Evaluating the state of dispersion on cellulosic biopolymer by rheology (original) (raw)
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Rheology of the cellulose nanocrystals filled poly(ε-caprolactone) biocomposites
Polymer, 2018
The pristine and acetylated cellulose nanocrystal (CNC) particles were incorporated with poly(ε-caprolactone) to prepare two kinds of green nanocomposite systems: the former is incompatible, while the latter compatible thermodynamically. A rheological study was then performed systematically with various flow fields, including linear and nonlinear dynamic shear flow, creep and start-up flow. Some interesting results were shown then. The pristine CNC filled system shows far lower percolation threshold than the acetylated CNC filled one because the improved phase affinity yields diluent effect. The formation and rebuild-up of percolated network is driven by the Brownian motion of particles, which are nearly independent of altered phase affinity. However, the improved phase affinity makes the system more sensitive to the strain-responded deformation, leading to the reinforced Maxwell spring unit during creep and to a weak strain overshoot during dynamic flow. The structural evolution and relaxations of two systems were further evaluated from different perspectives.
A large amount of non-recyclable waste generated by different sectors has become a serious problem for the environment. Among the waste generated by different sectors, plastic waste shares a major part. The generated plastic disposals and non-recyclable material keep accumulating in the environment and over a period of time, it does not only occupy the land space but also contaminate air and groundwater. Polylactic acid (PLA) has been proved as one of the most promising biodegradable polymers (biopolymers) and has been the subject of abundant literature studied over the last decade. PLA can be processed with a large number of techniques and is commercially available (large-scale production) in a wide range of grades. It is relatively cheap and can be combined with cellulose and other polymers easily and has remarkable properties, which make it suitable for a variety of applications. The objective of this project is to prepare bioplastics with natural fibers to reduce the cost & promote degradable material. In this project, we report, the study of mechanical & rheological properties of PLA-cellulose composite. A few experiments have been performed to prepare PLA-cellulose composite by varying degrees of cellulose crystals-PLA composition namely (1:1, 2%, 3% of cellulose in PLA). Keywords: PLA, biocomposite, cellulose fiber, rheological, mechanical properties.
Journal of Polymers and the Environment, 2012
Bionanocomposites of poly(lactic acid) (PLA) and chemically modified, nanofibrillated cellulose (NFC) powders were prepared by extrusion, followed by injection molding. The chemically modified NFC powders were prepared by carboxymethylation and mechanical disintegration of refined, bleached beech pulp (c-NFC), and subsequent esterification with 1-hexanol (c-NFC-hex). A solvent mix was then prepared by precipitating a suspension of c-NFC-hex and acetone-dissolved PLA in ice-cold isopropanol (c-NFC-hex sm), extruded with PLA into pellets at different polymer/fiber ratios, and finally injection molded. Dynamic mechanical analysis and tensile tests were performed to study the reinforcing potential of dried and chemically modified NFC powders for PLA composite applications. The results showed a faint increase in modulus of elasticity of 10 % for composites with a loading of 7.5 % w/w of fibrils, irrespective of the type of chemically modified NFC powder. The increase in stiffness was accompanied by a slight decrease in tensile strength for all samples, as compared with neat PLA. The viscoelastic properties of the composites were essentially identical to neat PLA. The absence of a clear reinforcement of the polymer matrix was attributed to poor interactions with PLA and insufficient dispersion of the chemically modified NFC powders in the composite, as observed from scanning electron microscope images. Further explanation was found in the decrease of the thermal stability and crystallinity of the cellulose upon carboxymethylation.
Rheological behavior of cellulose nanocrystal suspensions in polyethylene glycol
Journal of Rheology, 2018
The rheological behavior of cellulose nanocrystals (CNCs) in polar media based on polyethylene glycol (PEG) was investigated from aqueous suspensions to nanocomposites. The aim of this work is to improve our knowledge on the CNC behavior in polymer media and develop rheological indices to characterize the dispersion of nanoparticles in polymer matrices. CNCs were obtained from sulfuric acid hydrolysis of wood pulp and supplied after a spray-or freeze-drying process. Ultrasonication was used to break agglomerates and disperse CNCs in aqueous suspensions before mixing with an aqueous PEG solution at room temperature. The samples were subsequently dried and compression molded. From capillary and oscillatory shear rheology, no adsorption of PEG chains on CNCs could be detected, as many had previously hypothesized. The increase of PEG concentration in aqueous suspension favored the gelation by depletion effect and suggested CNC orientation. Viscoelastic properties and transmission electronic images of PEG/CNC nanocomposites highlighted the formation of a percolated network of CNCs for low concentrations 0.15 vol%. From Shih et al.'s model, a fractal dimension of 2 was obtained for these percolated nanocomposites, suggesting a 2D network of CNCs in the PEG matrix.
