A Self-Folding Dynamic Covalent Shape Memory Epoxy and Its

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Materials and Interfaces

A Self-Folding Dynamic Covalent Shape Memory Epoxy and Its Continuous Glass Fiber Composite Jiting Zhu, Guangqiang Fang, Zhengli Cao, Xiangkang Meng, and Hua Ren Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00222 • Publication Date (Web): 26 Mar 2018 Downloaded from http://pubs.acs.org on March 26, 2018

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Industrial & Engineering Chemistry Research

A Self-Folding Dynamic Covalent Shape Memory Epoxy and Its Continuous Glass Fiber Composite Jiting Zhu,1 Guangqiang Fang,2 Zhengli Cao,2 Xiangkang Meng, 1* Hua Ren1* 1

Institute of Materials Engineering, National Laboratory of Solid State

Microstructures, College of Engineering and Applied Sciences, Nanjing University, 22 Hankou Road, Jiangsu, 210093, P. R. China 2

Aerospace System Engineering Shanghai, 3805 Jindu Road, Shanghai, 201108, P. R. China

ABSTRACT: Continuous fiber reinforced thermoset composites are highly important in a variety of industrial applications because of their ultrahigh specific strength. However, conventional shaping techniques for such materials can hardly achieve very sophisticated shapes. In this paper, we present an unconventional method to enable complex shapes for continuous fiber reinforced thermoset epoxy composites that provided a capability of topology change due to the dynamic ester bonds. Thus, the corresponding composites providing largely enhanced mechanical strength can be endowed with complex permanent shapes via folding. Whereas at lower temperatures, the exchange reaction was frozen and the epoxy networks provided ideal shape memory behavior. Accordingly, the composites with complex permanent shapes

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enabled a self-folding shape recovery process. In addition, a laser half-cutting technique was applied to build controllable defects within the composites. As a result, more complex folding geometries which were extremely challenging for handwork can be easily fabricated.

Keywords: dynamic covalent bond, thermoset, shape memory polymer, self-folding, continuous glass fiber, plasticity Introduction：： For centuries, polymer materials have undergone great changes and innovations in research fields. While neat polymer materials cannot satisfy the increasing industrial requirements because of low hardness and material application limits, therefore various polymeric composites have been developed. In comparison to other composites, continuous fiber reinforced thermoset composites provide ultrahigh specific strength and are thus very commonly utilized in various industrial applications as well as our daily lives.28-33 However, shape processing of such materials commonly relies on hand layup and sheet molding, which can hardly provide the shape sophistication. Dynamic covalent bonds which possess high bond strength can carry out reversible exchange upon external stimuli, such as, heat and light exposure. Typical dynamic covalent bonds include disulfide bonds, Diels-Alder cycloaddition bonds, ester bonds, urethane bonds, etc.1-3 While conventional thermosets can hardly be reprocessed after curing, recently developed thermosets crosslinked by dynamic covalent bonds (namely exchangeable networks) can be reshaped while the materials ACS Paragon Plus Environment

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still hold a solid-like state.3 Based on such behavior, some non-traditional processing methods have been developed. Representatively, Bowman et al. developed a mechanophotopatterning method to fabricate complex surface features of a photo sensitive dynamic network via spatial stress relaxation under stretching of the material.4 Ji et al. used dynamic bond exchange under mechanical deformation to achieve monodomain of a liquid crystal elastomer and the according thermally induced reversible shape changing.5-6. Zhao et al. showed that complex permanent shapes of shape memory polymers crosslinked by dynamic covalent bonds can be achieved without the use of any mould, enabling highly sophisticated shape transformations. In addition, dynamically crosslinked thermosets incorporating dispersed additives have been prepared to achieve multi-functions such as photo-thermally induced locally shape transformation11-21. Although continuous fiber/dynamically crosslinked thermoset composites were also reported recently, the focus of these works was on the recycling of fibers rather than the enabling of shape complexity.22-26 In this paper, we report shape memory epoxy resins cured by anhydride. In addition to amine cured epoxy, the presented commercially available formulation is another commonly used system to prepare glass fiber/epoxy resin composites in industry.27 The difference is that the presented epoxy networks are enabled with a nature of topology rearrangement due to the transesterification of the ester bond linkages under the catalysis of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Permanent shapes of such epoxies can thus be processed via folding according to our form



