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25-30

Polyethylene – Colour masterbatch     

Title

POLYMER FAILURE ANALYSIS INVESTIGATION; CREAM MASTERBATCH UNDERGOING PINKING DISCOLORATION

Date

2013

Objective

To carry out an examination of the three colour masterbatch products.

Photo

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Figure 1. Colour shifting occurring with the polymer containing the ELJ21250masterbatch after weathering

Testing Undertaken

Accelerated weathering

Colorimeter Colour Space Measurements

EDAX

NMR

Failure Analysis

The masterbatch contained a yellow dye that faded when exposed to UV light thus changing the observed colour balance shifts from yellow to pink due to the highlighting of the underlying iron oxide red tints.

 

Polyethylene – Container

Title

INVESTIGATION OF FAILURE OF A POLYETHYLENE INTERMEDIATE BULK CONTAINER (IBC)

Date

2013

Objective

To investigate the cause of a cracking failure of a HDPE intermediate bulk container (IBC)

Photo

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Figure 1. Samples as received

Testing Undertaken

EDAX elemental scans

DSC thermal analysis

OIT

Carbonyl Index Measurements

Failure Analysis

The samples of the failed tank underwent oxidative embrittlement. Fracture could have occurred during normal handling of the tank as the material was extensively degraded and very brittle.

 

Polyethylene – Electrofusion weld

Title

FAILED ELECTROFUSION WELD FITTING

Date

2012

Objective

To assess the reason for the failure of an electrofusion fitting.

Photo

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Figure 1. Interior of electrofusion fitting showing the very limited amount of fusion around the heating coils area and no fusion along any other part of the fitting

Testing Undertaken

Failure analysis

Failure Analysis

Failure may have been caused by out of round pipes, lack of, or inadequate cleaning/scraping of the pipe or the time of application of electrical current to the fitting being too short to allow fusion to occur. The failed joint had not been heated for long enough for an adequate amount of fusion to occur

 

Polyethylene – Milk bottles

Title

IDENTIFICATION OF CONTAMINANTS

Date

2013

Objective

To identify contaminants found in two separate milk bottles.

Photo

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Figure 1a and 1b (x200 mag). Black contaminant (stain) on inside of bottle wall

 

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Figure 2. Red contaminant

Testing Undertaken

IR spec

Microscopy

DSC

Conclusion

IR spec of the black contaminant showed characteristics of polyethylene and spreads in a similar way to oils, thus is likely a degraded polyoil.

IR spec of the Red contaminant also showed characteristics of that of polyethylene

 

Polyethylene – Rotomolded tank

Title

FAILURE ANALYSIS OF ROTOMOLDED POLYETHYLENE TANK

Date

2013

Objective

To determine the causes of failure of a large polyethylene water tank used to aerate mine water at a gold mine

Photo

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Figure 1. Failed and collapsed tank

 

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Figure 2. Fracture surface near base of tank showing initiation site of fracture. The changing crack surface morphology reflected the change in the speed of the crack.

 

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Figure 3. Textured patterns associated with ductile slow crack growth in tank wall near location of lower outlet penetration. Note radiating crack fronts

 

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Figure 4. Lower-mid side wall of tank showing parabolic crack fronts.

 

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Figure 5. Lower-mid side wall of tank showing ductile tearing

Testing Undertaken

Failure analysis

Failure Analysis

Tank failure was partly due to its installation and partly due to its mode of use where it was subject to a higher SG performance and stresses for which the tank design did not adequately cater. The investigation showed that the initiation site of failure was at the lower tank wall in the immediate vicinity of the outlet penetration.

The addition of metal reinforcing bands for the lower side-wall would have lessened the destructive hoop stresses on the lower side wall and hence avoided the failure of the tank.

 

Polyethylene – Sheet (1 of 2)

Title

DEGRADED INCLUSION DEFECTS IN HDPE SHEET

Date

2013

Objective

To investigate the nature and effect of inclusion defects in HDPE geomembrane sheet

Photo

 

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Figure 1. Inclusion at 100x mag

 

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Figure 2. Inclusion at 100x mag

Testing Undertaken

Sectioning by microtoming

Transmission optical microscopy (TOM)

Conclusion

Figure 1 inclusion was identified as a carbon black agglomerate since discrete aggregates of carbon black particles were visible in transmission.

 

Figure 2 inclusion was identified as a lump of degraded and carbonized polymer containing a fragment of metal suggesting this inclusion originated from the extruder barrel or screw.

 

Polyethylene – Sheet (2 of 2)

Title

SCRATCH-MARKS ON HDPE SHEET

Date

2013

Objective

To investigate the effect of scratch marks in HDPE sheet

Photo

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Figure 1. Tensile specimen

 

Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Description: Job # 3396 Roll 806552381 P67-4 after tensile test.jpg

Figure 2. Tensile specimen breaks at scratch

 

Testing Undertaken

Sectioning and microscopy

Tensile testing (ASTM D 6693)

NCTL (ASTM D 5397)

Failure Analysis

The scratches were found to reduce the break elongation and the break tensile strength. Stress crack test was ongoing at 300 hours prior to any breaks being observed.

 

 

Accreditation

plastics

Gallery

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Polymer Testing (Division of ExcelPlas)

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