| The extensive use of petroleum-based plastics directly leads to the problem of "white pollution".In order to solve this problem,the use of biodegradable materials to replace traditional plastics is a very ideal method.Polylactic acid(PLA)is a chemically synthesized degradable plastic made from renewable plant resources.At present,the research on the enhancement and modification of PLA is mainly concentrated in the binary composite system of PLA mixed with starch or plant fiber mixed with PLA.PLA accounts for a large proportion,which has the problems of high production cost and limited performance.In this thesis,under the premise of ensuring that the properties of the composite material can meet the application needs,the relatively cheap straw fiber and potato starch are added to the PLA to make the composite material through the hot-press molding method,which can effectively reduce the amount of PLA,thereby reducing the production cost of the composite material.Moreover,the performance synergy between different materials can also effectively improve the performance of composite materials,which is conducive to the market promotion of products.However,There is a problem of uneven distribution of the temperature field of the hot plate in the process of hot pressing,and it is necessary to numerically simulate the temperature field of the hot plate to optimize the uniformity of the temperature field.In this thesis,from the aspects of device design,mechanism analysis,numerical simulation and experimental research,the heat transfer mechanism of CNC hot press hot plate under the action of hot pressing,the uniformity of hot plate temperature field and the properties of polylactic acid matrix composites under different parameters are systematically studied.The main research contents and conclusions of the thesis are as follows:(1)The research on the heat transfer mechanism of the hot plate under the action of hot pressing has been carried out.Based on Fourier’s fundamental law and temperature field theory,the temperature distribution gradient and direction of the hot plate,and the total heat flow through the section of the hot plate are obtained.Finally,based on the thermal conductivity differential equation and definite solution conditions,a mathematical model of the temperature field of the hot plate is established,and the temperature field distribution on the surface of the hot plate of the CNC hot press and the surface of the electric heating tube can be obtained by solving the thermal differential equation.(2)An experimental device for hot press molding was analyzed and designed.According to the technical requirements of hot pressing,the three-dimensional structure of the hot pressing device is analyzed,which mainly includes heating plate components,frame components,hydraulic components and guide components.According to the requirements of the electric heating type hot press,the temperature control system and temperature control process are designed.Through the electric heating numerical control hot pressing forming device designed in this paper,the control of the hot pressing temperature,hot pressing time,and holding time can be realized,which meets the needs of the hot pressing experiment.(3)The numerical simulation of the temperature field of the hot plate under the action of hot pressing was carried out.First,according to the basic design of the hot plate structure,the ABAQUS software is used to conduct transient thermal analysis and simulation of the hot pressing process,and the distribution characteristics of the temperature field of the hot plate are deeply studied.Secondly,the different electric heating tube spacing and different electric heating are investigated.The influence of tube power and other parameters on the uniformity of the temperature field of the hot plate,the hot plate structure and the power parameters of the electric heating tube with better temperature field uniformity are obtained.(4)The experimental research on the hot press molding of polylactic acid-based composites under different parameters were carried out.Single factor experiments were used to analyze the influence of factors such as hot pressing process parameters(hot pressing temperature,hot pressing time),straw fiber content,straw fiber pretreatment methods,and different compatibilizers on the properties of composite materials.Taking the mechanical properties of the composite material(all straw fibers are treated with KH550)as an index,the L9(34)orthogonal experiment was used to determine the optimal plan.In this thesis,through mechanism analysis,numerical simulation and experimental research,a systematic study of the technology and performance of the hot press molding of polylactic acid-based composites is carried out.The research results show that the new polylactic acid-based composite material prepared in this topic has good mechanical properties and water resistance,and is a new type of composite material with good application prospects.The hot press molding technology of polylactic acid-based composite materials proposed in this topic can be extended to the preparation of other composite materials,which can effectively avoid the problem of "white pollution" and contribute to the protection of a good ecological environment. |
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