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studies. Evidently, their continuous glass fiber composites can be also endowed with folded shapes while the mechanical strength can be largely improved in comparison to the neat epoxy samples. On the other hand, self-folding shape memory recovery can be manipulated. Furthermore, we proceed a laser half-cutting method to create controllable defects within the composites, enabling sophisticated origami permanent shapes of the materials which can hardly be achieved via common hand layup or sheet molding methods. Experimental Materials The epoxy monomer E44 (molecular weight ~450 g mol -1 and epoxy equivalent weight 210-240 g mol -1) was purchased from Petrochemical Co. Ltd., China. The epoxy

active

diluent

glycidyl

phenyl

ether

(PGE),

curing

agent

methylhexahydrophthalic anhydride (MHHPA), and transesterification catalyst 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) were purchased from J&K chemical. The chemical structures of these reactants are shown in Figure 1a. Glass fiber (thickness ~0.03mm) mesh was purchased from Suichina. Glass Fiber Co. Ltd., China. All materials were used as received without any purification. Sample preparation TBD and MHHPA were firstly weighed and then stirred until uniformly blended in a glass bottle at 80oC for 10-20 min. The involved TBD was 5 mol% of MHHPA. A stoichiometric amount of epoxy precursors with a certain proportion of E44 and PGE was added into the bottle (i.e., molar ratio between the epoxy groups and the


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anhydride groups was 1). The high viscosity liquid mixture was heated using an oil bath at 60 ºC under stirring for 30 min and then degassed in a vacuum oven at 60 ºC for 60 min until no visible air bubble. Afterwards, the mixture was poured into an assembled airtight mold and cured according to the following stepwise schedule: 120 ºC for 1 h, 150 ºC for 1 h, 180 ºC for 3 h. The mold was made up of two glasses separated by a polydimethylsiloxane (PDMS) spacer (0.1~0.4 mm). Polyimide films were covered on the glasses before the curing reaction to help demolding. To tune the glass transition temperature (Tg), namely the shape memory transition temperature of the materials, the molar ratio of PGE and E44 was altered. The resulting neat epoxy samples were labelled as Epoxy 0, Epoxy 1, Epoxy 2, and Epoxy 3, while the molar ratios between the PGE and E44 were 0, 1, 2, and 3, respectively. The gel contents were measured as 99.9%, 97.9%, 97.6%, and 90.3% respectively for the samples Epoxy 0 to Epoxy 3 via methylbenzene extraction. The sample Epoxy 3 was chosen to incorporate with glass fiber and conduct the complex shape changing process due to its relatively high relaxation speed and low Tg. For the preparation of the epoxy/glass fiber composite, a single layer continuous glass fiber mesh (0.03 mm) was placed in the mold before pouring the curing precursors. The precursors of the Epoxy 3 sample were chosen to make the composite. Other preparation procedures were the same as those of the neat epoxies. Thermomechanical analyses The dynamic mechanical properties of the neat epoxy resins were measured via dynamic mechanical analysis (DMA) using DMA Q800 (TA instrument).



Dumbbell-shaped samples with 10 mm external width, 2 mm measure (inner) width, and 26 mm total length were heated from room temperature to 180 ºC at a rate of 3 ºC min-1 and under a frequency of 1 Hz using a ‘multi-frequency strain’ mode. The stress relaxation of the samples was conducted via an iso-strain stress relaxation experiment at 180oC, and σ/σ0 were used to normalize the results where σ and σ0 represent the instantaneous stress and the initial stress respectively. The strain at break of the neat epoxies was measured by using a universal material testing machine (Zwick/Roell Z005) equipped with a thermal chamber. Dumbbell-shaped samples of Epoxy 0 to 3 were unidirectionally stretched under an extension speed of 3 mm min-1at respectively 120ºC, 120ºC,140ºC, and 160ºC which were well above their Tgs. At least three specimens were tested for each composition. The mechanical strength of the Epoxy 3 samples (labeled as Epoxy 0L for no glass fibers, Epoxy 4L for four layers’ fibers, and Epoxy 8L for eight layers’ fibers) incorporating different layers of glass fibers was measured by a universal material testing machine (Instron 5944) using bending mode under a speed of 1 mm min-1 at room temperature. At least five specimens were tested for each composition. Shape memory property Shape memory cycles were performed using the DMA Q800 under a control force mode.

