Plastic recycling
History of plastic
Plastic recycling
Plastic is a material that has played a huge role in our daily lives and has a tendency to increase usage because it can replace natural resources such as wood and iron very well and is cheap, lightweight, able to produce properties. various As required by choosing the type of raw material chemical reaction Production process and forming process.In addition, it can be easily cooked by adding additives such as plastic additives. (Plasticizer) Modifier, Filler, Stabilizer, Inhibitor, Lubricant and Pigment etc.
With advanced production technology And modern at present, we have a variety of plastic products And many colors to choose from With many outstanding properties, the plastic is quickly accepted and the volume of usage increases. Resulting in higher amounts of plastic waste as well so the use of recycled plastic or Recycling has received a lot of attention because in addition to reducing the amount of plastic waste, it is also a cost-effective resource. Technological developments over the past several years have made plastic recycling possible in many ways, divided into 4 main categories: Primary recycling, secondary recycling, Tertiary recycling and Quaternary recycling.
1. Primary recycling
Is the use of bottles or plastic debris of the same type and without contamination That occurs in the production process or forming a reuse within the factory Which can be reused all or added to mix with new granules at various ratios
2. Secondary recycling
Secondary recycling or re-melting process Is the use of plastic that has been used to clean, grind, melt and mold back into plastic products again This secondary recycling can also be subdivided into several techniques:
- Mechanical recycling
Is the simplest and most popular technique today By storing used plastic and sorting by type And paint to be washed before being grinded into small pieces And melted into second grade plastic granules or recycled plastic pellets to be used as raw materials for the production of new products or mixed with new granules to obtain the desired properties before being processed.The quality of this recycled plastic will determine the use and quantity of the desired mix. The problem in the plastic recycling process is that after each recycling process, the plastic will be of lower quality. The reaction of the lack of molecular chains of Making it impossible to use for maximum benefit And the price is getting cheaper.Sometimes not worth the investment The main reason is due to the contamination of dirt, small labels or glue fragments, resulting in the recycled plastic granules being darker or with reduced clarity. And the heat used in melting plastics is also an important factor causing decay Or the lack of a molecular chain of plastic polymers Causing the recycled plastic beads to have yellow color And with reduced mechanical properties.
- Chemical modification
Because recycled plastic pellets have limitations in properties Forming and use, therefore, improvements by chemical methods will reduce such restrictions or make recycled pellets look similar to new pellets. This improvement can be applied to either single plastic or mixed plastics. If it is a single plastic, it will be used to add chemicals or use radiation methods. But if it is a mixed plastic, it is often used as a compounding agent, commonly known as Compatibilizer.
- Coextrusion and Coinjection moulding
Is another technique of secondary recycling which is suitable for the production of packaging that requires food contact Plastic products produced from this process will have a layered structure. Like a sandwich Where the surface is a layer made of new plastic which has high tensile strength Good scratch protection and colorful to use The middle layer is a layer of recycled plastic.
3. Tertiary recycling
Tertiary recycling can be divided into 2 types: chemical and thermal recycling.
- Chemical recycling
Is a process that causes the chain structure of the polymer to be broken or broken (Depolymerisation) Monomer or oligomer is a product that is purified by distillation and crystallization, which is a high quality substrate that can be used to produce PET.
- Thermolysis
The structure of PET can be broken or broken by using heat, called thermolysis. Divided into 3 methods, namely, oxygen-free pyrolysis. (Gasification) and hydrogenation (Hydrogenation)
Pyrolysis is a process that causes polymer chains to break off using anaerobic heat. Products obtained from condensation are Liquid called Synthetic crude oil can be used in distilleries and non-condensed parts are used as fuel for heating within the process.
Gasification is a process that causes the chain of polymer to break out by using oxygen-based heat. This process occurs at temperatures higher than Pyrolysis. The result is Syngas, which consists of carbon monoxide and hydrogen. Can be used as a fuel directly But if separated before being used in the form of chemicals, the value will be 2 - 3 times higher
Hydrogenation Is a technique developed from a catalytic refining process The polymer chains of the petals will be broken or broken by heat and exposed to excess hydrogen at over 100 atmospheres until cracking and hydrogenation occur. (Hydrogenation) completely. Products that are mostly liquid fuels such as gasoline or diesel oil.
Thermal recycling process is considered a useful and cost-effective technology than chemical recycling because it can handle mixed plastic waste with other contaminants. Non-plastic While chemical recycling requires relatively high cleanliness of plastics and is mixed or contaminated only slightly Resulting in high cost of raw material preparation However, the plastics that are to be recycled via heat should be screened or removed.
4. Quaternary recycling
Plastic can be burned as a renewable fuel. By burning the plastic, the heat value is close to the coal (23 MJ / kg). It helps to burn the part that is wet. Thus reducing the amount of fuel required to burn waste.
Although today's plastic recycling has not been very popular But was receiving widespread attention Especially during times when we pay attention to the environment and natural resources Recycle recycled plastics is another way to help us maintain the beauty and abundance of natural resources.Which soon we will step into the new century where various technologies and technologies Will be developed more advanced People of the new century may have to change the vision about plastic. When the plastic that has been used in the next century has not become garbage anymore But turned out to be an important resource in producing products for environmental conservation
