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In this paper, with the application of a MARS 60 high-pressure rheometer, experimental tests are conducted on Shengli crude oil to test its gel point, viscosity and thixotropy under different static pressures. Consequently, the effect of static pressure on the rheological parameters of waxy crude oil is revealed. It is proven that with the increase in the static pressure, the gel point of Shengli crude oil increases linearly, and the viscosity also gradually increases. The power law equation is employed to describe the relationship between the apparent viscosity and shear rate of Shengli crude oil under different static pressures. With the increase in the static pressure, the consistency coefficient (K) increases linearly, and the rheological index (n) decreases linearly. The relationship between the viscosity of Shengli crude oil and the static pressure and shear rate can be obtained. The Cross thixotropic model is used to describe the thixotropic curve of Shengli crude oil under different static pressures. With the increase in the static pressure, the thixotropic coefficient of consistency (ΔK) and the structure fracture constant (b) increase linearly. This is because a high pressure results in high structure strength and strong non-Newton rheological behavior in gelled crude oil and also causes remarkable structure fracture in crude oil. The results in this paper can provide an important theoretical basis for crude oil production and transportation. [ABSTRACT FROM AUTHOR]

The present work is focused on the study of polyurethane adhesives in the presence of functional fillers (encapsulated enzymes) intended to make them degradable. This is part of a general strategy aiming to recycle multilayer films for packaging, at their end of life, by means of separating the constituent layers as a result of adhesives degradation. Primarily, it was found that the presence of small quantities of functional filler greatly affects both, the quality of the coating process and the kinetics of the adhesive curing. The former, because of the dependency on particle size distribution, leads to high variations in thickness and mechanical properties of multilayers and, the latter, because of a significant catalytic effect (higher curing rates). Indeed, an assessment of the adhesives' kinetics by rheology showed that the pot‐life and the cross‐over point (G′ = G″) for the enzyme‐containing system were obtained three times faster in comparison to the control formulation. These findings were also confirmed by differential scanning calorimetry measurements. On the other hand, by reducing and homogenizing the filler's particle size using separated sieved material (≤50 μm), improvements in coating control as well as in the quality and final properties of the multilayers were evidenced. Highlights: Recycling multilayer plastic films for flexible packaging.Encapsulated enzymes to degrade the polyurethane adhesive in specific conditions.The presence of functional fillers affects the coating process.Process optimization to ensure the coating quality control. [ABSTRACT FROM AUTHOR]

We investigated the shear thinning of normal and diabetic blood experimentally. The shear thinning of the blood has been analyzed using the Power-law model. Over the viscosity time course, the coagulation process of blood samples from diabetic and healthy subjects was observed. The shear thinning behavior of blood samples was examined in the shear rate ranging from 5 s−1 to 222 s−1, and viscosity time-course was studied at a shear rate of 50 s−1. The consistency coefficients were 8.638 ± 0.4860 mPa·s, and 6.658 ± 0.3219 mPa·s for diabetic blood and control, respectively. This difference was statistically significant (p < 0.0001). The parameters extracted from the viscosity–time curve were the time-to-gel point (TGP), maximum clot viscosity (MCV), and final clot viscosity (FCV). The diabetic blood exhibited a significantly high (p < 0.0001) shorter TGP (148.8 ± 6.024 s) than control (199.1 ± 4.865 s). A considerably higher MCV for diabetic blood (26.39 ± 1.451 cP) than the control (17.54 ± 2.324 cP) was reported. FCV for diabetic blood (10.89 ± 1.12 cP) was significantly higher than control (7.6 ± 0.8 cP). The viscosity time course as well as features obtained via the power-law model reflected the flow state of diabetic blood.

We investigated the shear thinning of normal and diabetic blood experimentally. The shear thinning of the blood has been analyzed using the Power-law model. Over the viscosity time course, the coagulation process of blood samples from diabetic and healthy subjects was observed. The shear thinning behavior of blood samples was examined in the shear rate ranging from 5 s−1 to 222 s−1, and viscosity time-course was studied at a shear rate of 50 s−1. The consistency coefficients were 8.638 ± 0.4860 mPa·s, and 6.658 ± 0.3219 mPa·s for diabetic blood and control, respectively. This difference was statistically significant (p < 0.0001). The parameters extracted from the viscosity–time curve were the time-to-gel point (TGP), maximum clot viscosity (MCV), and final clot viscosity (FCV). The diabetic blood exhibited a significantly high (p < 0.0001) shorter TGP (148.8 ± 6.024 s) than control (199.1 ± 4.865 s). A considerably higher MCV for diabetic blood (26.39 ± 1.451 cP) than the control (17.54 ± 2.324 cP) was reported. FCV for diabetic blood (10.89 ± 1.12 cP) was significantly higher than control (7.6 ± 0.8 cP). The viscosity time course as well as features obtained via the power-law model reflected the flow state of diabetic blood. [ABSTRACT FROM AUTHOR]

