Design Paradigm Utilizing Reversible Diels ... - ACS Publications

Subscriber access provided by University of Sussex Library

Article

A Design Paradigm Utilizing Reversible Diels-Alder Reactions to Enhance the Mechanical Properties of 3D Printed Materials Joshua R. Davidson, Gayan Adikari Appuhamillage, Christina M. Thompson, Walter E Voit, and Ronald Alexander Smaldone ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05118 • Publication Date (Web): 14 Jun 2016 Downloaded from http://pubs.acs.org on June 20, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25

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

ACS Applied Materials & Interfaces

A Design Paradigm Utilizing Reversible Diels-Alder Reactions to Enhance the Mechanical Properties of 3D Printed Materials Joshua R. Davidson,1,† Gayan A. Appuhamillage,1,† Christina M. Thompson,1 Walter Voit,*

2,3

Ronald A. Smaldone,* 1 1

The University of Texas at Dallas, Department of Chemistry and Biochemistry, 800 W.

Campbell Rd, Richardson, TX 75080, USA. 2

The University of Texas at Dallas, Department of Mechanical Engineering, 800 W. Campbell

Rd, Richardson, TX 75080, USA. 3

The University of Texas at Dallas, Department of Materials Science and Engineering, 800 W.

Campbell Rd, Richardson, TX 75080, USA. KEYWORDS: 3D printing; dynamic covalent chemistry; remendable polymers; additive manufacturing; Diels-Alder

ABSTRACT: A design paradigm is demonstrated that enables new functional 3D printed materials made by fused filament fabrication (FFF) utilizing a thermally-reversible dynamic covalent Diels-Alder reaction to dramatically improve both strength and toughness via selfhealing mechanisms. To achieve this, a partially cross-linked terpolymer consisting of furanmaleimide Diels-Alder (fmDA) adducts that exhibit reversibility at temperatures typically used

ACS Paragon Plus Environment

1


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

Page 2 of 25

for FFF printing to be used as a mending agent. When this mending agent is blended with commercially available polylactic acid (PLA) and printed, the resulting materials demonstrate an increase in the inter-filament adhesion strength along the z-axis of up to 130%, with ultimate tensile strength increasing from 10 MPa in neat PLA to 24 MPa in fmDA-enhanced PLA. Toughness in the z-axis aligned prints increases by up to 460% from 0.05 MJ/m3 for unmodified PLA to 0.28 MJ/m3 for the remendable PLA. Importantly, it is demonstrated that a thermallyreversible crosslinking paradigm based on the furan-maleimide Diels-Alder (fmDA) reaction can be more broadly applied to engineer property enhancements and remending abilities to a host of other 3D printable materials with superior mechanical properties.

Introduction – Improvements in 3D printing technology are projected to drive new innovations in the areas of medical devices and prosthetics1-5 as well as myriad industrial and commercial sectors

6-9

where specially designed materials are needed either on demand or in geometries not

conducive for conventional plastics processing like blow molding, injection molding, extrusion, or vacuum-assisted resin transfer molding. 3D printing, also known as additive manufacturing,10 will supplement and perhaps surpass some of these conventional plastics processing techniques over the next two decades. Some estimates point to a potential emerging $1 trillion market by 2030 for 3D printed parts, if techniques can be developed to print parts with uniform strength and toughness relative to the axis of orientation11 of the part in the 3D printer. In fused filament fabrication (FFF), one of the most versatile 3D printing methods, plastic filaments are heated above their melting points, deposited onto a printing bed, and built into the desired shape through subsequent filaments adhering to neighboring filaments to produce a physical object from a computer generated model. Today, the resulting interfacial strength is poor at interfilamentous


