Effective Reinforcement of Poly(methyl methacrylate) Composites with

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Effective Reinforcement of Poly(methyl methacrylate) Composites with a Well-Defined Bacterial Cellulose Nanofiber Network Yoshihiko Shimizu, Keita Sakakibara, Shuhei Akimoto, and Yoshinobu Tsujii ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.9b02602 • Publication Date (Web): 15 Jul 2019 Downloaded from pubs.acs.org on July 17, 2019

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ACS Sustainable Chemistry & Engineering

Effective Reinforcement of Poly(methyl methacrylate) Composites with a Well-Defined Bacterial Cellulose Nanofiber Network Yoshihiko Shimizu,†,‡ Keita Sakakibara, *,† Shuhei Akimoto,† and Yoshinobu Tsujii*, †

†Institute

for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan

‡Matsumoto

Yushi-Seiyaku Co., Ltd., 2-1-3 Shibukawa-cho, Yao, Osaka 581-0075, Japan

*To whom correspondence should be addressed. Tel: +81-774-38-3162; Fax: +81-774-38-3170; E-mail: [email protected] (K.S.); [email protected] (Y. T.).

KEYWORDS. Bacterial Cellulose, Composite, Nanofiber Network, Mechanical Property, Nanoindentation.

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ABSTRACT

Bacterial cellulose (BC) has a well-defined nanofiber network in the gel, potentially applicable as a reinforcement filler for ideal polymer composite materials. In this study, BC/poly(methyl methacrylate) (PMMA) composite materials with nanofiber network structures were prepared via a stepwise solvent exchange from water to methyl methacrylate (MMA) via tetrahydrofuran followed by free radical polymerization. The homogeneous distribution of the BC network in its original network structure in the composite was confirmed by confocal laser scanning microscopy. Mechanical properties were evaluated by nanoindentation experiments, revealing that the elastic modulus of the BC/PMMA composite significantly increased with the addition of only 0.3 vol% of BC. Using network model for mechanical properties of the polymer composites, the reinforcement improvement of PMMA by the embedded BC network was successfully described. We conclude that the BC network deformation was stretch-dominated and that the load was effectively transferred by both fine BC network reinforcement and lateral reinforcement of the matrix.


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INTRODUCTION From the viewpoint of energy and environmental issues, the preparation and application of polymer composite materials for lightweight construction design is one of the most important topics. Compared with conventional polymer composite materials using glass fiber, carbon black, talc, and carbon fibers as reinforcement fillers, cellulose nanofibers (CNF) are most advantageous because of the abundance, low cost, biodegradability, renewability, good physical properties, and safety. In general, CNFs produced from biomass resources such as wood and plants are microfibrils with diameters ranging from several nanometers to 50 nm and lengths of several micrometers. The most important characteristics of CNF are the remarkable mechanical properties such as high Young’s modulus (140 GPa1, 2) Since CNF has a hydrophilic surface, dispersion in polymer matrices such as polyolefin, polystyrene, and poly(meth)acrylate is difficult unless their surface is made hydrophobic.3-6 Recently, another successful approach involves using a preformed CNF network. Some examples of this strategy include immersion precipitation of the matrix solution with CNFs,7 casting and drying the matrix solution with CNF dispersion in organic solvents,8-10 and sol-gel processing with precipitation of the CNF suspension in poor solvents, followed by polymer impregnation11, 12 or in situ polymerization.13 Bacterial cellulose (BC), produced by the bacterium Acetobacter xylinus cultivated in a culture medium, is a naturally-occurring CNF with cross-sections of 4 to 80 nm and lengths of several m.14 Bacterial cellulose has high crystallinity (more than 70%)15 similar to other cellulosic resources.16 Therefore, BC also has high mechanical properties,17-20 and have been utilized as a reinforcement filler.21 Yano and coworkers have prepared BC composites by compressing and freeze-drying BC gels followed by polymer impregnation.22, 23 More importantly, the original BC gel possesses a very fine and pure CNF network, whose self-standing structure is maintained


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despite containing only less than 1% BC because of the high aspect ratio and high entanglement of BC. Besides, because CNFs in the BC gel are ideally dispersed without any surface modification, the reinforcement effect of the CNF network can be verified experimentally by estimating the mechanical properties of the BC gel embedded in a polymer matrix. Therefore, the CNF network structure in BC gels is expected to be the best choice for ideal composites. The in-situ polymerization of monomers within the BC network has been widely applied to make the BC hydrogel tough enough for several applications including cartilage-like supporting tissue,24 antimicrobial hydrogels,25 drug delivery,26 and fuel cell membranes.27 Acrylic and methacrylic monomers have been frequently used including acrylic acid,24 2-hydroxyethyl methacrylate,24, 2830

2-aminoethyl methacrylate,25 glycerol monomethacrylate,31 2-ethoxyethyl methacrylate,31 and

glycidyl methacrylate32, 33 with suitable crosslinkers. These studies demonstrated the need of a never-dried procedure for the preparation of BC/ poly(meth)acrylates interpenetrating network (IPN) hydrogels, where solvent exchange of BC hydrogels from water to monomer solutions via ethanol,24 or directly from water to aqueous monomer solutions29 was conducted in order to avoid the collapse of BC network structures. Different from these BC/ poly(meth)acrylates IPN hydrogel systems, we have reported the preparation and mechanical properties of solvent-free BC/ poly(ethyl acrylate) (BC/PEA) elastomeric composites.34 This BC-reinforced elastomer was successfully prepared by stepwise solvent exchange from water to monomer via tetrahydrofuran (THF), followed by free radical polymerization. Because of the well-maintained CNF network structure, this material exhibited highly-stretchable and strain-hardening properties. The CNF network structure in BC/ polymer composites materials is considered to be appropriate models for understanding network structure reinforcement mechanisms. In general, a network structure has been modeled using three composition elements: struts, crosslinks, and space. In this


