Reinforcement Effects from Nanodiamond in Cellulose Nanofibril Films

Subscriber access provided by Washington University | Libraries

Reinforcement Effects from Nanodiamond in Cellulose Nanofibril Films Seira Morimune-Moriya, Michaela Salajkova, Qi Zhou, Takashi Nishino, and Lars A. Berglund Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.8b00010 • Publication Date (Web): 05 Apr 2018 Downloaded from http://pubs.acs.org on April 7, 2018

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 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 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.

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 34 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

Biomacromolecules

Reinforcement Effects from Nanodiamond in Cellulose Nanofibril Films Seira Morimune-Moriya1, Michaela Salajkova2,3, Qi Zhou3,4, Takashi Nishino5, Lars A. Berglund2,3* 1. Department of Applied Chemistry, College of Engineering, Chubu University, Matsumoto, Kasugai 487-8501 (Japan) 2. Department of Fibre and Polymer Technology, Royal Institute of Technology, SE-100 44 Stockholm (Sweden) 3. Wallenberg Wood Science Center, Royal Institute of Technology, SE-100 44 Stockholm (Sweden) 4. School of Biotechnology, Royal Institute of Technology, AlbaNova University Centre, SE-106 91 Stockholm (Sweden) 5. Department of chemical science and engineering, Graduate School of Engineering, Kobe University, Rokko, Nada, Kobe 657-8501 (Japan)

KEYWORDS. Biocomposite, Hardness, Nanocomposite, Decoration, Strength, Modulus, Nanopaper

ACS Paragon Plus Environment

cellulose nanofibrils

Biomacromolecules 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

ABSTRACT. Although research on nanopaper structures from cellulose nanofibrils (CNF) is well established, the mechanical behavior is not well understood, especially not when CNF is combined with hard nanoparticles. Cationic CNF (Q-CNF) was prepared and successfully decorated by anionic nanodiamond (ND) nanoparticles in hydrocolloidal form. The Q-CNF/ND nanocomposites were filtered from a hydrocolloid and dried. Unlike many other carbon nanocomposites, the QCNF/ND nanocomposites were optically transparent. Reinforcement effects from the nanodiamond were remarkable, such as Young’s modulus (9.8 GPa 16.6 GPa) and tensile strength (209.5 MPa 277.5 MPa) at a content of only 1.9% v/v of ND, and the reinforcement mechanisms are discussed. Strong effects on CNF network deformation mechanisms were revealed by loading-unloading experiments. Scratch hardness also increased strongly with increased addition of ND.



Page 2 of 34

Page 3 of 34 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

Biomacromolecules

1. Introduction

Figure 1 Transmission electron microscopy image of nanodiamond particles. Diamond has a Young’s modulus as high as 1 TPa and a hardnessas high as 10 on the Mohs scale1. Nanodiamond (ND), can be readily prepared by a detonation method and can now be used in nanocomposites. ND nanoparticles have a diameter below 10 nm (see Figure 1 and Supporting Info Figure 1). These ND nanoparticles can be described as core-shell particles. The diamond particle forms the core, whereas the shell has oxygen containing groups2 attached to graphite. The properties of these ND are characteristic of diamond, with the added feature of nanoscale particle form. The characteristics of the shell makes water dispersion of ND facile, and ND can also be modified and functionalized for specific purposes3,4. Nanodiamond is a candidate nanoparticle for nanocomposites,5–8 where hardness is a desirable property.




In a previous study at Kobe University9, nanodiamond nanocomposites were prepared in water-assisted processing. Polyvinyl alcohol (PVA) was dissolved in water and used as a matrix. The properties of ND provided strong reinforcement of PVA in the nanocomposites, and an important reason for this was the good dispersion of nanodiamond in PVA. For example, from tensile tests, the Young’s modulus of PVA was doubled at a nanodiamond content of only 1 weight percent. One challenge in the analysis of reinforcement effects on PVA, is that the nanoparticle will influence crystalline morphology, time-dependence of deformation behavior and physical ageing. As a consequence, part of the measured reinforcement effect may be due to ND-induced changes in PVA structure and properties10. Here, a nanocomposite material is prepared from cellulose nanofibrils (CNF) reinforced by nanodiamond particles. Cellulose is a widely available nanofibrious polymer from renewable resources. Cellulose is a large research field, and it is widely used industrially. There is also substantial growth potential due to the increasing interest in eco-friendly materials11–13. CNF is cellulose in nanofibrillar form, and the fibrils are composed of high molar mass extended and ordered cellulose molecules. From X-ray diffraction studies of plant fibers under tension, the crystalline region of cellulose I is estimated to have an elastic modulus of around 135 GPa14,15 and it is interesting to compare this with the modulus for aluminum (70 GPa) or glass fiber (76 GPa), since the cellulose crystal density is much lower (≈1600 kg/m3). The strength of CNF disintegrated from wood pulp was estimated to be a few GPa16, although fibril strength in plants is expected to be higher (higher molar mass and fewer defects). Recently, the strength was suggested to be comparable to multiwalled carbon nanotubes17, although this will depend on the specific type of nanotube. In addition to high mechanical properties, CNF shows low thermal expansion in the axial direction and low density. Due to the properties and nanoscale dimensions,



