Steady Shear Viscosity Research Articles

Rheology of mRNA-loaded lipid nanodumbbells

In one important chemical engineering unit operation of messenger ribonucleic acid (mRNA) vaccine manufacture, the precious mRNA payload is encapsulated in lipid nanoparticles (LNPs). Recent elegant cryogenic-transmission electron microscopy [Brader et al., Biophys. J. 120, 2766 (2021)] reveals that these lipid nanoparticles take the form of dumbbell suspensions. When encapsulating their mRNA payloads, these dumbbells can be both lopsided and interpenetrating, with the smaller of the two beads carrying the payload. In this work, we arrive at analytical expressions for these suspensions of lopsided lipid nanoparticle dumbbells encapsulating mRNA payloads. For this, we first exploit rigid dumbbell theory [Abdel-Khalik and Bird, Appl. Sci. Res. 30, 268 (1975)], which relies on the orientation distributions of the lopsided dumbbells, to predict the suspension rheology, and specifically to predict how this departs from Newtonian behavior. We next exploit elastic dumbbell theory [Phan-Thien et al., Phys. Fluids 36, 071707 (2024)], which also relies on the orientation distributions of the lopsided dumbbells and to which we add dumbbell stretching. Our results include analytical expressions for the relaxation time, rotational diffusivity, zero-shear viscosity, shear stress relaxation function, steady-shear viscosity and both the viscous part and minus the elastic part of the complex viscosity. We determine the rotational diffusivity of the mRNA-loaded lipid nanoparticle nanodumbbells from small-amplitude oscillatory shear measurements.

Universality and nonuniversality in nonlinear shear rheology of entangled polystyrene solutions and melts with the same number of entanglements

The linear and nonlinear shear rheology of entangled polystyrene (PS) solutions diluted by styrene oligomers with various lengths was compared with the shear rheology of a pure melt having the same number of entanglements (Z) during startup shear and step-shear strain experiments using a cone partitioned-plate geometry. By fixing the same Z, the shear rheology of the PS solutions and the melt shows some universal features in the linear and nonlinear regimes. Undershoot of the shear stress growth coefficient is observed during the startup flow of the PS solutions and depends strongly on the length of the oligomers. The Rotation Zero Stretch model captures the stress overshoot and the steady shear viscosity quantitatively, except at the high shear rates when undershoot is observed. Stress relaxation after step-shear strain experiments reveals that the PS solutions show a transition from type A damping (close to the Doi–Edwards prediction) to type B (weaker than the Doi–Edwards prediction), while the pure melt having the same Z shows a type A response, which suggests that the length of the oligomers influences the nonlinear damping response. The nonuniversality of the nonlinear damping response of the solutions and the melt is possibly due to the changes in flow-induced friction reduction during step-shear strain deformation.

Rheology of automotive adhesives during dispensing: A direct comparison of epoxy and rubber based systems via drag and pressure driven flows

Construction of vehicles requires adhesive dispensing for body-in-white assembly, hemming of closure panels, decking of windshields and the manufacture of battery packs. Knowledge of the rheological properties of adhesives applied using common dispensing systems is important for optimization of dispensing and application conditions. However, flow behavior of adhesives at shear rates used in dispensing is not well understood. Therefore, this study combines parallel plate and capillary rheology techniques to directly compare the rheological properties of an epoxy structural adhesive used in hemming applications and a rubber ‘topical sealer’ used to seal water leak paths across the range of shear rates observed in dispensing. Shear viscosity (η) and complex viscosity (η*) master curves were created from time-temperature-superposition (TTS) of steady shear and dynamic oscillatory data. Both adhesives did not follow the Cox-Merz rule. It was found that the Carreau-Yasuda model fit the steady shear viscosity master curve of the epoxy structural adhesive, while a simpler power law model fit the steady shear viscosity master curve of the rubber topical sealer. An inexpensive capillary rheometer was developed to simulate the adhesive dispensing process. Viscosity data was corrected for entrance pressure losses and a non-Newtonian flow front using Bagley and Weissenberg-Rabinowitsch corrections, respectively. It was observed that complex viscosity master curves better predicted viscosity during dispensing, as compared to steady shear viscosity master curves. Linear stress ramp measurements showed that the adhesives have widely different yield stresses, while the capillary rheometry measurements showed they have similar viscosities during dispensing. Furthermore, the capillary rheometer ‘shot meter’ pressures were related to the apparent and doubly corrected viscosity values through power law functions. A new quality control method based on the capillary rheology data is proposed.

