Research Overview

Research Overview

Brief summary of PhD dissertation

Graphene nanoplatelets (GNP) are a new class of two dimension nanomaterials with it combination of extraordinary physical properties such as high thermal conductivity, superior mechanical properties, excellent electronic transport properties and its ability to be dispersed in a polymer matrix has created a new class of polymer nanocomposites (NC) called “graphene-polymer nanocomposite”

In order to develop GNP/polymer NC for various applications, efficient preparation of GNP at large scale and the dispersion technologies for GNP as well as the design of matrix polymers are indispensable. In this study, the preparation and properties of nanocomposite based on epoxy resin and polysiloxane filled with silver nanopartilce and functionalized graphene was investigated. The main results as follows:

Successfully preparation and characterization of pristine and functionalized graphene through a non-oxidative intercalation and microwave irradiated induced exfoliation. The method is comprised steps of preparation of low stage (stage 2+3) graphite intercalation compound (GIC) by intercalation of natural graphite with lithium metal dissolved in tetrahydrofurane and naphthalene followed by ion-exchanged with different tetra-alkylammonium cations to expand the interlayer gallery distance of GIC. The resulting GICs were then microwave irradiated to induce exfoliation, forming so called exfoliated graphite. The exfoliated graphite was further processed by a solvent sonication process or by an edge selective functionalization using Friedel-Crafts acylation reaction with benzoic acid derivatives in polyphosphoric acid/P₂O₅ medium. The resulting functionalized graphene showed well dispersion in some organic solvent such as NMP, DMF, ethanol.., and the dispersion was stable at least for several months for general application.

For the development of high electrical/thermal conductive graphene based polymer NC with improved mechanical properties as well as thermal stability, a novel epoxy-polysiloxane polymer matrix system was designed based on as synthesized epoxy-polysiloxanes containing cationically curable epoxy groups plus a crosslink able acrylate groups, and a conventional cycloaliphatic epoxy resin (Celloxide). Curing behavior as well as thermo-mechanical properties of epoxy-polysiloxane polymer matrix was evaluated. Then, NC of pristine graphene/functionalized graphene with above polymer matrix system in comparison with control matrix were formulated and comparative characterized in term of electrical/ thermal conductivity, rheological properties and thermo-mechanical properties. The extremely high thermally conductive nanocomposites from these pristine graphene and functionalized graphene were successful prepared with the thermal conductivity of nanocomposite reached ~18 W/mK at 20 vol % graphene or of 30 W/mK at 30 vol % of graphene. Beside graphene/functionalized graphene nanocomposites, preparation and properties of silver nanowire by a polyols hydrothermal reduction process as well as preparation and characterization of polymer nanocomposite based on hybrid filler of silver nanowire and functionalized graphene were carried out as a part of the thesis. The developed nanocomposites and hybrid nanocomposites in this thesis has a great potential application for electrical/thermally conductive adhesive for electronic parts.

Brief summary of MS Thesis

The main objective of the research work was to study a process to prepare polyisocyanates from depolymerized products of polyurethane rigid foam (PUR) scraps through a non-phosgene isocynation process. The results as follows: PUR scraps were firstly depolymerized into mixtures of polyols and polyamines using ethanolamine in the presence of sodium hydroxide as catalyst for aminolysis and hydrolysis process. The depolymerized product containing polyamines, polyols, and ethanolamine were then analyzed based on spectroscopy and chemical analysis. Polyamines and polyols were successfully separated by their different miscibility in water. Polyamines part obtained could be converted to polycarbamates by exchange reaction with dimethylcarbonate (DMC). It is found that the yield of the carbamation process increased with increasing the molar ratio of DMC/NH₂ group and reaction time. The yield of carbamation reached 86 % within 4 hours at molar ratio of DMC/NH₂ =7/1 at 180 ^oC. Polyisocyanates were then prepared from polycarbamates by an isocyanation process using methyltrichlorosilane /triethylamine in tetrahydrofuran at 60 ^oC. The yield of the isocyanation process was found to be dependent on some parameters such as molar ratios of chlorosilane/carbamate groups, solvent type, and reaction time. Isocyanate contents of the polyisocyanates were determined to be from 5.3 to 9.1% based on functional group analysis. It is postulated that the polyisocyanates could be useful as a partial replacement of polymeric MDI in the preparation of rigid polyurethane foams and polyurethane prepolymers. As this process to manufacture polyisocyanates does not use phosgene, it belongs to the environmentally compatible technologies.