Development Of Graphene-reinforced Tung Oil-based Unsaturated Polyester Nanocomposites And Foams

In this paper,graphene-reinforced tung oil-based unsaturated polyester nanocomposites were prepared via in situ melt polycondensation intergrated with Diels–Alder addition and their mechanical and thermal properties were carefully investigated.Meanwhile,dispersion state of graphene nanosheets in the obtained polymer composites was analyzed with scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Furthermore,functionalized graphene sheets(FGS),derived from the starting graphene oxide(GO),were extracted from the resultant composites and characterized by sedimentation experiments,FT-IR,atomic force microscopy(AFM),thermogravimetric analysis(TGA),X-ray photoelectron spectroscopy(XPS),and Raman spectroscopy.Finally,using the optimal biobased nanocomposite as the main resin,a series of plastic foams were prepared through blending and thermal curing,and their mechanical and thermal properties were also studied.The main conclusions of this paper are as follows:(1)Mechanical and thermal properties of the TO-based unsaturated polyester resin(UPR/TO)were greatly improved by the incorporation of GO.For example,at the optimal loading of GO(only 0.10 wt%),the obtained UPR/TO/GO composite showed the tensile strength and modulus of 43.2 MPa and 2.62 GPa,flexural strength and modulus of 66.6 MPa and 2.20 GPa,and glass transition temperature of 105.2°C,which were 159%,191%,163%,250%,and 49.4% higher than those of the unreinforced UPR/TO resin,respectively.This fabricated biocomposite even demonstrated superior comprehensive properties than neat petroleum-based UPR.Therefore,the developed biobased UPR nanocomposites are very promising for application in structural plastics.Furthermore,from the results of SEM and TEM,it can be observed the graphene sheets were shown to be sufficiently exfoliated in the polymer matrix with extremely low concent of GO(0.10 wt%)while aggregated in the matrix with higher content of GO(0.30 wt%).The sufficient exfoliation of graphene nanosheets greatly contributed to the dramtical enhancement in stiffness and thermal properties for the UPR/TO resins.(2)Based on the results of sedimentation experiments,FT-IR,AFM,TGA,XPS,and Raman spectroscopy,it can be deduced that the added GO nanomaterial were simultanesously reduced and grafted by unsaturated polyesters during in situ polymerization,and follwed by grafting with TO triglycerides onto polyesters via D–A addition.The generated FGS were composed of about 65%(or 68%)graphene,25%(or 27%)unsaturated polyesters,and 10%(or 5%)TO molecules,indicating strong interactions between the graphene,polymer,and biomodifer.The strong interations also played an important role in the improvement of stiffness and thermal properties for the UPR/TO resins.(3)The foams based on UPR/TO/GO showed higher compressive strengths than the foams based on pure UPR.When the dosage of BPO initiator was 4 wt% and the dosage of N,Ndimethylaniline(N,N-DMA)accelerator was 0.4 wt%,the compressive strength of the resulting foam reached a maximum value of 1.33 MPa.When the dosage of BPO initiator was 4 wt% and the the dosage of N,N-DMA accelerator was 0.3 wt%,the thermal conductivity was 0.045 W/(m·K).From theresults of SEM,it can be seen that in the foams with high dosages of accelerator and initiator(for example,4 wt%of BPO and 0.4 wt% of N,N-DMA),the cell distribution was uniform and the cell diameter was smaller than those with low dosages of accelerator and initiator.The developed biobased foams show promise to be applied in insulation materials.