A reexamination of the Cox–Merz rule through the lens of recovery rheology

Empirical rules play a crucial role in industrial and experimental settings for efficiently determining the rheological properties of materials, thereby saving both time and resources. An example is the Cox–Merz rule, which equates the steady-shear viscosity with the magnitude of the complex viscosity obtained in oscillatory tests. This empirical rule provides access to the steady-shear viscosity that is useful for processing conditions without the instabilities associated with experiments at high shear rates. However, the Cox–Merz rule is empirical and has been shown to work in some cases and fail in others. The underlying connection between the different material functions remains phenomenological and the lack of a comprehensive understanding of the rheological physics allows for ambiguity to persist in the interpretation of material responses. In this work, we revisit the Cox–Merz rule using recovery rheology, which decomposes the strain into recoverable and unrecoverable components. When viewed through the lens of recovery rheology, it is clearly seen that the steady-shear viscosity comes from purely unrecoverable acquisition of strain, while the complex viscosity is defined in terms of contributions from both recoverable and unrecoverable components. With recovery tests in mind, we elucidate why the Cox–Merz rule works only in a limited set of conditions and present an approach that could allow for universal comparisons to be made. This work further highlights the significance of recovery rheology by showing how it is possible to extend beyond phenomenological approaches through clear rheophysical metrics obtained by decomposing the material response into recoverable and unrecoverable components.

Correction to “A new slit‐radial die for simultaneously measuring steady state shear viscosity and first normal stress difference of viscoelastic liquids via capillary rheometry”

Correction to “A new slit‐radial die for simultaneously measuring steady state shear viscosity and first normal stress difference of viscoelastic liquids via capillary rheometry”

Development of “clean label” gluten-free breads fortified with flaxseed slurry and sesame cake: Implications on batter rheology, bread quality and shelf life

Following the recently emerged trends for products without additives and valorization of food processing by-products, “clean label” gluten-free (GF) breads were developed using a flaxseed slurry (FS) at 3% or 4.5% level (flaxseed basis), instead of the commonly used structurant in GF doughs, methylcellulose, and 3 or 6% (flour mixture basis) sesame cake (SC) for further product nutritional improvement. These alternative ingredients increased batter hardness and cohesiveness (back extrusion test) as well as elastic modulus, complex and steady shear viscosity (rheometry), compared to formulation containing only methylcellulose (control). The fortified breads had lower loaf specific volumes, than the control, but significantly higher than a GF bread made without any added hydrocolloid. FS and SC enhanced the formation of β-sheet structures (FTIR spectroscopy) in the batter and bread protein matrix. FS breads exhibited similar crumb hardness, cohesiveness, and springiness (TPA test) with the control, whereas inclusion of SC compromised these textural attributes. Nevertheless, the latter samples showed less pronounced textural changes upon storage (25°C-48 h), with similar extent of staling to control. For the fortified stored breads, there were no significant changes in protein conformation, compared to fresh products, whereas crumb starch retrogradation (calorimetry-DSC) was lower than the control. Additionally, the FS and SC increased the protein and dietary fiber contents and introduced nutty and sesame-like flavor notes to the breads, leading to improved overall acceptability scores. Overall, FS and SC seemed to be promising functional ingredients for the development of “clean label” GF breads with enhanced quality and shelf life.