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model, the network structure is mechanically characterized by the deformation behavior of the struts, including stretching and bending.35-37 The elastic modulus of this network is described to be proportional to its density with a scaling exponent that is dependent on the deformation modes. A scaling exponent close to 1 indicates stretch-dominated deformation behavior of the struts, whereas an exponent close to 2 indicates bend-dominated deformation.35-37 The deformation behavior of the network structure embedded in matrices has also been modeled using struts, crosslinks, and matrices. This model provides important information for characterizing the mechanical properties of both the network structure and the composites.38, 39 Here, we demonstrate the stretch-dominated deformation of a well-defined BC nanofiber network-reinforced polymer composite material. Poly(methyl methacrylate) (PMMA) was selected as a polymer matrix, since PMMA is a representative thermoplastic with glassy viscoelastic behavior and frequently used for polymer composite materials. First, the BC/ PMMA composite with a well-maintained CNF network structure was prepared via stepwise solvent exchange from water to monomer (MMA), followed by free radical polymerization. This process is similar to our previous work,34 where a BC-reinforced elastomer (BC/PEA) was successfully prepared with enhanced mechanical properties. The CNF network in the composite was characterized by confocal laser scanning microscope (CLSM) observation of fluorochromelabelled BC. Then, to reveal the effectiveness of CNF reinforcement, mechanical properties were evaluated by nanoindentation measurements, providing the elastic modulus in the submicrometer scale. Since indentation measurements are a reliable technique to analyze the elastic moduli in a geometry-independent manner, the reinforcement effect of BC with a very small amount of 0.3 vol% can be isolated. To summarize, we focused on the deformation behavior of BC nanofiber networks in several matrices including water (hydrogel), elastomer (BC/PEA elastomer), and


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glassy PMMA resin (BC/PMMA composite). In this study, the superior load transfer mechanism of BC-reinforced composite materials was revealed for the first time on the basis of the scaling theory E ~n, where the homogeneously embedded nanofiber network is crucial to realize stretchdominated deformation. It should be noted that though the impact of interphase on filler reinforced composite materials has been well recognized,40, 41 this paper mainly deals with the effect of the BC nanofiber network on the mechanical properties of the polymer composite materials. This is because the present mechanical test, nanoindentation, performs minimal mechanical deformation, so that in this study such an interphase effect would be negligible and thus the effect of the nanofiber network is mainly focused on.

EXPERIMENTAL SECTION Materials. Bacterial cellulose (BC) hydrogel was purchased from Fujicco Co. Ltd. and purified according to procedures detailed in the literature.42 BC was cut cubically with around 1 cm on a side. The weight and volume fraction of BC are shown in Table 1. Methyl methacrylate (MMA) (99%, Nacalai Tesque Inc., Kyoto, Japan) was purified by passing it through a column filled with activated neutral alumina to remove the polymerization inhibitor. 2,2’-Azobisisobutyronitrile (AIBN) (99%, Wako Pure Chemical Industries, Ltd., Osaka, Japan) was purified by recrystallization and used as an initiator for free radical polymerization. Tetrahydrofuran (THF) (99%, Nacalai), di-n-butyltin dilaurate (90 %, Wako), rhodamine B isothiocyanate (RITC) (mixed isomers, Sigma-Aldrich), and fluorescein isothiocyanate (FITC) (90%, Sigma-Aldrich) were used as received. Deionized water was used for all aqueous solutions. THF used in chromatography was distilled before use.


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Preparation of BC/PMMA Composites. Figure 1 shows the preparation of BC/PMMA composites. There are two main procedures: (1) solvent exchange treatment of the BC hydrogels from water to MMA via THF, and (2) free radical polymerization of MMA. To control the BC content, the BC/MMA gel was compressed to an arbitrary size, followed by free radical polymerization.

Polymerization

BC/H2O gel

BC/THF gel

BC/MMA gel Compression

BC/PMMA composite

Polymerization

c-BC/MMA gel

c-BC/PMMA composite

Figure 1. Schematic illustration for the preparation of BC/PMMA composite materials.

Stepwise Solvent Exchange. First, a nine-fold amount of THF was added to the purified BC/H2O gel and agitated for 12 h by shaking (EYELA Multi Shaker MMS, Tokyo Rikakikai Co., Ltd., Tokyo, Japan). This treatment was carried out three times. Then, residual water was completely removed using a Soxhlet extractor with THF for 6 h, yielding a BC/THF gel. Next, a nine-fold amount of MMA was added to the BC/THF gel and agitated in the same manner. This treatment was performed three times, yielding a BC/MMA gel. The weight fractions of BC in the BC/H2O and BC/MMA gels were estimated by comparing the weight of the BC gels and the dry samples, and then converting to the volume fraction using the density of BC. The molar fractions of water,


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THF, and MMA in the BC/MMA gel were estimated by 1H-NMR analysis, and converted to the weight and volume fractions. These results are shown in Table 1. Free Radical Polymerization of MMA. The BC/MMA gel was soaked into the MMA solution with AIBN in the total AIBN concentration of 5.0 × 10-3 mol%, and then was placed into a test tube with a three-way stopcock. The test tube was degassed under reduced pressure for several seconds before filling with argon. This treatment was carried out 20 times, then the test tube was placed in an oil bath at 60 C for 12 h, then at 70 C for 12 h, and finally at 100 C for 12 h, according to the method for the preparation of defect-free PMMA bulk materials.43 After polymerization, the BC/PMMA composite was trimmed to yield BC/PMMA-0.3, where BC/PMMA-0.3 means BC/PMMA composite with 0.3 vol% of BC (Table 1). The free PMMA in the BC composite was dissolved in THF and subjected to gel permeation chromatography (GPC) for the determination of weight-average molecular weight (Mw) and molecular weight distribution (Mw/Mn). The conversion of MMA in the composite was characterized by 1H-NMR in dchloroform. In the same way, pure PMMA was prepared and characterized. Compression of the BC/MMA Gel and Free Radical Polymerization. The weight and volume fractions of cellulose were controlled by compressing the BC/MMA gels using stainless 300 mesh sheets on two glass plates in the direction perpendicular to the layer structure of the BC gel derived from the activity of the bacterium near the surface of the culture medium,14,