Page 4 of 34

Page 5 of 34 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

Biomacromolecules

CNF has been widely used for nanocomposites18–29. In many cases, CNF was the reinforcement phase in polymer composites. For example, PVA20,21,24, epoxy resins21, polylactic acid22 and polyurethanes23 were investigated in their roles as matrix phase. Henriksson and colleagues.30 studied cellulose films (“nanopaper”) based on wood CNF. The nanopaper was not solvent cast, but rather filtered from a hydrocolloidal suspension. Despite high void content (28%), the modulus was high (≈13 GPa), the strength was high (≈210 MPa) and work to fracture (15 MJ/m3). High optical transparency31, oxygen barrier properties32 and favorable thermal expansion coefficient33,34 are other interesting characteristics of nanocellulose films. CNF is organized as a swirled, random-in-the-plane nanofiber network, where fibrils are strongly bonded due to small diameter (4-10nm), smooth fibril surfaces and the drying procedure. As water evaporates during drying of cellulose nanopaper, nanometer-sized fibrils are brought together facilitating molecular scale interaction, and the result is strong secondary fibril-fibril bonding. Benitez and Walther thoroughly reviewed the mechanical properties of cellulose nanopaper56. Effects from relative humidity are discussed as well as effects from fibril structure, counterions, porosity etc. An interesting possibility for increased property range and even new functionalities is to combine cellulose nanopaper with inorganic nanoparticles. Liu et al.35 combined CNF with montmorrillonite nanoclay for reinforcement purposes. The fire retardancy of the material was dramatically improved with delayed thermal degradation of cellulose. Furthermore, montmorrilonite strongly enhanced the gas barrier properties, also under humid conditions. Antibacterial properties were achieved by silver nanocluster addition36 and zinc oxide nanoparticles37. CNF/graphene nanocomposites38 showed greatly improved mechanical properties due to the high aspect ratio of graphene platelets.




In the present study, another class of inorganic cellulose hybrids was investigated. Nanodiamond nanocomposites were prepared by combination of cellulose nanofibrils with nanodiamond particles, so that the hard ND particles were decorating the CNF fibrils in the nanopaper structure. A key was to use quaternized cellulose nanofibrils (Q-CNF), so that the electropositive charge on the CNF could attract the electronegative ND particles. (Supporting Info, Table 1). First, the cationic Q-CNF was just mixed with anionic ND in hydrocolloidal state, so that ND could attach along the CNF fibrils. The Q-CNF/ND filtered and the hybrid nanocomposites were obtained in a similar manner as has been previously reported Sehaqui et al.39 Nanostructural details of the materials were investigated, as well as the reinforcement effects from the nanodiamond particles. The property improvements were quite remarkable at low particle content, and possible mechanisms are discussed.



Page 6 of 34

Page 7 of 34 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

Biomacromolecules

2. Experimental 2.1. Materials Q-CNF. Cationic CNF was prepared from chemical softwood pulp using glycidyl trimethylammonium chloride (GTAC, Sigma-Aldrich, USA), and the procedure provided in Pei et al.40 The sulphite pulp was never dried (Nordic Paper, Sweden) and subjected to beating in a PFI-mill (HAM-JERN, Norway), and mixed with a sodium hydroxide (Sigma-Aldrich, USA) solution in water. The quaternization reaction conditions were 65 °C for 8 h with stirring after adding GTAC to the suspension. The mixture was then neutralized with hydrochloric acid (37%, Sigma-Aldrich, USA) and washed with deionized water. The aqueous suspension of the chemically treated pulp (0.5% w/v) was stirred for 24 h at 600 rpm, and passed through a microfluidizer (M-110EH, Microfluidics Ind., USA) equipped with 200 and 100 µm chamber at a pressure of 1600 bar at room temperature (21 °C). The Q-CNF hydrocolloid showed a solid content of 0.3–0.4%. The ammonium chloride group content on the treated fibrils were determined by conductometric titration41. 100 mg (dry weight) of Q-CNF suspended in Milli-Q water (0.1% w/w) was titrated with 0.005 M silver nitrate (AgNO3, Sigma-Aldrich, USA) solution by adding 200 µL. The conductivity was recorded with a conductivity meter (Mettler Toledo, USA) in 60 second intervals. The amount of trimethylammonium groups in Q-CNF can be calculated based on the volume of AgNO3 used. The charge density of Q-CNF was 0.56 mmol/g.




Scheme 1. Method for processing of Q-CNF/ND materials. Q-CNF/ND nanocomposites. The preparation of the Q-CNF/ND nanocomposites is described in Scheme 1. The Q-CNF suspension was added to the ND aqueous suspension (Bando Chem. Ind.) to reach a Q-CNF concentration of 0.2%w/w. The ND content in the suspension was 0–5% w/w and the rest was Q-CNF. The Q-CNF/ND suspension was stirred for 48 h and filtered on a glass filter funnel (7.2 cm in diameter) using filter membrane (0.65 µm DVPP, Millipore, USA). The Q-CNF/ND suspension was stable. After the filtration, the wet cake of the nanocomposite, which contained 78–81% of water, was placed between the metal mesh sheets on filter paper and then dried at 93 °C for 15 min under vacuum by using Rapid Köthen (PTI, Austria). This resulted in the Q-CNF/ND nanocomposites with thickness in the range of 50–60 µm.



