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Article

Effect of Thickness Swelling and Termite Attack Resistance in Wood–Plastic Composites Produced with Pine Wood and Recycled Thermoplastics

by
Emilly Silva
1,
Yonny Lopez
2,
Juarez Paes
1,
Fernanda Maffioletti
3,
Gabrielly Souza
2 and
Fabricio Gonçalves
1,*
1
Department of Forest and Wood Science, Federal University of Espírito Santo, Jerônimo Monteiro 29.550-000, ES, Brazil
2
Xingu Studies Institute, Federal University of the South and Southeast of Pará, São Félix do Xingu 68.380-000, PA, Brazil
3
Institute of Biodiversity and Forests, Federal University of Western Pará, Santarém 68.040-255, PA, Brazil
*
Author to whom correspondence should be addressed.
Biomass 2025, 5(3), 43; https://doi.org/10.3390/biomass5030043
Submission received: 13 May 2025 / Revised: 1 July 2025 / Accepted: 17 July 2025 / Published: 21 July 2025
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Abstract

This research aimed to evaluate the biological resistance to xylophagous organisms and the dimensional stability related to water absorption in plastic wood panels manufactured by compression molding and produced with pine wood and recycled thermoplastics. The wood–plastic composites (WPCs) were prepared from 50% pine sawdust and 50% recycled plastics (polyethylene terephthalate-PET, high-density polyethylene-HDPE, and polypropylene-PP). The thickness swelling test was carried out by immersing of the WPC samples in water at room temperature (25–30 °C) and evaluating the total change in WPC thickness after 1500 h (≈9 weeks or two months). In addition, the coefficient of initial swelling was evaluated to verify the variability of the swelling. For the biological resistance evaluation of the WPCs, tests were carried out with soil or arboreal termites (Nasutitermes corniger) and drywood termites (Cryptotermes brevis). The WPC loss of mass and termite mortality were evaluated. The use of PP promoted the best response to thickness swelling. The simple mathematical model adopted offers real predictions to evaluate the thickness of the swelling of the compounds in a given time. For some variables there were no statistical differences. It was shown that treatment 3 (T3) presented visual damage values between 0.4 for drywood termites and 9.4 for soil termites, in addition to 26% termite mortality, represented by the lowest survival time of 12 days. The developed treatments have resistance to termite attacks; these properties can be an important starting point for its use on a larger scale by the panel industries.

