Special Issue "Wood Polymer Composites: Modification, Processing and Characterization"

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

Deadline for manuscript submissions: 31 August 2022 | Viewed by 10508

Special Issue Editors

Dr. Emmanuel Akpan
E-Mail Website
Guest Editor
Leibniz-Institut für Verbundwerkstoffe GmbH, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Strasse, Building 58, 67663 Kaiserslautern, Germany
Interests: wood chemistry and functional modifications; wood polymer composite processing and characterization; natural fibre property enhancement
Dr. Suchart Siengchin
E-Mail Website
Guest Editor
Department of Mechanical and Process Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand
Interests: polymer and composite processing; structure-property relationships; natural fiber; composite material; and modeling and rheology based on polymer
Dr. Bernd Wetzel
E-Mail Website
Guest Editor
Leibniz-Institut für Verbundwerkstoffe GmbH, Technische Universität Kaiserslautern (TUK), Erwin-Schrödinger-Strasse, Building 58, 67663 Kaiserslautern, Germany
Interests: nanocomposites; multifunctional thermosets; biocomposites; tribology; fracture mechanics; structure–property relationship

Special Issue Information

Dear Colleagues,

Wood polymer composites (WPCs) are gaining wide acceptance in the society for structural and semi-structural applications such as furniture, building construction and automotive engineering. In addition to sustainability, mechanical performance and lightweight advantages, WPCs do not compete with food production as the fibres are to a large extent obtained as wastes from other processes. Furthermore, the use of wood and wood fibre composites contributes substantially to environmental protection. Harvesting one kilogram of wood takes up 1.84 kg of carbon dioxide from the atmosphere. However, wood fibres possess high water adsorption capacity, poor surface adhesion, low thermal stability, poor UV weathering resistance, and poor dimensional stability. Solving these problems is the key to advancing the applications of wood polymer composites. Key variables governing the performance of wood polymer composites include the nature of the wood fibre (shape, size, composition, and surface quality), manufacturing process and parameters, and structure of the polymeric matrix (chemical and compositional structures). Recent strategies for performance improvement of WPC include chemical/thermal treatments and surface sizing of fibres, matrix functionalization, and hybridization. This Special Issue focuses on innovative approaches to overcome the shortcomings of wood polymer composites. High quality articles in the following areas will be considered for publication after extensive peer review:      

Novel chemical and enzymatic modification strategies of wood fibres for composite applications (studies reporting sustainable and green modification techniques will be given preference).

UV, plasma, and thermal modification strategies of wood fibres for WPC applications (preference will be given to articles reporting innovative attempts to improve UV resistance, thermal/dimensional stability, and impact toughness).

Matrix functionalization and fibre sizing for WPC applications (sustainable functionalization strategies will receive precedence).

Chemical resistance of wood fibre composites

Hybrid resin formulation for wood fibre composites.

Analytical and numerical modelling of processes and properties of wood fibre composites (e.g., porosity as it relates to properties, injection moulding processes and their effect on properties, damping and vibrational properties).

Innovative processing methods for cost reduction and performance improvement of wood polymer composites (e.g., additive manufacturing).

Hybridization of wood fibres towards extended durability, thermal stability, and toughness of wood polymer composites (preference will be given to articles reporting the use of environmentally friendly hybrid particles).

Using new characterization techniques to understand the structural relationship between fibres and matrix.

New application areas for WPC.

Application oriented design strategies for WPC materials (critical review).

Sustainability in wood fibre modifications for WPC (critical review).

