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Polymers
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Polymeric Foams II
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Polymeric Foams II

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Applications".

Deadline for manuscript submissions: closed (20 May 2021) | Viewed by 54532

Special Issue Editors

Prof. Dr. José Ignacio Velasco

E-Mail Website1 Website2
Guest Editor
Department of Materials Science and Engineering, Poly2 Group, Technical University of Catalonia (UPC BarcelonaTech), ESEIAAT, C/Colom 11, 08222 Terrassa, Spain
Interests: polymers; composites; foams; nanocomposites
Special Issues, Collections and Topics in MDPI journals
Dr. Marcelo Antunes

E-Mail Website1 Website2
Guest Editor
Department of Materials Science and Engineering, Poly2 Group, Technical University of Catalonia (UPC BarcelonaTech), ESEIAAT, C/Colom 11, 08222 Terrassa, Spain
Interests: additives; aerogels; composites; conductivity; extrusion; films; foaming; foams; foils; fracture; graphene; ignifugation; membranes; molding; nanocomposites; nanoparticles; oxides; permeability; polyfunctional materials; polymers; processing; properties; resistance; silicates; structure; supercritical fluid
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Polymeric foams have been gaining increasing interest in emerging sectors that demand increasingly more efficient materials to fulfill complex technical requirements, including enhanced specific properties and reduced energy consumption, among others. Polymeric foams, in particular, have been shown to display great versatility in recent years, both in terms of microstructure control and final properties, such as secondary rigid phases. Control of microstructure and final properties are influenced by the constituent nanoparticles that are dispersed throughout the polymer matrix (“nanocomposite foams”), which have been carefully chosen based on these considerations. In addition, new advanced foaming technologies have also been developed in recent years. These two strategies have allowed for the generation of new polymer-based foams with micro-, submicro-, or even nanocellular structures, extending the already vast array of applications of polymer foams and opening brand new possibilities, such as in tissue engineering, high temperature applications, and catalysis.

This Special Issue is the continuation of a published Special Issue entitled “Polymeric Foams”, which contains a total of 23 articles that dealt with all aspects of some of the most recent research of novel polymer-based foams, from thermoset-based to thermoplastic and even syntactic foams, including their design, composition (focusing on the addition of functional nanoparticles), processing and fabrication, microstructure, applications, service behavior, or recycling and reuse. This first volume (Polymeric Foams) is a testament to the great deal of interest in these materials and fully justifies the expansion to a second Special Issue on this topic.
Manuscripts related to the following topics are of interest for this Special Issue:

  • Thermoplastic, thermosetting, and elastomeric polymer foams;
  • Syntactic foams;
  • Biopolymer foams;
  • High temperature polymer foams;
  • Nanocomposite foams;
  • Microcellular, submicrocellular, and nanocellular foams;
  • Closed-cell, open-cell, and interconnected-cell foams;
  • Unimodal and multimodal foams;
  • Chemical and physical foaming methods;
  • Novel foaming methods;
  • Foams for 3D printing;
  • Recycling of foams;
  • PLA-based and other biodegradable foams;
  • Flame-retardant foams;
  • Thermally and electrically conductive polymer foams;
  • Modeling of polymeric foams;
  • New applications of foams, including electronics, batteries, fuel cells, catalysis, separation and filtration, gas absorption, electromagnetic interference (EMI) shielding, electrostatic discharge (ESD), electrostatic painting, tissue engineering, sandwich-like materials, and many more.

Prof. José Ignacio Velasco
Dr. Marcelo Antunes
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • polymeric foams
  • cellular composites
  • microcellular foams
  • nanocomposite foams
  • functional foams
  • new applications of foams

Related Special Issues

Published Papers (15 papers)

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21 pages, 6673 KiB  
Article
Biodegradable Polymeric Foams Based on Modified Castor Oil, Styrene, and Isobornyl Methacrylate
by James Anthony Dicks and Chris Woolard
Polymers 2021, 13(11), 1872; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13111872 - 04 Jun 2021
Cited by 4 | Viewed by 2610
Abstract
The environmental issues of petroleum-derived polymeric foams have necessitated seeking renewable alternatives. This work aims to prepare renewable free-radically polymerized polymeric foams with the ability to biodegrade. Furthermore, this work attempted to incorporate a bio-based reactive diluent, which has not been reported in [...] Read more.
