What are plastics?
Plastics are derived from natural and organic materials. These materials include cellulose, coal, natural gas and salt derived from crude oil. Crude oil is a complex mixture of thousands of compounds and needs to be processed before it can be used. Plastics are in general lightweight with significant degrees of strength. It can be molded, extruded, cast and blown into any shapes and sizes.
How are Plastics Made?
They are simply chains of molecules linked together. These chains are called polymers, and many plastics name begin with “poly,” such as polypropylene, polyethylene, and polystyrene. The production of plastics begins with the distillation of crude oil in a refinery. This step separates the heavy crude into groups of lighter components, called fractions. Each fraction has a mixture of different hydrocarbon chains attached to its own properties, structure, and size.
What are the types of plastic?
7 types of plastic are distinguished and separated based on the chemical makeup and codes allocated to them by international agreement. Below is a table explaining each type of plastic.
|1. Polyethylene Terephthalate (PETE or PET)||The most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, thermoforming for manufacturing, and in combination with glass fibre for engineering resins.|
|2. High-Density Polyethylene (HDPE or PEHD)||Made from petroleum, it has a high strength-to-density ratio. HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber.|
|3. Polyvinyl Chloride (PVC)||PVC is the world's third-most widely produced synthetic plastic polymer, after polyethylene and polypropylene.
The rigid form of PVC is used in construction for pipe and in profile applications such as doors and windows. It is also used in making bottles, non-food packaging, and cards (such as bank or membership cards)
|4. Low-Density Polyethylene (LDPE or PELD)||LDPE is most commonly used in the plastic bag, also found in containers, dispensing bottles, wash bottles, tubing, and various molded laboratory equipment.|
|5. Polypropylene (PP)||Polypropylene is the second-most widely produced commodity plastic. It is often used in packaging and labeling due to high chemical resistance.|
|6. Polystyrene or Styrofoam (PS)||Uses include protective packaging (such as packing peanuts and CD and DVD cases), containers (such as "clam-shells"), lids, bottles, trays, tumblers, disposable cutlery and in the making of models.|
|7. Other||Miscellaneous plastics such as polycarbonate, polylactide, acrylic, acrylonitrile butadiene, styrene, fiberglass, and nylon are often used in medical tools and food storage.|
How are different plastics distinguished?
TOUCH AND SOUND: LDPE feels soft and smooth, like the Zip-lock bag we enjoy storing our stuff in. Additionally, if you rub it together, it will make a soft swishing sound, as opposed to a crinkling, harsher sound.
HDPE feels harder and essentially, more crinkly. Many plastic shopping bags are manufactured from HDPE, and the easiest way to distinguish them from LDPE bags is from the sound they make when you crinkle them in your hands. If the sound is soft and swishing (think of green leaves blowing in the trees), then you have identified LDPE; if the sound is crisper and crinkly (think of dry leaves being squished together), then you have HDPE. The two sounds are quite distinct. PP, also known as polyprop or polypropylene sounds similar to HDPE and are crinkly. PP is generally used for packaging food, such as Ssuper Sack, food wrappers, or the clear packets. It feels much firmer and stiffer. When it is rips and tears, it does not stretch.
BURN: The polyolefins ignite quite readily. Be careful if you are testing this type of plastic because molten plastic can drip and will leave an ugly burn if you make contact with it.
FLAME: A blue flame with a yellow tip would be indicative of the polyolefins and nylon. You might think, well how would you separate these two if their flame is the same? Remember from above, the polyolefins would float and nylon (PA) would sink.
A yellow flame with a green tip on contact shows PVC (Polyvinyl Chloride), yellow with dark smoke could be PET or Poly-carbonate, and yellow with sooty, dark, smoke could be polystyrene or ABS (the plastic housing of your computer monitor).
SMELL: PET smells similar to burnt sugar (the odour reminds the author of eating candy-floss or sugar-candy in his childhood). PVC has an acrid smell like chlorine, so stay away from the smoke and gas given off by PVC. LDPE and HDPE smell like candle wax, while Polypropylene smells similar to candle wax, but with an element of paraffin to it. ABS and polystyrene both smell like styrene, but the ABS also has a faint rubbery smell to it. WARNING: if you have already identified the plastic from other methods and particularly in where you suspect the plastic is PVC, do not smell the smoke. If you must, we advise against it where possible, a small whiff of the smoke will give you further clues as to the plastic identification code under which your suspect can be classified
What are the Pros and Cons of Using Plastic?
- Need less energy to transport and distribute it.
- Can be recycled
- It is resistant to corrosion and chemicals
- It can be colored, melted, shaped, squashed, rolled into sheets or made into fibres
- They make excellent fishing lines, glues and paints.
- Small creatures like bacteria just can't eat them up or break them up, because plastic alone is non-biodegradable
- Often is not recycled
- The elements do not fully break down plastics
- They aren't as strong as metals like steel.
- When thrown on land it makes the soil less fertile.
- When thrown in water, it chokes our ponds, rivers and oceans and harms the sea life.