Thermal Degradation of Poly(vinylbutyral) - American Chemical Society

Dec 15, 1997 - composites, based on weight loss and evolved gas analysis (EGA), are presented. ... basis of EGA (evolved gas analysis) (Shih et al., 1...
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Ind. Eng. Chem. Res. 1998, 37, 49-57

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MATERIALS AND INTERFACES Thermal Degradation of Poly(vinylbutyral)/Ceramic Composites: A Kinetic Approach Leo C. K. Liau and Dabir S. Viswanath* Department of Chemical Engineering, University of Missouri, Columbia, Missouri 65211

Kinetic models for the thermal degradation of poly(vinylbutyral) PVB/Al2O3 and PVB/AlN composites, based on weight loss and evolved gas analysis (EGA), are presented. TG (sample weight loss) and FT-IR (mixture gas spectra) data were measured to elucidate the kinetic models using isothermal and nonisothermal approaches. The mixture IR spectra at each time or temperature were resolved using a least-mean-square (LMS) algorithm to obtain the dynamic information for each major volatile product formed during the degradation process. The kinetic results using isothermal and nonisothermal approaches showed excellent agreement. Activation energies of PVB thermal degradation are ∼300 kJ/mol in nitrogen and ∼200 kJ/mol in air for pure PVB and ∼100 kJ/mol for PVB/Al2O3 and PVB/AlN in nitrogen. The polymer residues at different isothermal treatments were subjected to DRIFTS spectra, and the carbon content of the residual samples was analyzed using a Leco analyzer. Introduction Polymer/ceramic composites, such as poly(vinylbutyral) (PVB) or poly(methyl methacrylate) (PMMA) with alumina (Al2O3) or aluminum nitride (AlN), are used in ceramic multichip modules (MCM) for electronic packaging. During the manufacture of the packages, the polymer binders have to be burned completely, without leaving any carbonaceous materials, during the firing cycle (Farooq et al., 1991). However, small amounts of carbonaceous residue are left behind at the end of the presintering stage. The carbon residue is removed by oxidation in the firing process in order to obtain high-quality products. As binder burnout is a very important step in the sintering stage, an understanding of the phenomenon allows one to improve the process design and operation. Binder burnout involves complex combination of physical and chemical processes (Cima et al., 1989). This includes heat and mass transport during degradation of the laminated green sheets and chemical reaction pathways and kinetics of complete polymer decomposition. The latter involves complex polymer scissions and interactions, and this is further complicated due to the polymer-ceramic interactions. Attempts have been made to study the mechanism of oxidation of carbonaceous residue generated from PVB or PMMA degradation with ceramics (Herron et al., 1991; Wall and Sohn, 1990; Sohn and Wall, 1990; Boddu et al., 1990; Chillara et al., 1994). In these studies, small amounts of carbon residue after polymer burnout were reported and steam oxidation was used to remove the residue in the temperature range of 673* Corresponding author. Telephone: (573) 884-0707. Fax: (573) 884-4940. E-mail: [email protected].

1297 K. In addition, kinetic models of steam oxidation of carbon removal were also proposed. However, the mechanism of polymer decomposition during the presintering process and the factors affecting the generation of carbon residue were not discussed. Thermal degradation of PVB with or without ceramics in different atmospheres has been investigated on the basis of EGA (evolved gas analysis) (Shih et al., 1988; Scheiffele and Sacks, 1988; Masia et al., 1989; Yamanaka et al., 1992; Liau et al., 1996a,b; White and Ai, 1992; Nair and White, 1996). In these studies, different combinations of analytical tools, such as TG/MS, TG/ GC/MS, GC/FT-IR, TG/FT-IR, and FT-IR/MS, were used for the EGA. Yamanaka et al. (1992) using TG/GC/MS showed the major decomposition products during the thermal degradation of PVB, PVB/PLZT, and PVB/PMN to be butyraldehyde (butanal), butenal, and butanoic acid. White and Ai (1992) and Nair and White (1996) identified the same major volatile products for PVB and PVB/ceramic thermal degradation via TG/MS. Masia et al. (1989) observed similar patterns of evolved gas for pure PVB and PVB/ceramic composites using FTIR. In all these studies, butanal was identified as the most abundant evolved gas for PVB thermal degradation. Liau et al. (1996a,b) constructed the reaction pathways and kinetic models for PVB thermal degradation in nitrogen and air atmospheres based on the dynamic EGA. In addition to the analysis of evolved gases, another approach to study the PVB degradation with ceramics is to observe the changes of the sintered polymer residues. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique (FT-IR), molecular weight distribution (GPC), or sample weight loss (TG) are usually applied for the residue phase analysis. DRIFTS method can be used to delineate the changes