Page 8 of 34

Page 9 of 34 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

Biomacromolecules

2.2. Characterization Atomic Force Microscopy (AFM). Nanoscope IIIa AFM (Picoforce SPM, Veeco, USA) was used to observe the Q-CNF decorated with ND. All measurements were performed in the tapping mode with a scan rate of 2 Hz/512 dots using standard noncontact silicon cantilevers (RTESP, Veeco, USA). The samples were prepared on a mica substrate by depositing the diluted QCNF/ND nanocomposite suspension. Transmission Electron Microscopy (TEM). A highly diluted Q-CNF/ND nanocomposite suspension was deposited on a copper grid (ultra-thin carbon film/holey carbon, Ted Pella, USA), and then stained by uranyl acetate negative stain. Excess suspension liquid was removed using filter paper and the remaining sample was carefully dried in order to minimize the risk for drying artifacts. The sample was observed at 80 kV using transmission electron microscopy (Hitachi HT-7700, Hitachi, Japan). Field-Emission Scanning Electron Microscopy (FE-SEM). The cross sections of the nanocomposites were observed by FE-SEM using Hitachi S-4800 (Hitachi, Japan) equipped with a cold field emission electron source. The samples were coated with graphite and platinumpalladium using Cressington 208 HR sputter coaters (Cressington Scientific Instruments Ltd., UK). Secondary electron detector was used for capturing images at 3 kV/5 µA. Ultraviolet-visible spectroscopy (UV-VIS). UV-VIS spectra of the nanocomposites were observed at room temperature using UV-Visible spectrophotometer (SHIMADZU UV-2550, Shimadzu, Japan) at a wavelength scan rate of 400 nm/min.




Page 10 of 34

Thermogravimetric analysis (TGA). The composition of the nanocomposites was obtained by TGA using Mellter-Toledo thermogravimetric analyzer (TGA/SDTA851, Switzerland). The heating rate of 10 °C/min was used under nitrogen flow. ND content of the nanocomposites was calculated by using the weight of residual at 550 °C, where the weight loss of CNF became constant, considering the weight loss of ND. Tensile test. The tensile properties were tested by Instron 5944 mechanical testing system (Instron, USA) equipped with 500 N load cell. The specimens were conditioned at 50%RH and 23 °C. The gauge length was set at 20 mm and the cross-head speed was 2 mm/min. A minimum of 6 specimens were tested for each sample. The loading-unloading test was carried out with the same instrument. The loading-unloading cycle was repeated with the step of 1% strain. Scratch test. The scratch resistance of the nanocomposites was measured by Nano scratch tester (CSM Instrument, Switzerland). The test was performed with a sphero-conical diamond tip (diameter 2 µm) and the maximum load of 10 mN was applied. The scratch map over 3 points on each sample were made and the width of the scratch marks were measured. The scratch hardness was calculated using the following equation (1)42; ‫ݍ=ܪ‬

ସி

(1)

గ௪ మ

where the F is normal load (N), w is residual width of the scratch mark and q is a function of the viscoelasticity of the material. q = 2 corresponds to the rigid plastic materials and 1 < q < 2 is for visco-elastic materials.



Page 11 of 34 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

Biomacromolecules

3. Results and Discussion 3.1. Characterization of the Q-CNF decorated with ND

A

C

BC

D

Figure 2. (A) AFM height image, (B) AFM phase image and (C, D) TEM image of decorated QCNF.




The Q-CNF fibrils were decorated with ND as described in the experimental section. AFM height and phase images of the decorated Q-CNF can be observed in Figures 2A and B. The contrast in the phase image is high and this is due to the large difference in modulus between QCNF and ND. In the phase image in Figure 2B, ND is present as distinct dots, whereas Q-CNF has similar color as the background. The nanodiamond dots are apparent along the Q-CNF, and this strengthens the hypothesis that ND is indeed adsorbed to Q-CNF. The Q-CNF and nanodiamond distribution was also studied by transmission electron microscopy. Figure 2C presents decorated Q-CNF in diluted Q-CNF/ND nanocomposite suspension. Although there is some CNF agglomeration, the information in the image is helpful. In this figure, ND appears on the surface of Q-CNF, in support of successful ND-decoration of Q-CNF. In contrast, the neat QCNF showed a smooth surface with a width below 10 nm (Supporting figure 2) as previously reported40. According to this previous study, Q-CNF dimensions are below 5 nm in diameter and around 1 µm in length. The fibrils are flexible, so that a swirled, intermingled network structure is obtained in dried films. From TEM images, the distribution of ND was studied (Figure 2D and Supporting figure 3). Q-CNF was primarily combined with agglomerates of ND with a size up to 50 nm. ND adsorbed to Q-CNF because of the opposite charge on the fibrils and the ND nanoparticles. Images support good small-scale dispersion of nanodiamond in the Q-CNF network.



Page 12 of 34

Page 13 of 34 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

Biomacromolecules

3.2. Structure of CNF-nanodiamond materials

A

B

C

D




Figure 3. (A) Photographic images for transparency impression and (B) UV-VIS spectra of QCNF film and Q-CNF/ND nanocomposites, (C) FE-SEM images comparing cross sections of QCNF reference film and (D) Q-CNF/ND nanocomposite (5% w/w). Table 1. Composition and estimated porosity of Q-CNF film and Q-CNF/ND nanocomposites.

Sample Q-CNF Q-CNF/ND 0.5%w/w Q-CNF/ND 1%w/w Q-CNF/ND 2.5%w/w Q-CNF/ND 5%w/w

ND (%v/v) 0

Porosity (%) 6.4

0.1

4.4

0.4

4.3

1.1

2.2

1.9

1.2

The optical transparency of nanocomposites based on carbon nanotubes or graphene tends to be poor even at low nanoparticle content. The transparency of polyvinyl alcohol (PVA) was reduced by about 35% when only 0.1 weight percent of carbon nanotubes (SWNT) were added. 43

Nanocomposites based on graphene and cellulose nanofibrils with a thickness below 10 µm

also lost transparency at 1.25% w/w graphene content38. In contrast, the present Q-CNF/ND nanocomposites maintain reasonably high optical transparency, even at a concentration of 5% w/w of ND, see Figures 3A and B. This indicates that the present composition and preparation strategy provide low porosity in the nanocomposites and fairly homogeneous dispersion of ND9. The content of nanodiamond was estimated from TGA and is presented in Table 1. The measured amount of nanodiamond for low congtent nanocomposites was almost the same as the starting content, while the nanocomposites with high nanodiamond concentration showed much



