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Wood Plastic Composites
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Wood Plastic Composites

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Biobased and Biodegradable Polymers".

Deadline for manuscript submissions: closed (20 December 2020) | Viewed by 30961

Special Issue Editors

Dr. Francesco Mollica

E-Mail Website
Guest Editor
Department of Engineering, University of Ferrara, 44122 Ferrara, Italy
Interests: natural-fiber-filled polymers; non-newtonian fluid mechanics; composites; 3D printing; mechanical modeling; biomaterials; tissue engineering
Special Issues, Collections and Topics in MDPI journals
Dr. Valentina Mazzanti

E-Mail Website
Guest Editor
Department of Engineering, University of Ferrara, 44122 Ferrara, Italy
Interests: polymeric and composite materials; manufacturing and compounding processes; innovative plastics filled with natural fibers; mechanical properties; rheological properties; thermal properties; 3D printing; ageing and degradation phenomena; tribology and wear
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Wood plastic composite (WPC) is a class of biocomposite material that is obtained by compounding wood flour with a thermoplastic polymer and suitable additives—mainly coupling agents and lubricants. It can be worked like natural wood, yet it can also be extruded or injection molded, much like standard plastic, and, as such, it can also be recycled.

The WPC global market is increasing at a very rapid pace, and is predicted to exceed 10 billion dollars by 2026. The driving force for the usage of these materials is for their applications in the building and construction sector, where natural wood can be conveniently substituted by WPC, thanks to its superior durability and lower maintenance requirements. Moreover, in recent years, the automotive industry has also been making more use of WPC, mainly for its relatively low density, recyclability, and the reduced environmental impact of natural fiber filled thermoplastics.

Despite its worldwide success, WPC still suffers from a number of drawbacks. For instance, there is still much room for improving its mechanical properties, particularly strength and toughness, as the material is generally brittle and prone to chipping and splintering. Furthermore, the material is inherently difficult to process, as it needs to be dried before processing, and the temperature must be carefully controlled in order to avoid thermo-oxidative degradation and a bad smell during processing. Among the other known problems are its flammability, hygroscopic swelling, and biological degradation.

The aim of this Special Issue is to share information that can contribute to tackling and solving some of these problems, thus leading to an improvement in the quality of the WPC materials, as well as discussing the novel applications and processing techniques of WPCs. Research and review articles on these subjects are warmly welcomed.

Prof. Dr. Francesco Mollica
Dr. Valentina Mazzanti
Guest Editors

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Keywords

  • Mechanical properties
  • Rheology
  • Processing
  • Viscoelasticity
  • Natural fiber treatments
  • Additives and compounding
  • Applications
  • Life cycle assessment
  • Degradation and biodegradability
  • Flammability

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Published Papers (7 papers)