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yielding a

compressed BC/MMA (c-BC/MMA) gel. For the BC/PMMA composite with the BC content of 0.8 vol% (c-BC/PMMA-0.8), the BC/MMA gel was first compressed with a spacer of polytetrafluoroethylene (PTFE) film (1 mm thickness), and then relaxed in the addition of monomer solution, followed by the subsequent free radical polymerization in a same manner as above. For c-BC/PMMA-3.7, the BC/MMA gel was first compressed with the PTFE spacer (1 mm


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thickness), clamped with double clips, soaked with monomer solution, and then subjected to the polymerization with keeping the compression. For c-BC/PMMA-19, the BC/MMA gel was first compressed fully without a spacer, clamped with double clips, soaked with monomer solution, and then subjected to the polymerization with keeping the compression. The characterization of cBC/PMMA composites is shown in Table 2. Fluorescent Labelling of Nanofibers. Fluorescein isothiocyanate (FITC, 1 wt%) dissolved in acetone was added into the BC hydrogel and agitated for 14 h with a shaking apparatus. Then, the BC hydrogel was washed repeatedly with water to remove unadsorbed FITC, yielding a fluorochrome-labeled BC/H2O gel. Rhodamine B isothiocyanate (RITC, 1 wt%) and a catalytic amount of di-n-butyltin dilaurate dissolved in acetone were mixed with the BC/THF gel and agitated for 3 h at 50 C with a shaking apparatus.44 Then, the BC/THF gel was washed repeatedly with THF to remove unreacted RITC. A nine-fold amount of MMA was added to the BC/THF gel and agitated in the same manner. This treatment was performed three times, yielding a fluorochrome-labeled BC/MMA gel. Free radical polymerization was conducted in the same way as above, yielding a fluorochrome-labeled BC/PMMA composite. Surface Polishing. For confocal laser scanning microscopy (CLSM) and nanoindentation measurements, PMMA and BC/PMMA composites were cleaved to expose the internal structure. Their surfaces were polished in water with abrasive papers in the order of the grit sizes of #1000, #2000, and #4000. The average roughness on the top surface was confirmed by 3D laser scanning microscopy (KEYENCE, VK-X) to range from 25 to 100 nm, smaller than the nanoindentation tip contact size. This means that the elastic moduli of the composites can be effectively determined by nanoindentation measurements.


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Characterization. To determine number-average molecular weight (Mn), weight-average molecular weight (Mw), and polydispersity index (Mw/Mn) of PMMA, GPC was carried out with a Shodex GPC-101 high speed liquid chromatography system equipped with a guard column (Shodex GPC KF-G), two 30-cm mixed columns (Shodex GPC KF-806L, exclusion limit = 2  107), and a differential refractometer (Shodex RI-101). THF was used as an eluent at a flow rate of 0.8 mL min-1. The GPC system was calibrated using PMMA standards (Polymer Laboratories, Mp = 1.31  103 – 1.64  106). 1H-NMR spectra were recorded on JNM-ECA600 (JEOL, Tokyo, Japan) (600 MHz) using deuterated chloroform as the solvent. Chemical shifts relative to tetramethylsilane (TMS) as an internal standard are given in  values. CLSM was carried out using an inverted-type microscope (LSM 5 PASCAL, Carl Zeiss, Germany) with a 532-nm wavelength laser and 63 objective lens (Plan Apochromat, Carl Zeiss). The contrast and brightness of the CLSM images were adjusted using standard imaging software. Nanoindentation Experiments. Nanoindentation experiments were carried out to determine the indentation elastic modulus of the PMMA and BC/PMMA composites using a Nano Indenter G200 (Agilent Technologies Inc.) with a Berkovich type indentation tip. Continuous stiffness measurement (CSM) was used to continuously obtain the depth profile of the indentation elastic modulus up to a depth of about 8000 nm. The optimum frequency, oscillation amplitude, and strain rate values were 45 Hz, 2 nm, and 0.05 s-1, respectively. The displacement-detected 200 N m-1 of stiffness was defined as the top surface of the samples. Calibration of the blunting of the indentation tip and the calculation of modulus are based on the Oliver-Pharr method.45 Nanoindentation experiments were conducted with over 5 indents for each sample, except for cBC/PMMA-0.8 (see Table 2 for their coding) with 23 indents near the edges in order to confirm uniformity of BC in a wide area, and 4 indents for c-BC/PMMA-19 in the edge direction because


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of the small cross-sectional area from the compression of BC. The average modulus at a specific depth was calculated. The distance between the indents was larger than 400 m to prevent influences from the other indents. The Poisson’s ratio of PMMA and BC/PMMA composites was a typical value of 0.3 taken from the literature.46 The average elastic modulus was calculated with the standard deviation taken as the error.

RESULTS AND DISCUSSION Preparation of Well-Defined BC/PMMA Composites. We first tried the direct exchange from water in original BC/H2O gels to MMA (see Supporting Information). However, the BC gel shrunk because of the immiscibility of water with MMA (Figure S1). Thus, solvent exchange via THF, miscible with both water and MMA, was used (Figure 1, Figure 2a-2c). Table 1 shows the composition of the BC/H2O and BC/MMA gels. The volume fractions of BC in BC/H2O and BC/MMA gels were almost the same. In addition, the BC/MMA gel had low water and THF contents. This indicates that the three-dimensional network structure of BC/MMA was well preserved throughout the solvent exchange. Aiming to compare the impact of different BC network densities on mechanical properties, BC/MMA gels were carefully compressed prior to free radical polymerization yielding three levels of compaction, i.e., the volume fraction of BC to be 0.8, 3.7, and 19 vol%.


