Thermal Stability Of Cellulose Nanocrystals Research Articles

Cellulose nanocrystals from rice bran as excellent emulsifiers for independently stabilizing Pickering emulsions

Rice bran as a kind of agricultural waste is anattractive and promising source of cellulose. In this paper, cellulose nanocrystals (CNC) from rice bran were prepared by the hydrolysis of sulfuric acid under ultrasonic treatment. CNC was explored as the stabilizer for Pickering emulsion. The morphological features, chemical structure, crystal property, particle size, surface charge, and thermal stability of CNC were investigated. The CNC with typical cellulose I structure produced by acidic treatment exhibited high thermal stability (>200°C). To evaluate the emulsion capability of CNC, the visual distribution and stability properties of Pickering emulsions were characterized. It was noted that Pickering emulsions stabilized by CNC exhibited excellent storage, oxidative, and environmental stability. This work provides evidence for the valuable utilization of CNC from rice bran. It could be used as a new kind of stabilizer for Pickering emulsions in biomedicine, cosmetics, and food.

RETRACTED: Green and efficient synthesis of cellulose nanocrystals from Hamelia patens leftover via hydrolysis of microwave assisted-ionic liquid (MWAIL) pretreated microcrystalline cellulose

The efficient bioconversion of the lignocellulosic agro-waste has immense importance in biorefinery processing in extracting the cellulose and saccharide fractions. To achieve this, a series of chemical pretreatments is employed, thus concerning environmental threats limit its use. Therefore, an ionic liquid is employed for pretreatment before sustainable extractions owing to its safe manipulation, recycling, and reusability. Specifically, microwave-assisted ionic liquid (MWAIL) pretreatment has significant importance in extracting high cellulose yield at less thermal power consumption. In this study, the leftover stalks of Hamelia patens were subjected to MWAIL pretreatment at 60, 70, 80, and 90 °C to extract microcrystalline cellulose (MCC). Subsequently, the MCC was fabricated into cellulose nanocrystals (CNC) through hydrolytic treatment using acidic and ionic liquids and denoted as CNC-AH and CNC-ILH. Thus obtained CNC was characterized by FTIR, FESEM, XRD, and TGA to investigate the influence of solvent on its morphology, crystallinity, and thermal stability of CNC. The results support that the CNC-ILH has comparatively more thermal and dispersal stability with a reduced crystallinity index than CNC-AH. The surprising results of CNC-ILH signify its utilization in diverse applications in the food and industrial sectors.

The Impact of Fibre Oxidation on the Preparation of Cellulose Nanocrystals (CNC)

This study aimed to evaluate the effect of fibre oxidation on the extent of substituted sulfate on cellulose nanocrystals (CNC). In this investigation, fully bleached softwood (SW) and hardwood (HW) pulps from an Alberta pulp mill were oxidized under low (4%), medium (10%), and the higher-end of medium (14%) oxygen consistencies. The oxidized pulp samples were hydrolyzed with concentrated sulfuric acid under conventional procedures to produce CNC. The CNC materials were then characterized by different qualitative and quantitative techniques to evaluate the effect of oxidations on the number of substituted sulfates and the overall sulfate charge of isolated CNC to develop novel high-value applications. The experimental data show that fibre oxidation helped improve the overall CNC yield, with lower half-ester sulfate contents compared to the controls. The half-ester sulfate contents and the viscosity for SW CNC were found to be higher than their HW CNC counterparts. However, the thermal stability of CNC was found to be better for HW than SW pulps. The emerging data help to prepare and engineer CNC tailored to specific applications.

Artemisia annua Stems a New Sustainable Source for Cellulosic Materials: Production and Characterization of Cellulose Microfibers and Nanocrystals.

