feature | Materials testing
accelerator pedal arms that had been moulded in China using an off-spec polyamide (PA) 6 supplied by a local vendor. In recall documents fi led with the US government, the OEM said the accelerator pedal arms could break, leaving cars inoperable. In automotive industry terms, this recall - which covered left-hand-drive cars produced since November 2007 and right-hand- drive cars manufactured since May 2012 – was small. For Aston Martin, however, it represented 75% of production over that period.
Above: The DSC 214 Polyma from Netzsch is a differential scanning calorimeter that analyzes recycled resins as accurately as virgin polymers
It is not just materials that factor into test
requirements. Vratsanos notes that increased regulatory rules mandate greater amounts of testing. “The levels of analysis have become increasingly more demanding, requiring complex analytical solutions,” he explains. At stake is the ability of compounds and products to
achieve problem-free acceptance, on time and within budget, in regional and international markets. The global supply chain in particular can be hazardous for compounders and OEMs that require consistent material and exacting quality control across manufac- turing operations around the world. Materials testing and analysis become critical ways of assuring that sub-standard or even slightly off-spec materials do not end up, however inadvertently, in compounds and parts. An example of what can happen when off-spec
materials are supplied occurred in 2014, when luxury automaker Aston Martin recalled 17,590 cars fi tted with
This and other examples demonstrate how the
market is moving towards more robust materials evaluation in general, argues John Duncan, managing director of equipment maker Lacerta Technology. “Companies realize they need to do more testing to make sure plastics are up to speed,” he says, adding that all segments of the supply chain are now expected to take full responsibility for product certifi cation. When it comes to supplied materials, he says this means compounders must be able to show that the resins, additives and other components they formulate are exactly as specifi ed.
Qualifying recyclate This need for qualifi cation is especially important in recycled polymers, which are found as key components in a growing number of compounds. The use of recycled resins in formulations has obvious environmental benefi ts, but in many cases quality can be hit-or-miss: commingled materials can affect reclaim properties; performance-robbing contaminants may be present; and the residue of additives, fi llers and colorants can make batch-to-batch quality assurance a challenge. “When using recycled materials, quality control is
even more important,” says Stefan Schmölzer, senior application scientist at equipment supplier Netzsch. “More sophisticated materials testing is needed, not only concerning the processability of the materials, but to get insight into the compound compositions which will infl uence properties of the fi nal product.” Netzsch offers thermal analysis instruments for
Compounders can use the DSC 214 Polyma for quality control. The red curve of a part supposedly molded of PA 6 generates only a 56.61% match with the green curve of a reference sample, indicating the use of an off-spec resin
58 COMPOUNDING WORLD | September 2015
polymer testing. These measure thermal transition, chemical reaction and decomposition, viscoelastic properties, and thermal conductivity and diffusivity as functions of parameters such as temperature, heating rate, deformation and atmosphere. Schmölzer says they can also be used to determine the composition of compounds and to develop information regarding the condition or processing history of random samples relative to references.
www.compoundingworld.com
PHOTO: NETZSCH
PHOTO: NETZSCH
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