The environmental issues of petroleum-derived polymeric foams have necessitated seeking renewable alternatives. This work aims to prepare renewable free-radically polymerized polymeric foams with the ability to biodegrade. Furthermore, this work attempted to incorporate a bio-based reactive diluent, which has not been reported in the literature. The synthesis of maleated castor oil glycerides was performed with products analyzed by Fourier transform infrared spectrometry using attenuated total reflection (ATR-FTIR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. Polymeric foams were prepared using maleated castor oil glycerides via free radical copolymerization with styrene and isobornyl methacrylate as reactive diluents. Scanning electron microscopy (SEM) was used to determine anisotropic macrocellular morphology, with log-normal cell diameter distributions. The compressive mechanical and energy absorption properties were investigated; the polymeric foams displayed Young’s modulus up to 26.85 ± 1.07 MPa and strength up to 1.11 ± 0.021 MPa using styrene as the reactive diluent, and Young’s modulus up to 1.38 ± 0.055 MPa and strength up to 0.088 MPa when incorporating isobornyl methacrylate. Furthermore, a thorough analysis of the cellular structure–property relationships was performed, indicating relationships to cell diameter, cell wall thickness and apparent density. The polymeric foams displayed rapid mass loss in an aerobic soil environment with multiple erosion sites revealed by SEM. In conclusion, renewable polymeric foams with excellent compressive properties were achieved using styrene as reactive diluent, but the incorporation of isobornyl methacrylate decreased strength-related properties. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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19 pages, 9167 KiB  
Article
Insight into the Influence of Properties of Poly(Ethylene-co-octene) with Different Chain Structures on Their Cell Morphology and Dimensional Stability Foamed by Supercritical CO2
by Dongyang Li, Yichong Chen, Shun Yao, Hong Zhang, Dongdong Hu and Ling Zhao
Polymers 2021, 13(9), 1494; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13091494 - 06 May 2021
Cited by 21 | Viewed by 3187
Abstract
Poly(ethylene-co-octene) (POE) elastomers with different copolymer compositions and molecular weight exhibit quite distinctive foaming behaviors and dimensional stability using supercritical carbon dioxide (CO2) as a blowing agent. As the octene content decreases from 16.54% to 4.48% with constant melting index of [...] Read more.
Poly(ethylene-co-octene) (POE) elastomers with different copolymer compositions and molecular weight exhibit quite distinctive foaming behaviors and dimensional stability using supercritical carbon dioxide (CO2) as a blowing agent. As the octene content decreases from 16.54% to 4.48% with constant melting index of 1, both the melting point and crystallinity of POE increase, due to the increase in fraction of ethylene homo-polymerization segment. the foaming window of POE moves to a narrow higher temperature zone from 20–50 °C to 90–110 °C under 11 Mpa CO2 pressure, and CO2 solubility as well as CO2 desorption rate decrease, so that the average cell diameter becomes larger. POE foams with higher octene content have more serious shrinkage problem due to lower compression modulus, weaker crystal structure and higher CO2 permeability. As POE molecular weight increases at similar octene content, there is little effect on crystallization and CO2 diffusion behavior, the foaming window becomes wider and cell density increases, mainly owing to higher polymer melt strength, the volume shrinkage ratio of their foams is less than 20% because of similar higher polymer modulus. In addition, when the initiate expansion ratio is over 17 times, POE foams with longer and thinner cell wall structures are more prone to shrinkage and recovery during aging process, due to more bending deformation and less compression deformation. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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18 pages, 3736 KiB  
Article
Kinked Bisamides as Efficient Supramolecular Foam Cell Nucleating Agents for Low-Density Polystyrene Foams with Homogeneous Microcellular Morphology
by Bastian Klose, Daniel Kremer, Merve Aksit, Kasper P. van der Zwan, Klaus Kreger, Jürgen Senker, Volker Altstädt and Hans-Werner Schmidt
Polymers 2021, 13(7), 1094; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13071094 - 30 Mar 2021
Cited by 8 | Viewed by 3007
Abstract
Polystyrene foams have become more and more important owing to their lightweight potential and their insulation properties. Progress in this field is expected to be realized by foams featuring a microcellular morphology. However, large-scale processing of low-density foams with a closed-cell structure and [...] Read more.
