Preparation of Two-dimensional Molybdenum Disulfide/Polymer Nanocomposites and Investigation on Their Mechanical Property, Thermal Behavior and Combustion Performance


Student thesis: Doctoral Thesis

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Awarding Institution
  • Kim Meow LIEW (Supervisor)
  • Yuan Hu (External person) (External Supervisor)
Award date19 Jan 2018


With the development of polymer science and nanotechnology, polymer nanocomposites have aroused enormous research interests in various areas. For general usage, the mechanical property, thermal stability and flame retardancy of polymer nanocomposites are of special concern. Because of the geometric feature, two-dimensional nanomaterial is becoming increasingly popular in reinforcing polymer materials. There a considerable improvement of mechanical and thermal properties always can be observed at a low inclusion content of two-dimensional nanofillers, as well as a higher fire-retarding effect than commercial flame retardants. Due to its geometric character, robust feature and excellent thermal properties, two-dimensional molybdenum disulfide (MoS2) is expected to be a promising nanofiller to enhance the properties of polymeric materials. Basically, fabricating two-dimensional MoS2 in large scale and improving the compatibility of MoS2 within polymer matrix are pivotal issues to achieve the high-performance MoS2/polymer nanocomposites. Therefore, developing appropriate methods to obtain MoS2/polymer nanocomposites and systematic study on their properties are of great importance.

In this dissertation, firstly, four different techniques were utilized to prepare two-dimensional MoS2. For the purpose of fabricating polymer nanocomposites, Li- intercalation exfoliation and direct sonication exfoliation stood out from these four methods for achieving the MoS2/polymer nanocomposites. Benefited from latex premixing approach, the bare MoS2 nanosheets were homogeneously distributed in polypropylene matrix and serve as a barrier effect enhancing filler. Both covalent and non-covalent methods were adopted to achieve the surface modification of MoS2 in order to improve the interface interaction between MoS2 nanosheets and polymer matrix. Incorporating a low content of modified MoS2 nanosheets can obviously improve the mechanical properties, thermal stability and crystallization behavior of polymer nanocomposites. Furthermore, two-dimensional MoS2 was served as a template and synergist for conventional flame retardants to fabricate sandwich-like inorganic-organic hybrid flame retardants. With this design, the integrated flame retardant effect of these MoS2 based nanohybrids endowed the polymer nanocomposites with low flammability. The inorganic hybrid nanotechnology was adopted to further enhance the catalysis performance of MoS2 based inorganic hybrids during the combustion of polymers. The research work of this dissertation is composed of the following parts.

1. Li-intercalation exfoliation, mechanical exfoliation by ball milling, direct sonication and electrochemical exfoliation method were performed to exfoliate MoS2 nanosheets from initial bulk. With the benefits of high quality and easy to tune the surface characters, direct sonication and Li-intercalation exfoliation are regarded as the suitable methods for fabricating MoS2/polymer nanocomposites. Moreover, cetylpyridinium chloride (CPC) was chosen to modify the chemically exfoliated MoS2 for improving its compatibility within polyurethane acrylate (PUA) matrix. The inclusion of CPC modified MoS2 leaded to an obviously increase in the mechanical properties of PUA nanocomposite films, which is mainly attributed to the inherent robust mechanical performance and homogeneous dispersion of modified MoS2 in PUA/MoS2 systems.

2. By a facile latex premixing combined with subsequent melt-blending method, bare MoS2 nanosheets were successfully incorporated into polypropylene (PP) matrix. The MoS2 nanosheets were fully exfoliated and homogeneously dispersed in PP matrix. The inclusion of bare MoS2 nanosheets obviously improved the thermal oxidative stability and influenced the thermal decomposition behavior of PP nanocomposites just by its considerable physical barrier action. Because the MoS2 is inert and very stable while treated at high temperature under nitrogen atmosphere. The MoS2 nanosheets with high aspect ratio can disrupt the oxygen and heat supply from the gas phase to the bulk of composites and prevent the emission of thermally degraded small gaseous molecules during degradation, as well as suppress the evolution of gaseous pyrolysis products, thus reducing the peak heat release rate (PHRR) value of PP nanocomposites.

3. The dodecanethiol and Pluronic were introduced to simultaneously exfoliate and modify MoS2 by direct liquid sonication. The modifier molecules were attached on the surface of exfoliated MoS2 sheets by covalent and non-covalent bonding, respectively. These two modified MoS2 nanosheets endowed the different polarity polymers, polyethylene (PE) and poly(ethylene oxide) (PEO), with significantly reinforced mechanical properties, thermal stability and crystallization performance, on the basis of the compatibility principle. There a gradient region can be formed within the phase interface of polymer/MoS2 nanocomposites. It can restrict the motion of polymer chains heavily by the molecular level entanglement and provide an effective load transfer region, therefore, leading to the improvements on mechanical and thermal properties.

4. Two kinds of sandwich-like organic-inorganic nanohybrids were fabricated by in situ synthesis of melamine cyanurate (MCA) or polyaniline (PANI) on MoS2 template as high-performance flame retardants for nylon 6 (PA6) and epoxy (EP) resin, respectively. By this design, these MoS2 based hybrids not only possess the high specific surface area of two-dimensional character but also exhibit an integrated flame-retarding effect in polymer nanocomposites. The phase interfacial interactions (hydrogen-bonding or covenant-bonding) and the integrated effect (inherent flame retarding effect, physical barrier performance and catalytic activity of MoS2 hybrids) are the essential to achieve the enhanced thermal oxidative stability, flame retardancy and smoke suppression performance of PA6/MCA/MoS2 and EP/PANI/MoS2 composites.

5. For improving the catalytic performance of MoS2 during thermal decomposition of EP resin, CoOOH nanoplatelets were in situ synthesized on MoS2 nanosheets to achieve a MoS2 based inorganic hybrid. Decoration of metal compound can prevent MoS2 nanosheets from re-stacking, thus improving their dispersion state within EP matrix. Once treated at high temperature, MoS2/CoOOH hybrid degraded into bimetallic oxides with labyrinth-like porous structure. It can lead to a reduction in the release of reducing pyrolysis gas and precursor of smoke particle because of the physical absorption and chemical oxidation effects.

    Research areas

  • Two-dimensional MoS2, Polymer nanocomposites, Mechanical properties, Thermal stability, Combustion performance