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of the functional groups of the residues during polymer or polymer/ceramics thermal degradation (Shih et al., 1988; Scheiffele and Sacks, 1988; White and Ai, 1992; Nair and White, 1996; Higgins et al., 1994). This technique was applied to the thermal degradation of PVB and PVB/Al2O3 in the temperature range of 300673 K, and similar DRIFTS spectra were obtained (Shih et al., 1988; Scheiffele and Sacks, 1988). The changes of the functional groups of PVB with SiO2, mullite, and alumina (White and Ai, 1992; Nair and White, 1996), as well as PMMA with Al2O3 (Higgins et al., 1994), as functions of temperature were illustrated by the DRIFTS spectra. Molecular weight distribution was applied to the study of thermal degradation of PMMA, and kinetic parameters were determined using GPC (Kashiwagi et al., 1985; Madras et al., 1996). Yang et al. (1996) studied the thermal degradation of PVB/ceramic composites and presented the overall kinetic models. The results of their work on the basis of the weight loss analysis showed that the activation energies of PVB/ ceramics degradation were much lower than that of PVB alone. The interactions between the functional groups of polymer binder and ceramics have been reported (Masia et al., 1989; White and Ai, 1992; Higgins et al., 1994; Howard et al., 1990; Cima and Lewis, 1988; Barone et al., 1988; Verweij and Bruggink, 1990). Masia et al. (1989) stated that the oxide surfaces of ceramics have a strong catalytic effect on binder burnout and affected the decomposition rate and the generation of the carbonaceous residue. There are also some investigations on the interactions of PVB with ceramics and factors affecting the amounts of carbonaceous residue. Cima and Lewis (1988) examined the chemical interactions in the degradation of PVB with alumina in different atmospheres. Unsaturated carbonaceous residue after PVB degradation was identified by FT-IR. They also stated that the temperature at which steam was introduced to the furnace influences the final amount of carbon residue. The rate of binder burnout which affects the residue generation and distribution in the composite material was discussed (Barone et al., 1988; Verweij and Bruggink, 1990). Scheiffele and Sacks (1988) investigated the effect of atmosphere, heating rate, and ceramic particle size on PVB/Al2O3 degradation. Based on the above analysis, two factors that affect binder burnout are material variations and operating variables which influence the final product quality (amount of carbonaceous residue left). These two factors can be subdivided into the following: (1) Material variations: ceramic (particle size and surface structure, surface impurity, amount of O2 adsorbed, and free water content (number of O-H)), polymer (molecular weight and number of functional (O-H and CdO) groups), and composite (density of packing, concentration of polymer, and sample size). (2) Operating variables: system atmosphere, carrier gas flow rate, operating temperature and pressure, heating rate, and steam temperature. In this work, polymer residues and evolved gas (EG) analyses were utilized to elucidate the mechanism of nonoxidative PVB/Al2O3 and PVB/AlN thermal degradation. In using EGA, an analytical algorithm developed earlier (Liau et al., 1996a,b) was used to determine the kinetic models by GC/MS, TG, and FT-IR measurements. Isothermal and nonisothermal approaches to

elucidate the kinetic mechanism are discussed. The polymer residues from isothermal treatments were analyzed to find out the structure of the burnout residues by DRIFTS technique. The amount of carbon in the residual samples has been quantified by a Leco analyzer. The results of PVB/Al2O3 and PVB/AlN have been compared. In addition, the results of kinetic analysis of PVB in different environments are also discussed. Analytical Methodology The analytical procedures included two parts: off-line qualitative analysis by GC/MS and on-line quantitative TG/FT-IR measurements. The objective of using offline GC/MS is to identify the evolved gaseous products and propose reaction pathways. On-line TG/FT-IR measurements provide the dynamic information of the burnout process with both weight loss of the sample and the evolved gases of the degraded sample. The dynamic mixture spectra measured from FT-IR were further resolved into each pure species using the LMS algorithm (Haykin, 1994) on the basis of the spectral patterns of the identified gases. Overall and detailed kinetic analysis has been established using the TG/FT-IR measurements. The objective of spectrum resolution was to obtain dynamic information on the quantitative estimate of each pure species of EG for the kinetic system. Based on the pattern recognition technique and the assumption that there are no interactions among spectral patterns of pure species, the diagram of an n-dimensional pattern system can be described as