In this study, Artemisia annua stem waste was identified, for the first time, as a potential natural source to produce cellulose microfibers (CMF), as well as cellulose nanocrystals (CNC) with unique functionalities by using various organic acids. The CMF extraction was carried out using alkali and bleaching treatments, while the CNC were isolated under acid hydrolysis by using sulfuric acid (S-CNC), phosphoric acid (P-CNC), and hydrochloric acid / citric acid mixture (C-CNC). The CMF and CNC physicochemical, structural, morphological, dimensional, and thermal properties were characterized. CMF with a yield of 53%, diameter of 5 to 30 µm and crystallinity of 57% were successfully obtained. In contrast, CNC showed a rod-like shape with an aspect ratio of 53, 95, and 64 and a crystallinity index of 84, 79, and 72% for S-CNC, P-CNC, and C-CNC, respectively. Results suggested that the type of acid significantly influenced the structure, morphology, and thermal stability of CNCs. Based on these results, Artemisia annua stem waste is a great candidate source for cellulose derivatives with excellent characteristics.Graphical

Preparation and characterization of cellulose nanocrystal extracted from ramie fibers by sulfuric acid hydrolysis

Cellulose nanocrystals (CNCs) were isolated from ramie fibers through chemical pretreatments accompanied by sulfuric acid hydrolysis. The influences of both temperature and hydrolysis time on the properties of CNCs were discussed in the present study. The characterization of CNCs was conducted using FT-IR, XRD, TEM, and TGA. The results showed the characteristics of obtained CNCs were influenced significantly by both temperature and time of hydrolysis. The crystallinity, dimensions, and thermal stability of CNCs were found to reduce by increasing both temperature and reaction time of hydrolysis. The optimal hydrolysis parameters were achieved at 45 °C for 30 min with 58% sulfuric acid to produce CNCs, rod-like particles with a high crystallinity (90.77%), diameter (6.67 nm), length (145.61 nm), and best thermal stability among all CNCs. The obtained CNCs had a higher potential for application of alternative reinforcing fillers in the nanocomposites.

Modification of cellulose nanocrystals by self-assembly nucleation agents to improve poly(L-lactide) nanocomposite’ properties

The poor thermal stability of cellulose nano-crystals (CNCs) and dispersion in polymer matrices are significant obstacles limiting their applications in modification of polymers, especially during melt processing. The self-assembly nucleation agent, decamethylene dicarboxylic dibenzoyl hydrazide (TMC300), was used to modify CNCs via physical adsorption methods. Because TMC300 adsorbed on the surface of CNCs shields the sulfonate on CNCs, the thermal stability of CNCs was significantly improved. Meanwhile, modified CNCs formed different self-assembly morphologies in confined and unconfined spaces, which influenced the crystallization behaviors and microstructures of poly(L-lactide) (PLLA). It improved the crystallization rate of PLLA, which increased the crystallinities and heat resistances of PLLA/CNC composites. More importantly, the self-assembly nucleation agent induced the shish-kebab structures of PLLA, which enhanced the interfacial structure as mechanically interfacial lock and simultaneously improved tensile strength and toughness. This physical and economical modification method of CNCs is anticipated to take full advantage of CNCs to modify PLLA or other semi-crystalline polymers via melt processing.

Preparation of bio-eco based cellulose nanomaterials from used disposal paper cups through citric acid hydrolysis

The Used Disposal Paper Cups (UDPCs) have become a concern to the solid waste management sector as scientists triggered the problems in recent years, to proceed forward in developing the process for this issue. Based on this concern, the present study emphasizes on the isolation of a novel bio-eco based Cellulose NanoCrystals (CNCs) from UDPCs through citric acid hydrolysis. The effect of acid concentration on microstructure and yield of CNCs are highlighted. The optimized yield (55 wt.%) has an appearance of rod-like structure with a width of 13.7 ± 0.6 nm which results due to 76 wt.% of acid hydrolyzed CNCs. The colloidal stability, crystallinity index, presence of functional groups and elemental composition in CNCs (76 wt.%) were identified by employing zeta potential, XRD, conductometric test and FTIR techniques. Finally, the thermal stability of CNCs (76 wt.%) was investigated by thermo-gravimetric analysis.