2

Page 3 of 25

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


junctions and the mechanical properties of parts are not competitive with those parts made via injection molding or milling. 12 The lack of uniform strength in printed materials has limited the uses of FFF-based 3D printing to prototyping and applications where mechanical strength has not been a primary consideration. To address these issues with FFF, we have created 3D printable polymeric materials that address filament adhesion at a molecular level utilizing dynamic covalent chemical functionality. Dynamic covalent chemistry utilizes reversible covalent bond forming reactions to form complex, but thermodynamically stable assemblies. These reactions have been used to develop highly ordered supramolecular arrangements13-16 as well as self-healing materials.17-20 Improving adhesion between two separate polymer surfaces (typically a fracture) has been a major area of research for the development of self-healing polymers.21-23 One of the most effective strategies for repairing polymers has been through the rearrangement or creation of new covalent bonds within the polymer structure via either an autonomic response, 24 or an external stimulus such as heat. 25 Processing complexities involved with developing and handling printable polymers have limited

the

use

of

self-healing

moieties

in

custom

manufacturing

techniques

to

photolithography,26,27 micro contact printing28 and methods that use soft materials like hydrogels.3,5,26,29-31 This prior work has contributed significant progress to the field at large, but unsolved problems, namely the inability to fabricate large-scale, mechanically robust 3D printed parts, remain. We hypothesized that the interfilamentous adhesion in FFF printing could be significantly improved by engineering a polymer system that thermally depolymerizes during the print process followed by re-polymerization during cooling to improve the fusion at the filament interface and therefore the strength of the printed object. Our strategy for developing an improved polymer


3


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

Page 4 of 25

system for mechanically robust FFF 3D printing involves the use of a thermally reversible furanmaleimide Diels-Alder (fmDA) reaction.32 The fmDA reaction has been used in a variety of polymer systems as a method to promote self-healing and damage repair.21,23,25,27,33-38 It is particularly desirable for these types of applications owing to its temperature controllable dynamics, and stability to external factors such as light, water, and oxygen. Polymers with fmDA functional groups can be made with the dynamic components incorporated as pendant groups on polymer backbones for crosslinking26,33,35,36 or in the main chain in step-growth polymers.39-41 At low temperatures (~40-50 ºC) this dynamic reaction favors the fmDA adduct, but at elevated temperatures (~100-120 ºC) the retro Diels-Alder reaction is favored.

32,42

Herein, we report the first use of a dynamic covalent chemical reaction for the purpose of improving the strength and toughness of FFF printed materials. For this study, we synthesized a crosslinked polymer containing fmDA functional groups that can be depolymerized at temperatures suitable for FFF printing, and then re-polymerized upon cooling, creating new covalent bonds between filament layers (Figure 1). To our knowledge this work represents the first mechanically robust, 3D printable material and offers a design paradigm with promise for engineering even tougher remendable thermoplastics.

Results – The polymer filament used in this study is comprised of commercially available PLA and a novel synthetic polymer that contains fmDA adducts in the main chain. PLA was chosen as the bulk printing material as it is inexpensive and readily compatible with most 3D printers currently available. The fmDA polymer was synthesized by mixing monomers 2F, 2M,43 and 3F44 in a 15 to 18 to 2 molar ratio (~5% crosslink density) in ethyl acetate at 75 ºC for 24 h and heated under vacuum at 60 ºC (Figure 2a) to remove excess solvent. As-synthesized mending


4

Page 5 of 25

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


agent was blended in ratios of 10 and 25 weight percent with PLA in dioxane at 80 ºC and the solvent was removed under vacuum at 60 ºC. The filaments of 3 mm in diameter were fabricated using a Filabot™ extruder using pellets of the remendable PLA blend and extruding them at 160 ºC. This filament was used to print dogbone samples for mechanical testing (Figure 2b). 1

H NMR studies were performed on the mending agent to confirm the formation of the fmDA

adduct and are shown in Figure S2-3. The proton signals at 2.85, 2.95, 5.25, 6.23, and 6.33 ppm represent the Diels-Alder adduct peaks. The retro Diels-Alder reaction was monitored at 110 °C in toluene for 30 min and an NMR spectrum was collected immediately afterwards. The fmDA adduct proton signals at 2.85, 2.95, and 5.25 ppm are reduced. The proton signals of the furan slightly shift to 6.25 and 6.35 ppm, and the maleimide vinyl peak reappears at 6.65 ppm (Figure S3).

Differential scanning calorimetry (DSC) was used to study thermal transitions of the mending agent alone, PLA, and the remendable PLA blends (Figure 3) to determine miscibility of the polymer system components. The mending agent shows two endothermic transitions beginning at 5.7 ºC and 120 ºC. The transition at 5.7 ºC is the Tg and the second value, 120 ºC, is indicative of the retro-fmDA reaction. PLA exhibits three transitions: a Tg at 61.8 ºC, an exothermic crystallization beginning at 100 ºC, and a Tm at 145 ºC. The blend ratios of 10% mending agent and 25% mending agent in PLA exhibit Tg values of 55.2 °C and 48.2 °C. The presence of a single Tg in the polymer blends demonstrates that the two materials are miscible and do not phase separate at elevated temperatures.

