Liquid launch

‘Liquid polymers’ used in many consumer product formulations will need to be produced – and disposed of – more sustainably in future. Lou Reade reports

Think plastics and most of us are likely to consider drinks bottles and food packaging or the light-weighting components of car parts and furniture. And increasingly, too, about the adverse impacts of plastics pollution on the environment and in our oceans. However, polymers occur not only in solid form, but also as liquids.

Low molecular weight polymers can be water-soluble, and many are used in consumer products such as paints, cosmetics and detergents - often helping to improve physical performance. Vinyl acetate, for example, is used as a ‘fixative’ to improve haircare and aerosol products.

In a recent report, the Royal Society of Chemistry (RSC) estimated that these ‘polymers in liquid formulations’ (PLFs) have a collective global value of more than $125bn/year. This equates to around 36m t of chemicals – most of which are likely to end their lives as waste. Polymeric ingredients in shampoos, for instance, are simply washed down the plughole as a matter of course.

‘The way that PLFs are made, used and disposed of is putting unnecessary strain on the environment – by releasing carbon dioxide, using up the earth’s resources and generating physical waste,’ says RSC President Tom Welton in the report’s foreword. ‘These issues create risks for all parts of the value chain, from monomer producers to product formulators and waste management companies.’

Industry taskforce

Since the report was published, the RSC has set up an industry taskforce to address how the sustainability of PLFs might be improved. The report suggests a number of approaches, including replacing petrochemicals with more sustainable precursors; re-using or recycling products such as paint more effectively; and developing better wastewater treatment processes, to remove PLFs from the environment.

There is no suggestion that production of PLFs will reduce in future. They are used across eight established markets, including agriculture, household cleaning, paints & coatings, and lubricants, with a combined value of nearly $1.3tn. Some PLFs are used in critical products such as fertilisers, whose performance affects millions of people.

Although improving PLF sustainability is the main aim of the report – and the taskforce – this will need to be balanced with performance. For instance, it would make sense to develop a biodegradable PLF for use in shampoos, as it could break down harmlessly in the environment. This would not be appropriate within a paint or coating, though, which needs to offer long-term decoration or protection. However, industry players have accepted that the overall sustainability of PLFs must be improved.

We need collaborative action in moving towards sustainable PLFs [Polymers in Liquid Formulations] – which not only involves the industry, but also academia, government and the general public.
Anju Massey-Brooker Polymers in Liquid Formulation Task Force Coordinator

The taskforce includes representatives from many PLF producers, including Croda, Unilever and BASF. Anju Massey-Brooker, who coordinates the taskforce, says: ‘PLFs incorporate more than 2000 different materials, several chemistries and multiple functions – including rheology modifiers, emulsifiers and flocculants.’ They are used in a diversity of applications, she says, including improving food productivity, treating wastewater and protecting buildings and infrastructure, for instance. Massey-Brooker spent many years in industry working in polymer science and development – notably as principal scientist at Procter & Gamble. She now holds academic positions at both Durham and Birmingham universities in the UK.

The initial RSC report that led to the creation of the taskforce pointed out that PLFs – unlike ‘standard’ plastics – have attracted little attention until now.

‘PLFs are less tangible and can’t be held in your hand like a plastic,’ she says. ‘They are ingredients with a wide range of purposes and properties.’

The term PLF is actually an ‘invented’ one – devised by the RSC to describe this broad range of polymeric additives. While research has been done in individual areas, such as on alternative flocculants for water treatment, or in acrylamides, the RSC says there is little coordinated research across this diverse group of chemicals. Addressing this in a coordinated way will help to prevent duplicated effort, and target innovation at areas that might have the most effect, says the organisation. ‘High-level strategy and leadership have been lacking – and that’s our aim,’ says Massey-Brooker.

For now, the taskforce comprises only industry players. However, Massey-Brooker says it is also setting up an advisory board – to include funding bodies, policymakers, academics and NGOs.

‘We need collaborative action in moving towards sustainable PLFs – which not only involves the industry, but also academia, government and the general public,’ she says.

Although this is early days – the taskforce only met for the first time in late January 2022 – Massey-Brooker believes this is an achievement in itself. ‘The taskforce needs to establish open and common goals – to think and act big,’ she says.

Technical answers

Technical solutions to these problems are at various stages of readiness. Some are already commercial, while others may take years to come to fruition – if they ever do.

One commercial example is seen in Procter & Gamble’s (P&G) washing detergents. For many years, these have used a PLF called carboxymethyl cellulose (CMC). CMC imparts a negative charge to both fabric and dirt – helping to keep them apart once they have been separated. It also reduces the transfer of dyes between separate garments during a washing cycle.

P&G has developed a ‘blocky’ version of CMC, called BCMC, which it says works four times more effectively. This means it can be used at lower concentrations and allows washes to be performed at lower temperatures. In developing BCMC, P&G used regioselectivity in the carboxymethylation process. This caused clustering (‘blockiness’) of the negatively charged groups – freeing up unsubstituted regions that can then adsorb onto textiles.

BCMC is made by carboxymethyl modification of wood cellulose. It is around 75% bio-based, and inherently biodegradable, according to P&G. In addition, its ability to inhibit dye transfer helps to extend the life of garments. BCMC is now used in commercial detergent formulations, at levels of 0.1-1%, says P&G. A washing detergent might typically use 0.5-2% CMC in a formulation.