Page 14 of 34

Page 15 of 34 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

Biomacromolecules

lower content compared with the initial value (Supporting Info, Table 2). This suggests that some excess free ND in the hydrocolloid was lost through the membrane, whereas ND particles adsorbed to the Q-CNF were preserved in the nanocomposites. Figure 3C shows FE-SEM images of the cross section of the Q-CNF. The structure is layered, which is typical for cellulose nanopaper30. For nanocomposites, a dense structure with low porosity was observed, see Figure 3D. Due to the filtration and drying procedure, the structural organization of the present nanocomposite is essentially a low-porosity random-in-plane nanofibril network with swirled, intermingled fibrils 10% w/w), large agglomerates were observed in the nanocomposite structure. Agglomerates are likely to form from clustering of excess individual ND, in particular free ND which were not lost during filtration. The estimated porosity of high ND content nanocomposites increased with increasing ND concentration (Supporting Info Figure 4 and Supporting Info Table 2).




3.3. Mechanical properties of nanocomposites in uniaxial tension

A

B

C

Figure 4. (A) Stress versus strain curves of Q-CNF film and Q-CNF/ND nanocomposites in uniaxial tensile loading; (B) Stress versus strain curves of Q-CNF/ND nanocomposites (1% w/w) from loading-unloading experiment; (C) Young’s modulus as a function of number of loading steps for Q-CNF film and Q-CNF/ND nanocomposite (1% w/w) specimen tested by loadingunloading. The modulus determined during loading and initial unloading are represented as square and triangular dots, respectively.



Page 16 of 34

Page 17 of 34 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

Biomacromolecules

Table 2. Properties for Q-CNF nanopaper and Q-CNF/ND materials. Work of fracture

Young’s modulus (GPa)

Tensile strength (MPa)

Yield strength (MPa)

Elongation at break (%)

(MJ/m )

Q-CNF

9.8 ± 0.9

210 ± 27

103

8.0 ± 0.7

8.2

Q-CNF/ND 0.5%w/w

10.0 ± 0.4

211 ± 17

110

8.0 ± 0.5

8.4

Q-CNF/ND 1%w/w

13.6 ± 0.8

250 ± 10

142

6.6 ± 1.3

8.1

Q-CNF/ND 2.5%w/w

15.6 ± 0.8

265 ± 27

147

7.3 ± 0.8

9.7

Q-CNF/ND 5%w/w

16.6 ± 1.5

278 ± 29

147

6.8 ± 0.7

9.2

Sample

3

Figure 4A and Table 2 present results from uniaxial tensile tests for the Q-CNF film and the Q-CNF/ND nanocomposites. The mechanical properties of the present Q-CNF nanopaper are lower than for films prepared from enzymatic CNF30,40. At low addition of nanodiamond, 0.5 weight percent the reinforcement effect was very small. Then at 1 weight percent of nanodiamond addition, the reinforcement effect was dramatic. For instance, modulus increased from 9.8 to 13.6 GPa and yield strength from 103 to 142 MPa. At 5% ND, the modulus was 16.6 GPa, and ultimate strength had increased from 210 MPa for neat CNF to 278 MPa for the nanocomposite. The strain to failure of the Q-CNF film was preserved with ND addition, resulting in increased work to fracture, corresponding to the area under the stress-strain curves. Modulus data are examined as a function of ND content. At 0.5% w/w, the ND is not effective in increasing modulus very much. At 1% w/w (0.4% v/v), the reinforcement effect is very strong, but then the relative effect decreases with higher ND content, due to agglomeration effects. The mechanism for strong reinforcement effects is unclear. Theoretical predictions based on the




Halpin-Tsai model for spherical particles in a polymer matrix44 do not predict strong reinforcement effects at low particle content. The presence of ND at the interfibril interface is significant. In interfibril stress transfer, shear deformation is important for modulus. One may speculate that in the present system, viscoelastic deformation effects are suppressed due to improved shear stress transfer as interfibril interactions are influenced by the presence of ND. Stress relaxation effects normally included in quasi-static tensile tests may be reduced and the material becomes strongly reinforced by the ND. Another factor, possibly related, is that the composites have lower porosity than Q-CNF as shown in Table 145. From Figure 4A, it is also apparent that yield strength is substantially increased. Yielding is related to irreversible interfibril deformation,30 so the yield strength effect is in support of the proposed reinforcement mechanism. Ultimate strength increases as a consequence of increased yield strength and conserved, or even increased strain hardening coefficient in the plastic deformation region. Strain-to-failure is similar for all materials, suggesting strain-controlled failure. Strongly increased mechanical properties were also reported for CNF/graphene nanocomposites38. There were substantial improvements in the Young’s modulus, toughness and tensile strengths. It was stated that the interface was a key reason, and that the amphiphilic nature of CNF and the hydrophobic nature of graphene was stabilized by π-interaction. The present explanation is more centered around effects of ND on CNF network deformation. The ND decoration of the Q-CNF, may constrain network deformation, in particular for nanocomposites where the nanodiamond content is higher than 1 weight percent. In the case of nanocomposites with exceptionally high ND content (7.5, 10, 25, 50% w/w) the reinforcement efficiency was



