New Adhesive for Bonding Polypropylene
Approximately one-fourth of today’s plastics applications involve polypropylene (PP), a popular choice because of its strength, durability, moisture resistance, and relatively low cost. But with such advantages comes a challenge: PP has low surface energy (LSE), making it difficult to use adhesives for bonding. That means engineers often opt for more costly joining methods, such as welding or mechanical fastening. Now, however, advances in adhesive chemistry have spawned a new generation of adhesives designed specifically for bonding LSE materials like PP, giving engineers new options for adding value to their product designs and making life easier for assemblers across many industries.
Polypropylene has a low surface energy, which means its molecules do not readily attract or adhere to other substances. This property is due to its non-polar molecular structure, composed mostly of carbon and hydrogen atoms without polar functional groups like hydroxyl (OH), a structure that offers fewer sites for the hydrogen binding, which is necessary for adhesion to many surfaces.
PP is chemically inert and resistant to many solvents, acids and bases. This resistance also reduces its reactivity with adhesives and coatings, making it challenging to establish strong bonds. Polypropylene often has a semicrystalline structure, where polymer chains are arranged in ordered crystalline regions. This structure reduces the surface area available for bonding, as compared to materials with an amorphous structure.
Because of its low surface energy, anyone wishing to fasten PP to other substrates has limited options. When bonding PP to itself, designers might increase the surface energy through hot welding techniques or plasma treatments. Increasing the surface temperature of PP may also enable it to bond to more standard adhesives that do bond to metals. Such approaches, however, can be complex and add a step to the process.
Using adhesives specially formulated to bond to LSE substrates allows for more intricate and innovative prototype designs. Designers can incorporate different materials with varying properties (such as flexibility, durability or chemical resistance) into prototypes without being limited by bonding constraints. They can also streamline the prototyping process by reducing the need for mechanical fasteners, complex welding processes, or surface treatments that may require additional time and resources. This efficiency can lead to faster turnaround times and reduced prototyping costs.
Source: IPS Adhesives