Morphological and rheological properties of zirconia filled polyethylene

Accepted Manuscript Morphological and rheological properties of zirconia filled polyethylene M.-C. Auscher, R. Fulchiron, T. Périé, P. Cassagnau PII:

S0032-3861(17)31044-3

DOI:

10.1016/j.polymer.2017.10.068

Reference:

JPOL 20110

To appear in:

Polymer

Received Date: 7 August 2017 Revised Date:

24 September 2017

Accepted Date: 31 October 2017

Please cite this article as: Auscher M-C, Fulchiron R, Périé T, Cassagnau P, Morphological and rheological properties of zirconia filled polyethylene, Polymer (2017), doi: 10.1016/ j.polymer.2017.10.068. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Morphological and rheological properties of zirconia filled polyethylene M.-C. Auschera,b, R. Fulchirona, T. Périéb, P. Cassagnaua*

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a) Univ Lyon, Université Lyon 1, Ingénierie des Matériaux Polymères, CNRS UMR 5223, 15 Boulevard Latarjet, 69622 Villeurbanne Cedex, France. b) Saint-Gobain CREE, Grains et Poudres, 550 Avenue Alphonse Jauffret, BP 20224, 84306 Cavaillon, France. *Corresponding author: Tel. +(33) 04 72 44 81 58; Fax: +(33) 04 78 89 25 83

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E-mail address: [email protected]

Abstract

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In the framework of a comprehensive study of the ceramic feedstocks in molten conditions, the viscoelastic behavior of zirconia-filled polymers has been studied over a broad span of particle concentrations (from 0 to 42 vol% i.e., from 0 to 82 wt%) . This study shows that the effect of stearic acid on the melt rheology depends on the filler content, suggesting that different dispersion mechanisms of the fatty acid are involved and prevail over others, depending on the solid concentration. It is shown, for instance, that stearic acid lowers the percolation threshold and modifies the dispersion state. For the first time, the existence of two main regimes in terms of concentration ranges with different network structures is highlighted. The dispersion contributions are discussed for each regime by coupling SEM dispersion characterization, dynamic and steady rheological measurements.

1. Introduction

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Key words: Stearic acid, zirconia, dynamic rheology, yield stress, dispersion

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Polymeric or water-based compounds filled with colloidal inorganic particles are nowadays often encountered in industry. Their rheological behavior and dispersion state play a major role regarding the processing and applications [1]. Additives, such as dispersants like fatty acids, are generally incorporated into the matrix to control the flow behavior, which is even more important when the solid concentration is close to the maximum packing fraction. For instance, Ceramic Injection Molding requires a high solid content, a low yield point and a homogeneous repartition of fine particles. The process can be briefly described in four steps: (1) mixing of the matrix and the fillers to prepare the mixture, (2) injection of the molten filled polymer in the mold to shape the part, (3) removal of the matrix and (4) sintering to obtain a dense part. All the stages need a required dispersion state to avoid defects such as shape distortion, cracks and voids [2]. Many of the requirements are linked to the structure of the three-dimensional space-filling network of particles in the polymer, which arises once the particle content exceeds the percolation threshold [3]. This network appears due to the interparticle potential caused by colloidal forces such as van der Waals, electrostatic and entropic forces between particles [4]. The state of the network can be characterized by rheological parameters like the shear modulus, viscosity or yield stress [5]. In particular, the latter can be understood as the maximum attractive force between particles multiplied by the number of bonds per unit area [6]. Indeed, the yield stress is the minimum 1

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stress required for a filled polymer to flow, i.e., when a lower stress is applied, the network can deform elastically, whereas beyond this critical stress, the network is broken and the compound flows viscously [7]. As underlined by Heymann et al. [7] and more recently by Coussot et al. [8], the yield stress has been a very controversial topic in the past, for instance about the real existence of a true yield stress. Nowadays, the term “apparent yield stress” is often reported and it must be highlighted that its value depends on the fitted model and the data range used to fit the flow curves. Besides, they insisted that the transition from elastic to viscous region occurs through an elasto-viscous region. The yield stress in the sense of a single value is therefore not relevant but rather representative of this transition.

