Study of Rheology and Plug Assist Thermoforming of Linear and Branched PP Homopolymer and Impact Copolymer
TL;DR: The polypropylene (PP) is one of the fastest growing thermoplastic polymers in the world, second only to polyethylene as discussed by the authors, due to its excellent balance of physical and chemical properties.
Abstract: Polypropylene (PP) is one of the fastest growing thermoplastic polymers in the world, second only to polyethylene. This is primarily due to its excellent balance of physical and chemical p...
Citations
More filters
TL;DR: In this paper, the role of the percentage of the mineral filler on the absorption of moisture in the compound has been studied and the thermo-rheological properties of the compound were also evaluated.
17 citations
TL;DR: In this article, the authors used multilayer sheets for thermoforming non-thermoformable polymers in order to face the challenge of semi-crystalline polymers like low melt-stiffness.
Abstract: Multilayer sheets were used for thermoforming non thermoformable polymers in order to face the challenge of semi-crystalline polymers like low melt-stiffness. Mono- and 2-layer sheets consisting of different polypropylene (PP) homopolymers were extruded on a twin screw extruder. The PP viscosity as was measured by melt flow rate (MFR) 3 g/10 min., 12 g/10 min., 22 g/10 min. and 50 g/10 min. The layer ratio was varied between the equal layer ratio (A50/B50) of the individual layers and the low (A30/B70) or high viscosity ratio (A70/B30). The extrusion results show that for extreme viscosity differences (MFR3 and MFR50), the critical layer ratios known from the literature are only valid to a limited extent. The critical viscosity ratio < 4, which is known from the literature, is much lower here and should be less than 3. The investigation of thermoformability on laboratory scale of the extruded PP sheets with different viscosities showed that the low viscous layer position has only a marginal influence on the general thermoformability. Thermoforming of materials that are not thermoformable, with a storage modulus of less than 10³ Pa and a ratio between storage and loss modulus (tan δ) greater than 1, becomes possible using a multilayer sheet independant of the layer ratio. If the layer with higher viscosity acts as a stabilizing layer, thermoforming is possible.
5 citations
Cites background from "Study of Rheology and Plug Assist T..."
...Another possibility to increase the melt stiffness is to use chain extenders like peroxides.(13) Here, the enhancement achieved in the thermoforming process is directly related to the degree of long-chain branching....
[...]
05 Aug 2020
1 citations
17 Jun 2022
TL;DR: In this article , the mechanical properties of multilayer polypropylenes with 3, 22, and 50 melt flow index (MFI) were investigated, and the authors focused on how the non-thermoformable material influenced the mechanical performance of the final part.
Abstract: Different viscous materials were chosen to simulate the behavior of degraded materials in the thermoforming process and to demonstrate the potential of using multilayer sheets for thermoforming non thermoformable materials without losing final part performance. The mechanical properties of thermoformed multilayer sheets with 3, 22, and 50 melt flow index (MFI) polypropylenes (PP) were investigated. Therefore, a thermoformable material (MFI-3) and difficult/non thermoformable (MFI-22 and MFI-50) material was combined in the bilayer sheet. The extruded bilayer sheets had equal layer thicknesses (A/B 50%/50%) and unequal layer thicknesses (A/B 70%/30%), whereby B is always the material difficult to thermoform. As the non thermoformable material can lead to inhomogenity in the wall thickness and therefore can cause different part performance, the investigation focused on how the non thermoformable material influenced the mechanical performance of the final part. This labortory scale thermoformability investigation of the extruded PP sheets with different viscosities showed that the low viscous layer position has only a marginal influence on the general mechanical properties of the thermoformed parts. The mechanical properties can be predicted more precisely by the mechanical properties of the thermoformable material used than by the rule of mixtures. Whereas the Young’s modulus and yield stress change only negligibly, the elongation at break after thermoforming significantly increases with the stable component.
TL;DR: In this paper , a series of hot tensile tests and sheet sag measurements were performed to determine the properties of the iPP sheet and the multilayer sheet between 130 and 180 °C.
Abstract: Due to its low cost, stiffness, and recyclability, isotactic polypropylene (iPP) is an excellent candidate for packaging applications. However, iPP is notoriously difficult to thermoform due to its low melt strength. The addition of just 10 thin layers of high-molecular-weight, linear low-density polyethylene (LLDPE) into iPP sheets by coextrusion significantly increased extensional viscosity and reduced sag. Both LLDPE and iPP were metallocene-catalyzed with excellent adhesion as measured in our previous work. We performed a series of hot tensile tests and sheet sag measurements to determine the properties of the iPP sheet and the multilayer sheet between 130 and 180 °C. To evaluate the thermoformability of these multilayer sheets, truncated conical cups were positive vacuum formed at different temperatures and heating times, and the crush strength was measured. Cups that released easily from the mold with good shape retention and a crush strength within 80% of the maximum value were used to define a temperature-time thermoformability window. We estimated the maximum stress that occurred during the thermoforming process to be 5 MPa. Layer thicknesses before and after thermoforming were used to estimate an average strain of 0.78. The thin LLDPE layers decreased the yield stress below 5 MPa. This enabled thermoforming at sheet temperatures as low as 150 °C. The immiscible LLDPE interfaces increased extensional viscosity, which decreased sag in the multilayer sheets compared to iPP. This broadened the thermoforming range to temperatures as high as 180 °C and allowed longer heating times. These highly thermoformable, layered sheets may be recycled as iPP since they contain only 8% of LLDPE.
