Plastic Bag Manufacturing

25 Sep 09

It is estimated that nearly 100 billion bags are sold around the world each year, and the vast majority of them are made of plastic. Plastic bags are ubiquitous and ever-present in daily life, so it is important to remember that there is a robust and well-established packaging industry responsible for manufacturing these products. While a plastic bag may appear to be a solid piece, it is actually formed by binding together two symmetrical plastic sheets along three sides.

Click here if you are seeking manufacturers and suppliers of plastic bags.

The materials and processes that packaging manufacturers use to construct plastic bags contribute to their versatility and appeal as containers. They are durable, extremely cost-efficient, lightweight, thin, and—despite some environmental concerns—can be transported and recycled with relatively low energy expenditure. The particular methods and resins used in constructing plastic bags result in these attributes.

Plastic Bag Materials

Most plastic bags are fabricated from polyethylene, a thermoplastic produced in large quantities and with widespread uses. Polyethylene is an ethene polymer composed of multiple carbon-hydrogen bonds. It can deteriorate under elevated temperatures or from exposure to certain solvents, but generally has strong chemical resistance. The average melting point for consumer-grade polyethylene usually falls between 100 and 120 degrees Celcius. This material is also categorized under various grades, depending on density. Plastic bags may be fabricated from low density polyethylene (LDPE), which has an approximate density range of 0.916 to 0.925 grams per cubic centimeter, or high density polyethylene (HDLE), with a range of 0.941 to 0.965 g/cm3. Some other materials that can be used for producing plastic bags include:

• Polypropylene: Like polyethylene, polypropylene is a thermoplastic polymer that can be used for making clear plastic material. It is composed of propylene gas that has been polymerized under reduced pressure and low temperature, and is also a component in the production of lightweight ropes, waterproof membranes, and lining for clothes.
• Polyvinyl chloride: Some plastic bags are made with polyvinyl chloride, more commonly known as PVC. This is another thermoplastic material created by polymerized vinyl chloride gas. With the addition of softening additives, PVC can be used to produce packaging or wires, while in its more rigid form it can be fabricated into pipes, signs, construction materials, and flooring.
• Ethylene vinyl acetate: This is a polymer that displays several elastomeric properties, but can be processed much like other thermoplastic materials. Ethylene vinyl acetate is commonly mixed with low density polyethylene to create plastic bags with improved stress and temperature resistance.

Plastic Bag Production

Extrusion is one of the common methods for fabricating polyethylene into plastic bags, while polyethylene itself is manufactured from processes that depend on crude oil and natural gas. Blown film extrusion involves melting the plastic resin into a pliable state and then extruding it into a die. This die differs from the standard extrusion die in that it is cylinder-shaped and has a small circular opening with an air ring attached to the top.

As the plastic resin is extruded, it forms a thin tube while air enters through the opening in the die and causes the tube to expand into a bubble. The air ring blows onto the plastic’s surface to cool it and the tube is moved upward by a pair of nip rollers. The speed at which these rollers move the plastic can determine the final product’s thickness. The nip rollers also flatten the plastic into a double-layered film with a width roughly half that of the bubble’s earlier circumference. This flattened film can then be cut into sheets or rolled up. To produce the bags, plastic sheets are sealed together across their width, which can be performed as part of the blown film extrusion process or at a later assembly stage.

Alternate Plastic Bag Applications

Aside from their traditional application as containers, plastic bags can also be used for a broad range of other purposes. For example, they can be used to line trash cans, as freezer bags, to shield wiper blades from frost, as anti-static bags, mailing bags, or for waterproofing clothing and other vulnerable goods.

The ubiquitous presence and inexpensiveness of plastic bags makes them quite convenient for many simple storage and packaging needs.

Click here if you are seeking manufacturers and suppliers of plastic bags.