Production Of Cellulose Nanofibrils Research Articles

Using Commercial Enzymes to Produce Cellulose Nanofibers from Soybean Straw

This study used commercial enzymes to isolate cellulose nanofibrils (CN) and produce sugars from chemically pretreated soybean straw (SS) (stem, leaves, and pods) by alkali (NaOH 5 or 17.5% v/v at 90°C for 1 h or at 30°C for 15 h) and bleaching (NaClO23.3% or H2O24%) pretreatments. Depending on the pretreatment applied to the soybean straw, the yield of CN varied from 6.3 to 7.5 g of CN/100 g of SS regardless of the concentration of the alkaline solution (5 or 17.5%). The CN had diameter of 15 nm, measured over 300 nm in length, and had high electrical stability (zeta potentials ranged from −20.8 to −24.5). Given the XRD patterns, the crystallinity index (CrI) of CN ranged from 45 to 68%, depending on the chemical pretreatment the starting material was submitted to. CN obtained from SS treated with NaOH 17.5% and H2O2(CrI = 45%) displayed better thermal stability probably because a lignin-cellulose complex emerged. The soluble fraction obtained in the first step of CN production contained a large amount of reducing sugars (11.2 to 30.4 g/100 g of SS). SS seems to be a new promising industrial source to produce CN via enzymatic-mechanical treatment, leading to large amounts of reducing sugars for use in bioenergy production.

A comparison of cellulose nanofibrils produced from Cladophora glomerata algae and bleached eucalyptus pulp

Cladophora, a fresh-water green macroalgae, has unique cellulose properties and thus may be promising for production of cellulose nanofibrils (CNFs). Cellulose was extracted from Cladophora glomerata and subjected to microfluidization with or without enzymatic hydrolysis pretreatment to produce CNFs. Increasing microfluidization passes produced smaller algal CNFs with more uniform sizes and lower crystallinity. Combining microfluidization with an enzymatic hydrolysis pretreatment, the algal CNFs’ crystallinity decreased further, but the diameter distribution showed little change. The algal CNFs were compared to CNFs produced from bleached eucalyptus pulp (BEP), with the algal CNFs having significantly higher crystallinity, smaller diameter and better thermal stability. The XRD spectra of algal and BEP CNFs were simulated by Mercury 3.0 software. The results indicated that BEP CNFs are mainly cellulose Iβ with a random orientation, while algal CNFs are likely a hybrid of cellulose Iα with preferred orientations along the [100] and [010] axes with a March–Dollase factor of 0.65.

Physical and Mechanical Properties of Cellulose Nanofibril Films from Bleached Eucalyptus Pulp by Endoglucanase Treatment and Microfluidization

A GH5 hyperthermostable endoglucanase (Ph-GH5) from the archaeon Pyrococcus horikoshii and a commercial endoglucanase (FR) were used to treat bleached eucalyptus pulp (BEP) fibers to produce cellulose nanofibrils (CNF) and subsequently to CNF films. TEM imaging indicated that Ph-GH5 produced longer and more entangled CNF than FR with the same number of microfluidization passes. Physical and mechanical properties of CNF films were characterized. Optical opacity of CNF films from FR (10 mg/g) at 40 passes through the microfluidizer can be as low as 3.7 %, compared with 18.2 % from untreated BEP at the same number of passes. CNF films exhibited similar thermal stability with untreated BEP. Highest specific modulus of CNF films was also obtained from FR (10 mg/g), reaching 56 MNm/kg, approximately 271 % of the CNF films from untreated BEP at 40 passes through the microfluidizer. CNF film from Ph-GH5 (1 mg/g) at 40 passes provided the highest specific maximum tensile strength at 120 kNm/kg.

Life cycle assessment of cellulose nanofibrils production by mechanical treatment and two different pretreatment processes.