X1W1 + X2W2 + ... + XnWn ) Xn+1Wn+1

(1)

W‚XT ) 0

(2)

or

where Xi (i ) 1, ..., n) is the pure species spectral pattern, or the reference pattern, Xn+1 is the mixture spectral pattern, and W is the corresponding weight vector. A LMS algorithm was used to resolve dynamic mixture IR spectra into each constituent species spectrum by adjusting the weight vector W. Detailed theory of the algorithm used in this work can be found in Liau et al. (1996a,b). All the dynamic data obtained by the spectral resolution were utilized for kinetic analysis. Practically, there are two ways to carry out the analysis based on isothermal and nonisothermal operations. The general rate equation for solid-state decomposition reaction can be written as

dRi ) Ki f(Ri) dt

(3)

where Ri is the conversion for species i. For the isothermal system, eq 3 can be integrated as

F(Ri) )

dR

∫f(R i) ) Kit

(4)

i

and rate constant Ki is given by the Arrhenius relation

Ki ) Ai exp[-Ei/RT]

(5)

Ind. Eng. Chem. Res., Vol. 37, No. 1, 1998 51

where Ai is the Arrhenius frequency factor, Ei is the activation energy, and R is the universal gas constant. For the nonhomogeneous and nonisothermal chemical reactions, Lee and Beck (1984) used integration by parts to solve eq 3 and obtained an approximate solution

ln

[ ] [ F(Ri) T

2

) ln

A iR

]

β(E + 2RT)

-

Ei RT

(6)

where β is the heating rate and F(Ri) is the integral form of f(Ri). This approach has been applied to the kinetic analysis of pyrolysis reactions (Lee and Beck, 1984; Ma et al., 1991; Yang et al., 1996). Experimental Section Commercial PVB type B-79 from Aldrich Chemical Co. was used as the binder. The weight-average molecular weight of PVB was approximately 65 000 and its glass transition temperature was 68 °C as measured using a Perkin-Elmer DSC-7 previously calibrated using sapphire and indium standards. Two ceramics, alumina (Al2O3) of size 5 µm from IBM and aluminum nitride (AlN) of about size 2-3 µm from Dow Chemical Co., were used in this work. The samples were prepared by dissolving PVB (14%) in a solution of methyl alcohol and methyl isobutyl ketone and then blending with the ceramic (86%) using an agitator for 2 h. The blended slurry was spread onto plates to make pellets and left in an oven at about 90 °C for 36 h to remove the organic solvents. A Perkin-Elmer FT-IR 2000 was interfaced with a Perkin-Elmer Model 1020 series TGA 7 to carry out EGA and to collect dynamic weight loss and EG spectral data. About 95 mg of the composite sample was used in the experiment, and the TG was programmed for isothermal or nonisothermal operations. The flow rate of nitrogen carrier gas was set at 90 cm3/min Degradation products were identified separately by a GC/MS system consisting of a Hewlett Packard (HP) 5890 series II gas chromatograph interfaced with a HP 5971 series mass spectrometer. The details of TG/FT-IR and GC/ MS systems were described earlier (Liau et al., 1996a,b). A programmable Thermolyne F6000 furnace with a high-pressure reactor was used to carry out presintering studies. The composite samples were placed in the reactor in a nitrogen atmosphere and heated in the furnace for over 1 h at a particular temperature. The reactor temperature was measured by thermocouples using a Simpson 460 series 4 digital multimeter. The burnt samples at different temperatures were analyzed for carbon content using a IR-212 Leco Analyzer from Leco Corp. (St. Joseph, MI). The burnt samples were also investigated by DRIFTS technique. A PerkinElmer FT-IR 2000 with COLLECTOR, a diffuse reflectance accessory supplied from Spectra Tech, was utilized in the DRIFTS system. Each DRIFTS spectrum was recorded in the range from 4000 to 700 cm-1 at a resolution of 4 cm-1, and 100 scans were recorded to increase the signal to noise ratio. Results Kinetic Analysis. Kinetic analysis of PVB/Al2O3 thermal degradation was carried out under isothermal and nonisothermal conditions using the analytical algorithm. A literature survey indicated that evolved gaseous products of PVB/ceramics were identified using

Figure 1. Stacked plot of PVB/Al2O3 degradation at 334 °C from 5 to 9.5 min.

