Effect of Coupling Treatment on Interfacial Bonding Properties of Wood Veneer/Wood Flour–Polyvinyl Chloride Composites with Sandwich Structure

Abstract

Wood–plastic composites (WPCs) have received growing attention due to their good water resistance, environmental friendliness, and recyclability. For the application of WPCs in interior decoration and other high–value fields, it is necessary to preserve these characteristics whilst enhancing their mechanical properties and surface aesthetics. In this study, we used a sandwich structure and four interface modifiers to prepare wood veneer/wood flour–polyvinyl chloride composites (WWPVCs). The results revealed that the WWPVCs treated with a silane coupling agent exhibited superior interfacial bonding and mechanical properties compared to those obtained using other interface modifiers. The interfacial bonding strength of the treated sample reached 1.22 MPa, which was 122% higher than that of the untreated sample. In addition, the wood failure ratio of the optimal sample reached 80%. Furthermore, the dipping–peeling length was found to be shorter than those achieved using other interface modifiers after tests at 63 and 100 °C, indicating that the material treated using the silane coupling agent exhibits an excellent resistance to moisture and heat. Notably, silane coupling agents are easily prepared as solvent–based modifiers, and they do not release harmful gases (e.g., formaldehyde), thereby rendering them highly effective in the preparation of environmentally friendly WPC products.

1. Introduction

Wood–plastic composites (WPCs) are environmentally friendly materials composed of natural fibers, thermoplastic polymers, and minor additives [1,2,3,4,5]. Due to their high plasticity and excellent water resistance, WPCs have extensive applications in outdoor furniture, packaging, railings, and pergolas, among other products [1,4,6]. During the manufacture of WPCs, thermoplastic polymers are used to encapsulate fibers and additives, and the final product is obtained after shaping and cooling. No adhesives are added during this process, thereby rendering the obtained WPCs environmentally friendly. However, WPCs are not currently used to any great extent in interior decoration and other high–value fields because of their plastic texture and limited mechanical properties [7]. To address the aesthetics issue, the surface color of WPCs can be altered by incorporating pigments during the melt compounding of WPC particles [8,9]. Other techniques, such as surface carving, three–dimensional (3D) printing, and film coating, can also enhance the aesthetics of WPC products. However, the surfaces of the WPCs generated by these techniques differ from that of natural wood [10], and the introduction of adhesives into the coating film diminishes the environmental friendliness of the WPC. Many studies have therefore focused on improving the surface decoration of WPCs using environmentally friendly methods. In addition, it is necessary to address the general lack of mechanical properties exhibited by WPCs along with their facile creep response, which prevent the application of WPCs in interior furniture, wallboards, and other similar products.

In recent years, natural fibers, such as cotton, hemp, bamboo, and wood, have gained attention as suitable materials for reinforcing the polymer resin [11,12,13,14,15]. It has been reported that the incorporation of these materials improves the mechanical properties of WPCs by controlling their contents and interfacial properties [13,16,17]. However, although the addition of rigid natural fibers can improve the flexural moduli of WPCs to a certain extent, any enhancements in the bending strength remain limited [6]. Furthermore, the introduction of natural fiber particles disrupts the homogeneous structure of the plastic, thereby rendering it susceptible to surface defects and increasing its brittleness [6,18,19]. Despite such advances, improving the mechanical properties of WPCs by simply adjusting the fiber content and the length–to–diameter ratio remains challenging [20,21]. Instead, the combination of heterogeneous materials with WPCs to prepare new composites has become an effective method for improving the mechanical properties of these materials. Current research has shown that combining WPCs with high–strength wood via coextrusion processes can substantially improve the mechanical performances of WPCs [6,22]. However, this coextrusion process has extremely high equipment requirements, and there are significant technical difficulties related to its use in continuous preparation. By comparison, hot–pressing processes offer greater maneuverability and lower costs. Liu et al. employed maleic anhydride–grafted polyethylene (MAPE) and maleic anhydride–grafted polypropylene (MAPP) films instead of adhesives to adhere thin wood veneers to the surfaces of WPCs via hot–pressing processes, endowing them with an authentic wood–like appearance without the generation of formaldehyde gas [7,23]. However, owing to the limited thicknesses of thin wood veneers, this method presents challenges in achieving significant improvements in the mechanical properties of WPCs. Similarly, Zhou et al. prepared wood veneered WPCs by increasing the thickness of the wood veneer, thereby confirming the effectiveness of wood veneers in enhancing the mechanical properties and surface aesthetics of WPCs [10].

