Extensional Viscosity Research Articles

Unravelling the relationships between wheat dough extensional properties, gluten network and water distribution

Wheat flour doughs were prepared from four commercial wheat flours at different mixing times and hydration levels in order to obtain variations in their rheological properties and gluten network structure. Their rheological behavior was assessed by Dynamic Mechanical Analysis (DMA) for their viscoelastic properties and by Lubricated Squeezing Flow (LSF) for their extensional properties. Gluten network structure was determined by quantitative analysis of confocal microscopy (CLSM) images. Among the rheological properties, the consistency index (k) derived from the extensional viscosity and the elastic modulus ratio (E′Max/E′Min) varied between 10 and 42 kPa.sn, and 4 and 26, respectively. They were found to be consistently linked to the gluten network structure. This structure was primarily described by the morphological descriptor, “protein width”, which defines the thickness of protein strands, the average value of which varied between 1.7 and 2.5 μm. Both rheological properties and morphological criteria were significantly influenced by dough hydration rather than by mixing time, whereas the flour characteristics did not play a major role. Interpretation of these results, supported by previous 1H time domain nuclear magnetic resonance (TD-NMR) results concerning water distribution profiles, showed that an optimal dough is defined by a high dough consistency index (k) and a highly cross-linked gluten network (low E'Max/E'Min ratio), presenting thin protein strands.

Extensional Viscosity of Immiscible Polymer Multi-Nanolayer Films: Signature of the Interphase

Extensional Viscosity of Immiscible Polymer Multi-Nanolayer Films: Signature of the Interphase

Modeling elongational viscosity of polystyrene Pom-Pom/linear and Pom-Pom/star blends

The elongational rheology of blends of a polystyrene (PS) Pom-Pom with two linear polystyrenes was recently reported by Hirschberg et al. (J. Rheol. 2023, 67:403–415). The Pom-Pom PS280k-2x22-22k with a self-entangled backbone (Mw,bb = 280 kg/mol) and 22 entangled sidearms (Mw,a = 22 kg/mol) at each of the two branch points was blended at weight fractions from 75 to 2 wt% with two linear polystyrenes (PS) having Mw of 43 kg/mol (PS43k) and 90 kg/mol (PS90k), respectively. While the pure Pom-Pom shows strong strain hardening in elongational flow (SHF > 100), strain hardening (SHF > 10) is still observed in Pom-Pom/linear blends containing only 2 wt% of Pom-Pom. The elongational start-up viscosities of the blends with Pom-Pom weight fractions above 10 wt% are well described by the Molecular Stress Function (MSF) model, however, requiring two nonlinear fit parameters. Here we show that quantitative and parameter-free modeling of the elongational viscosity data is possible by the Hierarchical Multi-mode Molecular Stress Function (HMMSF) model based on the concepts of hierarchical relaxation and dynamic dilution. In addition, we investigated the elongational viscosity of a blend consisting of 20 wt% Pom-Pom PS280k-2x22-22k and 80 wt% of a PS star with 11 arms of Mw,a = 25 kg/mol having a similar span molecular weight as PS43k and similar Mw,a as the Pom-Pom. This work might open up possibilities toward polymer upcycling of less-defined polymers by adding a polymer with optimized topology to gain the intended strain hardening, e.g., for film blowing applications.Graphical

An experimental study on the impact of Boger and Newtonian droplets on spherical surfaces

This study examined the impact of Boger droplets on spherical surfaces, considering the various properties of liquids and surfaces for the first time. The experimental setup involved spheres with three different diameters composed of hydrophilic and hydrophobic surfaces. The main innovative aspect of the present study lies in the examination of the effects of rheological properties including elasticity, elongational viscosity, and the first normal stress difference on the impact of Boger droplets on solid surfaces via stress analysis. For this purpose, the results of the impact of Boger droplets are compared to the impact of equivalent Newtonian droplets with the same viscosity and surface tension coefficient. The research also explored the influences of Weber number, diameter ratio, and surface wettability on the dynamic behaviors of viscoelastic droplets during the spreading and receding stages. The results suggested that increasing the Weber number increases the maximum spreading factor of the droplets. A smaller diameter ratio required more time to reach this factor. The surface wettability significantly affected the receding phase, while its effect on the spreading stage was minimal. Droplets exhibited more retraction on surfaces with higher contact angles. The Newtonian fluids showed greater spreading and retraction than viscoelastic fluids with the same viscosity, highlighting the influence of fluid elasticity. It is shown that the normal stress caused by extensional viscosity during droplet spreading is significantly higher than the normal stress difference resulting from shear deformation, showing different behaviors between these two types of stress concerning droplets.