Polystyrene foams have become more and more important owing to their lightweight potential and their insulation properties. Progress in this field is expected to be realized by foams featuring a microcellular morphology. However, large-scale processing of low-density foams with a closed-cell structure and volume expansion ratio of larger than 10, exhibiting a homogenous morphology with a mean cell size of approximately 10 µm, remains challenging. Here, we report on a series of 4,4′-diphenylmethane substituted bisamides, which we refer to as kinked bisamides, acting as efficient supramolecular foam cell nucleating agents for polystyrene. Self-assembly experiments from solution showed that these bisamides form supramolecular fibrillary or ribbon-like nanoobjects. These kinked bisamides can be dissolved at elevated temperatures in a large concentration range, forming dispersed nano-objects upon cooling. Batch foaming experiments using 1.0 wt.% of a selected kinked bisamide revealed that the mean cell size can be as low as 3.5 µm. To demonstrate the applicability of kinked bisamides in a high-throughput continuous foam process, we performed foam extrusion. Using 0.5 wt.% of a kinked bisamide yielded polymer foams with a foam density of 71 kg/m3 and a homogeneous microcellular morphology with cell sizes of ≈10 µm, which is two orders of magnitude lower compared to the neat polystyrene reference foam with a comparable foam density. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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14 pages, 13747 KiB  
Article
The Relationship between the Morphology and Elasticity of Natural Rubber Foam Based on the Concentration of the Chemical Blowing Agent
by Supitta Suethao, Saree Phongphanphanee, Jirasak Wong-ekkabut and Wirasak Smitthipong
Polymers 2021, 13(7), 1091; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13071091 - 30 Mar 2021
Cited by 17 | Viewed by 3507
Abstract
Concentrated natural latex was used to produce a rubber foam that is porous, elastic and well ventilated. The mechanical properties can be either soft or firm, depending on the formulation of the latex used. Briefly, concentrated natural latex was mixed with chemical agents [...] Read more.
Concentrated natural latex was used to produce a rubber foam that is porous, elastic and well ventilated. The mechanical properties can be either soft or firm, depending on the formulation of the latex used. Briefly, concentrated natural latex was mixed with chemical agents to make the rubber foam on a laboratory scale using the Dunlop process. In this work, we changed the concentration of the chemical blowing agent in the latex. The morphological properties of the rubber foam were characterised using scanning electron microscopy, and the mechanical properties, or elasticity, were studied using compression experiments and the Mooney–Rivlin calculation. The results show that the concentration of the chemical blowing agent affects the morphological properties of the rubber foam but not the mechanical properties, indicating the heterogeneous structure of the rubber foam. The thermodynamic parameters (∆G and ∆S) and the internal energy force per compression force (Fu/F) of the rubber foam with various amounts of chemical blowing agent were also investigated. This study could be applied in the foam industry, particularly for pillow, mattress and insulation materials, as the present work shows the possible novel control of the morphological structure of the rubber foam without changing its mechanical properties. The difference in cell sizes could affect the airflow in rubber foam. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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16 pages, 3684 KiB  
Article
Lignin-Based Phenolic Foam Reinforced by Poplar Fiber and Isocyanate-Terminated Polyurethane Prepolymer
by Guoliang Chen, Jian Liu, Wei Zhang, Yanming Han, Derong Zhang, Jianzhang Li and Shifeng Zhang
Polymers 2021, 13(7), 1068; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13071068 - 28 Mar 2021
Cited by 18 | Viewed by 2746
Abstract
Phenolic foams (PFs) are lightweight (<200 kg/m3), high-quality, and inexpensive thermal insulation materials whose heat and fire resistance are much better than those of foam plastics such as polyurethane and polystyrene. They are especially suitable for use as insulation in chemical, [...] Read more.