Under high–temperature conditions, chemical bonding and physical anchoring between a WPC and a wood veneer can be achieved by melting the surface layer of the WWPC and subjecting the combined structure to further pressurization. However, the free energy of WPCs and wood veneer is low [24], and so it is necessary to improve the compatibility and interactions between these two materials to provide a suitable composite [25]. For this purpose, films such as MAPE and MAPP, as mentioned above, are often used to substitute traditional adhesives to improve the interfacial bonding properties and produce environmentally friendly composites [7,10,11,26]. In addition to the above methods, silane coupling agents, such as KH550, can impart wood veneers with a surface polarity, effectively enhancing the interfacial bonding strength and water resistance simultaneously [10,23,27]. Aluminate coupling agents are known to promote compatibility between inorganic particles, natural fibers, and resin matrices [28,29]. Furthermore, treating wood veneers with aluminate coupling agents can reduce their degree of moisture absorption, consequently lowering the likelihood of interfacial damage between the wood veneer and the polymer resin under hydrothermal conditions. Moreover, the use of MAPE, MAPP, silane, and aluminate coupling agents can promote functional group modification to improve the surface wetting mechanism of WPCs, whilst also enhancing their interfacial bonding and mechanical properties [23,26,28,30]. However, few comparative studies of wood–veneered polymer composites treated by those four interface modifiers have been carried out to date.

In the manufacture of WPCs, polyvinyl chloride (PVC) has become the ideal choice to prevent the degradation temperature of lignin in wood flour [18]. PVC exhibits excellent adhesive properties owing to the presence of Cl atoms, and it is also less expensive compared to other thermoplastic resins. However, very few studies have been carried out on adhesive–free wood veneer/wood flour–polyvinyl chloride composites (WWPVCs). Thus, to enhance the interfacial properties between wood veneers and wood flour–polyvinyl chloride composites (WPVCs), we herein report the use of a PVC resin and KH550 silane coupling agent, aluminate coupling agent, MAPP, and MAPE as interface modifiers to obtain a WWPVC with a sandwich structure. Subsequently, the effectiveness of these treatments in improving the interfacial bonding strength between wood veneers and WPVCs is examined. Additionally, interfacial bonding strength, mechanical property, morphological, and infrared spectroscopy analyses were employed to explore practical approaches for improving WPCs’ mechanical properties and surface aesthetics.

2. Materials and Methods

2.1. Materials

A 2 mm thick poplar wood veneer was purchased from Fangzheng County, Harbin, China. The veneer was processed to 100 × 100 × 2 mm at a density of 0.38 g cm⁻³. The silane coupling agent (KH550) was purchased from Crystal Reagent Co., Ltd. Shanghai, China. The aluminate coupling agent (UP–801) was purchased from Youpu Chemical Co., Ltd., Nanjing, China. Maleic anhydride–grafted polypropylene (MAPP; grafting ratio ≈ 1%, melt index = 95 g 10 min⁻¹) and maleic anhydride–grafted polyethylene (MAPE; grafting ratio ≈ 1%, melt index = 1.70 g 10 min⁻¹) were purchased from Rizhisheng Co., Ltd. Nantong, China. PVC (S–700) was purchased from the Qilu Petrochemical Company, Zibo, China.

2.2. Preparation of the WPVCs

According to the quantities listed in

Table 1. Composition of the WPVC (phr).

PVC (wt%)	Wood Flour (wt%)	Calcium Zinc Stabilizer (wt%)	ACR (wt%)	PE Wax (wt%)	Stearic Acid (wt%)	Calcium Stearate (wt%)
100	40	6	4	0.6	0.4	0.3

, PVC resin, wood flour, and the various additives were added to a high–speed mixer and mixed for 10 min. After this, granulation was performed using a screw granulator. A WPVC with a width of 100 mm and a thickness of 4 mm was prepared using a single–screw extruder and sawn into 100 mm × 100 mm specimens for further use.

2.3. Preparation of the WWPVCs Using Various Coupling Agents

To prepare the wood veneer treated with the silane coupling agent, the wood veneer was dried for 24 h in an oven at 105 °C. Silane solutions were prepared by dissolving 1, 3, 5, and 7 wt% of the coupling agent in distilled water (wt% based on the average dry weight of the prepared veneer). Each solution was then sprayed evenly onto a wood veneer surface using a watering can. After allowing them to stand in a well–ventilated fume hood for 24 h, the veneers were dried in an oven at 105 °C for 15 min.

To prepare the wood veneer treated with the aluminate coupling agent, the wood veneer surface was uniformly coated with aluminate coupling agent at 80 °C by a brush. To control the amount of aluminate coating introduced onto the veneer, the weight gain of the veneer was calculated using gradients of 1, 3, and 5 wt% based on the average weight of the veneer.

