Manufacture of Syntactic Foams Using Starch as Binder: Post-Mold Processing

Abstract

Syntactic foam manufacturing method, ‘post-mold processing,’ based on the buoyancy of hollow microspheres was studied for potential building material applications. The post-mold processing involves mixing starch particles and ceramic hollow microspheres in water. It was found starch particles tend to adhere to hollow microspheres, forming agglomerations, during mixing. It was also found that “volume fraction of starch particles on a microsphere making a relative density of 1.0” (VFSMRD) is an indicator for mixture volume transitions. Both the maximum total volume expansion of mixture and a transition in formation, after phase separation, of mixture volume in water referred to as “top phase” in a mixing container were taken place at a calculated VFSMRD. It was found that hollow microsphere size effect on attracting starch particles was relatively high but IBVMS effect was not significant. Also, no effect of water volume for a given diameter of cylindrical container was found. Starch-microsphere inter-distance was discussed and considered to be an important parameter affecting starch content in an agglomeration. A Simple Cubic cell model for the starch-microsphere inter-distance was adopted to quantitatively explain various effects on starch content in agglomeration such as hollow microsphere size, initial bulk volume of hollow microspheres (IBVMS), and water volume. Further, the following were found for manufactured syntactic foams: (a) volume fraction of starch in foam is of linear relation with starch content before mixing for a given experimental data range and (b) shrinkage is relatively high for small hollow microspheres with high starch content.