phase separation of highly filled powder/polymer...

Phase Separation of Highly Filled Powder/Polymer Compounds

BERENIKA HAUSNEROVA1, PETR FILIP2, LUKAS JIRANEK1, PETR SAHA1

1Centre of Polymer Systems Polymer Centre

Tomas Bata University in Zlín nám. T.G.Masaryka 5555, 760 01 Zlín

CZECH REPUBLIC [email protected]; [email protected]; [email protected] http://web.utb.cz/

2The Institute of Hydrodynamics of the Academy of Sciences of the Czech Republic Pod Patankou 30/5, 166 12 Prague

CZECH REPUBLIC [email protected]

Abstract: Highly filled polymeric compounds naturally exhibit rather complex flow behaviour, accompanied with separation of material components (powder and polymer) during high shear deformation processes. An understanding of rheology of such systems thus plays a crucial role in solving the critical quality issues of the process. This paper proposes a new design of the testing mould allowing observing the flow pattern in geometrically critical situations causing separation. Then, scanning electron microscopy analysis of particular cross sections derived from this testing mould, combined with energy dispersive X-ray analysis of the distribution of elements typical for powder and polymer component, is employed in order to provide a quantitative evaluation of phase separation. In comparison to previous approaches reported heretofore it offers quantitatively significant results, and thus might be further used in the simulation approaches in order to optimize the processing of highly filled compounds.

Key-Words: highly-filled compounds, phase separation, flow pattern, testing mould, energy dispersive X-ray analysis

1 Introduction Many issues influencing quality of the moulded

products are directly connected to the flow behaviour of highly filled materials during processing. In some cases, a portion of final parts that does not meet the quality requirements, may reach up to 25 % of the production [1].

Flow parameters describing conditions in the mould cavity are fundamental for successful simulations provided prior to real mould construction, and thus preventing air traps, dead zones, or weld lines on the moulded part.

Currently, the separation of polymer and filler components during mould filling is the main critical processability point. Thornagel [2] has demonstrated (assuming no slip, i.e. good adhesion of feedstock to the channel wall) that the phase separation might arise as a consequence of local shear rate gradients occurring close to the wall of the flow channel. Particles flowing in the peak area close to the wall experience non-uniform shear rates leading to their rotation, which increases in severity as the shear stress gradients grow. Thus, rotating particles naturally move away from areas of high shear

gradients to the middle of the flow domain, which is consequently characterized by a plateau at a considerably lower shear rate level. As a result, high polymer content is typical for the area of the highest shear rate (Figure 1), while the plateau of the lower shear rate accommodates powder rich pools.

Figure 1 Detail of polymer-rich (separated) area.

Mathematical Methods and Techniques in Engineering and Environmental Science

ISBN: 978-1-61804-046-6 257

The description of separation phenomenon is complicated by the fact that the separation pattern changes continuously, demanding a multi-phase simulation, i.e. taking into account individual compound components.

2 Problem Formulation Prediction of a separation onset and its

development during mould filling requires consideration of relevant processing factors and conditions, and their relation to the separation phenomenon.

In the first place it is necessary to use proper mould geometry. Currently employed testing moulds - spiral, square spiral and zig-zag (Figure 2) - only partly fulfill the purpose.

Figure 2 Different cavity geometries of the testing

mould used in work of Jenni et al [3, 4].

The next task is to propose the method of quantitative determination of separation severity. Jenni et al. [3, 4] employed differential scanning calorimetry (DSC) to quantify local changes in powder concentration through the differences in glass transition temperatures. They compared the experimental findings derived from the three testing moulds (obtained through radiography, computer tomography and DSC) with a software simulation based on the balance model of the flow of rigid, spherical particles in a Newtonian fluid. However, DSC has not proved to be a suitable approach to detect the changes in powder concentrations for compounds containing multiple polymer components.

3 Problem Solution 3.1 Experimental Three highly filled (60 vol.%) compounds (abbreviated B, P, E) based on stainless steal powder 316L were tested; their densities are depicted in Table 1.

The injection molding machine ARBURG Allrounder 320C (EUROMAP size 600-100) was used for the testing.

Table 1 Flow properties of tested materials.

Material B P E

Density (g/cm3) 7.96 7.75 7.9

4 Results & Discussion New design of the testing mould (Figure 3) has

been developed at the Polymer Centre TBU in Zlín in cooperation with Fraunhofer IFAM, Bremen and designed by using the Autodesk® Inventor® 2010 software. The injection mold assembly was constructed by modifying standardized parts supplied by HASCO. It allows intercepting the main critical geometrical issues as inner and outer corners, radical thickness changes, weld-lines and very thin parts.