To prepare the MAPP and MAPE films, the desired weights of MAPP and MAPE particles were placed in a hot–press machine at 180 °C and pre–pressed for 9 min using a 1 mm thick gauge. A rapid pressure relief exhaust was performed 2–3 times to avoid bubble formation during the pre–pressure and pressure processes. MAPP and MAPE films with a thickness of 1 mm were prepared by cooling in a cold–press machine.

As outlined in Figure 1, the WWPVCs were prepared with a sandwich structure. The wood veneer with silane and aluminate treatment on the surface was bonded with WPVCs. MAPP and MAPE films were used as the interlayer of wood veneer and WPVCs.

The assembled samples were placed in a 6 mm thick gauge and pressed using a hot–press machine. Pre–pressing was performed using a flat curing press at 180 °C for 8 min, and subsequently, 10 MPa pressure was applied for 4 min. After hot pressing, the samples were cooled for 8 min in a cold–press machine to yield the desired WWPVCs. The blank control sample (Ctrl), the silane–treated sample (WSP), the aluminate–treated sample (WAP), and the samples using MAPP and MAPE films as the interlayers (WPP and WEP) were also prepared using the above method.

2.4. Methods

Using samples measuring 50 mm in width and length (1000 mm² area), the interfacial bonding strength was tested, as outlined in Figure 2. Eight samples were tested from each group. The bonding strength of each sample (accurate to 0.01 MPa) was calculated as follows for a loading rate of 2 mm s⁻¹:

$$\mathsf{\sigma }\perp =P_{\max }/A$$

(1)

where $\mathsf{\sigma }\perp$ is the bonding strength of the interface (MPa), $P_{\max }$ is the maximum load when the surface of the sample is damaged (N), and A is the bonding area between the test piece and the fixture (1000 mm²).

The wood failure ratio was calculated by determining the percentage of wood fiber tear residue on the shear failure surface relative to the tested area of the sample.

The dipping–peeling strength of each sample was analyzed using the Grade I (100 °C) and Grade II (63 °C) dipping–peeling tests. Each sample measured 75 × 75 × 18 mm, and four samples were tested for each group. The samples were then placed in a thermostatic water bath and subsequently dried in an oven. The peeling lengths of the four sides were measured and recorded, and each specimen was classified according to the criteria outlined in

Table 2. Dipping–peeling strength criteria.

Grade	0	1	2
Peeling length	L = 0	0 < L ≤ 25 mm	L > 25 mm
Characteristic	No peeling	Slight peeling	Severe peeling
Description	Qualified	Qualified	Unqualified

.

The fracture surfaces of the samples after the interfacial bonding strength tests and liquid nitrogen embrittlement fracture were locally magnified and analyzed using scanning electron microscopy (SEM; JSM7500F, JEOLDATUM Shanghai Co., Ltd. Shanghai, China).

Fourier transform infrared (FTIR; Nicolet 6700, Thermo Scientific, USA) spectroscopy was conducted on the WPVC and wood veneer layers before and after testing. A scanning resolution of 4 cm was employed along with a test range of 4000–400 cm⁻¹.

3. Results and Discussion

3.1. Interfacial Bonding Strength

The interfacial bonding strength results for the samples treated with different silane concentrations are presented in

Table 3. Interfacial bonding strengths of the WWPVC samples treated using different concentrations of the silane coupling agent.

Silane Dosage	0 wt%	1 wt%	3 wt%	5 wt%	7 wt%
Interfacial bonding strength (MPa)	0.55	0.88	1.22	0.96	0.86

and Figure 3. As indicated, upon increasing the silane concentration, the interfacial bonding strength of the WWPVC samples initially increased prior to decreasing, with the highest value being recorded with a 3 wt% silane content relative to the average weight of the treated wood veneer. Notably, this was 1.22 MPa and 122% higher than that of the untreated sample (i.e., 0.55 MPa).

A similar trend was observed upon increasing the amount of aluminate coating on the wood veneer surface. More specifically, as shown in

Table 4. Interfacial bonding strengths of the WWPVC samples treated using different concentrations of the aluminate coupling agent.

Aluminate Coating Amount	0 wt%	1 wt%	3 wt%	5 wt%
Interfacial bonding strength (MPa)	0.55	0.58	0.64	0.43

and Figure 4, the highest interfacial bonding strength of 0.64 MPa was reached with an aluminate content of 3 wt%, and this represented a 16.4% enhancement compared to that of the blank control sample (Ctrl) without the aluminate coating.