Dr. Emmanuel Akpan
Prof. Suchart Siengchin
Dr. Bernd Wetzel
Guest Editors

Manuscript Submission Information

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Keywords

  • Wood fibers
  • Polymer composites
  • Modification
  • Functionalization
  • Hybridization
  • Characterization
  • Sustainability
  • Durability

Published Papers (10 papers)

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Research

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Article
Long-Term Creep Compliance of Wood Polymer Composites: Using Untreated Wood Fibers as a Filler in Recycled and Neat Polypropylene Matrix
Polymers 2022, 14(13), 2539; https://doi.org/10.3390/polym14132539 - 22 Jun 2022
Viewed by 483
Abstract
Neat (NPP) and recycled (RPP) polypropylene matrix materials were used to prepare wood–polymer composites with untreated wood fibers up to 40 wt.%. Long-term creep properties obtained through the time-temperature superposition showed superior creep resistance of composites with NPP matrix. In part, this is [...] Read more.
Neat (NPP) and recycled (RPP) polypropylene matrix materials were used to prepare wood–polymer composites with untreated wood fibers up to 40 wt.%. Long-term creep properties obtained through the time-temperature superposition showed superior creep resistance of composites with NPP matrix. In part, this is attributed to their higher crystallinity and better interfacial adhesion caused by the formation of a transcrystalline layer. This difference resulted in up to 25% creep compliance reduction of composites with NPP matrix compared to composites with recycled (RPP) polypropylene matrix, which does not form a transcrystalline layer between the fibers and polymer matrix. Despite the overall inferior creep performance of composites with RPP matrix, from the 20 wt.% on, the creep compliance is comparable and even surpasses the creep performance of unfilled NPP matrix and can be a promising way to promote sustainability. Full article
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Article
High-Strength and Low-Cost Biobased Polyurethane Foam Composites Enhanced by Poplar Wood Powder Liquefaction
Polymers 2021, 13(17), 2999; https://doi.org/10.3390/polym13172999 - 04 Sep 2021
Viewed by 826
Abstract
An environmentally friendly liquefaction of wood powder was prepared by atmospheric pressure liquefaction technology to replace the non-renewable petroleum polyols in the preparation of polyurethane foam composites. The liquefaction time varied from 0 min to 140 min. The composition of liquefied products and [...] Read more.
An environmentally friendly liquefaction of wood powder was prepared by atmospheric pressure liquefaction technology to replace the non-renewable petroleum polyols in the preparation of polyurethane foam composites. The liquefaction time varied from 0 min to 140 min. The composition of liquefied products and the effects of liquefaction time on the morphology, apparent density and mechanical properties of polyurethane foam composites were investigated. The results showed that the optimal process time for the preparation of wood powder liquefaction products, which could replace traditional petroleum polyols, was 110 min. At this time, polyether polyols are the main liquefaction products, with an average molecular weight in Mn reaching 237 and average molecular weight in Mw reaching 246. The functional group of the liquefied product consisted mainly of hydroxyl, with the highest content of 1042 mg KOH/g and the lowest acid number of 1.6 mg KOH/g. In addition, the surface of the polyurethane foam based on poplar wood is dominated by closed cell foam; thus its foam has good heat insulation and heat preservation properties. At 110 min liquefaction time, the apparent density of polyurethane foam is 0.164 g/cm3 and the compression strength is 850 kPa, which is higher than that of traditional polyurethane foam (768 kPa), which is without wood powder modification. Replacing petroleum polyol with renewable wood powder liquefaction products to prepare biomass-based polyurethane foam composite materials, researching complex chemical changes in different liquefaction stages, and finding the best liquefaction conditions are of great significance to optimize the performance of polyurethane, address the shortage of resources and reduce environmental pollution. Full article
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Article
Thermal, Physical and Mechanical Properties of Poly(Butylene Succinate)/Kenaf Core Fibers Composites Reinforced with Esterified Lignin
Polymers 2021, 13(14), 2359; https://doi.org/10.3390/polym13142359 - 19 Jul 2021
Cited by 2 | Viewed by 962
Abstract