A certain stress (σ) was applied to the Epoxy 3 sample (dumbbell shape

as mentioned above) at 120 ºC. Then, the sample was cooled to 20 ºC under the stress. The temporary shape was kept after removal of the stress when maintaining the


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temperature at 20 ºC. The temporarily fixed sample was heated to 120 ºC again to recover its permanent shape under a stress-free condition, from where a next shape memory cycle began. The shape memory behavior was evaluated by shape fixity (Rf) and shape recovery (Rr) calculated as follows: Rf = (εd/εdload) × 100%

(1)

Rr = (εd - εrec)/εd × 100%

(2)

where εdload, εrec, and εd were the maximum strain under load, the recovered strain, and the fixed strain after cooling and load removal. Preparation of complex shapes via folding Various self-folding origami structures were manually folded from flat composite sheets. The folded composites based on Epoxy 3 matrix were thermally annealed at 200 ºC for 4 h under fixation of two glass slides. Before annealing, surfaces of the composites were covered by polyimide films to avoid self-sticking. To fabricate more complex origami structure, a half-cutting method was conducted to create regionalized defects within the composites. Flat composite sheets were placed in a laser cutting machine (Trotec Speedy 100R) and cut with specified pattern by tuning the laser energy to achieve that the cut thickness was about half of the whole composites. Afterwards, the half-cut samples can easily be folded into per-defined sophisticated structures since bending spontaneously occurred on the defect location



when squeezing the sheets. Permanent shape of the composites would transform into the folded shapes after the annealing. For the shape memory cycle of the composites, the permanent origami structures were firstly flattened by glass sheets at 120 ºC (above Tg) followed by cooling to room temperature (below Tg) to fix the flattened temporary shapes in the absence of the glass sheets. Upon being heated to 120 ºC again, the composites returned to the permanent origami shapes spontaneously. Results and discussion: Figure 1b shows the network structure of the cured polymer. Ordinary bisphenol A epoxy network (Epoxy 0) was highly crosslinked after cured by anhydride, providing a very high Tg and very low chain flexibility. To tune the properties of the cured resins, epoxy active diluent PGE was added to reduce the crosslinking density, as well as to tune the Tg and improve the deformable strain during the shape memory cycle. In comparison to dynamic epoxy networks cured via carboxylic acids reported in former literatures, the presented epoxy materials cured by anhydride are closer to industrial systems. The acid curing system contains abundant amount of hydroxyl groups within the network. Although the hydroxyl groups can enhance the activity of the transesterification, they may reduce the water resistance of the material. Moreover, the acid curing is typically much slower than the anhydride curing. It has been proven that the transesterification can still go on well without introducing additional hydroxyl groups. For these reasons, the anhydride curing system is considered to be a good candidate as an adaptable polymer matrix for a continuous fiber composite.


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Figure 1. Precursors and the network structure. a) Chemical structures of E44, PGE, MHHPA, and TBD; b) The network structure of the cured epoxy.

Figure 2.

Quantitative characterizations for the epoxies. a) DMA curves showing

the temperature sweep of storage modulus; b) Stress relaxation curves; c) Consecutive shape memory cycles; 3. d) Strain at break of different samples in their rubbery state. e) Bending strength of the composites with different layers of glass fibers.



Figure 2a shows the temperature sweep of storage modulus for different epoxy networks. A stepwise decrease of the storage moduli could be seen for all the samples due to the glass transition. Tgs are approximately 140 ºC, 105 ºC, 90 ºC, and 75 ºC for Epoxy 0, Epoxy 1, Epoxy 2, and Epoxy 3, respectively. The storage modulus for all the samples is approximately 3.0 GPa at room temperature, which shows no remarkable difference from common thermoset epoxy. On the other hand, the storage modulus at rubbery state of the samples decrease from approximately 10 MPa to 1MPa with the increase amount of the involved PGE, which implies the gradual decrease of the crosslink density from Epoxy 0 to 3. The platform of the rubbery modulus indicates that the materials hold intact network structures despite of the topology rearrangement due to the transesterification which is confirmed by the stress relaxation characterization as shown in Figure 2b. This finding suggests that the catalyst TBD used for the transesterification reaction promotes stress relaxation at a high temperature. The network topology can be almost rearranged when ester bonds are activated via elevated temperatures. Figure 2b shows that the value of σ/σ0 declining from 1 to almost 0.1 at the same temperature and the relax of the mechanical force takes about 200 min. The speed of stress relaxation increases remarkably from Epoxy 0 to Epoxy 3 with the decrease of the crosslink density of the samples. Theoretically, the stress relaxation could be completely achieved (the value of σ/σ0 declining to 0) since the networks contain abundant ester groups within the backbone. The incomplete relaxation may be attributed to that the industrial epoxy