An experimental study on the role and contribution of the first normal stress difference and elongational viscosity in immiscible viscoelastic Saffman-Taylor instability

This study experimentally examined the immiscible viscoelastic Saffman-Taylor instability (STI) in porous media. The viscoelastic displacing fluids are solutions of glycerin, water, and polyacrylamide with concentrations of 100, 200, and 400 ppm, and the immiscible displaced fluids are silicone oils with different viscosities. The viscosity of viscoelastic liquids is rather constant, so they could be considered Boger liquids The main innovative aspect of the present study is the analysis of the role and contribution of the first normal stress difference and elongational viscosity in the immiscible viscoelastic displacement. In this study, instead of using the simple geometry of the Hele-Shaw cell, some more applied results for viscoelastic STI in the low permeability transparent packed bed porous media have been presented. Another novel aspect of the current study is the analysis of the effect of different parameters, such as elasticity, flow rate, and viscosity ratio, on the viscoelastic STI for the case of immiscible displacement, experimentally. The results of the injection of Boger liquids were compared with the injection of equivalent Newtonian fluids to investigate the effect of fluid elasticity. Furthermore, the effects of flow rate and viscosity ratio on the flow instability were studied in detail by analyzing images of the propagation of finger-like patterns and the results of mixing length and sweep efficiency. The results indicate that the contribution of the first normal stress difference to the stabilizing effect of polymeric additives is less than 18% for the different scenarios of Boger liquid injection. Thus, the elongational viscosity of displacing fluid has the main role in enhancing the sweeping of the displaced phase. When decreasing the polymer concentration and increasing the flow rate, the contribution of the elongational viscosity on STI can become more important compared to the first normal stress difference.

Extensional rheometry of mobile fluids. Part II: Comparison between the uniaxial, planar, and biaxial extensional rheology of dilute polymer solutions using numerically optimized stagnation point microfluidic devices

Part I of this paper [Haward et al., J. Rheol. 67, 995–1009 (2023)] presents a three-dimensional microfluidic device (the optimized uniaxial and biaxial extensional rheometer, OUBER) for generating near-homogeneous uniaxial and biaxial elongational flows. Here, in Part II, the OUBER device is employed to examine the uniaxial and biaxial extensional rheology of model dilute polymer solutions, compared with measurements made under planar extension in the optimized-shape cross-slot extensional rheometer [OSCER, Haward et al. Phys. Rev. Lett. 109, 128301 (2012)]. In each case, micro-particle image velocimetry is used to measure the extension rate as a function of the imposed flow conditions, and excess pressure drop measurements enable estimation of the tensile stress difference generated in the fluid via a new analysis based on the macroscopic power balance for flow through each device. Based on this analysis, for the most dilute polymer sample tested, which is “ultradilute”, the extensional viscosity is well described by Peterlin’s finitely extensible nonlinear elastic dumbbell model. In this limit, the biaxial extensional viscosity at high Weissenberg numbers (Wi) is half that of the uniaxial and planar extensional viscosities. At higher polymer concentrations, although the fluids remain dilute, the experimental measurements deviate from the model predictions, which is attributed to the onset of intermolecular interactions as the polymer chains unravel in the extensional flows. Of practical significance (and fundamental interest), elastic instability occurs at a significantly lower Wi in uniaxial extensional flow than in either biaxial or planar extensional flow, thereby limiting the utility of this flow type for extensional viscosity measurement.

Electrospinning of pullulan-based orodispersible films containing sildenafil

Feasibility of electrospinning in the manufacturing of sildenafil-containing orodispersible films (ODFs) intended to enhance oxygenation and to reduce pulmonary arterial pressure in pediatric patients was evaluated. Given the targeted subjects, the simplest and safest formulation was chosen, using water as the only solvent and pullulan, a natural polymer, as the sole fiber-forming agent. A systematic characterization in terms of shear and extensional viscosity as well as surface tension of solutions containing different amounts of pullulan and sildenafil was carried out. Accordingly, electrospinning parameters enabling the continuous production, at the highest possible rate, of defect-free fibers with uniform diameter in the nanometer range were assessed. Morphology, microstructure, drug content and relevant solid state as well as ability of the resulting non-woven films to interact with aqueous fluids were evaluated. To better define the role of the fibrous nanostructure on the performance of ODFs, analogous films were produced by spin- and blade-coating and tested. Interestingly, the disintegration process of electrospun products turned out to be the fastest (i.e. occurring within few s) and compliant with Ph. Eur. and USP limits, making relevant ODFs particularly promising for increasing sildenafil bioavailability, thus lowering its dosages.