Figure 3 New design of a testing mould [5].

Testing compounds were molded at the conditions displayed in Table 2. Table 2 Conditions of injection moulding process.

Material B P E

Zone 1 temperature (°C) 160 170 100



Nozzle temperature (°C) 190 190 150

Mold temperature (°C) 80 80 60

Volume rate (cm3/s) 55 55 55

Injection pressure (bar) 2000 2100 900

Hold pressure (bar) 2200 2200 1500

Hold pressure time (s) 4 4 4

The most visible area of the phase separation, occurring on a surface of the testing specimen and located around the gates entering each square mould


ISBN: 978-1-61804-046-6 258

element can be seen from the scanning electron microscope (SEM) scans. The SEM analysis clearly shows the development of phase separation during the filling of the mould. The size of polymer-rich area significantly progresses as the flow front moves further.

Figure 4 SEM of phase separation area developing

with the flow front (from the top to the bottom).

Further, SEM combined with energy dispersive X-ray (EDX) analysis of the distribution of elements typical for powder and polymer, might provide a quantitative evaluation of the phase separation as demonstrated in Figure 5. The lower spectrum in Figure 5 represents the area without separation, giving distribution of elements typical for powder (Fe, Si, Cu) and polymer (O and C), while the upper spectrum is typical for polymer rich area, where Fe element is highly reduced, and other powder components (Cr and Si) disappear completely.

Figure 5 EDX analysis of polymer-rich (upper) and uniform (lower) areas.

In comparison to approaches reported heretofore,

SEM-EDX analyses offer quantitatively significant results as demonstrated with Table 3. Thus, any cross section might be divided into mesh windows with defined powder (or polymer) concentrations serving as a base for simulation approaches. Also, the resistance of various compounds to the separation can be evaluated.

Table 3 Quantification of separation phenomenon via combined SEM/EDX analysis.

Element (wt. %) 1- powder rich 2- binder rich

C 23.07 58.23

O 3.80 32.17

Fe 64.37 9.60

Cu 1.41 -

Si 0.30 -

Cr 7.05 -

Total 100 100


ISBN: 978-1-61804-046-6 259

5 Conclusion The design of testing specimen was created for a better understanding of the phase separation phenomenon occurring at high shear deformations of highly filled polymer/powder compounds. The geometry of this testing mould was developed to involve critical elements causing the phase separation as inner and outer corners, radical thickness changes, weld lines and a thin film part.

The designed geometry also allows observing the phase separation progression by including elements with different cross sections.

Further, scanning electron microscopy (SEM) analysis of particular cross sections derived from this testing mould, combined with energy dispersive X-ray (EDX) analysis of the distribution of elements typical for powder and polymer components, might provide a quantitative evaluation of phase separation. In comparison to previous approaches presented it offers quantitatively significant results.

Acknowledgment: The Grant Agency of the Czech Republic (103/08/1307) and the Ministry of Education, Youth and Sports of the Czech Republic (MSM 7088352101) are acknowledged for the financial support. This article was created with support of Operational Program Research and Development for Innovations co-funded by the European Regional Development Fund (ERDF) and national budget of Czech Republic, within the framework of project Centre of Polymer Systems (reg. number: CZ.1.05/2.1.00/03.0111).

References: [1] Williams N.: Fraunhofer IFAM: A Commitment to industry oriented research helps drive MIM product development. PIM Int. 3, 2009, 51-56. [2] Thornagel M.: MIM-Simulation: A virtual study on phase separation. In Proceedings of EURO PM2009 Congress. Shrewsbury: European Powder Metallurgy Association, 2, 2009, 135-140. [3] Jenni M., Schimmer L., Zauner R., Stampfl J., Morris J.: Quantitative study of powder binder of feedstocks. PIM Int. 2, 2008, 50-55. [4] Jenni M., Zauner R., Stampfl J.: Measurement Methods for Powder Binder Separation in PIM Components. In Proceedings of EURO PM2009 Congress. Shrewsbury: European Powder Metallurgy Association, 2, 2009, 141-146. [5] TOMAS BATA UNIVERSITY IN ZLIN. Testing Sample. Devisers: JIRANEK, L., HAUSNEROVA, B., HARTWIG, T. Community Design 001704974, Office for Harmonization in the Internal Market, Alicante, 2010-05-06.


ISBN: 978-1-61804-046-6 260

phase separation of highly filled powder/polymer...

Documents