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Table 1. Compositions of the BC/H2O and BC/MMA gels.a Weight fraction (%) / Volume fraction (%) BCa

H2O

THF

MMA

BC/H2O gel

0.51 / 0.34

99.49 / 99.66

0/0

0/0

BC/MMA gel

0.49 / 0.31

0/0

0.65 / 0.69

98.86 / 99.0

aDensities

of BC,47 THF and MMA were assumed to be 1.5, 0.89 and 0.94 g cm-3, respectively. Weight and volume fractions of water, THF, and MMA in the BC/MMA gel were estimated by 1H-NMR analysis in CDCl , those of BC in both gels and water in the BC/H O gel by gravimetry. 　 3 2

Radical polymerization was carried out for both the BC/MMA gel and the bulk MMA reference sample. As shown in Figure 2, defect-free BC/PMMA composite was obtained. Table 2 shows the monomer conversion, Mw, and Mw/Mn of PMMA for bulk, BC/PMMA, and c-BC/PMMA composites. The monomer conversion and Mw of PMMA in the composite were over 98 % and in the order of 106 g mol-1, respectively, indicating that high molecular weight PMMA matrix with very little amount of unreacted monomer was prepared. These values were comparable to that of bulk PMMA prepared in the absence of BC gels. This result suggests that both the BC network and potential impurities have a negligible impact on radical polymerization only. The volume fraction of BC in the c-BC/PMMA composites was estimated by attenuated total reflection (ATR)FT IR measurements (see SI and Figure S2–S4).


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Figure 2. Pictures of (a) the BC/H2O gel, (b) the BC/THF gel, (c) the BC/MMA-0.3 gel, and (d) the BC/PMMA-0.3 composite prepared in a test tube.

Table 2. Characterization of PMMA for bulk, BC/PMMA, and c-BC/PMMA composite. Conversion (%)

Mw (×106 g mol-1)

Mw/Mn

PMMA

98.7

6.3

2.3

BC/PMMA-0.3a

98.8

7.8

2.1

c-BC/PMMA-0.8b

98.5

6.3

2.0

c-BC/PMMA-3.7b

98.2

4.6

1.6

c-BC/PMMA-19b

98.2

5.4

1.7

aBC/PMMA-0.3

means BC/PMMA composite with 0.3 vol% of BC. bNumbers indicate the BC volume fraction in the composite gels

In order to visualize the BC network through the stepwise solvent exchange and free radical polymerization, the fluorochrome-labeled BC/H2O gel, BC/THF gel, and BC/PMMA composites were observed by CLSM (Figure 3). FITC was adsorbed on the BC surface, whereas RITC was reacted to the surface hydroxyl group of BC in non-aqueous reaction condition. The obtained pictures showing BC either in blue (FITC-labeled) or red (RITC-labeled) confirm both


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homogenous distribution of BC in the obtained composite materials and far-reaching preservation of the original BC network structure throughout free radical polymerization. The diameter of the observed fiber was approximately 200 nm, which was overestimated owing to the resolution limit set by the diffraction of light. Here, we focus on the distance between fibers. The observable maximum distance between the BC ribbons of BC/PMMA-0.3 composite was exemplarily estimated to be several submicrometer, similar to the BC/H2O gel and the BC/MMA gel. This clearly indicates successful immobilization of the BC network without BC aggregation. Figure 3d shows the CLSM image of the compressed BC/PMMA composite with 3.7 vol% of BC (cBC/PMMA-3.7). Homogeneous BC network was still observed similar to the uncompressed BC/PMMA composite and distance between BC fibrils was smaller than that of the uncompressed BC/PMMA composite.


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Figure 3. CLSM images of the BC network; (a) FITC labelled BC/H2O gel, (b) RITC labelled BC/THF gel, (c) RITC-labelled BC/PMMA-0.3 composite and (d) RITC labelled c-BC/PMMA3.7 composite.

Mechanical Properties of BC/PMMA Composites. Figure 4 shows the plots of the indentation elastic modulus of PMMA and BC/PMMA-0.3 on the edge and face sides of BC ranging from the top surface to 8000 nm contact depth. The elastic modulus at shallow contact depths was lower than that in deeper regions because of the considerable impact of top surface roughness. The


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indentation modulus became constant at 7000–8000 nm contact depth, so that the average value in this region was defined as the elastic modulus of the samples, as shown in Table 3. The elastic modulus of PMMA in bulk (4.8 ± 0.1 GPa) was almost the same as reported elsewhere.48 Figures S5–S7 also show the nanoindentation results for c-BC/PMMA-0.8, 3.7, and 19 vol%, exhibiting constant indentation modulus at 7000–8000 nm contact depth as similar to BC/PMMA-0.3. Table 3 shows the elastic modulus of bulk PMMA and of the various uncompressed and compressed BC/PMMA composites. The data clearly confirm the reinforcing effect of BC. While the modulus of BC/PMMA-0.3 was already 0.3 GPa higher than that of bulk PMMA, compression, and hence, increasing BC content further increased the elastic modulus. The modulus of cBC/PMMA on the edge side was a little bit higher than that of the composites on the face side. This is because of the in-plane orientation of BC upon compression in the direction parallel to the layer structure.


