Is our polyamide water-resistant?

Posted By Claire Chabaud on Feb 3, 2016 | 0 comments

If you are seriously considering using 3D printing to create your next project, then you probably know that , more than the strength and flexibility properties of your material, you need to know for which kind of use it is appropriate. . Don’t worry, you are not the only one. Among our customers, one of the top concerns is the water resistance of our material.  To provide you with a clear answer about the possibilities of our polyamide material in case of water contact, we decided to run empirical tests on its water resistance. Find out our results in this article!

Methodology of the tests

Test 1 – Waterproofness check and pressure levels.

Test 2 –  Waterproofness check and design features

Test 3 – Moistening test

How can you apply these results to your project?

Methodology of the tests

We run 3 tests.

The first one determines if polyamide is waterproof according to different pressure levels.

The second one determines if the water resistance of the polyamide is altered according different design parameters.

The third one determines if post-treatment of polyamide such as dying significantly changes its ability to resist liquid.

Test 1 and Test 2 are run on two spheres with technical properties described as follows:

Sphere A :

Diameter: 20 mm

Wall thickness: 1.5 mm

Weight: 2g

Material: Polyamide ( PA 2200)

Technology: SLS

Coating: None

Sphere B :

Diameter: 30 mm

Wall thickness: 2 mm

Weight: 5.5g

Material: Polyamide ( PA 2200)

Technology: SLS

Coating: None

24 hours before the test run, the caps have been glued with cyanoacrylate glue.

In order to make sure that the caps didn’t change the waterproofness of the material, we run a buoyancy test, which allowed us to consider the density of the sphere. The estimated density is 0.5.

Tests are run in a chamber made with aluminium and filled with water. The pressure is made with a manual pump that can reach 50 bars ( that is to say a depth of simulated flooding estimated of 500 m).

The pressure is measured with a Manometer.

Test 1 – Waterproofness check and pressure levels.

Purpose of the test:

Waterproofness test on hollowed 3D printed spheres.

The purpose of this test is to figure out if 3D printing and polyamide material allow the creation of watertight parts.

Assumptions:

If the final pressure on the manometer doesn’t lower compared to the initial pressure it means that there is no water absorption of the sphere, then the polyamide will be considered as a water resistant material, the result of the test is positive.

If the final pressure on the manometer is lower compared to the initial one, then there is  water absorption and polyamide is not considered to be a waterproof material. Then, the result of the test would be negative.

Test protocol:

The test is organised according 6 pressure stages. This test is only run on Sphere B, because we don’t want to have result altered by some design features. The purpose is just to test the material.

The test protocol is as following:

The sphere is placed in the chamber.

Various stages are reached according to the time and the pressure.

When the first stage is completed, if the result is positive, then we move on the next stage and so on.

The test is run until the final stage: 4 hours with 4 bars.

At the end of the test, the first observation about the buoyancy of the sphere is made.

Then the sphere is dried and weigh-in.

If the weight of the sphere isn’t modified, then the test is considered as positive.

Either way, if the weight is altered, then the test is considered as negative.

Test run:

The sphere is placed in the chamber. Then the increase of the pressure level is gradual.

Here are the results and observations.

5 mins with 5 bars: OK

10 mins with 10 bars: OK

10 mins with 15 bars: OK

30 mins with 20 bars: OK

30 mins with 30 bars: OK

4 hours with 40 bars: OK

The sphere buoyancy doesn’t seem altered.

Then the sphere is dried and weigh-in.

The weight of the sphere isn’t modified, so the test is considered as positive.

Test 2 –  Waterproofness check and design features

Purpose of the test:

After the success of Test 1, we are now going to compare the impact on the two spheres, to see if the thickness of the design can alter the material property.

The pressure and the time are higher than in the previous test. This trial should show that with a long and strong contact with water, it doesn’t start to percolate the polyamide.

Assumptions:

If the final weight is identical to the initial one, then there is no water absorption of the sphere even under strong pressure. Polyamide is considered as a water resistant material, no matter what its design properties are. The result of the test is said to be positive.

If the final weight is heavier compared to the initial one, then there is a water absorption and polyamide is not considered as a waterproof material regarding some specific design properties. Then, the result of the test would be negative.

Test protocol:

The two spheres are placed in a chamber and the pressure is increased at 50 bars.

( Flooding depth simulated estimated at 500m).

The test duration is 36 hours with 50 bars.

Test run:

The two spheres are placed in a chamber and the pressure is increased at 50 bars for 36 hours.

At the end of the test the spheres are taken out of the chamber.

Buoyancy seems unchanged for sphere B and altered for sphere A.

After weigh in, weight of sphere B is stable meanwhile weight of sphere A oscillates between 2 and 2.5 g

In order to check this result we split the sphere in two on an absorbing paper to spot possible dampness trace.

Sphere A has been percolated. One of the main assumption is this result is due to its thin walls (1.5mm), or a micro leak in the gluing.

While Sphere B hasn’t been percolated.

The result of the test is negative, polyamide cannot be water resistant according to some specific design features.

Test 3 – Moistening test

Test 3 is run on squares 3D printed in polyamide and dyed in different colors.

There are 4 samples and 4 categories:

• Raw polyamide (white), no dying
• Black polyamide, the black dying takes the longest time ( >10 minutes)
• Beige polyamide, the beige dying takes the shortest time (<3 minutes)
• Blue color dying, takes an average time of 6 minutes and represents other color such as Red, Green, Pink…

Wall thickness: 2mm

Purpose of the test:

To observe if the dying post-processing step of a part changed it’s waterproofness.

Assumptions:

If after two hours the water is not absorbed by the square and doesn’t leave a trace, then dying post-processing significantly didn’t altered the waterproofness of polyamide. The test is considered as positive

If after two hours the water is absorbed by the square and leaves a trace, then dying post-processing significantly altered the waterproofness of polyamide. The test is considered as negative.

Test protocol:

A drop of water is placed on each part.

Observation of the absorption is made after 5 minutes, 30 minutes, 1 hours and 2 hours.

Test run:

5 minutes: Black and Blue samples are already absorbing the water, nothing happened with the other samples

30 minutes: Black and Blue samples  have absorbed all the water, nothing happened with the other samples

1 hour: No evolution.

2 hours: Black and Blue samples have absorbed, the water drop is still appearing on Beige and White samples.

The results show that the dying step alters significantly the waterproofness of the polyamide. Not in the same way according to the color but it still implies an instability in the water resistance of the material. The test is negative. ( More intense tests should be run to see how beige can be water-resistant in time)

One of the possible explanations to this phenomenon is that the dying step implies a strong solvent in order for the color to impregnate the material. This solvent creates some micro leaks in the part and changes the waterproofness of the polyamide.

Nevertheless with painting which covers the surface of the material  we can expect the opposite result. It should improve the waterproofness by covering all porous aspect.

How can you apply these results to your project?

Well, there are 3 main takeaways from this series of test. Yes, you can use polyamide as a water resistant material for you project. But your design should have at least 2mm wall thickness to have the best waterproofness quality. The dying post-process cannot be used for a waterproof part as it’s altering the porosity of the polyamide.

Thanks to Syera company to have helped us to run these tests.