Physicochemical characteristics of cellulose nanocrystals isolated from seaweed biomass

Cellulose nanocrystals (CNCs) were successfully isolated from marine biomass of brown, red, and green seaweeds by a four step process of de-polymerization, bleaching, acid hydrolysis, and mechanical dispersion. Chemical composition, yield, and density were determined for each seaweed group and compared to other cellulose sources. Morphological analysis was performed by transmission electronic microscopy (TEM) and showed that CNCs from seaweed showed rod shape particles 21–248 nm length and 4.8–41 nm width. The obtained aspect ratio was varied from 2.5 to 15. Fourier transform infrared spectroscopy (FTIR) analysis was performed to investigate chemical structure of CNCs from seaweeds, which revealed obtained crystalline cellulosic from the extraction process. X-ray diffraction (XRD) data showed the main crystalline structure of CNCs was cellulose I in all cases. The crystalline index increased about 21.5% going from cellulose to CNCs. The thermal properties of untreated seaweeds, extracted cellulose, and CNCs were compared by thermogravimetric analysis (TGA). The onset thermal decomposition (Ton) increased in all cases and weight loss changes significantly decreased during the extraction process except Sargassum fluitans, indicating the thermal stability of CNCs.

Optimization of homogenization-sonication technique for the production of cellulose nanocrystals from cotton linter

Recently, cellulose nanocrystals (CNCs) have attracted a significant interest in different fields including drug delivery, biomedical, and food applications. In this study, homogenization-ultrasonication as a non-hazardous, time-saving, and organic solvent free technique was applied for fabrication of CNCs from cotton linter, containing over 90% cellulose. First, acid hydrolysis was applied on raw cellulose using sulfuric acid at 55, 60 and 65% for 3, 5 and 7 min and at various homogenization speeds. Final CNCs were produced by ultrasonication (350 W) for 3 min. The physicochemical properties of CNCs, particle size, X-ray diffraction (XRD) pattern, Fourier Transform Infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), atomic force microscopy (AFM) and transmission electron microscopy (TEM) were studied. Production yield of CNCs was 59–72%, and their water holding capacity was two times higher than raw cellulose. The average length of CNCs was 133 nm with a width of 10 nm and the XRD pattern revealed a 82% crystallinity degree. The FTIR spectrum detected almost similar frequencies in the raw and crystalline cellulose, while intensity of CNC peaks was reduced. TEM results showed rod-like CNCs with a length of 229 nm. TGA results also showed that thermal stability of CNCs was reduced compared to raw cellulose.

Insight into thermal stability of cellulose nanocrystals from new hydrolysis methods with acid blends

This study provides insight into the thermal degradation of cotton cellulose nanocrystals (CNCs) by tuning their physico-chemical properties through acid hydrolysis using blends of phosphoric and sulfuric acid. CNCs isolated by sulfuric acid hydrolysis are known to degrade at lower temperatures than CNCs hydrolyzed with phosphoric acid; however, the reason for this change is unclear. Although all CNCs are inherently relatively thermally stable, their application in polymer composites and liquid formulations designed to function at high temperatures could be extended if thermal stability was improved. Herein, thermogravimetric analysis was carried out on six types of CNCs (in both acid and sodium form) with different surface chemistry, surface charge density, dimensions, crystallinity and degree of polymerization (DP) to identify the key properties that influence thermal stability of nanocellulose. In acid form, CNC surface charge density was found to be the determining factor in thermal stability due to de-esterification and acid-catalyzed degradation. Conversely, in sodium form, surface chemistry and charge density had a negligible effect on the onset of thermal degradation, however, the DP of the cellulose polymer chains highly influenced stability. The presence of more reducing ends in lower DP nanocrystals is inferred to facilitate thermally-induced depolymerization and degradation. Degree of crystallinity did not significantly affect CNC thermal stability. Studying CNCs produced from single or blends of acids (and changing the counterion) elucidated the thermal behavior of cellulose and furthermore demonstrated new routes to tailor CNCs thermal and colloidal stability.

