How Plastic Bags Are Manufactured

Plastic Bag Making Machine

Plastic Bag Making Machine

Carbon has the incredible ability of forming long chains with different elements and it’s this ability which is responsible for the creation of plastic. The hydrocarbon, ethylene (C2H4), is a by-product of processing coal, oil and gas, and consists of four hydrogen atoms bonded to a carbon-carbon double bond. This simple molecule, or monomer, can join with many other hydrocarbon monomers to create a polymer.

By varying the amount of ethylene monomers, different types of plastic can be created to produce a variety of products, three types of which are used for producing plastic bags:

  • DPE – lower-density polyethylene
  • LLDPE – linear low-density polyethylene
  • HDPE – high-density polyethylene

LDPE is rarely recyclable but it is actually cheaper to make new LDPE than to recycle it. HDPE is usually recycled.

By introducing high temperature, high pressure and sometimes a catalyst, monomers in gases can be separated from each other (“cracking”).

Separated ethylene monomers are then chemically bonded to each other to form the polymer, polyethylene. The polyethylene is cast into small capsules and shipped to a plastic bag manufacturer who will heat and melt the polyethylene capsules and then blow the plastic (blown film extrusion) into the correct size and shape, similar to how children would blow bubbles.

Pigment is added at this stage if necessary and then the plastic is passed through cooling towers to solidify.

When solid and cool, large rollers will flatten the plastic which is subsequently cut, folded and sealed to form a plastic bag and if necessary, sent to other machines to be printed on or to have fastenings added. Once finished, the plastic bags are packaged and shipped.

Did You Know?

  • An estimated 500 billion to 1 trillion plastic bags are manufactured every year.
  • Plastic bags have been around since the 1950’s but the modern, lightweight shopping bag was created by Swedish inventor, Sten Gustaf Thulin for the packaging company, Celloplast, in the 1960’s.
  • Biodegradable bags can be manufactured from corn or potato starch but they aren’t as resilient to wet weather as the plastic bag.
  • Ethylene gas is actually a natural plant hormone which stimulates fruit ripening, something of which the Egyptians were well aware of. They would gas figs to help ripen them! Ethylene also has an adverse effect on vegetables (e.g. yellowing of broccoli) and plants. In 1864, gas leaks from street lights stunted plant growth, twisted plants and abnormally thickened stems.

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