Overview This procedure is used to measure the sheer strength of a glue sample. This test is aimed at comparing glues and their effectiveness in bonding to PET plastic. Adhesion quality to PET is usually not covered in manufacturers data sheets. The main purpose of this test is for quick evaluation of the glue whether it is suitable for splicing bottles. A sample that passes this test at a low load is very unlikely to be suitable for splicing. A sample that passes this test at a fairly high load is a good candidate for performing a more complicated splice test.

Equipment

• 2 clamps capable of holding a sample of PET plastic
• Weights, container for water
• Scale

Procedure

Sample preparation

1. Cut 1 cm wide strip approximately 10 cm in length from a PET bottle.
2. Clean the strip, removing any grease and dirt.
3. Cut the strip in half, and label both ends of the sample.
4. Lightly sand the end of each strip that will overlap.
5. Draw a line on both halves 1 cm from the end.
6. Apply enough glue to the strip to completely cover the 1cm overlap
7. Carefully overlap the two strips using the lines on each half and clamp if necessary.
8. Allow sample to fully cure according to the manufacturer's instructions before testing.

Test

1. Clamp both ends of the sample in the two clamps. Make sure the sample is well aligned so that the sample is not pulled to one side or twisted when load is applied.
2. Suspend one of the clamps from a strong support such as a door frame.
3. Suspend weights from the other clamp until the sample brakes. An empty container of water can be suspended from the clamp and water gradually poured in until the sample breaks.
4. After the break, use the scale to measure the weight that was suspended under the lower clamp. Don't forget to also include the weight of the clamp and any ropes used to hold the weight. This is the sample's breaking weight. Record this value.
5. Repeat the experiment a number of times and average the results.

Notes

• There can be a substantial amount of weight hanging from the sample. Make sure the weight dropping will not damage the floor.
• A second slack safety line can be used threaded through the weights so that it will stop the weights impacting with the ground.
• The safety line can also be used to prevent the water spilling from the water container so that it can be accurately measured.
• These tests can show a high variability in the results between samples. It is a good idea to make more than 3 measurements for each glue being tested.