Dual Light- and pH-Responsive Composite of Polyazo-Derivative Grafted Cellulose Nanocrystals.

As a type of functional group, azo-derivatives are commonly used to synthesize responsive materials. Cellulose nanocrystals (CNCs), prepared by acid hydrolysis of cotton, were dewatered and reacted with 2-bromoisobuturyl bromide to form a macro-initiator, which grafted 6-[4-(4-methoxyphenyl-azo) phenoxy] hexyl methacrylate (MMAZO) via atom transfer radical polymerization. The successful grafting was supported by Fourier transform infrared spectroscopy (FT-IR) and Solid magnetic resonance carbon spectrum (MAS 13C-NMR). The morphology and surface composition of the poly{6-[4-(4-methoxyphenylazo) phenoxy] hexyl methacrylate} (PMMAZO)-grafted CNCs were confirmed with Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The grafting rate on the macro-initiator of CNCs was over 870%, and the polydispersities of branched polymers were narrow. The crystal structure of CNCs did not change after grafting, as determined by X-ray diffraction (XRD). The polymer PMMAZO improved the thermal stability of cellulose nanocrystals, as shown by thermogravimetry analysis (TGA). Then the PMMAZO-grafted CNCs were mixed with polyurethane and casted to form a composite film. The film showed a significant light and pH response, which may be suitable for visual acid-alkali measurement and reversible optical storage.

Cellulose nanocrystals modified with a triazine derivative and their reinforcement of poly(lactic acid)-based bionanocomposites

In order to improve the thermal stability of cellulose nanocrystals (CNCs) and to weaken their hydrophilicity, extensive research has been conducted to graft hydrophobic molecular chains on CNC surfaces to cover and/or replace hydroxyl and sulfate ester groups. According to our previous research, it was proposed that triazine derivative is an ideal candidate to modify CNCs. In this study, triazine derivative-grafted CNCs were synthesized and incorporated into poly(lactic acid) (PLA) nanocomposites as a reinforcing filler. The synthesis of triazine derivative was confirmed by FT-IR and the characterization of modified CNCs was determined by TEM, FT-IR,13C NMR, EDX, TGA and contact angle measurements. It was found that the triazine derivative was successfully grafted onto the CNC surfaces. The thermal stability of the modified CNCs was improved, and hydrophobic CNCs were obtained. Moreover, the properties of CNC/PLA composites were investigated by SEM, UV–Vis spectrophotometer and DSC, and the mechanical properties of composites were measured. The compatability of the modified CNCs with the PLA matrix was improved, and the mechanical properties of PLA composites were improved without serious destruction of their transmittance.

Optimizing the yield and physico-chemical properties of pine cone cellulose nanocrystals by different hydrolysis time

Cellulose nanocrystals (CNCs) were isolated for the first time from pine cones (PC) by alkali and bleaching treatments and subsequent sulfuric acid hydrolysis (64%) at 45 °C. The influence of the hydrolytic reaction time (30, 45, and 90 min) on the yield, chemical composition and structure, and thermal stability of CNCs was evaluated. The removal of non-cellulosic constituents during the alkaline and bleaching treatment resulted in high pure cellulosic fibres. The isolation of CNCs from these cellulosic fibres at different reaction times was verified by the nano-dimensions of the individual crystals (< 3 and < 335 nm of average diameter and length, respectively). The highest yield (15%) and the optimum CNCs properties in terms of aspect ratio, thermal stability and crystallinity were obtained for an extraction time of 45 min. PC appeared to be a new promising source of cellulose fibres and CNCs with potential to be applied as reinforcement in composites and for food-packaging.

