Research Article pubs.acs.org/journal/ascecg
Pilot-Scale Twin Screw Extrusion and Chemical Pretreatment as an Energy-Efficient Method for the Production of Nanofibrillated Cellulose at High Solid Content Fleur Rol,† Blagoj Karakashov,† Oleksandr Nechyporchuk,† Maxime Terrien,† Valérie Meyer,‡ Alain Dufresne,† Mohamed Naceur Belgacem,† and Julien Bras*,†,§ †
Université Grenoble Alpes, CNRS, Grenoble INP, LGP2, F-38000 Grenoble, France Centre Technique du Papier (CTP), F-38000 Grenoble, France § Institut Universitaire de France (IUF), F-75000 Paris, France ‡
ABSTRACT: Production of nanofibrillated cellulose (CNF) has gained increasing attention during the last decades with its recent industrialization, but such a process consumes still too high of an amount of energy. Here, cellulose nanofibrils at high solid content (20−25 wt %) and consuming 60% less energy compared to conventional processes were produced from enzymatic and TEMPO-oxidized cellulose fibers thanks to a twin screw extruder equipped with kneading disks and fully flighted conveying screws. The morphology and properties of the produced CNF were characterized using optical microscopy, atomic force microscopy (AFM), mechanical properties, and light transmittance. CNF with a width in the range of 20−30 nm and mechanical properties close to those obtained with commercial CNF (Young’s modulus around 15 GPa) were produced. However, results from the degree of polymerization and crystallinity showed that twin screw extrusion (TSE) degrades the fibers as far as the supermasscolloider grinder is concerned. TSE appears as a new mechanical treatment that allows producing CNF at high solid contents and with low energy demand, which is a real asset for nanocellulose industrialization. KEYWORDS: Cellulose nanofibers (CNFs), Cellulose pretreatment, TEMPO oxidation, Enzymatic hydrolysis, Extrusion, Energy, Mechanical properties
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INTRODUCTION Production of cellulose nanofibrils (CNFs) has gained increasing attention during the last decades, as very recently reviewed by Nechyporchuk et al.1 Indeed, CNF is a renewable, biodegradable, and biocompatible material with interesting properties for many applications2 such as composites,3,4 packaging,5 paper,6,7 and, more recently, medical8,9 or printed electronics fields.10 Even if CNFs are the second priority of the European bioeconomy, there is still room for improving their preparation and consequently decreasing their cost. The possible strategies consist of either performing new pretreatment,11 using low-cost cellulose material or waste,12 or investigating new processes for mechanical fibrillation.13 This study will focus on the latter. The production of CNF involves usually several operations such as refining, chemical pretreatment, and mechanical treatment.5,14−19 Today, homogenizers, microfluidizers, and specific grinders are the most common mechanical equipment used to produce CNFs thanks to high shear delamination. These techniques are now suitable for upscaling; however, they still consume a lot of energy.20,21 Discovered in the 1980s by Turbak,22 it was only in the mid2000s that the interest for such material exponentially increased. This was mainly due to biological or chemical © 2017 American Chemical Society
pretreatment, which has helped decrease the energy consumption (divided by 5−10). TEMPO oxidation23 and enzyme hydrolysis16,18 are the most widely adopted pretreatments. Types of pretreatment and mechanical treatment influence also strongly the resulting CNF quality and properties. That is why a lot of studies are done to find more efficient chemical pretreatments. Despite pretreatment, the energy consumption when largescale production is concerned is still an issue that limits the industrialization of CNFs. Furthermore, CNFs at low solid content (98%, Sigma-Aldrich); sodium bromide (NaBr) (BioUltra, ≥99.5%); sodium acetate trihydrate (CH3COONa·3H2O) (ReagentPlus, ≥99.0%); sodium chloride (NaCl) (>99%); sodium hydroxide (NaOH); sodium hypochlorite (NaClO) (available chlorine 10−15%, Sigma-Aldrich, France). Microfibrillated cellulose produced by a homogenizer via enzymatic pretreatment was supplied by the Centre Technique du Papier (Grenoble, France) as a 2 wt % aqueous dispersion. These microfibrillated cellulose fibers (MFCs) are here called “Commercial MFCs”. Refining of Cellulose Pulp. Cellulose fibers suspended in water at a concentration of 2 wt % were refined using a disk beater. A Schopper−Riegler degree of 80 was determined in accordance with standard