Phenolic foams (PFs) are lightweight (<200 kg/m3), high-quality, and inexpensive thermal insulation materials whose heat and fire resistance are much better than those of foam plastics such as polyurethane and polystyrene. They are especially suitable for use as insulation in chemical, petroleum, construction, and other fields that are prone to fires. However, PFs have poor mechanical properties, poor abrasion resistance, and easy pulverization. In this paper, a polyurethane prepolymer was treated with an isocyanate, and then the isocyanate-terminated polyurethane prepolymer and poplar powder were used to prepare modified lignin-based phenolic foams (PUPFs), which improved the abrasion resistance and decreased the pulverization of the foam. The foam composites were comprehensively evaluated by characterizing their chemical structures, surface morphologies, mechanical properties, thermal conductivities, and flame-retardant properties. The pulverization ratio was reduced by 43.5%, and the thermal insulation performance and flame-retardancy (LOI) were improved. Compared with other methods to obtain lignin-based phenolic foam composites with anti-pulverization and flame-retardant properties, the hybrid reinforcement of foam composites with an isocyanate-terminated polyurethane prepolymer and poplar powder offers a novel strategy for an environmentally friendly alternative to the use of woody fibers. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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20 pages, 6184 KiB  
Article
Flexible Polyurethane Foams from Epoxidized Vegetable Oils and a Bio-Based Diisocyanate
by Angelica Cifarelli, Laura Boggioni, Adriano Vignali, Incoronata Tritto, Fabio Bertini and Simona Losio
Polymers 2021, 13(4), 612; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13040612 - 18 Feb 2021
Cited by 28 | Viewed by 6019
Abstract
Bio-polyols from epoxidized soybean and linseed oils and caprylic acid or 3-phenyl butyric acid were prepared using an environmentally friendly, solvent-free method evaluating the presence of triethylamine as catalyst. Side reactions, leading to a cross-linking structure with high density, were reduced, introducing the [...] Read more.
Bio-polyols from epoxidized soybean and linseed oils and caprylic acid or 3-phenyl butyric acid were prepared using an environmentally friendly, solvent-free method evaluating the presence of triethylamine as catalyst. Side reactions, leading to a cross-linking structure with high density, were reduced, introducing the catalyst and properly tuning the reaction conditions. A medium functionality value of around 3 along with a hydroxyl number up to around 90 mg KOH/g, narrow polydispersity index, and relatively low molecular mass up to 2400 g/mol were the experimental targets. From selected bio-polyols and an aliphatic partially bio-based isocyanate, a series of water blown polyurethane (PU) foams was produced, estimating the effect of the chemical nature of substituents in the polyol backbone on the PU properties. The apparent density of the foams was in the range of 79–113 kg/m3, with higher values for foams from the aromatic acid. Flexible polyurethane foams with open cell structure from bio-based polyols were obtained, with higher cavity size and lower pore sizes for foams from caprylic acid. The bio-based flexible PU foams showed comparable Young’s moduli (14–18 kPa) and compression deflection values (4.6–5.5 kPa) and exhibited an almost complete recovery of their initial size. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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16 pages, 11271 KiB  
Article
The Effect of Microcellular Structure on the Dynamic Mechanical Thermal Properties of High-Performance Nanocomposite Foams Made of Graphene Nanoplatelets-Filled Polysulfone
by Marcelo Antunes, Hooman Abbasi and José Ignacio Velasco
Polymers 2021, 13(3), 437; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13030437 - 29 Jan 2021
Cited by 2 | Viewed by 1783
Abstract
Polysulfone nanocomposite foams containing variable amounts of graphene nanoplatelets (0–10 wt%) were prepared by water vapor-induced phase separation (WVIPS) and supercritical CO2 (scCO2) dissolution. WVIPS foams with two ranges of relative densities were considered, namely, between 0.23 and 0.41 and [...] Read more.
Polysulfone nanocomposite foams containing variable amounts of graphene nanoplatelets (0–10 wt%) were prepared by water vapor-induced phase separation (WVIPS) and supercritical CO2 (scCO2) dissolution. WVIPS foams with two ranges of relative densities were considered, namely, between 0.23 and 0.41 and between 0.34 and 0.46. Foams prepared by scCO2 dissolution (0.0–2.0 wt% GnP) were obtained with a relative density range between 0.35 and 0.45. Although the addition of GnP affected the cellular structure of all foams, they had a bigger influence in WVIPS foams. The storage modulus increased for all foams with increasing relative density and GnP’s concentration, except for WVIPS PSU-GnP foams, as they developed open/interconnected cellular structures during foaming. Comparatively, foams prepared by scCO2 dissolution showed higher specific storage moduli than similar WVIPS foams (same relative density and GnP content), explained by the microcellular structure of scCO2 foams. As a result of the plasticizing effect of CO2, PSU foams prepared by scCO2 showed lower glass transition temperatures than WVIPS foams, with the two series of these foams displaying decreasing values with incrementing the amount of GnP. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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18 pages, 5627 KiB  
Article
Study on Temperature-Dependent Properties and Fire Resistance of Metakaolin-Based Geopolymer Foams
by Van Su Le, Petr Louda, Huu Nam Tran, Phu Dong Nguyen, Totka Bakalova, Katarzyna Ewa Buczkowska and Iva Dufkova
Polymers 2020, 12(12), 2994; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12122994 - 15 Dec 2020
Cited by 33 | Viewed by 2830
Abstract
This paper presents temperature-dependent properties and fire resistance of geopolymer foams made of ground basalt fibers, aluminum foaming agents, and potassium-activated metakaolin-based geopolymers. Temperature-dependent properties of basalt-reinforced geopolymer foams (BGFs) were investigated by a series of measurements, including apparent density, water absorption, mass [...] Read more.