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Research

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15 pages, 2668 KiB  
Article
Thermal Decomposition Kinetics of Basalt Fiber-Reinforced Wood Polymer Composites
by Xian Zhang and Runzhou Huang
Polymers 2020, 12(10), 2283; https://doi.org/10.3390/polym12102283 - 5 Oct 2020
Cited by 20 | Viewed by 3173
Abstract
Thermogravimetric analysis (TGA) was used for the observation of the pyrolysis kinetics characteristics of high density polyethylene (HDPE)-based composites enhanced by a variety of basalt fibers (BFs) and wood flour (WF). The improved Coats-Redfern (C-R), Flynn-Wall-Ozawa (F-W-O), Friedman, and Kissinger methods were utilized [...] Read more.
Thermogravimetric analysis (TGA) was used for the observation of the pyrolysis kinetics characteristics of high density polyethylene (HDPE)-based composites enhanced by a variety of basalt fibers (BFs) and wood flour (WF). The improved Coats-Redfern (C-R), Flynn-Wall-Ozawa (F-W-O), Friedman, and Kissinger methods were utilized to ascertain the specific apparent activation energy (Ea) of each component and composite material. The results indicate that BFs do not decompose under 800 °C, while the pyrolysis of WF and waste HDPE showed two significant weight loss zones (250–380 °C and 430–530 °C), relative to cellulose/hemicellulose and HDPE thermal degradation, respectively. The average Ea of WF/BF/HDPE composites over the entire pyrolysis process obtained by the modified C-R method fluctuated in a range of 145–204 kJ/mol and increased with the BF content, which was higher than that of WPC (115–171 kJ/mol). The value of Ea computed by the F-W-O method was significantly lower than that computed with the improved C-R method, which could validate the reliability of two methods by comparing with the literature. The Friedman and Kissinger methods were not applicable to this composite material reinforced by mixed fillers, so the obtained Ea values were quite different from the previous two methods. The changes in Ea showed that the addition of BFs could improve the average Ea and further enhance the thermal stability and flame resistance of the composites. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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15 pages, 3949 KiB  
Article
Plasma Treatment of Polypropylene-Based Wood–Plastic Composites (WPC): Influences of Working Gas
by Philipp Sauerbier, Robert Köhler, Gerrit Renner and Holger Militz
Polymers 2020, 12(9), 1933; https://doi.org/10.3390/polym12091933 - 27 Aug 2020
Cited by 16 | Viewed by 3867
Abstract
In this study, a polypropylene (PP)-based wood–plastic composite with maleic anhydride-grafted polypropylene (MAPP) as a coupling agent and a wood content of 60% was extruded and specimens were injection molded. The samples were plasma treated utilizing a dielectric barrier discharge (DBD) setup with [...] Read more.
In this study, a polypropylene (PP)-based wood–plastic composite with maleic anhydride-grafted polypropylene (MAPP) as a coupling agent and a wood content of 60% was extruded and specimens were injection molded. The samples were plasma treated utilizing a dielectric barrier discharge (DBD) setup with three different working gases: Ar/O2 (90%/10%), Ar/N2 (90%/10%), and synthetic air. This process aims to improve the coating and gluing properties of the otherwise challenging apolar surface of PP based wood–plastic composites (WPC). Chemical analysis with X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) showed the formation of oxygen-based functional groups on the surface, independently from the working gas used for the treatment. Laser scanning microscopy (LSM) examined the surface roughness and revealed that the two argon-containing working gases roughened the surface more than synthetic air. However, the contact angle for water was reduced significantly after treatment, revealing measurement artifacts for water and diiodomethane due to the severe changes in surface morphology. The adhesion of acrylic dispersion coating was significantly increased, resulting in a pull-off strength of approximately 4 N/mm2, and cross-cut tests assigned the best adhesion class (0), on a scale from 0 to 5, after plasma treatment with any working gas. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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11 pages, 1953 KiB  
Article
Correlation between Mechanical Properties and Processing Conditions in Rubber-Toughened Wood Polymer Composites
by Valentina Mazzanti, Lorenzo Malagutti, Andrea Santoni, Francesca Sbardella, Andrea Calzolari, Fabrizio Sarasini and Francesco Mollica
Polymers 2020, 12(5), 1170; https://doi.org/10.3390/polym12051170 - 20 May 2020
Cited by 21 | Viewed by 3562
Abstract
The use of wood fibers is a deeply investigated topic in current scientific research and one of their most common applications is as filler for thermoplastic polymers. The resulting material is a biocomposite, known as a Wood Polymer Composite (WPC). For increasing the [...] Read more.
The use of wood fibers is a deeply investigated topic in current scientific research and one of their most common applications is as filler for thermoplastic polymers. The resulting material is a biocomposite, known as a Wood Polymer Composite (WPC). For increasing the sustainability and reducing the cost, it is convenient to increase the wood fiber content as much as possible, so that the polymeric fraction within the composite is thereby reduced. On the other hand, this is often thwarted by a sharp decrease in toughness and processability—a disadvantage that could be overcome by compounding the material with a toughening agent. This work deals with the mechanical properties in tension and impact of polypropylene filled with 50 wt.% wood flour, toughened with different amounts (0%, 10%, and 20%) of a polypropylene-based thermoplastic vulcanizate (TPV). Such properties are also investigated as a function of extrusion processing variables, such as the feeding mode (i.e., starve vs. flood feeding) and screw speed. It is found that the mechanical properties do depend on the processing conditions: the best properties are obtained either in starve feeding conditions, or in flood feeding conditions, but at a low screw speed. The toughening effect of TPV is significant when its content reaches 20 wt.%. For this percentage, the processing conditions are less relevant in governing the final properties of the composites in terms of the stiffness and strength. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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13 pages, 5368 KiB  
Article
Properties of Poplar Fiber/PLA Composites: Comparison on the Effect of Maleic Anhydride and KH550 Modification of Poplar Fiber
by Zhaozhe Yang, Xinhao Feng, Min Xu and Denis Rodrigue
Polymers 2020, 12(3), 729; https://doi.org/10.3390/polym12030729 - 24 Mar 2020
Cited by 37 | Viewed by 4762
Abstract
To improve the interfacial adhesion and dispersion of a poplar fiber in a polylactic acid (PLA) matrix, maleic anhydride (MA) and a silane coupling agent (KH550) were used to modify the poplar fiber. The poplar fiber/PLA composites were produced with different modifier contents. [...] Read more.
To improve the interfacial adhesion and dispersion of a poplar fiber in a polylactic acid (PLA) matrix, maleic anhydride (MA) and a silane coupling agent (KH550) were used to modify the poplar fiber. The poplar fiber/PLA composites were produced with different modifier contents. The mechanical, thermal, rheological, and physical properties of composites were investigated. A comparison of different natural fiber modifications on the properties of composites was also analyzed. The results showed that both MA and KH550 could improve the interfacial adhesion between the poplar fiber and PLA, resulting in the enhanced mechanical properties of the composite, with 17% and 23% increases of tensile strength for 0.5% MA and 2% KH550, respectively. The thermal properties of the composites were improved at 6% KH550 (a 9% enhancement of T90%) and decreased at 0.5% MA (a 6% decrement of T90%). The wettability of the composites obtained a 11.3% improvement at 4% KH550 and a 5% reduction at 4% MA. Therefore, factors such as mechanical properties, economic efficiency, and durability should be carefully considered when choosing the modifier to improve the property of the composite. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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15 pages, 9889 KiB  
Article
Flame Retardancy of High-Density Polyethylene Composites with P,N-Doped Cellulose Fibrils
by Shuai Zhang, He Chen, Yin Zhang, Yi-meng Zhang, Weiyan Kan and Mingzhu Pan
Polymers 2020, 12(2), 336; https://doi.org/10.3390/polym12020336 - 5 Feb 2020
Cited by 29 | Viewed by 4110
Abstract
To derive P,N-doped cellulose fibrils, phosphoric acid and aqueous ammonia were placed in a one-pot reaction, and the phosphate groups and ammonium phosphates were successfully introduced into the cellulose surface. The obtained P,N-doped cellulose fibrils with high liberation were thereafter incorporated into a [...] Read more.
To derive P,N-doped cellulose fibrils, phosphoric acid and aqueous ammonia were placed in a one-pot reaction, and the phosphate groups and ammonium phosphates were successfully introduced into the cellulose surface. The obtained P,N-doped cellulose fibrils with high liberation were thereafter incorporated into a high-density polyethylene (HDPE) matrix to improve the flame retardancy of HDPE composites, and they had a significant improvement on flame retardancy of HDPE composites. In particular, 7 wt % P,N-doped cellulose fibrils considerably reduced the average and peak heat release rate (HRR) by 29.6% and 72.9%, respectively, and increased the limited oxygen index (LOI) by 30.5%. The presence of phosphate groups and ammonium phosphates within P,N-doped cellulose fibrils was found to promote the thermal degradation of HDPE composites at a lower temperature (i.e., 240 °C). The released acid catalyzed the dehydration of cellulose to form an aromatic carbonaceous structure with a higher crystalline orientation, which improves the flame retardancy of HDPE composites. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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12 pages, 1359 KiB  
Article
Nonisothermal Crystallization Kinetics of Acetylated Bamboo Fiber-Reinforced Polypropylene Composites
by Yu-Shan Jhu, Teng-Chun Yang, Ke-Chang Hung, Jin-Wei Xu, Tung-Lin Wu and Jyh-Horng Wu
Polymers 2019, 11(6), 1078; https://doi.org/10.3390/polym11061078 - 22 Jun 2019
Cited by 24 | Viewed by 4277
Abstract
The crystallization behavior of bamboo fiber (BF) reinforced polypropylene (PP) composites (BPCs) was investigated using a differential scanning calorimeter (DSC). The results showed that unmodified BF as a nucleation agent accelerated the crystallization rate of the PP matrix during cooling whereas there is [...] Read more.
The crystallization behavior of bamboo fiber (BF) reinforced polypropylene (PP) composites (BPCs) was investigated using a differential scanning calorimeter (DSC). The results showed that unmodified BF as a nucleation agent accelerated the crystallization rate of the PP matrix during cooling whereas there is no significant effect on the improved crystallization rate in BPCs with acetylated BFs. Based on the Avrami method, Avrami–Ozawa method, and Friedman method, the corresponding crystallization kinetics of PP reinforced with different acetylation levels of BFs were further analyzed. The results demonstrated that the crystal growth mechanism of the PP matrix for BPCs with unmodified and various acetylated BFs exhibited tabular crystal growth with heterogeneous nucleation. A higher cooling rate is required to achieve a certain relative crystallinity degree at the unit crystallization time for BPCs with a higher weight percent gain (WPG) of acetylated BFs (WPG >13%). Furthermore, based on the Friedman method, the lowest crystallization activation energy was observed for the BPCs with 19% WPG of acetylated BFs. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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Review