Page 18 of 34

Page 19 of 34 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

Biomacromolecules

very low, most likely since ND formed large agglomerates (Supporting Info, Table 3). An interesting observation is that scratch hardness increased with increased ND content (SI, Table 3). Another experiment was conducted by loading the material, followed by unloading, and this was repeated with increasing levels of strain. In Figure 4B, stress versus strain diagrams of QCNF/ND nanocomposites (1% w/w) are presented. The modulus determined during loading and initial unloading for Q-CNF nanopaper and Q-CNF/ND materials (1% w/w) is presented in Figure 4C. The modulus of the Q-CNF film increased with increased strain during loading steps, as previously observed for CNF nanopaper from enzymatic CNF30. The reason is increased orientation of the CNF fibrils in the network. For the nanocomposite, the yield strength is increased with increasing plastic strain, possibly due to increased CNF orientation. Interestingly, the nanocomposite modulus showed stronger increase than for the Q-CNF nanopaper. Henriksson et al.30 proposed that increased Young’s modulus and yield strength are due to network and CNF fibril orientation effects in the deformation direction46. One possibility is that the presence of ND nanoparticles is increasing the degree of Q-CNF orientation at a given strain, although the mechanism for such an effect is unclear.




3.4. Scratch resistance in Q-CNF/ND materials

Figure 5. Hardness obtained by model predictions (Equation (2) and (3)) as well as experimental scratch hardness data (Experimental) for Q-CNF/ND nanocomposites as a function of ND content. Table 3. Scratch hardness of Q-CNF film and Q-CNF/ND nanocomposites.

Sample

Scratch hardness (MPa)

Q-CNF

272 ± 88

Q-CNF/ND 0.5%w/w

302 ± 73

Q-CNF/ND 1%w/w

344 ± 92

Q-CNF/ND 2.5%w/w

352 ± 69

Q-CNF/ND 5%w/w

466 ± 64

Experiments were performed as described in experimental section. The scratch hardness is based on the width of the scratch mark. If the scratch mark is more narrow, then the scratch



Page 20 of 34

Page 21 of 34 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

Biomacromolecules

hardness and the scratch resistance is increased47. Increased scratch hardness is often expected when inorganic fillers are added to polymers48,49. Although the hardness of the filler is a key parameter, the filler can also act as a nucleation agent so that the intrinsic polymer properties are improved by increased crystallinity, resulting in improved scratch resistance50. Neizel et al.51 presented scratch resistance data for epoxy/nanodiamond materials of high ND content. The ND particles formed a connected network structure There was a decrease in penetration depth by 1.5 µm at 25 weight percent nanodiamond content. Zhang et al.52 showed 1% w/w acyl chloride functionalized ND enhanced the hardness of polyimide by ~30%. In this system, it was suggested that due to the modification of ND, strong chemical bonding was produced between polyimide and ND contributing to the significant increase in hardness. The hardness can be roughly estimated from the Young’s modulus and the yield strength. The following equations (2) and (3) were used53,54: ଶ

ா ୲ୟ୬ ఉ

‫ߪ × = ܪ‬௬ ቆ1 + ݈݊ ൬ ଷ ଷ(ଵିఔ మ ଶ

‫ߪ × = ܪ‬௬ ቆ1 + ݈݊ ൬ ଷ

ா ୡ୭ୱ ఏ ଷఙ೤

)ఙ೤

൰ቇ

൰ቇ

(2)

(3)

where H is hardness, σy is yield strength, E is Young’s modulus and ν is Poisson’s ratio. β and θ correspond to the indenter angles. Note that this hardness is not strictly equal to scratch hardness, so the comparison is rough, for the purpose of identifying underlying physical properties of the material. Figure 5 shows the predicted hardness and experimental data for scratch hardness for the Q-CNF/ND materials with increasing nanodiamond fraction. Predictions and experimental data show agreement up to 1




weight percent nanodiamond content. The hardness of the material is increasing since the nanostructured composite has well-dispersed nanodiamond particles. The width of the scratch mark is decreased in materials with nanodiamond. At 1 weight percent of nanodiamond, the width was decreased by 1 µm and as a consequence, the scratch hardness increased by 26%, see Table 3. The larger difference between experimental hardness and predicted data for the material with 5 weight percent nanodiamond is due to the less favorable dispersion of ND at higher reinforcement contents55. Interestingly, the scratch hardness of the Q-CNF/ND nanocomposites was increased by further addition of ND (> 10% w/w) while the Young’s modulus and the yield strength decreased (Supporting Table 3).



Page 22 of 34

Page 23 of 34 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

Biomacromolecules

4. Conclusions A nanocomposite based on Q-CNF nanofibrils decorated with ND was prepared by a simple paper-making process using an aqueous suspension. The Q-CNF was successfully decorated by ND. In the nanocomposite structure, ND nanoparticles appeared to reduce the slight porosity of the Q-CNF network. Despite the incorporation of nanocarbon material, the Q-CNF/ND nanomaterials were optically transparent since the nanodiamond particles were well dispersed in a low-porosity material. ND nanoparticles are embedded at the interfibril interface in a fibril “matrix” of very long (≈1µm) random-in-the-plane swirled Q-CNF nanofibrils, below 5 nm in diameter, forming an unusual type of nanocomposite material. The reinforcement effect from addition of nanodiamond particles by ionic interaction to nanofibrils and cellulose nanopaper was very strong, and ductility was preserved. For instance, at 1% of ND, modulus increased from 9.8 to 13.6 GPa and yield strength from 103 to 142 MPa. At 5% ND, the ultimate strength increased from 210 MPa for neat CNF to 278 MPa for the nanocomposite.. The modulus increase cannot be predicted by conventional micromechanics models. It may be speculated that the ND nanoparticles located at fibril-fibril interfaces, are constraining the viscoelastic nature of CNF network deformation, and thus causing a stronger reinforcement effect than expected. Loading-unloading experiments in the strain-hardening plastic deformation region, revealed stronger orientation effects in the Q-CNF/ND nanocomposites, compared with the neat Q-CNF cellulose nanopaper. This supports that there are specific effects of interfacially located ND on the deformation mechanisms in the Q-CNF network “matrix”. The scratch hardness was also strongly increased at ND contents up to 1 percent by weight, and comparable with rough theoretical estimates of hardness. The hardness




