Reconfigurable Shape Memory and Self-Welding Properties of Epoxy Phenolic Novolac/Cashew Nut Shell Liquid Composites Reinforced with Carbon Nanotubes

Abstract

Conventional shape memory polymers (SMPs) can memorize their permanent shapes. However, these SMPs cannot reconfigure their original shape to obtain a desirable geometry owing to permanent chemically or physically crosslinked networks. To overcome this limitation, novel SMPs that can be reconfigured via bond exchange reactions (BERs) have been developed. In this study, polymer composites consisting of epoxy phenolic novolac (EPN) and bio-based cashew nut shell liquid (CNSL) reinforced by multi-walled carbon nanotubes (CNTs) were prepared. The obtained composites exhibited shape memory and self-welding properties, and their shapes could be reconfigured via BERs. Their shape memory mechanisms were investigated using variable-temperature Fourier transform infrared spectroscopy and dynamic mechanical analysis. The EPN/CNSL composite containing 0.3 wt % CNTs showed the highest shape fixity and shape recovery ratio. Furthermore, shape memory behavior induced by irradiation of near-infrared (NIR) light was also observed. All samples showed high shape recovery ratios of nearly 100% over five cycles, and increasing the CNT content shortened the recovery time remarkably. The ability of shape reconfiguration and stress relaxation affected the photo-induced shape memory properties of reshaped samples. Additionally, the self-welding properties were also influenced by stress relaxation. The hindrance of stress relaxation caused by the CNTs resulted in a decrease in adhesive fracture energy (Gc). However, the Gc values of EPN/CNSL composites were comparable to those of epoxy vitrimers. These results revealed that the material design concepts of thermal- and photo-induced shape memory, shape reconfiguration, and self-welding were combined in the EPN/CNSL composites, which could be feasible method for advanced smart material applications.

Multiwalled Carbon Nanotube Reinforced Bio-Based Benzoxazine/Epoxy Composites with NIR-Laser Stimulated Shape Memory Effects

“…However, the shape recovery value of MWCNT reinforced V-fa/ECO composite was dropped to 92% when the MWCNT weight percentage was 0.5 wt% due to the aggregation of the MWCNTs. Similar behavior was also observed in MWCNT-filled shape memory epoxy phenolic novolac and cashew nut shell liquid [49] and polyurethane/MWCNT composites [64].…”

“…The curing conversion of 94.8% was selected for further investigation. Partially bio-based systems of epoxy phenolic novolac (EPN)/cashew nut shell liquid composites reinforced with MWCNTs at curing conversions of 80 to 98% exhibited good shape memory performances as reported by Kasemsiri et al [49].…”

“…The glassy state modulus at −100 °C of MWCNT reinforced V-fa/ECO composites at MWCNT contents of 0, 0.1, 0.3, and 0.5 wt% were 1.33, 1.44, 2.01, and 1.03 GPa, respectively. The storage modulus values of MWCNT reinforced V-fa/ECO composites reached the maximum value when MWCNT mass concentration was 0.3 wt% due to the homogeneous dispersion of nanofiller within the polymer matrix [49]. During the V-fa/ECO binary mixture preparation, V-fa monomer might be adsorbed onto the surfaces MWCNTs, facilitating the dispersion of MWCNTs within the mixture [51].…”

Preparation of modified multi‐walled carbon nanotubes as a reinforcement for epoxy shape‐memory polymer composites

“…kind of connection is much weaker than chemical bonds, so unmodified MWCNTs only slightly improve the toughness of the structure. 31,32 The fracture surface of PM-COOH ( Figure 6E,F)…”

Vitrimer-Like Shape Memory Polymers: Characterization and Applications in Reshaping and Manufacturing

“…In recent years, many new types of vitrimers have been invented via different approaches for enhanced performance and/or for some special features (such as, the novel SME or self-folding/unfolding [ 21 , 22 , 23 , 24 , 25 ], i.e., reshaping), malleability and reprocessability by hot-pressing (i.e., associated with recycling as thermo-plastics) and heat-assisted healing, etc., [ 21 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Current methods to characterize vitrimers are mostly based on the Arrhenius law [ 17 , 33 , 35 ].…”