Treating PLA Increases Strength and Lengthens Life

Brown University scientists have created a polymer morphology in PLA that will make the resin stronger and last longer. They say the material could be used medical drug delivery systems, implants, and other applications.

The researchers found that by treating PLA at various temperatures and pressures, they were able to induce a new polymer phase in the material, one that could reduce the rate of degradation.

Altering PLA strength and degradation with heat and pressure. Image source: Mathiowitz lab / Brown University

PLA is semi-crystalline. Parts of its molecular structure are ordered crystals and the remaining are disordered, or amorphous. Previous work with the material has shown that treating PLA with heat increases the material’s crystalline makeup, which could increase its strength. By adding pressure to the treatment process, the Brown research team hoped to further influence the structure of the material.

Using pressures that ranged from 2,000 to 20,000 pounds per square inch at varying lengths of times and with a variety of temperatures, the researchers were able to show that the treatment increased the amount of crystalline area in the material. They also found that at higher pressure/temperature combinations, the amorphous areas of the material became birefringent, an optical property that gives material a refractive index dependent on the polarization and propagation direction of light that hits it. That finding indicates a substantial structural change in the amorphous sections of the material. The processed material showed more order and orientation in the amorphous strands, when viewed with X-ray diffraction. The more ordered strands have a higher glass transition temperature, allowing them to degrade at much slower rates.

With higher strengths and slower degradation, the material could be used for more effective drug delivery and implantation systems, but could also be used as plates and screws that stabilize broken bones. Because it would last longer before breaking down, patients could heal sufficiently to use the implant, and would not require a second surgery for removal.