Polypropylene bags are bags made from the synthetic plastic polymer polypropylene, a frequently used material in consumer goods and some industrial applications. It is used for bags because it is strong, flexible, and can be made transparent. Polypropylene bags are manufactured for a variety of uses. Polypropylene is used for bags less commonly than polyethylene, another plastic polymer and the most frequently used material for disposable plastic bags and packaging, but is superior to polyethylene for bags that are meant to be reused.
Polypropylene is a polymer, a type of large molecule made from a large number of smaller subunits called monomers. These monomers are chemically linked to each other in a long repeating chain. Polypropylene is made from a chain of monomers consisting of three carbon atoms and six hydrogen atoms. A single polypropylene molecule can contain thousands of these units.
In each individual monomer, one carbon atom and three hydrogen atoms are bonded together in what is called a methyl group, which is then bonded to another carbon atom. In addition to the methyl group, this carbon atom is bonded to another hydrogen atom,, the third carbon atom in the monomer, and one of the carbon atoms of the previous monomer in the chain. The third carbon atom is in turn also bonded to two additional hydrogen atoms and one of the carbon atoms of the next monomer in the chain. The orientation of each unit's methyl group affects the properties of the polymer as a whole, and so two chemically identical polypropylene molecules can have different characteristics.
Polypropylene is good material for bags because it is strong but has a low density and so is very lightweight. It has high resistance to fatigue and cumulative structural damage caused by the stress of repeated increases and decreases in the forces, or load, applied to the bag. Polypropylene is also popular for bags because of its visual qualities. It is translucent in its default state and can be made transparent, so polypropylene is useful for bags that are meant to have their contents visible. Polypropylene bags can also be easily manufactured in different colors by using different pigments.
Polypropylene bags are used for a variety of functions. Sealed, transparent polypropylene bags are often used to package food in order to make the food visible to potential buyers while retaining freshness. Polypropylene is a popular material for reusable bags such as tote bags and reusable shopping bags, as it is sturdy, resistance to fatigue damage over time, and can be readily made with different colors, designs, or graphics. Large woven polypropylene bags are used for bulk storage and shipping.