Study On Preparation And Properties Of MWCNTs/PLA Conductive Composite

As an emerging biodegradable material polylactic acid(PLA),It is mechanical properties are comparable to those of polystyrene(PS),and its production and processing properties are excellent.However,PLA itself has some shortcomings,such as low crystallinity and poor heat resistance,which greatly restrict the development and application of PLA products.The preparation of functionalized polylactic acid-based composite materials can effectively alleviate these shortcomings,which can not only retain the excellent properties of PLA itself,but also endow PLA with new properties,and the conductive filler multi-walled carbon nanotubes(MWCNTs)and PLA are blended to prepare Polylactic acid/conductive particle composite materials have become a hot research topic in recent years.In this paper,based on three aspects of product post-processing,crystal rejection,and double percolation structure,the crystallization,mechanical and electrical properties of polylactic acid-based composites were studied,in order to play a guiding role in the production and processing of PLA products.The specific research contents include:(1)The PLA standard specimens were annealed at different temperatures and times,and analyzed the evolution of the crystallization behavior of PLA after different annealed times and temperatures.And the PLA standard specimens were subjected by UV treatment at different times to study the effects of UV treatment on the crystallization and mechanical properties of PLA.(2)A series of MWCNTs/PLA conductive composite materials were prepared by melt-compounding to study the effect of MWCNTs content on the crystallization and conductivity of PLA.At the same time,the composite materials were annealed to further explore the correlation of crystallization,conductivity.and the internal connection network structures.(3)Polyurethane(TPU)as the second phase was added into MWCNTs/PLA to prepared a series of MWCNTs/TPU/PLA conductive composite materials.The selective distribution and phase evolution of MWCNTs are used to realize the double percolation structure of composite materials.On this basis,the influence of feeding method,composition ratio and MWCNTs content on the electrical conductivity of composite materials were studied.The results show that ultraviolet treatment and annealing treatment can promote the crystallization of PLA,and the annealing treatment has a more significant promotion effect on the crystallization of PLA.Compared with the unannealed PLA sample,the tensile strength of the PLA sample annealed for 60 min reaches 68.7 MPa,an increase of 8.46%,and the elongation at break reaches 4.9%,a decrease of 2.07%,and the impact strength reaches a maximum of 36.4 KJ·m^-2,an increase of 39.46%,and the elastic modulus increases to 823 MPa,an increase of 29.15%;compared to the PLA sample without UV treatment,the tensile stress of the PLA sample after 72h UV treatment reaches 70.62 MPa,an increase of 11.49%,and the elasticity modulus reaches 912.5 MPa,an increase of 43.2%,and the impact strength increase to 36.225 KJ·m^-2,an increase of 38.38%,and the elongation at break droppes to 6.1%,a decrease of 0.87%.Moreover,the percolation threshold P_c of the MWCNTs/PLA composite is 0.69 wt%,and the percolation threshold P_c of the annealed MWCNTs/PLA composite is 0.53 wt%,which is23%lower than that of the unannealed MWCNTs/PLA composite,and the influence of crystal repulsion caused by crystallization on conductivity is not comprehensive,and it is the limited range of 0.3-1.0 wt%.When the content of MWCNTs is 0.7 wt%,compared with pure PLA,X_cis 25.6%,an increase of 24.3%,and the tensile strength is 76.3 MPa,an increase of 20.4%,and the elongation at break is 7.3%,an increase of 0.33%,and the impact strength is 36.2 KJ·m^-2,an increase of 38.69%,and the elastic modulus is 867MPa,an increase of 36.06%.After annealing,the X_c of PLA increases to 39.22%,which is higher than unannealed.And the elastic modulus,tensile strength and impact strength are all improved,and the elongation at break decreases.Furthermore,the electrical conductivity of the composite material are changed with the addition of PLA,TPU and MWCNTs.Among them,the composite material prepared by blending TPU and MWCNTs to prepare MWCNTs/TPU masterbatch and then blending with PLA has the best conductivity.When the TPU mass fraction is 35 wt%,the percolation threshold P_c of the MWCNTs/TPU₃₅/PLA composite system is 0.32 wt%,which is lower than that of the MWCNTs/PLA composite system without TPU(P_c=0.69 wt%)53.6%.When the mass fraction of MWCNTs is 0.5 wt%and the mass fraction of TPU is 35%,compared with the composite material of MWCNTs_0.5/PLA,the tensile strength of the composite material of MWCNTs_0.5/TPU₃₅/PLA is 55.2 MPa,a reduce of 21.36%,and elongation at break is 128.5%,an increased of 121.53%,and impact the strength is 44.3 KJ·m^-2,an increase of 29.15%,and the elastic modulus is 561 MPa,a decrease of 26.28%.