World's strongest biomaterial now comes from a tree

A new method creates superstrong fibers out of cellulose
by Katharine Gammon
JUNE 19, 2018

Spider silk has long been considered the strongest biological material in the world and has inspired generations of materials scientists to understand and mimic its properties. However, new findings knock spider silk off its pedestal, reporting that engineered cellulose fibers, derived from plant cell walls, are the strongest biobased material (ACS Nano 2018, DOI: 10.1021/acsnano.8b01084). The material is more than 20% stronger than and eight times as stiff as spider silk. It could eventually be used in lightweight biobased composites for cars, bikes, and medical devices, the researchers say.

L. Daniel Söderberg of KTH Royal Institute of Technology and his colleagues took inspiration from trees in their search for lightweight, strong, renewable materials. The outer cell walls of woody trees provide strength and stiffness, helping trees to stand tall. Those cell walls contain cellulose nanofibers, which are aligned and embedded in a matrix of lignin and hemicellulose. That alignment transmits the exceptional strength and stiffness of individual nanofibers to the macroscale properties associated with wood, says study coauthor Nitesh Mittal. Even so, wood is not as strong as the nanofibers themselves because defects in alignment occur, which weaken the material.

Mittal’s team tried to mimic this structure using commercially available cellulose nanofibers from spruce and pine trees, 2 to 5 nm in diameter and up to 700 nm long. Using a process called hydrodynamic focusing, they squeezed the nanofibers together using streams of water into larger fibers 6 to 8 µm in diameter and up to a meter long.

Using electron microscopy, the team confirmed that the resulting structure mimicked the unique arrangement found in tree cell walls but was even better: The nanofibers aligned nearly perfectly, without defects, in a tight thread.

More:
https://cen.acs.org/materials/biobased-materials/Worlds-strongest-biomaterial-comes-tree/96/web/2018/06?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+biological_scene+%28Chemical+%26+Engineering+News%3A+Biological+SCENE%29