This paper presents temperature-dependent properties and fire resistance of geopolymer foams made of ground basalt fibers, aluminum foaming agents, and potassium-activated metakaolin-based geopolymers. Temperature-dependent properties of basalt-reinforced geopolymer foams (BGFs) were investigated by a series of measurements, including apparent density, water absorption, mass loss, drying shrinkage, compressive and flexural strengths, XRD, and SEM. Results showed that the apparent density and drying shrinkage of the BGFs increase with increasing the treated temperature from 400 to 1200 °C. Below 600 °C the mass loss is enhanced while the water absorption is reduced and they both vary slightly between 600 and 1000 °C. Above 1000 °C the mass loss is decreased rapidly, whereas the water absorption is increased. The compressive and flexural strengths of the BGFs with high fiber content are improved significantly at temperatures over 600 °C and achieved the maximum at 1200 °C. The BGF with high fiber loading at 1200 °C exhibited a substantial increase in compressive strength by 108% and flexural strength by 116% compared to that at room temperature. The enhancement in the BGF strengths at high temperatures is attributed to the development of crystalline phases and structural densification. Therefore, the BGFs with high fiber loading have extraordinary mechanical stability at high temperatures. The fire resistance of wood and steel plates has been considerably improved after coating a BGF layer on their surface. The coated BGF remained its structural integrity without any considerable macroscopic damage after fire resistance test. The longest fire-resistant times for the wood and steel plates were 99 and 134 min, respectively. In general, the BGFs with excellent fire resistance have great potential for fire protection applications. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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19 pages, 15277 KiB  
Article
Expanded Polycarbonate (EPC)—A New Generation of High-Temperature Engineering Bead Foams
by Nick Weingart, Daniel Raps, Justus Kuhnigk, Andreas Klein and Volker Altstädt
Polymers 2020, 12(10), 2314; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12102314 - 10 Oct 2020
Cited by 30 | Viewed by 4698 | Correction
Abstract
Bead foams serve in a wide variety of applications, from insulation and packaging to midsoles in shoes. However, the currently used materials are limited to somewhat low temperature or exhibit significant changes in modulus in the temperature range of many applications due to [...] Read more.
Bead foams serve in a wide variety of applications, from insulation and packaging to midsoles in shoes. However, the currently used materials are limited to somewhat low temperature or exhibit significant changes in modulus in the temperature range of many applications due to their glass transition. By comparison, polycarbonate (PC) exhibits almost constant mechanics for temperatures up to 130 °C. Therefore, it appears as an advantageous base material for bead foams. The aim of the publication is to provide comprehensive data on the properties of expanded PC (EPC) in comparison to already commercially available expanded polypropylene, EPP, and expanded polyethylene-terephthalate, EPET. A special focus is set on the thermo-mechanical properties as these are the most lacking features in current materials. In this frame, dynamic mechanical analysis, and tensile, bending, compression and impact tests at room temperature (RT), 80 °C, and 110 °C are conducted for the three materials of the same density. Already at RT, EPC exhibits superior mechanics compared to its peers, which becomes more pronounced toward higher temperature. This comes from the low sensitivity of properties to temperature as EPC is used below its glass transition. In summary, EPC proves to be an outstanding foam material over a broad range of temperatures for structural applications. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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20 pages, 6563 KiB  
Article
Low-Density Polybutylene Terephthalate Foams with Enhanced Compressive Strength via a Reactive-Extrusion Process
by Merve Aksit, Sebastian Gröschel, Ute Kuhn, Alper Aksit, Klaus Kreger, Hans-Werner Schmidt and Volker Altstädt
Polymers 2020, 12(9), 2021; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12092021 - 04 Sep 2020
Cited by 9 | Viewed by 4537
Abstract
Due to their appealing properties such as high-temperature dimensional stability, chemical resistance, compressive strength and recyclability, new-generation foams based on engineering thermoplastics such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) have been gaining significant attention. Achieving low-density foams without sacrificing the mechanical [...] Read more.