The strengths of 3D-printed PLA and the 10% and 25% remendable PLA blends were determined by tensile testing (Figure 4). Three print patterns (X, Y, Z), shown in Figure 4a,


5


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

Page 6 of 25

were tested to represent structural features inherent in FFF parts. The print variation X has a 45º alternating infill pattern, whereas print variations Y and Z are linear patterns printed parallel to (Y), or perpendicular to (Z), the direction of mechanical stress on the printed material. Objects printed using FFF techniques will rarely be comprised entirely of one of these patterns, but any printed object will contain some combination of these. Tensile tests demonstrated that the ultimate strength (Figure 4b) and toughness (Figure 4c) of the materials were largely unchanged with the alternating infill pattern (X) but showed improvements in both the Y and Z designs. Ultimate strength improved 27% for the Y printing pattern for both 10 and 25% remendable PLA blends. When printed in the Z direction the ultimate strength was improved 88% and 130% for the 10 and 25% remendable PLA blends respectively.

Toughness measurements for each

polymer blend are shown in Figure 4c. These values were determined through the integration of the stress vs. strain plots (Figure 4d). Toughness values for the X pattern were again statistically similar for each polymer sample.

The Y pattern however, demonstrated improvements in

toughness of 70% for the 10% remendable PLA and 109% for the 25% remendable PLA. The Z design showed even more dramatic increases of 260 and 460% for the 10 and 25% blends, respectively.

Cross-sectional optical images of a printed PLA material and the 25% remendable PLA blend printing using pattern Y are shown in Figure 5. The cross-section of a pure PLA material (Figure 5c) shows that the filament layers have a consistent, uniform packing arrangement with a clear, observable void space present at the inter-filament junctions. However, the filaments shown in the remendable PLA blend image (Figure 5d) are bound together with fewer observable voids and interfilamentous boundaries.


6

Page 7 of 25

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


Discussion – As illustrated in Figure 1, the polymer mending agent can influence the printing process through several mechanisms. Upon heating, thermal reversal of the fmDA crosslinks will allow the mending agent network to exhibit thermoplastic behavior. The retro Diels-Alder reactions within the linear portions of mending agent will reduce its overall molecular weight and plasticize the remendable PLA melt thereby improving its ability to mix with the previously added polymer filaments on the print bed. Upon cooling below ~70º C, the fmDA reaction will favor formation of the adducts and regenerate the mending agent network within the PLA blend. The reversibility of this reaction was confirmed by 1H NMR studies (Figure S3). The polymer mending agent alone is a soft, malleable material at room temperature and lacks the mechanical strength of bulk PLA or engineering thermoplastics. Blends of 10% and 25% mending agent with PLA were chosen to balance the remendable capability of the fmDA functionalizedpolymer with the mechanical properties of PLA.

In order to evaluate the effect that the mending agent had on PLA, three print variations were designed to capture different print orientations of a FFF printed part. The three print patterns, shown in Figure 4a, exhibit significant mechanical variations in the PLA samples. Due to the low Tg of pure mending agent, we would expect to see a slight plasticizing effect when blended with PLA resulting in lower ultimate strength. This effect was observed in the Tg of the blends (Figure 3); however, the strain capacity of remendable PLA blends was not compromised as evidenced in Figure 4b-d. In fact, the X printing patterns show equivalent strength compared to bulk PLA. We hypothesize that any potential loss in strength resulting from plasticization is offset by the crosslinked structure of the mending agent. The Y print design is used as a model to evaluate a raster infill pattern in which an applied tensile force is exerted parallel to the


7


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

Page 8 of 25

filament grain. Improvements in the observed mechanical properties of the remendable PLA blends could be attributed to the crosslinked network of the mending agent. Additionally, crosssectional images of the printed materials (Figure 5c-d) show that there are observable void spaces between each filament junction in the PLA sample, whereas the 25% remendable PLA blend displays essentially no void space and the filaments appear to be adhered to one another. The Z print pattern was designed to represent situations where mechanical stress is applied perpendicular to the print grain of the printed object. Under these conditions, which are the greatest source of mechanical anisotropy in FFF 3D printing, the printed material relies entirely on interfilamentous adhesion for strength.