Nanocellulose is a bionanomaterial with many promising applications, but high energy use in production has been described as a potential obstacle for future use. In fact, life cycle assessment studies have indicated high life cycle energy use for nanocellulose. In this study, we assess the cradle-to-gate environmental impacts of three production routes for a particular type of nanocellulose called cellulose nanofibrils (CNF) made from wood pulp. The three production routes are (1) the enzymatic production route, which includes an enzymatic pretreatment, (2) the carboxymethylation route, which includes a carboxymethylation pretreatment, and (3) one route without pretreatment, here called the no pretreatment route. The results show that CNF produced via the carboxymethylation route clearly has the highest environmental impacts due to large use of solvents made from crude oil. The enzymatic and no pretreatment routes both have lower environmental impacts, of similar magnitude. A sensitivity analysis showed that the no pretreatment route was sensitive to the electricity mix, and the carboxymethylation route to solvent recovery. When comparing the results to those of other carbon nanomaterials, it was shown that in particular CNF produced via the enzymatic and no pretreatment routes had comparatively low environmental impacts.

Optimizing cellulose fibrillation for the production of cellulose nanofibrils by a disk grinder

AbstractThe fibrillation of a bleached kraft eucalyptus pulp was investigated by means of a laboratory-scale disk grinder for the production of cellulose nanofibrils (CNF), while the parameters disk rotating speed, solid loading, and fibrillation duration were varied. The cumulative energy consumption was monitored during fibrillation. The degree of polymerization (DP) and water retention value (WRV) of the resultant cellulose fibrils were determined as measures of the degree of fibrillation, which was also visualized by scanning electron microscopy, field emission-scanning electron microscopy, and transmission electron microscopy imaging. A higher rotating speed than 1500 rpm did not improve the fibrillation judged by DP and WRV measurements. Solid loading has an insignificant effect on fibrillation in a wide range. The energy consumption (E) was determined as a function of the DP and WRV. The optimal grinding conditions were between 1200 and 1500 rpm at 2.0%–2.2% solid loading.

Repeated homogenization, a route for decreasing the energy consumption in the manufacturing process of carboxymethylated nanofibrillated cellulose?

Energy-efficient manufacturing is a requirement for the large-scale production of nanofibrillated cellulose systems. Today, most strides involve the development of new physicochemical pre-treatment processes or invention of new or further-development of existing mechanical delamination processes; these approaches are often costly. In this communication, it was shown that significant reduction in energy consumption (~30–50 %) of the nanofibrillated cellulose (NFC) manufacturing process is possible by the wise employment of existing machinery and processes—without deterioration of the attractive properties of the NFC product. The suggested approach has further the additional advantage of increasing the yield of nanofibrillation, robustness of the manufacturing process, and increasing the out-put of the process. These notions can lead to significant energy savings in the NFC production. The novel manufacturing protocol involved repeated homogenization of the pulp suspension at low (~400 bar) applied homogenization pressures (as compared to those currently applied, ~1700 bar). It was hypothesized that this manufacturing protocol leads to a more homogeneous and effective shearing of the fibres, than is achievable by one time homogenization of the pulp slurry at high applied pressures. The investigations further showed that there exists an apparent yield of fibrillation (of about 40 %), above which the rheological properties of the NFC systems and the mechanical properties of the resulting NFC films remain unaffected. This observation [which is in accordance to published observations by e.g. Fall (2013)] can be employed to reduce the specific energy consumption in the NFC manufacturing process. Finally, the investigations also showed that the route that is used for dilution of concentrated NFC systems can significantly alter the properties of resulting NFC-films. It was postulated that a protocol based on the severe shearing of the NFC suspension (prior to NFC-film formation), e.g. by high pressure homogenization, can lead to a more homogeneous and better fibrillated system, which in turn might lead to the overestimation of the actual properties of the studied NFC system.

Microemulsion systems for fiber deconstruction into cellulose nanofibrils.

A new method to produce cellulose nanofibrils (CNF) is proposed to reduce the energy demand during deconstruction of precursor fibers suspended in aqueous media. Microemulsions were formulated with aqueous solutions of urea or ethylenediamine and applied to disrupt interfibril hydrogen bonding. Compared to typical fibrillation of lignin-containing and lignin-free fibers, pretreatment with microemulsion systems allowed energy savings during microfluidization of 55 and 32%, respectively. Moreover, microemulsion processing facilitated smaller-scale CNF structures (higher degrees of deconstruction), with higher water retention value (WRV) and surface area. Urea-containing microemulsions were found to be most effective in reducing energy consumption and in weakening the cellulosic matrix. Films prepared from CNF processed after pretreatment with urea-containing microemulsions presented a more uniform fiber network and produced films with smoother surfaces compared to those based on ethylenediamine. The lignin-containing CNF (LCNF) produced denser films than those obtained from lignin-free CNF. The mechanical properties of films obtained after application of microemulsion pretreatment were compared, and the benefits of the proposed approach were further confirmed. Overall, fiber deconstruction after microemulsion treatment is a step toward energy-efficient production of nanocellulose.

