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Case study: Research shows performance benefits of syntactic plug assists for thermoforming of transparent PP parts.

Syntactic foam plug assists deliver greater performance benefits than solid polymer plug assists for thermoforming of transparent polypropylene (PP) parts, according to the findings of a study published by supplier of plug-assist materials for the thermoforming industry, CMT Materials. Inc.

While measuring the influence of different plug-assist materials, CMT scientists found "statistically significant improvements" in haze, material distribution and crush strength for thermoformed PP parts which utilised syntactic foam plug assists. Plug surface quality, which was affected by machining and polishing techniques, was also identified as a critical factor.

"Many thermoformers are responding to the increased use of PP for high-clarity applications, primarily in the food and beverage sectors," explained Conor Carlin, Sales Manager at CMT. "Because PP has a narrow thermoforming window compared to PET or PS, it is critical that the interface between the heated sheet and the plug-assist material is well understood."

Thermoforming trials with 1.39 mm-thick PP sheet, clarified with Milliken Millad NX 8000, were run to determine if CMT Materials' HYTAC-C1R copolymer syntactic foam could provide all the benefits of syntactic foam without any loss in optical properties compared to solid polymers such as polyetherimide (PEI) and acetal.

The formed part was an 89 mm-tall cup with a rim inner diameter of 66 mm and a bottom diameter of 51 mm, resulting in a draw ratio of 3.4. HYTAC-C1R resulted in cups with 20 percent lower haze compared to PEI. Forming cups with C1R instead of PEI also resulted in a 10 percent increase in cup weight. In addition, cups formed with C1R weighed three percent more than those formed with acetal.

"HYTAC-C1R has a high-friction copolymer base which maximizes the ability to pull sheet material into the tool compared to other plug materials," said Kathleen Boivin, Materials Engineer at CMT, who led the study. "Forming with the HYTAC-C1R increased the minimum sidewall thickness by 28 percent compared to PEI and 20 percent compared to acetal. For thermoformers, part thickness is related to crush resistance."

Boivin explained that the container must survive its intended use without any signs of failure. "For example, a clear drink cup needs to be rigid enough to avoid buckling and spillage when the lid is applied, and a berry basket needs to be strong enough to survive stacking of the filled containers to prevent damaging the fragile contents." she said.

The increased cup weight and minimum sidewall thickness obtained with HYTAC-C1R resulted in 31 percent higher cup crush strength compared to plugs made from PEI. Ultimately, HYTAC-C1R resulted in equivalent or improved optical properties compared to PEI and acetal, while improving material distribution and leading to stronger cups.


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Comment:Case study: Research shows performance benefits of syntactic plug assists for thermoforming of transparent PP parts.(THERMOFORMING NEWS)
Publication:British Plastics & Rubber
Date:Sep 1, 2015
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