| Aluminum-plastic composites are laminated by aluminum foil and plastic together in the compound process, which belongs to functional materials with packaging characteristics. China’s annual consumption of food packaging containing such materials is more than 400,000 tons, but the annual recovery rate is only 10%-20%.The composite materials are high quality renewable resources. Once abandoned, it will not only cause the environment pollution, but also a great waste of resources. The separation of waste aluminum-plastic composite materials at present is still in the process of the technology research, and the influences of separation agent and different separation conditions on the separation efficiency are investigated. On this basis, the separation theory of waste aluminum-plastic composite materials needs to be improved, and it will help us strive to create a green environmental protection and resource-saving society.First the interface characteristics and mechanism of aluminum-plastic composite materials were studied. The thickness of aluminum-plastic composite materials, its composition and the physical separation rate were measured in order to represent the structural characteristics of aluminum-plastic composite materials and the feature of difficulty to separate. The separation agent and its filtration residues after separation were analyzed by fourier transform infrared spectroscopy(FTIR), and adhesive oxide structural groups and polyethylene fragments were found. The separation factors affecting the separation process were studied, and the results showed that solvent with the solubility parameter solvent similar to the plastic was the core component in separation agent, ethanol and water could make the solvent an effective action on the interface between aluminum and plastic, in addition, high temperature, rotate speed and solvent polarity could intensify the effect of the separation on the interface. The characteristics of interface between aluminum and plastic were analyzed to represent the action on the interface in the separation process by a scanning electron microscope with optical ray spectrometer(SEM-EDS), and it could be combined with the characteristics of separation process to study the mechanism. The results showed that the separation actions on the interface were mechanical destruction effect and molecular forces destruction effect. The separation agent with a certain volume ratio reached the internal interface through the boundary layer, and destroyed the mechanical adhesive effect, while the polar forces were destroyed and dissolved by the similar dispersion force and polar force.Secondly the characteristics of separation agent were studied. The three phase diagram was drawn by visual titration. It indicated the presence of a single-phase and a two-phase region. The effect of phase behavior and action mechanism on the separation process was analyzed by the separation experiment in the single-phase and two-phase region. The results showed that the ethanol reduced the interfacial tension between toluene and water, so that the two components generated a miscible, which developed the single-phase or two-phase solution. In the two-phase zone separation, the W/O dispersion contained many micro-emulsion droplets in the upper solution and generated thermal movement, which made it fully touch with the materials that were separated finally. However in the single-phase, a small number of W/O dispersion and large number of O/W dispersion which could hinder the separation made the agent obtain an unstable performance. The separation agent which contained Na Cl was used to investigate the optimal performance. The results showed that Na Cl could reduce the repulsion force between droplets in the agent, make droplets together and enhance the separation performance.Thirdly, the aluminum-plastic separation kinetics and the correlation between separation conditions were studied. The solubility of plastic in the toluene-ethanol-water mixed agent at different temperatures was measured, then it could fit the best suitable dissolution kinetic equations that were 2391514])17160(1[0012120.-=.S/.r at 55℃, 05204120])80430(1[0263670..-=.S/.r at 60℃, and 1064.11.0-=Sr])6279.0/(1[069966.0 at 65℃. The curve of equations could represent the characteristics of separation kinetics. The results showed that the dissolved efficiency was reduced with the increase of dissolved quantity, and meanwhile the higher solubility and separation efficiency were brought by the higher temperature which also made the agent faster reach saturation and high loss rate. The regression of volume ratio(toluene/ethanol) and separation time was analyzed, the results show that the toluene/ethanol was 0.78 at the shortest separation time, and then the new technology conditions could be obtained by the combination between volume ratio of 0.78 and other factors. The new technology conditions contained the solid-to-liquid ratio of 0.98 g: 100 m L, the temperature of 60℃, the toluene-ethanol-Na Cl volume ratio of 16:20:64 and the stirring speed of 200 rpm.Finally, the recycling and reuse of waste separation solution were studied. The volatile consumption of the separation agent and its components were measured. It indicated that the consumption in separation was mainly from the adsorption of plastic and the rough surface of aluminum foil. The separation rate of waste solutions used for many times was measured to study the reuse value. The results showed that a certain amount of separation agent was absorbed in each reuse, and it made the upper solution decreased so that the separation agent was also decreased, but the solution still kept a high reuse value in the first three times reuse. The two reuse processes was discussed. It indicated that when the volume fraction of toluene was added in the waste solution more than the original separation agent, the new waste solution could obtain almost the same separation effect, and when the waste solution was used to replace the components of fresh agent, the separation rate was gradually decreased by the increased waste solution. The correlation between agent consumption and separation amount through least square fitting method was analyzed. The equation between the total consumption and separation amount was xy-=71.773.24, and the equation between the consumption of upper solution and separation amount was xy-=80.473.14. The two equations could provide the theoretical basis that contained the total usage, consumption and fresh dosage for waste separation solution recycling and reuse. |
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