Polymer Case Study: Molded In Stresses

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Used to create custom plastic designs, thermoforming is a manufacturing process that includes heat, vacuum, and pressure to form plastic sheets into three-dimensional molded shapes. Thermoformed packaging is created for the food, pharmaceutical and electronics industries.

Case Study

Cracks were observed in transparent thermoformed plastic packaging during routine visual quality checks. The failures were occurring in specific material lots that may have corresponded with a reported equipment change.

Analysis

A comparison was made between known good and known bad lots to investigate the root cause. Based on DSC, the bad lot exhibited an endothermic peak near the glass transition in the initial heating cycle that was absent in the good lot. This peak is an enthalpic recovery peak associated with molecular relaxation. Samples were examined under a strain optical polarimeter at a specific location on the thermoformed parts.

Result

The images revealed significant differences in the birefringence patterns, suggesting a higher level of residual stress in the bad lot. High residual stresses imparted during the thermoforming process were likely responsible for the cracking issue.

Failure Analysis of Polymers

For more than 50 years, scientists and engineers at Eurofins EAG have investigated and resolved product failures for clients. Our team of experts identify key failure indicators and follow them to the root cause.

Polymeric Materials Evaluated at EAG

Failure analysis of plastics, thermosets, and rubber materials is commonly performed on finished products and typically involve comparative analysis between failed and non-failed samples. Once the potential root cause is identified, experiments can be designed and conducted to test the hypothesis and recreate the failure in the laboratory. Eurofins EAG can evaluate a variety of polymer types, including:

Raw materials in polymer formulations
Adhesives (heat/moisture/UV-cured, silicones, epoxies, acrylates)
Coatings (functional or decorative)
Thermoplastics, thermosets, thermoplastic elastomers, composites
Molded, extruded, cast components

Eurofins EAG Laboratories offers a full suite of analytical techniques to evaluate the identity, composition, morphology, topography, and rheology of polymeric materials and components.

Chromatography: GC, GC-MS, HPLC, IC, LC-MS, Pyrolysis GC-MS, HS/TD/SPME GC-MS
Inorganic Identification and Quantification: ICP-MS, ICP-OES, SEM-EDS, XRD, XRF
Physical Testing: Contact Angle, Mechanical Testing, Rheometry, Viscometry
Spectroscopy: Ellipsometry, FTIR, NIR, NMR, Raman, UV-Vis
Surface Analysis: Auger, SEM, TOF-SIMS, XPS
Surface Metrology: AFM, Nanoindentation, Profilometry
Thermal Analysis: DMA, DSC, RGA, TGA, TGA-IR, TGA-MS, TMA

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