The effect of ink ball milling time on interparticle interactions and ink microstructure and their influence on crack formation in rod-coated catalyst layers

This work investigates the influence of ballmilling (sometimes also referred to as jar roller milling) time on cathode catalyst layer (CL) inks and electrode properties using formulations and coating methods relevant for industrial manufacturing. Four CL inks with the same composition were milled for 24, 48, 72, or 96 h. Rheological investigation of these inks showed a reduction of elastic moduli and steady-shear viscosity with continuous ink milling, which is correlated to a decrease in particle-particle interactions as well as formation of smaller agglomerates. Optical microscopy (OM) analysis of the fabricated electrodes revealed a trend in surface crack formation; formulations milled for 24 h contained the lowest average surface crack area percentages of 0.370% at heavy-duty loadings of ∼0.300 mgPt cm−2, compared to 2.418% for the ink milled for 96 h. Further characterization of the CL through transmission electron microscopy (TEM) imaging showed a decrease in the mean agglomerate and pore size with milling time. These smaller electrode features were consistent with reduced fracture resistance and, hence, development of larger stresses during drying. Our results highlight the need to consider ink processing as an important component in defect-free CL manufacturing.

Cox–Merz rules from general rigid bead-rod theory

The value of this work is in its macromolecular explanations of both Cox–Merz rules, thus of when to expect them to work. For polymeric liquids and their solutions, the measured values of the steady shear viscosity and the magnitude of the complex viscosity often equate, within experimental error, when compared at common shear rate (in units of t−1) and angular frequency (in units of rad t−1). Called the first Cox–Merz rule, this remarkable empiricism, with one exception, has defied most macromolecular explanations. This one exception is the suspension of multi-bead rods and its special case of rigid dumbbells. The second Cox–Merz rule equates approximately the slope of the first derivative of steady shear viscosity with respect to shear rate with the real part of the complex viscosity when compared at common shear rate (in units of t−1) and angular frequency (in units of rad t−1). In this paper, we explain both Cox–Merz rules for all axisymmetric macromolecules, be they prolate or oblate, of almost any lopsidedness. Furthermore, through the lens of general rigid bead-rod theory, we define under what conditions these rules do not apply. Specifically, the first Cox–Merz rule fails when the macromolecules are too oblate.

Electrospinning of epoxy fibers: Effect of curing conditions on solution rheological behavior

AbstractThe electrospinning of thermoplastic polymers is widely used in applications such as filters and coatings, but has only recently been applied to thermosetting polymers because of their chemical structure and reactivity. Epoxy is a thermosetting polymer which, when combined with a curing agent, chemically reacts to form a crosslinked matrix. In the present study, we demonstrate that to electrospin epoxy and obtain continuous micro and nanofibers, one must precisely control the curing reaction. Epoxy was mixed with triamine curing agent and, to enable electrospinnability, was dissolved in a mixture of tetrahydrofuran and dimethylformamide solvents. We identified a narrow working window wherein a proper solution for electrospinning is close to the gel point, right before the transition from liquid to solid gel state. The solution was characterized by means of (i) Fourier‐transform infrared spectroscopy to monitor the extent of reaction, (ii) steady shear viscosity to detect the divergence near the gel point, and (iii) oscillatory loss and storage shear moduli to identify the liquid‐to‐gel transition. Based on these measurements, it was possible to monitor the chemical transformations that the epoxy solution underwent with time, such as chemical interconnections and gelation, and thus define the working window for electrospinning.

The role of the weight function in the generalised distributed-order Maxwell model: The case of a distributed-springpot and a dashpot

In this work, our focus is on investigating the significance of the weighting function (c(α)) in the Generalised Distributed-Order Maxwell (GDOM) model. The GDOM model comprises a distributed springpot and a dashpot in series, rendering it more intricate than the Fractional Viscoelastic Fluid - FVF model (consisting of only one springpot and one dashpot in series). However, the GDOM model remains simple enough to facilitate a better comprehension of its behaviour in various flow scenarios, such as relaxation, creep compliance, steady shear viscosity, and small amplitude oscillatory shear. To validate our findings, we conduct fitting analyses using experimental data, which affirm that the single-element model demonstrates solid-like viscoelastic behaviour at low frequencies, while the GDOM model exhibits fluid-like viscoelastic behaviour, accurately capturing the rubbery plateau and transition region observed in polymer systems.

