The Structure Control And Temperature Response Behavior Of Polylactic Acid Composites

Conductive polymer composites（CPCs）have received extensive attention from researchers due to their excellent corrosion resistance,good processability,and light weight.By adding carbon nanotubes,graphene and metal conductive particles into the polymer matrix,the polymer was given the excellent conductive property and external field response behavior.In this study,the temperature-sensitive response behavior of composites prepared by nanoparticles of different dimensions and hybrid particles prepared by different hybridization methods is deeply studied.（1）GNPS/PLA and MWCNTs/PLA composites were prepared by ultrasonic melt blending,and it was found that the percolation threshold of GNPS/PLA composite was 3.17 wt%,while the percolation threshold of MWCNTs/PLA composite was 0.43 wt%.Introducing the MWCNTs into PLA/MWCNTs can significantly improve the crystalline properties and increase the thermal decomposition compared with PLA/GNPS composites.Through the analysis of iso-thermal temperature resistance data,the PLA/MWCNTs composite own the short response time about 12.83 min compared with PLA/GNPS composite.Moreover,during the cyclic temperature field testing,the GNPS/PLA exhibited a cycle-stable PTC behaviour in the temperature field,while the MWCNTs/PLA composite exhibited high temperature NTC behaviour.（2）The effect of the hybrid ratio of GNPS and MWCNTs on the properties of PLA/GNPS/MWCNTs composites was investigated in detail.The electrical conductivity of PLA/（GP_x/CNT_y）_0.6 composites gradually decreased with the decrease of the proportion of MWCNTs in the hybrid particles.Through the analysis of iso-thermal temperature resistance data,the PLA/（GP₁/CNT₂）_0.6 composites own the stable conductive network and conductive property.In the cyclic temperature test,PLA/（GP₁/CNT₂）_0.6 composites show a relatively stable PTC effect.In addition,adjusting the proportion of hybrid particles in the composites can improve the temperature response performance of the composites between NTC behaviour and PTC behaviour.In order to further improve NTC behaviour at high temperature,the CNTs-D-GNPS hybrid material was successfully prepared by amidation reaction.It is found that the percolation threshold of PLA/（GP₁/CNT₁）_xcomposite is 0.48 wt%,.while the percolation threshold of PLA/CNTs-D-GNPS composite is 2.98 wt%.When the conductive particles content was fixed at 1 wt%,the T₀ and T_p of the PLA/（GP₁/CNT₁）_x composite are 4℃and 7.8℃higher than those of PLA/CNTs-D-GNPS,while the T_1/2 is reduced by 1.7 min.The hybrid particles prepared by the chemical method have a more obvious effect on promoting the crystallization of PLA.Compared with the temperature-sensitive response behaviors of the two hybrid particle composites,it is found that under the cyclic temperature field,the hybrid particle composite prepared by chemical method can eliminate the high temperature NTC effect produced by the hybrid particle prepared by physical method.（3）The effect of the hybrid ratio of GR and MWCNTs on the temperature-sensitive response behavior of the hybrid particle composites was deeply explored.Under the cyclic temperature field,the two different hybrid particle composites with the hybrid ratio showed the better PTC effect and NTC effect,but the changes range of PLA/（GR₁/CNT₁）_0.6 composites are more obvious.Thuswe the PLA/（GR₁/CNT₁）_0.6 composites was chosen and mixed with dispersed phase PEG to further explore the effect of the addition of the second phase on hybridization the effect of particle composites on the properties of the composites.It was found that the addition of PEG can increase the electrical conductivity of the PLA/（GR₁/CNT₁）composites.Morevoer,under the cyclic temperature field,when the PEG content of the PLA/（GR₁/CNT₁）_0.6 composites was 1wt%,the high-temperature NTC effect of the PLA/（GR₁/CNT₁）_0.6 composites was eliminated.More importantly,when the PEG content reached 5wt%,the PLA/（GR₁/CNT₁）_0.6 composites in the cooling process,there is a phase transition energy storage platform and with the increase of PEG content,the energy storage platform becomes wider.We believe that the strength of this energy storage effect mainly depends on the magnitude of the externally applied temperature field.