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

Deadline for manuscript submissions: closed (5 August 2024) | Viewed by 23744

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Prof. Dr. Thomas Neumeyer

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Leibniz Institute for Composite Materials (IVW), University of Kaiserslautern-Landau (RPTU), 67663 Kaiserslautern, Germany
Interests: processing of polymer composites; fiber reinforced composites; polymer foams; lightweight materials; injection molding; additive manufacturing; sustainability

Prof. Dr. Volker Altstädt

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Guest Editor

Department of Polymer Engineering, University of Bayreuth, 95444 Bayreuth, Germany
Interests: environmentally friendly polymers; lightweight materials; functional polymers; advanced processing & testing
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Dear Colleagues,

Polymer–matrix composites play a central role in the energy transition with their low density. Wind rotor blades, pressure tanks for hydrogen, battery housings—none of these applications can operate without those materials. Lightweight materials combined with a high degree of functional integration offer many opportunities to reduce moving masses and thus significantly contribute to resource efficiency and sustainability. The properties of the composite parts can be tailored based on the type of reinforcement and the selected processing technique.

In the future, processing methods for polymer–matrix composites must not only be economical but also use a minimum of energy and resources. Furthermore, aspects of circular economy and the use of secondary materials with varying properties must be taken into account. Sustainability assessments must play a central role in process development. Additionally, it is important to meet the growing trend towards individualization of products without reducing productivity.

In this Special Issue, new approaches with respect to the processing of polymer composites will be presented and discussed. The aim is to understand the interactions between process, structure of the reinforcement, and resulting properties. Special attention will be given to sustainable approaches with a focus on circular economy and energy-efficient processing. Adaptive and customizable technologies will also be part of this issue.

Contributions focused on the manufacturing of polymer–matrix composites in any of the following topics are of particular interest:

Novel processing approaches for thermosets as well as for thermoplastic polymer composites;
Fibers and textiles;
Additive manufacturing technologies for polymer composites;
Resource-efficient processing technologies for polymer–matrix composites;
Joining technologies for polymer composites;
Process monitoring, modeling, and control.

Prof. Dr. Thomas Neumeyer
Prof. Dr. Volker Altstädt
Guest Editors

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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

polymer–matrix composites
composite processing
filament winding
pultrusion
resin transfer molding
prepreg technologies
tape placement
injection overmolding
additive manufacturing
resource-efficient processing

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Published Papers (11 papers)

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Research

17 pages, 13381 KiB

Open AccessArticle

Vacuum Chamber Infusion for Fiber-Reinforced Composites

by Benjamin Grisin, Stefan Carosella and Peter Middendorf

Polymers 2024, 16(19), 2763; https://doi.org/10.3390/polym16192763 - 30 Sep 2024

Viewed by 724

Abstract

A new approach to an automatable fiber impregnation and consolidation process for the manufacturing of fiber-reinforced composite parts is presented in this article. Therefore, a vacuum chamber sealing machine classically used in food packaging is modified for this approach—Vacuum Chamber Infusion (VCI). Dry fiber placement (DFP) preforms, made from 30 k carbon fiber tape, with different layer amounts and fiber orientations, are infused with the VCI and with the state-of-the-art process—Vacuum Assisted Process (VAP)—as the reference. VCI uses a closed system that is evacuated once, while VAP uses a permanently evacuated open system. Since process management greatly influences material properties, the mechanical properties, void content, and fiber volume fraction (FVF) are analyzed. In addition, the study aims to identify how the complexity of a resin infusion process can be reduced, the automation potential can be increased, and the number of consumables can be reduced. Comparable material characteristics and a reduction in consumables, setup complexity, and manufacturing time by a factor of four could be approved for VCI. A void content of less than 2% is measured for both processes and an FVF of 39% for VCI and 45% for VAP is achieved. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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27 pages, 6668 KiB

