Classification of plastics, types of recycling

What are they?

Plastics are materials formed by the union of great molecular chains called polymers, which are formed by smaller molecules called monomers.

Plastics are produced through a chemical process called polymerization, which causes the chemical union of monomers to form polymers.

Polymers may be either natural or synthetic. Natural polymers, such as cotton, wood, hair, ox horn, latex, among others, are commonly found in plants and animals. Synthetic polymers, such as plastics, are obtained by man through chemical reactions.

The polymer molecule size and structure determine the plastic material properties.

Raw Material

The raw material for plastics is oil. Oil is formed by a complex compound mixture. As such compounds have different boiling temperatures, it is possible to sort them through a process known as distillation or cracking.

The naphtha fraction is provided to petrochemical plants, where it undergoes several processes and originates the main monomers, as for instance, ethene.

Polymer Classification


Thermoplastics
Thermoplastics are plastics that have their chemical structure changed during heating and that can be molded once again after cooled. Examples: Polypropylene (PP), High-density polyethylene (LDPE), Low-density polyethylene (HDPE), Polyethylene terephthalate (PET), Polystyrene (PS), Polyvinyl chloride (PVC), etc.

Plastic waste classification


Post-industrial: Post-industrial plastic waste mainly originates from scraps from production and transformation processes, shavings, burrs, etc.

Post-consumption: Post-consumption plastics are those disposed by consumers. Most of them consist of packaging.

Uses and Benefits


Utilizados em quase todos os setores da economia, tais como: construção civil, agrícola, de calçados, móveis, alimentos, têxtil, lazer, telecomunicações, eletroeletrônicos, automobilísticos, médico-hospitalar e distribuição de energia.

They are used in almost every economy sector, such as: Construction, agriculture, shoemaking, food, textile industry, entertainment, telecommunications, electronics, automobiles, hospitals, and energy distribution.

Plastics are present in a great variety of products. One example is the geosynthetics, which become increasingly important in draining, erosion control, landfill soil reinforcement, industrial tanks, among other uses.

The food and drink packaging industry is increasingly using plastics due to their excellent characteristics, such as: Transparency, resistance, lightness and atoxicity.

What are they

Polyethylene terephthalate — PET

• Products: flasks and bottles for food and hospital use, cosmetics, microwave trays, films for audio and video, textile fibers, etc
• Benefits: transparent, unbreakable, impermeable, light.

High-density polyethylene - HDPE

• Products: detergent and automotive oil packaging, shopping bags, cellarets, caps, paint cans, pots, home appliances, etc.
• Benefits: unbreakable, resistant to low temperatures, light, impermeable, rigid and chemical resistant

Polyvinyl Chloride - PVC

• Products: mineral water bottles and packaging for edible oils, mayonnaise, and eggs. Profiles for windows, water pipes and sewer, hoses, packaging for medicines, toys, blood bags, hospital supplies, etc. • Benefits: rigid, transparent, impermeable, temperature-resistant and unbreakable.

Low-density polyethylene - LDPE
 

Linear low-density polyethylene - LLDPE

• Products: shopping bags, films to pack milk and other food, industrial bags, films for disposable diapers, medical serum bags, garbage bags, etc.
• Benefits: flexible, light, transparent and impermeable.

Polypropylene - PP

• Products: films for packaging and food, industrial packaging, ropes, hot water pipes, wires and cables, flasks, drink boxes, auto parts, carpet and household utility fibers, pots, diapers, disposable syringes, etc.
• Benefits: aroma retaining, unbreakable, transparent, shiny, rigid, temperature-resistant.

Polystyrene - PS

• Products: pots for yoghurt, ice-cream, candy, flasks, supermarket trays, refrigerators (internal part of the door),
dishes, caps, disposable razors, toys, etc.
• Benefits: impermeable, unbreakable, rigid, transparent, light and shiny.

Others this group comprises, among others, the following plastics: ABS/SAN, EVA and PA.
• Products: soles, auto parts, slippers, tires, sporting and nautical accessories, special and engineering plastics, CDs, home appliances, bodies of computers, etc.
• Benefits: flexible, light, abrasion resistant, possibility of differentiated design

Advantages of using Plastics

• Lower energy consumption during production
• Reduced garbage weight.
• Lower collection and final disposal costs.
• Low handling risks.
• In addition to be convenient, they are completely recyclable

Factors that encourage Recycling

• Reduced volume of garbage to be transported: treatment and disposal.
• Increased life cycle of waste disposal facilities

Plastic Recycling

Brazilian garbage contains about 5-10% plastics, depending on the location. Such materials, as glass for instance, occupy a considerable environmental space. They should ideally be recovered and recycled. Plastics are byproducts of oil, which is an imported product (60% of total in Brazil). Plastic recycling requires approximately 10% of energy used for the primary process.