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Different methods exist to measure the yield stress [9], but capillary and dynamic rheometers are generally used. Similar tendencies are obtained from the various methods; however, the precise values may differ [10]. The model proposed by Casson [11] has been successfully applied to a number of systems [12,13] exhibiting a non-linear Bingham-type flow, expressed as: / / (1) = + where is the shear stress, the shear rate, and c is a constant. It can be noted that the Casson model is actually a derivative model of the power law Herschel-Bulkley model.

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Several empirical equations have been proposed to calculate the yield stress from a theoretical point of view, depending on the compound properties [14–16]. In particular, Firth et al. [15] postulated: 3 (2) 2 where is the static yield stress, Φ is the volume solid concentration, a the particle radius, R the center to center distance between particles and V their potential energy of interaction. This highlights a linear relationship between the yield stress and the attractive van der Waals potential, which has also been proposed elsewhere [17]. More generally, it is commonly shared that the yield stress scales as:

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(3) ≈ with k a constant and m an exponent in the range of a few units, which increases with smaller particles [3,6,13]. The yield stress is also reported to depend on the filler shape, filler–matrix and filler–filler interactions as well as wall slip [9,10]. The influence of temperature is unclear; in some cases, it is said to reduce the yield point with increasing temperature [16,18], while some others claim that it does not modify its value [10]. The surface chemistry of the filler is also a key parameter, particularly in aqueous suspensions where the pH and the electrolyte concentration greatly influence the yield stress [19,20]. Fatty acids like stearic acid are often added to improve the dispersion, i.e., to promote the breakdown of agglomerates and repartition of small aggregates, and lower the viscosity and yield stress of the composite, which is desired in order to adapt to the process [12]. In the case of oxide particles like zirconia or alumina, esterification reactions between the carboxylic acids and the hydroxyls at the particle surface occur after heating at elevated temperature for sufficient time [21]. the most of the quantification models used to explain the effect of stearic acid are based on the extended DLVO theory [22]. When added in a sufficient concentration to cover the particles, the fatty acid supplies some stabilization thanks to entropic interactions like steric and osmotic ones [4], but its chain length is too short to supply a full steric repulsion [21]. In the case of polar fillers in a non-polar matrix, stearic acid helps to compatibilize both components by turning the filler’s surface from hydrophilic to hydrophobic [21]. In a parallel study, 2

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the kinetics of the hydrophobization was investigated thanks to contact angle measurements [23]. In particular, it was shown that at 180°C, i.e., at the mixing temperature, the hydrophobization occurs within five minutes so that the reaction takes place during mixing, as confirmed by the FTIR analysis. Once particles are dispersed in a polyethylene matrix at a concentration of 40 vol%, the minimum storage modulus and dynamic viscosity were obtained once the concentration of stearic acid exceeded a critical value corresponding to a monolayer of chemical modifier around the particles. This minimum concentration went together with improved dispersion so that all agglomerates were broken down to aggregates and spread over the matrix. This behavior was assigned to reduced interparticle attractive interactions.

2.1. Materials

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2. Experimental details

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By extension, provided that stearic acid sufficiently covers the particle, it is expected that it will improve the dispersion and the rheological behavior (e.g., lower storage modulus and yield stress) at all particle contents. However, contrary to what is commonly accepted, it is observed that its effect on the flow depends on the filler content. Different mechanisms are suggested, which is the topic of the present study.

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Yttria-stabilized zirconia powder (CY3Z-MA, Saint-Gobain ZirPro, France) with a D50 of 0.2 µm and a specific surface area of 14.3 m²/g was used as filler. The raw powder was relatively spherical and was constituted of agglomerates with a diameter of about 60 µm. The matrix was composed of low density polyethylene (PE, Riblene MV10, Versalis Eni, Italy) as the binder. The zero shear viscosity of this PE is η0=250 Pa.s at 190°C and the steady shear compliance is Je0=10-3 Pa-1. Irganox 1010 (Sigma-Aldrich, France) was added to prevent the thermo-oxidative degradation of the PE. Stearic acid (Sigma-Aldrich, France) was used as the dispersant. According to our previous study [23], the stearic acid concentration of 2.2 wt% (by weight of particles) was used in the present study.