ISO 5267-1. Measurements were made at least in triplicate. Enzymatic Hydrolysis of Fibers. Cellulose suspension at 2 wt % was hydrolyzed using endoglucanase FiberCare R enzyme solution. The reaction was performed at a temperature of 50 °C and pH of 5. The enzyme solution was finally added: 300 ECU/g of cellulose. After 2 h, the enzymatic activity was stopped by heating the suspension at 90 °C for 15 min. The suspension was filtered and washed with deionized water. The yield of enzymatic hydrolysis was 95%. Cellulose TEMPO Oxidation Pretreatment. TEMPO-mediated oxidation was performed at a cellulose fiber content of 1 wt % and at 25 °C. The reaction protocol was based on the well-known procedure of Saito et al.39 The TEMPO/NaBr/NaClO system was used with 0.1/ 1/5 mmol of the reactants per gram of cellulose, respectively. The TEMPO-oxidized cellulose was filtered and washed with deionized water. The yield of TEMPO-oxidized cellulose was 90%. CNF Production Using a Grinder. The pretreated cellulose suspensions at 2 wt % were fibrillated using an ultrafine friction grinder supermasscolloider (model MKZA6-2, disk model MKG-C 80, Masuko Sangyo Co., Ltd., Japan) equipped with recirculation at 2500 rpm for 2.5 h. The maximum gap used between the two disks was −10 μm. In this case, the pulp pass was approximately 60 times per hour in the nip zone for 1 s. The time in the nip zone of the grinder was then only 3 min after 2.5 h of treatment. However, the equipment should work in a continuous way. CNF Production Using a Twin Screw Extruder. The solid content of the refined pretreated pulp was adjusted between 18 and 20 wt %. Pulp was then fed into the TSE (Model Thermoscientific HAAKE Rheomex OS PTW 16 + HAAKE PolyLab OS RheoDrive 7) with a ratio (L/D) of 45. The TSE screws were a combination of kneading disks and fully flighted conveying screws, as shown in Figure 1. The temperature was maintained close to 10 °C, and the speed was 400 rpm The temperature was set to 10 °C thanks to circulation of 6525
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ACS Sustainable Chemistry & Engineering Table 1. Processing Parameters and CNF Properties reference commercial refined-EnzTSE1p refined-Enz-TSE 7p refined-Enzgrinder refined-TEMPOoxidized-TSE1p refined-TEMPOoxidized-TSE7p refined-TEMPOoxidized-grinder
mechanical pretreatment
number of pass
solid content [%]
Young’s modulus [GPa]
tensile strength [MPa ]
elongation at break [%]
transparency [%]
thickness for nanopaper [μm]
film density for nanopaper [kg/m3] 944 ± 55 1111 ± 9
homogenizer extruder
5 1
2 18.2
11.9 ± 3.9 10.1 ± 0.2
67.9 ± 3.5 25.6 ± 1.1
1.1 ± 0.1 0.8 ± 0.4
90.6 ± 0.6 89.4 ± 0.3
51 ± 1.5 58 ± 0.6
extruder
7
18.7
15.1 ± 0.4
33.9 ± 9.5
0.6 ± 0.2
89.6 ± 0.1
76 ± 4
902 ± 29
grinder
2.5 h
2
21.3 ± 0.1
84.6 ± 1.8
0.8 ± 0.2
88.0 ± 0.7
45 ± 2
1029 ± 64
extruder
1
17.2
1.4 ± 0.1
41.2 ± 1.0
0.4 ± 0.1
55.4 ± 2.3
94 ± 12
924 ± 67
extruder
7
17.3
11.2 ± 3.4
30 ± 8.7
0.4 ± 0.1
89.6 ± 0.3
105 ± 6
827 ± 94
grinder
2.5 h
2
20.8 ± 1.8
80.8 ± 13.2
0.6 ± 0.1
89.7 ± 1.5
57 ± 2
921 ± 10
Transmission Electron Microscopy (TEM). Analysis was done using an FEI, Tecnai Osiris S, U.S. Samples were prepared as those for AFM analysis. Around 10 pictures per sample were taken. Crystallinity Index (CI). Wide-angle X-ray diffraction (XRD) spectra were used to determine the CI of nanofibrillated cellulose. After placing the samples into (onto or above) a zero-background Si holder, a PANanalytical X’Pert PRO MPD diffractometer, equipped with an X’celerator detector, was used to make the measurements. Xrays were generated with a copper anode (Kα radiation λ = 1.5419 Å). The measuring range of the measurements was 5−56° (2θ scale) with a step of 0.067° and a counting time per step of 3.2 s. The cellulose CI (%) was determined according to the peak height method.41
cooled water in order to avoid warming in the kneading area and, therefore, a change in the moisture of the pulp. Energy Demand Calculation. Energy consumed by TSE was evaluated calculating the power P thanks to the torque (T) measured by the TSE software in N·m and the angular velocity (ω) of the screws in rad/s. The energy consumption (kWh) was finally calculated by multiplying the residence time of the pulp in the TSE by the calculated power (P) in kilowatts (kW). For each pass through the extruder, the energy was calculated, and finally after seven passes, energies were added. Nanopaper. Two methods were used. In the first method, 50 mL of aqueous cellulose suspension at 0.5 wt % was prepared using an ultra turrax (5 min, 15000 rpm) and cast