Agriculture crop residues as a source for the production of nanofibrillated cellulose with low energy demand

Nanofibrillated cellulose (NFC) from three agricultural crop (rice straw, corn and rapeseed stalk) residues was isolated with high-yield production using either high pressure homogenisation or a high speed blender. The fibres were extracted from the neat biomass via an NaClO2/acetic acid and alkali pulping process. TEMPO-mediated oxidation pretreatment at pH 7 and 10 was accomplished to facilitate the release of the cellulose microfibrils. The fibrillation yield, transparency degree and morphological characteristics of the ensuing NFC were analysed using the centrifugation method, transmittance measurement and SEM observation. The energy consumption during the disintegration process was also accessed. It was shown that the mode of lignin removal and the fibre pretreatment notably affected the nanofibrillation efficiency and energy demand. A successful production of NFC with yield exceeding 90 %, using a simple Waring blender, was achieved when the NaClO2/acetic acid delignification followed by a TEMPO-NaBr–NaClO oxidation at pH 10 was adopted.

Production of cellulose nanofibrils from bleached eucalyptus fibers by hyperthermostable endoglucanase treatment and subsequent microfluidization

A GH5 hyperthermostable endoglucanase from the archaeon Pyrococcus horikoshii (Ph-GH5) and a commercial endoglucanase FR were used to treat bleached eucalyptus pulp (BEP) fibers to produce cellulose nanofibrils (CNFs) through subsequent microfluidization. Enzymatic treatments facilitated CNF production due to the reduced degree of polymerization (DP) of the fibers. SEM imaging indicated that FR reduced fiber DP drastically and resulted in much shorter fibers than with Ph-GH5, even at very low dosages (1 mg protein/g fiber) of FR treatment compared with a high dosage (10 mg protein/g fiber) of Ph-GH5. The fibers treated with FR were much more uniform in length perhaps due to the presence of exoglucanase and beta-glucosidase saccharifying short microfibers into glucose. TEM imaging indicated that Ph-GH5 produced longer and entangled CNFs than FR with the same number of microfluidization passes. However, the CNF diameters were approximately the same for all CNFs from enzyme-treated fibers using both endoglucanases at two dosages (1 or 10 mg protein/g fiber). CNFs produced from BEP fibers without enzymatic treatment showed larger diameters than those with enzymatic treatment.

The state of carboxymethylated nanofibrils after homogenization-aided dilution from concentrated suspensions: a rheological perspective

The rheological properties of a carboxymethylated (D.S. ≈ 0.1) nanofibrillated cellulose (NFC) were investigated at different solid contents. The critical overlap concentration was determined to be in the range between 0.04 and 0.07 % (w/w) using shear stress versus shear rate measurements. From the critical overlap concentration using the simple Mason excluded volume formalism, the apparent aspect ratio was estimated to be 75 [at a critical overlap concentration of 0.04 % (w/w)]. The aspect ratio of the NFC system was also estimated by using the Einstein–Simha equation together with the intrinsic viscosity value of the system (corrected for the electroviscous effects). The obtained value was found to be around 80, which is in good agreement with the value obtained from the excluded volume calculation. Further, by combining oscillatory measurements and the equation of Shankar et al. the apparent fibril length was determined to be 4 µm. As the production of NFC through homogenization occurs at concentrations far above the critical overlap concentration an NFC-gel is constituted by a severely entangled structure. The disentanglement of the fibrils is therefore difficult and the employed dilution method was found not to lead to fully liberated nanofibrils, which was also indicated by atomic force microscopy-imaging.