Morphological and rheological investigation of emulsified asphalt/polymer composite based on gray-level co-occurrence matrix

Emulsified asphalt/polymer is one of the most applied composite materials in pavement industry, which is also defined as emulsified polymer modified asphalt (PMA). PMA exhibits the transition behavior of multi-physical states with corresponding viscoelastic characteristics, and studies had focused on the application performances of PMA. However, few had paid proper attention to the morphological compatibility of PMA, which dominated its viscoelastic transition and failure probability directly. This paper aims to establish a gray-level co-occurrence matrix (GLCM) model with morphology theory to quantitatively describe the morphological compatibility of PMA, combined with fluorescent microscope. Furthermore, waterborne polymers with self-crosslinking characteristics are introduced to modify emulsified asphalt, including acrylate, epoxy resin, polyurethane and liquid rubber. The rheological characteristics of PMA are comprehensively evaluated through performance grade, steady shear viscosity, and master curve tests. Finally, a statistical analysis is conducted to establish the relationship between morphological compatibility and rheological characteristics of PMA. The approach introduced in this study could be a promising method to investigate the multi-physical transition behaviors and morphological compatibility of emulsified asphalt/polymer composite material.

Confined steady simple shear flow of polymeric liquids

In a confined simple shear flow, the macromolecules of a polymeric liquid reorient near the walls so that the measured viscosity decreases. For instance, in a small-amplitude oscillatory shear flow, the real part of the complex viscosity decreases with confinement, and macromolecular orientation explains this. These effects in oscillation have been explained analytically for a rigid dumbbell suspension and, for a confined small-amplitude oscillatory shear flow, the summation coefficients have been determined. By contrast, for the confined steady shear flow, the summation coefficients are undetermined. In this paper, we determine these coefficients and use them to evaluate the steady shear (i) viscosity and (ii) normal stress coefficients for a rigid dumbbell suspension. We find that the zero-shear viscosity and the zero-shear first normal stress coefficients decrease with confinement. We further find that the dimensionless (i) steady shear viscosity curve increases with confinement and (ii) first normal stress coefficient first decreases with light confinement and then increases with greater confinement. We confirm our theory, at low confinement, by comparing with our new measurements of the confined zero-shear viscosity of a polystyrene solution.

Rheological and Fatigue Characteristics of Asphalt Mastics and Mixtures Containing Municipal Solid Waste Incineration (MSWI) Residues

The large-scale implementation of municipal solid waste incineration (MSWI) has put great pressure on waste management and environmental protection. Road construction engineering has also been confronted with the challenges of the heavy consumption of non-renewable mineral resources. Therefore, we evaluated the feasibility of recycling and reusing MSWI residue as an alternative to limestone filler (LF) in transport infrastructure. We investigated the rheological characteristics and fatigue performance of asphalt mastics and mixtures containing MSWI residue. Firstly, a particle size analyzer and environmental scanning electron microscope were adopted to characterize the particle distribution and surface micromorphology of the investigated fillers, respectively. Then, tests for determining the steady shear viscosity and multiple-stress creep recovery were conducted to evaluate the high-temperature rheology of five asphalt mastics. Meanwhile, we used Burgers models with fitting parameters to describe the classic creep recovery measurements and viscoelastic responses. The wheel-tracking test revealed the rutting resistance, and the linear amplitude sweep (LAS) and time sweep tests were combined to investigate the fatigue performances of the five asphalt mastics. A dynamic creep test identified the fatigue life of the asphalt mixtures according to the flow number index. Finally, statistical analysis was conducted to identify the correlations between the rheological and fatigue properties of the mastics and mixtures (R2 over 0.87 and 0.78, respectively). Since the fatigue life predictions for the asphalt mastic decreased by over 42.9% according to the MSWI residue/LF volume ratio, the results of the correlations could improve pavement designs. The substitution of the mineral filler in asphalt mixtures with MSWI residue could be a sustainable strategy for the road construction sector.