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6 5

Indentation modulus (GPa)

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


4 BC/PMMA-0.3 Edge BC/PMMA-0.3 Face PMMA Bulk

3 2 1 0 0

2000

4000

6000

8000

Indentation depth (nm)

Figure 4. Averaged indentation modulus of PMMA and BC/PMMA-0.3 composite in face and edge directions versus indentation depth. Standard error is indicated by error bars. Table 3. Averaged indentation modulus and standard deviation of PMMA and BC/PMMA composites at a range of indentation depth of 7000–8000 nm

Composites

Number of scan areas Edge

PMMA

Face

Elastic modulus (GPa) Edge

10

Face 4.8 ± 0.1

BC/PMMA-0.3

11

11

5.1 ± 0.1

5.1 ± 0.1

c-BC/PMMA0.8

23

13

5.4 ± 0.2

5.3 ± 0.1

c-BC/PMMA3.7

5

3

6.3 ± 0.0

6.0 ± 0.0

c-BC/PMMA-19

3

4

7.9 ± 0.2

7.3 ± 0.3

Here, we discuss the BC network structure embedded in the composites and its reinforcement effect on mechanical properties. We assumed that the BC network was periodically


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entangled with high connectivity and the connectivity was independent of the compression ratio, that is, the volume fraction of BC. This assumption is considered to be valid on the basis of the CLSM images (Figure 3), showing that the morphology of the BC network was largely preserved and did not show any larger aggregates or cracks. It has been reported that the relative modulus of networks with similar geometry is scaled as E ~n, in general, where E and  are the relative modulus and density of a network, respectively.35, 36 A scaling exponent n close to 1 indicates mainly the expansion or contraction behavior of fibers in the axial direction, i.e., stretch-dominated deformation, whereas exponent n close to 2 indicates mainly bending behavior of fibers in the lateral direction, i.e., bend-dominated deformation. An exponent n larger than 2 indicates that some parts in the network are inefficient for load transfer due to the inhomogeneity of the network from defects, loops, or dangling chains. We adapted this model to the present composites. Figure 5 shows the double logarithmic plots of the modulus of the BC network (𝐸𝐵𝐶 𝑛𝑒𝑡𝑤𝑜𝑟𝑘) estimated for BC/PMMA composites versus the volume fraction of BC. The elastic modulus of the BC network in the composites (𝐸𝐵𝐶 𝑛𝑒𝑡𝑤𝑜𝑟𝑘) was estimated based on the rule of mixtures49 as follows, 𝐸𝐵𝐶 𝑛𝑒𝑡𝑤𝑜𝑟𝑘 = 𝐸𝑐 ― 𝐸𝑚(1 ― 𝑉BC)

(1)

where 𝐸𝑐 and 𝐸𝑚 are the elastic modulus of BC/PMMA composites (𝐸𝑐) and matrix PMMA (𝐸𝑚), respectively, and 𝑉𝐵𝐶 is the volume fraction of the BC network. The 𝐸𝐵𝐶 𝑛𝑒𝑡𝑤𝑜𝑟𝑘 linearly increased with the increase of 𝑉𝐵𝐶. From the linear fitting and the extrapolation of these plots, the slope n and the modulus of BC bulk (𝐸𝐵𝐶 𝑏𝑢𝑙𝑘) were predicted (Table 4). The value EBC bulk (13 GPa) was roughly consistent with the theoretically estimated modulus of BC (23 GPa) (see the section “theoretical estimation of compression modulus of BC bulk” in SI), therefore, this BC network model is valid.


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Modulus of BC network EBC network (GPa)

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101 100 10-1 10-2 10-3 10-4 10-5 10-6 10-3

10-2

10-1

100

Volume fraction of BC (VBC)

Figure 5. Double logarithmic plots of the modulus of BC network estimated for BC/PMMA composites in face (open squares) and edge (closed squares) directions, BC/PEA elastomer (circles), and a BC/H2O gel (triangles) versus volume fraction of BC. Black lines represent linear fitting of moduli in the edge direction of the BC/PMMA composites, the BC/PEA elastomer, and the BC/H2O gel.


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Table 4. Parameters for linear fitting of BC/PMMA and PC/PEA composites and BC/H2O gels in Figure 5. Slope n

𝐸𝐵𝐶 𝑏𝑢𝑙𝑘 (GPa)

BC/PMMA composite

0.62

13

BC/PEA elastomer

0.92

2.3

BC/H2O gel

3.0

54

The slope n for BC/PMMA composites was estimated to be 0.62 and thus close to 1. This indicates that the BC network in the PMMA composites behaved with mainly stretch-dominated deformation. For comparison, the BC-reinforced elastomer using poly(ethyl acrylate) (PEA) as a matrix polymer, prepared based on our previous paper34 and characterized by the tensile test (see SI), also exhibited the slope n of 0.92 and was thus categorized as stretch-dominated deformation. Both BC/PMMA and BC/PEA composites showed stretch-dominated deformation, suggesting that the viscoelastic properties of the matrix filling the void system between entangled BC ribbons may not be related to the deformation behavior. On the contrary, the BC/H2O gel has a slope n = 3.0 (see SI), indicating that the BC/H2O gel deformation is bend-dominated. The difference between BC/PMMA and BC/PEA composites and BC/H2O gels is the nature of the matrix: the first two are solid polymer matrices while the last is a liquid matrix. Thus, it can be safely concluded that the deformation modes of the BC network is highly dependent on the nature of matrix. Because of stretch-dominated deformation, the load for the BC/PMMA composites could be effectively transferred. In other words, any aggregation or deformation of the BC network associated with inefficient load transfer, which occurred in the BC/H2O gel, did not occur in the polymer matrices. This is presumably because bend-dominated


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deformation of the BC network in the hydrogel can be suppressed by the lateral reinforcement of the polymer matrix. Interestingly, such matrix-reinforced nanofiber network deformation can be seen in living cell systems where microtubes are reinforced by the surrounding elastic cytoskeleton.50 Consequently, owing to the homogenously embedded fine nanofiber networks, the ideal reinforcement of composites has been achieved even with a small amount of BC.

