Break­through Smart Plastic: Self-Heal­ing, Shape-Shift­ing and Stronger Than Steel

The break­through — fun­ded by the U.S. Depart­ment of Defense and pub­lished in Mac­ro­molec­ules and the Journ­al of Com­pos­ite Mater­i­als — was led by Dr. Mohammad Naraghi, dir­ect­or of the Nano­struc­tured Mater­i­als Lab and pro­fess­or of aerospace engin­eer­ing at Texas A&M, in close col­lab­or­a­tion with Dr. Andreas Polycarp­ou at The Uni­ver­sity of Tulsa.

Their work explored the mech­an­ic­al integ­rity, shape-recov­ery and self-heal­ing prop­er­ties of an advanced car­bon-fiber plastic com­pos­ite called Aro­mat­ic Ther­moset­ting Copoly­es­ter (ATSP)

Heal­ing Dam­age On Demand

ATSP opens new fron­ti­ers in indus­tries where per­form­ance and reli­ab­il­ity are crit­ic­al, and fail­ure isn’t an option.

“In aerospace applic­a­tions, mater­i­als face extreme stress and high tem­per­at­ures,” Naraghi said. ​“If any of these ele­ments dam­age any part of an air­plane and dis­rupt one of their main applic­a­tions, then you could per­form on-demand self-healing.”

As ATSP matures and scales, it holds the poten­tial to trans­form com­mer­cial and con­sumer indus­tries, par­tic­u­larly the auto­mot­ive sector. 

“Because of the bond exchanges that take place in the mater­i­al, you can restore a car’s deform­a­tions after a col­li­sion, and most import­antly, sig­ni­fic­antly improve vehicle safety by pro­tect­ing the pas­sen­ger,” Naraghi said.

ATSP is also a more sus­tain­able altern­at­ive to tra­di­tion­al plastics. Its recyc­lab­il­ity makes the mater­i­al an ideal can­did­ate for indus­tries aim­ing to reduce envir­on­ment­al waste without com­prom­ising dur­ab­il­ity or strength.

“These vit­ri­mers, when rein­forced with dis­con­tinu­ous fibers, can under­go level cyc­ling — you can eas­ily crush and mold it into a new shape, and this can hap­pen across many, many cycles, and the chem­istry of the mater­i­al basic­ally doesn’t degrade,” he said.

Uncov­er­ing ATSP’s Capabilities

“ATSPs are an emer­ging class of vit­ri­mers that com­bine the best fea­tures of tra­di­tion­al plastics,” Naraghi said. ​“They offer the flex­ib­il­ity of ther­mo­plastics, with the chem­ic­al and struc­tur­al sta­bil­ity of ther­mosets. So, when com­bined with strong car­bon fibers, you get a mater­i­al that is sev­er­al times stronger than steel, yet light­er than aluminum.”

What sets ATSP apart from tra­di­tion­al plastics is its self-heal­ing and shape-recov­ery capabilities.

“Shape recov­ery and self-heal­ing are two facets of the same mech­an­ism,” Naraghi explained. ​“With shape recov­ery, it refers to the bond exchange with­in a con­tinu­ous piece of mater­i­al — a kind of built-in ​‘intel­li­gence.’ And, in self-heal­ing, there’s dis­con­tinu­ity in the mater­i­al like a crack. These are the prop­er­ties we investigated.”

To invest­ig­ate its prop­er­ties, the research­ers used a nov­el stress-test called cyc­lic­al creep testing.

“We applied repeated cycles of tensile, or stretch­ing, loads to our samples, mon­it­or­ing changes in how the mater­i­al accu­mu­lated, stored and released strain energy,” Naraghi said.

Using cyc­lic­al load­ing, the research­ers iden­ti­fied two crit­ic­al tem­per­at­ures with­in the material.

“The first is the glass trans­ition tem­per­at­ure, or the tem­per­at­ure at which the poly­mer chains can move around eas­ily, and the second is the vit­ri­fic­a­tion tem­per­at­ure. That’s the tem­per­at­ure at which these bonds are thermally activ­ated enough that you can see massive bond exchanges to cause heal­ing, reshap­ing and recov­ery,” he said.

The team then con­duc­ted deep-cycle bend­ing fatigue tests, peri­od­ic­ally heat­ing the mater­i­al to around 160 degrees Celsi­us to trig­ger self-healing.

Their res­ults showed that the ATSP samples not only endured hun­dreds of stress and heat­ing cycles without fail­ure, but that they actu­ally grew more dur­able dur­ing the heal­ing process.

“Much like skin can stretch, heal and return to its ori­gin­al shape, the mater­i­al deformed, healed and ​‘remembered’ its ori­gin­al shape, becom­ing more dur­able than when it was ori­gin­ally made,” Naraghi said.

Crack, Heal, Repeat

Naraghi and his team put the heat-res­ist­ant ATSP through five gruel­ing stress cycles, each fol­lowed by high tem­per­at­ure expos­ure at 280 degrees Celsius.

The goal? To assess the material’s per­form­ance and self-heal­ing properties.

After two full dam­age-heal­ing cycles, the mater­i­al returned to nearly full strength. By the fifth cycle, heal­ing effi­ciency dropped to about 80% because of mech­an­ic­al fatigue.

“Using high-res­ol­u­tion ima­ging, we observed that the com­pos­ite after dam­age and heal­ing was sim­il­ar to the ori­gin­al design, though repeated dam­age caused some loc­al­ized mech­an­ic­al wear attrib­uted to man­u­fac­tur­ing defects,” Naraghi said.

Still, the material’s chem­ic­al sta­bil­ity and self-heal­ing beha­vi­ors remained reli­able across all five cycles.

“We also observed that there was no thermal degrad­a­tion or break­down in the mater­i­al, demon­strat­ing its dur­ab­il­ity even after dam­age and heal­ing,” Naraghi said.

Power­ing Innov­a­tion Through Stra­tegic Partnerships

Naraghi’s work, sponsored by the Air Force Office of Sci­entif­ic Research (AFOSR) and in col­lab­or­a­tion with ATSP Innov­a­tions, under­scores Texas A&M’s com­mit­ment of driv­ing tech­no­lo­gic­al innov­a­tions into revolu­tion­ary cap­ab­il­it­ies that advance U.S. defense and industry priorities.

“Our part­ner­ships are very import­ant,” Naraghi said. ​“In addi­tion to sup­port­ing us fin­an­cially, the pro­gram man­agers at AFOSR col­lab­or­ate with us and offer valu­able guid­ance on ques­tions that could have been over­looked. Our close col­lab­or­a­tion with ATSP Innov­a­tions has also proven to be very fruit­ful and very important.”

The research team’s break­through rep­res­ents more than an emer­ging class of mater­i­als; it’s a blue­print for how bold sci­ence and stra­tegic part­ner­ships can redefine a future where plastics don’t just endure, they evolve and adapt.

“My stu­dents and post-docs do the heavy lift­ing — I can­not thank them enough,” Naraghi added. ​“It’s through tri­al and error, col­lab­or­a­tions and part­ner­ships that we turn excit­ing curi­os­ity into impact­ful applications.”