Big bags, as crucial packaging tools in modern logistics and transportation, play an indispensable role in the movement of goods. These bags are primarily made from two types of materials: polypropylene and polyethylene.

Polypropylene (PP) is a thermoplastic resin derived from the polymerization of propylene. This translucent, odorless polymer with high crystallinity has a density of only 0.90 to 0.91g/cm³, making it one of the lightest plastics available. PP exhibits excellent heat resistance and can withstand sterilization temperatures exceeding 100 degrees Celsius without deformation, even up to 150 degrees Celsius without external force. While it boasts good formability, PP also has a significant shrinkage rate, making thick-walled products prone to sagging and challenging the production of parts with high dimensional accuracy. Nevertheless, PP offers a glossy surface finish and exceptional stability in water, with an absorption rate of only one-thousandth.

Another commonly used material is polyethylene (PE), a thermoplastic resin typically produced through the polymerization of ethylene. PE shares similar characteristics with PP in terms of being odorless and non-toxic, with a wax-like texture. It exhibits outstanding low-temperature resistance, with a minimum service temperature ranging from -100 to -70 degrees Celsius. Among its variants, high-density polyethylene (HDPE), often referred to as low-pressure polyethylene, surpasses low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) in temperature resistance, oil resistance, steam permeability, and resistance to environmental stress cracking. Additionally, HDPE demonstrates excellent electrical insulation, impact resistance, and cold resistance.

In the manufacturing process of big bags, raw materials in the form of particles or powders of PP or PE are typically purchased and then heated, mixed, and drawn into filaments before being cut into the desired yarns. Subsequently, circular looms are used to weave these yarns into base fabrics of various specifications for future use. For custom-made bags, these woven base fabrics are cut and sewn into bags of different sizes. While most big bags are made from polypropylene, some manufacturers apply a layer of low-density polyethylene film on the outer surface of the bags for waterproofing purposes.

In summary, the basic materials of big bags consist of polypropylene and polyethylene, with the addition of other auxiliary materials during production to meet specific usage and environmental requirements.