Study On Synthesis And Properties Of Electrically And Thermally Conductive Phenolic Resin Composites

As heat management and dissipation are becoming more and more crucial for highlyintegrated electronic devices with high-power output, novel heat releasing packagematerials are highly desired and the thermal conductivity of most polymers should besubstantially improved. Currently, Inorganic fllers, such as metal, ceramic and nanofillerwere used to improve thermal and electrical conductivities of polymers. In addition,graphene has attracted the attentions from the researches in the world since2004.As amember of fullerenes family, graphene is usually regarded as the single-atom-thick graphite,which possessed distinct properties, such as mechanical, optical, thermal and electricalproperties. However, there are many obstacles in the mass production and homogenousdispersion in host polymers need to be addressed. Graphene oxide (GO) is treated as theprecursor of graphene for its similarity to graphene. By thermal treatment or chemicalmethods, GO can be reduction to graphene, Amounts of oxygen-containing groups attachedon the surface of GO sheets provided active sites for the covalent modification.The detailsand results in this paper are as follows:1) PF/BN composites and PF/T-ZnO were prepared by a solution blending and curingmethod. With the addition of BN flakes, the thermal conductivity of PF is improvedaccompanying with an anisotropic thermal conductance, which is attributed to the naturaltendency for platelet fillers to align parallel with one another especially at high contents.Itis seen that Maxwell-Eucken model and Nielsen model are suitable to evaluate the thermalconductivity at low loadings of BN flakes. At a constant filler loading of60wt.%, thepartial replacement of BN with T-ZnO results in a striking synergistic effect on thermalconductivity of PF. With30wt.%BN and30wt.%T-ZnO, the in-plane thermalconductivity of composite shows71.9%higher than that of the PF composite with thesame BN content. The flexural strength of the PF composite is56.2%higher than that ofthe PF composite with60wt.%BN. Due to its stereo structure with four needles, T-ZnOplays an important role in bridging the BN flakes in through-plane and in-plane directions,thus facilitating the formation of heat conductance.2) In order to study synergetic effect of tetrapod-shaped ZnO whiskers and graphiteflakes, an similiar method is developed. A maximum in-plane thermal conductivity of9.2Wm-1K-1is observed with a T-ZnO/G mass ratio of1/2, which is88.6%higher than that ofPF/G composite with the same filler content. The flexural strength and elongation at break are also improved with filler content. The hollow glass microsphere (HGM) and BN flakewere filled into PF matrix with the same method. The results show that a striking synergiceffect on thermal conductivity with different HGM/BN mass ratio (1:4<HGM/BN（w/w）<3:1). The synergetic effect may originate from the size exclusion effect of rigid HGM.3）An efficient one-step approach to reduce and functionalize graphene oxide (GO)during the in situ polymerization of phenol and formaldehyde was reported. Thehydrophilic and electrically insulating GO is converted to hydrophobic and electricallyconductive graphene with phenol as the main reducing agent. Simultaneously,functionalization of GO was realized by the nucleophilic substitution reaction of epoxidegroups of GO with hydroxyl groups of phenol or phenol prepolymer in the alkali condition.The electrical conductivity of PF composite with0.85vol.%of GO is0.2S/m, nearly nineorders of magnitude higher than that of neat PF. Moreover, the efficient reduction andfunctionalization of GO endows the PF composites with high thermal stability and flexuralproperties. A striking increase in decomposition temperature is achieved with2.3vol.%ofGO. The flexural strength and modulus of the PF composite with1.7vol.%GO areincreased by318and56%, respectively.