If you drink juice, water, or milk from a box, you probably take it for granted that the paperboard that the carton is made of won’t let the liquid it contains leak out. And when you reach for a paper cup filled with hot cocoa, coffee, or tea, you certainly don’t want those beverages to soak through the paper and burn you or stain your clothes.
There are precise chemical recipes used to treat different types of paper used to make juice boxes, coffee cups, and other useful paper products. These innovative chemical formulas are discovered by analytical chemists like William C. Johnson, who works for Ecolab.
Johnson does experiments to figure out what kinds of chemicals paper-making companies can add to their products to make them safer, more effective, and ecologically sustainable. “I work for a company that supplies chemicals to the paper maker — the person taking the fiber from trees and turning it into a board or sheet of paper. We innovate and sell chemicals to them” to help them improve the performance of their end products.
It’s not obvious that liquids wouldn’t pass through paper. The cellulose (wood fibers) used in paper-making is hydrophilic: it loves water!
Trees drink water — they need it for photosynthesis, the chemistry their leaves use to turn water and carbon dioxide into energy-rich sugar and oxygen. They absorb some of the water they need through tiny holes in their leaves. In addition to absorbing water through their leaves, trees pull it up from the soil through the xylem (long pipe-like structures with tiny diameters) in their wood. This is why the cellulose we get from wood pulp is absorbent and not necessarily the best resource for carrying liquids. It’s more obviously useful for creating tissue, including paper towels and toilet paper.
So why use paper for liquid-containing cups and boxes?
Glass is heavy and breakable. Plastic bottles are not easily recycled and tend to end up polluting Earth’s soil and water. And it takes a lot of energy to produce metal cans, which might rust.
Paper does not weigh much and is easily recycled. Finding ways of using it to hold liquids makes a lot of sense, especially if we can make its surface less absorbent.
This is where Analytical Chemist William C. Johnson’s expertise in surface-based chemistry comes in handy. He does something called “sizing,” adding ingredients to paper to make it work better in the cups, boxes, and other products that use it. Johnson puts polymers on the surface of paper and studies the ways that they improve what the paper can do. (Polymers are large molecules made up of repeating units called monomers. Some occur in nature while others (like most types of plastic) are created by chemists like Johnson.)
How do the polymers (or how does paper containing them) behave when exposed to different liquids? Do they absorb just enough ink, without letting letters and pictures on the outside of a container sink too far towards the inner surface? Do they make the paper hydrophobic, preventing it from absorbing water and other liquids? These are just two of the many questions Johnson answers in his lab.
Do the polymers leach into the liquids inside a container? What happens when they are exposed to liquids at different temperatures? Coffee is brewed at temperatures above 93 degrees Celsius / 200 degrees Fahrenheit and milk freezes below 0 degrees Celsius / 32 degrees Fahrenheit. Coffee cups and milk cartons need to be made of paper that can handle these types of temperatures.
Johnson runs experiments to explore questions like these. His knowledge of math and chemistry helps him every step of the way.
“I definitely use math when I design my experiments,” Johnson tells Math4Science. It helps him figure out why a particular molecule added to paper works as well as it does. “Is charge driving performance? Structure? (Is it more linear? More string-like? More clustered?)” And how about size: “how big is this polymer molecule?” And how much does that affect its performance?
Statistical analysis software helps Johnson analyze the results of his experiments in detail. He creates computer models of whichever molecule he wants to know more about, exploring how different charges, shapes, or sizes affect a paper’s behavior.
For instance, Johnson uses computer models to explore the ways that molecules with different molecular weights are affected by temperature, as molecular weight can change a molecule’s stability and performance. Will the structure and conformation of polymers added to coffee cups allow them to hold liquids above water’s boiling point (100 degrees Celsius / 212 degrees Fahrenheit)? Will they keep liquids from penetrating the paper’s surface and its edge? How will paper containing these polymers behave on very hot machines?