Open AccessArticle

Multi-Objectives Optimization of Plastic Injection Molding Process Parameters Based on Numerical DNN-GA-MCS Strategy

by Feng Guo, Dosuck Han and Naksoo Kim

Polymers 2024, 16(16), 2247; https://doi.org/10.3390/polym16162247 - 7 Aug 2024

Viewed by 1261

Abstract

An intelligent optimization technique has been presented to enhance the multiple structural performance of PA6-20CF carbon fiber-reinforced polymer (CFRP) plastic injection molding (PIM) products. This approach integrates a deep neural network (DNN), Non-dominated Sorting Genetic Algorithm II (NSGA-II), and Monte Carlo simulation (MCS), collectively referred to as the DNN-GA-MCS strategy. The main objective is to ascertain complex process parameters while elucidating the intrinsic relationships between processing methods and material properties. To realize this, a numerical study on the PIM structural performance of an automotive front engine hood panel was conducted, considering fiber orientation tensor (FOT), warpage, and equivalent plastic strain (PEEQ). The mold temperature, melt temperature, packing pressure, packing time, injection time, cooling temperature, and cooling time were employed as design variables. Subsequently, multiple objective optimizations of the molding process parameters were employed by GA. The utilization of Z-score normalization metrics provided a robust framework for evaluating the comprehensive objective function. The numerical target response in PIM is extremely intricate, but the stability offered by the DNN-GA-MCS strategy ensures precision for accurate results. The enhancement effect of global and local multi-objectives on the molded polymer–metal hybrid (PMH) front hood panel was verified, and the numerical results showed that this strategy can quickly and accurately select the optimal process parameter settings. Compared with the training set mean value, the objectives were increased by 8.63%, 6.61%, and 9.75%, respectively. Compared to the full AA 5083 hood panel scenario, our design reduces weight by 16.67%, and achievements of 92.54%, 93.75%, and 106.85% were obtained in lateral, longitudinal, and torsional strain energy, respectively. In summary, our proposed methodology demonstrates considerable potential in improving the, highlighting its significant impact on the optimization of structural performance. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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23 pages, 14159 KiB

Open AccessArticle

A Study of Deployable Structures Based on Nature Inspired Curved-Crease Folding

by Gaurab Sundar Dutta, Dieter Meiners and Gerhard Ziegmann

Polymers 2024, 16(6), 766; https://doi.org/10.3390/polym16060766 - 11 Mar 2024

Cited by 2 | Viewed by 1387

Abstract

Fascinating 3D shapes arise when a thin planar sheet is folded without stretching, tearing or cutting. The elegance amplifies when the fold/crease is changed from a straight line to a curve, due to the association of plastic deformation via folding and elastic deformation via bending. This results in the curved crease working as a hinge support providing deployability to the surface which is of significant interest in industrial engineering and architectural design. Consequently, finding a stable form of curved crease becomes pivotal in the development of deployable structures. This work proposes a novel way to evaluate such curves by taking inspiration from biomimicry. For this purpose, growth mechanism in plants was observed and an analogous model was developed to create a discrete curve of fold. A parametric model was developed for digital construction of the folded models. Test cases were formulated to compare the behavior of different folded models under various loading conditions. A simplified way to visualize the obtained results is proposed using visual programming tools. The models were further translated into physical prototypes with the aid of 3D printing, hybrid and cured-composite systems, where different mechanisms were adopted to achieve the folds. The prototypes were further tested under constrained boundary and compressive loading conditions, with results validating the analytical model. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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14 pages, 5763 KiB

Open AccessArticle

Numerical Modelling of the Thermoforming Behaviour of Thermoplastic Honeycomb Composite Sandwich Laminates

by Varun Kumar Minupala, Matthias Zscheyge, Thomas Glaesser, Maik Feldmann and Holm Altenbach

