Understanding Plasma Activation of Polypropylene (PP) Benefits and Applications

Polypropylene (PP) is a thermoplastic superhero, ideal for manufacturing tough, robust products ranging from car bumpers and medical devices to high-performance fabrics for harsh environments. In fact, polypropylene is used to make products found in just about every major industry and market.

However, polypropylene is a polymer with relatively low surface energy, requiring it to be modified to better accept a variety of treatments, such bonding, painting, and coating. Recently, plasma treatment has become increasingly popular as a surface activation and modification technique for a wide range of polypropylene products, including textiles, where it’s used to enhance material wettability. Many manufacturers now use plasma systems to perform surface preparation to enhance bonding and adhesion performance for products throughout the consumer, commercial, and industrial worlds.

The 3 Types of Plasma for Activating Polypropylene

There are 3 primary plasma system options for treating polypropylene:

	Atmospheric Plasma This method utilizes electrically-energized air or gases that are passed through a nozzle at surrounding atmosphere or normal pressure using a pulsed electric arc generated by high voltage discharge. It is generally used for spot treatment of materials or low area in-line processing because it does not require a vacuum chamber and integrates well with a manufacturing assembly process.
	Low Pressure Plasma This type of system generates plasma in a chamber that has been evacuated and then injected with small amounts of gas – usually oxygen, argon, hydrogen, nitrogen, or air. This method is better-suited for large batch parts processing and can easily handle difficult geometries.
	Corona Plasma Corona treatment is an electrical process that uses ionized air to increase the surface tension. Corona plasma is generated by the application of high voltage to an electrode that has a sharp tip where the plasma forms. This method is typically used for in-line wider area manufacturing applications that require a lower shift in surface energy.

Ways Manufacturers use Plasma to Activate Polypropylene

There are several ways to use plasma systems to activate polypropylene depending upon the treatments needed for the specific product. Here are some examples of how the methods described above are used to enhance this thermoplastic material:

• Atmospheric plasma is highly effective for activating broad fabric surfaces in normal manufacturing environments
• Both atmospheric and low-pressure plasma methods are used to treat bulk material or large surfaces where the entire surface must be treated
• Polypropylene powders can be treated with low-pressure plasma so that the powder can be mixed covalently in a solution
• Plasma is used to enhance polypropylene’s ability to bond with pressure-sensitive adhesives; for example, to enable the use of double-sided adhesive tape instead of glue
• Plasma effectively boosts polypropylene’s low surface energy to improve painting, printing, and coating processes, enabling them to bond covalently and produce more reliable, longer-lasting finishes

How Much Does Plasma Activation Improve Wettability of Polypropylene?

Wettability is a surface characteristic that is defined as the tendency of a fluid to spread or adhere to a solid surface and the ability of that surface to hold contact with it. One way to measure wettability is to use a test that registers a unit of force called a dyne.

Most manufacturing applications in which good wettability is desired require at least 72 dynes as a benchmark for acceptable product performance – a result difficult to achieve with polypropylene’s inherent low surface energy. By activating the surface of the polypropylene with plasma, its surface energy can be increased from 28 dynes to more than 105 dynes – well beyond the acceptable performance level. This significant improvement increases the number of manufacturing applications for polypropylene and its value as a versatile raw material, reinforcing its reputation as a workhorse of the thermoplastic industry.

Plasma Activation Integrates Nicely on Manufacturing Lines

Atmospheric, low-pressure, and corona plasma systems are all well-suited for production line integration. Flexible, versatile, and streamlined for manufacturing use, these methods are efficient and effective, capable of providing highly accurate, automated, and reliable service in high-volume production environments. Plasma activation of polypropylene on an automated production line can occur at rates of 100 to 400 mm/second, and batch processes can occur in process times of less than 10 minutes for a large batch of parts.

Unlike other surface treatment technologies that produce toxic by-products and pose health risks for workers, plasma technology is a cost-effective solution that does not produce any volatile organic compounds, providing a safe industrial hygiene environment that protects worker health.

Manufacturing process development using plasma to treat polypropylene is simple to implement and is a highly reliable form of surface treatment. The combination of polypropylene’s popularity and the availability of high-quality, cost-efficient plasma systems make them a perfect combination for developing and manufacturing new and innovative products.

Discover how your business can utilize plasma activation technology to modify polypropylene surfaces for high-performance bonding, coating and painting. Downloading the eBook, "Manufacturer’s Surface Activation Guide for Improved Adhesion" to learn more.