1. Introduction

Among the physical properties, water transport kinetics and the resulting loss of dimensional stability due to water absorption by wood particles are the most important properties of wood–plastic composites (WPCs); these technological conditions, when these boards are used outdoors, can determine their strength and final use. Studies related to wood treatment before starting the production process become important to reduce water absorption by the composites. One of the treatments performed on wood can be based on ionic liquids. This treatment allows improving water transport kinetics and moisture swelling in wood–plastic composites (WPCs) in the presence of two imidazolium-based ionic liquids (ILs). This demonstrates that the presence of ILs can improve adhesion between the polymer matrix and cellulosic materials, reducing gaps in the interfacial region and blocking hydrophilic groups [1,2].
One of the main consequences of water absorption in wood composites is its interference in density and swelling, affecting their functionality and structural integrity. Considering that these properties can be improved by using recyclable raw materials such as thermoplastics, constitutes an advance for the development of the board industry, creating more resistant and higher quality boards that satisfy the growing needs of the construction sector [3].
Conventional boards such as plywood, medium density fiberboard (MDF) or high density fiberboard (HDF), medium density particleboards (MDP), and oriented strand board (OSB) have a tendency to be damaged by water absorption, causing severe dimensional deformations [4]. In this sense, to control this situation, wood–plastic composites allow a better reaction to water absorption through the fusion of thermoplastics with wood particles [5].
In the manufacture of wood–plastic composites (WPC), recycled and virgin thermoplastics are used, due to their compatibility with the lignocellulosic material that will be subjected to the production process. In addition, products and additives such as organic peroxide can be added, which plays a key role in making the materials compatible with the compounds [6]. In this sense, the study of dosages is a fundamental aspect to avoid irregular areas on the board surface that negatively affect its strength. The particle size parameters of wood and thermoplastics also have a significant influence on the material’s stiffness and resistance to loads [7].
Studies on the use of different lignocellulosic materials as filling materials or binder in WPC allow us to appreciate the comparability of different materials in the same compound. In this sense, WPC boards were made using semi-bio-based polypropylene (bioPP) and micronized argan shell (MAS) by-products. To improve the interaction between the filler or binder and the polymeric matrix, a compatibilizer was used, PP-g-MA [8].
Regarding biological resistance, one of the main conditions for wood products to be attacked by xylophagous organisms such as subterranean termites and drywood termites is the chemical composition of the wood such as cellulose, hemicelluloses, and other simple sugars, such as starch and pectin [7,9]. In addition to termites, wood-rotting fungi can affect the technological properties of wood, making it necessary to implement treatments that allow for greater resistance in wood products and wood–plastic panels [10].
However, the study of creating products with greater biological resistance to biodeterioration is in a growing field of interest for several scientists and scholars on the subject. This concept allows for the creation of materials with better responses to biological organisms and thus could satisfy consumer expectations with products of better quality and durability [11,12].
There are two main groups of termites that most affect wood; they are scientifically recognized as drywood termites Cryptotermes brevis Walker [13,14,15]; this termite finds in the water retained in the wood one of its main food sources. Another termite group recognized as subterranean termites, soil termites, and arboreal termites, is the Nasutitermes corniger Motsch. conehead termite.
Their survival habits include attacking hard or soft wood (dry or wet), particleboard, and generally being very aggressive and destructive [16]. Thus, it is one of the main species of the genus, due to the great damage it causes to wood and other lignocellulosic materials, to have successfully invaded urban areas, where this type of material is available [17,18].
WPC is not exempt from attacks by these biological agents, with wood being one of the main components in its manufacture and with the reality that it can also be deteriorated and damaged. This situation can be corrected based on previous studies on the raw material and based on the use of appropriate formulations according to how the board is used [19,20].
The creation of products with natural resistance capacity is a recurring theme for furniture and construction material industries. This study relates to important aspects such as the treatment of industrial waste, molding techniques, and biological the resistance of wood–plastic composite. This issue relates to some academic topics that consider the modification of products with higher added value and that allow for the incorporation a positive impact on waste-based products, in addition to their impact on strengthening the innovation of resistant materials.
Thus, this research aimed to evaluate the thickness swelling rates and termite attack resistance of compression-molded wood–plastic composites (WPC). Furthermore, it is hypothesized that incorporating plastic into wood particles to form the wood–plastic composite improves the dimensional stability and termite resistance of the formed particleboards.

2. Materials and Methods

2.1. Manufacture of the Particleboard

The experimental conditions for the development of each treatment were based on previous studies of the raw material, in which parameters such as density were analyzed, which was established between 900 and 1100 kg m−3. Pinus elliottii wood was used; it was crushed into particles with approximate dimensions between 3 and 8 mm. The pine wood particles were dried in a kiln to reach a moisture content of approximately 6% (dry basis), and the thermoplastics used were post-consumer. As a commercial adhesive, urea-formaldehyde (MDP1021, 10 parts by mass of the panel, solids content of 64%, pH 8.5, viscosity of 371.86 mPa s−1 and density of 1.23 g cm−3) was used.
The use of this adhesive is justified because in the technological compression process the thermoplastic particles do not fully melt; this occurs mainly in the center of the board matrix where the temperature is lower in relation to the surface; under these conditions the adhesive allows an interaction between the wood and thermoplastic particles. This parameter is not necessary when using the extrusion or injection method for these types of boards; however, it was also used and ammonium sulfate (NH4)2SO4 as a catalyst (2% in proportion to the total mass of adhesive solids).
The mixing process was carried out in a rotating container of ≈1.2 m in diameter and 0.5 m wide, (Figure 1a) with an approximate rotation speed of 26 revolutions per minute. In that same container, an injection gun was adopted and activated by an air compressor to apply the adhesive to the particles; it took approximately 10 min.
After adhesive mixing, the particles were placed in a bottomless box with dimensions of 500 × 500 × 400 mm (width × length × height), (Figure 1b) and it was supported on an aluminum sheet (Figure 1c), where the pre-pressing took place. The particle mattress was placed and adjusted under pressure (42 kgf cm−2; 4.12 MPa) from a hydraulic press of heated dishes (SL12, Solab, Piracicaba, Brazil) (Figure 1d); the temperature conditions were (160 °C), and the board was limited by two iron bars 1.2 cm thick while being pressed (Figure 1c).
The technological design was prepared to define three different treatments whose dosages can be seen in Table 1. After cutting to the proper dimensions for each test, the specimens were stabilized in an acclimatization room (25 ± 2 °C, 65 ± 5% relative humidity) for 24 h.