2.2. Methods

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The samples were prepared by melt mixing the components in a twin-screw extruder (Leistritz ZSE18; Diameter D= 18 mm and ratio diameter over length L/D=60) at 180°C at solid concentrations ranging from 0 to 42 vol%, i.e., from 0 to 82 wt%. The screw speed was fixed to N=1000 rpm and the global flow rate to Q=3kg.h. Under these conditions, the mean residence time distribution is close to tm∼20 s [24]. The polyethylene is then first added with the antioxidant in the main solid feeding zone of the barrel. Once molten through the first mixing zone, the zirconia particles were incorporated with the stearic acid as surface modifier in view of improving the dispersion quality. Actually the zirconia particles are introduced in the molten PE at the characteristic length L=22D with the aid of a side feeder specifically devoted to powder feeding. The filler concentration was checked by TGA analyses on several parts for each batch. The samples were then pressed into disks of 1 mm thickness for the rheological experiments. A parallel-plate geometry, for a convenient way to place the highly concentrated samples, was chosen with a diameter of 8 and 25 mm respectively for the yield stress and dynamic shear measurements.

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The rheometer (DHR2, TA instruments) has been used in both dynamic and steady shear modes. All tests were performed at 190°C under nitrogen to prevent from degradation. For dynamic tests, frequency sweeps were performed at a shear stress of 100 Pa, while for steady tests, the shear stress was logarithmically increased from 102 to 105 Pa with 20 points per decade in view of precisely determining the yield stress. The latter was extrapolated at zero shear rate from a linear regression in the shear rate range of 0.5 to 2 s-1/2 as illustrated in Figure 1.

Figure 1: Example of yield stress determination using the Casson equation.

Besides, in comparison with experiments like Large Amplitude Oscillatory Shear (LAOS), this method measures a static yield stress instead of a dynamic one. It is worth noting that the static yield stress might be larger than the dynamic one [9].

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To evaluate the dispersion state of the compounds, observations were performed by scanning electron microscopy (SEM). Samples were fractured in liquid nitrogen, and the cross-section was coated with a thin layer of metal and analyzed by back-scattered electron microscopy. Very well dispersed samples suggest a homogeneous repartition of individual zirconia particles within the matrix. Due to the high uncertainties of image analysis, no quantification of the dispersion could be undertaken. Though, as a first approach, the dispersion is said to be improved if fewer agglomerates are detected in the sample at an intermediate magnification.

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3. Results and discussion

In a first step, dynamic frequency sweeps were performed to study the network state when increasing the solid concentration and adding dispersant. Figure 2 (a) (without stearic acid) and 2 (b) (with 2.2 wt% stearic acid) show the variation of the storage moduli vs the angular frequency for polymers filled with different particle concentrations up to 42.5 vol%. It must be pointed out that we showed [23] from contact angle measurements by the sessile drop method, that a maximum value of about 120° (contact angle between water and zirconia modified surface), is achieved once the fatty acid practically covers its entire surface at the monolayer scale (1.6 mg/m² of stearic acid corresponding to a concentration of 2.2 wt% (by weight of particles).

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It can be observed that an equilibrium plateau at low angular frequencies appears once a critical filler concentration is exceeded. This is known as the percolation threshold, referred to as Φc, which denotes the existence of a particles network [25]. Below this critical concentration, the rheological behaviors are very close to the matrix behavior, with a slight modification of the terminal relaxation zone, whereas beyond these thresholds the storage moduli drastically increase. This behavior is even more pronounced without stearic acid.

Figure 2: Dynamic frequency sweeps at σ= 100 Pa, 190°C of polymers filled with zirconia particles, (a) without and (b) with 2.2 wt% stearic acid (SA).

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To characterize the rheological behavior of the filled polymer, the equilibrium storage modulus at low frequency ( ) and the yield stress (σy) have been investigated. The first one is related to the elastic properties of the percolated network under dynamic conditions, while the second one is more representative of the brittleness of the network under static conditions. Both dependencies on solid concentrations and stearic acid are plotted in Figure 3 (a) and Figure 3 (b) respectively. Below the percolation threshold, there is no yield stress and the storage modulus does not exhibit a plateau value at low frequency. The storage modulus at 0.15 rad.s-1 is given in order to characterize polymers with low filler contents in the terminal zone. This corresponds to the lowest frequency so that the signal is still accurately measurable for all samples.

