Case Studies | The Polymer Lab

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Case Studies

Product Failure Analysis #1_ Incorrect Material Type

The customer contacted The Polymer Lab for help in determining why a plastic locking component that was assembled into their product was cracking during normal use. The customer purchased the component from an outside supplier. The prototypes that they originally tested proved to be very robust. The specified material was Nylon 6/6.

DSC (Differential Scanning Calorimetry) and FTIR (Fourier Transform Infrared Spectrometry) testing performed by The Polymer Lab showed that the components were molded from an ABS-based plastic resin, not Nylon 6/6 as specified. The undisclosed material change by the component supplier proved to be the reason for the product failure. As a result of this discovery, new parts were molded from Nylon 6/6. Our lab confirmed that the new parts were indeed Nylon 6/6. When the customer tested the new parts, they performed as well as the initial prototypes.

Incoming Raw Material Verification

A plastic processor uses The Polymer Lab to verify incoming materials for ongoing Quality Assurance. At the beginning of this process, a control sample was tested to establish a reference data set for the particular material. Test results from new material lot samples were then compared to the reference data from the control sample. Through this procedure, any changes to the material composition or any contamination is readily seen. Various methods are used in incoming inspection, including: DSC (Differential Scanning Calorimetry), FTIR (Fourier Transform Infrared Spectroscopy), TGA (Thermogravimetric Analysis), Melt Flow Rate / Melt Index / Melt Rheology, and Ash Content Testing.

This continuous monitoring program has identified a number of raw material concerns. For example, in one case the material did not include the required flame retardant additive, and in another, the amount of glass filler content did not match the specified percentage. These material quality issues, left undetected, would have resulted in rejected parts, expensive warranty claims and possibly, product recall. Since the materials were never processed into finished product, the customer saved both time and money. They protected their quality reputation with their customers as well.

Product Quality / Process Verification

Our customer, an injection molding company, needed to verify the percent crystallinity of their molded parts. The crystallinity of a molded part is an important consideration because it affects many of its aspects such as mechanical properties and dimensional stability. Our customer’s client specified 100% crystallinity for their parts. Samples were submitted to The Polymer Lab for analysis.

DSC (Differential Scanning Calorimetry) analysis indicated that the submitted parts were not fully crystalline as evidenced by the observed cold-crystallization of the test specimen. Based on the data our customer decided to make changes to their molding process designed to increase to percent crystallinity of the molded parts. A follow-up set of samples was submitted and verified to being 100% crystalline. The Polymer Lab still routinely receives samples from this customer for crystallinity verification.

Product Failure Analysis #2_ Material Contamination Analysis

A plastic processing company was having trouble with parts that were cracking during operation. The specified material was a post-industrial grade of nylon 6,6 with an allowance of some regrind to be used. Samples of virgin material, regrind, reference parts, and failing parts were submitted to The Polymer Lab for analysis.

The analysis began with a preliminary FT-IR (Fourier Transform Infrared Spectroscopy) testing of the four samples. The FT-IR data for the four samples matched nylon 6,6 reference data from our lab’s internal material database. There was, however, an extra set of peaks in the FT-IR data of the virgin material, regrind, and the failing part that corresponded to polyester. This extra set of peaks was not observed in the FT-IR data of the reference part. It was concluded that our customer received a defective lot of material from their supplier that was contaminated with polyester and that this contamination was the cause for failure of the molded parts. We provided a written report of our findings to our customer that they were able to present to their client and vendor.

**This sort of issue is more common with post-industrial and post-consumer grades of plastic resin. Our ability to verify a plastic resin’s purity and quality allows our customers to utilize these cost-saving materials more effectively.

Product Failure Analysis #3_ Process Degradation Analysis

During routine impact testing of an overmolded fiberglass tool handle, a significant number of handles shattered on initial impact. In previous testing, the handles only developed a crack after multiple impacts. The specified material was glass fiber reinforced Nylon 6. The customer brought their problem to The Polymer Lab to identify the cause of the test failure.

DSC (Differential Scanning Calorimetry) and Ash Content analysis verified that the material was Nylon 6, as specified. The next step was to perform degradation analysis via dilute solution viscosity testing. This analysis showed a 40% change in relative viscosity (RV) from virgin material to finished part. The specified change limit was 20%. These results suggested that material had undergone severe process degradation.

The process was then adjusted, new parts molded and samples sent to The Polymer Lab for degradation analysis. The new parts showed only a 7% change in RV, putting them well within the limit. The new parts passed the impact test without shattering.

Reverse Engineering

A customer who manufactures agricultural equipment was purchasing a plastic assembly from an outside supplier who suddenly went out of business. The customer did not know what materials were used in the assembly so could not respecify the product with another vendor. The Polymer Lab was contacted to reverse engineer all components of the assembly in order to identify the materials.

DSC (Differential Scanning Calorimetry), FTIR (Fourier Transform Infrared Spectroscopy), and Ash Content testing were used to successfully identify all seven of the material types in the assembly. With this information, the customer was able to provide the needed information to their new supplier.

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