2.2. Thickness Swelling Test

In order to determine the different parameters that relate to the swelling in thickness after immersion in water, the dimensional deformation of the samples was systematically considered and evaluated for times of 4, 8, 16, 32, 48, 64, 96, 128, 192, 256, 320, 384, 448, 576, 640, 768, 832, 960, 1216 and 1500 h; this process was carried out for two months until reaching the equilibrium thickness in each treatment. Thickness swelling in time (TSt) was evaluated, being a key indicator of how much the size of a wood board will change with changes in humidity. Lower TSt values mean better dimensional stability. To calculate the swelling percentage, Equation (1) was used. The thickness swelling model was used to determine the coefficient of initial swelling (KSR) and was applied to the analyzed data to quantify swelling. For each treatment, five repetitions were performed in accordance with the European Committee for Standardization (CEN), European Standard (EN 317) [21]:
TSt = [(Tf − T0)/T0] × 100
where: TSt: Thickness swelling in time, in percentage. Tf: Final thickness. T0: Initial thickness.

2.3. No-Choice Feeding Test with Nasutitermes corniger Termite

The no-choice feeding test was carried out with the termite species Nasutitermes corniger (Motsch.). It was developed from the specifications of the ASTM D-3345-22 [22] with some modifications suggested in the literature [23]. Therefore, some materials were placed inside a cement box, with a capacity of approximately 250 L; these dimensions can vary according to the size of the termite colony [24].
At the bottom of this box, a layer of sand of 10 to 15 cm is placed, and on top of the sand two to three layers of moistened cardboard are placed, which will be one of the sources of accommodation for the termites when they leave the colony in search of food, and it will be the way to capture the termites that will be used in the no-choice feeding assay. The termite colony should be on a 30 × 40 cm plastic grid resting on a sand layer of two bricks.
For the test, an approximately 600 mL bottle with a screw-on lid is used, lightly closed to allow aeration, to prevent termites from escaping, and prevent possible predators from entering. Inside each bottle, 200 g of sand, moistened as mentioned in ASTM D 3345-22 [22], is added to allow the insects to remain; and the test specimens are placed; the termites are incorporated into the test in quantities of 1 ± 0.05 g (≈360 individuals), of which it is necessary that the proportion of workers is ±90% and ±10% of soldiers. Figure 2 shows the test characteristics.
The samples were exposed to the action of the termites in an air-conditioned room (25 ± 2 °C and 65 ± 5% RH) for 28 days. The natural durability of the WPC was evaluated as a function of the loss of mass (%), visual damage of the specimens, and mortality of the termites (%). The mass loss was corrected by means of loss of operational mass [23,24].

2.4. Drywood Termites Test with Cryptotermes brevis Termite

The Cryptotermes brevis species was used in the no-choice feeding test for drywood termites, and the evaluation was carried out based on the specifications of the Technological Research Institute [25]. The test considered the attack as the degree of scarification, the number of holes in the samples that denote loss of mass, and the degree of visual damage to the samples. This test has some similarities with the one described by Maistrello [26] except for the number of termites and time used to evaluate the test.
The dimensions of the samples were 2.3 × 0.6 × 7.0 cm (radial × tangential × longitudinal). Afterwards, the samples were grouped in pairs and joined with adhesive tape. On top of the samples, a container (pipe) of polyvinyl chloride (PVC) with a diameter of 3.5 cm and a height of 4.0 cm was fixed with paraffin, where the termites were placed (in the ratio of one soldier to 39 workers), and the container was covered with filo-like fabric to prevent possible attacks from predators, such as ants, spiders, and wall lizards; the samples were arranged in Petri dishes to prevent termites from escaping if they pierced or escaped from the sample (Figure 3).
For a better identification and evaluation of the damage caused by these xylophagous agents, scanning electron microscopy (SEM) (JSM-IT200, Akishima, Tokyo, Japan) images were made to verify the main failure zones of the treatments that allowed the entry of such biological agents. The assay was maintained in an air-conditioned room (25 ± 2 °C and 65 ± 5% RH) for 45 days.
At the end of the test, the termites were counted for mortality rate assessment, with subsequent visual evaluation. Grades were assigned varying damage scores: zero (no damage), 1 (surface damage), 2 (moderate damage), 3 (severe damage), and 4 (deep damage), following the aforementioned standard [25]. The mass loss was corrected by means of the loss of operational mass [23,24].