Due to their appealing properties such as high-temperature dimensional stability, chemical resistance, compressive strength and recyclability, new-generation foams based on engineering thermoplastics such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) have been gaining significant attention. Achieving low-density foams without sacrificing the mechanical properties is of vital importance for applications in the field of transportation and construction, where sufficient compressive strength is desired. In contrast to numerous research studies on PET foams, only a limited number of studies on PBT foams and in particular, on extruded PBT foams are known. Here we present a novel route to extruded PBT foams with densities as low as 80 kg/m3 and simultaneously with improved compressive properties manufactured by a tandem reactive-extrusion process. Improved rheological properties and therefore process stability were achieved using two selected 1,3,5-benzene-trisamides (BTA1 and BTA2), which are able to form supramolecular nanofibers in the PBT melt upon cooling. With only 0.08 wt % of BTA1 and 0.02 wt % of BTA2 the normalized compressive strength was increased by 28% and 15%, respectively. This improvement is assigned to the intrinsic reinforcing effect of BTA fibers in the cell walls and struts. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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19 pages, 4903 KiB  
Article
Foams with Enhanced Ductility and Impact Behavior Based on Polypropylene Composites
by Santiago Muñoz-Pascual, Cristina Saiz-Arroyo, Zina Vuluga, Mihai Cosmin Corobea and Miguel Angel Rodriguez-Perez
Polymers 2020, 12(4), 943; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12040943 - 18 Apr 2020
Cited by 12 | Viewed by 4230
Abstract
In this work, formulations based on composites of a linear polypropylene (L-PP), a long-chain branched polypropylene (LCB-PP), a polypropylene–graft–maleic anhydride (PP-MA), a styrene-ethylene-butylene-styrene copolymer (SEBS), glass fibers (GF), and halloysite nanotubes (HNT-QM) have been foamed by using the improved compression molding [...] Read more.
In this work, formulations based on composites of a linear polypropylene (L-PP), a long-chain branched polypropylene (LCB-PP), a polypropylene–graft–maleic anhydride (PP-MA), a styrene-ethylene-butylene-styrene copolymer (SEBS), glass fibers (GF), and halloysite nanotubes (HNT-QM) have been foamed by using the improved compression molding route (ICM), obtaining relative densities of about 0.62. The combination of the inclusion of elastomer and rigid phases with the use of the LCB-PP led to foams with a better cellular structure, an improved ductility, and considerable values of the elastic modulus. Consequently, the produced foams presented simultaneously an excellent impact performance and a high stiffness with respect to their corresponding solid counterparts. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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11 pages, 2862 KiB  
Article
Warp-Knitted Spacer Fabric Reinforced Syntactic Foam: A Compression Modulus Meso-Mechanics Theoretical Model and Experimental Verification
by Chao Zhi, Mingjuan Du, Zhaoling Sun, Mengjie Wu, Xiaoyi He, Jiaguang Meng and Lingjie Yu
Polymers 2020, 12(2), 286; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12020286 - 01 Feb 2020
Cited by 12 | Viewed by 4006
Abstract
In this study, a new type ternary composite, called warp-knitted spacer fabric reinforced syntactic foam (WKSF-SF), with the advantages of high mechanical properties and a lower density, was proposed. Then, a meso-mechanics theoretical model based on the Eshelby–Mori–Tanaka equivalent inclusion method, average stress [...] Read more.