Polymer and surfactant flows through a periodically constricted tube

The flow of three non-Newtonian fluids, comprising polymer and surfactant additives, in a periodically constricted tube (PCT) are experimentally compared. The radius of the tube walls is sinusoidal with respect to the streamwise direction. The three fluids are aqueous solutions of flexible polymers, rigid biopolymers and surfactants, which are typically used for drag-reduction in turbulent flows. Steady shear viscosity measurements demonstrate that rigid and flexible polymer solutions are shear-thinning, while surfactant solutions have a Newtonian and water-like shear viscosity. Capillary driven extensional rheology demonstrates that only flexible polymer solutions produce elastocapillary thinning. Particle shadow velocimetry is used to measure the velocity of each flow within the PCT at five Reynolds numbers spanning roughly 0.5 to 300. Relative to the Newtonian flows, rigid polymer solutions exhibit a blunt velocity profile. Flexible polymer solutions demonstrate a distinct chevron-shaped velocity contour and zones of opposing vorticity when the Deborah number exceeds 0.1. Using the vorticity transport equation, it is revealed that the opposing vorticity zones are coupled with a non-Newtonian torque. The PCT reveals that the surfactant solutions have similar non-Newtonian features as flexible polymer solutions – those being a chevron velocity pattern, opposing vorticity and a finite non-Newtonian torque. This observation is of practical importance since conventional shear and extensional rheometric measurements are not capable of demonstrating non-Newtonian features of the surfactant solutions. The investigation demonstrates that the PCT serves as a viable geometry for showing the non-Newtonian traits of dilute surfactant solutions.

Steady State and Dynamic Oscillatory Shear Properties of Carbon Black Filled Elastomers

A correlation between the steady shear viscosity and complex dynamic viscosity of carbon black (CB) filled rubbers was found by evaluating the Cox-Merz rule and an alternative approach originally proposed by Philippoff for dilute polymer solutions, but since applied to amorphous polymers and concentrated suspensions. This was done by measuring the rheological properties of 16 industrially important rubber mixes containing CB N660 at concentrations of 20 and 35% by volume. A capillary rheometer at various shear rates and a dynamic oscillatory shear rheometer at small and large amplitude oscillatory shear (SAOS and LAOS) were used. The apparent viscosity, storage and loss moduli, complex dynamic viscosity and Fourier transform harmonics were measured. Generally, the shear stress, storage and loss moduli increased with increasing CB loading. Also, the ratio of third and fifth stress harmonics to first harmonics increased with increasing strain amplitude and filler loading. Viscous Lissajous figures (shear stress versus shear rate) at a strain amplitude of 14% showed a nearly linear response for compounds containing CB at 20% by volume. All other shear stress responses demonstrated a strong nonlinearity. The stress waveforms at a strain amplitude of 140% for compounds containing 35% CB by volume displayed a backwards tilted shape expected for highly filled compounds. The stress waveforms at a strain amplitude of 1,000% tended toward a rectangular shape expected for pure polymer. Generally, the nonlinear response of the compounds appeared to be dominated by the filler at strain amplitudes of 14% and 140% and by the rubber matrix at a strain amplitude of 1,000%. The Cox-Merz rule was not applicable for any of the compounds with their complex dynamic viscosity being greater than the apparent viscosity. However, a modification of the approach proposed by Philippoff provided reasonable agreement between the apparent viscosity and complex dynamic viscosity.