Mechanical tests of the Z pattern materials

demonstrated the largest increases in both strength and toughness for any of the print directions. This indicates that the improvements observed cannot be completely attributed to the use of a stronger bulk polymer, but rather to the increased interfilamentous adhesion arising from a combination of improved polymer filament adhesion between the previously deposited filament and the melted filaments added subsequently, combined with the ability of the mending agent to repolymerize owing to the dynamic covalent nature of the fmDA functionalized polymer network.

Conclusion – In conclusion, we have synthesized a printable PLA blend material that demonstrates improved mechanical strength and toughness for FFF 3D printing applications without the need to chemically modify the bulk polymer, in this case, PLA. This was achieved through the use of a dynamic furan-maleimide Diels-Alder reaction that allows for the improved remending of interfilamentous junctions that are created as part of the FFF process.

The

concepts demonstrated in this study are generally applicable for the development of FFF


8

Page 9 of 25

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


printable materials that reduce the impact of mechanical defects introduced by the printing process.

Experimental Section – Jeffamine D-400 (diamine, weight-average molecular weight = 430 g/mol) was supplied by Huntsman and was used as received. Maleic anhydride and sodium bicarbonate were purchased from Alfa Aesar and were used as received. Tris(2aminoethyl)amine, p-phenylenediamine, ethyl acetate, acetone, methylene chloride, and methanol were purchased from Sigma-Aldrich and were used as received. Triethylamine, 2furaldehyde, and sodium borohydride were supplied by Acros Organics and were used as received. Acetic anhydride, magnesium sulfate, and 1,4-dioxane were supplied by Fisher Scientific and were used as received. PLA plastic in fine resin pellet form was produced by IC3D printers LLC. Dublin, Ohio. PLA plastic in high-grade 3D-printing filament form was purchased from ExcelFilTM TECH, Voltivo Group Ltd., Taiwan. The polymer blends 10 (wt%), 25 (wt%) fmDA-polymer/PLA were prepared according to the procedure in the Supporting Information (Synthetic Procedures section). These blends were then ground into small pieces followed by extrusion into 3 mm diameter filaments using a single-screw extruder (Filabot). Extrusion temperatures were 160 °C and 155 °C, respectively. Neat PLA was extruded using the same stock pellets (ExcelFilTM TECH) at 165 °C as the control. Extruded filaments of PLA, 10 (wt%) remendable PLA, and 25 (wt%) remendable PLA, were printed using a Taz-5 3D-printer from Lulzbot using the open-source MatterControl software. Print-head temperatures for PLA, 10 (wt%) remendable PLA, and 25 (wt%) remendable PLA were maintained at 205 °C, 200 °C, and 190 °C, respectively while print-bed temperatures were 60 °C, 55 °C, and 48 °C respectively. The materials were printed into rectangular prisms with the following dimensions (l x w x h)


9


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

Page 10 of 25

64.5 mm x 10.5 mm x 1.0 mm using a print resolution of 0.1 mm in each direction.

The

rectangular prisms were cut into American Society for Testing and Materials (ASTM) D638 Type V, standard dogbones using a Gravograph LS100 CO2 laser to ensure consistency in the samples and minimize error caused by print resolution. 1H-NMR and

13

C NMR spectra were

obtained using an Avance-500 500 MHz spectrometer (Bruker, Switzerland) with deuterated chloroform (CDCl3) as the solvent in order to monitor both fmDA bond formation and retrofmDA reaction. DSC analysis was performed with DSC 1 STARe System (Mettler Toledo AG, Analytical-Switzerland). All the samples were subjected to three heating cycles from -40 °C to 200 °C at a heating rate of 10 °C/min. Tensile tests were carried out according to ASTM D63804 using a universal testing machine (Instron 5848 MicroTester) at a loading speed of 3 mm/min and a temperature of 25 °C. Three dogbones were tested in each print/blend variation and the mean and standard deviation were calculated based on these and used to generate the error bars for each measurement. Cross-sectional areas of the printed dogbones were imaged using a versatile upright microscope (Leica DM4000 M LED) using 5X as the magnification to demonstrate mending between printed layers.