Based on previous reports, the strengths of the MAPP and MAPE films could be sufficient to prevent a damaged interface from appearing inside the film during the interfacial bonding tests [30,31,32]. With the above considerations in mind, the samples prepared with a silane concentration of 3 wt% and an aluminate dosage of 3 wt% were compared with those prepared using the MAPP and MAPE films. Thus, the interfacial bonding strengths of the samples treated with the different coupling agents are presented in Figure 5, wherein it can be seen that the highest interfacial bonding strength was obtained for the WSP sample (1.22 MPa). The interfacial bonding strengths achieved for the WAP and WPP samples were slightly higher than that of the Ctrl but were not considered improvements compared to the values obtained for the wood veneer and WPVC specimens. However, it should be noted that the interfacial bonding strength of the WEP sample was lower than that of the Ctrl sample, indicating that the MAPE film exhibited a specific inhibitory effect on the interfacial bonding between the wood veneer and the WPVC.

3.2. Wood Failure Ratio

As shown in Figure 6, the largest wood failure ratio was obtained for the WSP sample, and this led to the wood veneer being pulled from the WPVC (>80%; see Figure 6b). After these tests, the amount of wood fiber remaining on the WAP sample was slightly higher than that on the Ctrl sample (Figure 6a,c), indicating that the bonding strength between the wood veneer and the WPVC, combined with the penetration effect of the WPVC on the rough surface of the wood veneer, formed a physical and mechanical mosaic, which could produce a specific force to inhibit peeling of the wood fiber [23,26]. Furthermore, as shown in Figure 6d,e, no wood residue was observed on the surfaces of the WPP or WEP samples, where interface damage mainly occurred at the junction between the two films and the WPVC layer. The absence of wood residue in these test pieces indicates that the bonding strengths between the MAPP and MAPE films and the wood veneer are more significant than those between the MAPP, MAPE, and WPVC films.

3.3. Micromorphology

As shown in Figure 7, it was clear that the surface roughness of the wood was enhanced after silane treatment. The number of wood fibers extracted after the fracture also increased owing to the force. In addition, the WPVC remained attached to the wood veneer surface (Figure 7a), and the WPVC surface contained some residual wood fiber (Figure 7b), leading to an increased surface roughness. In terms of the solid interfacial bonding between the wood veneer treated with silane and the WPVC, the strength of this bonding was attributed to mechanical adhesion between the WPVC and the wood. After silane treatment, polar hydrogen bonds were enriched on the surface of the wood veneer, allowing crosslinking with the WPVC to effectively strengthen the interactions between these materials. As shown in Figure 7c, the surface of the brittle–fractured WSP sample is flat, and there is no apparent collapse at the interface junction.

As previously reported, the aluminate coupling agent can activate organic and inorganic materials to improve their mutual fusion with various organic resins [28,29]. As shown in Figure 8a, many wood fiber filaments were present on the surface of the damaged wood veneer, while the WPVC layer (Figure 8b) exhibited different degrees of compression, with few wood fibers being locally present. In addition, the WAP profile (Figure 8c) was flat after brittle fracture; however, despite this observation, the obtained results suggested that this treatment method did not significantly strengthen the bonding force between the wood veneer and the WPVC (Figure 5 and Figure 8).

Figure 9a,b show that the MAPP and WPVC surfaces were smooth and flat. It can also be observed from the section after brittle fracture (Figure 9c) that the overall area was flat, and there was no clear gap at the bonding interface. Overall, the interface between the MAPP film, the WPVC, and the junction of the wood veneer was smooth.

As shown in Figure 10a,b, the MAPE and WPVC layers of the stripped WEP sample had smooth and flat surfaces, and no apparent surface damage was caused by the applied force. Upon magnification of the MAPE surface, no evident drawing phenomenon was observed. In addition, the MAPE surface was smoother than that of the MAPP sample, indicating that the force generated by the combination of the MAPE film and the WPVC was weaker than that associated with the MAPP film. Furthermore, in Figure 10c, it can be seen that the boundary between the MAPE film and the wood veneer is flat, and the main damage was attributed to brittle fracture. However, the MAPP film exhibited a limited force on the wood veneer, mainly due to its higher fluidity at high temperatures, which allowed it to form more effective mechanical combinations when subjected to compression. However, the section morphology was found to be rough at the junction with the WPVC, and it can be seen from the enlarged view that many pores existed locally owing to the absence of the WPVC.