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Figure 3: Rheological behaviors of filled polymers at 190°C: (a) Storage modulus at low frequency; (b) yield stress. Full symbols: without stearic acid, open symbols: with stearic acid (SA) as surface modifier. Curve fit from Eq 4.

Beyond the percolation threshold,

and σy can be fitted by a percolation law of the following form [26]:

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(4) = − ! "# where A is either or σy, A0 is a constant, ! is the percolation threshold and p is the power law exponent. These different values are reported in Table 1. Table 1: Fitting parameters $% , A0 and p from the variations of G'0 and σy versus particle concentration and according to the percolation law (Eq. (4)), with and without stearic acid.

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Φc (vol%) A0 p G'0 σy G'0 σy G'0 σy 11 11 10 0.00040 5.0 3.6 No stearic acid 3.5 3.5 1 0.0025 3.6 2.1 Stearic acid It can be observed that the power law exponent p decreases both for the storage modulus at low frequency and the yield stress when stearic acid is added. As mentioned in the introduction, the yield stress is generally fitted by Eq. (1). Similarly, has been fitted by a power law equation several times in the literature. For both, the power law exponent has often been related to the type of interparticle interactions [6,27,28]. For instance, Paquien et al. studied the evolution of in the case of fumed silica in PDMS [27]. The exponent was reduced from 7.2 to 2.8 as the particles surface turned from hydrophilic to hydrophobic, i.e., as the interactions between particles decreased. Likewise, Yziquel et al. concluded that, for fumed silica in paraffin oil, the power law exponent from the fit of was reduced from 4.2 to 3.9 when the particles were coated to become hydrophobic. Thus, it can be inferred that stearic acid contributes lowering the interparticle interactions, as proposed by the previous study [23]. The percolation thresholds of systems with and without stearic acid as dispersant are about 3.5 and 11 vol% respectively. It can be pointed out that or σy exhibit the same percolation thresholds. Below the percolation threshold of both systems, the contribution of the fillers to the reinforcement of the matrix is only marginal, as suggested by the following equation for rigid spheres dispersed in a viscoelastic matrix [29]: ∗

'" =

∗

()*

'"

1 + 3/2 1−

(5) 6

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where ∗ '" and ∗ ()* '" are the complex moduli of the filled polymer and of the matrix at a frequency ' respectively. This suggests that the filler content is so low that the particles are sufficiently well separated and the interactions between agglomerates are negligible. Besides, the dispersion state is only slightly improved by the addition of the stearic acid, and the variation of the storage modulus shows a slight modification of the terminal relaxation zone.

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Furthermore, two rheological regimes can be defined depending on the percolation threshold observed with and without stearic acid. The first regime is defined by the concentration range between the two percolation thresholds, i.e., with and without stearic acid Φc≈ 3.5<Φ (vol%) < Φc≈ 11. Generally speaking, stearic acid is expected to reduce the interparticle forces and to improve the compatibility of the matrix with the fillers. First, it can then be observed that stearic acid drastically decreases the percolation threshold. In this range of particle contents, in the presence of stearic acid, the particles are percolated and a plateau value of the storage modulus at low frequency can be measured. It must be highlighted that higher values of the storage modulus and yield stress in the presence of stearic acid can be surprising in this range of filler concentrations. This is a direct consequence of the lower percolation threshold and can be interpreted as an additional effective volume concentration Φeff, due to either swelling or higher aspect ratios of the agglomerates and aggregates. In the first case, stearic acid would only help to swell the agglomerates by absorbing some amount of the matrix, while, in the second case, it would promote the formation of aggregates with high aspect ratios. For both options, this would imply that, at a given solid content, the effective particle concentration is higher than the true one and the compound behavior with the additive is equivalent to higher solid concentrations without stearic acid. The dependence of the rheological parameters on the solid content would hence be shifted toward lower filler concentrations in the case of using the additive.

