Special Issue "Wood Plastic Composites"

A special issue of Fibers (ISSN 2079-6439).

Deadline for manuscript submissions: closed (31 January 2021).

Special Issue Editor

Prof. Dr. Andreas Krause
E-Mail Website
Guest Editor
Department of Wood Science and Technology, University Hamburg, 21031 Hamburg, Germany
Interests: wood plastic composites; composite theory; composite interface behavior; durability of composites; recycling and use of recycled raw materials
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Composites from wood or other lignocellulose materials and thermoplastics are established on the market for many different applications. The name “wood plastic or polymer composites” (WPC) comprises many different raw materials, production technologies and products. Products made of WPC are worldwide available in increasing amounts. The quality of the products/composites are very diverse. Some producer guarantee more than 20 years, but other products fail after less than one year. The reason for this is that WPCs are not fully understood yet. Many studies, focusing on several aspects of the behavior, have been published. Most of these studies show particular effects, neglecting other influences, which interact with the system.

This Special Issue aims to comprise the current knowledge of all topics involved in the understanding of WPCs as a bio-based thermoplastic composite. The topic starts with theoretical approaches regarding composite behavior, and includes the influence of raw materials and additives, processing, including pretreatments and post treatments, up to the understanding of long-term material behaviors in service. Very welcome are studies that investigates the variability of composites, e.g., wood source, fiber, particle size, etc.

Prof. Dr. Andreas Krause
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 papers will be 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. Fibers is an international peer-reviewed open access monthly 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 1600 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

  • Wood plastic composites
  • Composite theory and interfaces
  • Fiber/particle analysis
  • Production methods
  • Raw materials
  • Recycling and reuse
  • Additives
  • Degradation of WPC

Published Papers (6 papers)