10

Page 11 of 25

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


Figure 1. (A) Synthesis of cross-linked mending agent. (B) Reversible reaction of Diels-Alder mending agent. (C) Forward reaction of Diels-Alder mending agent. (D) Structure and composition of a reversible fmDA polymer at different stages of the FFF printing process.

Figure 2.

(A) Synthesis of the mending agent polymer used in this study. (B) Filament

fabrication and mechanical testing process used for the remendable PLA blends.


11


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

Page 12 of 25

Figure 3. Differential scanning calorimetry of PLA, 10% MA/PLA, 25% MA/PLA and MA. PLA (blue) shows a Tg of 61.8 °C, 10% MA/PLA (black) 55.2 °C, 25% MA/PLA (red) 48.2 °C, The MA (orange) 5.7 °C and an endothermic thermal transition at near 120 °C (retro-DA).

Figure 4. (A) Printing patterns used to print each dogbone type for this study. (B) Ultimate strength values for neat PLA, and PLA with 10% and 25% mending agent as dogbones for each printing pattern.

(C) Toughness values for the PLA, 10% remendable PLA, and 25%


12

Page 13 of 25

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


remendable PLA dogbones for each printing pattern. (D) Representative stress vs. strain plots for each polymer blend and printing pattern tested in this study.

Figure 5. Illustrations and images of 3D-printed PLA and PLA blended with mending agent. (A) Illustration of 3D-printed PLA filaments (blue), (a’) inter-filament junctions. (B) Illustration of PLA blended with mending agent (purple). (C) Microscopic image of 3D-printed PLA filaments. (D) Microscopic image of 3D printed remendable PLA.

ASSOCIATED CONTENT Supporting Information Synthetic procedures and other supporting data are available in the electronic supporting information. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION


13


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

Page 14 of 25

Corresponding Authors *E-mail: [email protected] *E-mail: [email protected] Author Contributions †

These authors contributed equally to this work. The manuscript was written through

contributions of all authors. All authors have given approval to the final version of the manuscript. Notes W.E.V. founded and is affiliated with a 3D printing company, Adaptive3D that has licensed university technology in the area of 3D printing, but has no direct relationship to the work presented in this manuscript. ACKNOWLEDGMENTS We would like to acknowledge Jonathan Reeder for 3D modeling assistance, and Kejia Yang for helpful conversations and discussion. R.A.S. would like to acknowledge the University of Texas, Dallas and the State of Texas for support. W.E.V. would like to acknowledge funding from the DARPA Director’s Fellowship, DARPA Young Faculty Award and the UT Dallas Center for Engineering Innovation.


14

Page 15 of 25

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


REFERENCES (1)

Melchels, F. P. W.; Domingos, M. A. N.; Klein, T. J.; Malda, J.; Bartolo, P. J.; Hutmacher, D. W. Additive Manufacturing of Tissues and Organs Prog. Poly. Sci. 2012, 37, 1079-1104.

(2)

Chan, H. N.; Shu, Y.; Xiong, B.; Chen, Y.; Chen, Y.; Tian, Q.; Michael, S. A.; Shen, B.; Wu, H. Simple, Cost-Effective 3D Printed Microfluidic Components for Disposable, Point-of-Care Colorimetric Analysis ACS Sensors 2016, 1, 227-234.

(3)

Kirchmajer, D. M.; Gorkin III, R.; in het Panhuis, M. An Overview of the Suitability of Hydrogel-Forming Polymers for Extrusion-Based 3D-Printing J. Mater. Chem. B 2015, 3, 4105-4117.

(4)

Wang, M. O.; Vorwald, C. E.; Dreher, M. L.; Mott, E. J.; Cheng, M.-H.; Cinar, A.; Mehdizadeh, H.; Somo, S.; Dean, D.; Brey, E. M.; Fisher, J. P. "Evaluating 3D-Printed Biomaterials as Scaffolds for Vascularized Bone Tissue Engineering," Adv. Mater. 2015, 27, 138-144.

(5)

Hart, L. R.; Li, S.; Sturgess, C.; Wildman, R.; Jones, J. R.; Hayes, W. 3D Printing of Biocompatible Supramolecular Polymers and Their Composites ACS Appl. Mater. Int. 2016.