Strong and Optically Transparent Films Prepared Using Cellulosic Solid Residue Recovered from Cellulose Nanocrystals Production Waste Stream

We used a new cellulosic material, cellulosic solid residue (CSR), to produce cellulose nanofibrils (CNF) for potential high value applications. Cellulose nanofibrils (CNF) were produced from CSR recovered from the hydrolysates (waste stream) of acid hydrolysis of a bleached Eucalyptus kraft pulp (BEP) to produce nanocrystals (CNC). Acid hydrolysis greatly facilitated homogenization to fibrillate CSR to CNF with only 15 passes in a microfluidizer compared with at least 47 passes to fibrillate BEP to nanofibrils. CNF from CSR were nanowhiskers with a length between 50 and 400 nm and a diameter 3-10 nm with limited aggregation while CNF from BEP were entangled networks of nanofibrils with a length of 500-1000 nm and a diameter of 10-50 nm. CNFs from CSR had good spectral transparency from UV to infrared, i.e, transmittance of CNF-CSR suspensions at 0.1% solids consistency is greater than 90% at wavelengths greater than 340 nm, compared with less than 30% for CNF suspension produced from BEP. Specific tensile strength and modulus of CNF films from CSRs reached 75 kN·m/kg and 12 MN·m/kg, respectively, approximately 175% of the respective values for conventional paper made of refined BEP.

Morphological development of cellulose fibrils of a bleached eucalyptus pulp by mechanical fibrillation

This study reports the production of cellulose nanofibrils (CNF) from a bleached eucalyptus pulp using a commercial stone grinder. Scanning electronic microscopy and transmission electronic microscopy imaging were used to reveal morphological development of CNF at micro and nano scales, respectively. Two major structures were identified: (1) highly kinked, naturally helical, and untwisted fibrils that serve as backbones of CNF networks, and (2) entangled, less distinctively kinked (or curled) and twisted “soft looking” nanofibrils. These two major structures appeared in different features of CNF network such as “trees”, “net”, “flower”, single fibril, etc. Prolonged fibrillation can break the nanofibrils into nanowhiskers from the untwisted fibrils with high crystallinity. Energy input for mechanical fibrillation is on the order of 5–30 kWh/kg. The gradual reduction in network size of CNF with time may be used to fractionate CNF.

Self-assembly of cellulose nanofibrils by genetically engineered fusion proteins

One central problem for the function and manufacture of materials where performance relies on nanoscale structure is to control the compatibility and interactions of the building blocks. In natural materials, such as nacre, there are examples of multifunctional macromolecules that have combined binding affinities for different materials within the same molecule, thereby bridging these materials and acting as a molecular glue. Here, we describe the use of a designed multifunctional protein that is used for self-assembly of nanofibrillar cellulose. Recent advances in the production of cellulose nanofibrils have given inspiration for new uses of cellulosic materials. Cellulose nanofibrils have mechanical and structural features that open new possibilities for performance in composites and other nanoscale materials. Functionalisation was realised through a bi-functional fusion protein having both an ability to bind to cellulose and a second functionality of surface activity. The cellulose-binding function was obtained using cellulose-binding domains from cellulolytic enzymes and the surface activity through the use of a surface active protein called hydrophobin. Using the bi-functional protein, cellulose nanofibrils could be assembled into tightly packed thin films at the air/water interface and at the oil/water interface. It was shown that the combination of protein and cellulose nanofibrils resulted in a synergistic improvement in the formation and stability of oil-in-water emulsions resulting in emulsions that were stable for several months. The bi-functionality of the protein also allowed the binding of hydrophobic solid drug nanoparticles to cellulose nanofibrils and thereby improving their long-term stability under physiological conditions.

A comparative study of Eucalyptus and Pinus radiata pulp fibres as raw materials for production of cellulose nanofibrils

This work comprises a comparison between Eucalyptus and Pinus radiata pulp fibres, as raw materials for producing nanofibrils. The cellulose nanofibrils were produced mechanically and chemi-mechanically. Series of the fibres were subjected to a TEMPO mediated oxidation to facilitate the homogenization. The contents of carboxyl acids after the pre-treatment indicated a favourable situation for producing nanofibrils using Eucalyptus pulp fibres as raw material. However, films made of P. radiata-based nanofibrils evidenced less shrinkage and higher transparency levels, which were related to a higher fibrillation of the pulp fibres. The energy consumption during homogenization was quantified. The results demonstrated that for a given number of passes through the homogenizator, TEMPO pre-treatment will facilitate the homogeneous fibrillation of a given fibre. This implies that less energy is required for producing nanofibrils with homogeneous sizes.