Fawn M. Uhl

Polystyrene/graphite nanocomposites: effect on thermal stability

Abstract Nanocomposites consisting of polymer and clay have been shown to exhibit a significant reduction in flammability and an increase in mechanical properties. This work examines the effect of thermal stability and mechanical properties of nanocomposites prepared from potassium graphite and styrene. Synthesis of nanocomposites was accomplished by using potassium graphite (KC 8 ) as the initiator in the polymerization of styrene. A slight increase in thermal stability is observed but mechanical properties are decreased.

The thermal stability of cross-linked polymers: methyl methacrylate with divinylbenzene and styrene with dimethacrylates

Cross-linking of polymers is frequently presumed to enhance the thermal stability of polymer systems. Methyl methacrylate has been reacted with divinylbenzene and styrene with various dimethacrylates. These systems have been characterized by gel content, swelling ratio, infrared spectroscopy, thermal analysis, TGA/FT-IR, and solid state NMR. Both systems show enhanced thermal stability and char formation. This is most pronounced in the cases of methyl methacrylate with divinylbenzene and styrene with bisphenol A dimethacrylate.

Polybutadiene cross-linked with various diols — effect on thermal stability

The relationship between cross-linking and thermal stability as related to polybutadiene is the focus of current research. Cross-linked polybutadienes have been prepared using various diols as the cross-linking agent. Cross-linked polymers have been characterized by gel content, swelling ratios, infrared spectroscopy, and thermal analysis. These polymers are not highly cross-linked, as seen by gel content and swelling ratios, and cross-linking does not have a large effect on the onset temperature of the degradation. Nonetheless, extensive formation of a non-volatile residue occurs.

Processing and Properties of Graphene-based Nanocomposites

Fabrication of carbon nanotubes is expensive, particularly for the purifying process required to make them widely accepted for reinforcements and structural composite applications. Instead of trying to discover lower cost processes for nanotubes, we seek to develop an alternative nanoscale carbon material with comparable properties that can be produced cost-effectively and in larger quantities. These carbon nanomaterials are referred to as nanoscale graphene platelets (NGP). In this study, we fabricated and studied graphene-based nanocomposites by (1) exfoliating carbon or graphite materials using acid treatment, thermal and microwave expansion, and (2) examined the electrical and dielectric properties of the graphite reinforced polymers. Less than 1 wt% filler content was required to reach the percolation threshold (φc ) of transition in electrical conductivity and dielectric properties. Molecular dynamics simulation was employed to characterize the increase in elastic moduli for graphene platelets embedded in polymer matrices at molecular scale.Copyright

Nanoclay reinforced UV Curable High-barrier Coatings

Recent advances in functional nanocomposites have created new frontiers in research for radiation-curable organic coatings making use of nanocomposite technology. Such UV curable systems would enable the widespread use of nanocomposites in micro fabrication. Little is understood on incorporating organomodified clays in UV curable polymers. UV curable films were reinforced with organically modified montmorillonite (MMT). The organically modified MMT were prepared by an ion exchange process in which sodium ions were replaced by alkyl ammonium ions. Acrylate films were reinforced with organoclays, which serve as reinforcements and barrier fillers in the polymer matrix. The microstructures were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Physical properties were examined by real time infrared spectroscopy (RTIR), differential scanning calorimetry (DSC), photo-DSC, dynamic mechanical thermal analysis (DMTA), Instron, and pendulum hardness. Preliminary results showed that aliphatic urethane acrylate nanocomposite coatings exhibited an intercalated structure and enhanced properties. 10 to 20 percent increase in tensile strength and a 25 to 50 percent increase in Youngs Modulus were observed. Decreased cure time to a tack free film and a slight increase in conversion as seen by RTIR were interestingly reported, suggesting the presence of nanoclays can improve the cure speed of acrylate coatings. Thermal stability was also enhanced. Potential applications of UV curable materials exist in the electronics industry where it is desirable to have coatings with good flexibility, dimensional stability, chemical resistance, thermal stability, transparency, and fast cure. This work demonstrated coatings with nanoscale reinforcements are ideal in such applications.