Evaluation of processed cheese viscoelastic properties during sterilization observed in situ

Sterilized processed cheese is a specific dairy product with a prolonged shelf life intended for regular retail offer but also as food provisions for armies during peacetime, as well as during crisis and emergency situations, and for storage in state material reserves. Storage requirements are usually defined as ≤25°C for at least 24 mo. One of the ways to achieve such a shelf life is sterilization. Therefore, the aim of the work was to describe, for the first time in the available scientific literature, in situ changes in the viscoelastic properties of spreadable melt (34% wt/wt DM content, 45% wt/wt fat in DM content, and 14% wt/wt protein content) during an increase in temperature (target temperature 122°C), holding at sterilization temperature (20 min) and subsequent cooling (to ∼30°C). While increasing to the target sterilization temperature, a significant decrease occurred in the storage and loss moduli values. Both moduli started to increase again during the target sterilization temperature period and during the whole cooling phase. The values of the storage and loss moduli were significantly higher at the end of the cooling of the sterilized product, and conversely, the phase angle value was lower compared with the melt before sterilization. As a result of sterilization, an increase occurred in the levels of markers of the Maillard reaction complex and lipid oxidation processes. The value of hardness, corrected stress, and elongational viscosity also increased compared with nonsterilized products. As a result of sterilization, the flavor worsened and sterilized processed cheeses showed darker (brownish) color. However, even after sterilization, the products were evaluated as acceptable for consumers and maintained their spreadability.

A strategy for extending the processing temperature for polypropylene in foam extrusion and its theoretical validation

The quite narrow PP foaming temperature window is the main challenge for continuous extrusion foaming of polypropylene (PP) using supercritical CO2. In this study, high impact polystyrene (HIPS) is added to PP to widen the polypropylene foaming temperature range by reducing the temperature sensitivity of the melt strength of the blend. The behavior of crystalline, dynamic rheology, and extensional rheological of PP/HIPS blends are analyzed. The results show that the crystallinity and crystallization temperature of PP/HIPS blends decreased significantly, the temperature dependence of the blends’ extensional viscosity and melt strength became weaker, and the activation energy of extensional viscosity and melt strength activation energy decreased, while the elastic modulus and viscosity and the system relaxation time increased. It means that the addition of HIPS reduces the crystallinity of PP, improves the cell morphology and to a certain extent overcomes the problem of a sharp decrease in PP melt strength with increasing temperature. The addition of HIPS extends the foaming temperature range of the PP material from 4 K to a maximum of 12 K. Furthermore, we simply estimated the temperature window for extruded foams using the Arrhenius equation. The estimated values have the same trend as the experimental results and are analyzed.

Impinging blood droplets on different wettable surfaces: Impact phenomena, contact line motion, post-impact oscillation and dried stains

Understanding the underlying hydrodynamics of impinging blood droplets and finding out the physical parameters determining the bloodstain characteristics are of great importance in blood related forensic investigations. In this work, the impact of non-Newtonian blood droplets on solid surfaces ranging from lyophilic to superlyophobic was systematically investigated and compared to that of Newtonian droplets with a similar dynamic shear viscosity. We show that impinging blood droplets behave as low-viscosity Newtonian droplets in the short-time spreading, which is dominated by capillary and inertial forces, but their non-Newtonian viscoelasticity would notably affect the droplet retraction and post-impact oscillation occurring in large timescales. Whereas the strong liquid–solid adhesion and the non-Newtonian elongational viscosity hinder droplet recoiling and thus alter the impact phenomena on lyophobic and superlyophobic surfaces, the shear and elongational viscosities are coupled to result in higher damping coefficients of oscillating blood droplets after deposition, in comparison to that of impinging Newtonian droplets. The size of the dried bloodstain was found to be different from both the maximum spreading radius of the droplet that can reach during impact and the final radius of the deposited droplet after oscillation, and their correlations are highly dependent on the impact velocity and surface wettability. Moreover, the morphologic characteristics of the bloodstains would also be changed by varying either the impact velocity or the surface wettability. We envision that these findings can not only find applications in the bloodstain pattern analysis, but also provide useful information for medical diagnosis based on blood droplet test.

Investigation and prediction of the extensional viscosity of okra mucilage using the Giesekus model.

