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2009
Doctoral Thesis
Titel
Development of thermally stable nanofillers and their application in polyimide nanocomposites: Synthesis, characterization, and properties
Alternative
Entwicklung thermisch stabiler Nanofüllstoffe und deren Anwendungen in Polyimid-Nanocompositen: Synthese, Charakterisierung and Eigenschaften
Abstract
Thermally stable organo-modified Montmorillonites (OMMTs) were synthesized for preparing polyimide (PI) nanocomposites. Organic surfactants such as activated diamines, ammonium-, pyridinium-, phosphonium- and imidazolium salts which either possess high thermal stability or have similar chemical structure with the PI matrix were applied for silicate organo-modification. The synthesized OMMTs showed both improved thermal stability (the weight loss of the imidazolium OMMT in TG analysis even starts above 300°C) and chemical compatibility. For comparison, both commercially available pristine and organo-modified silicates and aluminas with different chemical and crystal structures are also used for PI nanocomposites preparation. Due to the excellent processability and moderate mechanical properties, the commercially available ULTEM® 1000 resin was chosen as the PI matrix in this study. In order to obtain valuable reaction parameters for in situ polymerization of PI nanocomposites, PIs with ULTEM® 1000 structure were synthesized by the classic two-step polyimidization method. The synthesized PIs have higher molecular weights and a broader molecular weight distribution. PI nanocomposites were produced mainly by melt compounding and solvent casting methods. The solvent cast hybrid films have 3 wt% of nanofiller content, whereas the melt compounded PI nanocomposites were loaded with 1, 3, 5 wt% of nanofillers and extruded by using a twin screw extruder at 340 °C under screw rotation speeds of 200, 400, 800 rpm. According to our investigation, both silicate and alumina nanofillers could increase tensile modulus of the related PI nanocomposites effectively but with big variety in elongation at break. The addition of pristine layered silicates and aluminas show limited improvements in tensile modulus and greatly decreased elongation and impact resistance due to the big-sized nanofiller agglomerates. However, under optimum processing condition, highly exfoliated OMMTs (i. e. synthesized highly thermally stable phosphonium and imidazolium OMMTs) and unmodified single crystal aluminas could increase PI nanocomposite tensile modulus without big loss of elongation. Moreover, higher extruder screw rotation speed support the dispersion of nanofiller but accelerate the degradation of PI matrix due to the stronger shearing effects.
ThesisNote
Berlin, TU, Diss., 2009
Verlagsort
Berlin