Date of Award
Summer 2009
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Wilkie, Charles A.
Second Advisor
Hossenlopp, Jeanne M.
Third Advisor
Donaldson, William A.
Abstract
The aim of this research was to study the fire, thermal and mechanical properties of layered double hydroxide (LDH) nanocomposites. The metals Zn2+/Mg2+ -Al3+ were used to prepare the LDHs since these are contained in additives known to have excellent fire retardant effects. It was expected that a combination of these metals in LDHs will have a significant influence in fire properties of the composites. Chapter I gives a brief introduction on fire problem, traditional fire retardants, structure of LDHs, test and characterization methods. This is followed by a description of the experimental procedure and materials in Chapter II. Chapter III is a preliminary investigation which examines the similarity of LDHs with montmorillonite (MMT) using a variety polymers. From this work, it has been shown that LDHs are more compatible with polar polymers and that organic modification of LDH is important for improving dispersion, thermal and fire properties of nanocomposites. It is also shown that there is no significant effect of the mode of preparing LDHs i.e. coprecipitation, anion exchange and rehydration of the calcined precursor on the fire and thermal properties. Since LDHs are synthetic, they present a great number of possible metal ion compositions and the ability to exchange intercalated anions. This is a key factor for optimizing LDHs for application in fire retardancy. Chapter VI examines the effect on fire and thermal properties of varying, (i) the chain lengths of linear alkyl carboxylates (C10-C22), (ii) functionality (sulfonates, carboxylates and phosphonates) of benzyl anions and (iii) metal cations Zn2+ /Mg2+ -Ar3+ with borate anion. It is shown that dispersion is improved with longer alkyl carboxylate anions and is poor in composites containing LDHs intercalated with shorter benzyl anions. The fire and thermal properties of these various LDHs are also compared to those of the commercial fire retardants i.e. ATH, MDH, zinc borate and their combinations. The utility of nanocomposites as flame retardants has been established and is well understood. Nowdays [sic], more focus is being directed to combining nanomaterials (LDHs, MMT, CNT, etc.) with conventional flame retardants so as to formulate multiple flame retardant additive packages that will achieve non-burning behavior. In Chapter V, we investigated the effect on fire and thermal properties of combining low loadings of LDHs with commercial additives such as ammonium polyphosphate (APP), melamine polyphosphate, boric acid and carbon nanotubes. This work was motivated by earlier studies from this laboratory which indicated improved fire properties by combining MMT with phosphorus-containing flame retardants. Synergistic effects have been observed when MgAl-LDH was combined with APP in polystyrene composites. Finally, the formulation of polyureas with improved fire properties using a wide range of potential fire retardants is described in Chapter VI, while future work is suggested in Chapter VII.