Research

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14 pages, 6461 KiB

Open AccessArticle

Effect of Mold Temperature on the Impact Behavior and Morphology of Injection Molded Foams Based on Polypropylene Polyethylene–Octene Copolymer Blends

by Santiago Muñoz-Pascual, Eduardo Lopez-Gonzalez, Cristina Saiz-Arroyo and Miguel Angel Rodriguez-Perez

Polymers 2019, 11(5), 894; https://doi.org/10.3390/polym11050894 - 15 May 2019

Cited by 11 | Viewed by 4670

Abstract

In this work, an isotactic polypropylene (PP) and a polyethylene–octene copolymer (POE) have been blended and injection-molded, obtaining solids and foamed samples with a relative density of 0.76. Different mold temperature and injection temperature were used. The Izod impact strength was measured. For [...] Read more.

In this work, an isotactic polypropylene (PP) and a polyethylene–octene copolymer (POE) have been blended and injection-molded, obtaining solids and foamed samples with a relative density of 0.76. Different mold temperature and injection temperature were used. The Izod impact strength was measured. For solids, higher mold temperature increased the impact resistance, whereas in foams, the opposite trend was observed. In order to understand the reasons of this behavior, the morphology of the elastomeric phase, the crystalline morphology and the cellular structure have been studied. The presence of the elastomer near the skin in the case of high mold temperature can explain the improvement produced with a high mold temperature in solids. For foams, aspects as the elastomer coarsening in the core of the sample or the presence of a thicker solid skin are the critical parameters that justify the improved behavior of the materials produced with a lower mold temperature. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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20 pages, 11933 KiB

Open AccessArticle

Simulation Studies on the Effect of Material Characteristics and Runners Layout Geometry on the Filling Imbalance in Geometrically Balanced Injection Molds

by Krzysztof Wilczyński and Przemysław Narowski

Polymers 2019, 11(4), 639; https://doi.org/10.3390/polym11040639 - 08 Apr 2019

Cited by 12 | Viewed by 5453

Abstract

Simulation studies were performed on filling imbalance in geometrically balanced injection molds. A special simulation procedure was applied to simulate properly the phenomenon, including inertia effects and 3D tetrahedron meshing as well as meshing of the nozzle. The phenomenon was investigated by simulation [...] Read more.

Simulation studies were performed on filling imbalance in geometrically balanced injection molds. A special simulation procedure was applied to simulate properly the phenomenon, including inertia effects and 3D tetrahedron meshing as well as meshing of the nozzle. The phenomenon was investigated by simulation using several different runner systems at various thermo-rheological material parameters and process operating conditions. It has been observed that the Cross-WLF parameters, index flow, critical shear stress (relaxation time), and zero viscosity, as well as thermal diffusivity and heat transfer coefficient strongly affect the filling imbalance. The effect is substantially dependent on the runners’ layout geometry, as well as on the operating conditions, flow rate, and shear rate. The standard layout geometry and the corrected layout with circled element induce positive imbalance which means that inner cavities fills out faster, and it is opposite for the corrected layouts with one/two overturn elements which cause negative imbalance. Generally, for the standard layout geometry and the corrected layout with circled element, an effect of the zero shear rate viscosity η₀ is positive (imbalance increases with an increase of viscosity), and an effect of the power law index n and the relaxation time λ is negative (imbalance decreases with an increase of index n and relaxation time λ). An effect of the thermal diffusivity α and heat transfer coefficient h is negative while an effect of the shear rate is positive. For the corrected layouts with one/two overturn elements, the results of simulations indicate opposite relationships. A novel optimization approach solving the filling imbalance problem and a novel concept of global modeling of injection molding process are also discussed. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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18 pages, 3667 KiB

Open AccessArticle

Effect of Polyethylene Glycol Content and Molar Mass on Injection Molding of Hydroxypropyl Methylcellulose Acetate Succinate-Based Gastroresistant Capsular Devices for Oral Drug Delivery

by Francesco Briatico-Vangosa, Alice Melocchi, Marco Uboldi, Andrea Gazzaniga, Lucia Zema and Alessandra Maroni

Polymers 2019, 11(3), 517; https://doi.org/10.3390/polym11030517 - 19 Mar 2019

Cited by 7 | Viewed by 3308

Abstract

Capsular devices for oral drug delivery were recently proposed and manufactured by injection molding (IM) as an evolution of traditional reservoir systems comprising a core and a functional coating. IM allowed the fabrication of capsule shells with release-controlling features based on the employed [...] Read more.