Thermal stability of cellulose nanocrystals prepared by succinic anhydride assisted hydrolysis

A variety of techniques have recently been developed that enable manufacturing of cellulose nanomaterials with optimal properties for certain applications. Acid catalyzed hydrolysis is currently the most popular method for the synthesis of cellulose nanocrystals (CNCs). However, the type of acids and hydrolysis conditions influence the CNCs thermal stability which is crucial parameter in polymer composite technology. In this work thermally stable CNCs were prepared by two step method − (i) hydrolysis in phosphoric acid solutions to produce fine microcrystalline cellulose (MCC), (ii) followed by modification of MMC with succinic anhydride (SA). The method allowed manufacturing CNC-SA material that showed higher thermal stability than the reference cellulose material (UFC-raw) both in the inert gas and air atmosphere. The kinetic parameters of the thermal degradation process of produced cellulose materials were determined by Friedman and Ozawa-Flynn-Wall model-free methods and compared with CNCs prepared in sulfuric acid. On the basis of changes of apparent activation energy Ea a plausible mechanism of stabilization was discussed. The presented results showed the technological potential of organic acid anhydride application for manufacturing and thermal stabilization of CNCs.

Cellulose nanocrystals with different length-to-diameter ratios extracted from various plants using novel system acetic acid/phosphotungstic acid/octanol-1

The novel system [acetic acid/phosphotungstic acid (H3PW12O40)/octanol] was proposed for catalytic solvolysis of cellulose and for obtaining cellulose nanocrystals (CNC). Several alternative experiments involving mixtures with different compositions were carried out; reaction time was also varied. CNC particles from cotton, linen, softwood and hardwood cellulose were prepared in the experiments performed for 40 min in the presence of 0.25 mol% of the heteropolyacid. CNC samples were characterized by transmission electron microscopy and atomic force microscopy, X-ray diffraction analysis, and thermogravimetric analysis. It was established that the resulting nanoparticles had high crystallinity and rod-like shape; their length varied from 160 to 400 nm (cotton CNC had the shortest length, and linen CNC had the longest length), and CNC thickness ranged from 6 to 10 nm. Thermal stability of CNC was lower than that of initial celluloses and decreasing in the following sequence: cotton > softwood > hardwood > linen cellulose.

Thermal stability increase in metallic nanoparticles-loaded cellulose nanocrystal nanocomposites

Due to the potential of CNC-based flexible materials for novel industrial applications, the aim of this work is to improve the thermal stability of cellulose nanocrystals (CNC) films through a straightforward and scalable method. Based of nanocomposite approach, five different metallic nanoparticles (ZnO, SiO2, TiO2, Al2O3 and Fe2O3) have been co-assembled in water with CNCs to obtain free-standing nanocomposite films. Thermogravimetric analysis (TGA) reveals an increased thermal stability upon nanoparticle. This increase in the thermal stability reaches a maximum of 75°C for the nanocomposites having 10wt% of Fe2O3 and ZnO. The activation energies of thermodegradation process (Ea) determined according to Kissinger and Ozawa-Flynn-Wall methods further confirm the delayed degradation of CNC nanocomposites upon heating. Finally, the changes induced in the crystalline structure during thermodegradation were followed by wide angle X-ray diffraction (WAXD). It is also observed that thermal degradation proceeds at higher temperatures for nanocomposites having metallic nanoparticles. Overall, experimental findings here showed make nanocomposite approach a simple low-cost environmentally-friendly strategy to overcome the relatively poor thermal stability of CNCs when extracted via sulfuric acid assisted hydrolysis of cellulose.