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To investigate the possible mechanisms, SEM observations were made on the polymers filled with about 9 vol% of particles, with and without stearic acid. As shown in Figure 4, many large agglomerates are still unbroken. However, when the stearic acid is added, the dispersion is greatly improved and many fewer agglomerates are seen.

Figure 4: SEM observations (x800) of about 9 vol% filled polymers (a) without and (b) with 2.2 wt% stearic acid, prepared by extrusion.

Furthermore, at a larger magnification (see Figure 5), larger aggregates seem to be found in the sample without stearic acid. Quantifying a possible swelling of aggregates or agglomerates is not relevant, due to 7

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the great uncertainty related to the image analysis. When considering the second option, some aggregates with high aspect ratios in the matrix are found in the dispersed phase, as highlighted for some of them in Figure 5 by dotted lines. This confirms that, during mixing, broken agglomerates are likely to leave units with high aspect ratios, which increases the effective concentration. This is expected to occur for both systems; however, as the energy barrier necessary to break down agglomerates is supposed to be lower in compounds containing stearic acid, more aggregates with high aspect ratios are likely to be produced in this case.

Figure 5: SEM observation (x50k) of about 9 vol% filled polymers, (a) without and (b) with 2.2 wt% stearic acid. Some high aspect ratio agglomerates are surrounded by a dotted line.

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To conclude on the rheological behaviors in this concentration regime, the stearic acid, which reacts at the particle surface, promotes the dispersion of aggregates by an erosion mechanism and consequently increases the connectivity, i.e., the number of particle–particle interactions, as in lamellar nanocomposites by exfoliation. This reduces the interparticle potential so that it can be suggested that the energy barrier to break down agglomerates is lowered. As a consequence, the dispersion is made easier. Besides, aggregates with high aspect ratios, i.e., with higher interconnectivity, are created.

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The second regime is observed for the particle concentrations higher than the percolation threshold without stearic acid (Φ (vol%) >11). Actually, most of the studies in the literature focus on this concentration regime [12,18,30] and are in agreement with the tendencies observed in the present work. Interestingly, both smaller yield stress and storage modulus in the presence of stearic acid suggest that, in this range of filler concentrations, the decrease of particles network strength prevails over other contributions, like the increase of particle bonds that had been predominant in the previous concentration range. As discussed previously, stearic acid strongly reduces the attractive interparticle interactions, as shown by the lower power law exponent. On the contrary, the effect on the dispersion appears to be reduced. This is illustrated in Figure 6: SEM observations of about 26.5 vol% filled polymers (a), (c) without and (b), (d) with 2.2 wt% stearic acid. Magnification (a), (b) x7.5k and (c), (d) x50k. for polymers filled with 26.5 vol% of particles, with and without stearic acid. Once all the agglomerates are broken and dispersed, the effect of stearic acid on the dispersion state is less pronounced. At least, the electronic microscopy is no longer suitable to pronounce on the particle dispersion at these high 8

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concentrations. It should be underlined that the dispersion is seen to be already greatly improved when increasing the particle concentration. Indeed, by comparing Figure 4 (a) and Figure 6 (a), the solely addition of particles favors the breakdown and repartition of agglomerates, so that the contribution of stearic acid to the increase of interconnectivity is lower. As a consequence, the particle network is more brittle and less rigid when stearic acid is added and has reacted at the particle surface.

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Figure 6: SEM observations of about 26.5 vol% filled polymers (a), (c) without and (b), (d) with 2.2 wt% stearic acid. Magnification (a), (b) x7.5k and (c), (d) x50k.

4. Conclusion

The dispersion and rheology of zirconia-filled polymers was investigated over a wide range of filler contents up to 42.4 vol%. When stearic acid is added in a sufficient concentration, interparticle forces are reduced so that the dispersion is promoted and the percolation threshold is triggered at a lower solid content. The effect on the rheology is therefore highly dependent on the zirconia particle content. However, it is shown that the fatty acid always helps to break down the agglomerates and to distribute the particles in the polymer matrix. Two main rheological regimes have been defined depending on the percolation threshold observed with and without stearic acid. The first regime is defined by the concentration range between the two percolation thresholds, i.e., with and without stearic acid Φc≈ 3.5<Φ (vol%) < Φc≈ 11. Stearic acid, which 9

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reacts at the particle surface, promotes the disperson of aggregates and consequently increases the connectivity, i.e., the number of interparticle interactions. The second regime is observed for the particle concentrations higher than the percolation threshold without stearic acid (Φ (vol%) >11). In this domain of highly filled polymers, the decrease of the particles network strength in the presence of stearic acid prevails over other contributions. It is believed that stearic acid contributes to reduce the attractive interaction between particles. Therefore, the particle network is more brittle and less rigid when stearic acid is added and has reacted at the particle surface.