Okra is a vegetable that is widely grown around the world. Okra mucilage contains a high mucus concentration that can be useful for supporting the swallowing process. Although the extensional rheology of okra mucilage is essential to its flow, its extensional viscosity has not received much attention. Using a filament stretching rheometer, the extensional viscosity of the mucilage in okra was examined. The Giesekus model was used to predict this parameter. The okra mucilage with different concentrations was extracted from fresh okra. The extensional viscosity was measured using a filament breakup apparatus. The diameter of the liquid bridge was measured by a laser micrometer and it was also observed by a high-speed camera. A rotational rheometer was used to measure the shear viscosity. In addition, the master curves for the shear viscosity were plotted to eliminate the influence of solvent and shear rate and evaluate the influence of concentration on the elasticity of okra mucilage. The okra mucilage shear and extensional viscosity were predicted using the Giesekus model. Every sample of okra mucilage exhibited shear thinning behavior. In addition to having a high extensional viscosity that is hundreds of times higher than its shear viscosity, okra mucilage also exhibited stretching phenomena. The master curves demonstrated that the pseudoplasticity of the okra mucilage increased along with the concentration. The rheological behavior of the mucilage in okra can be explained by the Giesekus model. Okra mucilage's shear viscosity exhibited shear thinning behavior and a strong extensional viscosity that was significantly higher than its shear viscosity. The shear and extensional viscosity of okra mucilage can be described and predicted using the Giesekus model.

Rheology of saliva in health and disease.

Saliva is a complex fluid that lubricates the oropharynx and facilitates chewing, swallowing, and vocalization. Viscoelasticity is critical for the ability of saliva to fulfill these functions. Xerostomia, or a sensation of dry mouth, occurs in 17-26% of the population. Although many equate xerostomia with hyposalivation, high-risk patients frequently report oral dryness in the absence of decreased salivary flow. This study aims to determine if xerostomia is associated with alterations in the rheological properties of saliva in addition to decreased salivary production. The study population included patients with post-radiation xerostomia, patients with anticholinergic-induced xerostomia and healthy controls. Salivary volumetric flow rate was measured, shear viscosity was measured using oscillatory rheometry, and extensional viscosity was measured using capillary thinning methods. Groups were compared using descriptive statistics and univariate analysis. A total of 36 subjects were included: 15 with post-radiation xerostomia, 9 with anticholinergic-induced xerostomia and 12 controls. Salivary volumetric flow was significantly decreased in post-radiation and anticholinergic-induced patients compared to controls. On capillary thinning testing, saliva from xerostomia patients had significantly greater extensional viscosity compared to controls. However, saliva from the three groups showed no significant difference in the complex viscosity or the storage or loss modulus of saliva with oscillatory rheology. Xerostomia is associated with decreased salivary volumetric flow and quantitative changes in the rheologic properties of saliva.

Shear banding predictions for wormlike micellar systems under a contraction–expansion complex flow

This study focuses on computational modeling of shear-banded wormlike micellar solutions (WLM) in a complex planar Couette flow, driven by a moving top plate over a rounded-corner 4:1:4 obstruction. The BMP+_τp model is used, which is constructed within an Oldroyd-B-like form, coupled with a thixotropic fluidity-based structure equation. Solute energy dissipation drives fluid–structure adjustment in a construction–destruction dynamics affected by viscoelasticity. This model reproduces conventional WLM features, such as shear thinning, extensional hardening/softening, viscoelasticity, apparent yield stress, and shear banding, with a bounded extensional viscosity and an N1Shear upturn at high deformation rates. The BMP+_τp characterization for shear banding is based on extremely low solvent fractions and appropriate shear-banding intensity parameters. Flow structure is analyzed through velocity, stress, and fluidity, whereupon banded and non-banded response is contrasted at appropriately selected flow rates. Solutions are obtained with our hybrid fe-fv algorithm, capturing essential shear-banded flow features reported experimentally. For a fluid exhibiting banding, banded solutions are generated at a flow rate within the flow curve unstable branch. In the fully developed simple shear flow regions, a split velocity profile is observed, with different viscosity bands at equal stress levels, enhanced with a shock-capture procedure. Non-banded solutions are derived for the lowest and highest flow rates sampled, located in the stable branches. Within the constriction zone, banded profiles are lost due to the mixed non-homogeneous deformation. Shear-banding fluids display less intense viscosity/stress features, correlated with their relatively stronger shear thinning response. The constriction resistance provokes a pressure-level adjustment, leading to fully developed Couette-like constant values upstream–downstream.