in a Teflon mold. Films were dried in a conditioned room at 23 °C and 50% RH. Those films are called “casted film”. In the second method, CNF suspension was filtered through a standard sheet former equipped with a nylon sieve with a mesh size of 1 μm. Sheets were then dried in a dryer at 90 °C for 20 min. Those films are called “nanopaper”. Optical Microscopy. CNF suspension was redispersed to a concentration of 0.5 wt %, and optical microscopy images were taken using a Carl Zeiss Axio Imager M1 optical microscope in transmission mode equipped with an AxioCam MRc 5 digital camera. For each sample, at least four images were taken. Atomic Force Microscopy (AFM). Suspensions were redispersed to a concentration of 10−2 wt %, and one drop was deposited on a mica disk. AFM was performed in scan assist mode using a Dimension Icon atomic force microscope with an OTESPA cantilever. At least 10 different areas of the sample were scanned for each sample. Nanosized Fraction. The nanosized fraction of the pulp was determined according to a method developed by Naderi et al.40 CNF suspensions were diluted and then centrifuged using a Sigma 3-18 KS, Germany centrifuge. Three tests were done per sample. Total Transmission. The total transmission of films produced by the casting method was measured using a haze meter (BYK Gardner, Haze-Gard Plus) according to the standard NF T 54-111,1971. Three tests were done to characterize each film, and the average data are presented. Degree of Polymerization (DP). The DP was measured according to ISO 5351:2010 standard. The intrinsic viscosity (ηint) of cellulose dissolved in copper(II) ethylenediamine was measured, and then, the DP was deduced using the Mark− Houwink−Sakurada equation. Three measurements were made for each sample. Mechanical Properties. Mechanical properties of CNF films produced thanks to the second method were measured using an Instron 5965 machine equipped with a load cell of 5 kN capacity. Tests were done on rectangular film (50 mm × 15 mm) samples at a cross-head speed of 5 mm/min. Films were previously stored at 23 °C and 50% RH. For each sample, an average of three measurements was calculated.
CI = (I002 − Iam) × 100/I002 where I002 represents the diffraction intensity of the main crystalline peak at 2θ ≈ 22.5° and Iam is the intensity at 2θ ≈ 18.7°. All of the samples were tested at least in duplicate.
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RESULTS AND DISCUSSION Nanofibrillated Cellulose Produced by Twin Screw Extrusion. Cellulose nanofibers at high solid contents have been produced thanks to a pilot scale twin screw extruder. The solid content ranging between 17 and 19% increases slightly with the number of passes through the extruder as shown in Table 1. Solid content was maintained around 20% in order to not have problem of filtration in the extruder and so formation of mats of solids.42 Any die was used to not limit the processability. Processability of the cellulose was improved by the enzymatic and chemical pretreatment. The screw profile, as shown in Figure 1, is composed of three shearing zones with reverse elements that allow retention of the pulp and an increase of the residence time in kneading areas. Shearing zones are composed of kneading disks traditionally used to mix polymers. Here, kneading disks oriented with different degrees allow application of a higher shear rate to the pulp. Three kneading parts and an increase in the disk orientation have been chosen because we assumed that nanofibrillation occurs in the nip and in the kneading parts. The stress history is a key question in nanofibrillation, and we are working on it. The time of residence is about 3 min per pass. Seven passes through the twin screw extruder will consume 21 min, and 2.5 h in the supermasscolloider grinder corresponds to 3 min in the nip zone. The flow rate and maximum processing rate depend a lot on the pretreatment, fiber morphology, and dry content. Under our conditions, TSE allows production of CNFs at 1.2 kg/h (dry or 6 kg/h in the wet state), which is not the maximum processing rate of the extruder. The maximum processing rate of the TSE used is 10 6526
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Figure 2. Optical microscopy images for refined eucalyptus pulp extruded with (a) 0, (d) 1, or (g) 7 passes or with (j) a grinder; refined TEMPOoxidized pulp extruded with (b) 0, (e) 1, and (h) 7 passes or with (k) a grinder; enzymatically refined treated pulp extruded with (c) 0, (f) 1, and (i) 7 passes or with (l) a grinder (l). NF = nanosized fraction.