TG/GC/MS, GC/FT-IR, or TG/MS, and major species identified were acetic acid, butanoic acid, butanal, butenal, and butanol. These species were also reconfirmed by GC/MS in the present study. Each spectral pattern of the major products was used as an independent pattern variable for the IR spectrum resolution method for both isothermal and nonisothermal operations and other products. In the isothermal approach, TG/FT-IR was set up in the temperature range of 200-500 °C. In this section, the results of the isothermal treatment at 334 °C and the formation of butanal, the main degradation product in the operating temperature ranges, are used as an example to demonstrate the isothermal kinetic approach. The same procedure was used at other temperatures. Figure 1 shows the dynamic mixture IR spectra of the evolved gases from PVB/Al2O3 degradation at 334 °C. The significant gas evolution was between 6 and 8 min and reached a maximum intensity at 7 min. The mixture spectra at each time were resolved by the resolution method into each pure species spectrum represented by each maximum peak intensity, i.e., corresponding to a wavenumber of 1750 (CdO stretching) for butanal, as shown in Figure 2. The intensity of butanal, which was the main degradation product, was significantly higher than other species. The dynamic data were transformed into conversion of each species as a function of time, as illustrated in Figure 3. Rate constants of the reaction pathways illustrated in Figure 4 for any particular temperature were determined on the basis of the conversion data and eq 4. A first-order parallel reaction scheme was assumed for each major product. This results in F(R) equal to -ln(1 - R). Thus, the rate constants, slope of F(R) against time in Figure 5, for each species at different temperatures were determined, and the results for each species are given in Table 1. The activation energy of each species was determined using the rate constants obtained at different temperatures. Taking butanal as an example to demonstrate the calculation procedure, Figure 6 shows the intensities of butanal at each time evaluated from the resolved IR

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Figure 2. Intensity changes of each evolved gas as a function of time at 334 °C.

Figure 4. Possible mechanism and reaction pathways of PVB thermal degradation from EGA.

Figure 3. Conversion of each evolved gas as a function of time at 334 °C.

mixture spectra using the resolution method. As the temperature increased, the intensity increased because a higher fraction of polymer degraded. This is shown more clearly in Figure 7, where the conversion of butanal as a function of time at each temperature is plotted. Again, the rate constants of butanal were determined by using the conversion data and eq 4. Figure 8 illustrates the results of the rate constants, the slope of the plots, as given in Table 1. Rate constants for the other species at each temperature were calculated using the same approach and are given in Table 1. These rate constants were then plotted for each species as shown in Figure 9. Activation energies for the species were obtained from eq 5. The kinetic parameters are listed in Table 2. The other kinetic analysis is the nonisothermal approach carried out by setting a heating rate. Figure 10 shows the mixture IR spectra of the evolved gas from 23 min (553 K) to 30 min (623 K) at a heating rate of 10 °C/min. The spectral intensity reached a maximum at 25.6 min (579 K). The mixture spectra at each time were then resolved into each pure species. In this work, all the spectral patterns used in the resolution method were normalized; therefore, the value of weight w is located between 0 and 1. The resolution results are illustrated by the weight vector W in Figure 11, and the resolved results represented by the intensity for each species are shown in Figure 12 as a function of temperature. Figure 11 shows that the weight factor w for

Figure 5. Plots of the degradation rate constants (slope) for each major volatile product at 334 °C. Table 1. Reaction Rate Constants (min-1) of Thermal Degradation of PVB/Al2O3 at Different Isothermal Treatments acetic acid butanoic acid butanal butenal butanol

229 °C

252 °C

280 °C

313 °C

334 °C

0.0146 0.0676 0.0208 0.0166 0.00104

0.052 0.1169 0.0682 0.0542 0.0085

0.133 0.4817 0.420 0.326 0.143

0.985 1.404 1.67 1.46 1.103

3.423 2.462 2.25 1.83 1.366

butanal is distributed around 0.9, higher than other species, which means the mixture spectral patterns are more similar to the butanal spectral pattern. Figure 13 shows the conversion of each species as a function of temperature transformed from the data in Figure 12. The activation energy for the formation of each species

Ind. Eng. Chem. Res., Vol. 37, No. 1, 1998 53

Figure 6. Changes of butanal intensity during PVB/Al2O3 degradation at each temperature.

