Epoxy/Clay Nanocomposites Prepared By Pressure Induced Flow Processing

Epoxy resin has excellent adhesion, mechanical properties, chemical stability, etc., which are widely used in coatings, adhesives, electronic and so on. Due to its poor toughness, there were several ways to modified epoxy resin to improve toughness in recent years.In this article, melt intercalation of epoxy resins and montmorillonite （MMT） was carried out in order to improve toughness. Pressure induced flow （PIF） processing was introduced to further improve the mechanical properties. Various methods of characterization such as differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, transmission electron microscope （TEM）, scanning electron microscope （SEM）, dynamic mechanical analyzer （DMA） and mechanical properties testing were used to study the characteristics of composites, and PIF-processed samples were compared with unprocessed. The curing reaction kinetics was investigated and showed that the composites had lower cure temperature and activation energy, which due to the contribution of organ clay. Thermodynamic parameters k₁, k₂, m and n were calculated by isothermal DSC analysis, the curing reaction rate reaches its maximum when the curing degree between 0.1～0.2 and acid catalysis effect by MMT was confirmed by activation energy E₁ and E₂. The interlayer spacing of epoxy/MMT composites had increased by stirring, ultrasonic dispersion and the reaction heat of curing process, TEM photographs showed that MMT lamellar spacing were between 20～35nm which indicated that the molecular chain of epoxy would be intercalated and exfoliated in the layered silicate of MMT, in addition, there were orientation of MMT lamellar in flow direction and layered structure of parallel after PIF-processing.Tensile strength, Young’s modulus and impact strength increased continuously with increasing MMT content, and achieved the best performance for addition of 4～6wt. % of MMT which played a role in strengthening and toughening after exfoliated. Implementing PIF-process further improved the mechanical properties and even exceeded the neat epoxy in tensile strength. PIF-processing resulted in an ordered arrangement of alternating layers construction and gained the optimal mechanical properties in the deformation rate of 200～250%, 10～11 hours curing time before pressure. According to SEM photographs of impact fractures, neat epoxy showed brittle fracture while there were a certain amount of plastic deformation in unprocessed samples even the section lines were loose and scattered. However, with the characteristics of ductile fracture, the PIF-processed samples’ section showed an orderly ridge-like pattern. DMA indicated that MMT decreased the glass transition temperature of epoxy while increased the storage modulus. The PIF-processed samples had much higher storage modulus and gentle downward trend in storage modulus, which showed that the composites had more excellent heat resistance and mechanical properties after PIF-processing.