Polymers 2024, 16(5), 594; https://doi.org/10.3390/polym16050594 - 21 Feb 2024

Viewed by 1247

Abstract

Lightweight component design is effectively achievable through sandwich structures; many past research studies in the aerospace and racing sectors (since the 1920s) have proven it. To extend their application into the automotive and other transport industries, manufacturing cycle times must be reduced. This can be achieved by sandwich materials made of continuous fibre-reinforced thermoplastic (CFRTP) cover layers and thermoplastic honeycomb cores. To widen the application of flat thermoplastic-based sandwich panels into complex parts, a novel forming technology was developed by the Fraunhofer Institute of Microstructure of Materials and Systems (IMWS). Manufacturing defects like wrinkling and surface waviness should be minimised to achieve high reproducibility of the sandwich components. Studying different manufacturing parameters and their influence on the final part is complex and challenging to analyse through experiments, as it is time-consuming. Therefore, a finite element (FE) modelling approach is implemented to reduce such efforts. Initially, a thermoforming model is developed and validated with experimental results to check its reliability. Further, different simulations are performed to optimise the novel sandwich-forming process. In this study, a thermoplastic sandwich made of polypropylene (PP) honeycomb core and polypropylene glass fibre (PP/GF) cross-ply as cover layers was used, and its numerical model was executed in LS-DYNA software release R11.2.1. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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23 pages, 2297 KiB

Open AccessEditor’s ChoiceArticle

Bringing Light into the Dark—Overview of Environmental Impacts of Carbon Fiber Production and Potential Levers for Reduction

by Tobias Manuel Prenzel, Andrea Hohmann, Tim Prescher, Kerstin Angerer, Daniel Wehner, Robert Ilg, Tjark von Reden, Klaus Drechsler and Stefan Albrecht

Polymers 2024, 16(1), 12; https://doi.org/10.3390/polym16010012 - 19 Dec 2023

Cited by 2 | Viewed by 5524

Abstract

Carbon fibers (CFs) are a crucial material for lightweight structures with advanced mechanical performance. However, there is still a paucity of detailed understanding regarding the environmental impacts of production. Previously, mostly singled-out scenarios for CF production have been assessed, often based on scarce transparent inventory data. To expand the current knowledge and create a robust database for future evaluation, a life cycle assessment (LCA) was carried out. To this end, a detailed industry-approved LCI is published, which also proved plausible against the literature. Subsequently, based on a global scenario representing the market averages for precursor and CF production, the most relevant contributors to climate change (EF3.1 climate change, total) and the depletion of fossil energy carriers (EF3.1 resource use, fossil) were identified. The energy consumption in CF manufacturing was found to be responsible for 59% of the climate change and 48% of the fossil resource use. To enable a differentiated discussion of manufacturing locations and process energy consumption, 24 distinct scenarios were assessed. The findings demonstrate the significant dependence of the results on the scenarios’ boundary conditions: climate change ranges from 13.0 to 34.1 kg CO₂ eq./kg CF and resource use from 262.3 to 497.9 MJ/kg CF. Through the investigated scenarios, the relevant reduction potentials were identified. The presented results help close an existing data gap for high-quality, regionalized, and technology-specific LCA results for the production of CF. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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21 pages, 7921 KiB

Open AccessArticle

New Approach for Processing Recycled Carbon Staple Fiber Yarns into Unidirectionally Reinforced Recycled Carbon Staple Fiber Tape

by Martin Detzel, Peter Mitschang and Ulf Breuer

Polymers 2023, 15(23), 4575; https://doi.org/10.3390/polym15234575 - 30 Nov 2023

Cited by 1 | Viewed by 1914

Abstract

This study describes a novel process in which staple fiber yarns made from recycled carbon fibers (rCFs) and polyamide 6 (PA6) fibers are further processed into semi-finished tape products in a modified impregnation and calendaring process. In this process, the staple fiber yarns are heated above the melting temperature of the polymer, impregnated, and stretched to staple fiber tapes (SF tapes) in the calendaring unit. SF tapes with different degrees of stretching and/or repasses were produced. The individual width and thickness were measured in line by a laser profile sensor. From these tapes, preforms were manually laid and processed into laminates in an autoclave. The important physical properties of the unidirectionally reinforced laminates made of the tapes were compared with organic sheets wound from staple fiber yarns. With increasing stretching, both the fiber orientation and mechanical properties improved compared to the organic sheets made from unstretched staple fiber yarns. An improvement in fiber orientation relative to the process direction from 66.3% to 91.9% (between ±10°) and 39.1% to 71.6% (between ±5°), respectively, was achieved for a two-stage stretched tape. The tensile and flexural moduli were increased by 15.2% and 14.5%, respectively. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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22 pages, 7449 KiB