Figure 9. Arrhenius plots of activation energies of each volatile product for isothermal operation. Table 2. Kinetic Parameters for Each Major Volatile Product of PVB/Al2O3 Thermal Degradation under Isothermal and Nonisothermal Conditions isothermal acetic acid butanoic acid butanal butenal butanol

nonisothermal

E (kJ/mol)

A (1/min)

E (kJ/mol)

A (1/min)

126 87 116 118 179

1.76 × 1011 6.85 × 107 3.13 × 1010 3.44 × 1010 5.92 × 1015

128 110 127 153 158

3.62 × 1011 2.02 × 109 7.68 × 1010 1.43 × 1013 2.41 × 1013

Figure 7. Conversion of butanal from PVB/Al2O3 degradation as a function of time at each temperature.

Figure 10. Stacked plot of PVB/Al2O3 thermal degradation with 10 °C/min for nonisothermal operation. Figure 8. Plots of the degradation rate constants (slope) for butanal at each temperature.

can be calculated using the dynamic conversion data (Figure 13) and eq 6. With the assumption of a firstorder parallel reaction scheme for each species, F(Ri) turns out to be ln[-ln(1 - Ri)] for nonisothermal operation. Thus, the activation energy for each species, the slope of the plots in Figure 14, is determined and given in Table 2. The kinetic model of thermal degradation of a PVB/AlN composite can also be determined using the same procedure, and the results are given in Table 2.

Burnt Sample Analysis. Fourteen weight percent PVB with Al2O3 or AlN composite samples were used for binder burnout analysis in the temperature range of 300-823 K. Each run was carried out in an isothermal mode in a temperature-programmable furnace. Each sample was kept in a closed reactor and placed in the furnace for over 1 h. One hour heating was deemed sufficient for the sample to reach a steady state at each isothermal treatment. Therefore, it was assumed that the molecular structure of the polymer residue at the end of 1 h represents a stable structure at that temperature. The residual sample was analyzed to find out the temperature effects on PVB thermal degradation.

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Figure 11. Weight vector obtained from the spectral resolution results for nonisothermal operation.

Figure 12. Intensity changes of each evolved gas as a function of temperature during nonisothermal operation.

Figure 13. Conversion of each evolved gaseous product of PVB/ Al2O3 thermal degradation as a function of temperature for nonisothermal operation.

The direct and significant observation of the burnt sample is the color. The color of the unburned composite sample was white at the ambient temperature. As the temperature increased, the color changed from brown, to yellow, and finally to black. There was a significant color change from yellow to black between 591 and 652 K, indicating that the morphology or structure of the PVB/Al2O3 composite changed due to the thermal treatment.

Figure 14. Arrhenius plots of activation energy of each evolved gas for nonisothermal operation.

Figure 15. DRIFTS spectra of Al2O3, PVB, and AlN at room temperature.

DRIFTS technique was utilized to monitor the spectral changes of the residue for each burnt sample. All the DRIFTS spectra were obtained at ambient environment, and the spectrum of the KBr powder was used as a background. Figure 15 illustrates the spectra of Al2O3 and AlN powders and commercial PVB used in this work. The PVB sample contains 11% hydroxyl group of poly(vinyl alcohol) and 1% acetate group of poly(vinyl acetate). The significant band near 1100 cm-1 for pure alumina is the Al-O stretching and that between 1300 and 1000 cm-1 for pure aluminum nitride the Al-N stretching. Therefore, it is expected that there should be prominent bands in the spectra of the PVB/Al2O3 and PVB/AlN composite samples near the region of 1300-1100 cm-1. The spectra of PVB/Al2O3 burnt samples are shown in Figure 16 in the region of 3200-1500 cm-1 at each temperature. The C-H stretching (3000 cm-1) bands significantly disappear between 591 and 625 K. This is the zone in which the sample color changed significantly. No signal of the C-H group was detected after 652 K for the residual samples, which means that the hydrocarbon group of the polymer residue has been removed. The other observable changes of the spectra in Figure 16 were in the region between 1500 and 2000 cm-1. The possible functional groups in the region are CdO (∼1750 cm-1), CdC (∼1650 cm-1), and O-C-O (∼1600 cm-1). There is a small peak of the unburned

