Gel-Cast Organic-Inorganic Systems
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GEL-CAST ORGANIC-INORGANIC
SYSTEMS
K. Maes, M.R. Silsbee, D.M. Roy, J.H. Adair* and B.E. Scheetz Materials Research Laboratory, The Pennsylvania State University, University Park, PA *Materials Science and Engineering Department, University of Florida, Gainesville.
ABSTRACT The studies reported herein were designed to develop a better understanding of the influence of different crosslinking agents on the polymerization of acrylamide gel systems and upon the resulting physical properties of the composites. Specimens were developed via a gel-casting process for viscoelastic and diametral tensile strength testing and the chemical reactions were monitored by Raman spectroscopy and isothermal calorimetry. The studies have demonstrated the ability to tailor the properties of a gel-cast system over a relatively wide range of reaction rates and the resulting mechanical properties by utilizing small adjustments to the overall chemistry of the system.
INTRODUCTION Chemically bonded ceramics (CBC) are low-temperature materials, whose strength approaches those of many traditional high-temperature ceramics, and are a novel way of forming high strength ceramic materials. These materials are formed by a bonding that takes place via chemical reaction at low temperature, as opposed to fusion or sintering at elevated temperature. Gel-casting was chosen as the processing approach for this study, as it is envisioned to have potential application in cement solidification. In this process, the monomers and crosslinking agents are separately added to the ceramic (or cement) powder, mixed and the near final shaped object cast. The final step in the process is the induced polymerization of the monomer and crosslinking agents. A major objective of this specific study was to develop a better understanding of the influence of different crosslinking agents on the polymerization of acrylamide and on the physical properties of the composite. The applications of these studies extends to such diverse fields as soil grouting systems [1], heavy metal stabilization and/or composite CBC products.
EXPERIMENTAL The gel-casting process Two monomers were used in this study: the di-functional monomer acrylamide (Am) and the di-functional monomer, NN'methylene-bis-acrylamide (BisAAm). The acrylamide system was chosen for this study because its polymer has already been successfully used in MDF-cements prepared from ordinary portland cement (OPC) [2,3,4,5]. The crosslinking reaction utilized the BisAAm in order to create a three-dimensional structure. Additional 2 crosslinking was obtained with metal ions Ca + and Na+, which were added in the hydroxide form to the aqueous mixing solution before polymerization. These ions were chosen to simulate contents of cement solutions. The basic aqueous solutions initiate in-situ polymerization [1] conversion of the carboxamide groups to carboxyl groups. Optimization of the crosslinking in the presence of inorganic cations is a function of pH, Eh and concentration [6,7]. The overall system must be carefully designed
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