Abstract: The extensive use of polyethylene aluminum-plastic composite packaging materials has resulted in a huge amount of non-degradable waste. Moreover, there are many imperfections in the recycling of such materials, which brings another huge pressure on environmental protection. In this study, industrial pure acetic acid or formic acid was used as a layered release agent to completely separate the recyclable materials in polyethylene (PE) aluminum-plastic composites. Compared with the current recycling technology of this kind of material, the greatest advantage of this technology is that it can completely separate, recycle, and reuse waste polyethylene plastic-plastic composite packaging materials.
Keywords: polyethylene aluminum plastic composite packaging material; weak acid; separation; stripping agent
Polyethylene aluminum plastic composite packaging materials are widely used in the fields of food, medicine, chemicals and daily necessities packaging, such as: Tetra Pak's Tetra series products and parts, with its characteristics of light blocking, constant temperature, non-toxicity and low cost. Milk beverage bottle closure materials, etc., are all belong to polyethylene aluminum plastic composite packaging materials.
Due to the wide range of applications and large quantities of polyethylene-aluminum-plastic composite packaging materials, a large number of non-degradable waste products have been generated. If handled improperly, it will put tremendous pressure on environmental protection. In addition, the raw materials used to produce the packaging materials are: high-quality industrial aluminum, natural wood pulp paper and polyethylene plastic, which are materials with high recovery value. Especially industrial aluminum, its high price, low supply, if it is recycled, the economic benefits must be considerable. 'Accordingly' the recycling of polyethylene plastic-plastic composite packaging material has very important social and economic value.
1 separation principle of polyethylene aluminum plastic composite packaging material
The aluminum foil is combined with polyethylene plastic film and paper to form a polyethylene aluminum-plastic composite packaging material. The specific process is: using high frequency and hot pressing to melt the bonding surface of polyethylene (PE) plastic layer, and then make it with aluminum foil. Aluminum oxide formed on the surface and paper are bonded together. Since the oxide properties of aluminum are very stable, it is difficult to completely separate the three materials that are bonded together. Moreover, polyethylene plastics are resistant to acid and alkali corrosion, and ordinary organic solvents cannot dissolve or swell, which gives the material Recycling brings greater difficulty. There are two kinds of material recycling processes currently in use: one is the use of the principle that both aluminum and aluminum oxides are soluble in acid and alkali, and the aluminum in the material is dissolved by using an acid-soluble or alkali-soluble method to recover the polyethylene plastic film. And paper, and then aluminum waste into polyaluminum chloride or aluminum sulfate; Second, Tetra Pak use of hydraulic method to separate the three materials into pulp and aluminum plastic two parts, and then separately use. However, the above two methods all have many shortcomings such as low economic efficiency, incomplete recovery, etc. Therefore, this article will be based on experimental results. Promote a new treatment method in order to achieve the best recycling effect.
The principle of operation is that organic weak acid molecules such as acetic acid and formic acid can penetrate the polyethylene plastic layer and the paper layer, thereby dissolving and bonding the aluminum oxides of the various layers without dissolving the characteristics of the simple aluminum, and the aluminum foil in the packaging material can be Ethylene plastic and paper layers were completely separated.
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 Hongxing Chemical Factory), lime water (made into supersaturated solution), oxalic acid (CR, Beijing Yili Fine Chemicals Co., Ltd. Company) Mengniu pure milk with Tetra Pak, Mengniu pure milk Tetra Pak, Wahaha lactic acid beverage bottle closure material.
2.2 Experimental methods
2.2.1 Weak Acid Delamination and Separation
The schematic diagram of the process flow of the weak acid layered separation method is shown in Figure 1:
The sample was added to a layered container with a weak acid, and the separation was performed using the characteristic that the weak acid molecules were able to penetrate the polyethylene plastic layer and the paper layer. Weak acid gradually dissolves the aluminum oxide layer at the junction of each layer of the sample, making it completely separated. The fully separated composite was drained and then soaked in saturated lime water to neutralize the wash until the pH was between 6 and 8 and washed with clear water. After washing, the peeled composite is dried, then placed in a centrifuge, and centrifuged to obtain clean PE plastic, aluminum foil and pulp.
2.3 Experimental results
The delamination rate of industrial pure acetic acid (98.5%) and industrial pure formic acid (85%) is the fastest. In the case of no heating, the fully layered samples can be obtained in 4 hours and 4.5 hours respectively. When heated to 50Â°C, it can be completely separated in about 1 hour. Industrial pure acetic acid and formic acid can be recycled, but with the increase in the number of uses, the concentration of acetic acid and formic acid gradually becomes smaller, and the peeling time will be extended. When the weak acid concentration is less than 15%, the time required for stripping will increase significantly and will take about 12 hours.
3 Results and Discussion
During the experiment, oxalic acid with a large dissociation constant (pK) was also tried as a separating agent, but the layers could not be successfully separated even when the solution was saturated and heated to boiling. This is due to the fact that oxalic acid molecules do not easily penetrate the paper and plastic layers and dissolve the oxides of aluminum between the layers. The "weak acid separation method" using acetic acid or formic acid succeeded in completely recovering and utilizing the material.
Through experiments, it can be seen that this process is simple and easy, and the various materials obtained after separation have high purity and good quality, and can be used as high-quality raw materials for reproduction in related fields. This method is superior to the current hydrodynamic separation of aluminum-plastic composite packaging materials promoted by Tetra Pak, because the hydraulic method can only separate paper from aluminum and plastic, and it cannot successfully and completely separate aluminum foil from aluminum and plastic. Although aluminum plastic can be used to make colored music boards and other products, aluminum and plastic are more difficult to recycle after these products are aged and discarded, which causes secondary pollution. The technology proposed in this study separates aluminum foil, plastic, and paper to achieve complete recycling. Effectively avoid secondary pollution.
In addition, because industrial pure acetic acid and formic acid can be recycled (neolitic 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, lime water with weak alkalinity is used for the residue. The separation is neutralized with weak acid to eliminate environmental pollution. 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 Civil Engineering and Architecture Source: Journal of Beijing Institute of Civil Engineering and Architecture
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