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Research

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Article
Online Pre-Treatment of Thermomechanical Pulp with Emulsified Maleated Polypropylene for Processing of Extruded Thermoplastic Composites
Fibers 2021, 9(3), 17; https://0-doi-org.brum.beds.ac.uk/10.3390/fib9030017 - 03 Mar 2021
Viewed by 514
Abstract
The effectiveness of maleated polypropylene (MAPP) in emulsified form for the pre-treatment of thermo-mechanical pulp (TMP) before extrusion with polypropylene fibres was evaluated. MAPP in pellet form, which was applied during the compounding step, served as a benchmark. In addition, commercial softwood flour [...] Read more.
The effectiveness of maleated polypropylene (MAPP) in emulsified form for the pre-treatment of thermo-mechanical pulp (TMP) before extrusion with polypropylene fibres was evaluated. MAPP in pellet form, which was applied during the compounding step, served as a benchmark. In addition, commercial softwood flour was included as a reference. The influence of the temperature during the defibration process and the presence or absence of the coupling agent on composite performance were evaluated. Composites were processed with a high wood content of 70 wt.%, which is common for extruded profiles. It was found that TMP based on Robinia (Robinia pseudoacacia L.) conferred higher strength properties to the composites compared to TMP based on Scots pine (Pinus sylvestris L.), which was attributed to the higher length/diameter ratio of fibres in Robinia. However, under the conditions of this study, strength properties were superior and water uptake and swelling were reduced when wood flour was used instead of TMP. On the other hand, in many formulations, larger improvements in flexural and tensile strength due to MAPP were found for the TMP-based composites compared to the wood flour-based composites. This could be due to the larger surface/volume ratio for TMP compared to wood flour and more efficient stress transfer from fibres to the matrix. Results from X-ray photoelectron spectroscopy (XPS) showed that TMP surfaces were more hydrophobic than wood flour due to coverage with lignin, which reduced the effectiveness of MAPP. Esterification between the emulsified MAPP and fibre surfaces was determined using Fourier-Transform Infrared (FTIR) spectroscopy, but some non-activated maleic anhydride remained. Under the conditions of this study, MAPP added during compounding provided better performance compared to MAPP which included a non-ionic emulsifier and which was added during the refining process. Lower temperature (150 °C) during defibration was shown to be beneficial for the strength properties of composites compared to high temperature (180 °C) when MAPP was included in the formulations. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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Article
Bonding Wood Veneer with Biobased Poly(Lactic Acid) Thermoplastic Polyesters: Potential Applications for Consolidated Wood Veneer and Overlay Products
Fibers 2020, 8(8), 50; https://0-doi-org.brum.beds.ac.uk/10.3390/fib8080050 - 31 Jul 2020
Viewed by 1526
Abstract
This study reports on the use of poly(lactic acid) (PLA) as a renewable thermoplastic adhesive for laminated panels using birch, spruce, and pine veneers. Consolidated panels were prepared from veneer and PLA foils by hot-pressing from 140 to 180 °C to achieve minimum [...] Read more.
This study reports on the use of poly(lactic acid) (PLA) as a renewable thermoplastic adhesive for laminated panels using birch, spruce, and pine veneers. Consolidated panels were prepared from veneer and PLA foils by hot-pressing from 140 to 180 °C to achieve minimum bondline temperatures. Evaluation of panel properties revealed that the PLA-bonded panels met minimum tensile strength and internal bond strength performance criteria. However, the adhesion interface which developed within individual bondlines varied with distinctions between hardwood and softwood species and PLA grades. Birch samples developed greater bondline strength with a higher pressing temperature using semi-crystalline PLA, whereas higher temperatures produced a poorer performance with the use of amorphous PLA. Panels formed with spruce or pine veneers had lower bondline performance and were also similarly distinguished by their pressing temperature and PLA grade. Furthermore, the potential for PLA-bonded laminated panels was demonstrated by cold water soak testing. Samples exhibiting relatively greater bondline adhesion had wet tensile strength values comparable to those tested in dry state. Our study outcomes suggest the potential for PLA bonding of veneers and panel overlays with the added benefits of being renewable and a no added formaldehyde system. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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Article
Resistance of Injection Molded Wood-Polypropylene Composites against Basidiomycetes According to EN 15534-1: New Insights on the Test Procedure, Structural Alterations, and Impact of Wood Source
Fibers 2019, 7(10), 92; https://0-doi-org.brum.beds.ac.uk/10.3390/fib7100092 - 21 Oct 2019
Viewed by 2714
Abstract
In this study, we investigated injection molded wood-polypropylene composites based on various wood sources and their decay resistance against white rot (Trametes versicolor) and brown rot (Coniophora puteana) in a laboratory test according to EN 15534-1:2014. The manufactured composites [...] Read more.
In this study, we investigated injection molded wood-polypropylene composites based on various wood sources and their decay resistance against white rot (Trametes versicolor) and brown rot (Coniophora puteana) in a laboratory test according to EN 15534-1:2014. The manufactured composites consisted of poplar (Populus spp.), willow (Salix spp.), European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) H. Karst.), and a commercial wood source (Arbocel® C100), respectively. All formulations were compounded on a co-rotating twin screw extruder and subsequently injection molded to wood–PP specimens with a wood content of 60% or 70% by weight. It was found that the test procedure had a significant effect on the mechanical properties. Loss in mechanical properties was primarily caused by moisture and less by fungal decay. Moisture caused a loss in the modulus of rupture and modulus of elasticity of 34 to 45% and 29 to 73%, respectively. Mean mass and wood mass losses were up to a maximum of 3.7% and 5.3%, respectively. The high resistance against fungal decay was generally attributed to the encapsulation of wood by the polymer matrix caused by sample preparation, and enhanced by reduced moisture uptake during the preconditioning procedure. Notable differences with respect to the wood particle source and decay fungi were also observed. Structural characterization confirmed the decay pattern of the fungi such as void cavities close the surface and the deposition of calcium oxalates. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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Article
