Synthesis Of Ag@PAA-g-MWNTs And Its Application In UV Curable Polyurethane- Polyacrylate Flexible Electrical Conductive Adhesive

An important trend in electronics is mechanical flexibility, which require the interconnect materials to be flexed, rolled and bent around without degradation of their power providing and signal transmitting functions. Recently flexible electrical conductive adhesive(FECA), the polymer composite materials with electrically conductive fillers, have been intensively studied, which show great promise to meet the requirement of flexible electronic used interconnect materials. An effective and stable conductive network is crucial to ensure the conductivity and flexibility of FECA. Starting from the design of conductive network, the purpose the present work is to prepare a UV curable FECA with high electrical conductivity and maintain during rolling, which will help to broaden the study and application of FECA.UV curable PUA-FECA was prepared by composited of polyurethane- polyacrylate(PUA) and micron sized Ag-coated Cu flakes with dendritic structure. The impact of the formula and the curing process on the properties of PUA-FECA were studied. Experimental results show that improvement of the resin matrix cure shrinkage can improve the electrical conductivity PUA-FECA and the conductive filler is rearranged to build a better conductive network during the standing procedure before curing. The lowest volume resistivity PUA-FECA can reach 3.62×10-4Ω?cm and R/R0 is about 1.65 after rolling 1000 times at a radius of 5mm.Polyacrylic acid(PAA) was graft to the multiwalled carbon nanotubes(MWNTs) and PAA-g-MWNTs were obtained in acetone, the poor solvent of PAA. Moreover, the structure and morphology of PAA-g-MWNTs were characterized by FTIR 、 XPS 、 Raman spectroscopy、TEM and TGA. The results confirm PAA covalently connected to the surface of MWNTs and the highest grafting rate was about 11.2%. The grafting process without introducing any strong oxidation and the structure of MWNTs was preserved. PAA-g-MWNTs can be stably dispersed in water and ethanol.To prepared nano silver particles(Ag NPs) hybrid MWNTs(Ag@PAA-g-MWNTs), Ag+ was reduced by Na BH4 and tannic acid, respectively, in the present of PAA-g-MWNTs. Moreover, the structure of Ag@PAA-g-MWNTs was studied by UV-vis、XRD、XPS、SEM and TEM. Na BH4 reduces Ag+ into Ag NPs rapidly at room temperaturebut the particles form aggregates in solution as the lack ofadequate stabilizing agent. Ag@PAA-g-MWNTs with uniform Ag NPs size and distribution was prepared by the addition of tannic acid solution which maintained at an alkaline p Hto Ag NO3 solution in the present of PAA-g-MWNTs at room temperature.Ag@PAA-g-MWNTs was used to modify PUA-FECA. By adding 0.4wt% Ag@PAA-g-MWNTs, the shear strength and the volume resistivity of PUA-FECA was improved 14.5% and decreased 40.1%, respectively, and the R/R0 after rolling 1000 times at a radius of 5mm was reduced from 1.61 to 1.33. SEM images show that Ag@PAA-g-MWNTs could build a ―bridge‖ between Ag-coated Cu particles, which improve the efficiency and stability of conductive network.