Fracture in elongational flow of two low-density polyethylene melts

Samples of two commercial low-density polyethylene melts were investigated with respect to their fracture behavior in controlled uniaxial extensional flow at constant strain rate in a filament stretching rheometer. In order to assess the possible influence of grain boundaries on fracture, the samples were prepared by three different types of pre-treatment: by compression molding of (1) virgin pellets used as received, (2) pellets homogenized in a twin-screw extruder, and (3) pellets that were milled into powder by cryogenic grinding under liquid nitrogen. The elongational stress growth data were analyzed by the Extended Hierarchical Multi-mode Molecular Stress Function (EHMMSF) model developed by Wagner et al. (Rheol. Acta 61, 281-298 (2022)) for long-chain branched (LCB) polymer melts. The EHMMSF model quantifies the elongational stress growth including the maximum in the elongational viscosity of LDPE melts based solely on the linear-viscoelastic relaxation spectrum and two nonlinear material parameters, the dilution modulus GD and a characteristic stretch parameter {overline{lambda}}_m. Within experimental accuracy, model predictions are in excellent agreement with the elongational stress growth data of the two LDPE melts, independent of the preparation method used. At sufficiently high strain rates, the fracture of the polymer filaments was observed and is in general accordance with the entropic fracture criterion implemented in the EHMMSF model. High-speed videography reveals that fracture is preceded by parabolic crack opening, which is characteristic for elastic fracture and which has been observed earlier in filament stretching of monodisperse polystyrene solutions. Here, for the first time, we demonstrate the appearance of a parabolic crack opening in the fracture process of polydisperse long-chain branched polyethylene melts.

Structural and shear and extensional rheological properties of hairy basil seed mucilage for potential application as oropharyngeal dysphagia diets

In this study, mucilage was extracted from the swollen hairy basil (Ocimum × africanum Lour.) seeds using ultrasonic-assisted extraction. Clear mucilage (BSM) was subsequently obtained by centrifugation for studies on its structural and shear and extensional rheological properties. The results revealed that the extracted BSM was rich in galactose and xylose, but low in mannose and galacturonic acid contents which indicated the presence of arabinogalactan and xylan. Small amounts of proteins (∼5%) were also detected. The average molecular weight of BSM was estimated as ∼480 kDa. Shear rheology results showed that aqueous dispersions of BSM at 1.0–2.5%w/v exhibited solid-like viscoelastic behavior with small frequency dependency, resembling a cross-linked gel. All BSM samples also exhibited shear thinning behavior that could be described by the power law model. However, the Cox-Merz rule was not obeyed for all studied BSM gels. The gel's elasticity was enhanced with increasing BSM concentration. For extensional rheology, the apparent extensional viscosity showed an extensional strain-softening behavior and demonstrated higher filament breakup time and extensional viscosity with increasing BSM concentration. A comparison between BSM and commercial thickening agents widely used in dysphagia management showed comparable rheological characteristics, thus suggesting the promising potential of BSM as a thickening agent for this application.

The effect of extensional viscosity on the core structure of fiber orientation for injection-molded fiber composites

Abstract The famous informed isotropic (IISO) viscosity successfully dominates the broader core structure of fiber orientation distributions for injection-molded long fiber composites, due to the flow-fiber coupling effect of stretching deformation. Recently, the GNF-X (Generalized Newtonian Fluid eXtended) constitutive equation of weighted shear/extensional viscosity has been shown to possess the potential to demonstrate the extension-induced corner vortex in the entry flow of a polymer melt. Using GNF-X, three-dimensional injection-molding flow simulations of a center-gated disk are, therefore, performed for verifying the effect of extensional viscosity on the core structure of fiber orientation, namely, the extension-induced fiber orientation. The equivalent of GNF-X and IISO is demonstrated for predicting fiber orientation distribution, while their primary parameter relationship is particularly found herein. It is significant to visualize dramatic patterns of extensional rate occurring in the center-gated disk simulation.

