The Heat Treatment Technology With Lower Mechanical Strength Loss Of Rubber Wood

As a physical modification method to effectively improve the biological durability of wood,heat treatment can effectively solve the problem of poor biological durability caused by the high content of starch and free sugar in rubber wood.However,heat-treated wood material becomes brittle and the strength is significantly reduced,which seriously limits the practical application of heat treatment.In this paper,based on the problem of mechanical strength loss caused by heat treatment,rubber wood was carried out by atmospheric pressure superheated steam heating method and hot plate contact heating method.The influence of high temperature heat treatment process parameters on the wood properties of rubber was systematically studied.The correlation between material properties and chemical composition and crystallinity was constructed.The mathematical model of surface visual physical quantity was constructed.The influence mechanism of heat treatment on the properties was revealed.The heat treatment process was classified.The optimal process parameters achieve the goal of reducing the mechanical strength loss of heat treatment.The main research contents and results of this paper are as follows:(1)The atmospheric pressure steam method and the flat plate contact method can effectively reduce the equilibrium moisture content of the rubber wood and improve the dimensional stability.The equilibrium moisture content is negatively correlated with the heat treatment temperature and time,and the dimensional stability is positively correlated with the heat treatment temperature and time.With the increase of the cooling rate of the atmospheric pressure steam method,the equilibrium moisture content tends to increase gradually,and the shrinkage and shrinkage rate first increases and then decreases.(2)atmospheric superheated steam treatment will reduce mechanical properties.Increasing cooling rate can reduce mechanical losses within a certain range.As the cooling rate increases,the bending strength,elastic modulus,compressive strength of the grain,hardness and the screwing force are gradually increased.Plate contact method can effectively control the loss of mechanical properties.With the increase of treatment temperature and the extension of treatment time,the bending strength gradually decreases,and the elastic modulus,hardness,compressive strength along the grain and the screw holding force first increase and then decrease.(3)Correlation analysis and regression analysis of rubber wood and surface visual physical quantities were carried out by SPSS software to determine the dependent variables of mathematical models and improve the fitting degree of mathematical models.The bending strength,the compressive strength of the grain,the screwing force and the mathematical model of the surface visual physical quantity are highly fitted,R~2>0.9.(4)The heat treatment process is classified by cluster analysis.The atmospheric pressure steam method can divide the process into three categories:mild high temperature heat treatment group(170/185/200/215?,1.5h),medium high temperature heat treatment group(170/185/200??3h,170/185??4.5h)and heavy high temperature heat treatment group(200??4.5h,215??3/4.5h,230??1.5/3/4.5h);flat contact method can be divided into four categories:mild high temperature heat treatment group(250??5min),medium high temperature heat treatment group(230??5/10/15/20min),severe high temperature Heat treatment group(250??10/15/20min,270??5/10/15/20min)and ultra-high temperature heat treatment group(290??20min).(5)For atmospheric pressure superheated steam method,the optimal process is 200?and 1.5 h,with the cooling rate of 4?/min.The diameter surface hardness,elastic modulus,along the grain compressive strength are 2925.59 N,8154.11 MPa,45.13 MPa respectively,with the loss rate of 8.73%,11.77% and 9.23%,respectively,the screw force is 2368.14 N,increased by 6.72%,It meet the requirements.(6)For hot plate contact method,the optimal process of 270?,10 min.the bending strength,chord surface hardness and compressive strength along the grain were 82.10 MPa,4295.18N and 47.54 MPa,respectively,and the loss rate were 10.44%,10.08%and 4.38%,respectively.The elastic modulus,diameter surface hardness and screw holding force were improved to 9282.47 MPa,3480.72N and 2396.92N,by 0.45%,29.36% and 8.09%,respectively.It meet the requirements.