That's why PP has been used as a common polymer matrix in making the composites by the incorporation of fillers such as carbon nanotubes (CNTs), montmorillonites (MMTs) and nanoparticles including silica, graphite and calcium carbonate, although the dispersion of fillers is a challenging issue 20. By upgrading the mechanical performance of polypropylene, its applications in different industrial zones can be expanded 19. Polypropylene (PP) is an essential plastic, which is being broadly used for the manufacturing of domestic articles and automotive industrial spare parts. reported that a number of reinforcements can be used to reinforce the thermoplastics matrices. Dendritic polyamidoamine-grafted HNTs is found effectively improving interfacial interactions between HNTs and epoxy matrix and ultimately improving their dispersion in final epoxy nanocomposites imparting improve impact strength, modulus and fracture toughness 17.įig- 4 SEM photographs of (a) pristine HNTs and (b) 100 h-PPA-modified HNTs 18 Figure 3 shows the HNTs particle size distributions measured by a particle size analyzer. However, results demonstrated that PA treatment is an effective treatment for reduction of HNTs particle cluster (agglomerates) size in epoxies and ultimately enhanced the mechanical properties 13. Other chemical treatments involved treatment of HNTs with potassium acetate (PA), silane and cetyl trimethylammonium chloride (CTAC) were not found much suitable for intercalation of HNTs. For example, HNTs grafting with polyacrylonitrile (PAN) and polystyrene prepared by atom transfer radical polymerization (ATRP) 15, HNTs grafting with PMMA and PVA/PMMA by radical polymerization 16. Polymer grafting of HNTs via chemical process also proved a good method to get composites with homogenized disperse HNTs. For example, the intercalation and exfoliation of organic or inorganic compounds in the layers of HNTs expanded their basal spacing and produced a homogenized dispersion of HNTs within polymer matrices under mixing 14. Literature study reveals that surface modification of HNTs is a much better method to disperse them in polymer matrices as compared to conventional mixing methods. However, severe shear stresses like melt extrusion 12 and ball mill homogenization 13 methods may break agglomeration of HNTs to achieve fine homogeneous dispersion of HNTs in polymer matrices. The conventional mixing methods such as ultrasonic dispersion methods and shear stresses like mechanical and magnetic bar stirring have proven to break agglomeration of HNTs to some extent. In case of HNTs, their relatively large surface energy (due to large surface area = ~ 60 m 2/g) causes their agglomeration owing to presence of van der Waals forces between tubes 11. Methods of dispersion of nanoparticles in a polymer matrix have always remained under special consideration due to their agglomeration, which adversely reduces the performance of nanoparticles in the matrix.
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Literature suggests that the proper choice of material and design of process are of crucial importance to get the full benefits of HNTs as reinforcing nanofiller for polymer matrices. Modified halloysite show improved compatibility and interactions with polymer matrices and hence a uniform dispersion can achieve. A homogeneous dispersion of filler results in enhanced mechanical performance whereas agglomerated particles lead to adversely affect the mechanical performance. Disperion state of the filler greatly influences the mechanical properties of nanocomposites. The final performance of polymer nanocomposites depends upon the degree of dispersion of filler and its interactions with the polymer matrices 10. observed the improvements in properties like stiffness, thermal, barrier, electrical properties, dimensional stability, toughness and fire retardant augmentations as compared to the bulk polymer 9. Polymer nanocomposites are a new class of materials in which nano-fillers are used as reinforcement and they show better physical and thermo-mechanical properties than conventional polymer nanocomposites 8. Halloysite nanotubes are used as a template in nanotechnology 7. The presence of tubular or cylindrical particles indicates halloysite on the other hand with platy particles are termed as kaolinite. Fig- 2 Structural of halloysite and its chemical similar kaolinite 6
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