Plastic recycling: Does micron size matter?

In plastics recycling, does smaller always mean better? When it comes to melt filtration, not necessarily.

Micron size plays a critical role in removing contaminants from molten plastic, but selecting the smallest possible filtration aperture doesn’t guarantee better results. In fact, getting the specification wrong can increase melt pressure, restrict throughput and compromise production efficiency.

ActionLaser is one of the most experienced and sought-after manufacturers of precision laser-drilled filtration solutions for the plastics recycling industry.  Since 1996, our experience has shown that smaller filtration apertures don’t automatically translate to better filtration performance.

Understanding how micron size, aperture geometry, and melt flow work together is essential to recycling efficiency, material quality and operating costs.

A micron, also known as a micrometre (µm), is one-thousandth of a millimetre. In melt filtration, micron measurements are commonly used to describe the size of openings through which molten plastic passes. For example, a filtration screen with 100-micron apertures has openings measuring approximately 0.1 millimetres across.

Generally speaking, smaller apertures can retain finer solid contaminants, while larger apertures allow material to pass through more freely. However, filtration performance is influenced by more than the nominal aperture size.

The characteristics of the contaminants, the polymer being processed, melt viscosity, operating pressure and screen design all affect how a filtration system performs.

This means two screens with similar micron ratings may behave quite differently in an operating recycling facility.

A common misconception is that the smallest possible filtration openings produce the cleanest recycled plastic. It isn’t quite that simple.

As molten plastic passes through a filtration screen, the apertures create resistance to flow. Smaller openings can increase this resistance, particularly when the material contains significant contamination. This contributes to increased melt pressure, reduced throughput and more frequent filter cleaning or replacement.

For recycling operations processing heavily contaminated post-consumer plastics, these considerations can have commercial implications. The objective is not to achieve the finest possible filtration, but to achieve the level of filtration required without unnecessarily compromising production performance.

Two filtration discs were manufactured to the same nominal micron specification. One contains apertures that are highly consistent in size and shape. The other contains greater variation, with some openings larger or smaller than specified.

Although both products are described using the same micron rating, their filtration characteristics will differ. Oversized openings can allow unwanted contaminants to pass through, while undersized apertures increase flow resistance or contribute to uneven loading. A consistent aperture geometry helps deliver predictable filtration performance.

At ActionLaser, precision laser drilling allows us to manufacture stainless-steel filtration discs with carefully controlled aperture dimensions and distribution. Our quality assurance procedures include measuring and verifying aperture sizes to ensure our filtration products meet their specified requirements.

An important consideration is the effective open area of a filtration screen. Open area refers to the proportion of the filtration surface available for molten plastic to pass through.

A screen with a greater effective open area can create higher flow rates or reduce flow resistance, depending on its overall design and operating conditions. However, increasing the number or size of apertures must be balanced against the screen’s structural integrity.

Melt filtration discs operate under elevated temperatures and high pressure, making material strength and dimensional stability essential. The engineering challenge is to optimise aperture size, hole distribution, open area and screen durability as an integrated design.

Not all recycled plastics behave the same way during extrusion. Polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET), for example, have different processing characteristics and often require different filtration specifications. Post-industrial plastic waste also presents different challenges from post-consumer material, which often contains more variable contamination. The appropriate filtration solution depends on several factors, including:

• Polymer type and melt characteristics.
• Contamination type, size and concentration.
• Required recycled material quality.
• Operating temperature and pressure.
• Production throughput and filtration system design.

Our involvement in plastics recycling filtration began in 1996. Today, our LaserFilter and MeltFilter products reflect decades of specialist experience in precision laser drilling, aperture measurement and filtration engineering.

We understand that achieving reliable filtration performance requires more than meeting a nominal micron specification. It involves carefully considering how the screen will perform within the complete recycling process.

The right filtration screen will influence the quality of recycled material, production efficiency, and long-term operating costs. With nearly 30 years of specialist experience, ActionLaser combines precision laser manufacturing with a practical understanding of the demands of plastics recycling.

Whether you’re looking to improve filtration accuracy, optimise melt flow or address recurring filtration problems, our experienced team can help assess your operating requirements and identify an appropriate solution.

Talk to us about your plastics recycling filtration requirements. Our precision-engineered LaserFilter and MeltFilter solutions can support more consistent, efficient and reliable production.