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Phenolic Resins and Lignin

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By Anthony Maiorana, polymer chemist and writer of The Polymerist Newsletter

If we think about modern industrial chemistry, things really took off around the 1940s as steam cracking, catalytic cracking, and the use of synthetic materials started to become widespread. The widespread availability of refined oil at low costs over the last 60 years created less of a need for refining chemicals from biomass, but crude oil is inherently finite in a human time scale. Over the last few decades we have seen the growth of green chemistry and engineering principles in academia and the chemical industry for numerous reasons, but one of them is the potential future scarcity of oil as a chemical feedstock. If you are reading this article, it is likely through the ACS Green Chemistry Institute and I won’t get into the specifics of green chemistry principles, but I will attempt to write about the utilization of biomass in industrially relevant specialty polymers and plastics.

Before we dive in, I think it’s worth a few sentences to explain who I am and why I am writing here. I’m a professional chemist with some amount of training in synthetic thermosetting polymers. My doctoral thesis was about utilizing biobased feedstocks to make epoxy resins and after graduate school I went straight to the chemical industry. I started a newsletter called The Polymerist after about four years of working in the industry to try and address some persistent issues I’ve seen in the chemical industry.

I’ve seen that there are bigger and deeper problems within the chemical industry that are beyond pure technical feasibility. We have an enormous amount of chemical talent out there in the form of chemists and chemical engineers, but industrially many of them are focused on cost cutting and efficiency projects. Getting from technical possibilities of new polymers made from biomass or renewable feedstocks to commercial viability is the largest hurdle to overcome in order to realize commercial success.

I have spent a significant amount of time during my tenure as an industrial chemist attempting to get lignin into phenolic resins and on paper it seems like a logical choice. Phenolic resins were the first synthetic polymer to be invented and are still used today in a myriad of applications including brake pads, grinding wheels, acoustic and residential insulation, refractory bricks, foundry crucibles, oilfield proppants, composites, and engineered wood. Whenever you stop a car it’s a phenolic resin holding the brake pad together and as the brake pads are worn down over time, its phenolic resin and other materials are released into the natural environment.

Being able to incorporate biomass into phenolic resins is a great idea and lignin is the best source of biologically abundant phenolic moieties; it’s a byproduct of paper making or cellulose purification, and it’s the third most abundant biomacromolecule on the planet. Lignin under the right conditions can also have some reactivity towards formaldehyde so it lends itself to being able to undergo many of the electrophilic aromatic substitution reactions that are traditionally done with phenols. The problem is that chemists thought of this back in the 1940s-1960s and it tends to pop back up every subsequent decade since. Synthetic chemists who get jobs making phenolic resins think, “This time is different,” when it comes to putting lignin in phenolic resins. Scientists often only talk about their successes, but I’m here to talk about some failures.

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Challenges Incorporating Lignin into Phenolic Resins

Lignin has some niche applications in phenolics right now with applications targeted for refractory bricks for instance, but lignin might comprise 5-10% by weight of the actual phenolic resin. In my experience, a 5-10% composition of lignin (w/w) is the best that will be achieved for a few reasons.

  • Performance. Phenolics with lignin are just not as good as phenolics without lignin in terms of typical performance.
  • Pricing. Lignin is typically about $0.75-1.25 per pound, which is either equivalent or more expensive than phenol and significantly more expensive than formaldehyde. Paper mills can generate energy by burning lignin so selling lignin needs to be more profitable than generating energy.
  • Smell. Of all the different types of lignin, lignosulfonate has historically been the most cost-efficient in my experience, but it smells terrible due to the sulfonate groups that are introduced to the structure.

 

Lignin Performance

A typical cured phenolic resin has a glass transition temperature that is close to the degradation temperature and phenolics are often used in high-temperature applications. When phenolics do degrade thermally they often produce a large amount of carbon. High-temperature performance is critical for phenolic applications such as brake pads.

Imagine driving 80 miles per hour on a highway and needing to come to a sudden stop due to traffic. The brake pads and rotors of a car will experience high temperatures and if I asked a driver if they would sacrifice performance for a margin of sustainability, I think 90% of people would pick performance. The thermal properties of phenolic resins will be reduced due to the introduction of the aliphatic portions of lignin, which is primarily composed of p-coumaryl, coniferyl and sinapyl alcohols. If the main use of lignin right now is to be burned to produce energy and then it's introduced into a polymer where one of the key properties is heat and fire resistance, there are going to be some problems. There are instances of aliphatic moieties such as dicyclopentadiene increasing specific thermal properties of a cured resin, but this is not one of them.

Refractory bricks are the only place where I’ve heard of lignin being utilized and it’s primarily to increase the fracture toughness of the bricks in the event that one is dropped. I heard a story once about how to demonstrate refractory brick toughness—the people who made the bricks would just throw them on the ground to see which ones broke most easily. To anyone who has studied fracture toughness in depth, I hear the moan you just made. This might sound odd, but testing like this is not uncommon; as a scientist working in the industry you might think, “am I really doing this?” when you perform certain tests.

 

Lignin Pricing and Phenolic Resin Capacity

The phenolic resin industry—like many others—is one driven by low costs and large volumes. Right now lignin is on par with the price of finished phenolic resin—about a dollar a pound. Substituting some lignin for phenol means raising the price of the finished good while compromising its properties. I briefly tried to entertain some lignin start-ups out of Europe trying to do electrolysis of lignin to break it into small oligomeric pieces, but for a 1-kilogram sample they were asking me to pay them $2,500 or the costs they had at that moment to make a kilogram sample. In an industry driven by free samples, the work died via email before it could get started. Pulp mills are probably some of the most efficient cellulose and lignin separation operations in the world and the prices are primarily driven by the costs due to the separation of lignin from water, which is typically done through spray drying, and even then the costs are prohibitive.