Journal of Applied Polymer Science, 2014
The rheological behavior of cellulose nanocrystals (CNCs) in polar media based on polyethylene glycol (PEG) was investigated from aqueous suspensions to nanocomposites. The aim of this work is to improve our knowledge on the CNC behavior in polymer media and develop rheological indices to characterize the dispersion of nanoparticles in polymer matrices. CNCs were obtained from sulfuric acid hydrolysis of wood pulp and supplied after a spray-or freeze-drying process. Ultrasonication was used to break agglomerates and disperse CNCs in aqueous suspensions before mixing with an aqueous PEG solution at room temperature. The samples were subsequently dried and compression molded. From capillary and oscillatory shear rheology, no adsorption of PEG chains on CNCs could be detected, as many had previously hypothesized. The increase of PEG concentration in aqueous suspension favored the gelation by depletion effect and suggested CNC orientation. Viscoelastic properties and transmission electronic images of PEG/CNC nanocomposites highlighted the formation of a percolated network of CNCs for low concentrations ! 0.15 vol. %. From the model of Shih et al., a fractal dimension of 2 was obtained for these percolated nanocomposites, suggesting a 2D network of CNCs in the PEG matrix. V
2016
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Applied Rheology, 2018
Novel-produced never-dried and dried microcrystalline cellulose (MCC) was previously compared with a commercial MCC. The novel MCC was shown to be a suitable starting material for producing cellulose nanofibrils, in turn having similar molecular weight Mw, crystallinity, and particle size comparable to those from sequentially enzymatic and mechanically treated softwood sulphite pulp, but at lower cost. The study here presents a rheological parameterisation of the aqueous suspension throughout the process, aimed at delivering a correlation between specific surface area, at equal material particle size, and adsorptive coupling between neighbouring cellulose particles and interstitial water under flow. We conclude that combining dynamic viscosity with an independent measure of particle size provides a suitable quality control of MCC-derived cellulose nanofibrils, obviating the need for individual property-raw material relationships to be evaluated, and this principle may provide a gene...
Rheological, Mechanical, and thermal properties of polylactide/cellulose nanofiber biocomposites
Polymer Composites, 2016
Different PA/PVB blends and PA/PVB/nanoclay nanocomposites were prepared and their rheological, mechanical and thermal properties were studied and correlated with their phase morphology. According to the morphological observations, phase inversion occurred near 60 wt.% PVB. Also, the TEM micrographs showed that nanoclay particles mostly localized in the interface of the PA and PVB phases. The rheological properties of the blends were considerably influenced by the morphological changes. In fact, increase in the PVB weight fraction and nanofiller content led to changes in flow behavior of the samples, especially near the phase inversion point. Good agreement between the experimental results and predictions of different models were seen for the tensile behavior of the blends. The blends containing 50-60 wt.% PVB possessed promising impact strengths. Furthermore, localization of the Cloisite 30B at the interface helped to achieve extensive plastic deformation, and hence high toughness for the PA/PVB50 blend filled with 1 phr nanoclay. Investigation of Izod impact-fractured surfaces showed that cavitation and multiple crazing are the main toughening mechanisms in the blends. The TGA analysis suggested that the thermal degradation of the PVB is improved by blending with PA, while incorporation of nanoclay didn't have any significant effect on thermal stability of the blends.
Cellulose Nanoparticles: Structure–Morphology–Rheology Relationships
ACS Sustainable Chemistry & Engineering, 2015
The present study aims to investigate the structure− morphology−rheology relationships for cellulose nanoparticles (CNPs), including cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs). CNCs were extracted from never dried CNFs using sulfuric acid with controlled hydrolysis time. The crystalline structure, surface charge, morphology, and rheological behavior of the CNPs were measured and contrasted. The CNF suspensions exhibited rigid solid-like viscoelastic behavior even at a low concentration due to the formation of a highly entangled network. Upon acid hydrolysis, the network of rigid, long, and highly entangled nanofibers was eliminated, resulting in a significant loss of viscoelastic properties. Both steady-state and dynamic rheological measurements showed that the rheological behavior of the CNC suspensions was strongly dependent on the concentration and acid hydrolysis time. The CNC suspensions exhibited elastic gel-like rheological behavior at high concentrations but viscous liquid-like rheological behavior at low concentrations. Longer acid hydrolysis time produced CNCs with a lower aspect ratio, leading to higher critical transition concentration for the formation of anisotropic phase. The aspect ratio of CNCs was predicted from the intrinsic viscosity using the Simha's equation. The theoretically predicted aspect ratio values corresponded well with the transmission electron microscopy results. Finally, the network of CNF and CNC suspensions were schematically proposed.
Fibres & Textiles in Eastern Europe, 2007
The dissolving of cellulose in suitable solvents to prepare fibre-forming and film-forming solutions has been a very attractive field of research for more than a hundred years. In this paper we present the rheological properties of alkali solutions of enzyme-treated cellulose (BiocelsolTM) and the blend of Biocelsol-viscose solutions. The effect of solution composition, storage temperature and time on the viscosity and deviation from the Newtonian flow were investigated. The reproducibility of the basic rheological parameters of Biocelsol alkali solutions was also investigated. The effect of the rheological properties of Biocelsol/viscose blend solutions on the tenacity of the regenerated cellulose films is discussed, as well.