CONCLUSIONS We successfully prepared ideal BC/PMMA composites reinforced with a well-defined fine BC nanofiber network structure and achieved mechanical properties predicted theoretically from the elastic modulus of BC. These composites were prepared by in situ stepwise solvent exchanges followed by polymerization, in which BC hydrogels were placed in MMA via THF and free radical polymerization of MMA. The CLSM images of BC gels and BC/PMMA composites showed homogenous distribution of the BC networks in BC/PMMA composites. In addition, nanoindentation measurements was performed to discuss the reinforcement mechanisms by the nanofiber network structure. The load transfer mechanism was confirmed by the scaling theory E ~n, where E and  are the relative elastic modulus and density of a network, respectively. The scaling exponent n is 1 and 2 or over for stretch-dominated and bend-dominated deformation. In this study, we successfully measured the scaling exponent n of BC/PMMA (glass), BC/PEA (elastomer) and BC/H2O (hydrogel) as a function of volume fraction of BC (Figure 5 and Table 4). It was revealed that BC/PMMA and BC/PEA composites showed the exponent n~1, indicative of the stretch-dominated deformation behavior, whereas the BC hydrogel showed n~3, indicative of the bend-dominated deformation. Therefore, under compression, the BC nanofiber network exhibited stretch-dominated deformation in the PMMA matrix instead of bend-dominated


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deformation as in BC hydrogels, leading to effective load transfer. Thus, restricted stretch deformation was attained, derived from both reinforcement by the fine BC network and the lateral reinforcement of matrix. Understanding the effect of matrices will provide useful guidelines for designing mechanically controlled composites with network structures.


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ASSOCIATED CONTENT Supporting Information. Experimental procedure for the direct solvent exchange from water to MMA, estimation of volume fraction and compression modulus of BC, preparation and characterization of BC/PEA, images of a BC/H2O gel placed in MMA, ATR FT-IR spectra, indentation modulus versus indentation depth, compression stress-true strain curve.

AUTHOR INFORMATION Corresponding Author *To whom correspondence should be addressed. Tel: +81-774-38-3162; Fax: +81-774-38-3170; E-mail: [email protected] (K.S.); [email protected] (Y. T.). Funding Sources This work was partly supported by grants from the JSPS KAKENHI (17H06238), the Joint Usage/Research Program on Zero-Emission Energy Research, Institute of Advanced Energy, Kyoto University (ZE27B-14, ZE28B-14), and the research grant for Exploratory Research on Sustainable Humanosphere Science from Research Institute for Sustainable Humanosphere (RISH), Kyoto University. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT


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Nanoindentation measurements were performed with help from Prof. Ryuta Kasada (IAE, Kyoto University).


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REFERENCES 1. 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. 2. Nishino, T.; Takano, K.; Nakamae, K. Elastic Modulus of the Crystalline Regions of Cellulose Polymorphs. J. Polym. Sci., Part B: Polym. Phys. 1995, 33, 1647–1651. 3. Sato, A.; Kabusaki, D.; Okumura, H.; Nakatani, T.; Nakatsubo, F.; Yano, H. Surface Modification of Cellulose Nanofibers with Alkenyl Succinic Anhydride for High-density Polyethylene Reinforcement. Composites, Part A 2016, 83, 72–79. 4. Sakakibara, K.; Yano, H.; Tsujii, Y. Surface Engineering of Cellulose Nanofiber by Adsorption of Diblock Copolymer Dispersant for Green Nanocomposite Materials. ACS Appl. Mater. Interfaces 2016, 8, 24893–24900. 5. Petersson, L.; Kvien, I.; Oksman, K. Structure and Thermal Properties of Poly(lactic acid)/Cellulose Whiskers Nanocomposite Materials. Compos. Sci. Technol. 2007, 67, 2535– 2544. 6. Kim, J.; Montero, G.; Habibi, Y.; Hinestroza, J. P.; Genzer, J.; Argyropoulos, D. S.; Rojas, O. J. Dispersion of Cellulose Crystallites by Nonionic Surfactants in a Hydrophobic Polymer Matrix. Polym. Eng. Sci. 2009, 49, 2054–2061. 7. Fahma, F.; Hori, N.; Iwata, T.; Takemura, A. The Morphology and Properties of Poly (methyl methacrylate)‐Cellulose Nanocomposites Prepared by Immersion Precipitation Method. J. Appl. Polym. Sci. 2013, 128, 1563–1568.


25


Page 26 of 32

8. Kiziltas, E. E.; Kiziltas, A.; Bollin, S. C.; Gardner, D. J. Preparation and Characterization of Transparent PMMA–Cellulose-based Nanocomposites. Carbohydr. Polym. 2015, 127, 381–389. 9. Fujisawa, S.; Ikeuchi, T.; Takeuchi, M.; Saito, T.; Isogai, A. Superior Reinforcement Effect of TEMPO-oxidized Cellulose Nanofibrils in Polystyrene Matrix: Optical, Thermal, and Mechanical Studies. Biomacromolecules 2012, 13, 2188–2194. 10. Dong, H.; Sliozberg, Y. R.; Snyder, J. F.; Steele, J.; Chantawansri, T. L.; Orlicki, J. A.; Walck, S. D.; Reiner, R. S.; Rudie, A. W. Highly Transparent and Toughened Poly(methyl methacrylate) Nanocomposite Films Containing Networks of Cellulose Nanofibrils. ACS Appl. Mater. Interfaces 2015, 7, 25464–25472. 11. Capadona, J. R.; Shanmuganathan, K.; Trittschuh, S.; Seidel, S.; Rowan, S. J.; Weder, C. Polymer Nanocomposites with Nanowhiskers Isolated from Microcrystalline Cellulose. Biomacromolecules 2009, 10, 712–716. 12. Capadona, J. R.; Van Den Berg, O.; Capadona, L. A.; Schroeter, M.; Rowan, S. J.; Tyler, D. J.; Weder, C. A Versatile Approach for the Processing of Polymer Nanocomposites with Selfassembled Nanofibre Templates. Nat. Nanotechnol. 2007, 2, 765–769. 13. Shi, Z.; Huang, J.; Liu, C.; Ding, B.; Kuga, S.; Cai, J.; Zhang, L. Three-dimensional Nanoporous Cellulose Gels as a Flexible Reinforcement Matrix for Polymer Nanocomposites. ACS Appl. Mater. Interfaces 2015, 7, 22990–22998. 14. Iguchi, M.; Yamanaka, S.; Budhiono, A. Bacterial Cellulose—a Masterpiece of Nature's Arts. J. Mater. Sci. 2000, 35, 261–270.


