A theoretical modelling framework was proposed to predict tensile moduli and tensile strengths of bioepoxy/clay nanocomposites in terms of clay content and epoxidised soybean oil (ESO) content, which could be influenced by properties of blended matrices in nanocomposites, clay filler type, orientation and dispersion status, clay morphological structures, and filler-matrix interfacial bonding. The random orientation of dispersed clay fillers played a significant role in predicting elastic moduli of bioepoxy/clay nanocomposites at clay contents of 1-8 wt% (ESO content: 20 wt%) according to Hui-Shia (H-S) laminate model and Halpin-Tsai (H-T) laminate model. In addition, when clay content was fixed at 5 wt%, H-S laminate model coincided well with the experimental data of bioepoxy/clay nanocomposites at the ESO contents of 0-40 wt%. Whereas, Hirsch model showed closer estimated values with experimental data at the ESO content of 60 wt%. Finally, Turcsányi-Pukànszky-Tüdõs (T-P-T) model predicted better tensile strengths of bioepoxy/clay nanocomposites at clay contents of 1-5 wt% (ESO content: 20 wt%) and at an ESO content of 20-60 wt% (clay content: 5 wt%).
A holistic study was conducted to investigate the combined effect of three different pre-mixing processes, namely mechanical mixing, ultrasonication and centrifugation, on mechanical and thermal properties of epoxy/clay nanocomposites reinforced with different platelet-like montmorillonite (MMT) clays (Cloisite Na + , Cloisite 10A, Cloisite 15 or Cloisite 93A) at clay contents of 3-10 wt%. Furthermore, the effect of combined pre-mixing processes and material formulation on clay dispersion and corresponding material properties of resulting composites was investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), flexural and Charpy impact tests, Rockwell hardness tests and differential scanning calorimetry (DSC). A high level of clay agglomeration and partially intercalated/exfoliated clay structures were observed regardless of clay type and content. Epoxy/clay nanocomposites demonstrate an overall noticeable improvement of up to 10 % in the glass transition temperature (T g ) compared to that of neat epoxy, which is interpreted by the inclusion of MMT clays acting as rigid fillers to restrict the chain mobility of epoxy matrices. The impact strength of epoxy/clay nanocomposites was also found to increase by up to 24 % with the addition of 3 wt% Cloisite Na + clays. However, their flexural strength and hardness diminished when compared to those of neat epoxy, arising from several effects including clay agglomeration, widely distributed microvoids and microcracks as well as weak interfacial bonding between clay particles and epoxy matrices, as confirmed from TEM and SEM results. Overall, it is suggested that an improved technique should be used for the combination of pre-mixing processes in order to achieve the optimal manufacturing condition of uniform clay dispersion and minimal void contents.
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