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Figure 18. Changes of carbon content for PVB/Al2O3 and PVB/ AlN samples as a function of temperature. Figure 16. DRIFTS spectra of PVB/Al2O3 residual samples at different isothermal treatments. Table 3. Activation Energies (kJ/mol) for PVB Thermal Degradation in Different Environments

acetic acid butanoic acid butanal butenal butanol TG (overall)

PVB (in nitrogen)

PVB (in air)

PVB/Al2O3

PVB/AlN

231 407 349 334 475 327

300 199 208 226 203 194

128 110 127 153 158 91

133 131 140 147 162 105

Discussion

Figure 17. DRIFTS spectra of PVB/AlN residual samples at different isothermal treatments.

sample (298 K) spectrum near 1750 cm-1 before the pyrolysis due to the acetate group of the polymer binder. There are some carbonyl (CdO) and ethyl groups (OC-O) generated during the degradation process. As the temperature is increased to 798 K, the carbonaceous residue of the sample contains the possible functional structures of CdO and O-C-O. The results were similar for PVB/AlN samples and are shown in Figure 17. The amount of carbon residue for each sample was determined by the Leco Analyzer. Figure 18 shows the results of the analysis of carbon content for PVB/Al2O3 and PVB/AlN. At 298 K, the carbon content in the composite sample is about 10%, which is reasonable if the unit structure of PVB is taken as C8H14O2. For both samples, the carbon content remains at about 8 wt % until the operating temperature is close to 600 K. In the temperature range of 600-700 K, the carbon content decreases from 8 to 2 wt %. If the operating temperature increases to 800 K, the carbon content decreases to about 0.5 wt % for PVB/Al2O3 and 1.0 wt % for PVB/ AlN.

The structure of PVB which has a symmetric ether group is shown in Figure 4. If the ether groups, C*1 and/or C*2, are surrounded and attacked by nucleophilic reagents, i.e., alumina, then B-I to B-IV bonds breaking generate the side-group elimination products, as shown in Figure 4. The volatile products of PVB degradation are generated randomly and simultaneously. From the kinetic analysis, it is a first-order parallel reaction with respect to each major product. The analytical results of the kinetic parameters are very consistent with using isothermal and nonisothermal approaches as shown in Table 2. The activation energies of the formation for each species and the overall PVB degradation in different environments are listed in Table 3. The activation energies of PVB/ceramics thermal degradation are significantly lower compared to pure PVB. For the formation of butanal or the overall degradation of PVB, the activation energies are about 300 kJ/mol in nitrogen, ∼200 kJ/mol in air, and ∼100 kJ/mol with Al2O3 or AlN in nitrogen. Lower activation energy with the ceramics is due to the fact that the ceramic material acts as a strong nucleophilic catalyst and is able to accelerate bond breaking of PVB. The initial reaction temperature of PVB with alumina in nitrogen is about 100 K lower than that of PVB in nitrogen. For the PVB/Al2O3 sample, carbon composition was tracked by observing the C-H, CdO, and O-C-O functional groups. The intensity variations of the C-H, CdO, and O-C-O were due to the structural changes of PVB (cyclic or cross-linked reactions) and/or the reaction of PVB with the hydroxyl group of the composite system and/or with the ceramic surface (Higgins et al., 1994). The hydrocarbon (C-H) group decreased gradually and disappeared after 652 K (Figure 16)

56 Ind. Eng. Chem. Res., Vol. 37, No. 1, 1998

during the thermal treatment. At lower temperatures, the intensity of the CdO group was higher than that in the unburned sample and then nearly disappeared at higher temperature around 798 K. This phenomenon of increased unsaturation and carbonyl content at lower temperature was also observed by White and Ai (1992). At 798 K, the carbon content was 0.5% and the structure of the carbonaceous residue was identified as CdO and O-C-O or another pure carbon structure. Liau et al. (1996b) studied the thermal oxidative degradation of pure PVB and observed that there was no hydrocarbon in the residue at the final pyrolysis stage as only CO2 was detected from the oxidation of the residue with FTIR measurement. In the case of PVB/AlN, the intensity of the CdO group did not change significantly with an increase in temperature as shown in Figure 17 compared with the case of PVB/Al2O3 at 477 K. The C-H stretching peak for this case vanished at about 700 K. The carbon contents as a function of temperature for PVB/AlN and PVB/Al2O3 were similar, although the PVB/AlN sample had about 0.5 wt % higher carbon residue at the end of the pyrolysis stage. From the polymer residue analysis, there are two kinds of residual carbons formed during the polymer/ ceramic degradation (Yan et al., 1992). “Intrinsic char” is generated from the polymer binder pyrolyzed with ceramic powder; “gas phase mediated char” is formed due to the interaction of volatile products with ceramic surfaces (Higgins et al., 1994). The amounts of carbon residue in the composite material changed significantly in the region between 600 and 700 K, as shown in Figure 18. The intensity changes of the functional groups of PVB residues at different temperatures collected using the DRIFTS spectra and shown in Figures 16 and 17 appear to indicate the composition of “intrinsic char” as simply the carbon with oxide groups.