Capsular devices for oral drug delivery were recently proposed and manufactured by injection molding (IM) as an evolution of traditional reservoir systems comprising a core and a functional coating. IM allowed the fabrication of capsule shells with release-controlling features based on the employed materials and the design characteristics. These features are independent of the drug, with significant savings in development time and costs. In previous work, IM was used to produce enteric-soluble capsules from blends of hydroxypropyl methylcellulose acetate succinate, with polyethylene glycol (PEG) as the plasticizer. In this work, the range of plasticizer concentrations and molar mass was broadened to evaluate in-depth how those parameters affect material processability and capsule performance over time. As expected, increasing the amount of the low molar mass plasticizer decreased the viscosity and modulus of the material. This simplified the molding process and enhanced the mechanical resistance of the shell, as observed during assembly. However, some samples turned out translucent, depending on several factors including storage conditions. This was attributed to plasticizer migration issues. Such results indicate that higher molar mass PEGs, while not significantly impacting on processability, lead to capsular devices with consistent performance in the investigated time lapse. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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16 pages, 5835 KiB

Open AccessArticle

Vegetable Tannin as a Sustainable UV Stabilizer for Polyurethane Foams

by Maria Oliviero, Mariamelia Stanzione, Marco D’Auria, Luigi Sorrentino, Salvatore Iannace and Letizia Verdolotti

Polymers 2019, 11(3), 480; https://doi.org/10.3390/polym11030480 - 12 Mar 2019

Cited by 29 | Viewed by 4133

Abstract

A vegetable tannin, a flavonoid-type natural polyphenolic compound, was used to promote the stabilization of polyurethane foams against UV radiation. Several polyurethane foams were synthesized by using an isocyanate, and a mixture of ethoxylated cocoalkyl amine and vegetable tannin. The content of vegetable [...] Read more.

A vegetable tannin, a flavonoid-type natural polyphenolic compound, was used to promote the stabilization of polyurethane foams against UV radiation. Several polyurethane foams were synthesized by using an isocyanate, and a mixture of ethoxylated cocoalkyl amine and vegetable tannin. The content of vegetable tannin was varied from 0 to 40 wt %. The effects of tannin and water (used as a blowing agent) on the foaming kinetics and cellular morphology of foams were investigated. Samples were subjected to accelerated weathering under UV radiation for 3 to 24 h, and FTIR and DMA analyses were conducted to assess the performance change. The former analysis revealed a strong inhibiting effect of tannin on urethane linkage degradation during the UV treatment. The mechanical properties were significantly affected by the addition of tannin. The capability of the foams to withstand UV radiation was dependent on the amount of tannin. At tannin contents higher than 20%, the decrease in mechanical properties under UV irradiation was almost avoided. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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12 pages, 6505 KiB

Open AccessArticle

Warpage Reduction of Glass Fiber Reinforced Plastic Using Microcellular Foaming Process Applied Injection Molding

by Hyun Keun Kim, Joo Seong Sohn, Youngjae Ryu, Shin Won Kim and Sung Woon Cha

Polymers 2019, 11(2), 360; https://doi.org/10.3390/polym11020360 - 19 Feb 2019

Cited by 27 | Viewed by 5104

Abstract

This study analyzes the fundamental principles and characteristics of the microcellular foaming process (MCP) to minimize warpage in glass fiber reinforced polymer (GFRP), which is typically worse than that of a solid polymer. In order to confirm the tendency for warpage and the [...] Read more.