Hyperbranched polymers (HBPs) are widely applied nowadays as functional materials for biomedicine needs, nonlinear optics, organic semiconductors, etc. One of the effective and promising ways to synthesize HBPs is a polyaddition of AB2+A2+B4 monomers that is generated in the A2+CB2, AA′+B3, A2+B′B2, and A2+C2+B3 systems or using other approaches. It is clear that all the foundational features of HBPs that are manufactured by a polyaddition reaction are defined by the component composition of the monomer mixture. For this reason, we have designed a structural kinetic model of AB2+A2+B4 monomer mixture polyaddition which makes it possible to predict the impact of the monomer mixture's composition on the molecular weight characteristics of hyperbranched polymers (number average (DPn) and weight average (DPw) degree of polymerization), as well as the degree of branching (DB) and gel point (pg). The suggested model also considers the possibility of a positive or negative substitution effect during polyaddition. The change in the macromolecule parameters of HBPs formed by polyaddition of AB2+A2+B4 monomers is described as an infinite system of kinetic equations. The solution for the equation system was found using the method of generating functions. The impact of both the component's composition and the substitution effect during the polyaddition of AB2+A2+B4 monomers on structural and molecular weight HBP characteristics was investigated. The suggested model is fairly versatile; it makes it possible to describe every possible case of polyaddition with various monomer combinations, such as A2+AB2, AB2+B4, AB2, or A2+B4. The influence of each monomer type on the main characteristics of hyperbranched polymers that are obtained by the polyaddition of AB2+A2+B4 monomers has been investigated. Based on the results obtained, an empirical formula was proposed to estimate the pg = pA during the polyaddition of an AB2+A2+B4 monomer mixture: pg = pA = (−0.53([B]0/[A]0)1/2 + 0.78)υAB2 + (1/3)1/2([B]0/[A]0)1/2, where (1/3)1/2([B]0/[A]0)1/2 is the Flory equation for the A2+B4 polyaddition, [A]0 and [B]0 are the A and B group concentration from A2 and B4, respectively, and υAB2 is the mole fraction of the AB2 monomer in the mixture. The equation obtained allows us to accurately predict the pg value, with an AB2 monomer content of up to 80%. [ABSTRACT FROM AUTHOR]

When applying electron or gamma irradiation to poly-3-hydroxybutyrate (P3HB), main chain scissions are the dominant material reactions. Though propositions have been made that crosslinking in the amorphous phase of P3HB occurs under irradiation, a conclusive method to achieve controlled additive free irradiation crosslinking has not been shown and no mechanism has been derived to the best of our knowledge. By applying irradiation in a molten state at 195 °C and doses above 200 kGy, we were able to initiate crosslink reactions and achieved gel formation of up to 16%. The gel dose Dgel was determined to be 200 kGy and a range of the G values, the number of scissions and crosslinks for 100 eV energy deposition, is given. Rheology measurements, as well as size exclusion chromatography (SEC), showed indications for branching at doses from 100 to 250 kGy. Thermal analysis showed the development of a bimodal peak with a decrease in the peak melt temperature and an increase in peak width. In combination with an increase in the thermal degradation temperature for a dose of 200 kGy compared to 100 kGy, thermal analysis also showed phenomena attributed to branching and crosslinking. [ABSTRACT FROM AUTHOR]

Any thermoset resin's processing properties and end-use performance are heavily influenced by the gel time. The complicated viscosity of resin as a function of temperature is investigated in this work, with a particular emphasis on identifying the gel point and comprehending polymerization. Rheology studies carried out using a plate-plate controlled stress rheometer under isothermal conditions were used to compare three experimental techniques for figuring out an epoxy resin's gel point. We also look at the basic modifications that take place during polymerization. We verify the reliability of the three strategies by including Principal Component Analysis (PCA), an unsupervised machine learning methodology. PCA assists in uncovering hidden connections between these methods and various affecting factors. PCA serves a dual role in our study, confirming method validity and identifying patterns. It sheds light on the intricate relationships between experimental techniques and material properties. This concise study expands our understanding of resin behavior and provides insights that are essential for optimizing resin-based processes in a variety of industrial applications. [ABSTRACT FROM AUTHOR]

This study aims to provide a comprehensive understanding of the key factors influencing the rheological behavior and the mechanisms of natural polyelectrolyte complexes (PECs) as flocculation agents for cellulose microfibers (CMFs) and nanofibers (CNFs). PECs were formed by combining two polyelectrolytes: xylan (Xyl) and chitosan (Ch), at different Xyl/Ch mass ratios: 60/40, 70/30, and 80/20. First, Xyl, Ch, and PEC solutions were characterized by measuring viscosity, critical concentration (c*), rheological parameter, ζ-potential, and hydrodynamic size. Then, the flocculation mechanisms of CMF and CNF suspensions with PECs under dynamic conditions were studied by measuring viscosity, while the flocculation under static conditions was examined through gel point measurements, floc average size determination, and ζ-potential analysis. The findings reveal that PEC solutions formed with a lower xylan mass ratio showed higher intrinsic viscosity, higher hydrodynamic size, higher z-potential, and a lower c*. This is due to the high molecular weight, charge, and gel-forming ability. All the analyzed solutions behave as a typical non-Newtonian shear-thinning fluid. The flocculation mechanisms under dynamic conditions showed that a very low dosage of PEC (between 2 and 6 mg PEC/g of fiber) was sufficient to produce flocculation. Under dynamic conditions, an increase in viscosity indicates flocculation at this low PEC dosage. Finally, under static conditions, maximum floc sizes were observed at the same PEC dosage where minimum gel points were reached. Higher PEC doses were required for CNF suspensions than for CMF suspensions. [ABSTRACT FROM AUTHOR]