2.5. Statistical Analysis

Statistical analysis was performed using software SPSS (edition 21.0). Before carrying out the analysis of variance, the normality of the data (Lilliefors test) and the homogeneity of the variances (Cochran test) were checked. The Tukey test (p < 0.05) was used to compare the means of treatments considered significant by the F test (p < 0.05). The correlation between variables was evaluated with the Pearson correlation analysis [23].

3. Results

3.1. Wood–Plastic Composite on the Thickness Swelling During Water Immersion

Figure 4 shows the increase in swelling thickness with the increasing immersion time in water, taking into account the effect of the differences between thermoplastics for each treatment. The curves also show the differences between each of them when they reached their state of equilibrium.
Table 2 shows the effect caused by the thermoplastic residues in the evaluated swelling parameters. It can be verified that the properties resistant to swelling by immersion in water were more favorable in T3-WPC (PP) and lesser in T1-WPC (PET).
Figure 5 shows images of the scanning electron microscopy (SEM) that detects fault zones in the treatments. These fault zones can facilitate termite access to the composite structure, contributing to scarification and contact with the wood present in the matrix, and thus contributing to the removal of plastic particles that cover the wood, and to its digestibility by termites.

3.2. Test with Soil or Arboreal Termites (Nasutitermes corniger)

In relation to this test, the evaluated treatments showed a high resistance to termites. However, despite all having this biological resistance, treatment 3 (50% wood and 50% PP) showed the lowest results of mass loss, and a higher density and lower survival of termites in the shortest exposure time to the test, with the results obtained for the control treatment being different (Table 3).

3.3. Test with Drywood Termites (Cryptotermes brevis)

From the results obtained in this analysis, it can be inferred that all the treatments were highly resistant to these termites, as the physical parameters to evaluate the damage to the treatments after the test verified that the tested samples remained almost intact. Although all the treatments showed high resistance, it is important to highlight that the best values were reached by treatment 3 (PP) with a visual score of 0.4 classified without damage. Table 4 shows the values obtained in relation to the resistance of the WPC on drywood termites.

4. Discussion

4.1. Thickness Swelling of Wood–Plastic Composite by Water Immersion

The statistical parameters of regression (Figure 4) show differences between each of the models obtained and the values of the coefficient of determination. The coefficients of the selected models were statistically significant (p < 0.05), in this way it is inferred that the independent variable perfectly explains the behavior of the dependent variable. It is considered that the type of thermoplastic used provides a significant effect in properties of thickness swelling compounds.
The values obtained from the water absorption equilibrium reach values ranging from 0.60 (WPC-PET), 0.55 (WPC-HDPE) to 0.40 (WPC-PP); similar results were reported by San, Nee, and Meng [27] for polypropylene (PP); 60% of sawdust and 1% chemical additives have reported similar results by injection molding, showing values of 2.65%.
Composites produced with HDPE and 40% Pinus radiata wood sawdust, without additives, showed thickness swelling values of 0.18%, using injection molding; and with more than 60% sawdust, 0.29% swelling [28]. They indicate that wood influences the moisture resistance process in particleboards.
On the other hand, similar research was carried out that showed values of 0.7% from high-density polyethylene (HDPE) with more than 30% Pinus radiata wood sawdust without additives by compression molding; and in turn, they obtain values of 1.60% for compounds made with high-density polyethylene (HDPE) with plus 50% of sawdust from the same species of wood [29,30].
The favorable physical properties exhibited wood–plastic composite can be seen; they may be further associated with the addition of chemical additives because they allow for a greater dispersion of flour or wood fibers in the thermoplastic matrix, generating more homogeneous and better physical properties of compounds [30].
According to studies carried out on conventional particleboards, in relation to density and swelling, it is inferred that the higher the density, the higher the swelling should be [31]; this condition is not compatible with wood–plastic composite, because immersion in water does not release the possible irreversible swelling stresses that allow water to enter and cause some type of dimensional deformation [30].
It is important to consider that to produce plastic composite, thermoplastic matrices are used more than PET, HDPE, and PP, taking into account that the melting temperature can range between 170 and 205 °C for favorable conditions to mix with the wood particles [32].
The results obtained confirm and corroborate those obtained by Cazella et al. [33]: that it is possible to obtain particleboard panels made from recycled plastics, which are non-biodegradable, highly used, and discarded. Their use implies a smaller volume of adhesive, and they produce WPC that meets the expected performance for this product.
The search for more environmentally friendly products that can replace some petroleum-based adhesives (due to their toxicity) has been ongoing, such as the replacement of urea formaldehyde with tannin [15,34] or lignosulfonate-based [35,36] products in technological processes for wood-based panels.
In addition, there are manufacturing technologies that combine controlled temperatures and pressures [37] that can help minimize the release of formaldehyde during the production process. It is recognized that formaldehyde-based adhesives are the most widely used by the panel industries worldwide and this is a subject that can be analyzed from a production and environmental perspective.
In this study, the urea formaldehyde-based adhesive was used due to its availability and its ability to bond plastic and wood particles in a technological process using compression, which would eliminate the use of adhesives in other processes such as extrusion and injection [20].

