by Dr. Fozia Parveen
Sometimes I wonder when I do all the ‘no to plastic because a plastic bag takes 200-1000 years to degrade’ campaigning that what has the humble plastic got to do with all this? It has only been around to help us, completely misused by us. Plastic is not the monster. We are the monsters. There is a plastic monster in each and every one of us that needs to be exorcized. Thus, as a part of our campaign against single use plastic and in celebration of plastic free July, I decided to write a series of blogs for awareness and education on plastic so that it can be refused. This is a basic scientific article on plastic and what all of us should know about it. The blogs to follow will recommend future steps and ways to avoid them. So, here we go!
The first synthetic plastic called celluloid was plant based, made from cellulose. In 1869, John Wesley Hyatt used cellulose nitrate as a substitute for ivory. Celluloid found its use in photographic films, buttons, combs, eye frames etc. Other naturally occurring substance such as horns of animals, shellac, gutta-percha were also used as plastic material.
John Rex Whinfield invented a new polymer in 1941 when he condensed ethylene glycol with terephthalic acid. The condensate was polyethylene terephthalate (PET or PETE).
It was in 1951, that two chemists at Phillips Petroleum Company in Bartlesville discovered polypropylene and polyethylene and revolutionised the world of plastic as we know it today. This great discovery although inexpensive has cost a great deal to our environments as the environment has evolved to deal with this discovery. It has therefore resulted in a large amount of solid waste dominated by plastic that will take thousands of years to degrade. The road from petroleum to plastic is as follows:
Petroleum drilling –> Crude oil and natural gas refining to petrochemicals, fuel, ethane and propane etc –> Ethane and propane are cracked into ethylene and propylene at high temperature –> Catalysts are combined with them to form fluff (polymer) –> Fluff is combined with additives –> Polymer is melted in an extruder –> Melted plastic is turned into small pellets by a pelletizer –> Pellets are shipped and converted into desired products using various processes (see Annexe I for the processes)
Nearly all the plastic around us is now synthetic and made from polymers, as presented already. There are different types of plastics (Figure 2)
Polyethylene terephthalate (PET or PETE)
PET has good gas and moisture barrier, high heat resistance, is clear, hard, tough and solvent resistant, Items made from PET are mostly recycled.PET(E) plastic is used to make many common household items like mineral water, beverage bottles, medicine jars, rope, clothing and carpet fibre etc
High Density Polyethylene (HDPE)
HDPE has Excellent moisture barrier properties, excellent chemical resistance, hard to semi-flexible and strong Soft waxy surface, permeable to gas, HDPE films crinkle to the touch ,pigmented bottles and stress resistant. High-Density Polyethylene products are very safe and are not known to transmit any chemicals into foods or drinks. HDPE products are commonly recycled. Items made from this plastic include containers for milk, motor oil, shampoos and conditioners, soap bottles, detergents, toys, buckets, rigid pipes, plant pots, plastic furnitures and bleaches. It is NEVER safe to reuse an HDPE bottle as a food or drink container if it didn’t originally contain food or drink.
PVC has excellent transparency, is hard, rigid (flexible when plasticised), has good chemical resistance, long term stability, good weathering ability, stable electrical properties, low gas permeability. Polyvinyl Chloride is sometimes recycled. PVC is used for all kinds of pipes and tiles, but is most commonly found in plumbing pipes. Credit cards, carpet backing and other floor covering, window and door frame and synthetic leather products. This kind of plastic should not come in contact with food items as it can be harmful if ingested.
Low Density Polyethylene (LDPE)
LDPE is tough hand flexible, waxy surface, soft – scratches easily, good transparency, low melting point, stable electrical properties, good moisture barrier properties. Low-Density Polyethylene is sometimes recycled. It tends to be both durable and flexible. Items such as cling-film, sandwich bags, squeezable bottles, irrigation pipes, thick shopping bags, wire and cable application, and plastic grocery bags are made from LDPE.
PP has excellent chemical resistance, high melting point, hard but flexible, waxy surface, translucent, strong. Polypropylene is occasionally recycled. PP is strong and can usually withstand higher temperatures. It is used to make lunch boxes, margarine containers, ketchup and syrup bottles, potato crisp bags, biscuit wrappers, drinking straws, hinged lunch boxes, yogurt pots, syrup bottles, prescription bottles. Plastic bottle caps are often made from PP.
PS has clear to opaque glassy surface rigid or foamed hard, brittle, high clarity, affected by fats and solvents. Polystyrene is commonly recycled, but is difficult to do. Items such as disposable coffee cups, plastic food boxes, plastic cutlery, egg boxes, coat hangers, fast food trays, and packing foam are made from PS.
There are other polymers that have a wide range of uses, particularly in engineering sectors. They are identified with the number 7 and OTHER (or a triangle with numbers from 7 to 19). e.g. Nylon (PA), Acrylonitrile butadiene styrene (ABS), Polycarbonate (PC), Layered or multi-material mixed polymer.
Code 7 is used to designate miscellaneous types of plastic not defined by the other six codes. Polycarbonate and Polylactideare included in this category. These types of plastics are difficult to recycle. Polycarbonate (PC) is used in baby bottles, compact discs, and medical storage containers.
note: A number of additives are added to plastic and they include colorants, foaming agents, antioxidant, lubricants, flame retardants, anti microbials, plastisizers, etc to achieve the desired quality in the final products
The more you learn about plastic the more complicated it gets but perhaps to unlearn our plastic use habit we need to know all of this..
Talk to you soon
Meanwhile refuse all plastic you can
and don’t forget to spread love and not plastic pollution
Injection Molding: The plastic compound, heated to a semifluid state, is squirted into a mold under great pressure and hardens quickly. The mold then opens and the part is released. Suited for mass production such as bottle caps and toys etc
Extrusion Molding: Most widely used. A heated plastic compound is forced continuously through a forming die made in the desired shape (like squeezing toothpaste from a tube, it produces a long, usually narrow, continuous product). The formed plastic cools under blown air or in a water bath and hardens on a moving belt. Rods, tubes, pipes, and sheet and thin film (such as food wraps) are extruded then coiled or cut to desired lengths.
Blow Molding: pressure is used to form hollow objects, such as the soda pop bottle or two-gallon milk bottle, in a direct or indirect method. In the direct blow-molding method, a partially shaped, heated plastic form is inserted into a mold. Air is blown into the form, forcing it to expand to the shape of the mold. In the indirect method, a plastic sheet or special shape is heated then clamped between a die and a cover. Air is forced between the plastic and the cover and presses the material into the shape of the die.