Any thermoset resin’s processing properties and end-use performance are heavily influenced by the gel time. The complicated viscosity of resin as a function of temperature is investigated in this work, with a particular emphasis on identifying the gel point and comprehending polymerization. Rheology studies carried out using a plate-plate controlled stress rheometer under isothermal conditions were used to compare three experimental techniques for figuring out an epoxy resin’s gel point. We also look at the basic modifications that take place during polymerization. We verify the reliability of the three strategies by including Principal Component Analysis (PCA), an unsupervised machine learning methodology. PCA assists in uncovering hidden connections between these methods and various affecting factors. PCA serves a dual role in our study, confirming method validity and identifying patterns. It sheds light on the intricate relationships between experimental techniques and material properties. This concise study expands our understanding of resin behavior and provides insights that are essential for optimizing resin-based processes in a variety of industrial applications.

This study aims to provide a comprehensive understanding of the key factors influencing the rheological behavior and the mechanisms of natural polyelectrolyte complexes (PECs) as flocculation agents for cellulose microfibers (CMFs) and nanofibers (CNFs). PECs were formed by combining two polyelectrolytes: xylan (Xyl) and chitosan (Ch), at different Xyl/Ch mass ratios: 60/40, 70/30, and 80/20. First, Xyl, Ch, and PEC solutions were characterized by measuring viscosity, critical concentration (c*), rheological parameter, ζ-potential, and hydrodynamic size. Then, the flocculation mechanisms of CMF and CNF suspensions with PECs under dynamic conditions were studied by measuring viscosity, while the flocculation under static conditions was examined through gel point measurements, floc average size determination, and ζ-potential analysis. The findings reveal that PEC solutions formed with a lower xylan mass ratio showed higher intrinsic viscosity, higher hydrodynamic size, higher z-potential, and a lower c*. This is due to the high molecular weight, charge, and gel-forming ability. All the analyzed solutions behave as a typical non-Newtonian shear-thinning fluid. The flocculation mechanisms under dynamic conditions showed that a very low dosage of PEC (between 2 and 6 mg PEC/g of fiber) was sufficient to produce flocculation. Under dynamic conditions, an increase in viscosity indicates flocculation at this low PEC dosage. Finally, under static conditions, maximum floc sizes were observed at the same PEC dosage where minimum gel points were reached. Higher PEC doses were required for CNF suspensions than for CMF suspensions.

The present work analyzes the effect of process variables and the method of characterization of cellulose micro/nanofibers (CMNFs) obtained by different treatments. A chemical pre-treatment was performed using oxalic acid at 25 wt.% and 50 wt.%. Moreover, for mechanical pre-treatments, a rotary homogenizer or a PFI mill refiner were considered. For the mechanical fibrillation to obtain CMNFs, 5 and 15 passes through a pressurized homogenization were considered. The best results of nanofibrillation yield (76.5%), transmittance (72.1%) and surface charges (71.0 µeq/g CMNF) were obtained using the PFI mill refiner, 50 wt.% oxalic acid and 15 passes. Nevertheless, the highest aspect ratio (length/diameter) determined by Transmission Electron Microscopy (TEM) was found using the PFI mill refiner and 25 wt.% oxalic acid treatment. The aspect ratio was related to the gel point and intrinsic viscosity of CMNF suspensions. The values estimated for gel point agree with those determined by TEM. Moreover, a strong relationship between the intrinsic viscosity [η] of the CMNF dispersions and the corresponding aspect ratio (p) was found (ρ[η] = 0.014 p2.3, R2 = 0.99). Finally, the tensile strength of films obtained from CMNF suspensions was more influenced by the nanofibrillation yield than their aspect ratio. [ABSTRACT FROM AUTHOR]

In this study, soft magnesium silicates were prepared via sol-gel method starting from diethylphosphatoethyltriethoxysilane (SiP), magnesium ethoxide and magnesium acetate. The thermal reaction of the different systems without any solvent was studied by a thermogravimetric analysis coupled to gas chromatography and mass spectroscopy in order to identify the volatile by-products and then suggest a reaction mechanism. The identification of several by-products formed during the reactions evidenced a non-hydrolytic sol-gel based route between the ethoxy and acetoxy groups of magnesium ethoxide and magnesium acetate respectively with the ethoxy groups of SiP. In addition, X-ray photoelectron spectroscopy analyses highlighted the creation of Mg–O–Si bonds. The viscoelastic behavior of the reactive systems allowed to confirm the formation of the network but also the determination of the gelation time. It corresponded respectively to 2150 and 1020 s for the reaction between magnesium ethoxide and SiP and magnesium acetate and SiP carried out at 170 °C. All these data confirm the formation of a "soft" inorganic network in that range of temperature. Highlights: Soft magnesium silicate were obtained through a solvent free sol–gel chemistry XPS analysis confirmed the formation of Si–O–Mg bonds. Sol–gel transition is observed at 2150 s at 170 °C for magnesium ethoxide + SiP reactions. Sol–gel transition is observed at 1020 s at 170 °C for magnesium acetate + SiP reactions. [ABSTRACT FROM AUTHOR]

