TY - GEN
T1 - A Stress-Responsive Shape Memory Polymer via Chemical Grafting Functionalized Cinnamoyl-Based Mechanophore
AU - Zhao, Xingbang
AU - Whitney, Chris
AU - Roman, Jose
AU - Chattopadhyay, Aditi
AU - Dai, Lenore L.
N1 - Publisher Copyright:
© 2023 by DEStech Publications, Inc. and American Society for Composites. All rights reserved.
PY - 2023
Y1 - 2023
N2 - Due to the intrinsic mechanochemical characteristics, shape memory polymers (SMPs) with multifunctionalities are highly desirable for structural applications. The capability of self-sensing for early damage has been extensively investigated. The general fabrication technique for feature incorporation is to blend stress-responsive additives directly; however, this approach usually leads to performance tradeoffs. Here, we have developed a method to attach a cinnamoyl-based mechanophore to the backbone of the SMP matrix via a chemical grafting technique. We have varied weight ratios of mechanophore, which exerts its amine functionality to mingle with Jeaffmine D230 forming an advanced crosslinker and allowing for the fabrication of a stress-responsive polymeric network inside an SMP matrix. Dynamic mechanical analysis (DMA) and quasi-static tensile tests were performed to characterize the mechanical and thermal properties of SMP thermoset samples and investigate the optimal weight ratio. Meanwhile, the rubber elasticity plateau is utilized to calculate the crosslinking densities for the SMP samples. The storage moduli and glass transition temperatures of SMP-based thermoset samples were slightly reduced with the lower weight ratio of mechanophore on 5 wt.% and 7.5 wt.%. With increasing mechanophore loading weight to 9 wt.%, the storage modulus and glass transition temperatures of baseline SMP improved by 9.0 % and 15.7 %, respectively. Interestingly, increasing the weight ratio of mechanophore to 10 wt.% and 12.5 wt.% caused the property reduction again. This could be attributed to the over-saturation from self-polymerization or unreacted mechanophore affecting the SMP matrix negatively. Quasi-static tensile tests were performed while the instrument is coupled with in situ fluorescence detection setup to monitor the self-sensing capabilities under given loading conditions. As shown in Figure 1, the mechanophore-activated mechanism is accomplished via a reversible [2+2] cycloaddition process. The stress-responsive mechanophore, upon bond scission resulting from material strain, undergoes cycloreversion to produce a measurable fluorescent signal. In situ fluorescence responsive behavior on the comparably better sample, 9 wt.% mechanophores functionalized SMP, was successfully captured by a UV camera and quantified in situ by the stress-strain curves. Additionally, the reversibility of mechanophore can be achieved by re-exposure to a UV light source through the [2+2] cycloaddition process to facilitate a feasibility study of photochemical-aided self-healing capable mechanophore functionalized SMP. We further quantify the shape recovery performance via a modified thermal loading profile through the DMA experiment. Cyclic testing was performed to determine the recovery ratio and fixity ratio. The characterization enables understanding the significance of mechanophore on the SMP matrix and investigating the tradeoff between improvements in SMP multifunctionality. This synergistic method provides a promising approach to associating various features and characteristics of the multifunctional SMP for implementation in fiber-reinforced composites with superior mechanical and thermal properties as well as self-sensing capabilities.
AB - Due to the intrinsic mechanochemical characteristics, shape memory polymers (SMPs) with multifunctionalities are highly desirable for structural applications. The capability of self-sensing for early damage has been extensively investigated. The general fabrication technique for feature incorporation is to blend stress-responsive additives directly; however, this approach usually leads to performance tradeoffs. Here, we have developed a method to attach a cinnamoyl-based mechanophore to the backbone of the SMP matrix via a chemical grafting technique. We have varied weight ratios of mechanophore, which exerts its amine functionality to mingle with Jeaffmine D230 forming an advanced crosslinker and allowing for the fabrication of a stress-responsive polymeric network inside an SMP matrix. Dynamic mechanical analysis (DMA) and quasi-static tensile tests were performed to characterize the mechanical and thermal properties of SMP thermoset samples and investigate the optimal weight ratio. Meanwhile, the rubber elasticity plateau is utilized to calculate the crosslinking densities for the SMP samples. The storage moduli and glass transition temperatures of SMP-based thermoset samples were slightly reduced with the lower weight ratio of mechanophore on 5 wt.% and 7.5 wt.%. With increasing mechanophore loading weight to 9 wt.%, the storage modulus and glass transition temperatures of baseline SMP improved by 9.0 % and 15.7 %, respectively. Interestingly, increasing the weight ratio of mechanophore to 10 wt.% and 12.5 wt.% caused the property reduction again. This could be attributed to the over-saturation from self-polymerization or unreacted mechanophore affecting the SMP matrix negatively. Quasi-static tensile tests were performed while the instrument is coupled with in situ fluorescence detection setup to monitor the self-sensing capabilities under given loading conditions. As shown in Figure 1, the mechanophore-activated mechanism is accomplished via a reversible [2+2] cycloaddition process. The stress-responsive mechanophore, upon bond scission resulting from material strain, undergoes cycloreversion to produce a measurable fluorescent signal. In situ fluorescence responsive behavior on the comparably better sample, 9 wt.% mechanophores functionalized SMP, was successfully captured by a UV camera and quantified in situ by the stress-strain curves. Additionally, the reversibility of mechanophore can be achieved by re-exposure to a UV light source through the [2+2] cycloaddition process to facilitate a feasibility study of photochemical-aided self-healing capable mechanophore functionalized SMP. We further quantify the shape recovery performance via a modified thermal loading profile through the DMA experiment. Cyclic testing was performed to determine the recovery ratio and fixity ratio. The characterization enables understanding the significance of mechanophore on the SMP matrix and investigating the tradeoff between improvements in SMP multifunctionality. This synergistic method provides a promising approach to associating various features and characteristics of the multifunctional SMP for implementation in fiber-reinforced composites with superior mechanical and thermal properties as well as self-sensing capabilities.
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M3 - Conference contribution
AN - SCOPUS:85178595500
T3 - Proceedings of the American Society for Composites - 38th Technical Conference, ASC 2023
SP - 2131
EP - 2142
BT - Proceedings of the American Society for Composites - 38th Technical Conference, ASC 2023
A2 - Maiaru, Marianna
A2 - Odegard, Gregory
A2 - Bednarcyk, Brett
A2 - Pineda, Evan
PB - DEStech Publications
T2 - 38th Technical Conference of the American Society for Composites, ASC 2023
Y2 - 18 September 2023 through 20 September 2023
ER -