Isopropyl alcohol (also called isopropanol or IPA) is a common solvent with a wide range of uses in industry and consumer products. It is used extensively as an antiseptic (rubbing alcohol) most notably in hand sanitiser. A large portion of it is also used in the production of acetone. However, there is a particular interest in replacing IPA in printing inks – so why and how?

Why replace IPA?

IPA is a very high production solvent found commonly in a variety of consumer products and used widely in industry. So why consider it for replacement? 

Almost all IPA comes from the hydration of propene from petroleum distillation, which makes it undesirable as we transition to a biobased economy. It is a highly flammable liquid with a flash point of 12°C and a vapour pressure of 6.02 kPa at 25°C. In terms of physical hazard, it’s not quite as dangerous as acetone. But in a poorly ventilated space, IPA can emit narcotic fumes that pose a risk to workers. It is also a serious eye irritant, which may mean greater PPE requirements in the workplace.

In addition to safety and sustainability concerns, there are economic reasons to move away from IPA. It’s a very popular disinfectant, making it susceptible to supply issues when a spike in demand occurs. This happened during the first wave of the COVID-19 pandemic, when there was a dramatic increase in demand for hand sanitiser. The price of IPA rose dramatically, causing budgetary issues for printing operations that rely on it. Although it is a low cost solvent, it evaporates quickly so may need to be replaced frequently in applications such as component cleaning. This can ultimately lead to higher operating costs. 

Swapping isopropanol with a greener alternative can be better for your workers and also better for your bottom line.

What makes a chemical ‘green’?

The definition of ‘green’ is complicated, and often depends on the application. Most simply, a greener chemical is better for humans and the environment. What ‘better’ means varies by use case, but can include:

• Less hazardous to human health
• Fewer harmful environmental emissions
• Less waste in manufacturing
• Improvements in process efficiency
• Biodegradation
• Easy reuse or recycling
• Biobased or renewable feedstock

You can read more about choosing green solvents here.

In some cases, green chemicals can let you enter new markets. Biobased products made from renewable sources and materials – algae, plant waste, even marginal crops – offer opportunities to stay ahead of your competitors, and sometimes even reduce costs. As long as product performance doesn’t slip, authentically green products can significantly increase market share.

What makes IPA unique?

Solvent Characteristics

IPA is the simplest secondary alcohol. It is a polar protic solvent with a mid-range polarity that has some ability to dissolve both polar compounds, such as ions, and nonpolar compounds, such as grease residues. This means it is effective as a cleaning agent and general solvent, while its antimicrobial properties allow widespread use as an antiseptic (rubbing alcohol).

Volatility

IPA is a volatile liquid, which means it quickly evaporates at room temperature and pressure. This can be both good and bad. It is useful for cleaning and coating applications where fast evaporation without residue is desirable. But this evaporation can lead to unsafe solvent levels in the air when used in unprotected work environments.

Volatility can also pose logistical challenges during solvent storage and use. Specialised, safe storage is needed to handle build-up of gas pressure, and speciality pumps may be needed for safe transfer. A volatile solvent is harder to recycle, as capturing the evaporated gas requires specialised equipment that is impractical in many applications. Recycling of the liquid alone will be inefficient, and regular input of solvent will be needed to replace what wasn’t captured, raising costs and reducing process sustainability. 

Finally, volatile solvents are more likely to be released into the environment as a gas. This can cause issues with legislation around air pollution, as well as workers and consumers if the gas comes with a noticeable odour. As awareness grows of problems with indoor air quality, consumers increasingly prefer products that don’t pollute their homes.

What is IPA used for?

IPA is commonly used as an antiseptic for first aid purposes, as it is good at killing most microbes. For the same reason, it’s widely used as a disinfectant in hospitals, cleanrooms, and other settings. Other medical uses include as a liniment for muscle aches, as an astringent, and to guard against swimmer’s ear. Industrially, it is a high volume chemical used in the manufacture of acetone, glycerol and isopropyl acetate, as well as being a solvent for various reactions and cleaning applications.

IPA as an antiseptic

Due to its size and solvation ability, IPA can enter the cell wall and kill bacteria, fungi, and viruses. It has, therefore, found widespread use as an antimicrobial agent in products such as surface disinfectants and hand sanitiser. 70% IPA in water is considered most effective for this purpose, as the inclusion of water helps IPA penetrate the cell wall and kill the microbe. Stronger solutions tend to damage the outside of the cell without killing it. 

IPA in cosmetics and medicine

IPA is a popular choice for cosmetic formulations as it is both an effective solvent and preservative due to its antimicrobial properties. IPA acts as an astringent, tightening the pores of the skin to give a smoother appearance. In medical applications, IPA restricts capillaries and can reduce bleeding of minor cuts. Conversely, when applied on uncut skin, IPA irritates the skin, which helps to increase blood flow to that area. This is useful to help improve localised muscle aches. Lastly, the high vapour pressure of IPA compared to water makes it an effective preventative for swimmer’s ear since it can mix with water inside the ear and speed up the evaporation process. 

IPA in industrial washing

IPA is the recommended solvent for washing liquid resin off 3D printed components, as it is effective and evaporates quickly. For the same reason, it is used to clean electronic components, removing dirt and grease without leaving a residue. 