Open AccessArticle

Challenges in Manufacturing of Hemp Fiber-Reinforced Organo Sheets with a Recycled PLA Matrix

by Maximilian Salmins, Florian Gortner and Peter Mitschang

Polymers 2023, 15(22), 4357; https://doi.org/10.3390/polym15224357 - 8 Nov 2023

Viewed by 1514

Abstract

This study investigates the influence of a hot press process on the properties of hemp fiber-reinforced organo sheets. Plain-woven fabric made from hemp staple fiber yarns is used as textile reinforcement, together with a recycled poly-lactic acid (PLA) matrix. Process pressure and temperature are considered with three factor levels for each parameter. The parameter influence is examined based on the B-factor model, which considers the temperature-dependent viscosity of the polymer, as well as the process pressure for the calculation of a dimensionless value. Increasing these parameters theoretically promotes improvements in impregnation. This study found that the considered recycled polymer only allows a narrow corridor to achieve adequate impregnation quality alongside optimal bending properties. Temperatures below 170 °C impede impregnation due to the high melt viscosity, while temperature increases to 185 °C show the first signs of thermal degradation, with reduced bending modulus and strength. A comparison with hemp fiber-reinforced virgin polypropylene, manufactured with identical process parameters, showed that this reduction can be mainly attributed to polymer degradation rather than reduction in fiber properties. The process pressure should be at least 1.5 MPa to allow for sufficient compaction of the textile stack, thus reducing theoretical pore volume content to a minimum. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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16 pages, 7191 KiB

Open AccessArticle

Finite Element Simulation and Experimental Assessment of Laser Cutting Unidirectional CFRP at Cutting Angles of 45° and 90°

by Jan Keuntje, Selim Mrzljak, Lars Gerdes, Verena Wippo, Stefan Kaierle, Frank Walther and Peter Jaeschke

Polymers 2023, 15(18), 3851; https://doi.org/10.3390/polym15183851 - 21 Sep 2023

Cited by 1 | Viewed by 1277

Abstract

Laser cutting of carbon fibre-reinforced plastics (CFRP) is a promising alternative to traditional manufacturing methods due to its non-contact nature and high automation potential. To establish the process for an industrial application, it is necessary to predict the temperature fields arising as a result of the laser energy input. Elevated temperatures during the cutting process can lead to damage in the composite’s matrix material, resulting in local changes in the structural properties and reduced material strength. To address this, a three-dimensional finite element model is developed to predict the temporal and spatial temperature evolution during laser cutting. Experimental values are compared with simulated temperatures, and the cutting kerf geometry is examined. Experiments are conducted at 45° and 90° cutting angles relative to the main fibre orientation using a 1.1 mm thick epoxy-based laminate. The simulation accurately captures the overall temperature field expansion caused by multiple laser beam passes over the workpiece. The influence of fibre orientation is evident, with deviations in specific temperature data indicating differences between the estimated and real material properties. The model tends to overestimate the ablation rate in the kerf geometry, attributed to mesh resolution limitations. Within the parameters investigated, hardly any expansion of a heat affected zone (HAZ) is visible, which is confirmed by the simulation results. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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14 pages, 2376 KiB

Open AccessArticle

Sustainable Pultruded Sandwich Profiles with Mycelium Core

by Marion Früchtl, Andreas Senz, Steffen Sydow, Jonas Benjamin Frank, Andrea Hohmann, Stefan Albrecht, Matthias Fischer, Maximilian Holland, Frederik Wilhelm and Henrik-Alexander Christ

