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Know Your Plastic – Polyethylene

Updated on July 5, 2016

Polyethylene Structure

Source

Polyethylene (PE) is industrial grade thermoplastics. Various industrial studies concluded that annual global production is 80 million tons, and consumption rates exceed more than 50 billion pounds. PE is a chemically resistant material used in a variety of applications. Some of the well-known applications include plastic wraps, grocery bags, medical devices, bulletproof vests, and drain pipes. Let’s see what works in the favor of this plastic.


Properties
Polyethylene exhibits following types of properties.

  • Mechanical: Low strength, rigidity, and hardness, high impact strength, high melting point, high fatigue resistance, and high ductility.
  • Chemical: Excellent chemical resistance, low water, and gas vapor permeability, and can be customized without pretreatment.
  • Electrical: Polypropylene offers high electrical resistance, and is used in various electronic components. It provides high tracking resistance as well.
  • Toxicity: This plastic is not toxic in solid form, but it can be toxic in liquid or vapor form.
  • Translucent Hue: This is a translucent thermoplastic, which is why it is used in applications or products, where transparency is required.


Types of Polyethylene

Following are the main types of polyethylene used in several applications. This classification is made on the basis of its branching structure, and density.

  • High-density Polyethylene (HDPE): This plastic polymer has a density range from 0.93 to 0.97 g/cm3, or 970 kg/m3. It has little branching (lower carbon rate than LDPE), which contributes to its strong intermolecular forces, and high tensile strength. It is used in applications such as food storage containers, 3-D printer filaments, arena boards, backpacking frames, bottle caps, etc.
  • Low-density Polyethylene (LDPE): This plastic material has a density range from 0.910 to 0.940 g/cm3. It has 2% more carbon than HDPE, so it has weak intermolecular forces, low tensile strength, and high resilience. It is used to produce various daily use items. Some of the common applications include dispensing bottles, containers, tubing, wash bottles, plastic bags for computer components, juice and milk cartons, and laboratory equipment.
  • Linear Low-density Polyethylene (LLPDE): It has a similar branching to LDPE, however its chemical properties can be altered by adjusting constituents. Some of the common applications include plastic wraps, stretch wraps, toys, pipes, buckets, and pouches.


Consumer Products Made from Polypropylene

The versatility of polypropylene makes it a choice for various everyday consumer products. Below given are some of examples of consumer products made from this plastic.

  • Carpets: PP is a colorfast material, which is why it is used in all forms of carpets, upholstery, and area rugs. The colorfast property ensures that colors will stay bright and fresh during the service life of a product.
  • Ropes: This plastic is used to make ropes because it is lightweight. These ropes look similar to polyester ropes, but they can easily float on water.
  • Bottles and Caps: PP is a fatigue resistant material, and is used to produce bottles, spouts, and bottle caps. The bottles produced from this plastic are widely used for packaging different types of products including detergents, toiletries, mineral water, etc. Thin-walled PP yoghurt containers are a common sight in supermarket shelves.
  • Garden and Patio Furniture: Polypropylene garden and patio furniture are well-known for their recyclability, durability, and affordability.
  • Stationary and Storage Boxes: PP sheets are used for making stationary folders and storage boxes. Its durability, colorfast property, resistance to dirt, and affordability makes it an ideal material for protective coverings for a paper, envelope window, etc.
  • Non-Woven Bags: Non-woven polypropylene plastic bags are very popular, and used for branding purposes. These bags are made from eco-friendly, non-woven polypropylene fibers. These bags are handed out at supermarkets, jewelry stores, gift shops, and more.



Industrial Applications of Polypropylene

The following applications indicate the popularity of this thermoplastic for industrial applications.


  • Building Foundations: Polypropylene fibers are added to the concrete mixture for building foundations in earthquake prone areas. These fibers help reduce spalling and cracking incidents.
  • Electric Cables: This plastic is considered a safe alternative to PVC insulation, and is used in LSZH (Low Smoke Zero Halogen) cables. These cables are used in a variety of low-ventilation environments because it does not produce toxic halogens, or smoke.
  • Medical: The mesh medical kits made from this plastic are used in many pelvic organ operations. Non-absorbable surgical sutures made from crystalline polypropylene are considered perfect alternatives to nylon sutures.
  • Automotive Parts: This plastic can be easily molded into desirable shapes using injection molding. Thus, it is used for a variety of automotive applications, including cladding, bumpers, and exterior trim.
  • BOPP Sheets: BOPP sheets (Biaxially Oriented Polypropylene Films) are ideal replacements for cellophane tapes, aluminum foils, and waxed paper. Today, BOPP sheets are used for packaging snacks, confectionery products, etc.

Interesting Facts about Polypropylene

Following are few interesting and less known facts about this plastic.

  • The plastic has number 5 resin identification code.
  • PP is a low cost, and durable material with a wide range of mechanical properties, which accounts for its vast use in automotive applications.
  • Polypropylene produces less solid waste than other plastic materials.
  • Polypropylene applications can be easily recycled and converted into applications such as paint cans, battery cases, flower pots, home storage, crates, pallets, etc.
  • PP and HDPE produces less CO2 than PVC, PS, and PET.
  • Unlike many other plastics, this material does not absorb water.
  • The plastic is not affected by weather elements, or molds.
  • The new PP varieties are elastic, and have a durable, but rubbery composition. Thus, advanced PP plastics are used in various challenging applications.
  • Polypropylene structures were used to reconstruct La Laguna Cathedral at Tenerife Spain between 2002 and 2014.
  • Many fashion designers use PP to produce recyclable jewelry, and other wearable items.
  • When used to make sanitary products, PP is treated to be hydrophilic.
  • Polypropylene fibers are used to prepare undergarments and long-sleeve shirts because they can retain body odors.


Methods of Joining Polyethylene Parts

Generally, polyethylene parts are joined by any of the following methods.

  • Fastening
  • Heat Sealing
  • Heat Fusion
  • Infrared Welding
  • Hot Gas Welding
  • Laser Welding

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