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.
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.