Figure 3. Optical microscopy, AFM imaging, and TEM imaging of refined enzymatic hydrolyzed and TEMPO-oxidized pulp passed seven times through the TSE.
kg/h. For enzymatic hydrolyzed pulp, the flow rate of the supermasscolloider grinder was 0.6 kg/h (dry). The maximum flow rate of the homogenizer used was 1 kg/h (dry). The processing rates used here are very low compared to those of an industrial extruder. Optical microscopy images of the starting nontreated and pretreated pulp material before and after passing through the TSE are displayed in Figure 2. As reported previously, the extrusion process had a strong effect on the fibrillation of the cellulose fibers24 and fiber dimensions decrease with the number of passes through the grinder.43 The nonpretreated refined pulp material was fibrillated to a lower extent, but not all fibers were nanofibrillated, contrary to Ho et al.24 who produce CNFs from nontreated pulp. However, good-quality CNFs were produced by extrusion of refined
enzymatic and TEMPO-oxidized pulps. Indeed, the pretreatment facilitates the production of CNFs and also decreases the energy needed.16,39 Microsized fibers were still present after the first pass for both pretreatments. Fibril aggregates and microsized fibers still existed even after seven passes for TEMPO-oxidized pulp due to the low oxidation rate (820 μmol/g). However, the rheological behavior of TEMPOoxidized pulp was different from that of enzymatic pulp, and it can be hypothesized that the TEMPO-oxidized pulp slips into the extruder barrel and that some fibers do not undergo the action of the kneading areas. Finally, after seven passes, enzymatically pretreated pulp seemed to be fiber-free and displayed a similar morphology as the pulp passed through the grinder. 6527
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ACS Sustainable Chemistry & Engineering As demonstrated elsewhere,24 the higher the number of passes through the extruder, the higher the fibrillation effect, as for other disintegration methods such as grinding.19,44,45 However, after a number of passes, there is no further effect of the TSE on the fibrillation. Ho et al.24 showed that CNFs can be obtained after six passes through the TSE and that more passes can create degradation. The objective here is to produce CNFs after one pass; therefore the number of passes was limited to seven. Runs with 1, 3, 5, 7, and 10 passes for one pulp have been done, and 7 passes was the optimum. Studies were actually done to modify the screw profile in order to have CNFs after 1 passes. AFM images in Figure 3 confirm the nanometric sizes of the extruded pulp. Enzymatic CNFs with a width of 25.8 (±7.1) nm and TEMPO-oxidized CNFs with a width of 34.6 (±7) nm were obtained. These results are in agreement with the literature and close to those obtained with a grinder.43 TEM images show that the fibers treated seven times through TSE are highly entangled. Finally to characterize the morphology of CNFs, the nanosized fraction was measured and compared with that of the commercial MFCs. Whereas commercial CNFs contain 73% (±14) of nanometric materials, enzymatic CNFs produced by TSE contain 55% (±13) of nanofibrils after one pass through the extruder and 65% (±7) after seven passes. Naderi et al.40 obtained a nanosized fraction between 15 and 68% for CNFs produced thanks to a homogenizer. The lower nanosized fractions of TEMPO-oxidized pulp, as shown in Figure 2, can be explained by the low surface charge content or by the slipping effect during the process. Finally, TSE allows production of CNFs with similar morphologies as the one produced conventionally. CNF Properties. Mechanical properties and transmittance of CNF nanopapers are reported in Table 1. CNF films do not scatter light due to their nanometric components and are transparent.17,46 Usually, increasing the number of passes through the mechanical treatment increases the fibrillation and improves the size homogeneity and, therefore, the transparency.44 After seven passes through the extruder, we obtained CNF films with high transparency (90%), which confirms pulp nanofibrillation as much as that with the grinder. CNF produced thanks to TSE after seven passes presents better or similar Young’s modulus values than the commercial one. Young’s modulus results are in agreement