The dispersion degree of cellulose micro and nanofibrils (CMFs/CNFs) in water suspensions is key to understand and optimize their effectiveness in several applications. In this study, we proposed a method, based on gel point (Øg), to calculate both aspect ratio and dispersion degree. This methodology was validated through the morphological characterization of CMFs/CNFs by Transmission Electronic Microscopy. The influence of dispersion degree on the reinforcement of recycled cardboard has also been evaluated by stirring CMF/CNF suspensions at different speeds. Results show that as stirring speed increases, Øg decreased to a minimum value, in which the aspect ratio is maximum. Then, Øg increased again. Suspensions with lower Øg, in the intermediate region of agitation present very good dispersion behavior with an open and spongy network structure, in which nanofibril clusters are totally dispersed. Higher stirring speeds shorten the nanofibrils and the networks collapse. Results show that the dispersion of the nanocellulose at the minimum Øg before their addition to the pulp, produces higher mechanical properties, even higher than when CNFs and pulp are agitated together. This method allows for the determination of the CMF/CNF dispersion, to maximize their behavior as strength agents. This knowledge would be crucial to understand why some industrial trials did not give satisfactory results. [ABSTRACT FROM AUTHOR]

Current knowledge on the properties of different types of cellulose nanofibers (CNFs) is fragmented. Properties variation is very extensive, depending on raw materials, effectiveness of the treatments to extract the cellulose fraction from the lignocellulosic biomass, pretreatments to facilitate cellulose fibrillation and final mechanical process to separate the microfibrils. Literature offers multiple parameters to characterize the CNFs prepared by different routes. However, there is a lack of an extensive guide to compare the CNFs. In this study, we perform a critical comparison of rheological, compositional, and morphological features of CNFs, produced from the most representative types of woody plants, hardwood and softwood, using different types and intensities of pretreatments, including enzymatic, chemical and mechanical ones, and varying the severity of mechanical treatment focusing on the relationship between macroscopic and microscopic parameters. This structured information will be exceedingly useful to select the most appropriate CNF for a certain application based on the most relevant parameters in each case. [ABSTRACT FROM AUTHOR]

The influences of several operating factors on the viscosity of the Isfahan refinery waxy crude oil sample are studied through conducting some rheological shear rotational tests. The Taguchi design method is adopted to determine the impact of factors such as shear rate, temperature, cooling rate, wax content, and asphaltene content on the viscosity of the waxy crude oil. The results show that temperature with a contribution of 53.61% is the most influential factor. The wax content, shear rate, and asphaltene content have a contribution of 20.86, 14.75, and 3.11% respectively. The cooling rate does not have a statistically significant effect on the viscosity. The results of the rheological oscillatory tests confirm that the temperature and wax content change the viscoelastic properties of the waxy crude oil completely. An increase in the wax content from 12 to 22 wt.% raises the wax appearance temperature (WAT) from 19.1 to 34.9 °C and improves the gel point from 13 to 34.1 °C. By decreasing the temperature or increasing wax content, the viscoelastic nature of the oil sample changes from a viscoelastic fluid to a viscoelastic solid.

The present work analyzes the effect of process variables and the method of characterization of cellulose micro/nanofibers (CMNFs) obtained by different treatments. A chemical pre-treatment was performed using oxalic acid at 25 wt.% and 50 wt.%. Moreover, for mechanical pre-treatments, a rotary homogenizer or a PFI mill refiner were considered. For the mechanical fibrillation to obtain CMNFs, 5 and 15 passes through a pressurized homogenization were considered. The best results of nanofibrillation yield (76.5%), transmittance (72.1%) and surface charges (71.0 µeq/g CMNF) were obtained using the PFI mill refiner, 50 wt.% oxalic acid and 15 passes. Nevertheless, the highest aspect ratio (length/diameter) determined by Transmission Electron Microscopy (TEM) was found using the PFI mill refiner and 25 wt.% oxalic acid treatment. The aspect ratio was related to the gel point and intrinsic viscosity of CMNF suspensions. The values estimated for gel point agree with those determined by TEM. Moreover, a strong relationship between the intrinsic viscosity [η] of the CMNF dispersions and the corresponding aspect ratio (p) was found (ρ[η] = 0.014 p2.3, R2 = 0.99). Finally, the tensile strength of films obtained from CMNF suspensions was more influenced by the nanofibrillation yield than their aspect ratio.