4.2. Biological Resistance of Wood–Plastic Composite to Soil or Arboreal Termites

WPC density may be one of the most relevant properties in relation to mass loss caused by termite attack [20]. According to the statistical results of the Pearson correlation, it appears that there is an inversely proportional relationship of approximately 87%, in the same way that occurs when relating density to the survival of termites (Table 5), whose probability of death during the test period is 85%.
The hybrid agglomerate sandwich produced with sugarcane, thermally-treated pine wood, and malva fiber exhibited a mass loss of 11.38% and visual damage of 8.03% caused by termite attack (Nasutitermes corniger), for the same situation and period of test [24]. This being similar to the values obtained for WPC (PET), WPC (HDPE), and WPC (PP), and having caused high mortality in the termites (Table 3). Considering that termites feed on natural materials that contain cellulose, thermoplastics can also have a negative influence on the deterioration of wood–plastic composite.
Termite mortality found in each treatment (Table 3 and Table 4) may be related to chemical components in the wood that act as repellents to termite attacks [38]. Some of these components are made up of terpenoids, quinones, and technoquinones, which are part of the extractable substances of wood and can be sensitive to its digestive system, causing its death [39].
Furthermore, the apparent density of the panels may be associated with damage resistance [40,41] and time of exposure to termites [42]. The literature also mentions that some species of termites can remove the plastic that surrounds wood particles and degrade wood–plastic composites over time [43].
The values for T3 (PP), Table 3, in relation to T1 (PET) and T2 (HDPE), showed a score of 9.4, indicating less damage caused by the soil termites, as well as the lowest mass loss value of 1.53, a damage score of 0.4, and the lowest mass loss value of 0.55 caused by the drywood termites. Regarding the percentage of termite mortality represented in Table 5, it can be verified that treatment 3 (T3) also has the lowest percentage of mortality.
This value is associated with the termites’ survival capacity during the 45-day test, demonstrating that they only managed to survive for a period of 12 days. This parameter is also confirmed by the Pearson correlation test, which explains the relationship between density and damage by 79%, implying that the higher the density, the less damage caused by the termites.
It is considered that pine wood does not present a marked resistance to the attack of wood deteriorating organisms, and that the behavior of the treatments may be related to the encapsulation of the wood particles by the thermoplastic [44]; this is a limitation hampered by a lack of nutrition with the possible degradation of the oral apparatus.
On the other hand, compounds found in pine wood, such as terpenes and terpenoids (monoterpenes and triterpenes), also have a negative influence on the attack of termites of the genus Nasutitermes on wood. This is especially true in wood from recently cut trees, where the content of such compounds is higher. During the production process of wood–plastic composite (WPC), high temperatures are used that favor the connection between the wood and plastic particles; however, some fault zones can also form due to poor casting during the production process (Figure 5), in this way the wood’s particles are exposed on the surface of the board and to possible termite attacks [45].
It is also inferred that the properties of the boards may depend on the type of technological processing. It can be done by injection, extrusion, and compression. These technical conditions allow a better combination of factors such as temperature and pressure, and thus avoid areas of failure or poor internal adherence between the particles.

