Researcher develops flexible PLA that withstands boiling water
For the past several years, University of Akron Professor Shi-Qing Wang has worked on the development of a polylactic acid resin with improved mechanical properties.
In his lab in UA's School of Polymer Science and Polymer Engineering, he and his team are focused on turning brittle polymers such as PLA into tough and flexible materials. Currently, the range of applications for these polymers have remained somewhat limited, because they break relatively easily under moderate load.
While petroleum-based polymer materials offer well-known advantages such as strength and light weight, these materials are increasingly causing problems at the end of life.
The group has now reported its first success: It has produced a prototype PLA cup that is transparent, extremely tough and does not shrink when filled with boiling water.
Ramani Narayan, distinguished professor in Michigan State University's Department of Chemical Engineering and Materials Science, and a renowned scientist in the bioplastics space, said Wang's research has the potential to be a breakthrough in the PLA market.
Narayan was not involved in the research, but learned about the work being done by Wang when one of Wang's former students, who is currently on the faculty at MSU, invited Wang to present a seminar there.
"PLA is the world's foremost 100 percent bio-based and fully compostable polymer," Narayan said. "But it has low toughness and a low heat distortion temperature. It softens and structurally collapses around 140º F, making it unusable in many hot food packing applications and disposable containers.
"Wang's research could be disruptive technology because his prototype PLA cup is tough, transparent, and yet rigid enough to hold boiling water," Narayan said.
The challenge facing Wang and his team was to gain insight into why one polymer is tougher than the other, and how to make these tougher and more resistant to breaking. They first looked at the origin of ductility in semicrystalline polymers.
As Wang explains it, polymer strands are similar to intertwined cooked spaghetti, forming chain networks that give thermoplastics their toughness. However, crystallization can remove or disrupt the intertwining of these chains.
Properly manipulated, the chain network ensures that the PLA beverage cup is mechanically strong without crystallization. But such a commercial cup collapses when boiling water is poured into it.
"Cups made from normally crystallized PLA can hold boiling water but are terribly brittle and opaque," Wang said.
What Wang and his research group have done is to develop a way to limit crystals in PLA while preserving the network, resulting in the clear, tough and heat resistant cup. Its optical transparency is a key characteristic. The cup can hold hot tea and coffee and has the potential to replace most plastic beverage cups on the market.
In addition, compared to conventional crystalline PLA, this new form of PLA should be easier to undergo hydrolysis, the first step in its biodegradation, he says.
"The impact of our new understanding could finally stimulate the PLA market to grow exponentially," Wang said. "And if PLA finds wider use, the price will come down more. It's a matter of making PLA more competitive in terms of its mechanical and other characteristics."
A U.S. patent on how to modify PLA based materials has been filed through UA's Office of Technology Transfer. However, the team has not yet explored the possibility of finding industrial partners to commercialize the development.