(6)

Symes, M. D.; Kitson, P. J.; Yan, J.; Richmond, C. J.; Cooper, G. J. T.; Bowman, R. W.; Vilbrandt, T.; Cronin, L. Integrated 3D-Printed Reactionware for Chemical Synthesis and Analysis Nature Chem. 2012, 4, 349-354.

(7)

Kitson, P. J.; Symes, M. D.; Dragone, V.; Cronin, L. Combining 3D Printing and Liquid Handling to Produce User-Friendly Reactionware for Chemical Synthesis and Purification Chem. Sci. 2013, 4, 3099-3103.


15


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

(8)

Page 16 of 25

Eckel, Z. C.; Zhou, C.; Martin, J. H.; Jacobsen, A. J.; Carter, W. B.; Schaedler, T. A. Additive Manufacturing of Polymer-Derived Ceramics Science 2015, 351, 58-62.

(9)

Duan, S.; Yang, K.; Wang, Z.; Chen, M.; Zhang, L.; Zhang, H.; Li, C. Fabrication of Highly Stretchable Conductors Based on 3D Printed Porous Poly(Dimethylsiloxane) and Conductive Carbon Nanotubes/Graphene Network ACS Appl. Mater. Int. 2016, 8, 21872192.

(10)

Lipson, H.; Kurman, M. Fabricated: The New World of 3D Printing, 2013.

(11)

Gorsche, C.; Seidler, K.; Knaack, P.; Dorfinger, P.; Koch, T.; Stampfl, J.; Moszner, N.; Liska, R. Rapid Formation of Regulated Methacrylate Networks Yielding Tough Materials

for

Lithography-Based

3D

Printing

Polym.

Chem.

2016,

10.1039/C1035PY02009C. (12)

Shaffer, S.; Yang, K.; Vargas, J.; Di Prima, M. A.; Voit, W. On Reducing Anisotropy in 3D Printed Polymers Via Ionizing Radiation Polymer 2014, 55, 5969-5979.

(13)

Meyer, C. D.; Joiner, C. S.; Stoddart, J. F. Template-Directed Synthesis Employing Reversible Imine Bond Formation Chem. Soc. Rev. 2007, 36, 1705-1723.

(14)

Mastalerz, M. Shape-Persistent Organic Cage Compounds by Dynamic Covalent Bond Formation Angew. Chem., Int. Ed. 2010, 49, 5042-5053.

(15)

Roy, D.; Cambre, J. N.; Sumerlin, B. S. Future Perspectives and Recent Advances in Stimuli-Responsive Materials Prog. Poly. Sci. 2010, 35, 278-301.

(16)

Jin, Y.; Yu, C.; Denman, R. J.; Zhang, W. Recent Advances in Dynamic Covalent Chemistry Chem. Soc. Rev. 2013, 42, 6634-6654.


16

Page 17 of 25

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


(17)

Wojtecki, R. J.; Meador, M. A.; Rowan, S. J. Using the Dynamic Bond to Access Macroscopically Responsive Structurally Dynamic Polymers Nat. Mater. 2011, 10, 1427.

(18)

Urban, M. W. Dynamic Materials: The Chemistry of Self-Healing Nature Chem. 2012, 4, 80-82.

(19)

Brandt, J.; Oehlenschlaeger, K. K.; Schmidt, F. G.; Barner-Kowollik, C.; Lederer, A. State-of-the-Art Analytical Methods for Assessing Dynamic Bonding Soft Matter Materials Adv. Mater. 2014, 26, 5758-5785.

(20)

Roy, N.; Bruchmann, B.; Lehn, J.-M. Dynamers: Dynamic Polymers as Self-Healing Materials Chem. Soc. Rev. 2015, 44, 3786-3807.

(21)

Bergman, S. D.; Wudl, F. Mendable Polymers J. Mater. Chem. 2008, 18, 41-62.

(22)

White, S. R.; Caruso, M. M.; Moore, J. S. Autonomic Healing of Polymers MRS Bull. 2008, 33, 766-769.

(23)

Burattini, S.; Greenland, B. W.; Chappell, D.; Colquhoun, H. M.; Hayes, W. Healable Polymeric Materials: A Tutorial Review Chem. Soc. Rev. 2010, 39, 1973-1985.

