| Development in the green,innovative and recycling of packaging materials are common goals and essential requirements pursued by all countries in the world.Cushioning packaging accounts for the largest proportion of all packaging formats.At present,Expanded Polystyrene(EPS)and Expanded Polyethylene(EPE)are the main buffer materials used in China.They are not naturally degradable and cause significant pollution to the environment,although they are light,waterproof,oil resistant,cheap,and have good compression properties.But the use of EPS and EPE has become a blessing because there is no better alternatives.However,plant fiber foaming cushioning packaging materials have broad market space and development advantages in cushioning packaging materials due to their extensive raw materials,environmental friendliness and low cost.Wood fiber is the best raw material for the preparation of green buffer material because of its lignification thickening pore wall,porosity and appropriate aspect ratio of fiber.It has been widely concerned by scholars at home and abroad,and has become a new research focus.New products and new achievements are constantly emerging.In this paper,poplar fiber and wood powder were used as the main raw materials,and foaming agent and adhesive as the auxiliary material to develop a poplar fiber porous cushioning packaging material.The pore structure parameters and quantitative characterization methods of the material were determined,the material forming process was determined,the material formulation was optimized,the static and dynamic buffering properties of the material were characterized and the mechanical model was established,the foaming mechanism and the influencing factors in foaming process of the material were studied.The study lays a foundation for regulating the pore structure and provides theoretical and practical support for the industrialization of poplar fiber porous cushioning packaging materials.The main research contents and results of this thesis are as follows:(1)According to the characteristics of poplar fiber porous cushioning packaging material,the porosity,the average pore diameter and the standard deviation of the pore size distribution were determined as parameters for characterizing the pore structure of the poplar fiber porous cushioning packaging material.The microscope-digital image processing method which based on stereology principle and digital image processing technology was used as the quantitative characterization method for pore structure parameters.(2)Through the study of the effects of different molding processes on the micro morphology,composition,structural parameters,static characteristics and energy consumption of the poplar fiber porous cushioning packaging material,the preparation process of the porous cushioning packaging material was determined.The research results showed that the poplar fiber porous cushioning packaging material prepared by microwave molding process had more uniform pore structure,and excellent static characteristics.And microwave molding process heated up quickly and had high thermal efficiency.The microwave molding process was determined as the molding process of poplar fiber porous cushioning packaging material.The process parameters were 280 W microwave power for 3 min in the first stage,and 700 W microwave power for 7 min in the second stage.(3)The optimum formula of poplar fiber porous cushioning packaging material was obtained by single factor test and orthogonal test.Through single factor test,6.8%,7.1%and 7.4%were selected as the three levels of wood fiber dosage in orthogonal test,61.0%,61.4%and 61.8%as the three levels of water dosage in orthogonal test,1.2%,1.4%and 1.6%as the three levels of AC dosage in orthogonal test,and 9.0%,9.5%and 10.0%as the three levels of wood powder dosage in orthogonal test.The optimal formula was optimized by orthogonal test method:wood fiber dosage 6.8%,water dosage 61.8%,AC dosage 1.6%,wood powder dosage 9.0%,and the performance of the material was improved by verification test.(4)The static and dynamic cushioning properties of the materials were evaluated by static and dynamic compression tests,and the static and dynamic cushioning performance curves of poplar fiber porous cushioning packaging materials were established by MATLAB.The results showed that,the minimum cushioning coefficient of poplar fiber porous cushioning packaging materials was smaller than that of several commonly used cushioning packaging materials,and the poplar fiber porous cushioning packaging materials were suitable for products with large brittleness.The maximum acceleration-static stress curve of the material was concave valley shape,and the opening was upward.Under the same drop height and impact load,the greater the thickness,the better the dynamic cushioning performance of the material.The static stress-strain curves of materials conformed to the tangent plus hyperbolic tangent model and the maximum acceleration-static stress curve conformed to the quadratic model.(5)The mechanism of the pore wall formation of the poplar fiber porous cushioning material was studied by discussing the influence of the fiber beating degree on the structure parameters of the porous material.The foaming mechanism of the porous cushioning packaging material was studied by gradual decomposition of the foaming process of the porous cushioning packaging material.The effect of the embryo body viscosity and temperature on the growth of the material bubbles was studied by investigated the effects of PVA dosage and microwave power on the pore structure of the poplar fiber porous cushioning packaging materials.The results showed that,the pore wall was a fiber space network structure made of poplar fiber and wood powder.The combination of the bubble hole wall was mainly through the bonding force of hydrogen bond,the bonding force of poplar fiber and wood powder to the adhesive.The uniformity of the mixture,the addition of the nucleating agent,the external pressure and the internal pressure in the foam system,and the curing time were the key factors to the mixing of raw materials,the nucleation of the bubbles,the growth of bubbles and the steady solidification of the bubbles,which determined the rationality of the pore parameters of the porous material and the quality and effect of the foaming.The viscosity of the embryo body affected the size and uniformity of the pore diameter of the poplar fiber porous cushioning packaging material by regulating the external pressure of the bubble during the growth process,and the temperature by controlling the decomposition of the foaming agent and the internal pressure of the bubbles.When PVA dosage was 3.3%and microwave power was 280 W,the porous structure parameters of poplar fiber cushioning packaging material were better. |
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