Layered double hydroxides for packaging applications

Abstract

The primary aim of this thesis is to synthesise and modify layered double hydroxides (LDHs) for using in packaging applications. Chapter One provides an introduction of the basic manufacturing process of paper-based and flexible packaging and the relevant aspects of using inorganic materials in packaging materials. The principles of gas permeation and the role of two-dimensional platelets on the concept of a tortuous pathway are reviewed. In addition, the structure, synthesis methods and applications of LDHs are presented. Chapter Two details the synthesis of LDH/cellulose fibre composites and their use as fillers in the papermaking process. The strength and optical properties of the obtained LDH/cellulose fibre based paper sheets are examined. Superhydrophobic organo-LDHs are synthesised and applied as a pigment in a water resistant coating for paper. Chapter Three describes the novel post treatment for LDHs using aqueous immiscible solvents (AIM solvents). The effect of solvent functional groups and structure, along with some post treatment parameters such as rising volume, dispersion time, Mg/Al ratios, and solvent recycling on physicochemical properties of AIM LDHs are explored. The interactions between solvents and LDHs via hydrogen bonding are investigated using solid state nuclear magnetic resonance spectroscopy (SSNMR). Chapter Four presents the preparation of LDH nanoplatelets using a reconstruction of layered double oxides (LDOs) in a concentrated aqueous solution of amino acids. The effect of amino acid structure and other highly water-soluble compounds on the textural and chemical properties of the reconstructed LDHs are examined. The LDH nanoplatelets produced are used to formulate water-based dispersions for coating on polyethylene terephthalate films (PET). The effect of LDHs morphology, number of coating layers and loading amount of LDHs in the coating dispersion on an oxygen barrier performance and optical properties of the coated PET films are discussed. Chapter Five provides an alternative method for preparation of LDH nanoplatelets using direct reconstruction of LDOs in water, water-soluble polymer (polyvinyl alcohol or PVA), and non aqueous solvents. The effects of calcination temperature, reconstruction time, LDHs morphology, and PVA selection on the structural and physical properties of the reconstructed LDHs were investigated. Finally, the directly reconstructed LDHs are formulated into the coating dispersions and applied on PET films. The oxygen barrier and optical properties of the coated PET films are evaluated. Details of the experimental procedures performed are included in Chapter Six. Supplementary information and data referred to in the main thesis are found in the Appendices.