Abstract:Polypropylene (PP), a semi-crystalline material, is typically solid phase thermoformed at temperatures associated with crystalline melting, generally in the 150° to 160° Celsius range. In this very narrow thermoforming window the mechanical properties of the material rapidly decline with increasing temperature and these large changes in properties make Polypropylene one of the more difficult materials to process by thermoforming. Measurement of the deformation behaviour of a material under processing condition… Show more
“…The sagging could be due to the material viscoelastic characteristics. 39 Figure 8 shows the influence of nanoclay on sagging depth of the film series. Figure 8.Sagging depth of unfilled and nanoclay-filled biopolymer film series.…”
This study focuses on the thermoformability of biopolymer films derived from corn starch and filled with montmorillonite-based nanoclay fillers. Biopolymer films with nanoclay concentrations from 0 to 5 wt% were prepared by solution casting and followed by thermoforming. The result shows that nanoclay addition improves the formability (dimensional stability and plugging property) of thermoformed specimen and also depends on the nanocomposite structure and clay concentration. Improved product stability with optimized properties was observed at 2–3 wt% nanoclay concentration due to exfoliated structure and better nanoclay particle dispersion in the polymeric matrix. Thermogravimetric analysis and dynamic mechanical analysis show maximum of 27℃ increased decomposition temperature, 12% increased storage modulus and 4℃ increased Tg at 5 wt% nanoclay-filled biopolymer film. Tensile result shows 13% increased strength, two-fold increased modulus and 29% reduced elongation for 3 wt% nanoclay-filled biopolymer series.
“…The sagging could be due to the material viscoelastic characteristics. 39 Figure 8 shows the influence of nanoclay on sagging depth of the film series. Figure 8.Sagging depth of unfilled and nanoclay-filled biopolymer film series.…”
This study focuses on the thermoformability of biopolymer films derived from corn starch and filled with montmorillonite-based nanoclay fillers. Biopolymer films with nanoclay concentrations from 0 to 5 wt% were prepared by solution casting and followed by thermoforming. The result shows that nanoclay addition improves the formability (dimensional stability and plugging property) of thermoformed specimen and also depends on the nanocomposite structure and clay concentration. Improved product stability with optimized properties was observed at 2–3 wt% nanoclay concentration due to exfoliated structure and better nanoclay particle dispersion in the polymeric matrix. Thermogravimetric analysis and dynamic mechanical analysis show maximum of 27℃ increased decomposition temperature, 12% increased storage modulus and 4℃ increased Tg at 5 wt% nanoclay-filled biopolymer film. Tensile result shows 13% increased strength, two-fold increased modulus and 29% reduced elongation for 3 wt% nanoclay-filled biopolymer series.
“…Arruda-Boyce models to numerical simulate the thermoforming process for thickness distribution. Afterwards, the authors continued to use the Sweeny viscoelastic model to simulate and optimize the process [5]. However, optimized process parameters were still missed.…”
In this study, an experimental investigation of the development of a thermoforming apparatus and the thickness uniformity of its samples was performed based on the axiomatic design theory in conjunction with the Taguchi method. Thermoforming is a powerful tool for both consumer product needs and packaging industry. Such traditional technology has been investigated in many aspects for a long time ago. However, there are still needs for the development and characterization of thermoforming devices aiming at shorter construction time and less cost involved. Therefore, an experimental analysis was performed to systematically realize all the functional structures of the device using axiomatic design theory. The combination of orthogonal array (OA) and analysis of variance revealed the influences of the relatival processing factors, showing that the thickness of the plastic sheet and areal draw ratio had crucial roles to play. Furthermore, an optimization process using the Taguchi method was utilized to determine all accurate and optimum processing parameters. The outcomes obviously verified that the present combination method can overcome the current development and optimization method’s limitation and also conclusively give accurate optimal outcomes without using complicated algorithms and software solutions. Therefore, it promises a simple and powerful tool for engineers on-site in medium or small scale manufactories.
“…Peng et al [4] proposed a novel phenomenological model consisting of springs, dashpot, stress-locks, and sliders to describe the nonlinear viscoelastic properties of PP via indentation creep tests at different load levels. However, PP has a very narrow thermoforming window and the mechanical properties rapidly decrease with increasing temperature [5]. Drozdov reported some observations on PP in uniaxial tensile tests with various strain rates and relaxation tests at temperatures ranging from 23 to 120°C [6].…”
Finite element method (FEM) is used to analyze the mechanical properties of carbon nanotubes (CNTs) reinforced polypropylene (PP) composites. Firstly, polypropylene is assumed as a viscoelastic material, while carbon nanotubes are assumed as linear elastic materials to study the effect of temperature on the mechanical properties of neat PP and CNT/PP nanocomposites. Secondly, to compare the viscoelastic properties of neat PP and CNT/PP nanocomposites, the relaxation time at a specific temperature is used to investigate the relaxation of the nanocomposites for fixed tensile displacements. Thirdly, the effect of CNT volume fraction on the viscoelastic properties of nanocomposites is studied at different temperatures. Finally, to better understand the stress distribution along the CNT axial direction, a single carbon nanotube is isolated in the matrix to compare the stress distribution with nonisolated CNTs.
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