The forces driving the phenolic resin industry, and much of the specialty chemicals industry, are economic. There is an abundance of capacity around the world, which has turned this specialty business in a race to the bottom on prices. The only way to remove costs from manufacturing once sufficient scale and as much efficiency as possible have been achieved is to cut labor costs. Since most phenolic resins are somewhat easy to make for a skilled polymer chemist, there is more capacity in lower labor cost countries around the world, which is also often close to customer manufacturing operations. Eliminating 8-16 hours of shipping costs and a few dollars per hour of wages for operators sounds marginal, but these can mean the difference of gaining or losing multi-million dollar customers.

 

Bad Smells

If you’ve ever been outside of a large chemical plant you know that smells are a big deal—even more so if you live in the same neighborhood as a chemical plant. I once ran a scale-up of a lignosulfonate reaction at a pilot plant that specialized in handling things that smelled really bad. Afterward, they said that they would never do the reaction again because they could not handle the smell. Bad smells in a small laboratory might be something that scientists can endure with Schlenk lines and fume hoods, but when you are doing small-scale reactions in an industrial lab this means 1-5 liters and a small pilot reaction is 50-250 gallons of material. Any irritating smell from a 5 liter reaction gets amplified at 200 gallons and then way worse at 10,000 gallons. If industrial polymer chemists are seeking to build good relationships with nearby residential communities, which have historically been horrendous, then doing chemistry that doesn’t smell terrible is really important.

I don’t have a good answer for solving these issues, but these are the challenges a chemist or chemical company would face in trying to scale up a new technology around phenolic resins.

 

Systemic Challenges to Conducting Greener Business

The only economic event that I could see incentivizing lignin in the short term would be very high oil prices. As I write this, demand for refined oil is in question for the long term as hybrid or fully remote work schedules are being determined for a world still dealing with Covid-19. ExxonMobil recently lost board seats due to a shareholder rebellion based on the company not diversifying out of oil. Still, the concept of biomass competing with oil seems unlikely when oil prices are under $100 per barrel. This low cost of oil has killed many start-ups attempting to commercialize biofuels in the past.

The gigantic consulting and professional services firm Deloitte is rolling out a remote-first option for their employees, which will likely cause a cascade of their competitors to follow. The amount of work travel and commuting is likely going to decrease compared to pre-pandemic levels, which is good from an emissions perspective, but from an oil price perspective it will keep prices from going up if production is kept constant. This means that pricing for biomass materials will become even more important as we progress through the 2020s.

 

New Opportunities to Push Greener Chemistry Forward

What is harder to predict here would be new opportunities around byproducts from a new business that is disruptive to the status quo. If high-value chemicals could be produced from cellulose and we had a more efficient method to separate cellulose, lignin, and hemicellulose than pulping, we in theory would have an abundance of lignin with little to no demand. I’m not an economist, but I think a large supply without a strong demand means lower prices and lower prices mean opportunities to try new things that were once not possible.

My advice right now, after five years of being an industrial chemist, is to try and move past thinking about trying to substitute biomass and to invent completely new supply chains for chemicals and polymers where biomass is the only option. Nylon-11 is a great example of how castor oil is needed to make this particular type of polyamide. Rosin esters and hydrogenated rosin ester tackifiers are also great examples of chemicals made possible only through a biomass route. It might not be obvious, but alpha-pinene is in such high demand right now for personal care that it’s no longer possible to make tackifiers with it, which many adhesive chemists lament to me about as they search for substitutes to no avail. If you have a route to making alpha-pinene that is new and is not constrained by pine trees, please feel free to contact me at polymerist@substack.com. This is easy for me to write, but I understand that it can take a decade or more for something to become viable. For those of you interested in alpha-pinene, start here or here.

In the short term of the next few years, there are business opportunities around making our conventional chemicals from non-food biomass, with companies like Origin Materials and Avantium as examples around terephthalic acid and ethylene glycol. Being able to produce phenol, ethylene, propylene, and benzene at lower costs than from petroleum for example could unlock biobased routes to chemicals and polymers that our chemical industry can make right now with minimal investment or capital expenditure. If you have a potential route to any industrially relevant platform chemical you should strike up a collaboration with someone in the business school, file a patent before you publish, and see if you can raise some money from venture capitalists.

Graduate school is a great time to work on things that make no economic sense, and when they do make economic sense, a start-up can move much faster than a large chemical company in getting a product to market. Large chemical companies can even become the contract manufacturer for start-ups or provide a viable exit for shareholders and founders. If food delivery companies can raise billions of dollars then I think a promising idea around making platform chemicals from biomass could garner a few million.

I once attended a talk by Stephen Cheng and he explained that a multitude of new polymers are discovered every year, but none of them make it past the laboratory. As a former synthetic polymer chemist I can tell you that it doesn’t pay very well to be a synthetic polymer chemist and the opportunities to be an employed synthetic polymer chemist are somewhat rare. If you are at a point in your life where you can afford to take a risk on a start-up, the upsides are enormous if you can build a successful company. If you’ve tried or you are just trying to get a job in the chemical industry, reach out to me and I’ll help you as much as I can.

If you want to read more things like this, but maybe a bit shorter or longer depending on how I am feeling, check out my weekly newsletter The Polymerist. It’s free to read.

 

Contributed articles reflect the author’s views and not necessarily those of the American Chemical Society.