A team at Osaka University (Japan) have developed tough biodegradable plastics that bring the goal of a resource-circulating society one step closer.
The key, they found, is developing polymers with movable crosslinks. The crosslinks not only increase their strength but also promote degradation by enzymes under mild conditions.
According to their paper, published this month in Chem, the movable crosslinks are ring-like cyclodextrins, which are threaded on one polymer strand and attached to another, endowing the resulting plastics with increased toughness and durability.
In fact, according to tests, the crosslinks increased polymer toughness by over eight times
"Stiffness, ductility, fracture stress, and fracture strain all improved because the cyclodextrin groups effectively dispersed local stress,” said lead author of the study Jiaxiong Liu.
The cyclodextrin crosslinks also facilitated degradation of the polymers during subsequent enzymatic treatment because their bulky structure increased the free volume in the polymer network, which improved access of the enzyme to the target cleavage sites on the polymer chains.
"The polymers were readily degraded by Novozym 435, an enzyme that specifically attacks the ester bonds of the polymer backbone," said Yoshinori Takashima, senior author. "The presence of the bulky cyclodextrin crosslink groups decreased entanglement and aggregation of the polymer chains, which facilitated the access of the enzyme to the ester bonds for cleavage."
As a result, biodegradability was improved by 20 times compared with that of the polymer without cyclodextrin groups.
These advanced biodegradable plastics can readily be broken down by enzymes into useful precursor molecules that could be reused in further materials, ultimately contributing to the advancement of a resource-circulating society.
Information provided by Osaka University.