Effect of polydispersity and bubble clustering on the steady shear viscosity of semidilute bubble suspensions in Newtonian media

In this work, we examine the steady shear rheology of semidilute polydisperse bubble suspensions to elucidate the role of polydispersity on the viscosity of these systems. We prove theoretically that the effect of polydispersity on suspension viscosity becomes apparent only if the bubble size distribution is bimodal, with very small and very large bubbles having similar volume fractions. In any other case, we can consider the polydisperse suspension as monodisperse, with the average bubble diameter equal to the De Brouckere mean diameter (d43). To confirm the theoretical results, we carried out steady shear rheological tests. Our measurements revealed an unexpected double power-law decay of the suspension relative viscosity at average capillary numbers between 0.01 and 1. To investigate this behavior further, we visualized the produced bubble suspensions under shear. The visualization experiments revealed that bubbles started forming clusters and threads at an average capillary number around 0.01, where we observed the first decay of viscosity. Clustering and alignment have been associated with shear-thinning behavior in particle suspensions. We believe that the same holds for bubble suspensions, where bubble clusters and threads align with the imposed shear flow, reducing the streamline distortions and, in turn, resulting in a decrease in the suspension viscosity. Consequently, we can attribute the first decay of the relative viscosity to the formation of bubble clusters and threads, proving that the novel shear-thinning behavior we observed is due to a combination of bubble clustering and deformation.

Extensional Rheology of Poly(vinylidene fluoride)/N,N-dimethylformamide Solutions

Typical extension flow occurs in electrospinning process of Poly(vinylidene fluoride) (PVDF) solutions such that researchers focus on extensional rheological behaviors of PVDF solutions. The extensional viscosity of PVDF solutions is measured to know the fluidic deformation in extension flows. The solutions are prepared by dissolving PVDF powder into N,N-dimethylformamide (DMF) solvent. A homemade extensional viscometric device is used to produce uniaxial extension flows and the feasibility of the viscometric device is verified by applying the glycerol as a test fluid. Experimental results show that PVDF/DMF solutions are extension shinning as well as shear shinning. The Trouton ratio of thinning PVDF/DMF solution is close to three at very low strain rate and then reaches a peak value until it drops to a small value at high strain rate. Furthermore, an exponential model may be used to fit the measured values of uniaxial extensional viscosity at various extension rates, while traditional power-law model is applicable to steady shear viscosity. For 10~14% PVDF/DMF solution, the zero-extension viscosity by fitting reaches 31.88~157.53 Pa·s and the peak Trouton ratio is 4.17~5.16 at applied extension rate of less than 34 s-1. Characteristic relaxation time is λ~100 ms and corresponding critical extension rate is ε˙c~5 s-1. The extensional viscosity of very dilute PVDF/DMF solution at very high extension rate is beyond the limit of our homemade extensional viscometric device. This case needs a higher sensitive tensile gauge and a higher-accelerated motion mechanism for test.

Rheology of non-Brownian particle suspensions in viscoelastic solutions. Part II: Effect of a shear thinning suspending fluid

The shear rheology of particle suspensions in shear-thinning polymeric fluids is studied experimentally using parallel plate measurements and numerically using fully resolved, 3D finite volume simulations with the Giesekus fluid model. We show in our experiments that the steady shear viscosity and first normal stress difference coefficient of the suspension evolve from shear-thickening to substantially shear-thinning as the degree of shear-thinning of the suspending fluid increases. Moreover, in highly shear-thinning fluids, the suspension exhibits greater shear-thinning of the viscosity than the suspending fluid itself. Our dilute body-fitted simulations show that in the absence of hydrodynamic interactions, shear-thinning can arise from the particle-induced fluid stress (PIFS), which ceases to grow with increasing shear rate at low values of β (solvent viscosity ratio) and finite values of α (the Giesekus drag coefficient). In a Giesekus suspending fluid, the polymers surrounding the suspended particle are unable to stretch sufficiently at high Weissenberg numbers (Wi) and the reduced polymer stress results in a lower PIFS. When coupled with the shear-thinning stresslet, this effect creates an overall shear-thinning of the viscosity. We then explore the effects of particle-particle interactions on the suspension rheology using immersed boundary simulations. We show that multiparticle simulations are necessary to obtain the shear-thinning behavior of the per-particle viscosity of suspensions in shear-thinning fluids at moderate values of β. Particle-particle interactions lead to a substantial decrease in the PIFS and an enhancement of the shear-thinning of the stresslet compared to the single particle simulations. This combination leads to the shear-thinning of the per-particle viscosity seen in experiments. We also find that very low values of β and finite values of α have opposing effects on the per-particle viscosity that can lead to a nonmonotonic per-particle viscosity versus shear rate in a highly shear-thinning fluid. Overall, the addition of rigid particles to highly shear-thinning fluids, such as joint synovial fluid, leads to increased viscosity and also increased shear-thinning at high shear rates.