was also increased at very high ND content (5, 7.5, 10, 25, 50 wt%). The increase continued although ND agglomeration effects were significant. Strength and modulus data did not increase beyond 7.5wt% ND content. In summary, by attaching ND ionically to Q-CNF, the unique properties of ND were synergetically exploited for strongly improved properties of Q-CNF/ND hybrid nanomaterials. The present nanocomposite is of renewable resource base, it is strong, exceptionally stiff and optically transparent, at very low content of ND (0.1-1.9% v/v). Most “homeopathic” reinforcement effects reported for nanocomposites in literature are due to significant changes in the polymer matrix structure compared with the neat polymer reference, such as increased crystallinity or orientation. The present “matrix” is unchanged in structure. It is therefore an interesting system for further studies on reinforcement effects in this class of nanoparticle composites.



Page 24 of 34

Page 25 of 34 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

Biomacromolecules

Supporting Information. Figures showing size distribution of ND in aqueous suspension, STEM image and AFM images of Q-CNF from the diluted suspension, TEM image of distribution of ND in Q-CNF/ND nanocomposite suspension, FE-SEM image of the cross section of Q-CNF/ND nanocomposite (25% w/w). Table presenting zeta potential of ND, composition (TGA) and the porosity of QCNF film and Q-CNF/ND nanocomposites and table summarizing mechanical properties and scratch hardness of Q-CNF film and Q-CNF/ND nanocomposites. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Tel: 46-8-7908118, Fax: 46-8-7908108, E-mail: [email protected] Notes. The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by Grant-in-Aid for Japan Society for the Promotion of Science (JSPS) Fellows. We are grateful to staff at WWSC and in the Biocomposites group at KTH for technical help and the thoughtful discussions.




References (1) Kidalov, S. V.; Shakhov, F. M.; Vul', A. Y. Thermal conductivity of nanocomposites based on diamonds and nanodiamonds. Diamond Relat. Mater. 2007, 16, 2063–2066. (2) Osawa, E. Recent progress and perspectives in single-digit nanodiamond. Diamond Relat. Mater. 2007, 16, 2018–2022. (3) Meinhardt, T.; Lang , D.; Dill, H.; Krueger, A. Pushing the Functionality of Diamond Nanoparticles to New Horizons: Orthogonally Functionalized Nanodiamond Using Click Chemistry. Adv. Funct. Mater. 2011, 21, 494–500. (4) Wuest, K. N. R.; Trouillet, V. A.; Goldmann, S.; Stenzel, M. H.; Barner-Kowollik, C. Polymer Functional Nanodiamonds by Light-Induced Ligation. Macromolecules 2016, 49, 1712−1721. (5) Mochalin, V. N.; Shenderova, O.; Ho, D.; Gogotsi, Y. The properties and applications of nanodiamonds. Nat. nanotechnol. 2012, 7, 11–23. (6) Rej, E.; Gaebel, T.; Waddington, D. E. J.; Reilly, D. J. Hyperpolarized Nanodiamond Surfaces. J. Am. Chem. Soc., 2017, 139, 193–199. (7) Lee, D.-K.; Kim, S. V.; Limansubroto, A. N.; Yen, A.; Soundia, A.; Wang, C.-Y.; Shi, W.; Hong, C.; Tetradis, S.; Kim, Y.; Park, N.-H.; Kang, M. K.; Ho, D. Nanodiamond–Gutta Percha Composite Biomaterials for Root Canal Therapy. ACS Nano 2015, 9, 11490–11501. (8) Zhang, F.; Song, Q.; Huang, X.; Li, F.; Wang, K.; Tang, Y.; Hou, C.; Shen H. A Novel High Mechanical Property PLGA Composite Matrix Loaded with Nanodiamond–Phospholipid Compound for Bone Tissue Engineering. ACS Appl. Mater. Interfaces 2016, 8, 1087–1097.



Page 26 of 34

Page 27 of 34 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

Biomacromolecules

(9) Morimune, S.; Kotera, M.; Nishino, T.; Goto, K.; Hata, K. Poly(vinyl alcohol) Nanocomposites with Nanodiamond Macromolecules 2011, 44, 4415–4421. (10) Roumeli, E.; Pavlidou, E.; Avgeropoulos, A.; Vourlias, G.; Bikiaris, D. N.; Chrissafis, K. Factors Controlling the Enhanced Mechanical and Thermal Properties of NanodiamondReinforced Cross-Linked High Density Polyethylene. J. Phys. Chem. B 2014, 118, 11341– 11352. (11) Berglund, L. A.; Peijs, T. Cellulose biocomposites-from bulk moldings to nanostructured systems. Mrs Bull. 2010, 35, 201–207. (12) Eichorn, S. J.; Dufresne, A.; Aranguren, M.;Marcovich, N. E.; Capadona, J. R.; Rowan, S. J.; Weder, C.; Thielemans, W.; Roman, M.; Renneckar, S.; Gindl, W.; Veigel, S.; Keckes, J.; Yano, H.; Abe, K.; Nogi, M.; Nakagaito, A. N.; Mangalam, A.; Simonsen, J.; Benight, A. S.; Bismarck, A.; Berglund, L. A.; Peijs, T. Review: current international research into cellulose nanofibres and nanocomposites. J. Mater. Sci. 2010, 45, 1–33. (13) Klemm, D.; Kramer, F.; Moritz, S.; Lindstrm, T.; Ankerfors, M.; Gray, D.; Dorris A. Nanocelluloses: A New Family of Nature-Based Materials. Angew. Chem. Int. Edit. 2011, 50, 5438–5466. (14) Sakurada, I.; Nukushina, Y.; Ito, T. Experimental determination of the elastic modulus of crystalline regions in oriented polymers. J. Polym. Sci. 1962, 57, 651–660. (15) Nishino, T.; Takano, K.; Nakamae, K. Elastic Modulus of the Crystalline Regions of Cellulose. Polymorphs. J. Polym. Sci, Part B. 1995, 33, 1647–1651.




