A Study of the Thermolysis Behaviour of Pmma in Polymer/SiO 2 -PbO-B 2 O 3 Glass Powder Mixtures
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A STUDY OF THE THERMOLYSIS BEHAVIOUR OF PMMA IN POLYMER/SiO 2-PbO-B20 3 GLASS POWDER MIXTURES A. Aruchamy*, K. A. Blackmore*, B. J. J. Zelinski*, D. R. Uhlmann* and C. Booth" *Department of Materials Science and Engineering, University of Arizona, Tucson, AZ-85712 "5Experimental Station, E.I. du Pont de Nemours & Co., Wilmington, DE-19898 ABSTRACT The binder burn-out behavior in PMMA/glass powder composites was studied as a function of glass composition in the PbO-SiO 2-B20 3 system. The PbO content was varied to obtain glasses having optical basicities in the range of 0.62-0.81. TGA measurements on PMMA/glass composites show that the main decomposition end temperatures of PMMA increase with decreasing PbO content, and therefore, decreasing optical basicity. This indicates that PMMA interacts strongly with more acidic surfaces. The effect of the milling fluid was also studied. Milling in toluene does not significantly alter the behavior. Milling in water of a PbO-rich glass leads to significant leaching of lead. During drying, the leached lead deposits on the glass particle surfaces and drastically alters the thermal behaviour of the glass powder and PMMA/glass composites. INTRODUCTION In the processing of advanced multilayer ceramic(MLC) systems for electronic packaging, it is increasingly important that the organic binders are completely removed at low temperatures so that densification to hermeticity is achieved. In addition, the electrical and mechanical properties of electronic components can be considerably impaired if the carbonaceous products of binder thermolysis are not completely removed during processing[I]. Complete burnout of binders in polymer/ceramic composites is influenced by both physical and chemical factors[2-6]. In general, the chemical characteristics of the polymer determine the decomposition temperatures and products. A major part of the polymer binder degrades at nearly the same temperature at which the pure polymer undergoes decomposition. A small fraction of the binder molecules, however, may require higher temperature to obtain complete degradation and may form different degradation products if the interaction of polymer functional groups with the oxide(ceramic) surface is strong[4-5]. Retention of carbonaceous residues leading to carbon in the ceramic is possible if complete burn-out is not realized before temperatures at which sintering takes place. The polymer-oxide(ceramic) interaction depends on the nature of the functional groups on the polymer and the acid-base properties of the ceramic surface. Masia and co-workers[4] suggested that carbon retention after PVB decomposition is dependent on the isoelectric point(IEP) of the ceramic and is minimum for oxides with IEP near 7. Strong effects of calcination of the ceramic powder on PMMA burn-out temperatures were reported by Sun et al.[5] for A120 3 and Farneth et ai.[6] for TiO 2. Allara et al.[7] have reported that the adsorption of PMMA molecules is stronger on the acidic surface of SiO 2 than on the surface of Si0 2:A120 3(50:50)w
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