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E44 usually contains some impurities. In this case, the networks may contain some permanent crosslinks which contribute to the residual stress. Since the epoxy networks possess glass transitions from the former results, the materials meet the requirements of enabling shape memory property. Consecutive shape memory cycles of the sample Epoxy 3 are shown in Figure 2c. The sample provides highly consistent and reproducible shape memory performs under a control-force mode with identical deformation and recovery temperatures of 120oC. The shape fixity ratio is above 98% and the shape recovery ratio is approximately 100%. Figure 2d presents the strain at break for different epoxy samples in their rubbery state. The elongation break of Epoxy 0 displays a value of 19%, whereas the strain at break of Epoxy 3 is approximately 55%. More amount of PGE incorporated in the network will lead to lower crosslinking density, and thus, the elongation at break increase remarkably from epoxy 0 to epoxy 3. Figure 2e shows the bending strength of the composites with different glass fiber layers. In the absence of glass fiber, the epoxy is brittle providing a strength of around 20 MPa. Although neat glass fiber layers scarcely showing any bending resistance, they prevent cracks from propagating. As such, the sample Epoxy 8L shows a largely improved strength of around 180 MPa. It is not suitable for quantitatively testing the shape memory performances of the composites via static tensile method since the stretchability was restrained by the continuous glass fiber mesh. Nevertheless, qualitative shape memory characterization via manual bending showed that the composites provided nearly ideal shape fixity and



recovery no matter how many layers of glass fibers were incorporated. On the other hand, more glass fiber layers would bring on more difficulty of folding complex origami shapes. As such, composites with single layer glass fiber were representatively applied for the self-folding demonstrations. Figure 3 shows the shape recovery of three Epoxy 3 based composite sheets with various folded permanent shapes. Due to the transesterification at high temperatures, flat composite sheets can be permanently altered upon folding. To further enable the sophistication of permanent shapes, we present here a digitally controlled laser half-cutting method. The processing schema is shown in Figure 4a. The laser can easily burn out the resin component while can hardly cut across the glass fiber layer. The composites can thus be half-cut from both sides, creating controllable defects where provide much lower bending resistance. Upon bidirectional squeezing of the sheet, the cut locations trend to be yielded (folded) before the intact locations. Through such a method, sophisticated origami structures which can be extremely challenging to be fabricated (e.g. Figure 4b and 4c) can be easily achieved. After thermal annealing, permanent origami structure can be resulted, enabling shape-recovery-induced self-folding. Theoretically, the half-cutting method can be applied towards neat epoxies without glass fiber if the laser energy can be precisely manipulated. However, the cut lines will easily propagate throughout the materials during the annealing of the folding due to the stress concentration. As such, the half-cutting method and the composites’ layout are both critical towards the achievement of complex self-folding shapes.


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Figure 3.

Shape recovery of three Epoxy 3 composite sheets with various folded

permanent shapes.

Figure 4. Diagram of the laser half-cutting method (a) and complex shape manipulation (b and c).

Conclusion ACS Paragon Plus Environment


A series of shape memory epoxy resins and their glass fiber composites were fabricated. Various properties of the epoxies were investigated. By adjusting the component ratio between the epoxy and the anhydride precursors, widely tunable Tg ranges from 80-140 ºC can be resulted. The cured epoxies were provided idea shape memory performance confirmed by cyclic thermomechanical tests. External stress applied on the cured epoxies can be relaxed due to the transesterification under 180 ºC. Mechanical strength of the shape memory epoxies was largely improved after incorporation of continuous glass fiber meshes. The composites can be endowed with complex permanent shapes via folding and a succedent annealing. In addition, a laser half-cutting method was developed. Very complex self-folding origami structures which were extremely challenging for manual folding can be easily achieved. The self-folding epoxy composites may show potential advantages in a variety of engineering applications.

AUTHOR INFORMATION Corresponding Authors

∗ E-mail: [email protected] (H. Ren)

ORCID: 0000-0002-1274-3149 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS


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We thank Dr. Qian Zhao from Zhejiang University for his kind advice. This work was supported by Natural Science and Technology Project of Jiangsu Province (BK20131198，BE2014087)

REFERENCES (1) Zou, W.; Dong, J.; Luo, Y.; Zhao, Q.; Xie, T. Dynamic Covalent Polymer Networks: from Old Chemistry to Modern Day Innovations. Adv. Mater. 2017, 29, 1606100.

