Failure on a polyethylene tank

The tank to be tested presented a superficial ductile  fracture, with different damaged parts around it. SEM view. Thickness determination. Differential scanning calorimetry DSC. Degree of curing determination.
Fracture zone SEM viewFracture zone SEM view
Fracture zone SEM view
Sem view
The tank to be tested presented a superficial ductile  fracture, with different damaged parts around it. Our laboratory performed some tests on the tank, on damaged and undamaged parts. At the same time, a "new" tank has been tested too.
Thickness determination
A thickness measurement has been perfomed on different areas of the polymeric material
Differential scanning calorimetry DSC
The DSC test has been perfomed on the damaged tank both on the broken part and on an undamaged part. At the same time the DSC test has been perfomed on a "new" tank in order to have a standard reference. The melting points show that the material is a high density Polyethylene.
Damaged zone degree of curing determinationDamaged zone degree of curing determination
Damaged zone degree of curing determination
Degree of curing determination
The degree of curing has been determined both on the broken part and the new tank. The degree of curing is significantly higher on the new tank.
Final results
If crossed-link zones are present on a polymeric product, the general characteristics of the material are more efficient: at high temperature the efficiency concerns chemical resistance and aggressive organic solvents solubilization; while at low temperature it concerns resistance to tensile stress, resistance to scratches and resistance to ductile fracture.

Dott.ssa Emma Martin Gonzales
Technical details
In order to perform a SEM analysis, it is obviously necessary to use a scanning electronic microscope. It is possible to produce a microphotographic image of the sample area to be tested. The final result is a qualitative result (and not quantitative).

The differential scanninc calorimetry or DSC, is a thermoanalytical technique; the information about the material (in this case polymeric) are obtained exposing the sample to be tested at high or low controlled temperatures.

The degree of curing (cross-linking) is the percentage of thermoplastic material where the chemical union has happened among the molecules. This union produces a structural transformation of the material, transforming a part of the thermoplastic material in thermosetting. The cross-linking of a thermoplastic material improves certain characteristics as: resistance to the abrasion, chemical resistance and mechanical resistance in the time. The determination of this parameter allows ti establish the correct degree of compromise between mechanical resistance (due to crossed-linked zones) and flexibility (due to not crossed-linked zones); this compromise is necessary for the employment of the final product.
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