Modification Of Biodegradable Aliphatic Polyesters And Their Applications In 3D Printing

With the development of polymer science,plastics have been applied in many fields of production and life.The plastics have brought various conveniences,but it also brings some environmental crisis,such as white pollution and air pollution.In recent years,accompany with the development of advanced manufacturing technology,the application of polymer materials in fused deposition modeling(FDM)1s becoming more and more popular,which has the advantages of high efficiency.FDM has a light prospect,but the environment protections have to take into account.To develop the biodegradable polymers is an effective way to solve the above environmental problems.Polylactic acid(PLA)and poly(propylene carbonate)(PPC)are both fully biodegradable aliphatic polyesters.They are widely used in food packaging,and its thermoplastic properties are suitable for FDM.However,the brittleness of PLA and the Iow strength of PPC restrict their application.Thus,we modified PLA and PPC with the aim of improving the toughness of PLA and the strength of PPC.The structure and the properties of the blends were studied.The modified mechanism was analyzed.The FDM 3D printing formability of PLA/PPC composite material was also discussed.The PLA was toughening modified with PPC*The PLA/PPC blends were prepared by the way of melt blending.And their structure and performance were studied.The results indicated that there exists compatibility between PLA and PPC to a certain extent.The elongation at break and the impact strength of PLA was improved by PPC.but the tensile strength decreased.The melt flow rate was decreased with the increasing of PPC content,but the melt index was kept at more than 20g/10min.It still had good formability.Based on our study of PLA/PPC blends,in order to further improve the toughness of PLA/PPC blends,in-situ cross-linking reactions initiated by dicumyl peroxide(DCP)between PLA and PPC chains was carryed out.The study showed that the compatibility between PLA and PPC was increased as the formation of cross-linking structure after added DCP.Simultaneously,the phase morphology of the blends changed from the "sea-island" structure to a homogeneous phase structure with the DCP content increased.The elongation at break of the blends increased to 107%when the DCP content was 1wt%,which increased 2.7 times comparing with their original binary blends,and it increased more than forty times comparing with the pure PLA.So we can conclude that the toughness of PLA was improved greatly.The investigation of shape memory performance found that the blends with DCP had well recovery performance at the temperature of 45℃.Thus,the cross-linking structure decreased the shape recovery temperature.Combining the changes of phase structures induced by in-situ compatibilization,the mechanism of the shape memory was discussed.The extrusion formability of PLA/PPC monofilament was tested.It was found that the filaments with qualified size can obtained of the blends without DCP.There produced amount of gases and existed serious degradation reaction during the extrusion process of the blends with DCP.Thus,it is difficult to obtain suitable filaments of the blends with DCP.We measured the FDM 3D printing properties of 70PLA/30PPC blends.The experiments showed that the suitable printing temperature of the blends was 180℃～250℃.The products had smooth surface and obvious layers at this temperature.And the printing products had the better mechanical properties at 230OC.The mechanical properties of the print samples were better when the fill density was larger,the fill angle were O° or 90°,the layer height was lower and the perimeter was more.The print speed had no significant influence on the mechanical properties of the sample when the printing speed was in the range of 30～60mm/s.Based on the method of solution blending,the solvent replacement method was used in this paper to prepare the PPC/CS blends for the first time.The PPC/CS blends made by the method of direct blending were also prepared.And we compared the difference in mechanical properties and morphology of the blends made by the two methods.The experiments showed that the blends made by the solvent replacement method had the stronger interaction.The CS had the better dispersion state in the PPC matrix.And it showed obvious advantages in improving the tensile strength of PPC.When the CS content was 10wt%,the modified PPC made by solvent replacement method had high elongation at break and yield strength.The yield strength was increased from 4.7MPa to7,4MPa,which was 0.7MP higher than the direct blending samples.The graphene oxide(GO)was introduced to PPC/CS blends to further improving its strength.It was found that the GO was mainly distributed in CS in PPC/CS-GO blends.The interface between CS and PPC was good,and the CS had a strong interaction with GO.The tensile strength of PPC/CS blends was significantly increased by the GO.