2024.11.29
Polystyrene foam is ubiquitous in our daily lives. From food packaging to building insulation, from handicraft production to the protection of electronic products, polystyrene foam plays an important role with its unique properties.
Polystyrene foam is a lightweight polymer. It uses polystyrene resin to add a foaming agent, and heats it to soften it. After generating gas, it forms a rigid closed-cell foam. Its processing methods can be divided into modeling and extrusion methods according to different foaming methods. This uniform closed cavity structure gives it the characteristics of low water absorption, good thermal insulation, light weight and high mechanical strength.
With the widespread application of polystyrene foam, its recycling problem has also received increasing attention. On the one hand, if a large amount of polystyrene foam is not properly handled after use, it will cause serious pollution to the environment. On the other hand, as a resource, if polystyrene foam can be effectively recycled, it will help save resources, reduce energy consumption and achieve sustainable development.
Polystyrene foam is a light polymer, the main components of which include polystyrene resin, air and pentane. Its production process can be divided into modeling and extrusion according to different foaming methods. During the production process, polystyrene resin is added to a foaming agent and heated and softened at the same time, so that the foaming agent produces gas, thereby forming a rigid closed-cell foam plastic.
Light weight and low price. The density of polystyrene foam is generally between 10-45kg/m³. The apparent density of EPS used in engineering is generally between 15-30kg/m³. The density of EPS used as lightweight filler in road engineering is currently 20kg/m³, which is only 1%-2% of ordinary road filler. This low density makes polystyrene foam very light and easy to carry and construct. At the same time, compared with other materials, its price is relatively low and has a high cost-effectiveness.
Low water absorption and excellent cushioning performance. Polystyrene foam has a closed cavity structure, which makes water penetration extremely slow. The strength of EPS lightweight aggregate concrete mainly comes from the strength of cement paste, and its good workability ensures that it has certain buffering performance when under pressure.
Insulation material: EPS has a low thermal conductivity. The thermal conductivity of EPS boards of various specifications is 0.024W/m.K – 0.041W/m.K. Its good thermal insulation performance makes it widely used in building exterior wall insulation, roof insulation and other fields.
Roadbed filler: EPS is an ultra-light roadbed filler. When building embankments on soft soil foundations, it can effectively reduce the deadweight of embankments, reduce additional stress on the foundation, reduce the settlement of embankments on soft soil foundations, and improve the stability of the foundation.
Decorative components: EPS decorative components can reduce the impact on underground or adjacent buildings. The uneven settlement of the upper soil and the soil on both sides of the rigid structure buried under the embankment often produces excessive additional pressure on the top of the structure. Using EPS instead of fill to pave the top of the structure can improve the stress distribution on the structure and greatly reduce the soil pressure on the structure.
Industry: The products are widely used in construction, ocean, agriculture and packaging.
Transportation: In road construction, EPS can be used to lay insulation layers and prevent roadbed frost damage. When building roads in permafrost areas, traditional methods of treating frost damage are not ideal. However, EPS materials have closed bubbles on the inner wall, which are not interconnected, have low water absorption and good frost resistance, ensuring good thermal insulation performance even under flooding conditions.
The recycling of polystyrene foam is difficult, mainly due to the particularity of its materials. First, polystyrene foam is light and fragile, and is easy to break, which makes it face many challenges in the collection, storage and transportation process. The broken foam is small in volume but large in quantity, and it is easy to float, which not only increases the difficulty of collection, but also may cause pollution to the environment. Secondly, polystyrene foam is large in volume and occupies more space, which leads to high transportation costs. In the recycling process, it needs to be compressed to reduce transportation costs, but the compression process is not easy and requires special equipment and technology.
From a technical perspective, the main methods for recycling polystyrene foam are physical, chemical and biological. The physical method achieves recycling through mechanical crushing, compression, separation and other means. The operation is relatively simple and the equipment investment is low, but secondary pollution is easy to occur during the recycling process, and the recycling efficiency is low. The chemical method mainly recycles waste polystyrene through chemical reactions such as acid-base catalysis, pyrolysis, and oxidation, and can obtain recycled products with higher purity, but the chemical reaction process is complicated and may produce toxic and harmful substances, which will affect the environment. The biological method uses microorganisms to degrade polystyrene molecular chains and convert them into small molecules such as organic acids. It has the advantages of high environmental protection and good recycling efficiency, but it requires specific microbial populations and suitable degradation conditions, and is difficult to implement.
Recycling Status
At present, the recycling status of polystyrene foam is not optimistic. The world produces about 12 million tons of polystyrene foam plastics each year, of which China produces about 1.8 million tons. However, except for a few developed countries, the waste PS foam materials in most countries and regions have not been effectively recycled. According to incomplete statistics, the recycling rate of PS foam plastics in Nordic countries and Japan is 72%, South Korea is 64%, and the rest of the countries and regions are only 10-30%. In China, due to the imperfect recycling mechanism, 70% is buried or incinerated, and only 30% is recycled.
The main recycling methods of polystyrene foam are granulation after volume reduction, crushing and use as various filling materials, cracking and oil production or recycling styrene and others. Granulation after volume reduction is to melt and extrude polystyrene foam plastics into recycled granules, but because of its large volume, it needs to be reduced in volume first. The methods include mechanical method, solvent method and heating method. After crushing, it can be used as filler to make various products, such as re-molding into foam plastic products, concrete composite board products, gypsum sandwich bricks, asphalt enhancers, soil modifiers, etc. Cracking to make oil or recover styrene is a method of recycling through thermal decomposition. The waste polystyrene foam is put into the cracking kettle, the temperature is controlled to produce crude styrene monomer, and then styrene with a purity of more than 99% can be obtained through distillation and rectification. If waste polyolefin plastics including polystyrene are thermally cracked or catalytically cracked at a higher temperature, they can be turned into gasoline or diesel.