This study analyzes the fundamental principles and characteristics of the microcellular foaming process (MCP) to minimize warpage in glass fiber reinforced polymer (GFRP), which is typically worse than that of a solid polymer. In order to confirm the tendency for warpage and the improvement of this phenomenon according to the glass fiber content (GFC), two factors associated with the reduction of the shrinkage difference and the non-directionalized fiber orientation were set as variables. The shrinkage was measured in the flow direction and transverse direction, and it was confirmed that the shrinkage difference between these two directions is the cause of warpage of GFRP specimens. In addition, by applying the MCP to injection molding, it was confirmed that warpage was improved by reducing the shrinkage difference. To further confirm these results, the effects of cell formation on shrinkage and fiber orientation were investigated using scanning electron microscopy, micro-CT observation, and cell morphology analysis. The micro-CT observations revealed that the fiber orientation was non-directional for the MCP. Moreover, it was determined that the mechanical and thermal properties were improved, based on measurements of the impact strength, tensile strength, flexural strength, and deflection temperature for the MCP. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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16 pages, 5060 KiB

Open AccessEditor’s ChoiceArticle

Lightweight High-Performance Polymer Composite for Automotive Applications

by Valentina Volpe, Sofia Lanzillo, Giovanni Affinita, Beniamino Villacci, Innocenzo Macchiarolo and Roberto Pantani

Polymers 2019, 11(2), 326; https://doi.org/10.3390/polym11020326 - 13 Feb 2019

Cited by 61 | Viewed by 6712

Abstract

The automotive industry needs to produce plastic products with high dimensional accuracy and reduced weight, and this need drives the research toward less conventional industrial processes. The material that was adopted in this work is a glass-fiber-reinforced polyamide 66 (PA66), a material of [...] Read more.

The automotive industry needs to produce plastic products with high dimensional accuracy and reduced weight, and this need drives the research toward less conventional industrial processes. The material that was adopted in this work is a glass-fiber-reinforced polyamide 66 (PA66), a material of great interest for the automotive industry because of its excellent properties, although being limited in application because of its relatively high cost. In order to reduce the cost of the produced parts, still preserving the main properties of the material, the possibility of applying microcellular injection molding process was explored in this work. In particular, the influence of the main processing parameters on morphology and performance of PA66 + 30% glass-fiber foamed parts was investigated. An analysis of variance (ANOVA) was employed to identify the significant factors that influence the morphology of the molded parts. According to ANOVA results, in order to obtain homogeneous foamed parts with good mechanical properties, an injection temperature of 300 °C, a high gas injection pressure, and a large thickness of the parts should be adopted. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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18 pages, 6875 KiB

Open AccessArticle

Effect of Compatibility on the Foaming Behavior of Injection Molded Polypropylene and Polycarbonate Blend Parts

by Bei Su, Ying-Guo Zhou, Bin-Bin Dong and Cao Yan

Polymers 2019, 11(2), 300; https://doi.org/10.3390/polym11020300 - 11 Feb 2019

Cited by 21 | Viewed by 5298

Abstract

To improve the foaming behavior of a common linear polypropylene (PP) resin, polycarbonate (PC) was blended with PP, and three different grafted polymers were used as the compatibilizers. The solid and foamed samples of the PP/PC 3:1 blend with different compatibilizers were first [...] Read more.