Acknowledgments

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The authors are grateful to the French National Association for Research and Technology and SaintGobain CREE for their financial support (CIFRE convention n°2014/0524). The authors thank M. Oison for his help during SEM analyses and are grateful to Saint-Gobain ZirPro for providing the powders.

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References

Rueda MM, Auscher M-C, Fulchiron R, Périé T, Martin G, Sonntag P, et al. Rheology and applications of highly filled polymers: A review of current understanding. Prog Polym Sci 2017;66:22–53. doi:http://doi.org/10.1016/j.progpolymsci.2016.12.007. [2] Shivashankar TS, Enneti RK, Park S-J, German RM, Atre SV. The effects of material attributes on powder–binder separation phenomena in powder injection molding. Powder Technol 2013;243:79–84. doi:http://dx.doi.org/10.1016/j.powtec.2013.03.037. [3] Subbanna M, Malghan SG. Shear yield stress of flocculated alumina–zirconia mixed suspensions: effect of solid loading, composition and particle size distribution. Chem Eng Sci 1998;53:3073–9. doi:10.1016/S0009-2509(98)00158-4. [4] Israelachvili JN. Intermolecular and Surface Forces (Third Edition). Third Edition. San Diego: Academic Press; 2011. [5] Pugh RJ, Bergström L. Surface and colloid chemistry in advanced ceramics processing. vol. 51. CRC Press; 1993. [6] Megías-Alguacil D, Durán JDG, Delgado AV. Yield Stress of Concentrated Zirconia Suspensions: Correlation with Particle Interactions. J Colloid Interface Sci 2000;231:74–83. doi:http://dx.doi.org/10.1006/jcis.2000.7121. [7] Heymann L, Peukert S, Aksel N. On the solid-liquid transition of concentrated suspensions in transient shear flow. Rheol Acta 2002;41:307–315. doi:10.1007/s00397-002-0227-1. [8] Coussot P, Malkin AY, Ovarlez G. Introduction: yield stress—or 100 years of rheology. Rheol Acta 2017;56:161–162. doi:10.1007/s00397-017-1003-6. [9] Bonn D, Paredes J, Denn MM, Berthier L, Divoux T, Manneville S. Yield Stress Materials in Soft Condensed Matter. ArXiv150205281 Cond-Mat 2015. [10] Hornsby PR. Rheology, Compounding and Processing of Filled Thermoplastics. In: Jancar J, Fekete E, Hornsby PR, Jancar J, Pukánszky B, Rothon RN, editors. Miner. Fill. Thermoplast. Raw Mater. Process., Berlin, Heidelberg: Springer Berlin Heidelberg; 1999, p. 155–217. [11] Casson N. A flow equation for pigment oil suspensions of printing, ink type. Rheol. Disperse Syst. C.C. Mill, Oxford: Pergamon press; 1959, p. 84–104. [12] Tseng WJ, Liu D-M, Hsu C-K. Influence of stearic acid on suspension structure and green microstructure of injection-molded zirconia ceramics. Ceram Int 1999;25:191–5. doi:http://dx.doi.org/10.1016/S0272-8842(98)00024-8.

