Preparation And Thermal Conductivity Of Graphene Nanoplatelets Based Composites

Phase change materials?PCMs?and polymers play important roles in promoting balance between thermal energy demand and supply and replacing traditional high energy-consuming metal and ceramics.However,the low thermal conductivity limits their application in the field of thermal management.Therefore,the development of highly thermally conductive composite PCMs and polymer-based composites has always been a research focus for domestic and foreign scholars.Therefore,highly thermally conductive nanocomposites were prepared by incorporating non-covalently functionalized Graphene Nanoplatelets?GNPs?into Stearic Acid?SA?and Polylactic Acid?PLA?matrix,respectively.And then the mechanism of functionalized GNPs in enhancing the thermal conductivity of composites was studied by experimental methods and theoretical calculations.The main research contents are as follows:?1?The surface modification of GNPs.GNPs were modified with Sodium Humate?SH?,Tannic Acid?TA?and Graphene Oxide?GO?to obtain functionalized GNPs?SH-GNPs,TA-GNPs and GO-GNPs?,respectively.The results of FT-IR,Raman,TGA and TEM confirm that GNPs were successfully functionalized by SH,TA and GO through?-?conjugation without perturbing the lattice structure of GNPs.?2?Modified GNPs/SA composite PCMs.The obtained SH-GNPs and GO-GNPs were incorporated into SA by melt blending to fabricate SH-GNPs/SA and GO-GNPs/SA composites,respectively.The SEM,thermal constant analysis and DSC characterization results show that 1)Both SH and GO modification can effectively improve the dispersion of GNPs in SA,and enhance the GNPs-SA interfacial compatibility.By contrast,GO-GNPs are more likely to form filler networks.2)The thermal conductivity?TC?of SA-based composites is:GO-GNPs/SA>SH-GNPs/SA>GNPs/SA.3)Composite PCMs retain outstanding phase transition properties compared with pure SA.Moreover,SH modification can improve the cyclic stability of composite PCMs.?3?Modified GNPs/PLA nanocomposites.The obtained TA-GNPs and GO-GNPs were incorporated into PLA by solution blending to fabricate TA-GNPs/PLA and GO-GNPs/PLA composites,respectively.The TEM,thermal constant analysis and DSC characterization results show that 1)Both TA and GO modification can effectively improve the dispersion of GNPs in PLA and the GNPs-PLA interfacial compatibility.By contrast,GO-GNPs are more likely to form filler networks.2)When the filler content is below 8wt%,the TC of PLA-based composites is:TA-GNPs/PLA>GO-GNPs/PLA>GNPs/PLA.As the filler content continues to increase,the TC of GO-GNPs/PLA is higher than that of TA-GNPs/PLA.3)Compared with pure PLA,the glass transition temperature of composites increases,whereas the cold crystallization temperature and the crystallinity decrease.?4?Thermal conducting mechanism.Y.Agari and Chu Models were applied to analyze the TC of SA-and PLA-based composites.The thermal network factor C₂ and interface thermal resistance factor R_k were calculated.The results indicate that 1)Compared with GNPs,the modified GNPs can effectively increase the C₂ of the composites and reduce the R_k,resulting in a better heat transfer enhancement effect.2)Among the three modifiers,GO modification is able to increase C₂ and reduce R_k to a greater extent.3)The GO modification has a greater effect on lowering R_k of SA-based composites,while it mainly contributes to increasing C₂ of PLA-based composites.