26

Page 27 of 32 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


15. Sugiyama, J.; Vuong, R.; Chanzy, H. Electron Diffraction Study on the Two Crystalline Phases Occurring in Native Cellulose from an Algal Cell Wall. Macromolecules 1991, 24, 4168– 4175. 16. Watanabe, K.; Tabuchi, M.; Morinaga, Y.; Yoshinaga, F. Structural Features and Properties of Bacterial Cellulose Produced in Agitated Culture. Cellulose 1998, 5, 187–200. 17. Nishi, Y.; Uryu, M.; Yamanaka, S.; Watanabe, K.; Kitamura, N.; Iguchi, M.; Mitsuhashi, S. The Structure and Mechanical Properties of Sheets Prepared from Bacterial Cellulose. Part 2 Improvement of the Mechanical Properties of Sheets and their Applicability to Diaphragms of Electroacoustic Transducers. J. Mater. Sci. 1990, 25, 2997–3001. 18. Nishi, Y.; Uryu, M.; Yamanaka, S.; Watanabe, K.; Kitamura, N.; Iguchi, M.; Mitsuhashi, S. The Structure and Mechanical Properties of Sheets Prepared from Bacterial Cellulose. J. Mater. Sci. 1989, 24, 3141–3145. 19. Guhados, G.; Wan, W.; Hutter, J. L. Measurement of the Elastic Modulus of Single Bacterial Cellulose Fibers using Atomic Force Microscopy. Langmuir 2005, 21, 6642–6646. 20. Hsieh, Y. C.; Yano, H.; Nogi, M.; Eichhorn, S. J. An Estimation of the Young’s Modulus of Bacterial Cellulose Filaments. Cellulose 2008, 15, 507–513. 21. Iwamoto, S.; Nakagaito, A. N.; Yano, H.; Nogi, M. Optically Transparent Composites Reinforced with Plant Fiber-based Nanofibers. Applied Physics A 2005, 80, 93–97. 22. Nogi, M.; Yano, H. Transparent Nanocomposites Based on Cellulose Produced by Bacteria Offer Potential Innovation in the Electronics Device Industry. Adv. Mater. 2008, 20, 1849–1852.


27


Page 28 of 32

23. 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. 24. Kramer, F.; Klemm, D.; Schumann, D.; Heßler, N.; Wesarg, F.; Fried, W.; Stadermann, D. Nanocellulose Polymer Composites as Innovative Pool for (Bio)Material Development. Macromol. Symp. 2006, 244, 136-148. 25. Figueiredo, A. R. P.; Figueiredo, A. G. P. R.; Silva, N. H. C. S.; Barros-Timmons, A.; Almeida, A.; Silvestre, A. J. D.; Freire, C. S. R. Antimicrobial Bacterial Cellulose Nanocomposites Prepared by in situ Polymerization of 2-Aminoethyl Methacrylate. Carbohydr. Polym. 2015, 123, 443-453. 26. Saïdia, L.; Vilela, C.; Oliveira, H.; Silvestre, A. J. D.; Freire, C. S. R. Poly(N-methacryloyl glycine)/Nanocellulose Composites as pH-Sensitive Systems for Controlled Release of Diclofenac. Carbohydr. Polym. 2017, 169, 357-365. 27. Gadim, T. D. O.; Figueiredo, A. G. P. R.; Rosero-Navarro, N. C.; Vilela, C.; Gamelas, J. A. F.; Barros-Timmons, A.; Neto, C. P.; Silvestre, A. J. D.; Freire, C. S. R.; Figueiredo, F. M. L. Nanostructured Bacterial Cellulose−Poly(4-styrene sulfonic acid) Composite Membranes with High Storage Modulus and Protonic Conductivity. ACS Appl. Mater. Interfaces 2014, 6, 78647875. 28. Figueiredo, A. G P. R.; Figueiredo, A. R. P.; Alonso-Varona, A.; Fernandes, S. C. M.; Palomares, T.; Rubio-Azpeitia, E.; Barros-Timmons, A.; Silvestre, A. J. D.; Neto, C. P.; Freire, C.


28

Page 29 of 32 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


S. R. Biocompatible Bacterial Cellulose-Poly(2-hydroxyethyl methacrylate) Nanocomposite Films. BioMed Res. Int. 2013, 698141 (14 pages). 29. Hobzova, R.; Hrib, J.; Sirc, J.; Karpushkin, E.; Michalek, J.; Janouskova, O.; Gatenholm, P. Embedding of Bacterial Cellulose Nanofibers within PHEMA Hydrogel Matrices: Tunable Stiffness Composites with Potential for Biomedical Applications. J. Nanomater. 2018, 5217095 (11 pages). 30. Zhao, W.; Shi, Z.; Chen, X.; Yang, G.; Lenardi, C.; Liu, C. Microstructural and Mechanical Characteristics of PHEMA-based Nanoﬁbre-Reinforced Hydrogel under Compression. Composites, Part B 2015, 76, 292-299. 31. Hobzova, R.; Duskova-Smrckova, M.; Michalek, J.; Karpushkin, E.; Gatenholm, P. Methacrylate Hydrogels Reinforced with Bacterial Cellulose. Polym. Int. 2012, 61, 1193-1201. 32. Faria, M.; Vilela, C.; Mohammadkazemi, F.; Silvestre, A. J. D.; Freire, C. S. R.; Cordeiro, N.