Novel modified nanocellulose applicable as reinforcement in high-performance nanocomposites

The influence of modification and vacuum/supercritical CO2 (scCO2) drying methods on the surface properties, morphology and thermal stability of cellulose nanocrystals (NC) was presented in this study. Introduction of reactive vinyl groups on NC surface was performed by either direct esterification with oleic acid, linseed or sunflower oil fatty acids; or by amidation of maleic acid/ethylene diamine with methyl ester of fatty acid. Obtained modified NC (m-NC) were characterized using FTIR and Raman spectroscopy; and by determination of acid, iodine and ester values. Structural analysis of m-NC showed varieties of forms, from spongy to nanostructural non-uniform layered morphology with observable agglomeration, which confirmed morphology dependence on modification/processing methods Thermogravimetry-MS spectrometry showed different thermal stability and degradation pathways of NC/m-NC. Incorporation of 1 wt% of reactive m-NC in unsaturated polyester lead to high performance nanocomposites and contributed to increase of stress at break in the range from 76 to 93%.

Characterization of Cellulose Nanocrystals Extracted from Sugarcane Bagasse for Potential Biomedical Materials

Cellulose nanocrystals (CNCs) were extracted by sulfuric acid from cellulose purified via an environmentally friendly method. In this study, cellulose obtained from sugarcane bagasse (SCB) using steam-exploded and enzyme-treated pretreatment was confirmed using chemical composition analysis to have a 92.59 ± 0.12 whiteness index and 87% α-cellulose content. The morphology of extracted CNCs, characterized using atomic force microscopy images, transmission electron microscopy images and energy-dispersive x-rays, showed the diameter and length were in the ranges 9.8 ± 6.3 and 280.1 ± 73.3 nm, respectively, with an expected ratio (L/d) of 20–25 and a low concentration of sulfate (0.2%) on surface particles. Moreover, fourier transformed infrared spectroscopy and X-ray diffraction results demonstrated free noncellulosic contents and an improved crystallinity for CNCs, respectively. A decrease in the thermal stability of CNCs was examined by thermogravimetric analysis, and no evidence of cytotoxicity in the CNCs was obtained. The isolated CNCs from SCB may be considered as a potential biomedical material.

Effect of polymorphs of cellulose nanocrystal on the thermal properties of poly(lactic acid)/cellulose nanocrystal composites.

Cellulose nanocrystals (CNCs) with different polymorphs CNC I and II were fabricated from native and mercerized microcrystalline cellulose (MCC) by sulfuric acid hydrolysis. CNC I and II were successfully acetylated by a "green" method, which was performed in an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4). X-ray diffraction (XRD) proved that the crystal structure of CNC I and II was maintained after acetylation. Transmission electron microscopy (TEM) showed the rod-like structure for acetylated CNC I and spherical crystal morphologies for acetylated CNC II. Thermogravimetric analysis (TGA) revealed that the thermal stability of CNC I and II was enhanced after acetylation. The effect of CNC polymorphs on the crystallization behavior and thermal stability of poly(lactic acid)/acetylated CNC (PLA/ACN) composites was investigated by differential scanning calorimetry (DSC) and TGA, respectively. It was found that compared to ACN I, ACN II was better able to promote the cold crystallization of PLA-based composites, and PLA/ ACN II possessed higher thermal stability.

Isolation and characterization of cellulose nanocrystals from parenchyma and vascular bundle of oil palm trunk (Elaeis guineensis)

In this study cellulose nanocrystals were isolated through acid hydrolysis process from parenchyma and vascular bundle of oil palm trunk (Elaeis guineensis). The morphological properties of obtained cellulose nanocrystals were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microscopy images showed smoother and cleaner surface of parenchyma cellulose nanocrystals when compared to vascular bundle cellulose nanocrystals. The TEM image shows a higher length and diameter for parenchyma cellulose nanocrystals compared to vascular bundle cellulose nanocrystals. The Fourier transform infrared (FTIR) spectra showed changes in functional groups after acid hydrolysis due to removal of lignin, hemicelluloses and other impurities in both type of cellulose nanocrystals. Crystallinity index of cellulose nanocrystals was observed higher for vascular bundle as compared to parenchyma. Thermogravimetric analysis (TGA) was performed to study the thermal stability of cellulose nanocrystals and it was observed higher for parenchyma cellulose nanocrystals compared to vascular bundle.