In addition, there are some innovative recycling methods, such as a method developed by American researchers to use ultraviolet rays as energy and aluminum chloride as a catalyst to decompose the chemical structure of polystyrene, and then use the same catalyst and add dichloromethane to produce diphenylmethane, which is 10 times more valuable than polystyrene. The reaction can be carried out at ambient temperature and normal pressure, and requires less energy than existing polystyrene recycling or upgrading methods.
Methods for recycling polystyrene foam
The main methods for recycling polystyrene foam known at present are as follows:
Send to a specific recycling center: Many areas have special polystyrene foam recycling centers, where people can send used polystyrene foam products to these centers for centralized processing.
Recycling at a mechanical recycling plant: Civilian EPS foam is usually transported to a mechanical recycling plant in bags by semi-trailer trailers. At the recycling plant, impurities such as paper, metal, other polymers and food residues are first removed by manual separation. The polymer is then crushed into fluff, which then enters the washing and drying process. The fluff is first dried by centrifugation to remove a large amount of water, and then dried by convection heating. Then an extruder is used to compress and heat the fluff to 205°C, and finally it is extruded through a lace die and granulated. The granulated polystyrene can be used to make plastic products such as hangers, flower pots, videotapes, furniture, building materials or insulation materials.
The widespread use of polystyrene foam has brought about serious white pollution problems and has had a great negative impact on the environment. The recycling of polystyrene foam can effectively reduce this pollution.
First, if a large amount of polystyrene foam is not recycled, it will exist in the natural environment for a long time and is difficult to degrade. They may accumulate on the land, occupy a lot of space, and affect the normal use of the land. At the same time, polystyrene foam may also enter the water body and cause harm to aquatic life. For example, some marine organisms may accidentally eat polystyrene foam, causing blockage of the digestive system or even death. By recycling polystyrene foam, the accumulation of these foams in the environment can be reduced, reducing damage to the ecosystem.
Secondly, the recycling of polystyrene foam can reduce the demand for natural resources. Polystyrene is a petroleum-based plastic, and its production requires a large amount of petroleum resources. Recycling polystyrene foam can reprocess it into new products, reduce dependence on raw petroleum, and thus reduce the pressure on the exploitation of natural resources.
In addition, the recycling of polystyrene foam can also reduce greenhouse gas emissions. The production process of polystyrene consumes a lot of energy and also emits a lot of greenhouse gases. Recycling polystyrene foam can save energy, reduce greenhouse gas emissions, and help ease the pressure of climate change.
The recycling of polystyrene foam not only has environmental benefits, but also brings significant economic benefits.
On the one hand, recycling polystyrene foam can reduce production costs. Polystyrene is an important plastic material that is widely used in various fields. However, the price of polystyrene is relatively high, which makes the cost of products using polystyrene also high. By recycling polystyrene foam, it can be reprocessed into new polystyrene products, thereby reducing the cost of raw materials. For example, some companies recycle polystyrene foam and make it into recycled polystyrene particles, which are then used to produce plastic products such as hangers, flower pots, building materials, etc. The cost of these recycled polystyrene particles is relatively low, which can save companies a lot of raw material costs.
On the other hand, the recycling of polystyrene foam can achieve the reuse of resources. Polystyrene is a valuable resource. If it is not recycled, a large amount of polystyrene foam will be wasted. By recycling polystyrene foam, it can be reprocessed into new products to achieve the recycling of resources. For example, some companies make recycled polystyrene foam into insulation materials, filling materials, etc. These products can be used again in construction, packaging and other fields to create more value for society.
In addition, the recycling of polystyrene foam can also promote the development of related industries. With the continuous advancement of polystyrene foam recycling technology, more and more companies are beginning to get involved in the field of polystyrene foam recycling. This not only creates more employment opportunities for society, but also drives the development of related industries, such as recycling equipment manufacturing, recycled polystyrene product processing, etc. The development of these industries will further promote the process of polystyrene foam recycling and achieve a win-win situation of economic and environmental benefits.
As a widely used material, the recycling of polystyrene foam is of vital importance and feasible ways.
In terms of importance, the recycling of polystyrene foam has a positive impact on both the environment and the economy that cannot be ignored. In terms of the environment, the widespread use of polystyrene foam will bring serious white pollution problems if it is not properly recycled. A large amount of polystyrene foam piled up on the land will occupy space and affect the normal use of the land. If it enters the water body, it will harm aquatic life. By recycling, its accumulation in the environment can be reduced and the damage to the ecosystem can be reduced. At the same time, the recycling of polystyrene foam can reduce the demand for natural resources, because polystyrene is a petroleum-based plastic, and recycling and reuse can reduce dependence on raw oil and reduce the pressure on natural resource exploitation.
In terms of feasibility, there are currently a variety of recycling channels and methods. On the one hand, the existing recycling channels include sending it to a specific recycling center and mechanical recycling plants for recycling. Many areas have special polystyrene foam recycling centers, which provide people with a centralized processing channel. The mechanical recycling plant recycles civilian EPS foam into various plastic products or building materials through a series of professional processing processes. On the other hand, with the advancement of science and technology, new technologies have also been applied in recycling. In summary, polystyrene foam recycling is not only important but also feasible.
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