In this study, a new type ternary composite, called warp-knitted spacer fabric reinforced syntactic foam (WKSF-SF), with the advantages of high mechanical properties and a lower density, was proposed. Then, a meso-mechanics theoretical model based on the Eshelby–Mori–Tanaka equivalent inclusion method, average stress method and composite hybrid theory was established to predict the compression modulus of WKSF-SF. In order to verify the validity of this model, compression modulus values of theoretical simulations were compared with the quasi-static compression experiment results. The results showed that the addition of suitable WKSF produces at least 15% improvement in the compressive modulus of WKSF-SF compared with neat syntactic foam (NSF). Meanwhile, the theoretical model can effectively simulate the values and variation tendency of the compression modulus for different WKSF-SF samples, and is especially suitable for the samples with smaller wall thickness or a moderate volume fraction of microballoons (the deviations is less than 5%). The study of the meso-mechanical properties of WKSF-SF will help to increase understanding of the compression properties of this new type composite deeply. It is expected that WKSF-SF can be used in aerospace, marine, transportation, construction, and other fields. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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15 pages, 5171 KiB  
Article
A Novel Hybrid Foaming Method for Low-Pressure Microcellular Foam Production of Unfilled and Talc-Filled Copolymer Polypropylenes
by Gethin Llewelyn, Andrew Rees, Christian A. Griffiths and Martin Jacobi
Polymers 2019, 11(11), 1896; https://0-doi-org.brum.beds.ac.uk/10.3390/polym11111896 - 17 Nov 2019
Cited by 17 | Viewed by 4253
Abstract
Unfilled and talc-filled Copolymer Polypropylene (PP) samples were produced through low-pressure foam-injection molding (FIM). The foaming stage of the process has been facilitated through a chemical blowing agent (C6H7NaO7 and CaCO3 mixture), a physical blowing agent (supercritical [...] Read more.
Unfilled and talc-filled Copolymer Polypropylene (PP) samples were produced through low-pressure foam-injection molding (FIM). The foaming stage of the process has been facilitated through a chemical blowing agent (C6H7NaO7 and CaCO3 mixture), a physical blowing agent (supercritical N2) and a novel hybrid foaming (combination of said chemical and physical foaming agents). Three weight-saving levels were produced with the varying foaming methods and compared to conventional injection molding. The unfilled PP foams produced through chemical blowing agent exhibited the strongest mechanical characteristics due to larger skin wall thicknesses, while the weakest were that of the talc-filled PP through the hybrid foaming technique. However, the hybrid foaming produced superior microcellular foams for both PPs due to calcium carbonate (CaCO3) enhancing the nucleation phase. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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Fabrication of Poly(butylene succinate)/Carbon Black Nanocomposite Foams with Good Electrical Conductivity and High Strength by a Supercritical CO2 Foaming Process
by Zhou Chen, Junfeng Hu, Jiajun Ju and Tairong Kuang
Polymers 2019, 11(11), 1852; https://0-doi-org.brum.beds.ac.uk/10.3390/polym11111852 - 10 Nov 2019
Cited by 34 | Viewed by 4455
Abstract
Lightweight, high-strength and electrically conductive poly(butylene succinate) (PBS)/ carbon black (CB) nanocomposite foams with a density of 0.107–0.344 g/cm3 were successfully fabricated by a solid-state supercritical CO2 (ScCO2) foaming process. The morphology, thermal and dynamic mechanical properties, and rheological [...] Read more.
Lightweight, high-strength and electrically conductive poly(butylene succinate) (PBS)/ carbon black (CB) nanocomposite foams with a density of 0.107–0.344 g/cm3 were successfully fabricated by a solid-state supercritical CO2 (ScCO2) foaming process. The morphology, thermal and dynamic mechanical properties, and rheological behavior of the PBS/CB nanocomposites were studied. The results indicate that the CB nanofiller was well dispersed in the PBS matrix and the presence of a proper CB nanofiller can accelerate the rate of crystallization, improve the thermal stability, enhance the stiffness, and increase the complex viscosity of PBS/CB nanocomposites. These improved properties were found to play an important role in the foaming process. The results from foaming experiments showed that the PBS/CB nanocomposite foams had a much smaller cell size, a higher cell density, and a more uniform cell morphology as compared to neat PBS foams. Furthermore, the PBS/CB nanocomposite foams also possessed low density (0.107–0.344 g/cm3), good electrical conductivity (~0.45 S/cm at 1.87 vol % CB loading), and improved compressive strength (108% increase), which enables them to be used as lightweight and high-strength functional materials. Full article
(This article belongs to the Special Issue Polymeric Foams II)
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1 pages, 180 KiB  
Correction
Correction: Weingart et al. Expanded Polycarbonate (EPC)—A New Generation of High-Temperature Engineering Bead Foams. Polymers 2020, 12, 2314
by Nick Weingart, Daniel Raps, Justus Kuhnigk, Andreas Klein and Volker Altstädt
Polymers 2022, 14(10), 1991; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14101991 - 13 May 2022
Cited by 2 | Viewed by 873
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In the original publication [...] Full article
(This article belongs to the Special Issue Polymeric Foams II)
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