Of total plastics produced in Brazil, only 15% is recycled. One of the major obstacles is the great variety of plastic types. An alternative to this would be to define a specific type of plastic to be collected.

Recyclable plastics are: all types of pots, grocery bags, food packaging, bowls, containers and household items, pipes and PET bottles (which when converted into granules is used in rope production), sewing threads, broom and brush bristles.

Non-recyclable plastics are: pot handles, radio buttons, dishes, pens, imitation jewelry, foam, vacuum packaging, and disposable diapers.

The manufacture of recycled plastic saves 70% energy when taking into account the whole process, from the exploration of primary raw material to the finished product. Moreover, the wasted product, if left in the environment, could be causing more pollution. This may be regarded as an alternative for the supplying market oscillations and also as the preservation of natural resources, which may reduce raw material costs. Recycled plastic has endless applications, as in the traditional virgin resin markets as well as in new markets.

Recycled plastic may be used in the production of: bottles and flasks, except for the food and pharmaceutical industry; buckets, hangers, combs and other products manufactured using the injection process;“plastic wood”, bristles, brooms, brushes and other products manufactured using fibers; bags and other types of films; panels for construction.

Plastic Recycling Processes

Chemical Recycling

Plastics are reprocessed by chemical recycling, becoming basic petrochemicals to be used as raw material in refineries or petrochemical plants. Chemical recycling is aimed at recovering individual chemical components, enabling them to be reused as chemical products or to produce new plastics.

The newly-developed chemical recycling processes enable recycling mixtures of different plastics, accepting a certain degree of contaminants including inks and papers, among other materials.

The main chemical recycling processes are the following:
• Hydrogenation: The chains are broken as a result of the hydrogen and heat treatment, thus generating products that can be processed in refineries.
• Gasification: In this process, plastics are air or oxygen-heated, generating synthesis gas containing carbon monoxide and hydrogen.
• Chemolysis: It is the partial or total breakdown of plastics into monomers in the presence of Glycol/Methanol and water.
• Pirólise: It is the breakdown of molecules by heat in the absence of oxygen. This process generates fractions of hydrocarbons that can be processed in refineries.

Mechanical Recycling

The mechanical recycling process consists in the conversion of post-industrial or post-consumption plastic waste into granules to be reused in the production of other products such as garbage bags, soles, floors, conduits, hoses, auto parts, fibers, non-food packaging, among others.

This process comprises the following steps:

• Sorting: the different types of plastic are sorted in a shuttle conveyor, according to their respective identification or visual aspect. Labels from different materials, bottle caps and products composed of more than one type of plastic, metal packaging, clamps, among other products, are sorted in this stage.
As it is usually a manual step, the efficiency directly depends on the qualification of people performing this task. Another quality determining factor is the source of the material to be sorted. Those originating from selective collection are cleaner when compared to those originating from dumps and landfills.
• Grinding: After the different types of plastic are sorted, they are ground and fragmented into small parts.
• Washing: The ground plastic is then rinsed with water in order to remove contaminants. The rinse water must be treated in order to be reused or emitted as effluent.
• Agglutination: In addition to be completely dry, the material is compacted, thus reducing the volume to be sent to the extruder. The attrition of fragments against the rotating equipment wall increases the temperature, leading to the formation of a plastic mass. The binder is also used to incorporate addictives, such as loads, pigments and lubricants.
Extrusion: The extruder melts the plastic mass and makes it homogeneous. By the extruder output there is a header, which releases a continuous “spaghetti” that is cooled with water. Then, the “spaghetti” is perforated in a granulator, thus becoming pellets (plastic grains).

Energetic Recycling

Energetic recycling is the process to recover the energy contained in plastics through thermal processes.

The energetic recycling process differs from incineration as it uses plastic waste as fuel to generate electric energy. On the other hand, incineration does not take advantage from the materials' energy. The energy contained in 1kg plastic equals to that contained in 1kg oil-fuel. In addition to the economy and energy recovery, recycling also reduces from 70 to 90% the material mass, resulting in an inert, sterilized residue./p>

Plastic and Electricity Generation

• The use of plastics is essential, since it increases the efficiency of municipal waste incineration.
• Heat can be recovered in a boiler, which uses vapor to generate electricity and/or heating.
• In Europe, full-scale tests pointed out good technical, economic, and environmental results of plastic waste combustion by using charcoal, peat and wood.
• The burning of plastics in energetic recycling processes reduces the use of fuels (economy of natural resources).
• Energetic recycling is performed in several European countries, USA and Japan, using high-technology equipment with rigidly secure emission controls that prevent health and environmental risks.

Source: http://ambientes.ambientebrasil.com.br/residuos/reciclagem/reciclagem_de_plastico.htm