4.3. Biological Resistance of Wood–Plastic Composite to Drywood Termites

The percentage mortality results were analyzed over the 45 days of termite exposure; During this period the termites’ survival capacity was estimated, and the results show that for T1 (WPC-PET) and T2 (WPC-HDPE) there was a mortality percentage between 60 and 64.4%, respectively; the mortality for T3 (WPC-PP) was 26.7%, and the control had values of 97.8%.
Some study results show values between 0.58 and 1.05% for mass loss in thermo-modified eucalypt wood [46], and 1.46% (mass loss), 51% (mortality), and 1.88 (visual damage ratting) for Pinus taeda particleboard produced with heat-treated particles [24]. Based on these results, thermo-modified wood could be considered to reduce termite attacks on the WPC, and obtain a forest product of higher quality and biological properties.
However, the interface between wood particles and thermoplastics offered by plastic wood boards allow these boards to have good technological properties, and the type of thermoplastic used can influence biological resistance [30]. The results obtained in this research show that the use of recycled polypropylene offers good results for the biological resistance of the WPC. Thus, they are of interest to the furniture and WPC industries, since most of these particle boards have indoor applications and are subject to attack by drywood termites.
The results presented above allow the consideration of some factors that can influence the quality of the board, and the creation of products with desired technological properties that can be a strong competitor to conventional products. The results obtained in this research can be considered a starting point to develop good quality products and contribute to knowledge about biological resistance (including subterranean (soil or arboreal) termites, drywood termites and wood decay fungi) of wood–plastic composite obtained by compression.

5. Conclusions

The treatments produced showed favorable biological properties and minimal variations in dimensional stability, which can be verified through mathematical models to evaluate swelling thickness, with predictions above 90% for WPCs produced with PET and HDPE. However, boards produced with PP show better performance for the swelling equilibrium parameters (TSt, 4.13%) and a better initial swelling coefficient (Ksr, 5.00). Regarding biological resistance, treatment T3 (WPC-PP), produced with PP thermoplastic, showed a mass loss of 1.53% for Nasutitermes corniger and 0.55% for Cryptotermes brevis. This interpretation could be related to the failure zones observed in the scanning electron microscopy (SEM) images, which could serve as an entry point for termites into the boards. Treatment 3 (T3) was shown to present visual damage values ranging from 0.4 for drywood termites to 9.4 for soil termites, in addition to 26% termite mortality, represented by the shortest survival time of 12 days. All treatments produced can be classified as highly resistant.

Author Contributions

Conceptualization, Y.L. and J.P.; methodology, Y.L., F.G., and J.P.; validation, Y.L., F.G., and J.P.; formal analysis, Y.L.; investigation, Y.L., F.M., E.S., and G.S.; data curation, F.M., E.S., and G.S.; writing—original draft preparation, Y.L.; writing—review and editing, F.G., J.P., F.M., E.S., and G.S.; supervision, F.G. and J.P.; project administration, Y.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
PETPolyethylene Terephthalate
HDPEHigh-Density Polyethylene
PPPolypropylene
WPCWood–Plastic Composites