Nanocellulose is an emerging material that needs to be well characterized to control its performance during industrial applications. Gel point (Øg) is a convenient parameter commonly used to estimate the aspect ratio (AR) of cellulose nano/microfibers (CNFs/CMFs), providing critical information on the nanofiber network. However, its estimation requires many sedimentation experiments, tedious and time consuming. In this study, a simpler and faster technique is presented to estimate Øg, based on one or two sedimentation experiments, reducing the experiments by a factor of at least 2.5. Here, this new methodology is successfully validated by using the Øg of different CNF/CMF hydrogels calculated with the traditional methodology, showing an error lower than 7%. The error in the estimation of the AR is lower than 3% in all cases. Furthermore, the two mathematical models currently used to estimate Øg, the smoothing spline and the quadratic fit, are compared and the mathematical assumptions improved. [ABSTRACT FROM AUTHOR]

BACKGROUND: Diabetic ketoacidosis (DKA) is a medical emergency with a high mortality rate and is associated with severe metabolic acidosis and dehydration. DKA patients have an increased risk of arterial and venous thromboembolism, however little is known about this metabolic derangement in the first 24 hours of admission and to assess its effect on coagulation. We therefore utilised a novel functional marker of clot microstructure (fractal dimension - df) to assess these changes within the first 24 hours. METHODS: Prospective single centre observational study to demonstrate whether the tendency of blood clot formation differs in DKA patients. RESULTS: 15 DKA patients and 15 healthy matched controls were recruited. Mean df in the healthy control group was 1.74±0.03. An elevated df of 1.78±0.07 was observed in patients with DKA on admission. The mean pH on admission was 7.14±0.13 and the lactate was 3.6±2.0. df changed significantly in response to standard treatment and was significantly reduced to 1.68±0.09 (2–6& h) and to 1.66±0.08 at 24& h (p < 0.01 One-way ANOVA). df also correlated significantly with lactate and pH (Pearson correlation coefficient 0.479 and –0.675 respectively, p < 0.05). CONCLUSIONS: DKA patients at presentation have a densely organising less permeable thrombogenic clot microstructure as evidenced by high df. These structural changes are due to a combination of dehydration and a profound metabolic acidosis, which was reversed with treatment. These changes were not mirrored in standard clinical markers of thromboge-nicity. [ABSTRACT FROM AUTHOR]

Thermal hysteresis and stability of agarose–water gelling systems were studied by the spectrophotometer for different concentrations at different temperatures. Gelation temperature depends on the concentration of agarose. With the increase in the concentration of agarose gelation temperature, strength of agarose increases too. With the increase in the concentration of polymer solvent–gel phase transition, gel melting happens at higher temperatures. The price of enthalpy was determined (150.0127 KC/mol). In gelation process, the phase separation is completed and in this process, the value of this Δ t = t melting − t gelation equally increases. [ABSTRACT FROM AUTHOR]

The dispersion degree of cellulose micro and nanofibrils (CMFs/CNFs) in water suspensions is key to understand and optimize their effectiveness in several applications. In this study, we proposed a method, based on gel point (Øg), to calculate both aspect ratio and dispersion degree. This methodology was validated through the morphological characterization of CMFs/CNFs by Transmission Electronic Microscopy. The influence of dispersion degree on the reinforcement of recycled cardboard has also been evaluated by stirring CMF/CNF suspensions at different speeds. Results show that as stirring speed increases, Øg decreased to a minimum value, in which the aspect ratio is maximum. Then, Øg increased again. Suspensions with lower Øg, in the intermediate region of agitation present very good dispersion behavior with an open and spongy network structure, in which nanofibril clusters are totally dispersed. Higher stirring speeds shorten the nanofibrils and the networks collapse. Results show that the dispersion of the nanocellulose at the minimum Øg before their addition to the pulp, produces higher mechanical properties, even higher than when CNFs and pulp are agitated together. This method allows for the determination of the CMF/CNF dispersion, to maximize their behavior as strength agents. This knowledge would be crucial to understand why some industrial trials did not give satisfactory results.

In the current work, the thermal curing process of maleinated acrylated epoxidized linseed oil (MaAELO) mixed with reactive diluent, initiator, and accelerator was studied by using isothermal differential scanning calorimetry (DSC) and dynamic rheology. The investigations encompassed (1) the determination of the whole set of apparent kinetic parameters, Ea(α), A(α), and f(α) by using two accurate isoconversional kinetic analysis methods and the compensation effect, (2) the prediction of cure conversion curves, α(t), at arbitrary processing temperatures with all three kinetic parameters in comparison with the prediction based on Ea(α) alone, and (3) the determination of molecular and macroscopic gelation during the thermal cure of MaAELO resin mixture. The thermal cure of MaAELO resin mixture did not start immediately but after a remarkable induction period. It was possible to determine the kinetic parameters and use them to predict the induction period for arbitrary process temperature. In addition, the glass transition temperature, Tg, of thermally cured MaAELO resin mixture was measured by thermomechanical analysis and dynamic DSC. [ABSTRACT FROM AUTHOR]

The temperature and concentration dependences of the transmission spectrum of an aqueous solution of agar are investigated. Measurements taken in the heating and cooling modes show strong thermal hysteresis in the spectral properties. Analysis of the results suggests that the formation of a gel network occurs in a much narrower temperature range than its collapse. The study of the temperature dependence of transmittance indicates that the association bispirals by cooling the solution and responsible for the formation of network occurs at temperature about 4 0 ∘ C. A breakdown of these associates by heating of the gel begins at 6 0 ∘ C and covers a wide temperature range. The gel point T g and the gel melting point T m increase with increasing polymer concentration, but for T m this dependence is stronger. Growth of turbidity (light scattering) of gel by increasing of agar concentration is due to the increasing of number and size of gel associates. [ABSTRACT FROM AUTHOR]