Johnson also runs experiments to find out which chemicals added to paper come off, ending up in the environment. “We put polymers in the board and see what leaks out when [they come into] contact with aqueous liquids or dry food.” Government regulations and human health requirements make it important to make sure that drinking juice or water out of a box doesn’t mean putting extra chemicals from its container into your body. “As regulations get stricter, we need to make sure the chemistries we are developing meet stringent regulation standards.”
Remember the more absorbent types of paper — the tissues that take advantage of cellulose’s love of water (hydrophilia)? “You want a paper towel to pick up as much water as you can” and “to have strength as you’re using it.” And “if you flush toilet paper, you want it to break apart so it doesn’t mess up the septic system.” In other words, you want something that’s very strong when dry that “breaks apart very easily” when wet. Johnson and his colleagues “build different types of polymers to do these different types of things.”
To create new molecules, improving products used in homes, work places, and public spaces, “I have to have a solid knowledge of chemistry.” “My knowledge of organic chemistry allows me to build certain molecules that I know will interact with something, creating a desired bond.”
And it helps Johnson understand how the chemicals he builds will interact with other substances. “I have to have knowledge of chemistry to get the kind of reaction that I desire.” So when, for instance, bacteria feed on the lactose in packaged milk, producing lactic acid, Johnson can explore the effects of that acid on milk containers. In addition to investigating the structure of polymers, he also measures other properties, such as pH and viscosity. These factors can directly affect which reactions occur in the paper-making process.
His knowledge of science and math also helps Johnson when it comes to budgeting, responding to new commercial requirements, and creative marketing. “I have to make sure my work is cost-effective for my company. When I think about functionality, I have to try to think outside of the box.”
Until recently, industries have relied on “a lot of oil- or petroleum-based materials but as things go greener, we can use plant-based materials.” To help with that transition, Johnson and his colleagues “need a good, innovative knowledge of chemistry. Having that wide range of chemistry knowledge allows you to be creative and innovative.”
As a child growing up in Brunswick, a town on the coast of Georgia, Johnson was already asking important questions and looking for creative ways of solving them. “If I asked someone why the sky was blue and they said ‘God made it that way,’ that wasn’t enough for me.” Eager to understand the world around him, William read the magazine Popular Mechanics. His father, who got him that subscription, was an engineer — “he was a very inquisitive man also and had an innate ability to problem-solve.”
“But I wanted to understand things you couldn’t see, on a microscopic level.” Examining paints on different walls, William asked “Why is this so shiny?” And why could you wipe crayon marks off some painted walls but not others? “Now there are anti-graffiti walls: why does this paint not stick to [them]? Those are questions I would ask myself…. Nobody had answers for me, so I read a lot and learned to be self-taught.”
His curiosity, skills in math and science, and reading led Johnson to Tuskegee University, where he first chose mechanical engineering for his major. But “I didn’t like engineering much. Chemical engineers were manufacturing chemicals, but I wanted to build them from the ground up,” so Johnson became a chemistry major. And after finishing his Bachelors in Science, he went to the University of Michigan, where he completed his doctorate in analytical chemistry and learned surface science.
The pulp and paper industry still “needs more giant leaps forward. I accepted that challenge and have been with my company for twelve years now.” Johnson’s career has not always been an easy one. In his childhood town of Brunswick, where many people worked at a local paper mill and in the shrimping industry, “there weren’t a lot of mentors for me” or “PhDs in the sciences and I didn’t have a lot of people to talk with about my burgeoning aspirations.” He credits his parents with providing a safety net and allowing him to explore his dreams and let him find himself.
Because he understands the importance of mentorship and the ways that completing a PhD advances one’s career, Johnson makes a point of seeking out people who remind him of his younger self. He helps “send them to different schools with good programs” and points out how helpful it can be to “go to a certain university to work with the leading researcher in the area you’re interested in.” He urges students interested in science to ask themselves these questions: “Are you an independent thinker and problem-solver? Are you imaginative? Do you work well with others? In the industry, it’s all about working together. Most times, the best ideas are collaborative.”