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Figure 1. Apparatus used in the manufacture of composites. (a): Rotating container; (b): composite forming box; (c): particle mattress; and (d): hydraulic press.
Figure 1. Apparatus used in the manufacture of composites. (a): Rotating container; (b): composite forming box; (c): particle mattress; and (d): hydraulic press.
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Figure 2. Arrangement of samples for the soil (arboreal) termite no-choice feeding assay.
Figure 2. Arrangement of samples for the soil (arboreal) termite no-choice feeding assay.
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Figure 3. Arrangement of the PVC pipe on the test sample for the drywood termite test.
Figure 3. Arrangement of the PVC pipe on the test sample for the drywood termite test.
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Figure 4. Effect of thermoplastic content in wood–plastic composite on the thickness swelling during water immersion.
Figure 4. Effect of thermoplastic content in wood–plastic composite on the thickness swelling during water immersion.
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Figure 5. Scanning electron microscopy (SEM) images of the compound. T1–T3, see Table 1.
Figure 5. Scanning electron microscopy (SEM) images of the compound. T1–T3, see Table 1.
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Table 1. Organization of treatments designed in research for the proportions of sawdust and recycled thermoplastics content used.
Table 1. Organization of treatments designed in research for the proportions of sawdust and recycled thermoplastics content used.
TreatmentsSawdust Content
(%)		Recycled Thermoplastics (%)Density
(Kg m−3)
PETHDPEPP
T1—WPC (PET) *5050--918.17
T2—WPC (HDPE)50-50-964.33
T3—WPC (PP)50--501097.33
Control (pine particles)100---660.90
* WPC: wood–plastic composite; PET: polyethylene terephthalate; HDPE: high-density polyethylene; PP: Polypropylene.
Table 2. Swelling thickness values for wood–plastic composite during immersion in water.
Table 2. Swelling thickness values for wood–plastic composite during immersion in water.
TreatmentsWab (%) *T0 (mm)Tf (mm)TSt (%)Ksr (10−3 h−1)r
T1—WPC (PET)0.601617.9011.900.820.95
T2—WPC (HDPE)0.551617.7711.062.410.97
T3—WPC (PP)0.401616.664.135.000.98
* Wab: Equilibrium water absorption. T0: Initial thickness. Tf: Final thickness. TSt: Equilibrium thickness swelling. Ksr: Coefficient of initial swelling. r: Pearson correlation coefficient.
Table 3. Parameters evaluated for soil termites for each treatment and condition tested.
Table 3. Parameters evaluated for soil termites for each treatment and condition tested.
TreatmentsVisual Damage (Score)Mass Loss
(%)		Mortality (%)Classification
(ASTM D3345-22) [22]
T1—WPC (PET)6.4 (0.89) a *1.5182.4Heavy
T2—WPC (HDPE)7.2 (1.02) a1.4984.2Heavy
T3—WPC (PP)9.4 (1.09) a0.5389.8Heavy
Control (pine particles)1.8 (0.84) b8.9936.6Moderate
* Same letter in the column do not differ (Tukey, p < 0.05). Numbers in parentheses are standard deviations. T1–T3, see Table 1.
Table 4. Parameters evaluated for drywood termites for each treatment and condition tested.
Table 4. Parameters evaluated for drywood termites for each treatment and condition tested.
TreatmentsDamage
(Score)		ClassificationMass Loss
(%)		Mortality
(%)		Number of Days to Death
T1—WPC (PET)1.2Surface damage1.51 a *73 a27
T2—WPC (HDPE)1.6Surface damage1.49 a76 a29
T3—WPC (PP)0.4No damage0.53 b100 b12
Control (pine particles)3.6Severe damage16.48 c40 c44
* Same letter in the column, for each the evaluated parameter, do not differ (Tukey, p < 0.05). T1–T3, see Table 1.
Table 5. Relationship between density parameters and termite survival.
Table 5. Relationship between density parameters and termite survival.
TreatmentsDensity
(kg m−3)		Survival of Termites (Day)Percentage of Termite Survival (%)
T1—WPC (PET)918.172760
T2—WPC (HDPE)964.332964.4
T3—WPC (PP)1097.331226.7
Control (pine particles)660.904497.8
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MDPI and ACS Style

Silva, E.; Lopez, Y.; Paes, J.; Maffioletti, F.; Souza, G.; Gonçalves, F. Effect of Thickness Swelling and Termite Attack Resistance in Wood–Plastic Composites Produced with Pine Wood and Recycled Thermoplastics. Biomass 2025, 5, 43. https://doi.org/10.3390/biomass5030043

AMA Style

Silva E, Lopez Y, Paes J, Maffioletti F, Souza G, Gonçalves F. Effect of Thickness Swelling and Termite Attack Resistance in Wood–Plastic Composites Produced with Pine Wood and Recycled Thermoplastics. Biomass. 2025; 5(3):43. https://doi.org/10.3390/biomass5030043

Chicago/Turabian Style

Silva, Emilly, Yonny Lopez, Juarez Paes, Fernanda Maffioletti, Gabrielly Souza, and Fabricio Gonçalves. 2025. "Effect of Thickness Swelling and Termite Attack Resistance in Wood–Plastic Composites Produced with Pine Wood and Recycled Thermoplastics" Biomass 5, no. 3: 43. https://doi.org/10.3390/biomass5030043

APA Style

Silva, E., Lopez, Y., Paes, J., Maffioletti, F., Souza, G., & Gonçalves, F. (2025). Effect of Thickness Swelling and Termite Attack Resistance in Wood–Plastic Composites Produced with Pine Wood and Recycled Thermoplastics. Biomass, 5(3), 43. https://doi.org/10.3390/biomass5030043

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