The present paper proposes a novel approach for the morphological characterization of cellulose nano and microfibers suspensions (CMF/CNFs) based on the analysis of eroded CMF/CNF microscopy images. This approach offers a detailed morphological characterization and quantification of the micro and nanofibers networks present in the product, which allows the mode of fibrillation associated to the different CMF/CNF extraction conditions to be discerned. This information is needed to control CMF/CNF quality during industrial production. Five cellulose raw materials, from wood and non-wood sources, were subjected to mechanical, enzymatic, and (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidative pre-treatments followed by different homogenization sequences to obtain products of different morphologies. Skeleton analysis of microscopy images provided in-depth morphological information of CMF/CNFs that, complemented with aspect ratio information, estimated from gel point data, allowed the quantification of: (i) fibers peeling after mechanical pretreatment; (ii) fibers shortening induced by enzymes, and (iii) CMF/CNF entanglement from TEMPO-mediated oxidation. Being mostly based on optical microscopy and image analysis, the present method is easy to implement at industrial scale as a tool to monitor and control CMF/CNF quality and homogeneity.

Summary: It is essential to know the temperature‐time dependence on the chestnut starch gelatinisation process. With this aim, physicochemical and thermomechanical properties of native chestnut starch and with different gelatinisation degrees, isolated from discarded chestnut fruits under environmental friendly aqueous procedures, were studied. Isolated starch (144.96 ± 1.74 μm) presented high total starch (91.83 ± 0.24%), low damage starch (0.10 ± 0.04%), apparent amylose content of 20.31 ± 1.48% and relative crystallinity of 15.7 ± 0.4% with a C‐type pattern. Chestnut starch dispersions were formulated at 40% (w/w). Rheological measures indicated that temperatures below 60 °C were not able to form a hydrogel. The hydrogels formed between 62.5 and 65 °C (peak and final gelatinisation temperature, respectively) developed a stable and strong network with short maturation times and full thermoreversibility. Finally, hydrogels prepared above 65 °C were weaker and no completely thermoreversible. A linear relationship was identified between elastic features determined by rheology (G′gel,1 Hz) and texture (springiness, D1/D2). [ABSTRACT FROM AUTHOR]

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It has been shown that reversible and irreversible phase transitions of biogels can be represented by epidemic models. The irreversible chemical sol–gel transitions are modeled by the Susceptible-Exposed-Infected-Removed (SEIR) or Susceptible-Infected-Removed (SIR) epidemic systems whereas reversible physical gels are modeled by a modification of the Susceptible-Infected-Susceptible (SIS) system. Measured sol–gel and gel–sol transition data have been fitted to the solutions of the epidemic models, either by solving the differential equations directly (SIR and SEIR models) or by nonlinear regression (SIS model). The gel point is represented as the "critical point of sigmoid," defined as the limit point of the locations of the extreme values of its derivatives. Then, the parameters of the sigmoidal curve representing the gelation process are used to predict the gel point and its relative position with respect to the transition point, that is, the maximum of the first derivative with respect to time. For chemical gels, the gel point is always located before the maximum of the first derivative and moves backward in time as the strength of the activation increases. For physical gels, the critical point for the sol–gel transition occurs before the maximum of the first derivative with respect to time, that is, it is located at the right of this maximum with respect to temperature. For gel–sol transitions, the critical point is close to the transition point; the critical point occurs after the maximum of the first derivative for low concentrations whereas the critical point occurs after the maximum of the first derivative for higher concentrations. [ABSTRACT FROM AUTHOR]

An iterative approach is taken to develop a fractal topology that can describe the material structure of phase changing materials. Transfer functions and frequency response functions based on fractional calculus are used to describe this topology and then applied to model phase transformations in liquid/solid transitions in physical processes. Three types of transformation are tested experimentally, whipping of cream (rheopexy), solidification of gelatine and melting of ethyl vinyl acetate (EVA). A liquid-type model is used throughout the cream whipping process while liquid and solid models are required for gelatine and EVA to capture the yield characteristic of these materials.

The phase transition of nanocomposite hydrogels made of N-isopropylacrylamide (NIPAm) and clay (Laponite® XLS) was investigated under mechanical shear influencing the gelation. The hydrogels were synthesized by free radical polymerization. For the processing of cross-linked gels, the phase transition (liquid–solid) and its dependence on mechanical stress are of paramount importance. On the one hand, the determination of the gel point (tg) is possible with rheometry and, on the other hand, with dynamic light scattering (DLS). With rotational rheometry, by identifying the abrupt increase of viscosity, the gel point is evaluated. The DSL is an alternative method to rheometry, to investigate hydrogels under the action of the shear flow, to make results comparable to the rheometric investigations, with and without shear. Experimental parameters were chosen based on preparatory work to obtain comparable results regarding the determination of the gel point of a radically polymerized NIPAm hydrogel.