(16) Page, D. H.; EL-Hosseny, F. The mechanical properties of single wood pulp fibres. J. Pulp Paper Sci. 1983, 9, 99–100. (17) Saito, T.; Kuramae, R.; Wohlert, J.; Berglund, L. A.; Isogai, A. An Ultrastrong Nanofibrillar Biomaterial: The Strength of Single Cellulose Nanofibrils Revealed via SonicationInduced Fragmentation. Biomacromolecules 2013, 14, 248−253. (18) Samir, M.; Alloin, F.; Paillet, M.; Dufresne, A. Tangling Effect in Fibrillated Cellulose Reinforced Nanocomposites. Macromolecules 2004, 37, 4313–4316. (19) Nakagaito, A. N.; Yano, H. Appl. Phys. A: Mater. Sci. Process. 2004, 78, 547–552. (20) Zimmermann, T.; Pohler, E.; Geiger, T. Adv. Eng. Mater. 2004, 6, 754–761. (21) Bruce, D. M.; Hobson, R. N.; Farrent, J. W.; Hepworth, D. G. Composites, Part A 2005, 36, 1486–1493. (22) Iwatake, A.; Nogi, M.; Yano, H. The effect of morphological changes from pulp fiber towards nano-scale fibrillated cellulose on the mechanical properties of high-strength plant fiber based composites. Compos. Sci. Technol. 2008, 68, 2103–2106. (23) Seydibeyoglu, M. O.; Oksman, K. Novel nanocomposites based on polyurethane and micro fibrillated cellulose. Compos. Sci. Technol. 2008, 68, 908–914. (24) Gea, S.; Bilotti, E.; Reynolds, C. T.; Soykeabkeaw, N.; Peijs, T. Bacterial cellulose–poly (vinyl alcohol) nanocomposites prepared by an in-situ process. Mater. Lett. 2010, 64, 901–904.



Page 28 of 34

Page 29 of 34 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

Biomacromolecules

(25) Sehaqui, H.; Morimune, S.; Nishino, T.; Berglund, L. A. Stretchable and Strong Cellulose Nanopaper Structures Based on Polymer-Coated Nanofiber Networks: An Alternative to Nonwoven Porous Membranes from Electrospinning. Biomacromolecules 2012, 13, 3661–3667. (26) Sehaqui, H.; Mushi, N. E.; Morimune, S.; Salajkova, M.; Nishino, T.; Berglund, L. A. Cellulose nanofiber orientation in nanopaper and nanocomposites by cold drawing. ACS Appl. Mater. Interfaces 2012, 4, 1043–1049. (27) Hayase, G.; Kanamori, K.; Abe, K.; Yano, H.; Maeno, A.; Kaji, H.; Nakanishi, K. Polymethylsilsesquioxane–Cellulose Nanofiber Biocomposite Aerogels with High Thermal Insulation, Bendability, and Superhydrophobicity. ACS Appl. Mater. Interfaces 2014, 6, 9466– 9471. (28) Yu, P.; He, H.; Luo, Y.; Jia, D.; Dufresne, A. Reinforcement of Natural Rubber: The Use of in Situ Regenerated Cellulose from Alkaline–Urea–Aqueous System. Macromolecules 2017, 50, 7211–7221. (29) Yao, K.; Huang, S.; Tang, H.; Xu, Y.; Buntkowsky, G.; Berglund, L. A.; Zhou, Q. Bioinspired Interface Engineering for Moisture Resistance in Nacre-Mimetic Cellulose Nanofibrils/Clay Nanocomposites. ACS Appl. Mater. Interfaces 2017, 9, 20169–20178. (30) Henriksson, M.; Berglund, L. A.; Isaksson, P.; Lindström, T.; Nishino, T. Cellulose nanopaper structures of high toughness. Biomacromolecules 2008, 9, 1579–1585. (31) Nogi, M.; Iwamoto, S.; Nakagaito, A. N.; Yano, H. Optically Transparent Nanofiber Paper. Adv. Mater. 2009, 21, 1595–1598.




Page 30 of 34

(32) Fukuzumi, H.; Saito, T.; Wata, T.; Kumamoto, Y.; Isogai, A. Transparent and high gas barrier

films

of

cellulose

nanofibers

prepared

by

TEMPO-mediated

oxidation.