with those of Nair et al.,47 who observed a Young’s modulus of around 16 GPa for CNF produced with a grinder. Indeed, fibrillation unlocks OH groups, and therefore, mechanical properties are classically higher.24 However, for both pretreatments, extrusion leads to lower mechanical properties than the supermasscolloider grinder, which can reveal a lower fibrillation or a lower dispersion. High solid content CNFs produced by TSE are much more difficult to redisperse due to irreversible agglomerations.48,49 Aggregates can create porosity, which decreases significantly the mechanical properties.50 As shown previously, TEMPO-oxidized pulp is not totally fibrillated after seven passes, and therefore, mechanical properties are lower but still high after seven passes. TSE allows production of nanometric-scale material similar to that produced with a grinder or a homogenizer but leads to some fiber degradation, which affects the mechanical properties. Fiber Degradation Induced by Extrusion. The crystallinity calculated from XRD patterns for the different produced materials is presented in Figure 4. TSE has no significant
Figure 4. DP (black and gray) and CI (red) for nontreated pulp: (a)enzymatically hydrolyzed pulp through TSE and a grinder and (b) TEMPO-oxidized pulp through TSE and a grinder.
impact on the crystallinity of the cellulose fibers up to seven passes (less than ∼5%). Those results are in agreement with those of Ho et al.24 who observed a crystallinity decrease of less than 5% after five passes. Whereas a significant decrease in the crystallinity (20%) has been observed by increasing the number of passes through a grinder,17 we did not observe significant degradation with the pretreated pulp. Indeed, endoglucanases can hydrolyze amorphous regions of the cellulose and increase the CI.43 The DP decreases significantly but mainly as a result of the pretreatment step: 50 and 75% for enzymatic pretreatment and TEMPO oxidation, respectively. Indeed, enzymes attack the amorphous domains of cellulose, which results in a DP decrease.16 Some studies also reported a strong decrease for TEMPO-oxidized cellulose.51−53 The DP decrease can be due to β-elimination due to aldehyde groups created in carbon 6 of cellulose as an intermediate structure or can be caused by the cleavage of (1−4)-β-glycoside bonds by species created in situ as side reactions during the oxidation.54−56 The DP also decreases with mechanical pretreatment.57−59 Henriksson et al.16 reported a decrease between 30 and 50% for CNFs produced through a homogenizer, and Iwamoto et al.17 reported a decrease from 770 to 225 using a grinder. Unsurprisingly and as reported elsewhere,24 the DP value also decreases when using the extruder. After seven passes with the pretreated pulps, we observed a decrease of 42% for the enzymatic pulp and 33% for the TEMPO-oxidized pulp. Moreover, it seems that the first pass through the TSE is the 6528
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ACS Sustainable Chemistry & Engineering most impacting. Finally, by combining chemical/biochemical pretreatment and extrusion, DP decreases by 85% for enzymatic pulp and 77% for TEMPO-oxidized pulp, which is close to what is achieved with a grinder. Energy Consumption for Nanofibrillation by TSE. CNF is a promising material, but its industrialization is limited due to its high energy consumption. Indeed, at first, Eriksen et al.60 reported an energy of 70 000 kWh/t for the nanofibrillation of nonpretreated pulp through a Gaulin-type homogenizer. Today, the energy required to produced CNFs without chemical pretreatment is between 5000 and 30 000 kWh/t depending on the cellulose source, the mechanical process, and the CNF quality.20,45,47,60−6262 According to the literature,50,21 cellulose pretreatment allows one to decrease the energy consumption from around 20 000 to 1000−2000 kWh/ t. According to some researchers, nanofibrillation of TEMPOoxidized pulp consumes even less than 2000 kWh/t.2,21,39 More recently, Innventia showed that repeated homogenization at low pressures allows reduction from 30 to 50% for the energy needed without deteriorating the quality of CNFs produced.40 Each result and comparison shown here should be treated with caution due to the different modification rates, different cellulose sources, different