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EP

TE D

[1]

10

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[13] Liu D-M, Tseng WJ. Yield behavior of zirconia-wax suspensions. Mater Sci Eng A 1998;254:136–46. doi:http://dx.doi.org/10.1016/S0921-5093(98)00699-6. [14] Poslinski AJ, Ryan ME, Gupta RK, Seshadri SG, Frechette FJ. Rheological Behavior of Filled Polymeric Systems I. Yield Stress and Shear-Thinning Effects. J Rheol 1988;32:703–35. doi:http://dx.doi.org/10.1122/1.549987. [15] Firth BA, Hunter RJ. Flow properties of coagulated colloidal suspensions. J Colloid Interface Sci 1976;57:248–56. doi:http://dx.doi.org/10.1016/0021-9797(76)90200-9. [16] Liu D-M. Effect of Dispersants on the Rheological Behavior of Zirconia-Wax Suspensions. J Am Ceram Soc 1999;82:1162–8. doi:10.1111/j.1151-2916.1999.tb01890.x. [17] Liu D-M. Control of yield stress in low-pressure ceramic injection moldings. Ceram Int 1999;25:587–92. doi:http://dx.doi.org/10.1016/S0272-8842(98)00066-2. [18] Çetinel FA, Bauer W, Müller M, Knitter R, Haußelt J. Influence of dispersant, storage time and temperature on the rheological properties of zirconia–paraffin feedstocks for {LPIM}. J Eur Ceram Soc 2010;30:1391–400. doi:http://dx.doi.org/10.1016/j.jeurceramsoc.2009.12.003. [19] Leong Y, Boger DV, Parris D. Surface chemistry and rheological properties of zirconia suspensions. J Rheol 1991;35:149–65. doi:http://dx.doi.org/10.1122/1.550225. [20] Johnson SB, Franks GV, Scales PJ, Boger DV, Healy TW. Surface chemistry–rheology relationships in concentrated mineral suspensions. Int J Miner Process 2000;58:267–304. doi:http://dx.doi.org/10.1016/S0301-7516(99)00041-1. [21] Novak S, Vidovic K, Sajko M, Kosmac T. Surface Modification of alumina powder for LPIM. J Eur Ceram Soc 1997;17:217–23. [22] Lewis JA. Colloidal Processing of Ceramics. J Am Ceram Soc 2000;83:2341–59. doi:10.1111/j.11512916.2000.tb01560.x. [23] Auscher MC, Fulchiron R, Fougerouse N, Périé T, Cassagnau P. Zirconia based feedstocks: Influence of particle surface modification on the rheological properties. Ceram Int 2017. doi:https://doi.org/10.1016/j.ceramint.2017.09.100. [24] Fel E, Massardier V, Mélis F, Vergnes B, Cassagnau P. Residence Time Distribution in a High Shear Twin Screw Extruder. Int Polym Process 2014;29:71–80. doi:10.3139/217.2805. [25] Cassagnau P. Payne effect and shear elasticity of silica-filled polymers in concentrated solutions and in molten state. Polymer 2003;44:2455–62. doi:10.1016/S0032-3861(03)00094-6. [26] Cassagnau P. Melt rheology of organoclay and fumed silica nanocomposites. Polymer 2008;49:2183–96. doi:http://dx.doi.org/10.1016/j.polymer.2007.12.035. [27] Paquien J-N, Galy J, Gérard J-F, Pouchelon A. Rheological studies of fumed silica– polydimethylsiloxane suspensions. Colloids Surf Physicochem Eng Asp 2005;260:165–72. doi:http://dx.doi.org/10.1016/j.colsurfa.2005.03.003. [28] Yziquel F, Carreau PJ, Tanguy PA. Non-linear viscoelastic behavior of fumed silica suspensions. Rheol Acta 1999;38:14–25. doi:10.1007/s003970050152. [29] Graebling D, Muller R, Palierne JF. Linear viscoelastic behavior of some incompatible polymer blends in the melt. Interpretation of data with a model of emulsion of viscoelastic liquids. Macromolecules 1993;26:320–9. doi:10.1021/ma00054a011. [30] Tseng W, Teng K-H. Effect of surfactant adsorption on aggregate structure and yield strength of zirconia-wax suspensions. J Mater Sci 2001;36:173–8. doi:10.1023/A:1004805523977.

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Highlights

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The dynamic and static rheological behaviors of zirconia filled LDPE are studied Stearic acid lowers the percolation threshold At low solid contents, stearic acid mainly promotes interparticle connectivity At high solid contents, stearic acid mainly reduces interparticle interaction

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