Cup issues

One of the tykes has been too rough with a plastic cup and, while it isn't dead, it is not very happy.

Cup with an internal leak

Broken drinking straw

As the first of the 3 Rs is to reduce I wanted to try and prevent another plastic cup being bought.

The first job was the straw which was missing a bit, but not too much. A quick hacksaw and then I filed it flat and removed the burrs with a round file and that sorted that.

Repaired drinking straw

The next task was to deal with the cup. How to get the water out and how had it got in?

Getting it out meant giving it the opportunity to escape the air gap that gives the cup its' insulating properties.

Non-obvious holes

Drilled 1.5mm holes at 4 and 10 o'clock

Two small holes should give the water the ability to evaporate without compromising the insulating properties of the cup too much. Then it was just leaving it for long enough to do just that.

So it sat next to the central heating boiler for a month.

OK, so how is the water getting in?

Repaired cup

It seems to have developed a crack at some point (after being dropped perhaps?). Solvent welding using capillary action to wick the solvent into the area that needs to be bonded would probably be the best option. But what solvent to use?

The first thing is to identify the plastic that the cup is made out of. In this case the retailer's website wasn't helpful but as they only rebrand stuff (and slap on a healthy margin for the service) you can find similar items out there. Alibaba is a great resource for more detailed product information as you can get direct to the manufacturer. In this case a search for 'tumbler with straw' quickly yielded a couple of identical items (bar the printing/branding) [cut down links to ali items].

In this case it appears that the plastic is SAN, which is commonly used for food-ware and is a relative of ABS. A search for suitable solvents yielded

• Acetone [propan-2-one]
• Methylene chloride [dichloromethane]
• Methyl ethyl ketone [butan-2-one]
• Ethylene dichloride [1,2-dichloroethane]
• Tetrahydrofuran [1,4-epoxybutane]

Courtesy of the AdhesiveTechnology Handbook [p.222].

I have the first three to hand, but acetone is the more pleasant to work with, so I brushed on enough to saturate the fractured area to see if that could seal up the break.

The fracture wicked up the solvent OK and it has had an effect but not a complete one. I have another fix that will use a dichloromethane/MEK mix so I will return the cup to use and try again when I tackle that fix.

JOB (sort of) DONE

Time taken : 30 mins
Cost: Pretty much nil