Biomacromolecules 2009, 10, 162–165. (33) Yano, H.; Sugiyama, J.; Nakagaito, A. N.; Nogi, M.; Matsuura, T.; Hikita, M.; Handa, K. Optically Transparent. Composites Reinforced with Networks of Bacterial Nanofibers. Adv. Mater. 2005, 17, 153–155. (34) Okahisa, Y.; Yoshida, A.; Miyaguchi, S.; Yano, H. Optically transparent wood- cellulose nanocomposite as a base substrate for flexible organic light-emitting diode displays. Compos. Sci. Technol. 2009, 69, 1958–1961. (35) Liu, A.; Walther, A.; Ikkala, O.; Belova, L.; Berglund, L. A. Clay. Nanopaper with tough cellulose nanofiber matrix for fire retardancy and gas barrier functions. Biomacromolecules 2011, 12, 633–641. (36) Dı ´ ez, I.; Eronen, P.; Österberg, M.; Linder, M. B.; Ikkala, O.; Ras, R. H. Functionalization of nanofibrillated cellulose with silver nanoclusters: fluorescence and antibacterial activity. Macromol. Biosci. 2011, 11, 1185–1191. (37) Martins, N. C. T.; Freire, C. S. R.; Neto, C. P. l.; Silvestre, A. J. D.; Causio, J.; Baldi, G.; Sadocco, P.; Trindade, T. Antibacterial paper based on composite coatings of nanofibrillated cellulose and ZnO. Colloids Surf. A 2013, 417, 111–119. (38) Malho, J. M.; Laaksonen, P.; Walther, A.; Ikkala, O.; Linder, M. B. Facile Method for Stiff, Tough, and Strong Nanocomposites by Direct Exfoliation of Multilayered Graphene into Native Nanocellulose Matrix. Biomacromolecules 2012, 13, 1093−1099.



Page 31 of 34 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

Biomacromolecules

(39) Sehaqui, H.; Liu, A.; Zhou, Q.; Berglund, L. A. Fast Preparation Procedure for Large, Flat Cellulose and Cellulose/Inorganic Nanopaper Structures. Biomacromolecules 2010, 11, 2195– 2198. (40) Pei, A.; Butchosa, N.; Berglund, L. A.; Zhou, Q. Surface quaternized cellulose nanofibrils with high water absorbency and adsorption capacity for anionic dyes. Soft Matter 2013, 9, 2047– 2055. (41) Hasani, M.; Cranston, E. D.; Westman, G.; Gray, D. G. Cationic surface functionalization of cellulose nanocrystals. Soft Matter 2008, 4, 2238–2244. (42) Xiang, C; Chu, J; Masuda, K. Polym. Eng. Sci. 2001, 41, 23–31. (43) Li, C.; Lv, X.: Dai, J.: Cui, J.: Yan, Y. Synthesis of water-soluble single-walled carbon nanotubes and its application in poly (vinyl alcohol) composites. Polym. Adv. Technol. 2013, 24, 376–382. (44) Halpin, J. C.; Kardos, J. L. The Halpin-Tsai equations: A review. Polym. Eng. Sci. 1976, 16, 344–352. (45) Henriksson, M.; Berglund L. A. Structure and Properties of Cellulose Nanocomposite Films Containing Melamine Formaldehyde. J. Appl. Polym. Sci. 2007, 106, 2817–2824. (46) Gindl, W.; Martinschitz, K. J.; Boesecke, P.; Keckes, J. Structural changes during tensile testing of an all-cellulose composite by in situ synchrotron X-ray diffraction. Comp. Sci. Technol. 2006, 66, 2639–2647.




(47) Surampadi, N. L.; Pesacreta, T. C.; Misra, R. D. K. The determining role of scratch indenter radius on surface deformation of high density polyethylene and calcium carbonatereinforced composite. Mater. Sci. Eng., A 2007, 456, 218–229. (48) Hadal, R.; Dasari, A.; Rohrmann, J.; Misra, R. D. K. Susceptibility to scratch surface damage of wollastonite- and talc-containing polypropylene micrometric composites. Mater. Sci. Eng., A 2004, 380, 326–339. (49) Misra, R. D. K.; Hadal, R.; Duncan, S. J. Surface damage behavior during scratch deformation of mineral reinforced polymer composites. Acta Materialia 2004, 52, 4363–4376. (50) Yuan, Q.; Ramisetti, N.; Misra, R. D. K. Nanoscale near-surface deformation in polymer nanocomposites. Acta Materialia 2008, 56, 2089–2100. (51) Neitzel, I.; Mochalin, V.; Knoke, I.; Palmese, G. R.; Gogotsi, Y. Mechanical properties of epoxy composites with high contents of nanodiamond. Compos. Sci. Technol. 2011, 71, 710– 716. (52) Zhang, Q.; Naito, K.; Tanaka, Y.; Kagawa, Y. Grafting Polyimides from Nanodiamonds. Macromolecules 2008, 41, 536–538. (53) Bao, Y. W.; Wang, W.; Zhou, Y. C. Investigation of the relationship between elastic modulus and hardness on depth-sensing indentation measurements. Acta Mater. 2004, 52, 5397– 404. (54) Wredenberg, F.; Larsson, P. L. Scratch testing of metals and polymers: Experiments and numerics. Wear 2009, 266, 76–83.



Page 32 of 34

Page 33 of 34 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

Biomacromolecules

(55) Ayatollahi, M. R.; Alishahi, E.; Doagou-R, S.; Shadlou, S. Tribological and mechanical properties of low content nanodiamond/epoxy nanocomposites. Composites, Part B 2012, 43, 3425–3430. (56) Benitez, A.J.; Walther, A. Cellulose nanofibril nanopapers and bioinspired nanocomposites: a review to understand the mechanical property space. J. Mater. Chem. A 2017, 5, 16003-16024.




For Table of Contents Use Only

Strong and Stiff Nanocomposites based on Cellulose Nanofibrils Decorated with Nanodiamond Seira Morimune-Moriya1, Michaela Salajkova2,3, Qi Zhou3,4, Takashi Nishino5, Lars A. Berglund2,3*



Page 34 of 34

Reinforcement Effects from Nanodiamond in Cellulose Nanofibril Films

Recommend Documents