| Phase change materials are latent heat storage materials.They can be used to construct new energy-saving wood-based phase change composite materials due to their properties of absorbing or releasing heat through phase change.Moreover,they have the advantages of low energy consumption,energy storage and green.Wood based phase change composite has the advantages of wood low thermal conductivity and phase change energy storage and can be used in the field of energy conservation of wood structure buildings.Paraffin wax,as a phase change material,has the advantages of moderate melting and crystallization temperature range,strong heat storage capacity,low undercooling,non-toxic,low cost,small volume changes and a wide range of sources,good chemical and thermal stability,and has been applied in many fields.However,when using paraffin as phase change agent to prepare phase change materials,it is difficult to form,which seriously limits its application in actual production.At present,most of the solidliquid phase materials are prepared by encapsulation in microcapsule shell,impregnation and physical blending to solve the difficult problem of shaping.In order to solve these problems,the main method is to prepare phase change microcapsules by Pickering emulsion template method.Therefore,it is urgent to introduce Pickering emulsion template method to prepare phase change microcapsules to guide the design and preparation of solid-liquid phase change materials,and provide new ideas and methods to solve the difficult problem of its shaping,so as to expand its application range.In this paper,green and sustainable paraffin wax was used as phase change material,and hydrophobic CNC was used as Pickering emulsifier.The paraffin phase change microcapsules were prepared by Pickering emulsion template method,and the wood adhesive modified by paraffin phase change microcapsules with urea-formaldehyde resin and its application in plywood were explored.On the one hand,the wood adhesive can be endowed with the function of phase change heat storage,on the other hand,the wood adhesive can realize the large scale preparation of phase change plywood,so as to provide a new idea and method for the construction of energy saving plywood.The main research results are as follows:(1)Firstly,in order to understand the enthalpy values of the paraffin phase change microcapsules in Pickering emulsion at different oil-water ratios,the material ratio of paraffin was changed,and Pickering paraffin emulsion with oil-water ratios of 35:65,45:55 and 55:45were obtained and the application of PPE-1,PPE-2 and PPE-3 in plywood combined with ureaformaldehyde resin adhesive was investigated.The phase change temperatures of the obtained phase change microcapsules from PPE-1,PPE-2 and PPE-3 were 45.4,46.1 and 45.6 ℃,the enthalpy values of phase change were 120.2,122.9 and 151.9 J/g,respectively.In addition,the enthalpy values of phase change adhesive(PCA)PCA-3 were up to 67.53 J/g.Both microcapsules and adhesive showed good properties of phase change heat storage.Both the microcapsules and the adhesive showed good heat storage properties.According to the test standard of Class Ⅲplywood,the dry shear strength of urea-formaldehyde resin adhesive was 1.01±0.026 MPa,0.95±0.014 MPa,and 0.93±0.039 MPa,respectively.In the analysis of energy saving properties,the time for PCP-3 to rise to 55 ℃ was 181% longer than that of the blank control sample.With the increase of the content of paraffin phase change microcapsules in the adhesive layer,the temperature control performance of the plywood during phase change was better.The energy saving performance was analyzed by finite element simulation,and the simulation results were in good agreement with the test results.(2)Secondly,in order to improve the wet shear strength of plywood layer,UF/Pickering paraffin phase change microcapsules with paraffin phase change microcapsules as core material and UF prepolymer as shell material were prepared by Pickering emulsion template method.The wet shear strength of plywood layer could be improved by the construction of shell core structure.Its application in wood adhesive of urea-formaldehyde resin was investigated.The phase change temperatures of the obtained phase change microcapsules from 2PPE-1,2PPE-2 and 2PPE-3prepared with different UF prepolymers were 48.1 ℃,48.4 ℃ and 48.3 ℃,the enthalpy values of phase change were 83.23,104.7 and 85.32 J/g,respectively.In addition,the enthalpy values of 2PCA-2 were as high as 40.09 J/g.Both microcapsules and adhesive showed good heat storage properties.In the application of urea-formaldehyde resin adhesive,according to the test standard of Class Ⅱ plywood,the wet shear strength of 2PCP-1,2PCP-2,2PCP-3,2PCP-4 and 2PCP-5adhesive layer were as follows: 0.70±0.002 MPa,1.16±0.017 MPa,1.28±0.032 MPa,1.03±0.018 MPa and 0.71±0.008 MPa.In the analysis of energy saving properties,the time for 2PCP-2 to rise to 55 °C was 147% longer than that of the blank control sample,and the finite element simulation was used to analyze its energy saving performance.The simulation results of energy saving performance were consistent with the test results.(3)Finally,different proportions of hydrophobic CNC and CNC were selected to obtain paraffin phase change microcapsules with high enthalpy value,high wet shear strength of adhesive layer and excellent energy saving performance of plywood.Three kinds of hydrophobic CNC and CNC complex emulsions were prepared: 3PPE-1,3PPE-2 and 3PPE-3.The phase change temperatures of the paraffin phase change microcapsules in the emulsion were 45.7,44.2and 45.8 ℃,and the enthalpy values were 133.1,148.1 and 137.9 J/g,respectively.In addition,the enthalpy values of 3PCA-2 were up to 62.73 J/g.Both microcapsules and adhesive showed good properties of phase change heat storage.In the application of urea-formaldehyde resin adhesive,according to the test standards of Class II plywood,the shear strength of 3PCP-1,3PCP-2,3PCP-3 and 3PCP-4 were 1.38±0.034 MPa,1.53±0.032 MPa,0.99±0.021 MPa and1.17±0.071 MPa,respectively.In the analysis of energy saving properties,the time for 3PCP-2 to rise to 55 °C was 190% longer than that of the blank control sample,and the finite element simulation was used to analyze its energy saving performance.The simulation results of energy saving performance were consistent with the test results. |
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