retort ( Fig. 3 ) . The reactor consisted of a cover (1) and a body (2)) a manometer ( 7)) a thermocouple ( 5) and a rupture disk ( 6). A graphite seal was used. The retort was
303 TABLE 1 Gas-solid thermolysis of fiberglass-reinforced polyester composites in inert atmosphere Temperature, ’C
Weight loss at infinite time, %
370 362 355 348 345 344 338 329
25.1 25.3 21.8 24.8 24.4 24.4 24.2 23.5
externally heated by immersion in a fluidized sand bed; the reactor was agitated by a shaker. Experimental methodology consisted of preheating the fluidized bed to the desired temperature, putting the reaction medium (polyester composite sample and solvent with a liquid/solid mass ratio of about 10) into the reactor, closing the reactor and placing it on the shaking system into the fluidized bed. After the reaction, the retort was removed and immersed in cold water for 15 min, opened, and the reaction mixture analyzed. The operation was repeated for different times and temperatures. Dibutyl phthalate was used as the liquid because of its thermal stability, low vapor pressure and high boiling point. RESULTS AND DISCUSSION
Kinetics of gas-solid thermolysis in an inert atmosphere The mass loss of organic materials varies between 22 and 26 wt% and tends to rise as the temperature is increased (Table 1) , The conversion curves, expressed by the conversion ratio x versus time, are shown in Fig. 4 for various temperatures ( 338,348,362, and 370” C) . These are sigmoidal showing a short non-isothermal period. As for many pyrolysis reactions in inert gas, the thermolysis of the copolymer behaves like a first-order reaction ( d.r/dt = /+,[ 1 -xl ) from the inflection point. The rate constant 12,was numerically computed from 320 to 370°C (Table 2). It is characterized by an activation energy of 179 kJ/mol and a frequency factor of 2.22 x lOi min-‘. Kinetics of gas-solid thermolysis in an oxidizing atmosphere Organic materials are completely eliminated 35 wt%. Conversion curves are presented
up to a total mass loss of about versus temperature (Fig. 5,
time, Fig. 4. Gas-solid temperature.
thermolysis
mln
in an inert atmosphere.
Conversion
ratio versus time; effect of
333-353” C) and molar fraction of oxygen (Fig. 6,0.0625-0.5). Compared with thermolysis in an inert gas, the reaction rate is much more rapid and hence the thermolysis time much shorter. The conversion curves are complex in shape showing three distinct domains based on the value of X: (1) Low n values (O
k, and k,,, at various temperatures
T, “C
k; lo’, min
320 329 332 337 338 344 348 355 356 362 377
-
’
k,,,, min _ 1
0.74
0.21 -
1.03 1.95
0.42 0.54 -
2.63 4.29
1.45 -
4.78 5.84
2.72 -
305
10 time,
20
mln
Fig. 5. Gas-solid oxydative thermolysis. gen content: l/8). Fig. 6. Gas-solid oxydative (temperature: 348 ’C ) .
thermolysis.
time Conversion
Conversion
, mln
ratio versus time; effect of temperature
(oxy-
ratio versus time: effect of oxygen content
splits or cracks whose propagation weakens the sample and increases the gas-solid contact area. Thus it causes a self acceleration of the phenomena, leading to an infinite contact area of the highly cracked sample. The linear part of the profile is shorter when the thermolysis conditions are more drastic. The intermediate domain ends at the inflection point of the conversion curves. (3 ) High x values ( 0.7 < n:< 1) : Here, thermolysis is governed by the chemical conversion of polyester copolymer which obeys the following model: dx/dt=k,,Y,,(l-n)“+k,(l-x) where: k,, is the rate constant of oxidative thermolysis, YoZ the molar fraction of oxygen, and (Ythe reaction order. As the thermolyzing gas is flowing, Yo, is constant and so is the product ( Yo, Iz,, ) ; a is close to unity. The values of k,, are reported in Table 2 from 320 to 356°C. The activation energy and frequency factor are 204 kJ/mol and 1.84 X 1017min-1, respectively. Liquid-solid thermolysis Acid hydrolysis of the polyester composite material is unrealistic as a treatment method because of diffusional limitations, so thermolysis was carried out in an organic solvent. Two specific steps were identified: (1) The composite material swells due to the diffusion of the solvent and the sample achieves a rubber-like texture. (2) Due to thermolysis, the polyester copolymer is partly degraded and the resultant oligomers dissolve in the solvent. Figure 7 shows t.he temperature-time relation for completely dissolving the
1
1
2
3
4
J
tlme,hr
Fig. 7. Temperature-time
relationship
for complete dissolution
of polyester copolymer in solvent.
