Preparation Of Cellulose Nanocrystals Research Articles

Nanocomposites of acid free CNC and HDPE: Dispersion from solvent driven by fast crystallization/gelation

Among several applications, the use of cellulose nanocrystals (CNC) as reinforcement in composite materials with thermoplastic matrix stands out. However, both the conventional method for CNC production and the processes for composite production with non-water-soluble matrix show several drawbacks. The common method for CNC preparation based on the hydrolysis of cellulose with high concentrated sulfuric acid produces sulfated nanocrystals with low thermal stability and generates large amounts of acidic effluents. Although the presence of ionic groups on the surface of the nanocrystals prepared in sulfuric acid increases the stability of their suspensions in water, it promotes the degradation of the CNC in melt processing temperatures of thermoplastic composites, such as extrusion or injection molding. Here we describe the use of high thermal stable cellulose nanocrystal prepared by subcritical water as reinforcement for high density polyethylene (HDPE) using a three step processing: i) solvent exchange in order to produce a suspension of CNC in xylenes, ii) dissolution of HDPE followed by iii) the fast crystallization/gelation/flocculation, leading to the isolation of the composite. This process leads to the production of a well-dispersed nanocomposite with higher thermal stability (higher than 250 °C) and improved mechanical properties. An increase of ~20% in Young's modulus was observed when compared with the neat matrix.

Hydrochloric Acid Hydrolysis of Pulps from Oil Palm Empty Fruit Bunches to Produce Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) were successfully isolated by hydrochloric acid hydrolysis followed by ultrasonic homogenization of oil palm empty fruit bunches (OPEFB), which are a major form of agricultural waste in Southeast Asia. Currently sulfuric acid is mainly used in CNC preparation to achieve high dispersibility; however, we demonstrated that CNC suspensions prepared from OPEFB by hydrochloric acid hydrolysis remained stable without any sedimentation over 6 months. The obtained CNCs were fully characterized by elemental analysis, electron microscopic observation, X-ray diffraction measurement, and thermal analysis. The OPEFB-derived CNCs exhibited higher aspect ratios of 23–29 and higher thermal stability of 347–359 °C as maximum degradation temperature, as compared with those of woody CNCs prepared by sulfuric acid hydrolysis (15 and 311 °C, respectively). Although as-prepared CNCs showed comparable morphological and physicochemical properties to those prepared from oil palm biomass by other methods including sulfuric acid hydrolysis, use of hydrochloric acid and ultrasonication for hydrolysis of OPEFB was effective to yield crystalline CNCs with long-term nanodispersibility showing clear birefringence.

Recent Strategies in Preparation of Cellulose Nanocrystals and Cellulose Nanofibrils Derived from Raw Cellulose Materials

The recent strategies in preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were described. CNCs and CNFs are two types of nanocelluloses (NCs), and they possess various superior properties, such as large specific surface area, high tensile strength and stiffness, low density, and low thermal expansion coefficient. Due to various applications in biomedical engineering, food, sensor, packaging, and so on, there are many studies conducted on CNCs and CNFs. In this review, various methods of preparation of CNCs and CNFs are summarized, including mechanical, chemical, and biological methods. The methods of pretreatment of cellulose are described in view of the benefits to fibrillation.

Acid-Free Preparation of Cellulose Nanocrystals by TEMPO Oxidation and Subsequent Cavitation.

Softwood bleached kraft pulp (SBKP) and microcrystalline cellulose (MCC) were oxidized using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated system. The TEMPO-oxidized SBKP prepared with 10 mmol/g NaClO (SBKP-10) had a higher mass recovery ratio and higher carboxylate content than the other prepared celluloses including the TEMPO-oxidized MCCs. The SBKP-10 was then exposed to cavitation-induced forces through sonication in water for 10-120 min to prepare aqueous dispersions of needle-like TEMPO-oxidized cellulose nanocrystals (TEMPO-CNCs) with homogeneous width of 3.5 to 3.6 nm and average lengths of ∼200 nm. The average chain lengths of the cellulose molecules that make up the TEMPO-CNCs were less than half the average lengths of the TEMPO-CNCs. Compared with conventional CNCs prepared by acid hydrolysis, the TEMPO-CNCs prepared by the acid-free and dialysis-free process exhibited higher mass recovery ratios, significantly higher amounts of surface anionic groups, and smaller and more homogeneous widths.