(24)

White, S. R.; Sottos, N. R.; Geubelle, P. H.; Moore, J. S.; Kessler, M. R.; Sriram, S. R.; Brown, E. N.; Viswanathan, S. Autonomic Healing of Polymer Composites Nature 2001, 409, 794-797.

(25)

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, 16981702.


17


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

(26)

Page 18 of 25

Adzima, B. J.; Kloxin, C. J.; DeForest, C. A.; Anseth, K. S.; Bowman, C. N. 3D Photofixation Lithography in Diels–Alder Networks Macromol. Rapid Commun. 2012, 33, 2092-2096.

(27)

Berg, G. J.; Gong, T.; Fenoli, C. R.; Bowman, C. N. A Dual-Cure, Solid-State Photoresist Combining a Thermoreversible Diels-Alder Network and a Chain Growth Acrylate Network Macromolecules 2014, 47, 3473-3482.

(28)

Thongsomboon, W.; Sherwood, M.; Arellano, N.; Nelson, A. Thermally Induced Nanoimprinting of Biodegradable Polycarbonates Using Dynamic Covalent Cross-Links ACS Macro Lett. 2013, 2, 19-22.

(29)

Gordon, M. B.; French, J. M.; Wagner, N. J.; Kloxin, C. J. Dynamic Bonds in Covalently Crosslinked Polymer Networks for Photoactivated Strengthening and Healing Adv. Mater. 2015, 27, 8007-8010.

(30)

Zhang, M.; Vora, A.; Han, W.; Wojtecki, R. J.; Maune, H.; Le, A. B. A.; Thompson, L. E.; McClelland, G. M.; Ribet, F.; Engler, A. C.; Nelson, A. Dual-Responsive Hydrogels for Direct-Write 3D Printing Macromolecules 2015, 48, 6482-6488.

(31)

Highley, C. B.; Rodell, C. B.; Burdick, J. A. Direct 3D Printing of Shear-Thinning Hydrogels into Self-Healing Hydrogels Adv. Mater. 2015, 27, 5075-5079.

(32)

Boutelle, R. C.; Northrop, B. H. Substituent Effects on the Reversibility of FuranMaleimide Cycloadditions J. Org. Chem. 2011, 76, 7994-8002.

(33)

Canary, S. A.; Stevens, M. P. Thermally Reversible Crosslinking of Polystyrene via the Furan–Maleimide Diels–Alder Reaction J. Polym. Sci., Part A: Polym. Chem. 1992, 30, 1755-1760.


18

Page 19 of 25

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


(34)

Zhang, Y.; Broekhuis, A. A.; Picchioni, F. Thermally Self-Healing Polymeric Materials: The Next Step to Recycling Thermoset Polymers? Macromolecules 2009, 42, 1906-1912.

(35)

Nimmo, C. M.; Owen, S. C.; Shoichet, M. S. Diels-Alder Click Cross-Linked Hyaluronic Acid Hydrogels for Tissue Engineering Biomacromolecules 2011, 12, 824-830.

(36)

Imbesi, P. M.; Fidge, C.; Raymond, J. E.; Cauët, S. I.; Wooley, K. L. Model Diels–Alder Studies for the Creation of Amphiphilic Cross-Linked Networks as Healable, Antibiofouling Coatings ACS Macro Lett. 2012, 1, 473-477.

(37)

Zeng, C.; Seino, H.; Ren, J.; Hatanaka, K.; Yoshie, N. Bio-Based Furan Polymers with Self-Healing Ability Macromolecules 2013, 46, 1794-1802.

(38)

Heo, Y.; Sodano, H. A. Self-Healing Polyurethanes with Shape Recovery Adv. Funct. Mater. 2014, 24, 5261-5268.

(39)

Durmaz, H.; Hizal, G.; Tunca, U. Linear Tetrablock Quaterpolymers Via Triple Click Reactions, Azide-Alkyne, Diels–Alder, and Nitroxide Radical Coupling in a One-Pot Fashion J. Polym. Sci. A: Polym. Chem. 2011, 49, 1962-1968.

(40)

Polaske, N. W.; McGrath, D. V.; McElhanon, J. R. Thermally Reversible Dendronized Linear AB Step-Polymers Via “Click” Chemistry Macromolecules 2011, 44, 3203-3210.