Other technologies take aim at different parts of the PLF chain. Puraffinity, for instance, has developed a molecular binding technology that captures target molecules in wastewater. Molecular receptors bind electrostatically to a specific target compound that would otherwise be released into the environment. The technology has been developed to handle perfluoroalkyl substances (PFAS), but could be modified to recover PLFs, says the company.

Some schemes are completely non-technical and instead rely on a change in consumer behaviour, backed by industry support.

PaintCare, for instance, is an industry scheme that encourages paint users to return unused products, which can then be re-used or recycled (see Box). This could have a huge effect, because paints and coatings are by far the largest volume of PLF-containing substances produced worldwide, accounting for nearly 22m t/year.

‘The barriers to establishing a coherent UK network of paint recycling and reuse are not technological,’ says Massey-Brooker. ‘It’s about time we solved this issue.’

Catalytic approach

One way to improve the sustainability of PLFs is to use fewer petrochemicals in their manufacture. A UK start-up, ViridiCO₂, says its catalyst technology could replace fossil resources with an abundant alternative: carbon dioxide.

If successfully commercialised, the catalyst could convert carbon dioxide – emitted from factory chimneys – into PLFs and other organic chemicals.

‘We’re looking to replace the usual carbon source – crude oil – with CO₂, to make a range of low molecular weight polymers,’ says ViridiCO₂ CEO Daniel Stewart.

The catalyst takes the concept of carbon capture and storage (CCS) into a new realm, dubbed CCU for carbon capture and utilisation. This overcomes the impracticality of storing large amounts of waste CO₂. ViridiCO₂ is a spin-out from Southampton University, UK, where Stewart carried out the original research into the catalyst. This is now the subject of a patent application – with Stewart as co-inventor, alongside his former research supervisor, Robert Raja.

In the laboratory, the catalyst has been used to create polyols, which are used in the production of polyurethanes. Stewart says the catalyst can be ‘tuned’ to produce other substances, including PLFs. ‘By swapping bits in and out, we can tailor the system to make a specific product target,’ he says. ‘It can make water-soluble polymers – such as those used in detergents and shampoos.’

Stewart is reticent to reveal details of the catalyst, but says its main advantage is the ability to convert CO₂ into a variety of ‘high value chemicals’ under relatively mild conditions. The patent application document claims the new catalyst has advantages over others – such as zinc glutarate, double metal cyanide and metal oxide framework (MOF) designs – that can incorporate CO₂ into polymeric structures. One aspect of the invention describes the importance of having two separate reaction sites: one containing a hydroxyl group, the second capable of binding to a CO₂ molecule, that are close enough to one another ‘to maximise catalytic activity’.

‘The reaction can be carried out at lower temperatures, pressures and for much shorter reaction times,’ says the document. A table lists the catalyst’s reaction conditions: a temperature range of 45-65°C, reaction times of 0.3-6 hours and pressures of 0.1-2MPa. While the ViridiCO₂ catalyst operates at a similar temperature to ‘traditional’ catalysts, its reaction times and pressures are significantly lower.

There are already commercial examples of using CO₂ as a raw material. Chemicals giant Covestro uses it as a starting material for making polyurethane foam, but Stewart believes his company’s catalyst has some advantages. ‘Covestro’s is a heterogeneous [solid] catalyst like ours, but operates at much higher temperatures and pressures,’ he says.

ViridiCO2 has received around £900,000 in support, from equity funding and a research grant. This, says Stewart, will help to move the catalyst towards commercialisation. ‘The next 12 months is about proving it can work on a larger scale. We’re also working with early adopter customers, who want first dibs on it.’

By this time – the end of 2022 – he is confident that his company will have secured its first commercial ‘early adopter’ customer. Beyond this, he says a pilot scale plant could be ready in one to two years. Stewart says this equates from moving its ‘Technology Readiness Level’ from 4 up to 5 or 6. Full industrialisation might take five to 10 years, he adds.

ViridiCO₂’s approach is to work with partners, tweaking the catalyst so that it makes a ‘substance of interest’ for them.

‘We can modify the catalyst easily, to make different products,’ he says.

On a large scale, he envisages a chemical company ‘piping’ its waste CO₂ to a separate part of its facility, where the catalyst can then convert the gas into a high value chemical such as a PLF. ‘This would help chemical companies spend less on petrochemicals,’ he says. ‘I think it has massive potential to change the way that we make chemicals.’

This is just one of many approaches that could improve the sustainability of PLFs in future. No single solution – technical or otherwise – will address the complexity of such a broad field. As the RSC said in its report: ‘It is a challenge bigger than any single organisation, market or research group.’

Greener paint

The British Coatings Federation (BCF) has devised a scheme to reduce the environmental impact of unused paint in the UK. Its PaintCare initiative aims to recover and re-use more waste paint, by encouraging its return to recycling centres and DIY outlets.

‘We estimate that 55m litres of waste paint is generated in the UK each year,’ says Tom Bowtell, CEO of BCF. ‘PaintCare sees left-over paint as a valuable resource and plans to recover and reuse it.’

More than one-third of this amount – around 20m litres – is considered usable. The scheme aims to increase paint recovery levels from 2% today to 75% by 2030. This represents a volume of around 275m litres. PLFs in the paint, including acrylic, styrene-acrylic and vinyl copolymers and alkyd polymers, could be recovered and re-used. The waste paint could be used to make new paint. One social enterprise in Leeds, Seagulls Reuse, collects waste paint from local households, before remixing it for sale at a low price.

Cat Hyde, founder of Seagulls Reuse, says: ‘I don’t think awareness of paint recycling has moved much over the past 20 years. Even if paint has gone bad, it can be remade or recycled into other products.’