A recycling and utilization technology of polyethylene aluminum plastic composite packaging materials
Abstract: the massive use of polyethylene aluminum plastic composite packaging materials has produced a huge amount of non degradable waste. Moreover, there are many imperfections in the current recycling of such materials, which has brought another huge pressure to environmental protection. In this study, industrial pure acetic acid or formic acid was used as layered stripping agent, Completely separate the recyclable substances in polyethylene (PE) aluminum-plastic composites. Compared with the current recycling technology of such materials, the biggest advantage of this technology is that it can be completely controlled, otherwise the control effect is not clear, and the control is still blind. Separate, recycle and reuse the waste polyethylene aluminum-plastic composite packaging materials.
Keywords: Polyethylene aluminum-plastic composite packaging materials; Weak acid; Separation; Stripper
polyethylene aluminum plastic composite packaging materials are widely used in the packaging fields of food, drugs, chemicals and daily necessities because of their light barrier, constant temperature, non-toxic safety and low cost. For example, Tetra Pak's Tetra Pak series products and some milk containing beverage bottle mouth sealing materials belong to polyethylene aluminum plastic composite packaging materials.
because polyethylene aluminum plastic composite packaging materials are widely used and used in a large amount, Therefore, a large amount of non degradable waste is produced, which will bring great pressure to environmental protection if not handled properly. In addition, the raw materials for the production of this packaging material are: high-quality industrial aluminum, natural wood pulp paper and polyethylene plastic, which are materials with high recycling value. Especially industrial aluminum, which has high price and few supply sources, if recycled, The economic benefits must be considerable. 'therefore,' the recycling and reuse of polyethylene aluminum plastic composite packaging materials has very important social significance and economic value.
1 separation principle of polyethylene aluminum plastic composite packaging materials
aluminum foil interacts with polyethylene plastic film and paper to form polyethylene aluminum plastic composite packaging materials. The specific process is to melt the joint surface of polyethylene (PE) plastic layer by means of high-frequency wave and thermal pressing, Then it is bonded with the oxide of aluminum formed on the surface of aluminum foil and paper. Because the oxide property of aluminum is very stable, it is difficult to completely separate the three materials bonded together. Moreover, polyethylene plastic can resist acid and alkali corrosion, and ordinary organic solvents can't dissolve or swell it, This brings great difficulty to the recycling of this material. At present, there are two kinds of recycling processes of this material being used: one is to regularly check and revise the principle that the hydraulic testing machine is soluble in acid and alkali by using both metal aluminum and aluminum oxide, dissolve the aluminum in the material by acid or alkali dissolution, so as to recover polyethylene plastic film and paper, and then turn the waste liquid containing aluminum into polyaluminum chloride or aluminum sulfate; Second, Tetra Pak uses hydraulic method to separate the three materials into pulp and aluminum plastic, and then use them respectively. However, the above two methods have many disadvantages, such as low economic benefits, incomplete recycling and so on. Therefore, this paper will be based on the experimental results. Introduce a new treatment method to achieve the best recycling effect.
the operation principle is: use organic weak acid molecules such as acetic acid and formic acid to penetrate the polyethylene plastic layer and paper layer, and then dissolve the oxide of aluminum bonded to each layer without dissolving the characteristics of simple aluminum Polyethylene plastic and paper layer are separated completely respectively.
2 experimental part
2.1 main reagents and raw materials
acetic acid (industrial pure, 98.5%, Beijing chemical plant), formic acid (industrial pure, 85%, Beijing Red Star Chemical Plant), lime water (prepared into supersaturated solution), oxalic acid (Cr, Beijing Yili Fine Chemicals Co., Ltd.), Tetra Pak pillows for Mengniu pure milk, Tetra Pak bricks for Mengniu pure milk, Wahaha lactic acid beverage bottle mouth sealing material.
2.2 experimental method
2.2.1 weak acid layered separation method
the process flow diagram of weak acid layered separation method is shown in figure 1:
add the sample into the layered container containing weak acid, and separate it by using the characteristics that weak acid molecules can penetrate polyethylene plastic layer and paper layer. The weak acid gradually dissolves the aluminum oxide layer at the junction of each layer of the sample, so as to completely separate it. Drain the completely separated composite material, and then soak it in saturated lime water for neutralization and washing. When the pH value is between 6 and 8, use clean water for washing. After washing, dry the stripped composite material, and then put it into a centrifugal separator for centrifugal separation, so as to obtain clean PE plastic Aluminum foil and pulp
2.3 experimental results
industrial pure acetic acid (98.5%) and industrial pure formic acid (85%) have the fastest delamination stripping speed. Without heating, it takes 4 hours and 4.5 hours respectively to obtain fully layered samples. When heated to 50 ℃, it can be completely separated in about 1 hour. Industrial pure acetic acid and formic acid can be recycled, but with the increase of use times, The concentration of acetic acid and formic acid decreases gradually, and the stripping time will be prolonged. When the concentration of weak acid is less than 15%, the stripping time will increase significantly, and it will take about 12 hours.
3 results and discussion
in the process of experiment, oxalic acid with large dissociation constant (PK) has also been tried to be used as the separating agent, However, even when the solution is saturated and heated to boiling, it cannot be successfully separated from each layer. This is due to the fact that oxalic acid molecules are not easy to penetrate the paper layer and plastic layer and dissolve the oxide of aluminum between the layers. While the "weak acid separation method" using acetic acid or formic acid has successfully achieved the complete recovery and utilization of this material.
through experiments, this process is simple and easy, The materials obtained after separation are of high purity and good quality, and can be used as high-quality raw materials for reproduction in various related fields. This method is superior to the hydraulic separation of aluminum-plastic composite packaging materials promoted by Tetra Pak at present, because the hydraulic method can only separate paper from aluminum-plastic, but cannot successfully and completely separate aluminum foil and plastic in aluminum-plastic. Although aluminum-plastic can be made into products such as Caile board, However, after these products are aged and discarded, aluminum and plastic are more difficult to recycle, which causes secondary pollution. The technology proposed in this study separates aluminum foil, plastic and paper respectively, and achieves complete recycling. In addition, because industrial pure acetic acid and formic acid can be recycled (the new acid needs to be replaced when the concentration is reduced to 15%), the recovery cost is low and the economic benefit is considerable; After separation, the residual separation is neutralized with weak acid with weak alkaline lime water to eliminate the pollution to the environment. Therefore, this separation method can achieve good economic and social benefits at the same time.
author/Wang chongchen, Wang Peng, Department of urban construction engineering, Beijing Institute of architecture and engineering
source: Journal of Beijing Institute of architecture and engineering
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