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Polymer Foams: Processing and Characterization

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

Deadline for manuscript submissions: closed (25 December 2021) | Viewed by 24808

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Prof. Dr. Patrick Lee

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Multifunctional Composites Manufacturing Laboratory (MCML), Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, ON M5S 3G8, Canada
Interests: foams; multiphase foam materials; lightweight and smart polymeric materials; hybrid polymer materials and foams; micro-/nanolayer coextrusion; modelling of polymeric foams; super high R-value foams; conductive and functional foams; sound insulation foams
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Dear Colleagues,

Over the past decade, there has been a global increase in environmental awareness, leading to the implementation of regulatory constraints to reduce the carbon footprint of consumer products. The prevailing approach adapted by industries, to fulfil these new regulations, is to utilize lightweight materials to decrease the energy consumption and the amount of material used in fabricated products. Polymeric foams have acquired a predominant role in industrial applications to satisfy the need to fabricate these lightweight products, due to their intrinsic low densities. Recent advancements in technology have led to the mass production of nanosized fillers, which are available in different shapes and sizes (1–100nm), giving rise to new possibilities in terms of their material properties and functionalities. Incorporating nanosized fillers into polymeric foams can lead to advanced lightweight polymer composites whose mechanical and conductive properties can be tailored based on their application. Today, novel processing and characterization techniques have paved the way for new polymeric foam products, suitable for modern and future applications, such as electromagnetic interference (EMI) shielding, tissue engineering, advanced structural components, and many more.

This Special Issue encapsulates recent research on polymer-based foams highlighting advanced novel processing and characterization technologies, while providing insights into the next generation of environmentally sustainable and energy efficient commercialized products.

Manuscripts related to the following topics are welcomed for this Special Issue:

Thermoplastic and thermosetting polymer foams;
Syntactic foams;
Biopolymer foams;
Nanocomposite foams;
Micro-/nanocellular foams;
Closed-cell, open-cell, and interconnected-cell foams;
Reticulated foams;
Chemical and physical foaming methods;
Recycling of foams;
Biodegradable foams;
Thermally and electrically conductive polymer foams;
Novel foaming technologies;
Novel characterization technologies;
Modelling of polymeric foams;
Modern and future applications of foams, including: electronics, separation and filtration, gas absorption, electromagnetic interference (EMI) shielding, tissue engineering, micro-/nanolayer materials, structural components, and many more.

Prof. Dr. Patrick Lee
Guest Editor

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
Micro-/nanocomposite foams
Biopolymer foams
Biodegradable foams
Functional foams
Novel foaming technologies
Novel characterization technologies
Modern foam applications
Future foam applications

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Published Papers (9 papers)

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Research

19 pages, 5190 KiB

Open AccessArticle

An Industrial Case for Polypropylene Nanocomposite Foams: Lightweight, Soundproof Exterior Automotive Parts

by Burcu Girginer Ozunlu and Fatma Seniha Guner

Polymers 2022, 14(6), 1192; https://doi.org/10.3390/polym14061192 - 16 Mar 2022

Cited by 7 | Viewed by 2441

Abstract

Lightweighting is a challenge for the automotive industry, and foaming is a key technology used to address this problem. A new practical approach is studied to regulate the cell formation of copolymer polypropylene (co-PP) by utilizing graphene nanoplatelets (xGnP) as a process aid during foam injection molding. The approach was designed to enable process freedom to tune part performance by adjusting the amount of xGnP masterbatch. Two different levels of 1–2 wt % xGnP and 0.25–0.35 wt % supercritical fluid (SCF) were investigated. Prepared samples were compared with samples prepared by the traditional method (twin-screw extrusion followed by foam injection molding). The nanocomposite with 2 wt % xGnP comparatively showed about twofold reduction in cell size magnitude. Although the increment in SCF amount resulted in a 47% and 122% enhancement in flexural modulus and strength, respectively, and a 45% loss in Izod unnotched impact strength, the cell size was prone to increasing with regard to low melt strength as compared to neat foams. In conclusion, a 12% weight reduction fulfilled the desired performance parameters in terms of mechanical and sound insulation by utilizing 2 wt % xGnP as a process aid. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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12 pages, 2569 KiB

