Preparation And Properties Of High Thermal Conductivity Waterborne Polyurethane Composites

With the development of Electronic Science and technology,micro integrated circuits are gradually developing towards intelligence and thinness.Due to the large amount of waste heat generated in the closed space,it is very easy to cause problems such as performance degradation and service life shortening.Polymer as the thermal interface material of electronic components has been studied for a long time.It has the characteristics of low cost,easy processing and excellent mechanical properties,but its thermal conductivity is relatively low.It is necessary to add high thermal conductivity filler to improve the thermal conductivity to meet the use demand.How to select the appropriate thermal conductivity filler and its filling content is particularly important for polymer based thermal conductivity composites.In this paper,based on the internal crosslinking modification of waterborne polyurethane(WPU),modified boron nitride and graphene are used to modify WPU respectively,which not only improves the thermal conductivity of the film,but also minimizes the impact on its mechanical and other properties.The contents of this paper are as follows:(1)Using polytetrahydrofuran ether glycol(PTMG)and isophorone diisocyanate(IPDI)as raw materials,trimethylolpropane(TMP)as internal crosslinking agent,2,2-dihydroxymethylpropionic acid(DMPA)as hydrophilic chain extender and1,4-butanediol(BDO)as small molecule chain extender,the effects of isocyanate index(R value)and DMPA content on the comprehensive properties of waterborne polyurethane were systematically investigated.On the one hand,the R value increased,the particle size of WPU emulsion increased,the heat resistance,crystallinity,water contact angle and glass transition temperature(Tg)of the film decreased,the mechanical properties of the film increased first and then decreased,and the water resistance of the film became worse.On the other hand,the increase of DMPA content and the decrease of particle size of WPU emulsion can improve the adhesion of emulsion to various substrates in a certain range.However,the higher DMPA content will lead to the increase of surface tension of WPU,the R value is 1.3 and DMPA content is 5 wt%,the comprehensive properties of WPU emulsion and film are the best.(2)WPU with R value of 1.3 and DMPA dosage of 5 wt% was used as the matrix,and boron nitride modified by silane coupling agent KH-550 was added into WPU by in-situ polymerization to explore the effect of filler mass fraction(W)on the comprehensive properties of adhesive film.With the increase of BN content,the crystallinity and TG of the adhesive film decrease,and the addition of fillers can act as the WPU hard segment structure.The thermal stability improves,the water resistance and tensile strength first increase and then decrease,the water contact angle of the adhesive film increases from 68.95 ° to 88.1 °,and the hydrophobicity becomes stronger.The adhesion performance of the lotion on various substrates is significantly improved compared with that of the WPU lotion.When the load is 15%,the thermal conductivity reaches the maximum value of 0.621W/(m·K),At the same time,the thermal interface heat dissipation experiment was carried out,and the heat source temperature was 2.2 ℃ lower than that of pure WPU film.(3)Graphene oxide was aminated with 3-aminopropyl triethoxysilane(APTES),then reduced with diethanolamine(DEA),which was used as a thermal conductive filler and polymerized in situ with WPU to obtain a film sample.With the increase of graphene content,the crystallinity and TG of the adhesive film decrease,and the thermal stability,water absorption and water contact angle increase.SEM test shows that the adhesive film with low filling amount is flat and smooth,high filling amount is easy to agglomerate,and the tensile strength and thermal conductivity first increase and then decrease.The thermal interface heat dissipation experiment with 3 wt%adhesive film shows that the heat source temperature is 2.4 ℃ lower than that of pure WPU adhesive film.Compared with boron nitride / waterborne polyurethane composites,graphene / waterborne polyurethane composites have better mechanical properties,but the improvement of thermal conductivity and adhesion is not obvious.