Quantitative Assessment and Visualisation of the Wood and Poly(Lactic Acid) Interface in Sandwich Laminate Composites
Fibers 2019, 7(2), 15; https://0-doi-org.brum.beds.ac.uk/10.3390/fib7020015 - 11 Feb 2019
Cited by 2 | Viewed by 3075
Abstract
Fluorescence microscopy was applied to understand adhesion interfaces developed within laminated composite sandwiches formed between poly(lactic acid) (PLA) and wood veneers. Composites formed with maple veneer had greater tensile bond strength when manufactured at 200 °C (10.4 N/mm2) compared to formation [...] Read more.
Fluorescence microscopy was applied to understand adhesion interfaces developed within laminated composite sandwiches formed between poly(lactic acid) (PLA) and wood veneers. Composites formed with maple veneer had greater tensile bond strength when manufactured at 200 °C (10.4 N/mm2) compared to formation at 140 °C (8.7 N/mm2), while significantly lower bond strength was achieved using spruce veneers, at 5.2 and 3.5 N/mm2, respectively. Qualitative and quantitative confocal microscopy assessments revealed differing bondline thicknesses and PLA ingress within the wood ultrastructure. Forming maple veneer composites at 200 °C promoted greater PLA mobility away from the bondline to reinforce the wood–PLA interface and deliver associated greater composite bond strength. The addition of 25% wood fibre to PLA led to fibre alignment and overlap within bondlines contributing to relatively thicker, heterogeneous bondlines. Study outcomes show that the composite processing temperature impacts the adhesion interface and composite performance and will have broad application over veneer overlays, laminates and wood plastic composites (WPCs) using wood, particles or fibres with PLA. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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Article
Utilization of Recycled Material Sources for Wood-Polypropylene Composites: Effect on Internal Composite Structure, Particle Characteristics and Physico-Mechanical Properties
Fibers 2018, 6(4), 86; https://0-doi-org.brum.beds.ac.uk/10.3390/fib6040086 - 07 Nov 2018
Cited by 10 | Viewed by 3483
Abstract
In this study, various wood material sources were used for the manufacture of wood-polymer composites (WPC). The materials were categorised as virgin wood particles (VWP), reprocessed WPC particles (RWP) and recycled thermoset composite particles (RCP) and derived from two virgin wood sources, three-layer [...] Read more.
In this study, various wood material sources were used for the manufacture of wood-polymer composites (WPC). The materials were categorised as virgin wood particles (VWP), reprocessed WPC particles (RWP) and recycled thermoset composite particles (RCP) and derived from two virgin wood sources, three-layer particleboards, medium-density fibreboards (MDF) boards, or two different wood/polypropylene composites. All produced wood-polypropylene compounds contained 60% wood material and were manufactured using a co-rotating extruder. Malleated polypropylene was used as a coupling agent. Specimens were injection moulded and subsequently tested for their physico-mechanical properties. To characterize particles before and after processing, dynamic image analysis (DIA) measurement were performed. Additionally, X-ray micro-computed tomography (XµCT) was used to characterize the internal structure of the composites and to verify the obtained particle’s characteristics. It was found that length and aspect ratio of particles were remarkably different before and after processing (loss in length of 15–70% and aspect ratio of 10–40%). Moreover, there were notably differences between the particle sources (RCP retained the highest length and aspect ratio values, followed by VWP and RWP). The results suggest that increased aspect ratios can indeed significantly improve mechanical properties (up to 300% increase in impact bending strength and 75% increase in tensile strength, comparing WPC based either on virgin spruce or MDF material). This phenomenon is suggested to be partially superimposed by improved dispersion of particles, which is expected due to lower variance and increased mechanical properties of RWP composites. However, no notable alterations were observed for composite density. Reprocessed WPC and, particularly, RCP material have proved to be an appealing raw material substitute for the manufacturing of wood–polymer composites. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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Technical Note
Density Profile Analysis of Laminated Beech Veneer Lumber (BauBuche)
Fibers 2021, 9(5), 31; https://0-doi-org.brum.beds.ac.uk/10.3390/fib9050031 - 05 May 2021
Cited by 1 | Viewed by 801
Abstract
An irreversible swelling was detected in laminated beech veneer lumber within the initial moistening. Supported by the facts that the lay-up of the glued veneers is exposed to high pressure during hot pressing, and that the density of the finished material exceeds that [...] Read more.
An irreversible swelling was detected in laminated beech veneer lumber within the initial moistening. Supported by the facts that the lay-up of the glued veneers is exposed to high pressure during hot pressing, and that the density of the finished material exceeds that of solid beech, it was hypothesised that the wood substance is compressed. Laboratory X-ray density profile scans were performed to check this and to identify the part of the material cross section in which the densification has taken place. The higher density was found to be located in the area of the adhesive joints, uniformly over the cross section, while the density in the middle of the veneers corresponds to that of solid beech wood. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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