Usage of Flexfill PEBA 90A
in TECNOFAB-DEFAM Research Group

The research group TECNOFAB-DEFAM is part of the Department of Mechanical Engineering at the Polytechnical University of Catalonia. The team has been working on the mechanical characterization of different Fillamentum materials used by a 3D printing technique such as PLA, ABS, Timberfill®, and some of the types of Flexfill. All of them manufactured by Fillamentum.

This case study aims to define the qualitative properties of Flexfill PEBA 90A, which is a flexible filament based on polyether-block-amide. It is a co-polymeric material with both thermoplastic and elastomeric properties. PEBA 90A is certificated for food and skin contact and is able to work at very low temperatures even at -40 ºC. That is the reason why this study focuses on two different applications: a ski boot fastener and shoe insoles.

SKI BOOT FASTENER

The main advantages of Flexfill PEBA 90A are working very well in low temperatures having a high impact resistance like one could have while skiing. Therefore, one of the applications is its use for ski boot fasteners (Figure 1), which must resist low temperatures and need to be resistant at contact. Additionally, this material shows good resilience which is required for this application.

Figure 1. Ski boot fastener printed with Flexfill PEBA 90A

shoe insoles

The second usage of this material was printing the insole of a shoe, as shown in Figures 2 and 3. The reason for printing this was because of its flexibility, high energy returns, its resistance to cyclic loading without damage, and high reversible deformation. These properties make it ideal for an object that is in constant on and off load and needs to be flexible.

Figuer 2. Parts of a shoe
Figure 3. Flat view of shoe inside (A). Sample of the flexibility of the shoe insole (B). Real application (C)

The printer used for both objects was an Ender-3 Pro with a mirror bedding and the extrusion heat was set up at 245 °C and the bed heat at 60 °C.

This material fulfils all the conditions that both applications needed, besides, it is a recyclable material. This is an important fact as the goal of 3D printing is to lessen the environmental impact, therefore the use of new materials with new properties, like PEBA, can be achieved. Moreover, it has been proved that 3D printing helps with time, cost, and waste reduction.

Tensile test

In order to determine some tensile properties of the Flexfill PEBA, there were two tensile tests done following two different standards: ASTM D638 – Standard Test Method for Tensile Properties of Plastics and ASTM D412 – Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers: Tension. From the data obtained in the tensile tests, two mechanical properties (Young’s modulus and yield strength were processed, deduced and subjected to an ANOVA. Both were done at normal conditions.

ASTM D638

The first tensile test was done according to the norm ASTM D638 and the specimen dimensions established by it are shown on the plan of Figure 4.

Figure 4. Plan of the specimen (mm), ASTM D638

And the specific dimensions of the part of the specimen that is tested are in Table 1:

Configuration Dimensions (mm)
Length: 57
Width: 13
Thickness: 7
Cross section (mm2) 91

The first tensile test was done according to the norm ASTM D638, specifically for plastics. And the results obtained are shown in Table 2:

 

 Layer height (mm)Percentage of filling (%)Young’s modulus (MPa)Yield strength (MPa)
10.202532.85 ± 7.900.67 ± 0.22
20.302530.64 ± 3.871.06 ± 0.14
30.207534.56 ± 2.351.41 ± 0.26
40.307542.55 ± 1.011.31 ± 0.25
5

0.25

5032.46 ± 1.591.31 ± 0.13

The results projected in table 2 show that the combination of parameters that leads to a higher Young’s modulus (42,55 MPa) using the ASTM D638 standard is a 75% infill density and a 0,3 mm layer height.

ASTM D412

The second tensile test was done based on the norm ASTM D412, this one, specific for thermoplastic elastomeric materials. The dimension followed are specified in Figure 5 and Table 3

Figure 5. Plan of the specimen (mm), ASTM D412
ConfigurationDimensions (mm)
Length:59
Width:12
Thickness:3.30
Cross section (mm2)91

Table 3. Dimensions selected, ASTM D4112

The results of which are presented in Table 4. 

 Layer height (mm)Percentage of filling (%)Young’s modulus (MPa)Yield strength (MPa)
10.102524.57 ± 1.850.86 ± 0.04
20.302522.13 ± 3.760.82 ± 0.19
30.107546.28 ± 17.890.61 ± 0.59
40.307535.60 ± 0.951.04 ± 0.09
50.2050 30.17 ± 3.430.95 ± 0.16

If the standard used is ASTM D412, that the combination of parameters that leads to a higher Young’s modulus (46,28 MPa) is a 75% infill density and a 0,1 mm layer height. Although this standard is not used for most of the papers published by researchers of this field of study, the use of this standard would be recommended for PEBA as it is specific for Vulcanized Rubbers and Thermoplastic Elastomers.

Charpy teSt

To test the impact resistance of this material a Charpy test was done by the specifications of the ISO 179 norm. The specimen has the dimensions shown in Figure 6.

Figure 6. Plan of the specimen (mm), ISO 179

The conditions of this test were executed on the frozen specimen at -20 °C and the result was that it did not break.

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