In this study, Kraft lignin was esterified with phthalic anhydride and was served as reinforcing filler for poly(butylene succinate) (PBS). Composites with different ratios of PBS, lignin (L), modified lignin (ML) and kenaf core fibers (KCF) were fabricated using a compounding method. The [...] Read more.
In this study, Kraft lignin was esterified with phthalic anhydride and was served as reinforcing filler for poly(butylene succinate) (PBS). Composites with different ratios of PBS, lignin (L), modified lignin (ML) and kenaf core fibers (KCF) were fabricated using a compounding method. The fabricated PBS composites and its counterparts were tested for thermal, physical and mechanical properties. Weight percent gain of 4.5% after lignin modification and the FTIR spectra has confirmed the occurrence of an esterification reaction. Better thermo-mechanical properties were observed in the PBS composites reinforced with modified lignin and KCF, as higher storage modulus and loss modulus were recorded using dynamic mechanical analysis. The density of the composites fabricated ranged from 1.26 to 1.43 g/cm3. Water absorption of the composites with the addition of modified lignin is higher than that of composites with unmodified lignin. Pure PBS exhibited the highest tensile strength of 18.62 MPa. Incorporation of lignin and KCF into PBS resulted in different extents of reduction in tensile strength (15.78 to 18.60 MPa). However, PBS composite reinforced with modified lignin exhibited better tensile and flexural strength compared to its unmodified lignin counterpart. PBS composite reinforced with 30 wt% ML and 20 wt% KCF had the highest Izod impact, as fibers could diverge the cracking propagation of the matrix. The thermal conductivity value of the composites ranged from 0.0903 to 0.0983 W/mK, showing great potential as a heat insulator. Full article
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Article
The Integral Utilization of Date Palm Waste to Produce Plastic Composites
Polymers 2021, 13(14), 2335; https://doi.org/10.3390/polym13142335 - 16 Jul 2021
Cited by 4 | Viewed by 762
Abstract
In this work, date palm waste (DPW) stemming from the annual pruning of date palm was used as a reinforcing filler in polypropylene matrix at 20–60 wt.%. Only a grinding process of the DPW has been performed to ensure no residue generation and [...] Read more.
In this work, date palm waste (DPW) stemming from the annual pruning of date palm was used as a reinforcing filler in polypropylene matrix at 20–60 wt.%. Only a grinding process of the DPW has been performed to ensure no residue generation and full utilization. The present work investigates how the DPW use affects mechanical properties and water absorption of the ensuing composite. The effect of the addition of maleated polypropylene (MAPP) as a coupling agent on the composite properties was also studied. It was shown that the reinforcing potential of DPW was strongly dependent on aspect ratio and interface quality. The MAPP addition resulted in a composite with higher strength and stiffness than the neat PP, meaning that DPW behaves as reinforcement. The difference in the reinforcing effect was explained by the change in the quality of the interface between date palm waste and the polypropylene polymeric chain. Full article
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Article
X-ray Shielding, Mechanical, Physical, and Water Absorption Properties of Wood/PVC Composites Containing Bismuth Oxide
Polymers 2021, 13(13), 2212; https://doi.org/10.3390/polym13132212 - 04 Jul 2021
Cited by 4 | Viewed by 1307
Abstract
The potential utilization of wood/polyvinyl chloride (WPVC) composites containing an X-ray protective filler, namely bismuth oxide (Bi2O3) particles, was investigated as novel, safe, and environmentally friendly X-ray shielding materials. The wood and Bi2O3 contents used in [...] Read more.
The potential utilization of wood/polyvinyl chloride (WPVC) composites containing an X-ray protective filler, namely bismuth oxide (Bi2O3) particles, was investigated as novel, safe, and environmentally friendly X-ray shielding materials. The wood and Bi2O3 contents used in this work varied from 20 to 40 parts per hundred parts of PVC by weight (pph) and from 0 to 25, 50, 75, and 100 pph, respectively. The study considered X-ray shielding, mechanical, density, water absorption, and morphological properties. The results showed that the overall X-ray shielding parameters, namely the linear attenuation coefficient (µ), mass attenuation coefficient (µm), and lead equivalent thickness (Pbeq), of the WPVC composites increased with increasing Bi2O3 contents but slightly decreased at higher wood contents (40 pph). Furthermore, comparative Pbeq values between the wood/PVC