7 Need-to-Know Polypropylene Material Properties

January 16, 2020 | Coatings for Baskets & Racks


Custom wire baskets are frequently outfitted with different polymers to improve the basket’s structural durability or to better hold and protect delicate parts. Finding the right polymer for your steel wire basket coating is determined by your process. One of the more popular polymers used for basket coatings, polypropylene, has distinct properties that may make it ideal for your needs.

What Is Polypropylene Material?

Polypropylene is a material that is frequently compared to PVC (polyvinyl chloride). While not as frequently used as PVC, polypropylene is still a useful material for coating custom wire baskets. 

A rigid, crystalline thermoplastic, polypropylene is produced from propene or propylene monomer. It’s one of the cheapest plastics available today and is used in applications both as a plastic and a fiber in industries such as automotive manufacturing, furniture assembly, and the aerospace sector.  

What Is Polypropylene Used For?

Due to polypropylene structure’s rigidity and relative cheapness, it’s used in various applications. It has good chemical resistance and weldability, which makes it ideal for the automotive industry, consumer goods, furniture market, and industrial applications such as custom wire baskets.

Some common uses of polypropylene include:

  • Packaging Applications: Polypropylene’s structure and strength make it a cheap and ideal packing application.

  • Consumer Goods: Polypropylene is used for many consumer goods—including translucent parts, housewares, furniture, appliances, luggage, toys and more.
  • Automotive Applications: Polypropylene is widely used in automotive parts because of its low cost, weldability, and mechanical properties. It can mostly be found in battery cases and trays, bumpers, fender liners, interior trim, instrumental panels and door trims.

  • Fibers and Fabrics: Polypropylene is utilized in a host of fiber and fabrics applications including raffia/slit-film, tape, strapping, bulk continuous filament, staple fibers, spun bond, and continuous filament.

  • Medical Applications: Due to polypropylene’s chemical and bacterial resistance, it is used for medical applications including medical vials, diagnostic devices, petri dishes, intravenous bottles, specimen bottles, food trays, pans, pill containers, and disposable syringes.
  • Industrial Applications: The high tensile strength of polypropylene’s structure, combined with its resistance to high temperatures anc chemicals, makes it ideal for chemical tanks, sheets, pipes, and Returnable Transport Packaging (RTP).

What Are the Properties of Polypropylene?

Some of the polypropylene structure and material properties that you should know when choosing a coating for your custom wire basket include:

  • Chemical Resistance. Polypropylene is generally noted as having a high resistance to chemicals compared to polyethylene (“regular” plastic). Polypropylene will resist many organic solvents, acids, and alkalines. However, the material is susceptible to attack from oxidizing acids, chlorinated hydrocarbons, and aromatics.

  • Tensile Strength. Compared to many materials, polypropylene’s structure has a good tensile strength—somewhere around 4,800 psi. This allows the material to withstand fairly heavy loads, despite being lightweight.

  • Impact Tolerance. While polypropylene has a good tensile strength, its impact resistance leaves something to be desired when compared to polyethylene.

  • Water Absorption. Polypropylene is highly impermeable to water. In a 24-hour soak test, the material absorbs less than 0.01% of its weight in water. This makes polypropylene ideal for total immersion applications where the basket material underneath has to be protected from exposure to various chemicals.

  • Surface Hardness. The hardness of polypropylene is measured on the Rockwell R scale as 92—placing it on the high end of the softer materials measured on that scale. This means the material is semi-rigid. This makes it more likely to bend and flex with an impact.

  • Operating Temperature. The maximum recommended operating temperature for polypropylene is 180°F (82.2°C). Beyond this temperature, the performance values of the material may be compromised.

  • Melting Temperature. At 327°F (163.8°C), polypropylene will melt. This makes polypropylene unsuited to high-temperature applications of any kind.

What Are the Advantages & Disadvantages of Polypropylene?

Why You Should Use Polypropylene

Liquid Cleaning Processes

An ideal use case for polypropylene would be an aqueous parts washing process where the basket being coated would be submerged in non-oxidizing agents for prolonged periods of time.

In such an environment, the impermeability of polypropylene would allow it to completely protect the coated basket from the liquid cleaning solution. Additionally, so long as the internal temperatures in the wash do not exceed 180°F, the coating would most likely last for many uses.

Additionally, polypropylene is dense enough to make it nearly impervious to water. This makes it an ideal material for sealing custom wire baskets against liquids. 

Parts Protection

Another reason to use polypropylene would be to protect delicate parts from getting scratched. While not quite as soft as some formulations of PVC, polypropylene is still a semi-soft material that will absorb impacts—helping minimize the risk of parts getting scratched during the agitation cycle of many aqueous-based cleaning processes. Since a polypropylene structure  will absorb shock rather than redistribute it, a polymer-coated basket would be ideal  for processing delicate parts such as glass tubes or crystal components. 

When You Shouldn’t Use Polypropylene

Extreme Temperatures & Environments

Polypropylene is not recommended for any high-temperature processes because of its low melting point. The integrity of polypropylene structure is compromised in low temperatures as well. Below 20°C, polypropylene embrittles.

Additionally, any processes that use oxidizing acids, chlorinated hydrocarbons (such as trichloroethylene), and aromatic solvents should be avoided. Polypropylene swells rapidly in chlorinated and aromatic solvents. 

Limited Impact Durability

Sharp, sudden impacts from other objects can cause damage to a polypropylene coating. So, if you’re considering a polypropylene coating, it’s important to examine your production process to see if there are any points where such impacts are likely to repeatedly occur.

Besides being susceptible to impacts and scratches, polypropylene has poor resistance to UV and its heat- aging stability can be adversely affected by contact with metals. Additionally, polypropylene has poor paint adhesion.

Is a polypropylene coating right for your custom wire basket or tray? To answer that question, it’s important to know about your process! Contact Marlin Steel to learn more about custom wire basket coatings or to get a custom basket quote with our recommendations!

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