(2) Kloxin, C. J.; Bowman, C. N. Covalent Adaptable Networks: Smart, Reconfigurable and Responsive Network Systems. Chem. Soc. Rev. 2013, 42, 7161-7173.

(3) Wojtecki, R. J.; Meador, M. A.; Rowan, S. J. Using the Dynamic Bond to Access Macroscopically Responsive Structurally Dynamic Polymers. Nat. Mater. 2011, 10, 14-27.

(4) Kloxin, C. J.; Scott, T. F.; Park, H. Y.; Bowman, C. N. Mechanophotopatterning on a Photoresponsive Elastomer. Adv. Mater. 2011, 23, 1977-1981.

(5) Yang, Y.; Pei, Z.; Li, Z.; Wei, Y.; Ji, Y. Making and Remaking Dynamic 3D Structures by Shining Light on Flat Liquid Crystalline Vitrimer Films without a Mold.

J. Am. Chem. Soc. 2016, 138, 2118-2121.



(6) Pei, Z.; Yang, Y.; Chen, Q.; Terentjev, E. M.; Wei, Y.; Ji, Y. Mouldable Liquid-Crystalline Elastomer Actuators with Exchangeable Covalent Bonds. Nat.

Mater. 2014, 13, 36-41.

(7) Zheng, N.; Fang, Z.; Zou, W.; Zhao, Q.; Xie, T. Thermoset Shape-Memory Polyurethane with Intrinsic Plasticity Enabled by Transcarbamoylation. Angew. Chem.

Int. Ed. 2016, 55, 11421-11425.

(8) Liu, Y.; Boyles, J. K.; Genzer, J.; Dickey, M. D. Self-folding of polymer sheets using local light absorption. Soft Matter. 2012, 8, 1703-2044.

(9) Siegel, A. C.; Phillips, S. T.; Dickey, M. D.; Lu, N.; Suo, Z.; Whitesides, G. M. Foldable Printed Circuit Boards on Paper Substrates. Adv. Funct. Mater. 2010, 20, 28-35.

(10) Zhang, G.; Zhao, Q.; Yang, L.; Zou, W.; Xi, X.; Xie, T. Exploring Dynamic Equilibrium of Diels-Alder Reaction for Solid State Plasticity in Remoldable Shape Memory Polymer Network. ACS Macro Lett. 2016, 5, 805-808.

(11) Zhao, Q.; Qi, H. J.; Xie, T. Recent Progress in Shape Memory Polymer: New Behavior, Enabling Materials, and Mechanistic Under- standing. Prog. Polym. Sci. 2015, 49−50, 79−120.

(12) Pei, Z.; Yang, Y.; Chen, Q.; Wei, Y.; Ji, Y. Regional Shape Control of Strategically Assembled Multishape Memory Vitrimers. Adv. Mater. 2016, 28, 156-160.


Page 16 of 20

Page 17 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(13) Montarnal, D.; Capelot, M.; Tournilhac, F.; Leibler, L. Silica-Like Malleable Materials from Permanent Organic Networks. Science 2011, 334, 965-968.

(14) Lu, Y. X.; Tournilhac, F.; Leibler, L.; Guan, Z. Making Insoluble Polymer Networks Malleable via Olefin Metathesis. J. Am. Chem. Soc. 2012, 134, 8424-8427.

(15) Taynton, P.; Yu, K.; Shoemaker, R. K.; Jin, Y.; Qi, H. J.; Zhang, W. Heat- or Water-Driven Malleability in a Highly Recyclable Covalent Network Polymer. Adv.

Mater. 2014, 26, 3938-3942.

(16) Chen, X.; Dam, M. A.; Ono, K.; Mal, A.; Shen, H.; Nutt, S. R.; Sheran, K.; Wudl, F. A. Thermally Re-Mendable Cross-Linked Polymeric Material. Science 2002, 295, 1698-1702.

(17) Voit, W.; Ware, T.; Dasari, R. R.; Smith, P.; Danz, L.; Simon, D.; Barlow, S.; Marder, S. R.; Gall, K. High-Strain Shape-Memory Polymers. Adv. Funct. Mater. 2010, 20, 162-171.

