Synthesis And Properties Of Polylactic Acid Based Thermoelectric Composites And Generator

Thermoelectric materials,as an environmentally friendly energy materials,have been widely studied in recent years because the energy crisis and environmental pollution are getting more seriously.According to Seebeck effect and Peltier effect,thermoelectric materials can convert heat energy into electrical energy directly.Thermoelectric devices have the advantages of simple structure,no pollution,no vibration,no wear and so on,therefore they are widely used in the field of thermoelectric power generation and refrigeration.Polymer-based thermoelectric composite materials have gradually become a research hotspot in the field of thermoelectricity due to their low thermal conductivity and good machinability.Here,thermoelectric composite wires were fabricated with degradable thermoplastic resin polylactic acid（PLA）as the matrix and p-type inorganic thermoelectric material Bi_0.5Sb_1.5Te₃（BST）by extruding,which was intended to make thermoelectric devices by 3D printing.The thermoelectric and mechanical properties of the composite wires were measured and studied.The relationships,between the electrical conductivity,the Seebeck coefficient,the power factor and the mass fraction of BST,whether carbon nanotubes（CNT）were added,were analyzed respectively.An original method was carried out to measure the themal conductivity of the wires,and then the thermoelectric figure of merit ZT was calculated.Compared with the ZT value of 0.006without CNT,the ZT value of the wires with 4 wt.%CNT reached 0.011 at room temperature,indicating that the addition of CNT could significantly improve the thermoelectric properties of the composite wires.Next,semiring p-type PLA/BST composite materials and n-type Bi₂Te_2.75Se_0.25（BTS）composite materials were prepared by mold forming method,which were used to assemble a two-thermocouples thermoelectric device,which successfully realized the conversion from heat energy to electrical energy.The device obtained 3.4 m V open circuit voltage and 126 n W maximum output power at a 10.5 K temperature difference.Then the power generation performances of the device with different lengths of cooling copper foils,different arrangement densities of thermocouples,the heat transfer coefficient of air convection,and different thickness of the semirings were investigated by a simulation method,which gived us the direction for the optimization of the power generation performance of our device.On the other hand,the research route of predicting the properties of materials by scientific calculation and selecting materials with high properties to do experimental verification has gradually become a trend,due to the high cost of direct scientific experiments.We collected and obtained 2860 ZT values of 303 kinds of layered thermoelectric materials at different temperatures from nearly 100 literatures.Considering the composition of the elements,the properties of the element,and the properties of the elemental simple substance,the model was trained with the dataset using Random Forest regression algorithm and the ZT values of unknown layered thermoelectric materials were predicted.Five materials with high ZT values of about 0.8at room temperature were discovered.This study has reference value for predicting the properties of materials in other fields by machine learning.