Sugru Event - Strength and Keeping Properties




As part of the Sugru Event held in September 2014, Leicester Hackspace (UK) decided to test the strength and keeping properties of Sugru. We had some packs bought in 2011 with a use by date of 06 Aug 2011 and kept in a domestic refrigerator all the time. For the event, Sugru supplied packs with a use by date of 02 Feb 2015, and we also had a packet of softener which made Sugru more flexible. So it was decided to try 3 samples - the 2011, 2015, and a 50:50 mix of 2015 and softener.

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Step 1: Preparation

Three pieces of 1cm thick wood 8cm X 25cm were cut, along with a further thicker batten 5cm wide X 26cm which could be held in a vice. Three samples of Sugru were prepared - a packet of Black 2011, Blue 2015, and red 2015 plus softener. The Sugru was rolled into a ball and placed on the end of each piece of wood and each piece was placed over the 5cm wide batten. The whole assembly was clamped in a vice and squeezed till the Sugru was just oozing to the edge of the wood - a 5cm diameter blob. It was left to cure for 14 days between the two Sugru events we held in September.

A line 20cm from the centre of the Sugru blob was marked on each of the samples.

Step 2: Testing

A tool box weighing 10 Kg was used with a tie-wrap to suspend it on the 20cm line on each sample in turn. Since the force was down and the Sugru joints were underneath the end of the piece of wood, it produced compression at the front and peeling at the rear of the joint. Each sample was able to withstand the 2 Kg-metres torque imposed by this load.

The weight was increased to 13.2 Kg - a torque of 2.64 Kg-metres. With this load the Black and Red were still OK, but to our surprise, the Blue - new batch Sugru broke.

In order to apply more torque to the test pieces, a longer piece of wood and clamps were applied to the two remaining samples - we didnt want to increase the weight any more for fear of making holes in the floor ;-) This new batten added an extra torque of 1 Kg - metre, and the 10 Kg weight could be slid further away from the joints.

The Red sample (new Sugru + softener) broke with a the 10 Kg weight at 22cm + 1 Kg-metre = 3.2 Kg-metres and the Black (old Sugru kept in fridge) broke at 28cm = 3.8 Kg-metres.

The video shows the final breaking of the Black sample - it peels slowly before failing catastrophically. The picture of the three detached joints shows that some Sugru stuck to the wood on either side of the joint.

Step 3: Conclusions

Admittedly this was a very small sample and each colour might have different characteristics, but we conclude that keeping Sugru in the refrigerator for 3 years past its use by date has no negative effect on its performance, apart from maybe making it stronger ;-)

Of course Sugru might like to reply to this Instructable and tell us they have reformulated it in those 3 years, or that Blue is the weakest colour.

We were quite surprised how strong Sugru is as an adhesive - even the weakest was was able to carry a weight of 2.6 Kg at a distance of 1 metre. Attached to a flat surface with no real leverage it would of course support a much greater load. The addition of the softener made no apparent difference to the strength of the joint.

There are obviously many more tests which could be performed on Sugru - eg strength of different colours, keeping properties at room temperature etc. I hope the community will be able to publish more of these.

You can of course just use it to identify your Apple Mac monitor cables or soft jaws for a crocodile clip as shown in the photos - other minor projects during our Sugru event.

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    7 Discussions


    4 years ago on Introduction

    Tony, awesome 'ible'! We decided to share it with the boffins in the Sugru lab and got quite a response back! Thought you'd like a read :)

    Hi TonyA3,

    It is nice to see someone doing adhesion tests on Sugru, and you have definitely found some interesting results.

    You have shown that Sugru can hold a a lot of weight as an adhesive. A couple points I noticed in your instructables post are;

    - Sugru is not typically clamped with such high forces, this could affect the adhesion and mechanical properties. Some force is required to make a good adhesion but too high and this can cause negative effects.

    - You use wooden planks to adhere the Sugru too. What you have to be wary of when using material like this is the naturally occurring oils which are found in the wood, and any surface treatment of the planks, such as varnish or oil as this can affect the chemical reaction between the Sugru and the surface of the substrate and make the adhesion weaker! To minimise this effect during experiments here at Sugru we perform our adhesion tests on Aluminium sheet.

    - From your instructable it is unclear to see, but if you were to sand down to the surface of your material with a rough grade sandpaper you would be able to maximise the adhesion of the sugru. This is because the sanding action will not only create more surface area for the Sugru to adhere too, but it will also remove any dirt/oil or oxide layers on the surface of the material.

    - Another point is that the blue Sugru looks a lot smaller that both the black and the red, this could be one of the reasons why the blue Sugru failed at a lower load.

    Your results for the red Sugru+ Softener are very interesting indeed as we usually find that the addition of softener seems to weaken the adhesion properties (the softener is a beta-formula so will improve with time), so thumbs up for a really interesting result!

    Here at Sugru we perform three types of adhesion test in Sugru in the lab (these are an ongoing WIP), it may interest you to know what they are (i've included some hyperlinks of you want to know a bit more). We perform;

    - Cleavage adhesion tests (ASTM D1062

    - Tensile adhesion tests (ASTM D2095

    - Lap Shear adhesion tests (ASTM D1002

    Following these standards we perform the tests on our in-house Column material tester, this allows us to apply a constant force until the Sugru fails meaning that we don't cause any spikes in force which could lead to premature failure in the Sugru.

    It is really great to see this kind of interest in the adhesive properties of Sugru! If you would like to see the set-up of the adhesive tests one day then get in touch and we may be able to facilitate a visit so you can see how the Sugru scientist's adhesion test!

    Keep up the good work!

    1 reply

    Reply 4 years ago on Introduction

    Hi Projectsugru
    Thanks for the kind words. Points taken about how to maximise adhesion, but I was surprised how good an adhesive it was, even with our bits of old wood, and of course the main conclusion of the test was that we showed that it keeps very well in a fridge - long past its use by date. I'm not sure where you make and test Sugru - our Hackspace - newly formed early this year is in Leicester, UK.


    5 years ago on Introduction

    THanks for sharing. I would suggest you put a different photo as the main image so we can easily tell what the project is about.

    1 reply

    Reply 5 years ago on Introduction

    OK Carleyy

    I have put the Sugru picture back as the main image, but added our Hackspace logo to it.


    5 years ago

    I have some spare sugru, if you want you can have some for a repeat test in 3 years