(41)

Mayo, J. D.; Adronov, A. Effect of Spacer Chemistry on the Formation and Properties of Linear Reversible Polymers J. Polym. Sci. A: Polym. Chem. 2013, 51, 5056-5066.

(42)

Kappe, O. C.; Murphree, S.; Padwa, A. Synthetic Applications of Furan Diels-Alder Chemistry Tetrahedron 1997, 53, 14179-14233.

(43)

Zhong, Y.; Wang, X.; Zheng, Z.; Du, P. Polyether–Maleimide-Based Crosslinked SelfHealing Polyurethane with Diels–Alder Bonds J. Appl. Polym. Sci. 2015, 132, 41944.


19


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

(44)

Page 20 of 25

Gandini, A.; Coelho, D.; Gomes, M.; Reis, B.; Silvestre, A. Materials from Renewable Resources Based on Furan Monomers and Furan Chemistry: Work in Progress J. Mater. Chem. 2009, 19, 8656-8664. A design strategy is demonstrated that enables new functional 3D printed materials made by fused filament fabrication (FFF) utilizing a thermallyreversible dynamic covalent Diels-Alder reaction to dramatically improve both strength and toughness. This approach takes inspiration from self-healing polymers to repair defects in polymeric materials to remedy

inherent issues with the mechanical strength of 3D printed parts.


20

A Page 21 of 25 75 °C 1 2 3 Cross-linker 4 5 Linear monomers 6 7 B 8 9 10 T >120 °C 11 12 13 14 Cross-linked 15 Mending Agent 16 C 17 18 19 20 RT 21 22 De-polymerized 23 Mending Agent 24 25 26

D ACS Applied Materials & Interfaces RT

Cross-linked Mending Agent

Filament

MendingAgent

T > 120 C

De-polymerizes

Printer head Mending Agent De-polymerizes

T < 120 C

Dog-bone Re-polymerizes

ACS Paragon Plus Environment Cross-linked Mending Agent

Printer stage

A 1 2 3 4 5 O 6 7 8 9 10 11 12 13 14 15 16 17 18 19 O 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

B


O

MA

Mix in Dioxane HN

NH

NH

O

80 °C PLA

MA/ PLA Blend

Vacuum Oven 60°C, 24 h Pelletize

MA/ PLA MA/ PLA

2F O N O

O O

n

N

HN

O

O

n ~ 6.1

2M

O

HN

H N

O

N

ethyl acetate 75 oC 24 h

N

O

O O

n ~ 6.1

n

O

N H

MA/ PLA

MA/ PLA !"# $%"&

Strength Testing

N

O

O

HN

3F

MA/ PLA

O

Page 22 of 25

HN

Filament Extrusion, 160 °C, 3 mm die

N NH

Mending Agent (MA)

Laser Cut

ASTM O Standard ACS Paragon Plus Environment Dogbones

3D Printing

Page 23 of 25

PLA

Exothermic

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


10% Remendable PLA

25% Remendable PLA Mending Agent

-40

0

40

80 120 Temperature (°C)

160

Material

T g (°C)

PLA

61.8

10% Remendable PLA

55.2

25% Remendable PLA

48.2

Mending Agent

5.7


200

B 40

50

D Stress (MPa)

Ultimate Strength (MPa)

30 20 10

Page 24 of 25

40 30

X

20

Y

10

PLA Z

0

Z

0.0

0.5

1.0

1.5

2.0

2.5

PLA 3.0

3.5

0

PLA

C

10% Remendable PLA

25% Remendable PLA

0.80

Stress (MPa)

50 40 30 20 10 0

0.60

10% Remendable PLA

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

50 0.40

Stress (MPa)

A

Toughness (MJ/m3)

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


0.20

0.00

PLA ACS Paragon Plus Environment

10% Remendable PLA

25% Remendable PLA

40 30 20

25% Remendable PLA

10 0

0.0

0.5

1.0

1.5 2.0 Strain (%)

2.5

3.0

3.5

A Page 25 of 25 1 2 a’ 3 4 5 6 7 C 8 9 10 11 12 13 14 15 16

B


D

ACS500 Paragon µm Plus Environment

500 µm

Design Paradigm Utilizing Reversible Diels ... - ACS Publications

Recommend Documents