devices used, and different sizes of nanofibrils produced. Moreover, the comparison between the Masuko grinder and extruder should be balanced due to the different methods used for the energy consumption measurement. Most of the time, energy used by the extruder is calculated thanks to the torque, whereas the energy consumed by a Masuko grinder is calculated thanks to an ammeter. To be more precise, we measured the energy consumed by the grinder and the extruder with and without cellulose pulp, and we reported the difference. Consequently, what is reported here for each device is just the energy used for the nanofibrillation. In this study, a comparison of different mechanical processes has been done for the same pretreated cellulose pulp and almost the same CNF qualities. As exposed in Figure 5, the energy consumed by the extruder to produce enzymatic CNFs is much lower than that with the grinder. After seven passes through the extruder, CNFs of good quality are obtained and the energy is reduced by 63%. One pass through TSE leads to 91% lower energy consumption than the grinder, but the fibrillation is not complete. Enzymatic pretreatment allows significant reduction of the energy needed. In addition, the refining step, which consumes only 680 kWh/t, disintegrates the fibers, increases their specific surface area, and allows reduction of the energy needed. Fibers are more accessible for the enzymes, and the fibrillation is easier.43 Concerning the TEMPO-oxidized pulp, fibers produced are not entirely nanofibrillated, and the energy is higher. However, another study has to be done to show that the higher the degree of oxidation, the lower the energy needed. From the number of passes through TSE, different energy consumptions were observed. Concerning the nonpretreated pulp, energy demand decreases between each pass because of high microsize dimensions of the fibers, strong cohesion between the fibers, and lack of swelling, whereas the energy demand for the pretreated pulp increased between each pass due to the positive nanofibrillation. Moreover, the production flow rate is considerably increased: multiplied by 2 compared to an industrial homogenizer. Those results are very positive and are presented for the first time.
Figure 5. Energy consumed by nanofibrillation through a twin screw extruder for (a) enzymatic pulp and (b) TEMPO-oxidized pulp.
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CONCLUSIONS Nanofibrillated cellulose at high solid contents (20%) was successfully produced from eucalyptus pulp using enzymatic pretreatment or TEMPO oxidation followed by seven passes through TSE. The energy demand for the nanofibrillation by TSE was 63% lower compared to the energy used by a supermasscolloider grinder for the same pulp. High solid content and energy efficiency are two main points for CNF industrialization and use in some fields. Production costs and transportation costs should decrease and, therefore, the CNF price. CNFs produced present similar properties as CNFs currently on the market: nanometric size, good mechanical properties, and transparency. It was shown that the properties of the produced CNFs strongly depend on the number of passes through the TSE. Consequently, different CNF grades can be produced. However, as most mechanical treatments, TSE leads to some fiber degradation, such as a decrease of the DP.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Oleksandr Nechyporchuk: 0000-0001-7178-5202 Alain Dufresne: 0000-0001-8181-1849 Julien Bras: 0000-0002-2023-5435 Notes
The authors declare no competing financial interest. 6529
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(16) Henriksson, M.; Henriksson, G.; Berglund, L. A.; Lindström, T. An environmentally friendly method for enzyme-assisted preparation of microfibrillated cellulose (MFC) nanofibers. Eur. Polym. J. 2007, 43 (8), 3434−3441. (17) Iwamoto, S.; Nakagaito, A. N.; Yano, H. Nano-fibrillation of pulp fibers for the processing of transparent nanocomposites. Appl. Phys. A: Mater. Sci. Process. 2007, 89 (2), 461−466. (18) Päak̈ kö, M.; Ankerfors, M.; Kosonen, H.; Nykänen, A.; Ahola, S.; Ö sterberg, M.; Ruokolainen, J.; Laine, J.; Larsson, P. T.; Ikkala, O.; et al. Enzymatic Hydrolysis Combined with Mechanical Shearing and High-Pressure Homogenization for Nanoscale Cellulose Fibrils and Strong Gels. Biomacromolecules 2007, 8 (6), 1934−1941. (19) Zimmermann, T.; Bordeanu, N.; Strub, E. Properties of nanofibrillated cellulose from different raw materials and its reinforcement potential. Carbohydr. Polym. 