Conclusions Mechanisms of thermal degradation of pure PVB, as well as PVB with oxide (Al2O3) and nonoxide (AlN) ceramics, were discussed on the basis of dynamic EGA. The reaction pathways and kinetic models of the degradation were determined as first-order parallel reactions for the cases. From the results of the kinetic analysis, both oxide and nonoxide ceramics show strong catalytic properties to accelerate the degradation process compared with the case of pure PVB. The overall activation energies of PVB degraded with the ceramics are around 100 and about 300 kJ/mol for pure PVB. The kinetic analyses using isothermal and nonisothermal operations are in good agreement. Two kinds of carbon residues were discussed via the Leco analyzer for carbon content determination and the DRIFTS technique for spectral analysis. The carbonaceous structure of the polymer residues at the final degrading stage was verified as a simple carbon oxide structure without a C-H functional group.

Acknowledgment Partial financial support from the Monsanto Chemical Co. is gratefully acknowledged.

Literature Cited Barone, M. R.; Ulicny, J. C.; Hengst, R. R.; Pollinger, J. P. Removal of Organic Binders in Ceramic Powder Compacts. In Ceramic Powder Science IIA; Messing, G. L., Fuller, E. L., Hausner, H., Jr., Eds.; American Ceramic Society: Westerville, OH, 1988; p 575. Boddu, V. M.; Viswanath, D. S.; Natarajan, G.; Knickerbocker, J. V. Activity and Reactivity of Carbon Formed by the Thermal Degradation of Poly(vinylbutyral) in Alumina Pellets. J. Am. Ceram. Soc. 1990, 73 (6), 1620. Chillara, S. N.; Boddu, V. M.; Viswanath, D. S. Steam Oxidation of Carbon Formed by Thermal Degradation of PMMA in Alumina. Chem. Eng. Commun. 1994, 130, 45. Cima, M. J.; Lewis, J. A. Firing-Atmosphere Effects on Char Content from Alumina-Poly(vinyl butyral) Films. In Ceramic Powder Science IIA; Messing, G. L., Fuller, E. L., Hausner, H., Jr., Eds.; American Ceramic Society: Westerville, OH, 1988; p 567. Cima, M. J.; Lewis, J. A.; Devoe, A. D. Binder Distribution in Ceramic Greenware During Thermolysis. J. Am. Ceram. Soc. 1989, 72 (7), 1192. Farooq, S.; Natarajan, G.; Reddy, S. S. N.; Shelleman, R. A.; Stoffel, N. C.; Vallabhaneni, R. V. Method for Forming Sealed Co-Fired Glass Ceramic Structures. U.S. Patent 5,073,180, 1991. Haykin, S. Neural NetworkssA Comprehensive Foundation; Prentice-Hall: Englewood Cliffs, NJ, 1994. Herron, L. W.; Knickerbocker, S. H.; Natarajan, G.; Reddy, S. S. N. Setter Tile for Use in Sintering of Ceramic Substrate Laminates. U.S. Patent 5,053,361, 1991. Higgins, R. J.; Rhine, W. E.; Cima, M. J.; Bowen, H. K.; Farneth, W. E. Ceramic Surface Reactions and Carbon Retention during Non-Oxidative Binder Removal: Al2O3/PMMA at 20°-700 °C. J. Am. Ceram. Soc. 1994, 77 (9), 2243. Howard, K. E.; Lakeman, C. D. E.; Payne, D. A. Surface Chemistry of Various Poly(vinyl butyral) Polymers Adsorbed onto Alumina. J. Am. Ceram. Soc. 1990, 73 (8), 2543. Kashiwagi, T.; Hirata, T.; Brown, J. E. Thermal and Oxidative Degradation of Poly(methyl methacrylate): Molecular Weight. Macromolecules 1985, 18 (2), 13. Lee, T. V.; Beck, S. R. A new Integral Approximation Formula for Kinetic Analysis of Nonisothermal TGA Data. AIChE J. 1984, 30 (3), 517. Liau, L. C. K.; Yang, T. C. K.; Viswanath, D. S. Reaction Pathways and Kinetic Analysis of PVB Thermal Degradation Using TG/ FT-IR. Appl. Spectrosc. 