composites and similar commercial X-ray shielding boards indicated that the recommended Bi2O3 contents for the 20 pph (40 ph) wood/PVC composites were 35, 85, and 40 pph (40, 100, and 45 pph) for the attenuation of 60, 100, and 150-kV X-rays, respectively. In addition, the increased Bi2O3 contents in the WPVC composites enhanced the Izod impact strength, hardness (Shore D), and density, but reduced water absorption. On the other hand, the increased wood contents increased the impact strength, hardness (Shore D), and water absorption but lowered the density of the composites. The overall results suggested that the developed WPVC composites had great potential to be used as effective X-ray shielding materials with Bi2O3 acting as a suitable X-ray protective filler. Full article
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Article
Investigation of Polymer Biofilm Formation on Titanium-Based Anode Surface in Microbial Fuel Cells with Poplar Substrate
Polymers 2021, 13(11), 1833; https://doi.org/10.3390/polym13111833 - 01 Jun 2021
Cited by 4 | Viewed by 1132
Abstract
Microbial fuel cells (MFCs) have attracted attention by directly converting the bioelectrochemical energy possessed by the organic materials that make up the biomass into electrical energy. In this study, the relationship between the biofilm formed on the titanium-based anode electrode surface, and the [...] Read more.
Microbial fuel cells (MFCs) have attracted attention by directly converting the bioelectrochemical energy possessed by the organic materials that make up the biomass into electrical energy. In this study, the relationship between the biofilm formed on the titanium-based anode electrode surface, and the chemical composition of the substrate, the energy source of MFC, was investigated. For this, MFCs were made by using poplar wood shavings rich in organic material as the substrate, titanium-based material as the anode electrode, and natural soil as bacterial habitat. Three types of MFCs containing 1%, 10%, and 20% poplar wood shavings by weight were made and named P1-MFC, P2-MFC, and P3-MFC, respectively. According to electrochemical analysis, P3-MFC provided the highest open circuit voltage with 490 mV value, and the highest power density with 5.11 mW/m2 value compared to other MFCs. According to optical microscopy examinations, there were Bacillus and Coccus species of bacteria in the soil structure, and these bacteria also existed around the fiber of poplar wood shavings in MFCs. Scanning electron microscopy (SEM), energy-dispersive spectrum (EDS), and Fourier transform infrared spectroscopy (FTIR) analysis showed that MFCs formed biofilm in the titanium-based anode, and the chemical composition of this biofilm with poplar tree was similar. As a result, due to the catalysis reactions of bacteria, the titanium-based anode electrode surface was coated with polymer biofilm released from poplar wood shavings. Full article
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Article
By-Products from Food Industry as a Promising Alternative for the Conventional Fillers for Wood–Polymer Composites
Polymers 2021, 13(6), 893; https://doi.org/10.3390/polym13060893 - 14 Mar 2021
Cited by 6 | Viewed by 988
Abstract
The present paper describes the application of two types of food-industry by-products, brewers’ spent grain (BSG), and coffee silverskin (ŁK) as promising alternatives for the conventional beech wood flour (WF) for wood–polymer composites. The main goal was to investigate the impact of partial [...] Read more.
The present paper describes the application of two types of food-industry by-products, brewers’ spent grain (BSG), and coffee silverskin (ŁK) as promising alternatives for the conventional beech wood flour (WF) for wood–polymer composites. The main goal was to investigate the impact of partial and complete WF substitution by BSG and ŁK on the processing, structure, physicochemical, mechanical, and thermal properties of resulting composites. Such modifications enabled significant enhancement of the melt flowability, which could noticeably increase the processing throughput. Replacement of WF with BSG and ŁK improved the ductility of composites, which affected their strength however. Such an effect was attributed to the differences in chemical composition of fillers, particularly the presence of proteins and lipids, which acted as plasticizers. Composites containing food-industry by-products were also characterized by the lower thermal stability compared to conventional WF. Nevertheless, the onset of decomposition exceeding 215 °C guarantees a safe processing window for polyethylene-based materials. Full article
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Review

