Which absorbents are better, man-made or natural fibres?

The answer is both, but it depends on the type of spill that needs to be absorbed and where it's located.

There is a considerable deal of confusion when it comes to selecting the most suitable type of sorbent for a spill recovery task. Find out more about how the economics and new technologies have and can influence sorbent choices.

 

Sorbents explained

What makes ESP an expert voice in the industry?

ESP has probably designed, constructed and run more meltblown manufacturing lines than any other group in the world. Our team was the first to develop different configurations to meltblown sorbents as far back as 1997. Others have now followed our lead, resulting in quite a few alternatives to meltblown polypropylene. Few however, match the performance and quality of our products.

Some of the factors that add to the overall confusion

  • A lack of understanding with regards to how a sorbent actually works.
  • Alternative technologies are now starting to gain market share but how do they compare?

Read on to find why meltblown polypropylene is best for some applications and less so for others. We'll also demonstrate why sustainable cellulose absorbents are better suited for the recovery of the vast majority of liquids.

Adsorbents made from Polypropylene

Better known as 'meltblown'

  • Polypropylene is produced when crude oil is cracked in the refining process; it's an oil-based product.
  • Meltblowing, was a technical breakthrough made in the 70's and presented a huge commercial opportunity for Exxon who made large quantities. This process developed very fine 'squirts' of polypropylene at a high speed and temperature - hence the term 'melt' - 'blown'.
  • Meltblown fine fibres are collected continuously and are laid down to form a mat. This fibre generating process imparts a huge charge on the surface of the fibres, making them repellent of water (hydrophobic).
  • The mat resists water but forms bonds with any other liquids that share the same molecular structure, like oil and other hydrocarbons.
  • The mat has no attraction to water based liquids, it opposes them in a similar way that the same poles of a magnet repel.
  • Maintenance meltblown sorbents were introduced as an after thought and are nowhere near as effective as the Oil only varieties.

The economics of Meltblown

When Exxon began developing the meltblowing process the glut of polypropylene available made it very cheap and considerably cheaper than the natural fibre alternatives.

  • Being the least expensive material, meltblown polypropylene made the meltblown industry a viable alternative.
  • Increasing prices of oil have reversed and cellulose based sustainable fibres and are now less expensive.
  • Polypropylene is now one of the most expensive plastic resins and the reason that meltblown will more than likely lose favour as the default sorbent material. It is too expensive and suffers from a compromised performance in some applications.

How does meltblown polypropylene work?

Meltblown is plastic. The fibres don't absorb anything; rather they get coated with the oil-based liquid. This type of product is called an adsorbent. The liquid is quite simply added to the surface of the fibres.

  • Meltblown is claimed to hold up to 15 times its own weight when absorbing petroleum-based liquids. To achieve these high numbers, the fibres must have a large amount of air space (loft) between them to allow high quantities of fluid retention. (A more realistic figure is around 12 times its own weight).
  • The more loft the weaker the fabric so a dense sturdy looking low lint bale of pads is durable but not particularly absorbent. Whereas a high loft, very soft pad, is a high performer, but structurally weak!
  • Meltblown adsorbs oil-based liquids best but the situation is reversed when trying to absorb none oil-based spills. Now the fibres need to be adapted with a surfactant to enable them to absorb anything that is not oil based and which they naturally repel.

Meltblown's weaknesses and strengths

Meltblown fibres are, in their oil only (hydrophobic) state, best at absorbing petroleum-based fluids whilst not absorbing any water. This makes meltblown a superior performer in the recovery of oil spills on water.

  • The features that make meltblown so good at adsorbing oil based spills unfortunately make it one of the worst choices for absorbing anything that is not oil based.
  • The slippery plastic fibres even when adapted with a surfactant simply will not hold large quantities of aqueous based fluids.
  • Another positive property of polypropylene is that it is chemically very stable and can absorb virtually all liquids. For these reasons, all Chemical (Hazmat - hazardous materials) sorbents should be polypropylene based.
  • Lastly, meltblown is more resistant to high heat and will melt before it burns. Any absorbent or adsorbent can be forced to burn regardless of the sorbent type, be it cellulose or meltblown, simply because the product will take on the physical or hazardous attributes of the absorbed liquid.

How do sustainable fibre sorbents work?

Cellulose fibres have an additional attribute that meltblown does not have; they can also absorb liquids. This means that they also take into their very structures the liquid presented to them.

Conveniently, they also adsorb just like meltblown. This additional property makes them perfectly suited for handling none oil-based slippery liquids.

  • On average cellulose sustainable fibre absorbents can absorb up to twelve times their own weight with low viscosity water based liquids and also are very good at absorbing oil-based products because they have so much surface area.
  • Cellulose fibres require adapting to make sure they don't absorb water-based fluids when making an oil only sustainable product.
  • ESP introduced the first Oil only natural based sorbent range and these are the most water repellent available.

Sustainable cellulose fibre absorbent strengths and weaknesses

These cellulose absorbents are better at absorbing none oil-based spills but are compromised when absorbing Oil only based spills in the presence of large quantities of water.

  • As the worldwide trend of reducing its dependency on oil continues, the types of oil based fluids in all industries also reduces which in turn means more spilled liquids are water based.
  • Cellulose fibres will not melt when coming in contact with high heat. It is best avoided in very hot environments and like meltblown, it will take on the physical or hazardous attributes of the absorbed liquid.

How the industry is developing

Recycled synthetic absorbents like AirmatrixTM feature a number of properties, which make them the 'next generation' in absorbents. ESP uniquely manufactures these from recycled fibres to deliver very high-capacity absorbency rates at the same time they are soft and drapeable. Poly-backing construction and laminations along with special additive like SpillLockTM further enhance their performance and move them far beyond comparison with more run of the mill sorbents.

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