Olive oil untangles plastic
This is one in a series presenting news on invention and innovation, made possible with generous support from the Lemelson Foundation.
Chefs often add olive oil to spaghetti to aid the cooking process and improve flavor. Now a study finds that olive oil and other vegetable oils can also help make one type of plastic into super-strong fibers. Those fibers are ideal for making products such as bulletproof fabrics or ropes that anchor offshore oil rigs.
All plastics are made of long, spaghetti-like chains of molecules called polymers. One particular polymer has super-long strands. This lightweight plastic is often used in garbage bags and other household products. It’s a type of polyethylene (Pah-lee-ETH-uh-leen), or PE. The chemical’s name is a mouthful: ultra high molecular weight polyethylene. Molecules of this plastic are more than 20 times as long as those in other polyethylenes.
“These are gigantic molecules,” notes Theo Tervoort. He’s a materials scientist who worked on the project at the Swiss Federal Institute of Technology in Zurich.
Those super long molecules are very strong. But the process for making them led them to tangle. You might think of them as being similar to a plate of spaghetti with lots of jumbled strands. Those long molecules must be straightened out and stretched before they’re turned into the fibers that can be woven into some fabric or braided into ropes. That’s where olive oil or other vegetable oils can help.
If you wanted to untangle a plate of spaghetti, you could drop the noodles into a big pot of water. The strands would spread apart. Factories that make fibers from the extra-long PE molecules now do something similar. But instead of water, they use fast-evaporating solvents.
Mixing the PE in a solvent untangles the strands, says Tervoort. Afterward, the PE strands are heated and stretched. “During the stretching, all the chains go nicely in one direction,” he says. That makes long, strong strands of the plastic. At the end of that process, the solvent simply evaporates.
But that’s a problem. Breathing in the solvent fumes can irritate a worker’s lungs or cause other health problems, including some cancers. The fumes also can help cause smog. So factories need to capture the fumes and recycle the solvent.
Despite those problems, these solvents have been part of the special-PE fiber-making process for about 40 years. “Everybody was doing it,” Tervoort says. “Sometimes the simplest thing,” he says — “you don’t question anymore.”
Tervoort and his co-workers stumbled onto using oils on plastic while trying to develop a better type of wax for skis. Applying melted wax helps skis glide more smoothly over snow. But rubbing the wax on is awkward and messy. Tervoort’s group added some of the extra-long PE molecules to the wax. They figured they could then make the wax into a film. That would be easier to put on skis. To their surprise, the wax straightened out the tangled PE molecules they were using.
Wax is a type of oil. So the group tried using oils instead of solvents to make strong, straight PE fibers. Olive oil and peanut oil both worked. So did stearic acid. That chemical is a big part of many animal and vegetable fats.
The researchers described their findings November 30 in the journal Macromolecules.
The veggie oils are safer and better for the environment than the solvents are. Using them is also more efficient. The PE stretches more during that step of the process. And that leads to longer fibers. “You actually get better fibers,” Tervoort says. His team’s finished PE fibers were up to twice as strong as other PE fibers that were untangled using solvents.
It’s still unclear just why the vegetable oils work better. One idea: Maybe they change how the PE forms crystals as it turns into a solid. “That’s what we’re looking at now,” Tervoort says.
The discovery of a new, more environmentally friendly way to make a commonly used polymer illustrates something important about science, says Jeffery White. He’s a polymer scientist at Oklahoma State University in Stillwater who did not work on the study. The discovery by Tervoort’s team’s “follows decades of very basic research” about molecules, says White. “So, a new technology is created because of curiosity-driven research asking [one of] the most fundamental of questions: ‘Why do things work this way?’”
(for more about Power Words, click here)
cancer Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.
chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.
crystal (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.
dissolve To turn a solid into a liquid and dispersing it into that starting liquid. For instance, sugar or salt crystals (solids) will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water
environment The sum of all of the things that exist around some organism or the process and the condition those things create for that organism or process. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.
fat A natural oily or greasy substance occurring in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy reserve. Fat is also a vital nutrient, though it can be harmful to one’s health if over consumed in excess amounts.
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.
polyethylene A plastic made from chemicals that have been refined (produced from) crude oil and/or natural gas. The most common plastic in the world, it is flexible and tough. It also can resist radiation.
polymer A substance whose molecules are made of 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).
recycle To find new uses for something — or parts of something — that might otherwise be discarded, or treated as waste.
smog A kind of pollution that develops when chemicals react in the air. The word comes from a blend of “smoke” and “fog,” and was coined to describe pollution from burning fossil fuels on cold, damp days. Another kind of smog, which usually looks brown, develops when pollutants from cars react with sunlight in the atmosphere on hot days.
solvent A material (usually a liquid) used to dissolve some other material into a solution.
solution A liquid in which one chemical has been dissolved into another.
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
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A.P. Stevens. “Tiny plastic, big problem.” Science News for Students. April 10, 2015.
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J. Raloff. “Home, plastic home.” Science News for Students. July 16, 2013.
E. Sohn. “Our plastic world.” Science News for Students. September 26, 2008.
Original Journal Source: R Schaller et al. High-performance polyethylene fibers “al dente:” improved gel-spinning of ultrahigh molecultar weight polyethylene using vegetable oils. Macromolecules. Vol. 48, November 30, 2015, p. 8877. doi: 10.1021/acs.macromol.5b02211.