Polymers reinforced with carbon or glass fibers, often called polymer composites, are widely used in building car body parts, from bumpers to interior panels. Engineers would prefer to reinforce polymers with plant fibers because they’re cheap, abundant, and environmentally friendly, but those materials often don’t bond well with the polymer and take up too much moisture, causing the composites to swell. Now, with a pinch of salt, researchers have shown a way to improve the fibers’ moisture resistance, tensile strength, and interaction with the polymer (ACS Omega 2026, DOI: 10.1021/acsomega.6c00108).
The researchers dipped hemp and jute fibers into an aqueous suspension with a mass fraction of 40% calcium carbonate, the soft white powder found in limestone, seashells, and antacid tablets. After they dried, fibers were left with calcium carbonate particles distributed across their surfaces. The treated hemp fiber had taken up only about 5% of its own weight in water, and the jute had taken up only about 3%. Tensile strength grew from approximately 498 MPa to 904 MPa in the hemp and from approximately 539 MPa to about 960 MPa in the jute. An increased roughness of the surface should also help the fiber to bond with the polymer, says Dounia Boushab, a mechanical engineer at Pacific Northwest National Laboratory and first author of the paper.
Scanning electron microscope images of hemp (top) and jute (bottom) fibers show their untreated (left) and treated (right) states. The calcium carbonate–treated fibers have more surface roughness and sheer more cleanly when pulled apart. Credit:
Adapted from ACS Omega
The calcium carbonate coats the surface but does not chemically interact with the fiber, Boushab says. That’s different from the outcome of a previous method of treating natural fibers using sodium hydroxide, which strips out components such as lignin and surface oils. That approach is “chemically harsh, and you might end up degrading the fiber,” she says.
The project focused on the main fibers used in automotive applications, but Boushab says this strengthening method should work on other plant fibers, such as cotton.