Influence of PMMA brushes grafted from GO on rheological properties of PMMA/SAN immiscible blend in shear and elongation flow

In real technological processes, both shear and elongational flow is present. The material properties may differ significantly under both types of flow. Hence, they both define the final morphology and thus properties of the materials. In this work, the morphology of immiscible blends containing polymer hybrid particles was related to extensional rheological properties for the first time. The effect of various lengths of polymer brushes grafted from graphene oxide particles (GO) surface was investigated. As a polymer matrix the immiscible blend of poly(methyl methacrylate)/styrene-co-acrylonitrile (PMMA/SAN) was used. Thus the poly(methyl methacrylate) (PMMA) brushes grafted from GO (GO-g-PMMA) with various number average molar masses (Mn) of PMMA brushes with respect to chain entanglement limit of freely dispersed PMMA were prepared. The extensional rheological properties were affected by Mn of PMMA brushes, while the rheological properties in shear were unchanged. Transmission electron microscopy revealed the compatibilization effect for short densely grafted brushes with Mn of 10,300 g/mol, as smaller domains were observed. On the contrary, the higher Mn PMMA brushes facilitated coalescence. With increasing length of brushes, the elongational viscosity at low elongation rates (∼< 0.1 s−1) decreased, which facilitated the coalescence. The increase of viscosity at higher elongation rates (∼> 0.1 s−1) was not sufficient enough to cause fiber breakup and thus elongated domains were formed.

Effects of Rheological Properties on 3D Printing of Poly(lactic acid) (PLA) and Poly(hydroxy alkenoate) (PHA) Hybrid Materials

Fused filament fabrication (FFF) has been extensively studied for conventional polymers, but there are few studies that address the processing challenges for biobased, biodegradable polymers such as poly(lactic acid) (PLA) and poly(hydroxy alkenoates) (PHA) in FFF processes. This study has investigated the elongational and shear rheological properties and thermophysical characteristics of PLA/PHA hybrid materials to determine the effects of processing conditions, including nozzle temperatures, bed temperatures, and speeds, on the quality of the PLA/PHA printed products, e.g., adhesion strength and tensile properties. Our findings showed that adding PHA to the composition of the PLA/PHA hybrid material leads to a reduction in shear and extensional viscosities, causing a rise in elongation at break and adhesion strength while showing comparable tensile strength with the PLA samples. In addition to the presence of PHA in the combination of the hybrid materials, processing conditions, including nozzle temperature, bed temperature, and print speed, were found to be effective on the adhesion strength and tensile characteristics of the printed products. Our results suggested that among processing parameters, nozzle temperature has the most significant effect on adhesion strength and tensile characteristics. Samples printed at the nozzle temperature of 215 °C showed an order of magnitude higher adhesion strength and up to 34% enhancement in elongation at break compared to the printed samples at 185 °C. This study sheds light on the significance of the material and processing parameters in obtaining quality products from biobased, biodegradable polymers.

Numerical investigation of pressure drop within isothermal capillary rheometry for viscous and viscoelastic fluids

Abstract In capillary rheometry of a polymer melt, the total pressure drop consists of three primary components: shear viscosity, extensional viscosity, and normal stress differences. Traditionally, viscoelastic constitutive equations have been used to produce accurate predictions regarding the pressure drop. It is difficult to investigate the primary components in past experimental measurements and numerical computations. The useful improvement of the classic White-Metzner viscoelastic constitutive equation coupled with the weighted shear/extension viscosity is performed in isothermal capillary flow simulations. It is significant to analyze the extension-induced pressure drop for a short die and the shear-induced pressure drop for a long die, along with a small contribution of normal stress differences.

Modeling and numerical simulation of flow processes of wood‐polymer composites

AbstractThe combination of natural fibers and polymers is finding expanding application in a range of industrial branches, and knowledge of the material behavior is essential for further improving the products and the processing procedure. In this work, the material behavior of wood‐polymer composites (WPC) will be modeled and numerical simulations will be used to investigate the flow behavior. By means of rheological measurements, a shear thinning flow behavior of the composite can be determined, which is also often taken into account in the numerical simulation of WPC processing tools. Increasing shear viscosity and a formation of a yield point with increasing wood content can be observed. However, in addition to the shear‐dominant deformation states, noticeable strain deformations also occur due to cross‐sectional changes. In order to experimentally investigate and model the behavior of WPC under strain, this work involves measurements on hyperbolic dies in which a uniaxial strain state is present and extensional viscosity can be derived from this. Different boundary conditions such as noSlip, navierSlip and full slip are investigated in the simulations. In addition, during the extrusion of WPC, wall shear stresses of about 0.1 MPa and above can be observed. Measurements in a high‐pressure capillary rheometer allow the wall slip velocity to be measured as a function of the wall shear stress at different wood contents. The wall slip behavior is modeled and taken into account accordingly as a boundary condition in the numerical simulations using OpenFOAM [8].