(18) Voit, W.; Ware, T.; Gall, K. Radiation crosslinked shape-memory polymers.

Polymer 2010, 51, 3551-3559.

(19) Denissen, W.; Winne, J. M.; Du Prez, F. E. Vitrimers: Permanent Organic Networks with Glass-Like Fluidity. Chem. Sci. 2016, 7, 30-38.

(20) Zhao, Q.; Zou, W.; Luo, Y.; Xie, T. Shape Memory Polymer Network with Thermally Distinct Elasticity and Plasticity. Sci. Adv. 2016, 2, e1501297.



(21) Fang, Z.; Zheng, N.; Zhao, Q.; Xie, T. Healable, Reconfigurable, Reprocessable Thermoset Shape Memory Polymer with Highly Tunable Topological Rearrangement Kinetics. ACS Appl. Mater. Interfaces 2017, 9, 22077-22082.

(22) Santiago, D.; Sanjuan, A. F.; Ferrando, F.; Flor, S. D. Hyperbranched-modified epoxy thermosets: Enhancement of thermomechanical and shape-memory performances. J. Appl. Polym. Sci. 2016, 134, 44623.

(23) Yu, K.; Shi, Q.; Dunn, M. L.; Wang, T.; Qi, H. J. Carbon Fiber Reinforced Thermoset Composite with Near 100% Recyclability. Adv. Funct. Mater. 2016, 26, 6098-6106.

(24) Philip, T.; Ni, H.; Zhu, C.; Yu, K.; Loob, S.; Jin, Y.; Qi, H. J.; Zhang, W. Repairable Woven Carbon Fiber Composites with Full Recyclability Enabled by Malleable Polyimine Networks. Adv. Mater. 2016, 28, 2904-2909.

(25) Yang, Z.; Wang, Q.; Wang, T. Dual-Triggered and Thermally Reconfigurable Shape Memory Graphene-Vitrimer Composites. ACS Appl. Mater. Interfaces 2016, 8, 21691-21699.

(26) Billiet, S.; Hillewaere, X. K. D.; Teixeira, R. F. A.; Prez, F. E. D. Chemistry of Crosslinking Processes for Self-Healing Polymers. Macromol. Rapid Commun. 2013,

34, 290-309.


Page 18 of 20

Page 19 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(27) Liu, Y.; Zhao, J.; Zhao, L.; Li, W.; Zhang, H.; Yu, X.; Zhang, Z. High Performance Shape Memory Epoxy/Carbon Nanotube Nanocomposites. ACS Appl.

Mater. Interfaces 2016, 8, 311-320.

(28) Matsuzaki, R.; Ueda, M.; Namiki, M.; Jeong, T.; Asahara, H.; Horiguchi, H.; Nakamura, T.; Todoroki, A.; Hirano, Y. Three-dimensional printing of continuous-fiber composites by in-nozzle impregnation. Sci. Rep. 2016, 6, 23058.

(29) Dong, L.; Hou, F.; Li, Y.; Wang, L.; Gao, H.; Tang, Y. Preparation of continuous carbon nanotube networks in carbon fiber/epoxy composite. Compos Part A: Appl Sci

Manufac. 2014, 56, 248-255.

(30) Withers, G. J.; Yu, Y.; Khabashesku, V. N.; Cercone, L.; Hadjiev, V. G.; Souza, J. M.; Davis, D. C. Improved mechanical properties of an epoxy glass–fiber composite reinforced with surface organomodified nanoclays. Compos Part B: Eng. 2015, 72, 175-182.

(31) Vu, C. M.; Nguyen, D. D.; Sinh, L. H.; Pham, T. D.; Pham, L. T.; Choi, H. J. Environmentally benign green composites based on epoxy resin/bacterial cellulose reinforced glass fiber: Fabrication and mechanical characteristics. Polym. Test. 2017,

61, 150-161.

(32) Vu, C. M.; Sinh, L. H.; Choi, H. J.; Pham, T. D. Effect of micro/nano white bamboo fibrils on physical characteristics of epoxy resin reinforced composites.

Cellulose 2017, 24, 5475-5486.



(33) Le Hoang, S.; Vu, C. M.; Pham, L. T.; Choi, H. J. Preparation and physical characteristics of epoxy resin/ bacterial cellulose biocomposites. Polym. Bull. 2017, 1-19.

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A Self-Folding Dynamic Covalent Shape Memory Epoxy and Its

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