Synergistic effects of chain extenders and natural rubber on PLA thermal, rheological, mechanical and barrier properties

Poly (lactic acid) (PLA) has high potential to replace conventional petroleum-based plastics in a wide range of applications. However, the high brittles, thermal degradation, low melt strength and low viscosities of PLA pose challenges for its processing and performance satisfied for industrial use. Previously, we have shown that natural rubber (NR) incorporated into PLA improved the melt strength and viscosity and thus the processability of biopolyesters. Chain extension is a practical and cost-effective method of improving PLA processability by enhancing the molecular weight and re-bonding degraded chains. We hypothesized that addition of epoxy-based chain extenders will work synergistically with natural rubber to improve the elongational viscosity and strain hardening of PLA. The thermal transition, thermal degradation, mechanical and moisture barrier properties were studied to provide a comprehensive view of the chain-extended and NR-modified PLA. The results shows that chain extender with higher functionality (Joncryl 4368) had a more significant effect on chain extending, branching and restoring of PLA. Although the chain extender or the NR alone reduced both the dynamic and steady shear viscosities and minimally affected the elongational viscosity of PLA, they together resulted in shear-thickening and strain-hardening of PLA, suggesting a synergistic effect of the chain extender and NR on improving PLA rheological performance. The improved elongational viscosity of PLA was comparable to film grade low density polyethylene (LDPE). Additionally, NR addition significantly reduced the water vapor permeability of PLA. The PLA with improved melt viscosity and moisture barrier are promising for film and flexible packaging applications.

Yogurt and curd cheese as alternative ingredients to improve the gluten-free breadmaking

Gluten-free products are on today's agenda since they represent the most hastily growing segments in the market, representing an opportunity for food companies. Nevertheless, it is well-known that gluten is a crucial network structure in the wheat dough systems, which accounts for the overall desired technological features of the final bakery goods. Therefore, the absence of gluten negatively affects the characteristics of gluten-free bread, triggering a technological challenge in the manufacturing of products with resembled characteristics of wheat-derived counterparts. The search for new protein sources has been studied as an approach to circumvent the technological drawbacks of gluten removal. Dairy proteins are functional molecules that can likely be capable of building up a protein-network structure so that it would improve the technological properties of gluten-free products. In the present work, different levels of dairy product addition (10 and 20%, w/w) were used to supplement the gluten-free bread formulas, and the impact on dough rheology properties was well correlated to the bread technological quality parameters obtained. Linear correlations (R 2 > 0.904) between steady shear (viscosity) and oscillatory (elastic and viscous moduli) values of the dough rheology with bread quality parameters (volume and firmness) were obtained, suggesting that the bread quality improvements are proportional to the levels of dairies added. Likewise, strong linear correlations (R 2 > -0.910) between pasting properties parameters and bread staling rate supported the hypothesis that the dairies tested have a high potential to generate bread with a low staling rate, which is an advantage to extending the shelf-life. In short, results confirmed that the addition of both dairy products, as bakery ingredients, can constitute a technological advantage to improve the overall gluten-free bread quality.