A study of high clay content polymer/organically modified montmorillonite hybrids

Studies of the mechanical, thermal and barrier properties of polymer / layered silicate nanocomposites have traditionally focused on systems with low clay contents, with very little work comparing theory and experiment over broad composition ranges. Here this will be addressed by studying a new branch of nanocomposites termed "nanolaminates". These typically consist of high aspect ratio platelets of nanometric thickness and a polymer matrix arranged in a "brick and mortar" morphology via appropriate processing steps to create a synthetic analog of the nacre, a natural composite common to seashells. Altering the types and proportions of platelets and polymer present allows for control of nanolaminate properties and adaptation to specific applications. For instance, some nanolaminates have been shown to possess extreme of mechanical and barrier properties, or unique combinations thereof. By utilizing a new spray deposition processing technique, nanolaminates of arbitrary composition may be produced, allowing for systematic studies of nanolaminate properties. In this work, barrier and mechanical properties are measured as a function of several composition variables, including organoclay type, aspect ratio and concentration and polymer type, as well as testing conditions (e.g. temperature, moisture content). In addition, the effects of intercalation and platelet orientation are analyzed as well. The resulting trends allow for the identification of those factors having the greatest impact on nanolaminate behavior, and enable improvements in existing models often used to describe stiffness and barrier properties in composites and nanocomposites more generally. These investigations further reveal evidence of the existence of a specific combination of phases as a function of composition and intercalation state, with the possibility to estimate phase content and thermomechanical transition temperature. These results not only provide an improved understanding of nanolaminates and their properties, but also provide further insight into structure-properties relations in (nano)platelet based composites in general.