| Electromagnetic radiation pollution has become the fifth pollution source which endangers the industry and daily life of us.It is of great significance to develop high performance of electromagnetic shielding materials.More recently,designing and exploring environment-friendly waterborne coatings for building materials has become an important research area of shielding materials.In this dissertation,a graphene-modified styrene-acrylic emulsion was designed and synthesized for preparing water-based graphene electromagnetic shielding coatings.The drawback of difficult dispersion of graphene in the resin is overcomed by preparing a high-concentration of stable graphene aqueous dispersion.Then,the graphene-modified styrene-acrylic emulsion is fabricated by in-situ polymerization method,which simultaneously introducing graphene aqueous dispersion during the synthesis of the styrene-acrylic emulsion.Finally,the architectural coatings with electromagnetic shielding properties were obtained.Firstly,the stable dispersion of graphene in aqueous solution was achieved by mechanically grinding with the assistance of surfactants[polyvinyl alcohol(PVA),sodium carboxymethyl cellulose(CMC),and sodium lignosulfonate(SLS)].For preparing high-concentration of graphene aqueous dispersions,the effect of surfactants on the texture of samples was investigated by scanning electron microscopy,Raman spectroscopic analysis,UV-visible spectroscopy,etc.The results show that a high-concentration of stable graphene aqueous dispersion can be prepared when the mixture of PVA and CMC were employed.Furthermore,when the adding proportions of CMC and PVA are 1.33 wt%and 2.67 wt%,the resultant graphene aqueous dispersion shows the highest dispersivity.The optimal of graphene aqueous dispersion shows high zeta potential of-28.83 m V,and the number of graphene layers is 3 or 4 in the dispersion.Secondly,styrene(St),butyl acrylate(BA),methyl methacrylate(MMA)and other monomers are used as the raw materials for synthesis of the styrene-acrylic emulsion.Then,the graphene-modified styrene-acrylic emulsion can be synthesized through in-situ polymerization route,in which simultaneously introducing the pre-emulsification of graphene aqueous dispersion with monomers.X-ray diffraction analysis,Fourier infrared spectroscopy,and thermogravimetric analysis were used to characterize the effects of the content of aqueous graphene dispersions on the performance of modified styrene-acrylic emulsions.The results show that the sedimentation occurs when the content of the graphene aqueous dispersion increases,which can be ascribed to the influence of graphene on its own gravity.Under the same process conditions,the dispersion stability of the styrene-acrylic emulsion is best when adding 4 wt%of the graphene aqueous dispersion.Furthermore,the electrical conductivity of it can reach 1.89×10-2s/cm.The above results indicated that the graphene can be stably and uniformly dispersed in styrene-acrylic emulsion.Finally,a series of architectural coatings was synthesized and their electromagnetic shielding performances were investigated.The graphene-modified styrene-acrylic emulsion or the pure styrene-acrylic emulsion was served as matrix,and calcium carbonate,titanium white and kaolin were used as fillers to prepare the architectural coatings.The results show that the resultant graphene/styrene-acrylic emulsion coating(G-St/Ac-C)meets the national standards,and some properties are higher than those of national standards.According to results of XRD,SEM,Raman,and rheological measurments,it can be found that fillers(calcium carbonate.etc)exhibit the orderly close stack structure in the coating due to the orientation effect of graphene.Meanwhile,the G-St/Ac-C also exhibits excellent storage stability.The loss tangent of G-St/Ac-C is significant larger than that of coatings prepared from pure styrene-acrylic emulsions.The results of electromagnetic shielding test show that G-St/Ac-C exhibits the high value of22.94 d B,suggesting the excellent electromagnetic shielding performance of G-St/Ac-C. |
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