Open AccessArticle

Development of Porous Polyvinyl Acetate/Polypyrrole/Gallic Acid Scaffolds Using Supercritical CO₂ as Tissue Regenerative Agents

by Diego Valor, Antonio Montes, Antonio Cózar, Clara Pereyra and Enrique Martínez de la Ossa

Polymers 2022, 14(4), 672; https://doi.org/10.3390/polym14040672 - 10 Feb 2022

Cited by 6 | Viewed by 2119

Abstract

Scaffolds are advanced devices employed in tissue engineering, as they are intended to mimic the characteristics of extracellular matrices. In this respect, conjugated materials are gaining relevance in the manufacturing of the foams used for therapeutic scaffolds, since they can provide certain properties that are missing in the other polymers used to form the scaffolds. This work has, therefore, focused on the development of functional scaffolds formed by conjugated-non-conjugated polymers such as polyvinyl acetate and polypyrrole, impregnated with gallic acid as the model drug and produced by means of a supercritical CO₂ foaming/impregnation process. The effects from a series of parameters such as pressure, temperature, depressurization rate, and contact time of the scaffold production process have been determined. The impregnated foams have been characterized according to their morphology, including their porosity and expansion factor, their drug loading and delivering capabilities, and their mechanical and electrical properties. The characterization of the experiments was carried out using scanning electron microscopy, liquid displacement, in vitro release, electrochemical impedance spectroscopy, and compression techniques. The results from our tests have revealed a considerable influence of all the input variables studied, as well as relevant interactions between them. Values close to 35% porosity were obtained, with a drug release of up to 10 h with a fast initial release. The best operating conditions were 353 K, 30 MPa, 0.5 MPa/min depressurization rate, and 1 h contact time. By means of the supercritical foaming/impregnation technique, scaffolds with potential in tissue engineering due to their studied properties were obtained. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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19 pages, 4866 KiB

Open AccessArticle

Tuning High and Low Temperature Foaming Behavior of Linear and Long-Chain Branched Polypropylene via Partial and Complete Melting

by Mu Sung Kweon, Mahmoud Embabi, Maksim E. Shivokhin, Anvit Gupta, Xuejia Yan, George Pehlert and Patrick C. Lee

Polymers 2022, 14(1), 44; https://doi.org/10.3390/polym14010044 - 23 Dec 2021

Cited by 12 | Viewed by 3736

Abstract

While existing foam studies have identified processing parameters, such as high-pressure drop rate, and engineering measures, such as high melt strength, as key factors for improving foamability, there is a conspicuous absence of studies that directly relate foamability to material properties obtained from fundamental characterization. To bridge this gap, this work presents batch foaming studies on one linear and two long-chain branched polypropylene (PP) resins to investigate how foamability is affected by partial melting (Method 1) and complete melting followed by undercooling (Method 2). At temperatures above the melting point, similar expansion was obtained using both foaming procedures within each resin, while the PP with the highest strain hardening ratio (13) exhibited the highest expansion ratio (45 ± 3). At low temperatures, the foamability of all resins was dramatically improved using Method 2 compared to Method 1, due to access to lower foaming temperatures (<150 °C) near the crystallization onset. Furthermore, Method 2 resulted in a more uniform cellular structure over a wider temperature range (120–170 °C compared to 155–175 °C). Overall, strong extensional hardening and low onset of crystallization were shown to give rise to foamability at high and low temperatures, respectively, suggesting that both characteristics can be appropriately used to tune the foamability of PP in industrial foaming applications. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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16 pages, 3737 KiB

Open AccessArticle

Development of a Rheology Die and Flow Characterization of Gas-Containing Polymer Melts

