The term “plastics” is used to describe a wide variety of resins or polymers with different characteristics and uses. Polymers are long chains of molecules, a group of many units, taking its name from the Greek “poly” (meaning “many”) and “meros” (meaning “parts” or “units”).
The term “polymer” is often used as a synonym for plastic, but many other types of molecules — biological and inorganic — are also polymeric. While all plastics are polymers, not all polymers are plastic. Polymers are rarely useful in themselves and are most often modified or compounded with additives (including colours) to form useful materials. The compounded product is generally termed a plastic. Most people have little contact with "polymers" because most articles that they come across are actually modified and coloured and therefore are actually plastics. Polymers can be classified in many ways, based on how they are developed and perform. For this discussion of recycling, an understanding of two basic types of polymers is helpful:
• Thermoplastic polymers can be heated and formed, then heated and formed again and again. The shape of the polymer molecules are generally linear or slightly branched. This means that the molecules can flow under pressure when heated above their melting point.
• Thermoset polymers undergo a chemical change when they are heated, creating a three-dimensional network. After they are heated and formed, these molecules cannot be re-heated and re-formed.
PETE Polyethylene Terephthalate (PET) - Soda & water containers, some waterproof packaging. Recycling PET is similar to the polyethylenes (PE). Bottles may be color sorted and are ground up and washed. Unlike polyethylene, PET sinks in the wash water while the plastic caps and labels are floated off. The clean flake is dried and often repelletized.
HDPE High-Density Polyethylene - Milk, detergent & oil bottles, Toys and plastic bags. HDPE is called natural since that is it's natural color, and it is the most valuable because it can be made into any color when it is recycled. Other products are often packed in brightly colored bottles whiched are mixed together at recycling plants into mixed color or rainbow bales. Most of this material is later dyed black after it is processed.
/Polyvinyl Chloride (PVC) - Food wrap, vegetable oil bottles, blister packages.
LDPE Low-Density Polyethylene - Many plastic bags. Shrink wrap, garment bags. It ic chemically similar to HDPE but it is less dense and more flexible. Most polyethylene film is made from LDPE which you often see as plastic bags and grocery sacks. This scrap may be clear or pigmented and it is hand sorted and baled at recycling processing
PP Polypropylene - Refrigerated containers, some bags, most bottle tops, some carpets, some food wrap
Aliphatic-aromatic Copolyesters (AAC)
These copolymers combine the excellent material properties of aromatic polyesters (e.g. PET) and the biodegradability of aliphatic polyesters. They are soft, pliable and have good tactile properties. Melting points are high for a degradable plastic (around 200°C).
Aliphatic polyesters (e.g. PCL)
Aliphatic polyesters are biodegradable but often lack in good thermal and mechanical properties. While, vice versa, aromatic polyesters (like PET) have excellent material properties, but are resistant to microbial attack. Typical aliphatic polyesters include polyhydroxy butyrate, polycaprolactone, polylactic acid and polybutylene succinate. Aliphatic polyesters degrade like starch or cellulose to produce non-humic substances such as CO2 and methane. They can be processed on conventional processing equipment at 140-260 °C, in blown and extruded films, foams, and injection moulded products.
The American Society of Testing and Materials defines biodegradable as "capable of undergoing decomposition into carbon dioxide, methane, water, inorganic compounds, or biomass in which the predominant mechanism is the enzymatic action of microorganisms, that can be measured by standardized tests, in a specified period of time, reflecting available disposal condition." It is important to note that the definition of biodegradation should specify a time limit. If the biodegradation process is sufficient to mineralise organic matter into carbon dioxide or methane respectively, water and biomass, the material can be termed "biodegradable".
REFERENCE LINK :-http://www.environment.gov.au/settlements/publications/waste/degradables/biodegradable/appendixa.html
Compostable is defined as 'capable of undergoing biological decomposition in a compost site as part of an available program, such that the plastic is not visually distinguishable and breaks down to carbon dioxide, water, inorganic compounds, and biomass, at a rate consistent with known compostable materials (e.g. cellulose).' A polymer is "compostable" when it is biodegradable under composting conditions.
A polymer is 'compostable' when it is biodegradable under composting conditions. The polymer must meet the following criteria:
Break down under the action of micro-organisms (bacteria, fungi, algae).
Total mineralisation is obtained (conversion into CO2, H2O, inorganic compounds and biomass under aerobic conditions).
The mineralisation rate is high and is compatible with the composting process.
The degree of degradability of the material shall be measured under controlled composting conditions as per ASTM D 5338-92. Those materials having a degree of biodegradation equivalent to that of cellulose (maximum permissible tolerance of 5%) will be considered to meet the compostability criteria.
Content given by Vipul Chauhan
ontent given by Gopal