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23 pages, 736 KiB  
Review
A Review of Wood Polymer Composites Rheology and Its Implications for Processing
by Valentina Mazzanti and Francesco Mollica
Polymers 2020, 12(10), 2304; https://doi.org/10.3390/polym12102304 - 8 Oct 2020
Cited by 49 | Viewed by 5627
Abstract
Despite the fact that wood polymer composites are interesting materials for many different reasons, they are quite difficult to shape through standard polymer processing techniques, such as extrusion or injection molding. Rheological characterization can be very helpful for understanding the role played by [...] Read more.
Despite the fact that wood polymer composites are interesting materials for many different reasons, they are quite difficult to shape through standard polymer processing techniques, such as extrusion or injection molding. Rheological characterization can be very helpful for understanding the role played by the many variables that are involved in manufacturing and to achieve a good quality final product through an optimized mix of formulation and processing parameters. The main methods that have been used for the rheological characterization of these materials are capillary and parallel plate rheometry. Both are very useful: rotational rheometry is particularly convenient to investigate the compounding phase and obtain structural information on the material, while capillary viscometry is well suited to understand final manufacturing. The results available in the literature at the moment are indeed very interesting and are mostly aimed at investigating the influence of the material formulation, the additives in particular, on the structural, mechanical, and morphological properties of the composite: despite a good number of papers, though, it is difficult to draw general conclusions, as many issues are still debated. The purpose of this article was to overview the state of the art and to highlight the issues that deserve further investigation. Full article
(This article belongs to the Special Issue Wood Plastic Composites)
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