To improve the foaming behavior of a common linear polypropylene (PP) resin, polycarbonate (PC) was blended with PP, and three different grafted polymers were used as the compatibilizers. The solid and foamed samples of the PP/PC 3:1 blend with different compatibilizers were first fabricated by melt extrusion followed by injection molding (IM) with and without a blowing agent. The mechanical properties, thermal features, morphological structure, and relative rheological characterizations of these samples were studied using a tensile test, dynamic mechanical analyzer (DMA), scanning electron microscope (SEM), and torque rheometer. It can be found from the experimental results that the influence of the compatibility between the PP and PC phases on the foaming behavior of PP/PC blends is substantial. The results suggest that PC coupling with an appropriate compatibilizer is a potential method to improve the foamability of PP resin. The comprehensive effect of PC and a suitable compatibilizer on the foamability of PP can be attributed to two possible mechanisms, i.e., the partial compatibility between phases that facilitates cell nucleation and the improved gas-melt viscosity that helps to form a fine foaming structure. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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18 pages, 7764 KiB

Open AccessArticle

Enhanced Foamability with Shrinking Microfibers in Linear Polymer

by Eric S. Kim, Heon E. Park, Carlos R. Lopez-Barron and Patrick C. Lee

Polymers 2019, 11(2), 211; https://doi.org/10.3390/polym11020211 - 26 Jan 2019

Cited by 9 | Viewed by 3591

Abstract

Strain hardening has important roles in understanding material structures and polymer processing methods, such as foaming, film forming, and fiber extruding. A common method to improve strain hardening behavior is to chemically branch polymer structures, which is costly, thus preventing users from controlling [...] Read more.

Strain hardening has important roles in understanding material structures and polymer processing methods, such as foaming, film forming, and fiber extruding. A common method to improve strain hardening behavior is to chemically branch polymer structures, which is costly, thus preventing users from controlling the degree of behavior. A smart microfiber blending technology, however, would allow cost-efficient tuning of the degree of strain hardening. In this study, we investigated the effects of compounding polymers with microfibers for both shear and extensional rheological behaviors and characteristics and thus for the final foam morphologies formed by batch physical foaming with carbon dioxide. Extensional rheometry showed that compounding of in situ shrinking microfibers significantly enhanced strain hardening compared to compounding of nonshrinking microfibers. Shear rheometry with linear viscoelastic data showed a greater increase in both the loss and storage modulus in composites with shrinking microfibers than in those with nonshrinking microfibers at low frequencies. The batch physical foaming results demonstrated a greater increase in the cell population density and expansion ratio with in situ shrinking microfibers than with nonshrinking microfibers. The enhancement due to the shrinkage of compounded microfibers decreasing with temperature implies that the strain hardening can be tailored by changing processing conditions. Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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Review

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39 pages, 9641 KiB

Open AccessEditor’s ChoiceReview

Chemical Modification and Foam Processing of Polylactide (PLA)

by Tobias Standau, Chunjing Zhao, Svenja Murillo Castellón, Christian Bonten and Volker Altstädt

Polymers 2019, 11(2), 306; https://doi.org/10.3390/polym11020306 - 12 Feb 2019

Cited by 128 | Viewed by 21893

Abstract

Polylactide (PLA) is known as one of the most promising biopolymers as it is derived from renewable feedstock and can be biodegraded. During the last two decades, it moved more and more into the focus of scientific research and industrial use. It is [...] Read more.

Polylactide (PLA) is known as one of the most promising biopolymers as it is derived from renewable feedstock and can be biodegraded. During the last two decades, it moved more and more into the focus of scientific research and industrial use. It is even considered as a suitable replacement for standard petroleum-based polymers, such as polystyrene (PS), which can be found in a wide range of applications—amongst others in foams for packaging and insulation applications—but cause strong environmental issues. PLA has comparable mechanical properties to PS. However, the lack of melt strength is often referred to as a drawback for most foaming processes. One way to overcome this issue is the incorporation of chemical modifiers which can induce chain extension, branching, or cross-linking. As such, a wide variety of substances were studied in the literature. This work should give an overview of the most commonly used chemical modifiers and their effects on rheological, thermal, and foaming behavior. Therefore, this review article summarizes the research conducted on neat and chemically modified PLA foamed with the conventional foaming methods (i.e., batch foaming, foam extrusion, foam injection molding, and bead foaming). Full article

(This article belongs to the Special Issue Foaming and Injection Moulding in Polymer Processing)

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