Polymers 2023, 15(15), 3205; https://doi.org/10.3390/polym15153205 - 28 Jul 2023

Cited by 4 | Viewed by 1600

Abstract

This research focuses on exploring the potential of mycelium as a sustainable alternative to wood or solid foam in pultruded glass fiber-reinforced plastic (GFRP) sandwich profiles. The study evaluates the performance and the environmental sustainability potential of this composite by mechanical tests and life cycle assessment (LCA). Analysis and comparison of pultruded sandwich profiles with mycelium, polyurethane (PUR) foam and chipboard demonstrate that mycelium is competitive in terms of its performance and environmental impact. The LCA indicates that 88% of greenhouse gas emissions are attributed to mycelium production, with the heat pressing (laboratory scale) being the main culprit. When pultruded profiles with mycelium cores of densities 350 and 550 kg/m³ are produced using an oil-heated lab press, a global warming potential (GWP) of 5.74 and 9.10 kg CO₂-eq. per functional unit was calculated, respectively. When using an electrically heated press, the GWP decreases to 1.50 and 1.78 kg CO₂-eq. Compared to PUR foam, a reduction of 23% in GWP is possible. In order to leverage this potential, the material performance and the reproducibility of the properties must be further increased. Additionally, an adjustment of the manufacturing process with in situ mycelium deactivation during pultrusion could further reduce the energy consumption. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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23 pages, 15313 KiB

Open AccessArticle

A Study of Free-Form Shape Rationalization Using Biomimicry as Inspiration

by Gaurab Sundar Dutta, Dieter Meiners and Nina Merkert

Polymers 2023, 15(11), 2466; https://doi.org/10.3390/polym15112466 - 26 May 2023

Cited by 1 | Viewed by 2124

Abstract

Bridging the gap between the material and geometrical aspects of a structure is critical in lightweight construction. Throughout the history of structural development, shape rationalization has been of prime focus for designers and architects, with biological forms being a major source of inspiration. In this work, an attempt is made to integrate different phases of design, construction, and fabrication under a single framework of parametric modeling with the help of visual programming. The idea is to offer a novel free-form shape rationalization process that can be realized with unidirectional materials. Taking inspiration from the growth of a plant, we established a relationship between form and force, which can be translated into different shapes using mathematical operators. Different prototypes of generated shapes were constructed using a combination of existing manufacturing processes to test the validity of the concept in both isotropic and anisotropic material domains. Moreover, for each material/manufacturing combination, generated geometrical shapes were compared with other equivalent and more conventional geometrical constructions, with compressive load-test results being the qualitative measure for each use case. Eventually, a 6-axis robot emulator was integrated with the setup, and corresponding adjustments were made such that a true free-form geometry could be visualized in a 3D space, thus closing the loop of digital fabrication. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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24 pages, 7977 KiB

Open AccessArticle

Approaching Polycarbonate as an LFT-D Material: Processing and Mechanical Properties

by Christoph Schelleis, Benedikt M. Scheuring, Wilfried V. Liebig, Andrew N. Hrymak and Frank Henning

Polymers 2023, 15(9), 2041; https://doi.org/10.3390/polym15092041 - 25 Apr 2023

Cited by 5 | Viewed by 2633

Abstract

Long-fiber thermoplastic (LFT) materials compounded via the direct LFT (LFT-D) process are very versatile composites in which polymers and continuous reinforcement fiber can be combined in almost any way. Polycarbonate (PC) as an amorphous thermoplastic matrix system reinforced with glass fibers (GFs) is a promising addition regarding the current development needs, for example battery enclosures for electromobility. Two approaches to the processing and compression molding of PC GF LFT-D materials with various parameter combinations of screw speed and fiber rovings are presented. The resulting fiber lengths averaged around 0.5 mm for all settings. The tensile, bending, Charpy, and impact properties were characterized and discussed in detail. Special attention to the characteristic charge and flow area formed by compression molding of LFT-D materials, as well as sample orientation was given. The tensile modulus was 10 GPa, while the strength surpassed 125 MPa. The flexural modulus can reach up to 11 GPa, and the flexural strength reached up to 216 MPa. PC GF LFT-D is a viable addition to the LFT-D process, exhibiting good mechanical properties and stable processability. Full article

(This article belongs to the Special Issue Manufacturing of Polymer-Matrix Composites)

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