Thermoforming Quarterly is a journal published quarterly by the Thermoforming Division of the Society of Plastics Engineers. The magazine is a great way to keep up with industry trends and developments. SPE Thermoforming Division members receive the magazine by mail four times a year. Non-members can access old issues here via PDF file. If you are not an SPE member this is a great reason to join! Become a member today to start receiving this valuable information in your mailbox.
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First Quarter 2020
Rheological Method Development: Using Rheological Tools to Predict Thermoformability
By Mary Ann Jones, Todd Hogan, Jamie Stanley, The Dow Chemical Company, Midland, MI
Paul Vantol, The Dow Chemical Company, Midland, MI – retired
Extrusion thermoforming of very large parts such as those used in the appliance industry can exceed the melt strength limits of a given polymer. This study was undertaken to define new rheological tests capable of defining the molecular design required to avoid excessive sag in the heating step of the thermoforming process and to identify the optimum temperature for forming. Damping factor (tan = G’’/G’), also known as “tan delta”, can be used as a tool to identify fabrication conditions, molding window size, and the effect of added recycle streams. In addition, we compare polymer families that challenge our ability to thermoform large parts. Semi-crystalline materials must be run at or above their melting point temperature (Tm). Tm is well above the glass transition temperature (Tg) and the temperature delta (Tm – Tg) may exceed the width of any rubber plateau region in the melt state. These rheological characteristics are related back to the entanglement density of a given polymer and compared to the width of the rubber plateau.
Samples were compression molded to a thickness of 1.5 mm. Samples were tested in dynamic mode on an RDSII Rheometrics Dynamic Spectrometer. Samples were analyzed in three ways. First, a Frequency/Temperature sweep approach was used to define the suitability of a material design and the associated thermoforming temperature, using parallel plate fixtures under nitrogen, keeping the strain as low as possible throughout the test while still generating sufficient torque. The data was used to create a master curve using time-temperature superposition principals. Polymer fabrication operating windows were defined through examination of the master curves, understanding the size of the rubber plateau and the slope of the elastic modulus and tan δ curves in the viscous flow region of the curve. The slope of these curves provides information as to how well the processability can be changed through changes in processing temperature or shear rate. These tests are designed specifically to define the melt strength of the sheet after heating but prior to forming, balancing this against the ability to form uniformly in a deep draw part.
Barrier Packaging Materials & Processes
By Jimmy A. Shah, Senior R&D Engineer at ICPG and Impact Plastics, Hamlet, NC
The use of plastics packaging across a wide range of industry segments is increasing due to plastics’ ability to keep products safe and retain their quality until final use by the end-consumer. The outlook for the global packaging industry forecasts steady growth, with several projections anticipating the industry will near the trillion-dollar mark by 2022. Assessing the value proposition among material options available today must transcend the absolute package cost because of the value today’s consumers put on factors such as sustainability, temperature flexibility, traceability, product safety/counterfeit protection, shelf-life, and convenience. As markets mature and become more reliant on ecommerce and online shopping, the global packaging industry must adapt by focusing on these needs. Creative adaptation of the work being done in material science is essential to finding the perfect balance between environmental responsibility and package functionality. This is especially true in our area of focus, rigid packaging, where the combination of material science and modern multi-layer extrusion technology has pushed the boundaries of barrier packaging to extend both product quality and shelf-life. These enhancements will ensure every market segment, e.g., food, medical, cosmetics or automotive will benefit along with our environment.
The environmental and aesthetic demands of today’s consumers related to package functionality as well as the sales growth of a product is well suited to the academic and industry work being done to enhance the physical properties of both polypropylene and polyethylene. In addition, when you consider the US abundance of low-cost natural gas, our crackers’ ability to crack both heavy and light feedstocks combined with the addition of on-purpose polymer-grade propylene projects in development, designing for the future using polyolefins is the most environmentally and cost-effective course of action.
Full articles appears in print magazine mailed to members.