Extensional rheometry of cellulose ether solutions: flow instability

Capillary breakup extensional rheometryof semi-dilute hydroxyethyl cellulose (HEC) solutionswas performed under several step-stretch conditions.The resulting parameters, i.e. terminal steady stateextensional viscosity (gE) and the timescale forviscoelastic stress growth, commonly referred to asthe extensional relaxation time (kE) were found to besensitive to the step-stretch conditions. The kEdecreased with increasing step-strain as opposed tothe gE. Prior to the filament break-up, a ‘bead-onstring’instability was observed close to the mid-plane.It is believed that this instability originated from theaccumulation of viscoelastic stresses near the filamentneck leading to the ‘elastic recoil’ of the extendedpolymer chains. The reasons for this belief arediscussed in detail with the perspective of the pastliterature. Such type of flow instability has beenreported for the first time for a cellulosic system.Various dimensionless numbers were plotted for theHEC solutions and compared with those obtained frompast studies for various biopolymers as well assynthetic polymers

Aqueous solutions of HEC and hmHEC: effects of molecular mass versus hydrophobic associations on hydrodynamic and thermodynamic parameters.

Aqueous solutions of amphiphilic polymersusually comprise of inter- and intramolecularassociations of hydrophobic groups often leading to aformation of a rheologically significant reversiblenetwork at low concentrations that can be identifiedusing techniques such as static light scattering andrheometry. However, in most studies published tilldate comparing water soluble polymers with theirrespective amphiphilic derivatives, it has been verydifficult to distinguish between the effects of molecularmass versus hydrophobic associations on hydrodynamic(intrinsic viscosity [g]) and thermodynamicparameters (second virial coefficient A2), owing to thedifferences between their degrees of polymerization.This study focuses on the dilute and semi-dilutesolutions of hydroxyethyl cellulose (HEC) and itsamphiphilic derivatives (hmHEC) of the same molecularmass, along with other samples having a differentmolecular mass using capillary viscometry, rheometryand static light scattering. The weight average molecularmasses (MW) and their distributions for the nonassociativeHEC were determined using size exclusion chromatography. Various empirical approaches developedby past authors to determine [g] from dilute solution viscometry data have been discussed. hmHEC with a sufficiently high degree of hydrophobic modification was found to be forming a rheologically significant network in dilute solutions at very low concentrations as opposed to the hmHEC with a much lower degree of hydrophobic modification which also enveloped the hydrophobic groups inside the supramolecular cluster as shown by their [g] and A2.The ratio A2MW/[g], which takes into account hydrodynamic as well as thermodynamic parameters, wasobserved to be less for associative polymers comparedto that of the non-associative polymers

Design data for the 3D printer modification to print gels and pastes and the corresponding firmware

In order to deposit gel and paste-like materials, a commercially available HICTOP Prusa i3 plastic 3D printer was modified. The modification included replacing the existing plastic microextruder with a customised 3D printed syringe pump which could hold a syringe containing the printing material. The arrangement also allowed the temperature in the syringe to be controlled. Since the hardware of the printer was changed significantly, a new firmware was loaded on the 3D printer which was customised to enable it to perform its new function.The present data consists of the 3D image files of the syringe pump assembly and instructions on how to assemble the components. It also provides a copy of the modified firmware with a list of the changes made to it.This data will allow the readers to modify a similar type of 3D printer to print pastes and gels. This can be achieved by recreating the entire syringe pump assembly by 3D printing the given 3D image file data. With some changes, these designs can also be adapted to a variety of different printers. Similarly, the given firmware can also be loaded onto a similar type of printer. The list and explanation of the changes made to the firmware also allow such changes to be made to the respective firmwares of a variety of different printers

High-shear rate rheometry of micro-nanofibrillated cellulose (CMF/CNF) suspensions using rotational rheometer

Suspensions of cellulose micro- and nanofibrils are widely used in coatings, fibre spinning, 3D printing and as rheology modifiers where they are frequently exposed to shear rates > 104 s−1, often within small confinements. High-shear rate rheological characterisation for these systems is therefore vital. Rheological data at high-shear rates are normally obtained using capillary and microfluidic rheometers, which are found in relative scarcity within research facilities compared to rotational rheometers. Also, secondary flows and wall depletion prevalent at such high-shear rates often go unnoticed or unquantified, rendering the measurement data unreliable. Reliable high shear rate rheometry using rotational rheometers is therefore desirable. Suspension of TEMPO-oxidised CMF/CNF was tested for its high-shear rate rheological properties using parallel plate geometry at measurement gaps 150–40 µm and concentric cylinder at 1 mm gap. The errors from gap setting, radial dependence of shear stress and wall depletion were quantified and accounted for. Viscosity data from 0.1 to 30,000 s−1 shear rates was constructed using both geometries in agreement. Possibilities of secondary flows, radial migration of fluid and viscous heating were ruled out