A Concise Review of the Components and Properties of Wood–Plastic Composites
Abstract
:1. Introduction
- The significant incompatibility of the polymeric matrix and the natural fillers, which leads to uneven dispersion and reduced mechanical properties values (by adding suitable additives, the properties can be favorably modified);
- Changes in color, which, unlike natural wood, settles within a few days;
- Higher acquisition costs (the ratio of initial investment and the service life of the product is ultimately favorable).
- In 1906, wood flour was used for the first time as an additional component in adhesives. The first composite with an organic filler and a phenol-formaldehyde matrix, referred to as bakelite (used on the knob in a Rolls Royce car);
- Since 1970, the Italian company GOR Applicazioni Speciali S. p. A. began to use wood fillers and resin composite material (in a ratio of 50/50) in car interior panels;
- Similarly, Italian extrusion in the production of material (car components) consisting of a polypropylene matrix and an organic filler (50% wood flour) occurred;
- In 1991, the first conference on organic-filled plastics was held (Madison, USA) with the participation of 50 research workers and the manufacturers themselves. Then, 12 years later, the 7th International Conference on WPCs was held in the same city with 400 participants in attendance;
- In 1993, the Andersen Corporation (Bayport, MN, USA) began producing wood-filled plastics with a PVC matrix used for the production of door components (the components contained 40% wood reinforcement); three years later, a US company grouping participated in the development of equipment for pallet production;
- In the 1990s, the WPC market expanded; the material started to be used for flooring in industrial zones, picnic tables, door frames, and beams. In the same period, the Strandex Corporation (Madison, WI, USA) patented a technology for extruding profiles with a high content of wood fibers (about 70% in volume) without the need for finishing technologies;
- The beginning of the 21st century marked an increase in the demand for these composite materials, and their production increased by 14% annually in the EU and 18% in North America. Over the last 5 years, there has been a 50% increase in interest in WPCs in the area of construction. Over the same time horizon, there has been a 15% increase in interest from automotive manufacturers in materials with natural reinforcement.
2. Components of Composite Materials Based on WPCs
2.1. Organic Fillers
2.2. Wooden Fillers
US Standard Mesh | Diameter of Particle | |
20 | 841 µm | |
30 | 595 µm | |
40 | 420 µm | |
50 | 297 µm | |
60 | 250 µm | |
70 | 210 µm | |
80 | 177 µm | |
100 | 149 µm | |
120 | 125 µm | |
140 | 105 µm | |
170 | 88 µm | |
200 | 74 µm | |
230 | 63 µm | |
270 | 53 µm | |
325 | 45 µm | |
400 | 37 µm |
- The values of the notch toughness of the WPC material increase with increasing time intervals of the wood flour crushing process;
- The highest values of the tensile strength and bending strength of WPC products were recorded when applying particles crushed for 30 min (regardless of the method of the particles’ drying).
2.3. Polymeric Matrices
2.4. Additives
- (a)
- Coupling agents are applied to the composite material components in the mixing phase; the process is called a one-step process;
- (b)
- Coupling agents are applied to the wood fibers before the components are mixed (two-step process);
- (c)
- Coupling agents are applied to a certain volume of wood fibers and polymer granulate as a concentration batch (the resulting mixture is formed by diluting the concentrate).
- External lubricants, which help to move the mixture in the melting screw barrel and ensure that it does not stick to the functional parts of the press (the molecules of the external lubricants are incompatible and do not mix with the mixture), as well as reduce the temperature of the process. These include paraffins, zinc stearates, and PE waxes;
- Internal lubricants, which reduce the shear forces and viscosity of the thermoplastic matrix at high shear rates and improve the melt viscosity. Acid esters and alcohols are included here; they are compatible with the mixture at high temperatures.
- Efficacy against a wide spectrum of microbial activity (fungi, mold, and bacteria);
- Efficacy at low concentrations;
- Harmlessness to higher organisms;
- Safety used.
3. Properties of Wood Plastic Composites
- Polymer type (Simonsen et al., 2004 showed higher protection of products against H2O via the application of the HDPE matrix, while the use of biopolymers was illustrated by Candelier et al., 2019);
- Modification of wood flour (Wei et al., 2013 used esterified wood flour from poplar, which increased the moisture resistance/dimensional stability when compared with a sample where the flour was not modified);
- Type of wood flour (Xu et al., 2015 compared six types of wood flour and their impact on resistance in different directions. For more information, see Figure 5);
- Additives and biocides (Verhey et al., 2001 and Klyosov, 2007 showed that the application of zinc borate, ZnB, increased the resistance to wood-decaying fungi. Similarly, the application of a 3% CCC regulator was performed in a study by Lu et al., 2008);
- Increasing the content of thermoplastics at the expense of wood flour.
4. Conclusions
- The application of composite materials with natural reinforcements can contribute to reducing the carbon footprint (natural fibers can fully replace some types of synthetic fibers);
- In addition to standard polymers, biodegradable plastics based on PLA, PHA, PHB, and PHBV can also be applied in the case of NFC (WPC) matrices (the processing temperature is a limiting factor);
- The final properties of products depend on several attributes, including the type of matrix/reinforcement, the volume of filler or fibers (in the case of fibers, also their orientation), the particle morphology, the technological process of filler/fiber production, the surface adhesion of the examined materials, the interphase formation between the components, etc.;
- Adding modifiers (additives) affects a wide range of properties that are mechanical/user-related. The type and percentage of the applied modifier should be determined based on the conditions in which the product will be applied. The portfolio of additives offered/used in the NFC (WPC) manufacturing process is currently sufficiently broad (compatibilizers, lubricants, biocides, pigments, flame retardants, fillers, etc.). Some additives serve multiple functions; for example, pigments with UV stabilizer functions.
Author Contributions
Funding
Institutional Review Board Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
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Material Function | Material | Percentage Volume |
---|---|---|
Matrix type | Polyethylene | Depending on other components |
Reinforcement | Natural fibers | 30–60% |
Coupling agents | Maleinated polyolefin | 2–5% |
Lubricants | Stearates/esters/others | 3–8% |
UV stabilizers | HALS/benzophenone | 0–1% |
Fillers | Talc | 0–10% |
Pesticides | Zinc borate | 0–2% |
Dyes | Pigments (unspecified) | As required |
Flame retardants | - | As required |
WPC Sample Components | Bending Strength [MPa] | Flexural Modulus [MPa] |
---|---|---|
PPr—PIE | 32.71 | 1929 |
PPr—PIE—PPgMA | 44.34 | 2064 |
PPr—PIE—PPgIA | 42.17 | 2271 |
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Mitaľová, Z.; Mitaľ, D.; Berladir, K. A Concise Review of the Components and Properties of Wood–Plastic Composites. Polymers 2024, 16, 1556. https://doi.org/10.3390/polym16111556
Mitaľová Z, Mitaľ D, Berladir K. A Concise Review of the Components and Properties of Wood–Plastic Composites. Polymers. 2024; 16(11):1556. https://doi.org/10.3390/polym16111556
Chicago/Turabian StyleMitaľová, Zuzana, Dušan Mitaľ, and Khrystyna Berladir. 2024. "A Concise Review of the Components and Properties of Wood–Plastic Composites" Polymers 16, no. 11: 1556. https://doi.org/10.3390/polym16111556
APA StyleMitaľová, Z., Mitaľ, D., & Berladir, K. (2024). A Concise Review of the Components and Properties of Wood–Plastic Composites. Polymers, 16(11), 1556. https://doi.org/10.3390/polym16111556