Poly(glycidyl

methacrylate)/Bacterial

Cellulose

Nanocomposites:

Preparation,

Characterization and Post-modiﬁcation. Int. J. Biol. Macromol. 2019, 127, 618-627. 33. Faria, M.; Vilela, C.; Silvestre, A. J. D.; Deepa, B.; Resnik, M.; Freire, C. S. R.; Cordeiro, N. Physicochemical Surface Properties of Bacterial Cellulose/Polymethacrylate Nanocomposites: An Approach by Inverse Gas Chromatography. Carbohydr. Polym. 2019, 206, 86-93. 34. Y. Shimizu, K. Sakakibara, Y. Tsujii, Strain Hardening of Highly Stretchable Elastomeric Composites Reinforced with Well-Defined Nanofiber Network of Bacterial Cellulose. J. Fiber Sci. Technol. 2018, 74, 17–23.


29


Page 30 of 32

35. Gibson, L. J.; Ashby, M. F. Cellular Solids: Structure and Properties; Cambridge University Press: Cambridge, U.K., 1999. 36. Ashby, M. F. The Properties of Forms and Lattices. Philos. Trans. R. Soc., A 2006, 364, 15–30. 37. Broedersz, C. P.; Mao, X.; Lubensky, T. C.; MacKintosh, F. C. Criticality and Isostaticity in Fibre Networks. Nat. Phys. 2011, 7, 983–988. 38. Wang, L.; Lau, L.; Thomas, E. L.; Boyce, M. C. Co-continuous Composite Materials for Stiffness, Strength, and Energy Dissipation. Adv. Mater. 2011, 23, 1524–1529. 39. Al-Ketan, O.; Assad, M. A.; Al-Rub, R. K. A. Mechanical Properties of Periodic Interpenetrating Phase Composites with Novel Architected Microstructures. Compos. Struct. 2017, 176, 9–19. 40. Hamdia, K. M.; Silani, M.; Zhuang, X.; He, P.; Rabczuk, T. Stochastic Analysis of the Fracture Toughness of Polymeric Nanoparticle Composites Using Polynominal Chaos Expansions. Int. J. Fract. 2017, 206, 215-227. 41. Msekh, M. A.; Cuong, N. H.; Zi, G.; Areias, P.; Zhuang, X.; Rabczuk, T. Fracture Properties Prediction of Clay/Epoxy Nanocomposites with Interphase Zones Using a Phase Field Model. Eng. Fract. Mech. 2018, 188, 287-299. 42. Hirai, A.; Inui, O.; Horii, F.; Tsuji, M. Phase Separation Behavior in Aqueous Suspensions of Bacterial Cellulose Nanocrystals Prepared by Sulfuric Acid Treatment. Langmuir 2009, 25, 497–502.


30

Page 31 of 32 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


43. Tsuchida, A.; Sakai, W.; Nakano, M.; Yamamoto, M. Electron Capture of Dopants in Ttwo-photonic Ionization in a Poly(methyl methacrylate) Solid. J. Phys. Chem. 1992, 96, 8855– 8858. 44. de Belder, A. N.; Wik, K. O. Preparation and Properties of Fluorescein-labelled Hyaluronate. Carbohydr. Res. 1975, 44, 251–257. 45. Oliver, W. C.; Pharr, G. M. An Improved Technique for Determining Hardness and Elastic Modulus Using Load and Displacement Sensing Indentation Experiments. J. Mater. Res. 1992, 7, 1564–1583. 46. Jee, A-Y.; Lee, M. Comparative Analysis on the Nanoindentation of Polymers Using Atomic Force Microscopy. Polym. Test. 2010, 29, 95-99. 47. Gindl, W.; Keckes, J. Tensile Properties of Cellulose Acetate Butyrate Composites Reinforced with Bacterial Cellulose. Compos. Sci. Technol. 2004, 64, 2407–2413. 48. Briscoe, B. J.; Fiori, L.; Pelillo, E. Nano-indentation of Polymeric Surfaces. J. Phys. D: Appl. Phys. 1998, 31, 2395–2405. 49. Tham, M. W.; Fazita, N.; Khalil, A.; Zuhudi, N. Z. M.; Jaafar, M.; Rizal, S.; Haafiz, M. Tensile Properties Prediction of Natural Fibre Composites Using Rule of Mixtures: A Review. J. Reinf. Plast. Compos. 2019, 38, 211-248. 50. Brangwynne, C. P.; MacKintosh, F. C.; Kumar, S.; Geisse, N. A.; Talbot, J.; Mahadevan, L.; Parker, K. K.; Ingber, D. E.; Weitz, D. A. Microtubules can Bear Enhanced Compressive Loads in Living Cells Because of Lateral Reinforcement. J. Cell Biol. 2006, 173, 733–741.


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SYNOPSIS. This work describes stretch-dominated load transfer mechanism of bacterial cellulose nanofiber reinforced poly(methyl methacrylate) composites. Table of Contents Graphic.

Modulus of BC network EBC network (GPa)

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 32 of 32

101

BC/polymer composites

Stretch

100 10-1 10-2 10-3

Bend

BC hydrogels

10-4 10-5 10-6 10-3

10-2

10-1

100

Volume fraction of BC (VBC)


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Effective Reinforcement of Poly(methyl methacrylate) Composites with

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