IPA in printing

IPA is prevalent in the printing industry due to a number of useful properties. It decreases the surface tension of the water-based dampening solution – a liquid used to keep blank areas of the design free of ink – and provides better wetting of the rollers and printing plate. IPA also gives stability to the ink-water balance (offset printing works on the principle that ink and water do not mix). Further to this, IPA helps to keep the printing surfaces cool by its quick evaporation.

Replacements for IPA

What makes a good IPA replacement?

The ideal IPA replacement has a lot of boxes to tick:

• Similar solvent properties
  Should dissolve the same things as IPA
• Non-toxic
  Avoiding negative health effects
• Not a volatile organic compound (VOC)
  Industrial emissions of VOCs are restricted by a variety of laws around the world, making a non-VOC alternative highly desirable
• Balanced volatility
  Staying useful but reducing solvent loss via evaporation
• Biobased
  Made from renewable resources such as waste plant matter
• Cost
  Similar to or cheaper than IPA is ideal

Easily recyclable
Low volatility will ease recyclability, but other factors also affect it

Replacing IPA with similar solvents

Depending on the application, it may be possible to replace IPA with another small alcohol, such as ethanol. However, solvents that are close in structure tend to have similar properties, and both ethanol and isopropanol are similarly flammable. Nonetheless, ethanol has a higher occupational exposure limit at 1000 ppm averaged over an 8-hour work shift (by inhalation), compared to a 400 ppm limit for IPA. Add to this that it is readily available in one step from biomass, and it may be a better choice where it meets performance needs. 

What IPA replacements are on the market?

Some products are being marketed as safer alternatives to isopropanol for specific applications.

VertecBio™ Clean ECO-Solv

This is a bio-based alternative to IPA intended for lacquer formulation and cleaning, as well as a potential solvent for paints and coatings, and a blend for ink formulations. It’s carbon neutral and biodegradable to non-toxic breakdown products, contains no hazardous air pollutants and can be recycled easily.

Electro-Wash CZ Degreaser

This is a flux remover for electronic components. It is an aerosol product that is marketed as non-flammable and non-ozone depleting. It is possible that the spray format of the product would make it easier to reduce the quantity used while cleaning, although it is worth bearing in mind that the product evaporates very quickly and would make reuse impossible. Although it is not flammable, the product is a gas under pressure and comes with the associated storage hazards.

Eco-dFluxer SMT100

This is a water-based cleaner containing 2-aminoethanol, for the purposes of industrial removal of solders and fluxes from circuit boards. It is non-flammable and marketed as an environmentally friendly option, largely due to lower VOC content. The product is corrosive to skin and eyes, so this would require appropriate PPE to be used by hand.

Replacing IPA with different solvents

You should also consider other classes of solvent. One 3D printing manufacturer recommends tripropylene glycol monomethyl ether (TPME) as a potential alternative for washing printed parts to remove liquid resin. TPME is non-flammable and non-toxic, though only available from petrochemical sources. It also evaporates much more slowly than IPA, allowing for more use without replacing, and is less easily absorbed into the solid resin, causing less damage to the product.

IPA blends to improve performance

Mixing solvents together creates a blend that has different properties than its components. Blending IPA with another solvent can create a higher-performance product, harnessing some of the benefits of IPA and reducing drawbacks. It will also reduce IPA use, potentially improving health and safety or sustainability of your product. It’s not a perfect solution, but if nothing else works, a lower-IPA blend can be a decent alternative.

Non-solvent choices for IPA replacement

Depending on your goal, you could consider a non-solvent replacement for IPA:

Offset printing

Technological advancements have meant that it is possible to reduce or remove IPA from the printing process. These advancements include more precise dampening rollers for even distribution of the liquid. This may mean that a different additive is required for the dampening solution, so the health and environmental impact of the additive should also be taken into account. 

Which IPA replacement is best?

This is a complicated question with no singular answer. Your best option for IPA replacement could be any of the options mentioned, depending on what physical and hazard properties you’re looking for. You should consider and test a range of alternatives before committing to one (here’s how).

If all else fails, why not go slightly greener by finding a biobased IPA? Most IPA is derived from petrochemical sources, but biobased options are growing. IPA can be produced by  catalytic hydrogenation of acetone, a product of Acetone-butanol-ethanol (ABE) fermentation from waste biomass. It’s the same chemical, but from a renewable source!

How to choose an IPA replacement

Some solvents, even those marketed to replace IPA, won’t dissolve the same things, resulting in poor product performance and wasted development time. This can be avoided with some computational modelling, using tools like Hansen solubility parameters (HSP) to predict solvent suitability for specific applications. 

Target solutes, like specific inks, have a solubility sphere which can identify solvents that are likely to dissolve them. Solvents outside the sphere are not likely to work, even if they are in the same solvent class as IPA (polar protic). It gets complicated! 

If you’d like some guidance with using HSP, or want someone to identify the right replacement for your specific needs, Green Rose Chemistry can help – we love learning about new problems!

Further reading

If you’d like to read more on IPA replacement, here are some useful sources:

General uses of IPA

IPA in the printing industry

Alcohol-free printing