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Review
Enriching WPCs and NFPCs with Carbon Nanotubes and Graphene
Polymers 2022, 14(4), 745; https://doi.org/10.3390/polym14040745 - 15 Feb 2022
Viewed by 854
Abstract
Carbon nanotubes (CNTs) and graphene, with their unique mechanical, electrical, thermal, optical, and wettability properties, are very effective fillers for many types of composites. Recently, a number of studies have shown that CNTs and graphene may be integrated into wood–plastic composites (WPCs) and [...] Read more.
Carbon nanotubes (CNTs) and graphene, with their unique mechanical, electrical, thermal, optical, and wettability properties, are very effective fillers for many types of composites. Recently, a number of studies have shown that CNTs and graphene may be integrated into wood–plastic composites (WPCs) and natural-fibre-reinforced polymer composites (NFPCs) to improve the existing performance of the WPCs/NFPCs as well as enabling their use in completely new areas of engineering. The following review analyses the results of the studies presented to date, from which it can be seen that that inclusion of CNTs/graphene may indeed improve the mechanical properties of the WPCs/NFPCs, while increasing their thermal conductivity, making them electroconductive, more photostable, less sensitive to water absorption, less flammable, and more thermally stable. This study indicates that the composition and methods of manufacturing of hybrid WPCs/NFPCs vary significantly between the samples, with a consequent impact on the level of improvement of specific properties. This review also shows that the incorporation of CNTs/graphene may enable new applications of WPCs/NFPCs, such as solar thermal energy storage devices, electromagnetic shielding, antistatic packaging, sensors, and heaters. Finally, this paper recognises key challenges in the study area, and proposes future work. Full article
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Review
The Compressive Behavior and Crashworthiness of Cork: A Review
Polymers 2022, 14(1), 134; https://doi.org/10.3390/polym14010134 - 30 Dec 2021
Cited by 1 | Viewed by 376
Abstract
Cork, a natural material from renewable resources, is currently attracting increasing interest in different industrial fields because of its cellular structure and the presence of the flexible suberin as its main chemical component. In an agglomerated form, it proved to be a compelling [...] Read more.
Cork, a natural material from renewable resources, is currently attracting increasing interest in different industrial fields because of its cellular structure and the presence of the flexible suberin as its main chemical component. In an agglomerated form, it proved to be a compelling product not only as a thermal and acoustic insulator, but also as core material in sandwich structures and as a liner or padding in energy absorbing equipment. From this perspective, the assessment of its compressive response is fundamental to ensure the right out-of-plane stiffness required to a core material and the proper crashworthiness in the safety devices. Considering the complex nature of cork and the resulting peculiar compressive response, the present review article provides an overview of this paramount property, assessing the main parameters (anisotropy, temperature, strain rate, etc.) and the peculiar features (near-zero Poisson’s ratio and unique dimensional recovery) that characterize it in its natural state. Furthermore, considering its massive exploitation in the agglomerated form, the design parameters that allow its compressive behavior to be tailored and the operating parameters that can affect its crashworthiness were assessed, reporting some potential industrial applications. Full article
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Review
Incorporation of Biochar to Improve Mechanical, Thermal and Electrical Properties of Polymer Composites
Polymers 2021, 13(16), 2663; https://doi.org/10.3390/polym13162663 - 10 Aug 2021
Cited by 6 | Viewed by 1357
Abstract
The strive for utilization of green fillers in polymer composite has increased focus on application of natural biomass-based fillers. Biochar has garnered a lot of attention as a filler material and has the potential to replace conventionally used inorganic mineral fillers. Biochar is [...] Read more.
The strive for utilization of green fillers in polymer composite has increased focus on application of natural biomass-based fillers. Biochar has garnered a lot of attention as a filler material and has the potential to replace conventionally used inorganic mineral fillers. Biochar is a carbon rich product obtained from thermochemical conversion of biomass in nitrogen environment. In this review, current studies dealing with incorporation of biochar in polymer matrices as a reinforcement and conductive filler were addressed. Each study mentioned here is nuanced, while addressing the same goal of utilization of biochar as a filler. In this review paper, an in-depth analysis of biochar and its structure is presented. The paper explored the various methods employed in fabrication of the biocomposites. A thorough review on the effect of addition of biochar on the overall composite properties showed immense promise in improving the overall composite properties. An analysis of the possible knowledge gaps was also done, and improvements were suggested. Through this study we tried to present the status of application of biochar as a filler material and its potential future applications. Full article
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