References
More filters
TL;DR: A critical review of the melt phase synthesis of polyolefin graft copolymers with reactive functionality is given in this article, which may serve as precursors to other polyolefins with grafted maleic anhydride, fumarate and maleate esters.
528 citations
Book•
01 Jan 1998
TL;DR: Polypropylene: The Definitive User's Guide and Databook as mentioned in this paper is a panoramic and up-to-the-minute user's guide for today's most important thermoplastic.
Abstract: Polypropylene: The Definitive User's Guide and Databook presents in a single volume a panoramic and up-to-the-minute user's guide for today's most important thermoplastic. The book examines every aspect science, technology, engineering, properties, design, processing, applications of the continuing development and use of polypropylene. The unique treatment means that specialists can not only find what they want but for the first time can relate to and understand the needs and requirements of others in the product development chain. The entire work is underpinned by very extensive collections of property data that allow the reader to put the information to real industrial and commercial use. Despite the preeminence and unrivaled versatility of polypropylene as a thermoplastic material to manufacture, relatively few books have been devoted to its study. Polypropylene: The Definitive User's Guide and Databook not only fills the gap but breaks new ground in doing so. Polypropylene is the most popular thermoplastic in use today, and still one of the fastest growing. Polypropylene: The Definitive User's Guide and Databook is the complete workbook and reference resource for all those who work with the material. Its comprehensive scope uniquely caters to polymer scientists, plastics engineers, processing technologists, product designers, machinery and mold makers, product managers, end users, researchers and students alike.
330 citations
TL;DR: In this paper, the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms were investigated and the cell morphologies for the two PPs were found to be significantly different.
Abstract: An investigation has been performed of the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms. These materials were foamed in extrusion with the two blowing agents, CO 2 and isopentane. The cell density generally increased with an increased content of the blowing agent, for both CO 2 and isopentane. The effect of processing pressure on the cell density was distinct when CO 2 was used, whereas no pressure effect was observed in the foam processing with isopentane. The cell morphologies for the two PPs were found to be significantly different. A slightly lower nuclei density was observed in the branched PP foams than in the linear PP foams. However, the phenomenon of cell coalescence was observed much less in the branched PP foams. Most cells in the branched PP foams were closed, whereas in the linear PP foams they were connected to each other. The experimental results indicated that the branched structure played an important role in determining the cell morphologies through its effects on the melt strength and/or melt elasticity.
298 citations
TL;DR: In this article, the extensional viscosity of several polypropylene polymers and their blends was measured and the foam processing of these blends using carbon dioxide blowing agent was studied.
Abstract: Extensional viscosity of several polypropylene polymers and their blends was measured and the foam processing of these blends using carbon dioxide blowing agent was studied. Foaming was carried out on a co-rotating twin-screw extrusion line, with a gear pump to build pressure. A linear isotactic polypropylene and two branched polypropylenes were considered. The uniaxial extensional viscosity was quantified and the foam characterized based on bulk density, cell size, and cell concentration. The linear polymer exhibits no strain hardening, while both branched polymers show pronounced strain hardening. Blends of low concentrations of branched polymer in the linear polypropylene show significant strain hardening down to 10-wt% branched polypropylene. Strain hardening is expected to prevent cell coalescence and lead to higher cell concentrations. The branched polymers were found to have a lower cell concentration than the linear polymer. Yet blends of linear and branched polypropylenes attained a cell concentration higher than either of the neat polymers. This suggests that even small amounts of branched polypropylene blended in linear polypropylene can improve the foaming process. Polym. Eng. Sci. 44:2090–2100, 2004. © 2004 Society of Plastics Engineers.
254 citations
TL;DR: In this article, a polypropylenes with long chain branches was obtained using reactive extrusion in the presence of peroxide, a polyfunctional acrylate monomer and a co-reactant: a sulfide compound such as thiuram disulfide.
Abstract: Polypropylenes with long chain branches were obtained using reactive extrusion in the presence of peroxide, a polyfunctional acrylate monomer and a co-reactant: a sulfide compound such as thiuram disulfide. By thermal decomposition, the thiuram disulfide gives two dithiocarbamate radicals. These radicals can be reacted with the macroradical PP, and this reaction is reversible. They induce a decrease in the instantaneous concentration of free radicals, favor the branching, and thus limit the effect of the β-scission. The long chain branches structure was confirmed by dynamic viscoelastic measurements and thermal analysis.
180 citations
"Study of Rheology and Plug Assist T..." refers background or methods or result in this paper
...These observations are in agreement with those reported in previous studies (Borsig et al., 2007; Graebling, 2002; Adams et al., 2000)....
[...]
...Therefore, in recent years, there is growing interest in developing High Melt Strength (HMS) grades of PP (Graebling, 2002)....
[...]
...Graebling (2002) obtained LCB PP using reactive extrusion in the presence of peroxide, 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane, a polyfunctional acrylate monomer, trimethylol propane triacrylate (TMPTA), and various sulphide compounds as coagents....
[...]