Innovation

Adhesive from trees could make tape more eco-friendly

Tape is convenient but not environmentally friendly. A new adhesive for tape comes from trees instead of crude oil. ANGINTARAVICHIAN/ISTOCKPHOTO

This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

When you have to wrap a gift or mend the ripped page of a book, you probably reach for a piece of tape. The sticky stuff is everywhere. But tape has a downside. Its adhesive — the substance that makes it stick — is made from a fossil fuel. Now a team of scientists has come up with a greener solution. They’ve made a new glue from chemicals found in trees.

They described their innovation online May 15 in the journal ACS Central Science.

Sticky tape has been around for more than 80 years. It relies on a special kind of glue. As you push down on a piece of tape, the adhesive on the sticky side seals tightly. But you can easily peel it back off. Some adhesives even come off without leaving anything behind.

Tape adhesives are polymers. These are long molecules made from chains of repeating chemical building blocks. To make polymers, researchers can use ingredients from many different sources. One common source is crude oil. Companies today use the hydrocarbons that make up this oil for their tape adhesives.

But crude oil is a fossil fuel. It takes millions of years to develop. So once people extract fossil fuels from the Earth, they can’t be quickly replaced. Processing them also emits pollution, including greenhouse gases.

A team of researchers at the University of Delaware, in Newark, thought they could find a greener option — one friendlier to the environment. “We wanted to make polymers from natural, renewable resources,” says Shu Wang. She is a materials scientist who now works at Bridgestone Americas in Nashville, Tenn.

Lignin is a natural polymer. It makes woody plants strong and stable. And viewed up close, lignin’s chemical structure resembles that of oil’s hydrocarbons. So Wang and her colleagues wondered whether they could substitute plants for oil as a starting ingredient. And their new data confirm that they can.

Turning trees into tape

Wang’s team started with poplar trees. They soaked its wood in chemicals to break the lignin’s long, chain-like molecules into smaller bits. They collected these small pieces. The

Sludge from paper making contains chemicals that could be used in many ways. Lignin, one of these chemicals, could become a raw ingredient for tape adhesives.
U.S. Department of Energy/Flickr

n they made some minor chemical tweaks. This gave their polymer the chemical traits that they wanted. Finally, the team linked these altered fragments to build new polymers. They designed these chains to mimic the oil-based types used for today’s tape adhesives.

They coated a thin, tape-like piece of plastic with the new glue. Then they conducted “peel tests.” They measured the force needed to peel off the tape after it had been pressed down flat. The researchers compared this test tape to types that you can buy today in the store.

And their new tape performed well. “The force needed to pull up tape with our adhesive on it was similar to the force needed to pull up Scotch tape, or Fisherbrand labeling tape,” Wang says. (Keep in mind, you don’t want tape to peel up too easily. If it does, those ripped book pages won’t stay mended.)

If this new adhesive were someday used for store-bought tapes, it could help the environment in more than one way. Lignin is a waste from making paper and ethanol from trees. So this glue wouldn’t just replace adhesives made from crude oil. It also would prevent lignin from going in the trash.

Thomas Epps III is a chemical engineer and materials scientist at the University of Delaware. He led the team that invented the new glue. “We have taken a renewable material that is normally thrown away,” he notes, “and turned it into something useful.”

Zhuohua Sun agrees. A chemist at the University of Groningen in the Netherlands, he did not take part in the new research. “They’ve made something useful from a renewable and widely available material,” he says.

Epps hopes that he and his colleagues can use different plants to make even more adhesives. “Could we use corn or switchgrass as an alternative to trees?” he asks. “If this is possible, it would certainly expand the types of glues we can create.”

Power Words

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemical engineer     A researcher who uses chemistry to solve problems related to the production of food, fuel, medicines and many other products.

colleague     Someone who works with another; a co-worker or team member.

crude oil     Petroleum in the form as it comes out of the ground.

develop     To emerge or come into being, either naturally or through human intervention, such as by manufacturing.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

ethanol     A type of alcohol, also known as ethyl alcohol, that serves as the basis of alcoholic drinks, such as beer, wine and distilled spirits. It also is used as a solvent and as a fuel (often mixed with gasoline, for instance).

extract     (v.) To separate one material or chemical (or component of something) from a complex mix.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

fossil fuel     Any fuel — such as coal, petroleum (crude oil) or natural gas — that has developed within the Earth over millions of years from the decayed remains of bacteria, plants or animals.

fuel     Any material that will release energy during a controlled chemical or nuclear reaction. Fossil fuels (coal, natural gas and petroleum) are a common type that liberate their energy through chemical reactions that take place when heated (usually to the point of burning).

glue     A sticky substance that attaches one material to another.

greenhouse gas     A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.

hydrocarbon     Any of a range of large molecules containing chemically bound carbon and hydrogen atoms. Crude oil, for example, is a naturally occurring mix of many hydrocarbons.

innovation     (v. to innovate; adj. innovative) An adaptation or improvement to an existing idea, process or product that is new, clever, more effective or more practical.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

lignin     A natural substance that helps strengthen the cell walls of plants. Although lignin is made from a large number of sugar molecules, which should provide energy, livestock can’t digest this material because of the way its sugars are chemically bonded together.

materials science     The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application. A scientist who works in this field is known as a materials scientist.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

plastic     Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

polymer     A substance made from long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).

trait     A characteristic feature of something.

waste     Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

wood     A porous and fibrous structural tissue found in the stems and roots of trees, shrubs and other woody plants.

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