1996a, 50 (8), 1058. Liau, L. C. K.; Yang, T. C. K.; Viswanath, D. S. Mechanism of Degradation of Poly(vinyl butyral) Using Thermogravimetry/ Fourier Transform Infrared Spectrometry. Polym. Eng. Sci. 1996b, 36 (21), 2589. Ma, S.; Hill, J. O.; Heng, S. A kinetic Analysis of The Pyrolysis of Some Australian Coals by Non-isothermal Thermogravimetry. J. Therm. Anal. 1991, 37, 1161. Madras, G.; Smith, J. M.; McCoy, B. J. Degradation of Poly(methyl methacrylate) in Solution. Ind. Eng. Chem. Res. 1996, 35 (6), 1795. Masia, S.; Calvert, P. D.; Rhine, W. E.; Bowen, H. K. Effect of Oxides on Binder Burnout during Ceramics Processing. J. Mater. Sci. 1989, 24, 1907. Nair, A.; White, R. L. Effect of Inorganic Oxides on Polymer Binder Burnout. I. Poly(vinyl butyral). J. Appl. Polym. Sci. 1996, 60, 1901. Scheiffele, G. W.; Sacks, M. D. Pyrolysis of Poly(vinyl butyral) Binders: II Effect of Processing Variables. In Ceramic Powder Science IIA; Messing, G. L., Fuller, E. L., Hausner, H., Jr., Eds.; American Ceramics Society: Westerville, OH, 1988; p 559. Shih, W. K.; Sacks, M. D.; Scheiffele, G. W.; Sun, Y.-N.; Williams, J. W. Pyrolysis of Poly(vinyl butyral) Binders: I Degradation Mechanisms. In Ceramic Powder Science IIA; Messing, G. L., Fuller, E. L., Hausner, H, Jr., Eds.; American Ceramic Society: Westerville, OH, 1988, p 549. Sohn, H. Y.; Wall, D. R. Removal of Carbonaceous Residue with Wet Hydrogen in Greensheet Processing for Multilayer Ceramic Module: II, Reaction in Large Modules Influenced by Pore Diffusion and Mass Transfer. J. Am. Ceram. Soc. 1990, 73 (10), 2953. Verweij, H.; Bruggink, W. H. M. Reaction-Controlled Binder Burnout of Ceramic Multilayer Capacitors. J. Am. Ceram. Soc. 1990, 73 (2), 226.

Ind. Eng. Chem. Res., Vol. 37, No. 1, 1998 57 Wall, D. R.; Sohn, H. Y. Removal of carbonaceous Residue with Wet Hydrogen in Greensheet Processing for Multilayer Ceramic Module: I, Residue Formation and Intrinsic Chemical Kinetics. J. Am. Ceram. Soc. 1990, 73 (10), 2944. White, R. L.; Ai, J. Effect of Silica on the Nonoxidative Thermal Degradation of Poly(vinyl butyral). Chem. Mater. 1992, 4 (1), 233. Yamanaka, S.; Maruyama, G.; Ueyama, T. The Thermal Decomposition of Poly(vinyl butyral)/PLZT, PMN Dielectric Powder Composite. J. Ceram. Soc. Jpn. 1992, 100 (5), 657. Yan, H.; Cannon, W. R.; Shanefield, D. J. Poly(vinyl Butyral) Pyrolysis: Interactions with Plasticizer and AlN Ceramic Powder. Mater. Res. Soc. Symp. Proc. 1992, 249, 377.

Yang, T. C. K.; Chang, W. H.; Viswanath, D. S. Thermal Degradation of Poly(vinyl butyral) in Alumina, Mullite, and Silica Composites. J. Therm. Anal. 1996, 47, 697.

Received for review June 19, 1997 Revised manuscript received October 6, 1997 Accepted October 23, 1997X IE970434B

X Abstract published in Advance ACS Abstracts, December 15, 1997.