The University of Tennessee has partnered with the Eastman Chemical Company for decades, repurposing waste from Neyland Stadium and driving innovation in materials design both on and off campus.
Their latest collaboration, published last year, resulted in a new method to ensure consistency and quality in rubber manufacturing.
“We had three senior Eastman participants and three UT team members collaborating,” said UT Fred N. Peebles Professor Dayakar Penumadu, the lead author on the paper. “The diversity of the team helped produce a very good project.”
Indeed, the paper has received the 2021 Publication Excellence Award from the journal of Rubber Chemistry and Technology.
“This award was a pleasant surprise and a great honor for everyone who contributed to this work,” said Penumadu.
The groundbreaking paper outlines a new method for visualizing how additives are distributed in a rubber mixture before the material is vulcanized (heated and set).
When they are evenly distributed, additives like zinc oxide and sulfur improve rubber strength, elasticity, and other favorable traits. However, poor distribution results in hard clumps and unpredictable quality.
“If components such as sulfur do not disperse well, that generates locally hard spots,” said Penumadu. “That hard stuff attracts a lot of mechanical and thermal stresses, making the material degrade prematurely.”
Even a flaw the width of a human hair can decrease the lifespan of a large rubber component, like a car tire.
“That leads to safety and economic impacts,” Penumadu said.
Finding such flaws before they cause problems is an issue that has long plagued the rubber industry.
“The current industry approach is to cut out a small sample of rubber, then observe it under an optical microscope,” Penumadu said. “Not only is this tedious and destructive, it’s unreliable. It requires you to guess beforehand where in an opaque sample you need to check for inconsistencies.”
Optical microscopes also cannot differentiate between rubber components—for example, sulfur and zinc oxide both appear as white specks.
Penumadu’s team has overcome this issue by switching from optical analysis to X-ray computed tomography (XCT). In this method, X-rays pass through the sample, getting scattered and absorbed differently depending on the materials they strike. A computer then reconstructs a digital 3D model of the rubber’s interior.
“This is a very important point,” Penumadu said. “XCT lets us see the inside of the material non-invasively, and we can actually see the distribution of each component.”
In the award-winning paper, Penumadu’s team was able to view the 3D dispersion of the sulfur in the uncured rubber, and even identify sulfur particles of problematic size.
“Physical test results after vulcanization agreed very well with what we predicted based on XCT,” said Penumadu. “That means our method is extremely powerful for quality control and assurance.”
Penumadu’s team will receive their award at the International Elastomer Conference in Knoxville in early October.