2010, 79 (4), 1086−1093. (20) Spence, K. L.; Venditti, R. A.; Rojas, O. J.; Habibi, Y.; Pawlak, J. J. A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods. Cellulose 2011, 18 (4), 1097−1111. (21) Tejado, A.; Alam, M. N.; Antal, M.; Yang, H.; van de Ven, T. G. M. Energy requirements for the disintegration of cellulose fibers into cellulose nanofibers. Cellulose 2012, 19 (3), 831−842. (22) Turbak, A. F.; Snyder, F.; Sandberg, K.Microfibrillated cellulose, a new cellulose product: properties, uses, and commercial potential; 1983; pp 815−827. (23) Saito, T.; Nishiyama, Y.; Putaux, J.-L.; Vignon, M.; Isogai, A. Homogeneous Suspensions of Individualized Microfibrils from TEMPO-Catalyzed Oxidation of Native Cellulose. Biomacromolecules 2006, 7 (6), 1687−1691. (24) Ho, T. T. T.; Abe, K.; Zimmermann, T.; Yano, H. Nanofibrillation of pulp fibers by twin-screw extrusion. Cellulose 2015, 22 (1), 421−433. (25) Kekäläinen, K.; Liimatainen, H.; Biale, F.; Niinimäki, J. Nanofibrillation of TEMPO-oxidized bleached hardwood kraft cellulose at high solids content. Holzforschung 2015, 69 (9), 1077− 1088. (26) Hietala, M.; Rollo, P.; Kekäläinen, K.; Oksman, K. Extrusion processing of green biocomposites: Compounding, fibrillation efficiency, and fiber dispersion. J. Appl. Polym. Sci. 2014, 131 (6), 39981/1−399981/9. (27) Suzuki, K.; Sato, A.; Okumura, H.; Hashimoto, T.; Nakagaito, A. N.; Yano, H. Novel high-strength, micro fibrillated cellulose-reinforced polypropylene composites using a cationic polymer as compatibilizer. Cellulose 2014, 21 (1), 507−518. (28) Yano, H.; Yano, K.; Motegi, Y. Process for production of aliphatic polyester composition, pulp and cellulosic fiber to be used therein, and process for microfibrillation thereof. WO2005003450 A1, 2007. (29) Heiskanen, I.; Harlin, A.; Backfolk, K.; Laitinen, R. Process for Production of Microfibrillated Cellulose in an Extruder and Microfibrillated Cellulose Produced According to the Process. WO2011051882 (A1), May 5, 2011. (30) Hiltunen, J.; Kemppainen, K.; Pere, J. Process for Producing Fibrillated Cellulose Material. WO2015092146 (A1), June 25, 2015. (31) Castro, N.; Durrieu, V.; Raynaud, C.; Rouilly, A.; Rigal, L.; Quellet, C. Melt Extrusion Encapsulation of Flavors: A Review. Polym. Rev. 2016, 56 (1), 137−186. (32) Harrington, J.; Schaefer, M. Chapter 8 - Extrusion-Based Microencapsulation for the Food Industry. In Microencapsulation in the Food Industry; Academic Press: San Diego, CA, 2014; pp 81−84. (33) Stanković, M.; Frijlink, H. W.; Hinrichs, W. L. J. Polymeric formulations for drug release prepared by hot melt extrusion: application and characterization. Drug Discovery Today 2015, 20 (7), 812−823. (34) Lee, S.-H.; Teramoto, Y.; Endo, T. Enhancement of enzymatic accessibility by fibrillation of woody biomass using batch-type kneader with twin-screw elements. Bioresour. Technol. 2010, 101 (2), 769−774. (35) Suzuki, K.; Okumura, H.; Kitagawa, K.; Sato, S.; Nakagaito, A. N.; Yano, H. Development of continuous process enabling nano-
ACKNOWLEDGMENTS This research was supported by Institut Carnot Polynat (Grant Agreement ANR-11-CARN-030-01), le Centre Technique du Papier (Grenoble, France), and LabEx Tec 21 (Grant Agreement ANR-11-LABX-0030). LGP2 is part of the LabEx Tec 21 (Investissements d’Avenir) and of the Énergies du Futur and PolyNat Carnot Institutes. The authors also want to acknowledge Thierry Encinas from the CMTC in Grenoble for XRD analysis.
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ABBREVIATIONS ref-Enz-TSE 7p: Refined pulp, enzymatically pretreated, extruded 7 passes ref-TEMPO-oxidized TSE 7p: Refined pulp, TEMPOoxidized, extruded 7 passes ref-Enz-grinder: Refined pulp, enzymatically pretreated, passed through the supermasscolloider grinder ref-TEMPO-oxidized-grinder: Refined pulp, TEMPO-oxidized, passed through the supermasscolloider grinder Commercial MFC: microfibrillated cellulose provided by the Centre technique du Papier CTP in France, produced by homogenization of enzymatic pulp
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