Green Preparation of Cellulose Nanocrystal and Its Application

A green method was used to prepare cellulose nanocrystals (CNCs) with no use of harsh chemicals or organic solvents. This method was simple via ball milling cellulose with water followed by centrifugation. The diameter and length of the CNCs were 3–10 nm and 120–400 nm, separately, with a aspect ratio of 20–60. The yield was about 20%. The thermal stability of the CNCs was the same as that of raw cellulose owing to lacking of chemical modification. So it was superior to CNCs prepared by acid hydrolysis. Then poly(vinyl alcohol) (PVA)/CNC composite film was made by solution casting. The results showed that the tensile strength of the composite film was 79% increased from neat PVA film when adding 5% CNCs to the PVA matrix. In addition, the composite films possessed good transparency and thermal stability.

An eco-friendly preparation of cellulose nano crystals from oil palm empty fruit bunches

Cellulose Nanocrystals (CNCs) have attracted a lot of attention as one of the promising green nanomaterials because of their interesting properties such as low density, high mechanical properties, high surface area, high biocompatibility and low toxicity. However, sulphuric acids is generally used in conventional method to prepare CNCs which is highly corrosive and harmful to environment. Replacing sulphuric acid with Ammonium Persulfate (APS), which possess lower toxicity, are desirable from environment point of view. In this research, preparation of CNCs from Oil Palm Empty Fruit Bunches (OPEFB) as alternative raw materials and using APS is reported. Three kinds of method were carried out before applying APS solution: (i) without pre-treatment, (ii) with alkali pre-treatment and (iii) with alkali-chloride pre-treatment. White-colored sample with crystallinity reaching 78% (XRD result) and particle size ranging between 31-113 nm (DLS result) was obtained. Those results implied that there were potential existence of CNCs in the samples.

Preparation of cellulose nanocrystals from empty fruit bunch of palm oil by using phosphotungstic acid

Empty fruit bunch (EFB) of palm oil, an abundant agro-waste in Indonesia, was used as raw material of Cellulose Nanocrystals (CNCs) preparation. Instead of conventional acid mineral, phosphotungstic acid (H3PW12O40, HPW) was used to hydrolyze cellulose due to recycling ability and easy handling. Before hydrolysis process, dried EFB was treated by 3% NaOH solution at 90°C for 2 hours and then bleached using 2% NaClO2 solution at 80°C for 3 hours to remove hemicellulose and lignin. Hydrolysis reaction parameters such as temperature, acid concentration, and reaction time were optimized with fixed solid-liquid ratio of 1:40. Response surface method was used for experimental design to determine the optimum condition of each parameter by using software Minitab. In this study, pulp from dried EFB produced 44.8% yield of CNCs. Dynamic Light Scattering (DLS) analysis showed that most of CNCs equivalent diameter was 140 nm. Crystallinity index was observed at 73.3% using X-ray Diffraction (XRD) analysis. Thus, a green established process for the preparation of CNCs was achieved.

Preparation of cellulose nanocrystals from lignin-rich reject material for oil emulsification in an aqueous environment

Cellulose nanocrystals (CNCs) with amphiphilic features were used in oil drop stabilization in diesel oil-in-water (o/w) emulsion. The functionalized CNCs were synthesized from a lignin-rich reject cellulose source from the pulp and paper industry, i.e., the non-bleached fines fractions of carton pulp. Partial periodate-chlorite oxidation, which was followed by reductive butylamination, was used to obtain surface-modified amphiphilic CNCs. All studied CNCs prevented droplet coalescence by stabilizing oil droplets in the emulsion thus resulting in stable o/w Pickering-like emulsions. CNCs from the fines fractions at concentrations 0.05–0.1% (weight by weight, w/w) provided high stability against creaming (i.e., phase separation), and they did not de-emulsify at low temperatures since the oil droplet size remained small at + 5 °C at a 0.05% (w/w) CNC concentration. Salinity improved the stability against creaming with the reference chemical pulp CNC, but negatively affected the emulsion creaming rate for CNCs that had a higher level of lignin. However, the non-bleached fines fraction of the pulp may provide one potential and cost-effective raw material source for the development of a novel bio-based chemical.