samples. Note that it is possible to degrade massive samples at relatively low ( T z 320-330’ C ) and short residence times ( ca. 1 h ) , which are temperatures milder conditions than for gas-solid thermolysis. EFFECT
OF
THERMOLYSIS
ON
MECHANICAL
STRENGTH
OF
COMPOSITE
MATERIALS
An advantage of the gas-solid thermolysis is the weakening of the composite’s structure, thus facilitating subsequent grinding of the waste. A weakened state can be characterized by measuring the mechanical strength as a function of thermolysis conditions. This was done by determining the rupture energy of samples. Table 3 presents values of Es, the rupture energy ratio, which expresses the.ratio between rupture energy of thermolyzed samples and rupture energy of non-thermolyzed samples. ER slightly increases at short thermolysis times, probably because of additional crosslinking, then decreases slowly due to developing splits in the sample. An extremely weakened state is found at high TABLE 3 Rupture energy ratio, ER, as a function of oxydative thermolysis Thermolysis min
time,
ER
5 I
1.08 1.03
9
0.96
11 17
0.88 0.84
30
0.30
time ( T=348’C,
Yc,, =0.125)
307
conversion ratios (X > 0.9). The effect of molar oxygen fraction important than thermolysis time. Thus, gas-solid thermolysis grinding of the composite wastes at low energy.
on ER is less would allow
Separation of glass fibers In liquid-solid thermolysis, organic material is totally dissolved and the minerals (glass fibers and fillers) are separated. Glass fibers can be recovered by filtration and washing (acetone). After drying, the glass fibers appear to be of good quality and suitable for recycling. In gas-solid thermolysis, the lower the thermolysis temperature, the more difficult is the separation of the glass fibers without breaking them. Samples can be split easily at high temperature and long residence times. In this case, glass fibers are separated by washing over a filter with dilute acid to remove fillers attached to the fibers. But the glass fibers are breakable and their quality is not as good as those from liquid-solid thermolysis. MANAGEMENT
OF POLYESTER
COMPOSITE WASTES
Fiberglass-reinforced polyester wastes are at present landfilled, which is relatively expensive due to the low bulk density. Based on the experimental results reported here, alternative waste management methods may be proposed, The wastes can be densified before landfilling. This would consist of thermolyzing wastes in the presence of an oxidizing gas at 340-370°C. The weakened composite waste can be ground to powder to increase its bulk density by a factor of 4 or 5. The powder contains fillers and short glass fibers and the mixture could be recycled for low-grade uses (embanking, filling for thermoplastic and thermosetting resins, reinforcing fillers for concrete). The glass fibers from the waste can be recycled. This is technically feasible, notably after liquid-solid thermolysis. However, it is necessary to recycle the spoiled liquid used in the thermolysis process. Also, a surface treatment is necessary for the recycled fibers if they are to be used in resin composites. Considering the prices of new glass fibers, the recycling of fibers from wastes does not seem economically feasible.
REFERENCES 1 M. Backman and K. Lidgren, 1986. Recovery of old plastic small craft. Resources and Conservation, 12: 215-224. 2 E. Morel, G. Richet and C. Martin, 1979. Examen des possibilit& de reutilisation des dechets thermodurcissables d’origine industrielle. Final Report, Contract No. CEE-IRCHA 222-77 EEF. 3 R. Vuichard and J.P. Lafosse, 1980. Recuperation de fibres de verre dans les dechets de produits thermodurcissables. Internal Report. No. 381, IRCHA, Vert-le-Petit, France.
308 4 5 6 7 8
SK. Baijal and A.N. Das, 1978. Thermal and oxidative degradation of crosslinked styrene-polyester copolymers. Ind. J. Chem., 16A: 1036-1038. A.N. Das, 1981. Degradation mechanism under isothermal conditions of crosslinked polymer by I.R. spectroscopy. Combust. Flame, 40: 1-5. A.N. Das and S.K. Baijal, 1982. Degradation mechanism of styrene-polyester copolymer. J. Appl. Polym. Sci., 27: 211-223. J.M. Bouvier and M. Gelus, 1986. Pyrolysis of rubber wastes in heavy oils and use of the products. Resources and Conservation, 12: 77-93. J.M. Bouvier, F. Charbel and M. Gelus, 1987. Gas-solid pyrolysis of tire wastes. Kinetics and materials balances of batch pyrolysis of used tires. Resources and Conservation, 15: 205-214.