by Clemens Kastner, Dominik Altmann, Eva Kobler and Georg Steinbichler

Polymers 2021, 13(19), 3305; https://doi.org/10.3390/polym13193305 - 27 Sep 2021

Cited by 1 | Viewed by 2144

Abstract

We present a novel measurement die for characterizing the flow behavior of gas-containing polymer melts. The die is mounted directly on the injection-molding cylinder in place of the mold cavity and thus enables near-process measurement of viscosity (i.e., under the conditions that would be present were a mold attached). This integration also resolves the issue of keeping gas-containing polymer melts under pressure during measurement to prevent desorption. After thermal characterization of the die, various correction approaches were compared against each other to identify the most suitable one for our case. We conducted measurements using polypropylene in combination with two different chemical blowing agents. Increasing the blowing-agent content to up to 6% revealed an interestingly low influence of gases on melt viscosity, which was confirmed by elongational viscosity measurements. For verification, we compared our results to corresponding measurements taken on a high-pressure capillary rheometer and found that they were in excellent agreement. Our die cannot only be used for rheological characterization. Combined with ultrasound sensors, it provides an innovative way of measuring the volumetric flow rate. This development represents an important step in improving the sustainability of gas-containing polymer processing. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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14 pages, 8637 KiB

Open AccessArticle

Effect of Material Properties on the Foaming Behaviors of PP-Based Wood Polymer Composites Prepared with the Application of Spherical Cavity Mixer

by Suwei Wang, Ping Xue, Wenxin Zhang, Gazi Hao, Lei Xiao and Wei Jiang

Polymers 2021, 13(18), 3179; https://doi.org/10.3390/polym13183179 - 19 Sep 2021

Cited by 1 | Viewed by 2386

Abstract

For the low weight and high strength, the microcellular extrusion foaming technology was applied in the preparation of polypropylene (PP)-based wood polymer composites, and the spherical cavity mixer was used to construct an experimental platform for the uniform dispersion of wood flour (WF). The effects of PP molecular configuration on the composite properties and cell morphology of samples were also investigated. The experimental results indicated that the application of a spherical cavity mixer with a cavity radius of 5 mm could effectively improve the mixing quality and avoid the agglomeration of WF. In addition, compared with the branched molecule, the linear molecule not only increased the melting temperature by about 10 °C, but also endowed composites with a higher complex viscosity at a shear rate lower than 100 s⁻¹, which contributed to the cell morphology of more microporous samples. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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15 pages, 2263 KiB

Open AccessArticle

Improved Cell Morphology and Surface Roughness in High-Temperature Foam Injection Molding Using a Long-Chain Branched Polypropylene

by Steven Mendoza-Cedeno, Mu Sung Kweon, Sarah Newby, Maksim Shivokhin, George Pehlert and Patrick C. Lee

Polymers 2021, 13(15), 2404; https://doi.org/10.3390/polym13152404 - 22 Jul 2021

Cited by 13 | Viewed by 3083

Abstract

Long-chain branched polypropylene (LCB PP) has been used extensively to improve cell morphologies in foaming applications. However, most research focuses on low melt flow rate (MFR) resins, whereas foam production methods such as mold-opening foam injection molding (MO-FIM) require high-MFR resins to improve processability. A systematic study was conducted comparing a conventional linear PP, a broad molecular weight distribution (BMWD) linear PP, and a newly developed BMWD LCB PP for use in MO-FIM. The effects of foaming temperature and molecular architecture on cell morphology, surface roughness, and mechanical properties were studied by utilizing two chemical blowing agents (CBAs) with different activation temperatures and varying packing times. At the highest foaming temperatures, BMWD LCB PP foams exhibited 887% higher cell density, 46% smaller cell sizes, and more uniform cell structures than BWMD linear PP. Linear PP was found to have a surface roughness 23% higher on average than other resins. The BMWD LCB PP was found to have increased flexural modulus (44%) at the cost of decreased toughness (−88%) compared to linear PP. The branched architecture and high molecular weight of the BMWD LCB PP contributed to improved foam morphologies and surface quality in high-temperature MO-FIM conditions. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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13 pages, 3563 KiB

Open AccessArticle

Characteristics of Microcellular Foamed Ceramic Urethane

by Jin Hong, Soo-hyun Cho, Chang-Seok Yun, Dong Hwi Kim, Youngjae Ryu, Sung Woon Cha and Yong Hoon Jang