Influence of the quality of microcrystalline cellulose on the outcome of TEMPO-mediated oxidation

In an attempt to prepare cellulose nanocrystals (CNCs) by TEMPO-mediated oxidation of microcrystalline cellulose (MCC), a new species of MCC called AaltoCell was placed under scrutiny. Unlike Avicel, AaltoCell is a never-dried species, still containing ca. 10% xylan in its structure. According to thermoporosimetry, the pore size distributions of AaltoCell and Avicel did not differ from each other but after TEMPO-oxidation, AaltoCell exhibited a far lower degree of porosity, hypothetically ascribed to its hemicellulose content. Surprisingly, the charge density imposed by TEMPO-oxidation did not vary between AaltoCell and Avicel despite the different microfibril widths observed, respectively. After TEMPO-oxidation and centrifugation the fine fraction share, indicating the CNC yield, was not more than 11% for AaltoCell, compared to 20% from Avicel.

Preparation of cellulose nanocrystals from Humulus japonicus stem and the influence of high temperature pretreatment

As one of the most abundant wild herbs in nature, the Humulus japonicus stem (HJS) is a new low-cost source of cellulosic material. In this work, cellulose nanocrystals (CNCs) were isolated from HJS using acid hydrolysis. The influence of high temperature pretreatment (HT pretreatment) on the properties and yields of these HT-HJS (HJS fibers after HT pretreatment at different temperatures) and HT-CNCs (CNCs prepared from the HT-HJS) was studied. The results showed that there was no variation of the chemical structure among the HT-HJS and HT-CNCs. The thermal stabilities and crystallinities of the HT-HJS were higher than bleached HJS. The average diameters of the HT-CNCs were significantly smaller while the average aspect ratios of them were obviously bigger than the CNCs, and the biggest average aspect ratio of HT140-CNCs (63.40) was almost twice of CNCs (32.00). Compared with the CNCs (70.05%, 212.8°C), the crystallinity and initial degradation temperature also showed increase for the HT-CNCs and increased up to maximum of 86.93% and 227.5°C for the HT160-CNCs.

Mild Oxalic‐Acid‐Catalyzed Hydrolysis as a Novel Approach to Prepare Cellulose Nanocrystals

AbstractThe traditional method to isolate cellulose nanocrystals (CNCs) is to subject cellulosic materials to strong acid hydrolysis by mineral acids, which usually causes problems such as corrosion of equipment, the need for large amounts of water, the difficulty of acid recovery, and over‐degradation of cellulose. Thus, a green and sustainable approach for the preparation of CNCs was developed where mild acid hydrolysis with diluted oxalic acid was used. The reaction kinetics of different preparation parameters, such as reaction temperature, oxalic acid dose, addition of HCl, and reaction time were thoroughly investigated. A high yield of up to 85 % was achieved by mild oxalic acid hydrolysis in comparison to the yield of 35 % using the most common approach with sulfuric acid hydrolysis. The CNCs from the above approach have a high thermal stability, that is, a maximum thermal degradation temperature of 350 °C in comparison to 200 °C when sulfuric acid hydrolysis was used. Importantly, oxalic acid solutions were readily recovered, and exhibited consistently high performance in several continuous runs of reaction. The hydrolysates contained mostly monomeric sugars, which could be further utilized for chemical or biofuel production.

Degradation and Crystallization of Cellulose in Hydrogen Chloride Vapor for High-Yield Isolation of Cellulose Nanocrystals.

Despite the structural, load-bearing role of cellulose in the plant kingdom, countless efforts have been devoted to degrading this recalcitrant polysaccharide, particularly in the context of biofuels and renewable nanomaterials. Herein, we show how the exposure of plant-based fibers to HCl vapor results in rapid degradation with simultaneous crystallization. Because of the unchanged sample texture and the lack of mass transfer out of the substrate in the gas/solid system, the changes in the crystallinity could be reliably monitored. Furthermore, we describe the preparation of cellulose nanocrystals in high yields and with minimal water consumption. The study serves as a starting point for the solid-state tuning of the supramolecular properties of morphologically heterogeneous biological materials.