Highlights • This paper proposes a new GNP/MWCNT sensor, because of its unique mesoporous structure, the GNP/MWCNT film has good compatibility with the composite. • During the manufacturing process, the sensor can effectively capture the change of the resin phase, which is characterized by resistance change. As the resin changes from a rubbery state to flowing liquid state, the resin infiltration sensor changes the conductive structure. It causes the resistance increase. When resin cross-links, the matrix contraction leads to the electrical structure recovery and resistance drop. Once the resin cured basically, the resistance rises slowly due to its negative temperature coefficient. • With a standard curing system, the gel point was demonstrated in the curve of the real-time resistance change of the sensor. Compared with DMA results, results are basically same. However, DMA is laboratory method under certain conditions. It requires specific samples that are small size and/or lightweight. The GNP/MWCNT film sensor can monitor gel points in different locations and thicknesses in real time. Therefore, this method readily be applied to the in-situ monitoring of composite curing on the industrial scale and results are more accurate. Abstract In this study, we developed a film sensor composed of multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates (GNPs) via a simple mixing and spray-vacuum filtration. This highly flexible and sensitive GNP/ MWCNT film sensor can be embedded into polymer composite to in situ monitor the resin phase changes and gel point during the composite manufacturing process. The resistance of the GNP/MWCNT film sensor was obtained using two-terminals method by Fluke 2638 A, and the resistance changes could be related to phase changes of the resin matrix. Dynamic mechanical analysis (DMA) was performed to obtain the gel point of the composite as a baseline to compare with the GNP/MWCNT film sensor output. Experimental results show that the GNP/MWCNT film sensor embedded in the composite laminates can effectively capture the change of the resin phase, which is characterized by resistance. As the resin changed from the rubber state to the flow state, the resistance increased from 2.5 × 10−3 to 1.04. When the resin was cross-linked, the resistance dropped from 1.04 to 0.88. Once the resin is substantially cured, the resistance rises from 0.88 to 0.97 slowly. GNP / MWCNT films have a good ability to respond to changes in the resin state. The gel point of resin obtained from the GNP/ MWCNT film sensor is 134℃, which is consistent with 137℃ from the DMA results. The accurate gel point can optimize the curing system and improve the quality of composite products. The GNP/MWCNT film sensor has great potential to establish and optimize manufacturing processes and to improve the cure quality of fibre-based resin composites. [ABSTRACT FROM AUTHOR]

Abstract A method of near-infrared spectroscopy combined with wavelet transform was proposed to determine in-situ the gel time and gel point of epoxy resin simultaneously. The reconstructed spectra of the low-frequency wavelet coefficients were used for determination of gel time, and the reconstructed spectra of some detail coefficients which are dominated by chemical information for determination of epoxy conversion. In-situ determination of gel point has been achieved using evolutionary near infrared spectra of epoxy curing. The accuracy of gel point achived to 0.01. Compared with the traditional determination method of gel point, in which TMA and DSC are respectively used for gel time and conversion, this method not only can determine in-situ gel time and conversion degree simultaneously, and remarkably improve accuracy of the gel point result but also is of low cost, and fast and easy to operate. Highlights • Gel time and gel point of epoxy curing can be determined simultaneously by in situ NIR spectroscopy combined with WT. • Accuracy of gel point has been remarkably improved using the reconstructed NIR spectra by WT detail coefficient. • Gel time can be easily monitored using the reconstructed NIR spectra by WT approximate coefficient. • The epoxy curing reaction has been interpreted at molecular level using the evolutionary NIR spectra. • The NIR method is obviously superior to the method of DSC combined with TMA because of low cost, fast and easy to operate. [ABSTRACT FROM AUTHOR]

Abstract Objective The viscosity of dental resin composites is important in their formulation and clinical use; it depends on the filler particle size and loading. We intend to study the viscosity and conversion of composites made of low dispersity spherical silica fillers. Methods Experimental dental resin composites were formulated using low dispersity spherical silica particles of graded sizes (75, 150, 500, 350, 500, 1000 nm) at several loading levels with resins based on Bis-GMA and UDMA. Their rheological properties and double bond conversion were measured with a rheometer and differential scanning calorimeter, respectively. Results The complex viscosity of the unpolymerized pastes can be fit to an extended Krieger–Dougherty equation that includes an adjustment factor to account for filler particle surface area. This relationship is also extended to estimate the degree of conversion, where the calculated or experimental viscosity is used to predict the resulting conversion. Significance The enhanced understanding of the relationship of filler size, composite viscosity, and monomer conversion will allow improved accuracy in the prediction of the properties of dental resin composite formulations to obtain ideal viscosity for their clinical use and a high degree of conversion. [ABSTRACT FROM AUTHOR]

