The term poly bag can refer to any bag made out of plastic, though it typically references polyethylene bags. Polyethylene (PE), also referred to as polythene, is one of the most frequently-used plastics in modern manufacturing. Although PE is used across industries, one of its primary functions is as an affordable and reliable packaging material. In this context, PE is used to create bags with varying weight-bearing capacities. PE’s hydrocarbon molecular structure gives poly bags the ideal combination of flexibility, tensile strength, and puncture resistance to protect contents of all shapes and sizes.
If you’re looking for a versatile and cost-effective bag for your packaging applications, this guide will help you determine exactly what poly bag suits your requirements.
- Poly Bag Materials
- Poly Bag Types: Flat or Gusseted?
- What Size Poly Bag Do You Need?
- Common Applications
- Custom Printed Poly Bags at Universal Plastic
Selecting the Best Poly Bag for Your Application
Poly bags of different shapes and materials are not always interchangeable. One poly bag may be large and dense, designed to hold concrete fill, while another is so light that it can be torn by hand. To accommodate diverse packaging needs, Universal Plastics offers LDPE or LLDPE poly bags in flat and gusseted designs. It’s important to consider the optimal material and bag shape in advance to get the desired results. Here, we discuss these variables to help you identify the proper fit for your application.
Poly Bag Materials
Poly bags vary dramatically in their physical properties and potential use cases. These distinctions arise from the different forms of PE, which vary at a molecular level in both density and configuration.
At its most basic, PE is a strand of linked ethylene hydrocarbons, which may be highly linear, highly branched, or somewhere in between. The degree of branching determines the density of the plastic as well as its performance characteristics. If the hydrocarbon chains are mostly linear, they tend to pack tightly together, which generates strong intermolecular forces that increase the material’s strength. By contrast, branches interfere with the molecules’ ability to pack together, so heavily-branched polymers tend to form lower-density PEs. In these plastics, the intermolecular forces pulling the chains together are weaker because of the additional distance between the atoms.
These chemical processes give rise to several primary varieties of PE:
- High-density polyethylene (HDPE). HDPE is the most linear ethylene polymer, sometimes having just a single ethyl branch per 100 molecule chains. As a result, HDPE is the densest and strongest version of PE, typically used to create pipes and other solid components. However, HDPE can also form stiff, moisture-resistant poly bags for delicate or heavy materials.
- Low-density polyethylene (LDPE). On the opposite end of the spectrum is LDPE, which comprises branching chains of various lengths. The loose molecular structure of LDPE creates a ductile plastic ideal for crafting film wraps and grocery bags. The primary disadvantage of LDPE is its low tensile strength, which decreases durability and makes LDPE bags prone to stretching or tearing.
- Linear low-density polyethylene (LLDPE). LLDPE is only slightly denser than LDPE, but it is composed of molecules with shorter branches, allowing for a more uniform linear structure. As a result, LLDPE is more durable and offers better tensile strength than other varieties.
The best material for an application depends on the product to be packed:
- HDPE. Stiff and durable HDPE is typically used to package fertilizer, cement, and bulky industrial components. It may also be used for bulk quantities of grain, animal feed, or similar products.
- LLDPE. LLDPE bags are available in light to heavy gauges and are ideal for packaging foods, consumer goods, and lightweight industrial products.
- LDPE. At the lightest gauges, LDPE bags are best for single-use produce and grocery bags. Stiffer variants can form a wider array of flat and gusseted poly bags, including FDA-compliant, food-safe varieties.
Universal Plastics specializes in LDPE and LLDPE poly bags suitable for products ranging from grapes to gravel.