Reuse of waste cotton cloth for the extraction of cellulose nanocrystals

Cellulose nanocrystals (CNCs) were prepared from waste cotton cloth and degreasing cotton was used as a comparison. The cellulose was first extracted by alkali and bleaching treatments, and then the CNCs were isolated by the mix acid solution hydrolysis of cellulose under the controlled conditions. The CNCs were analyzed by Attenuated total reflectance Fourier transform infrared spectroscopy, Transmission electron microscopy, X-ray diffraction analysis, thermogravimetric and differential scanning calorimetry analysis. The results confirmed that the resultant samples were the cellulose species, and the CNCs obtained from waste cotton cloth exhibited a high crystallinity index of 55.76±7.82%, which had higher thermostability than that from the degreasing cotton. The morphology analysis results showed that the ranges of length and diameter of CNC extracted from waste cotton cloth were from 28 to 470nm and 3 to 35nm. The preparation of CNCs with a high aspect ratio and good thermostability in this work paves the way for an alternative reuse of waste cotton cloth.

Cellulose nanocrystals grafted with polyacrylamide assisted by macromolecular RAFT agents

Graft modification is an excellent way to prepare cellulose nanocrystals (CNCs) with various functions. In this work, different water-soluble macro reversible addition fragmentation chain transfer (macroRAFT) agents were used to mediate grafting of polyacrylamide with cellulose nanocrystals. Fourier-transform infrared spectroscopy, 13C solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy, and elemental analysis were used to characterize the presence of polyacrylamide and quantify its content on the modified cellulose nanocrystals. The results show that two amphiphilic macroRAFTs, namely St5AA14RAFT and St7AA14RAFT, increased the weight ratio of polyacrylamide on the modified cellulose nanocrystals, whereas a corresponding hydrophilic macroRAFT (AA14RAFT) impeded growth of the polymer chains on the cellulose nanocrystals. Examination of the structure of the graft products and the cleaved polyacrylamide chains revealed that the amphiphilic macroRAFTs were involved in the graft reaction through effective chain transfer, thereby increasing the weight ratio of polyacrylamide on the modified CNCs.

Preparation of cellulose nano-crystals through a sequential process of cellulase pretreatment and acid hydrolysis

In this paper, a cellulase pretreatment was studied prior to the acid hydrolysis to decrease the total acid usage during the cellulose nano-crystals (CNC) preparation from a bleached softwood kraft pulp. Cellulase pretreatment facilitates the subsequent acid hydrolysis to produce CNC with similar quality to that of the control, but at a lower sulfuric acid concentration. The underline mechanism is that cellulase pretreatment led to the formation of more carbonyl groups which can be oxidized into carboxyl groups in the subsequent acid hydrolysis, furthermore, more hydroxyl groups are exposed, thus esterification into sulfonic groups can be enhanced. The results showed that with a cellulase dosage of 4.8 u/g (based on dry pulp) in the pretreatment stage, the sulfuric acid concentration can be decreased from 64 to 40 wt% without compromising the quality of resulting CNC particles. Other results from charge properties, Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) analyses also supported the conclusions.

Preparation of cellulose nanocrystals from asparagus (Asparagus officinalis L.) and their applications to palm oil/water Pickering emulsion

Nano cellulosic materials as promising emulsion stabilizers have attracted great interest in food industry. In this paper, five different sized cellulose nanocrystals (CNC) samples were prepared from stem of Asparagus officinalis L. using the same sulfuric acid hydrolysis conditions but different times (1.5, 2, 2.5, 3.0, and 3.5h). The sizes of these CNC ranged from 178.2 to 261.8nm, with their crystallinity of 72.4–77.2%. The CNC aqueous dispersions showed a typical shear thinning behavior. In a palm oil/water (30/70, v/v) model solution, stable Pickering emulsions were formed with the addition of CNC, and their sizes are in the range of 1–10μm based on the optical and confocal laser scanning microscopy (CLSM) observation. The CNC sample prepared at 3h hydrolysis time, showed a relative efficient emulsion capacity for palm oil droplets, among these CNCs. Other parameters including the CNC, salt, and casein concentrations on the emulsion stability were studied.