Polymers 2021, 13(11), 1817; https://doi.org/10.3390/polym13111817 - 31 May 2021

Cited by 2 | Viewed by 2842

Abstract

Ceramics are non-metallic inorganic materials fabricated from natural or high-purity raw materials through heating and cooling processes. Urethane is a three-dimensional plastic with both elasticity and chemical resistance; moreover, it is used as a rubber substitute. The use of both materials in various applications is gradually increasing. However, as ceramics and urethane have distinctly different properties, this prompted questions regarding the properties of a material that is fabricated using both materials. Therefore, we studied the characteristics of a composite material fabricated through physical foaming using a batch process. The process was conducted with gas saturation, foaming, cooling, and curing. When a specimen of 2 mm thickness was saturated in 5 MPa of CO₂ for 2 h, the solubility was 6.43%; when foaming was carried out at a temperature of 150 °C in boiled glycerin, the foaming ratio, cell size, cell density, and void fraction were found to be 43.62%, 24.40 µm, 9.1 × 10⁷ cells/cm², and 22.11%, respectively. Furthermore, the volume increased by 102.96%, color changed from dark to light gray, hardness decreased by 24%, thermal diffusivity increased by 0.046 mm²/s at 175 °C, and friction coefficient decreased to 0.203. Thus, the microcellular foamed ceramic urethane exhibits a larger volume, lighter weight, and improved thermal conductivity and friction coefficient. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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16 pages, 4663 KiB

Open AccessArticle

Determining the Optimal Conditions for the Production by Supercritical CO₂ of Biodegradable PLGA Foams for the Controlled Release of Rutin as a Medical Treatment

by Diego Valor, Antonio Montes, Marilia Monteiro, Ignacio García-Casas, Clara Pereyra and Enrique Martínez de la Ossa

Polymers 2021, 13(10), 1645; https://doi.org/10.3390/polym13101645 - 19 May 2021

Cited by 11 | Viewed by 2611

Abstract

Poly(D,L,-lactide-co-glycolide) (PLGA) foam samples impregnated with rutin were successfully produced by supercritical foaming processes. A number of parameters such as pressure (80–200 bar), temperature (35–55 °C), depressurization rate (5–100 bar/min), ratio lactide:glycolide of the poly(D,L,-lactide-co-glycolide) (50:50 and 75:25) were studied to determine their effect on the expansion factor and on the glass transition temperature of the polymer foams and their consequences on the release profile of the rutin entrapped in them. The impregnated foams were characterized by scanning electron microscopy, differential scanning calorimetry, and mercury intrusion porosimetry. A greater impregnation of rutin into the polymer foam pores was observed as pressure was increased. The release of rutin in a phosphate buffer solution was investigated. The controlled release tests confirmed that the modification of certain variables would result in considerable differences in the drug release profiles. Thus, five-day drug release periods were achieved under high pressure and temperature while the depressurization rate remained low. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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21 pages, 3827 KiB

Open AccessArticle

Depressurization-Induced Nucleation in the “Polylactide-Carbon Dioxide” System: Self-Similarity of the Bubble Embryos Expansion

by Dmitry Zimnyakov, Marina Alonova and Ekaterina Ushakova

Polymers 2021, 13(7), 1115; https://doi.org/10.3390/polym13071115 - 1 Apr 2021

Cited by 3 | Viewed by 1705

Abstract

Self-similar expansion of bubble embryos in a plasticized polymer under quasi-isothermal depressurization is examined using the experimental data on expansion rates of embryos in the CO₂-plasticized d,l-polylactide and modeling the results. The CO₂ initial pressure varied from 5 to 14 MPa, and the depressurization rate was 5 × 10⁻³ MPa/s. The constant temperature in experiments was in a range from 310 to 338 K. The initial rate of embryos expansion varied from ≈0.1 to ≈10 µm/s, with a decrease in the current external pressure. While modeling, a non-linear behavior of CO₂ isotherms near the critical point was taken into account. The modeled data agree satisfactorily with the experimental results. The effect of a remarkable increase in the expansion rate at a decreasing external pressure is interpreted in terms of competing effects, including a decrease in the internal pressure, an increase in the polymer viscosity, and an increase in the embryo radius at the time of embryo formation. The vanishing probability of finding the steadily expanding embryos for external pressures around the CO₂ critical pressure is interpreted in terms of a joint influence of the quasi-adiabatic cooling and high compressibility of CO₂ in the embryos. Full article

(This article belongs to the Special Issue Polymer Foams: Processing and Characterization)

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