This study investigated the effects of carboxyl content and mechanical treatment intensity on the morphological characteristics of carboxymethylated cellulose nanofibrils (CM CNFs) and on the rheological properties of CM CNF suspension. The mechanical properties of self-standing CM CNF film were also examined. CM CNFs produced under different conditions had similar, uniform widths of about 5 nm, as measured using transmission electron microscope images and Image J software. The aspect ratios of three CM CNFs were evaluated using gel point analysis and the crowding number theory. Higher carboxyl content in the CM CNFs reduced the amount of mechanical energy required and increased the aspect ratio. The rheological properties and the tensile properties of CNF film were all strongly influenced by the aspect ratio of the CM CNFs. The CM CNF samples with higher aspect ratios produced stronger suspension network structures and had greater tensile properties. [ABSTRACT FROM AUTHOR]

Abstract: In this article, we studied the multiwave rheology properties of a two-step tetraethoxysilane (TEOS) hydrolysis, as well as condensation processes and optimized particle synthesis conditions by focusing on the colloidal particle aggregation and growth behavior. Combining with the dynamic light scattering (DLS) technique, we systematically investigated the gelation process, network structure, overall apparent activation energy, DLS size growth trend and complex viscosity. Our results revealed that the overall apparent activation energy of the two-step-catalyzed process was lower than that of the single step and the gelation time was decreased with an increase in water-TEOS molar ratio. During our studies, we successfully simplified the rheological measurement for the two-step process by setting the base addition moment as the zero time. This method can also be applied for structure and density tuning, providing a new path to successfully synthesize customized materials in a sol-gel process.The five-stage scheme of the sol-gel transition. The viscosity and DLS size curves were divided into five parts. Based on this route and combined with rheological measurements, the control of our sol-gel process can be realized and eventually obtained desired features. Investigate the gelation time and the gel structure of a two-step sol-gel process by combining MWDT with DLS method.The rheological measurement for the two-step process was simplified by setting the base addition moment as the zero time.The synthetic strategy can be applied to other sol-gel systems for structure and density tuning. [ABSTRACT FROM AUTHOR]

To study the effect of mechanical treatments on the rheosedimentation behaviour of pulp fiber suspensions, the settling behaviour, gel point, compressive yield stress and hindered settling function of bleached softwood pulp with different beating degrees at low concentrations were investigated. Over the range of test concentrations, it was found that the settling rates for refined softwood pulps were slower than that without mechanical treatments, and the values of gel points increased approximately linearly with freeness; Both the compressive yield stresses and hindered settling functions of all pulp suspensions increased non-linearly with increasing crowding number, and the hindered settling function was found to be dependent on the crowding number through a power law relationship. Moreover, the compressive yield stresses for softwood pulp suspensions with mechanical treatment were higher than that without refining. However, the same tendency for hindered settling functions was observed only for suspension at crowding number more than 16. The rheosedimentation studies on softwood pulp suspensions revealed that fiber morphology has a great influence on the settling and compressive behaviour. [ABSTRACT FROM AUTHOR]

The thermal phase transition temperatures of high (HMP) and low melting point (LMP) agarose gels were investigated by using UV-vis spectroscopy techniques. Transmitted light intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol-gel) processes. It was observed that the transition temperatures, Tm, defined as the location of the maximum of the first derivative of the sigmoidal transition paths obtained from the UV-vis technique, slightly increased by increasing the agarose concentration in both the HMP and LMP samples. Here, we express the phase transitions of the agar-water system, as a representative of reversible physical gels, in terms of a modified Susceptible-Infected-Susceptible epidemic model whose solutions are the well-known 5-point sigmoidal curves. The gel point is hard to determine experimentally and various computational techniques are used for its characterization. Based on previous work, we locate the gel point, T0, of sol-gel and gel-sol transitions in terms of the horizontal shift in the sigmoidal transition curve. For the gel-sol transition (heating), T0 is greater than Tm, i.e. later in time, and the difference between T0 and Tm is reduced as the agarose content increases. For the sol-gel transition (cooling), T0 is again greater than Tm, but it is earlier in time for all agarose contents and moves forward in time and gets closer to Tm as the agarose content increases. [ABSTRACT FROM AUTHOR]

Liquid silicone rubber (LSR) is becoming increasingly popular due to its chemical, UV, and heat resistance as well as its excellent optical properties. However, there is currently a lack of research and understanding of the rheological properties of the material. During the processing of liquid silicone rubber, the material can assume different rheological states. In the present work, both the physical and the chemical gel behavior are investigated rheologically. For this purpose, measurements are carried out with a rotational rheometer and a high-pressure capillary rheometer. Depending on the temperature and pre-shear rate, times are given for the physical gel point, after which a significantly destroyed physical network is recovered. Investigations at higher temperatures, which lead to chemical crosslinking and, therefore, to a chemical gel point, resulted in a representation of the temperature-dependent chemical gel point. The presented results serve as a material database for reliable simulations. [Display omitted] • Uncured Liquid Silicone Rubber (LSR) has both a physical and a chemical gel point. • In the unstressed state, uncrosslinked LSR can also be present as a physical gel at room temperature. • The physical gel of hydrogen bonds, entanglements, Van-der-Waals forces and filler-matrix interaction can be destroyed by pre-shearing. • Depending on temperature and pre-shear rate, the reversible network rebuilds to a physical gel in a very short time. • A chemical gel replaces the physical gel at higher temperatures and is irreversible due to the formation of covalent bonds. [ABSTRACT FROM AUTHOR]