Extraction of Cellulose Nanocrystals with a High Yield of 88% by Simultaneous Mechanochemical Activation and Phosphotungstic Acid Hydrolysis

An efficient approach for extracting cellulose nanocrystals (CNCs) was put forward through phosphotungstic acid (PTA) hydrolysis of cellulose raw materials under mechanochemical activation. Response surface methodology was employed for experimental design to determine the optimum conditions of CNCs preparation with software Design Expert. The results showed that quadratic polynomial model was qualified to represent the relationship between the response and independent variables and the regression model defined well the true behavior of the system. Under the optimal conditions, a high yield of up to 88.4%, crystallinity index of 79.6%, and a higher thermal stability can be achieved by combining mechanochemical activation and phosphotungstic acid hydrolysis. This process can improve effectively the hydrolysis efficiency, avoid a lengthy separation process, and reduce the preparation time. Meanwhile, compared to other techniques, mechanochemical activation is an energy-intensive method, and the process is en...

Ionic Compatibilization of Cellulose Nanocrystals with Quaternary Ammonium Salt and Their Melt Extrusion with Polypropylene.

On account to their high mechanical properties along with high reinforcing capacity, cellulose nanocrystals (CNCs) could be the ultimate choice for polymer nanocomposites as filler. Recently, different strategies have been investigated for the melt extrusion of CNC-based polymer nanocomposites because it is a solvent-free process and because this technique is more viable for commercial industrialization. However, most thermoplastic polymers are processed at high temperatures, and sulfuric acid preparation of CNC limits the processing because of surface sulfate groups degradation. In this study we profitably used these negatively charged groups, and quaternary ammonium salt was ionically adsorbed on CNC by a simple aqueous method. Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction were used to characterize adsorbed CNC, and changes in polarity were investigated by contact angle measurements. Modified CNC was extruded with polypropylene at 190 °C, and the ensuing composites were characterized in terms of mechanical (by dynamic mechanical analysis and tensile tests), thermal (by differential scanning calorimetry), and morphological (scanning electron microscopy) properties. The melt rheology of PP-based nanocomposites was also reported.

Cellulose Nanocrystals Prepared by Persulfate One-Step Oxidation of Bleached Bagasse Pulp

This article describes a novel one-step method to prepare cellulose nanocrystals (CNCs) from bleached bagasse pulp via ammonium persulfate (APS) oxidation. The obtained persulfate oxidation cellulose nanocrystals (POCNs) were characterized for their microstructure, crystal properties, and chemical composition. The POCNs were successfully prepared with a total yield of 44.6%. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements indicated that the POCNs had an average length of 150 to 300 nm and an average width of 10 to 30 nm, as well as a rod-like morphology. Fourier transform infrared (FTIR) spectroscopy confirmed the introduction of carboxyl groups on the surface of cellulose. The X-ray diffraction (XRD) spectra proved the existence of cellulose type I, with a highly crystalline nature (79.2%), and thermogravimetric analysis (TGA) showed that the thermal stability decreased.

Further characterization of cellulose nanocrystal (CNC) preparation from sulfuric acid hydrolysis of cotton fibers

Cellulose nanocrystal (CNC), as a natural/sustainable material, has attracted considerable attention, and its preparation from the sulfuric acid hydrolysis process has attained the precommercial demonstration stage. In this study, the process was further characterized by following the alkali solubility in an 18 % sodium hydroxide solution (S18) and the degree of polymerization (DP) of the cellulosic substrate during the sulfuric acid hydrolysis of cotton fibers. The results showed that the S18 increased as the hydrolysis progressed until reaching a nearly constant level at about 45 min, while the DP exhibited a decrease and approached a nearly constant level at 55 min. The emergence of the constant S18 coincided with the formation/appearance of CNC; thus, a “critical stage” with irregular CNC particle size but high yield was identified during the hydrolysis. The optimization of the CNC preparation process was realized under a shortened reaction time with 41.7 % yield (with a CNC size of <150 nm). Therefore, the amount of S18 can be used as a new characterization method for the preparation of CNC or other cellulose-derived products during the acid hydrolysis process with the advantage of a favorable product yield.