3.4. Analysis of the Surface Chemical Elements

Figure 11a shows the FTIR spectra of the silane–treated wood veneers. It is well known that wood veneers are rich in active functional groups, such as hydroxyl, ester, and carboxyl groups [23]. After treatment with the silane coupling agent, the peaks at 1742 and 1030 cm⁻¹ were significantly weakened, indicating that the number of carboxyl functional groups decreased, and the hemicellulose present in the wood was partially decomposed. In addition, the peak at 1030 cm⁻¹ was relatively wide and overlapped with the Si−O−Si peak present in the range of 1020–1090 cm⁻¹. A weak peak corresponding to the absorption vibration of Si−C appeared at 862 cm⁻¹, and this was likely caused by the low amount of the silane coupling agent that was employed. Furthermore, it can be seen from the FTIR spectra of the WPVC before and after hot pressing that the peak intensities at 2919, 2850, 1742, and 1200–1750 cm⁻¹ decreased after hot pressing. These peaks were associated with the −CH₂, C=O, and C−O groups, and so these observations suggest that degradation took place in some branched chains of the WPVC after hot pressing at high temperatures.

Upon examination of the FTIR spectra of the wood veneer treated with the aluminate coupling agent (Figure 11b), it is clear that the intensity of the hydroxyl absorption peak decreased (3340 cm⁻¹). This was attributed to a reaction between the alkoxy groups (RO) present in the aluminate and the cellulose hydroxyl groups on the wood surface. In addition, the peak at 1742 cm⁻¹ shifted to 1700 cm⁻¹ after modification, likely because of ester group formation (−COOR). Furthermore, the peaks at 2919 and 2850 cm⁻¹ originating from the stretching and asymmetric CH₂ stretching vibrations increased in intensity due to the alkane chain constituting part of the aluminate coupling agent. These observations clearly indicate that the wood veneer was successfully modified with the aluminate coupling agent. Compared with the infrared spectrum of the original WPVC, the peaks at 2919 and 2850 cm⁻¹, corresponding to the cellulose CH₂ stretching vibrations, increased in intensity after high–temperature hot pressing. In addition, a peak corresponding to the aluminate ester group appeared at 1700 cm⁻¹ after hot pressing, further confirming that the aluminate coupling agent was successfully bonded to the WPVC surface.

As shown in Figure 11c, two clear characteristic absorption peaks corresponding to the maleic anhydride carbonyl groups of the MAPP film can be observed at 1700 and 1800 cm⁻¹. In addition, peaks were observed at 2916, 2850, 1470, and 718 cm⁻¹ corresponding to the CH₂ stretching vibrations, while the peak at 2958 cm⁻¹ was attributed to the CH₃ stretching vibration. The FTIR spectra recorded for the MAPP film and the WPVC before and after hot pressing show that the peaks corresponding to the MAPP film were similar to those of the WPVC, and so it was considered likely that the MAPP peaks were overlapped by those of the WPVC. Upon comparison of the FITR spectra of the WPVC specimen prior to hot pressing, it was clear that no new bonds were formed after hot pressing. However, the intensities of almost all characteristic absorption peaks decreased, possibly owing to functional group degradation on the branch chain after hot pressing at high temperatures.

Moreover, the spectra presented in Figure 11d show peaks at 2916, 2850, 1470, and 718 cm⁻¹, which correspond to the CH₂ stretching vibrations in the MAPE layer. Two clear characteristic absorption peaks corresponding to the maleic anhydride C=O group also appeared in the range of 1700–1800 cm⁻¹, and the C−OR stretching vibration was observed at 1030 cm⁻¹. Interestingly, it was found that after hot pressing, the functional groups of the MAPE film did not change, thereby indicating that the MAPE film did not affect the chemical composition of the WPVC material.

After treatment of the wood veneer with KH550, a new absorption peak appeared at 757 cm⁻¹, and this was attributed to the formation of O−Si−O bonds (Figure 11a) [23]. In addition, the Si−OH formed by the self–condensation of the silane coupling agent reacted with the wood veneer to form Si−O−C under dehydration conditions (Figure 12). As a result, hydrogen bonds could form between the modified veneer and the PVC. Indeed, it has been previously reported that during the hot–pressing process, the silane coupling agent can penetrate the WPVC and form Si−O−C bonds with the wood flour in the wood plastic [23,33]. These factors ultimately improved the interfacial and mechanical properties of the silane–treated samples.

3.5. Dipping–Peeling Strength

Five sets of samples were tested for the Grade I (100 °C) and Grade II (63 °C) dipping –peeling strengths, and the results are presented in Figure 13 and

Table 5. Peeling lengths of the various samples after the dipping–peeling strength test.

Category	Ctrl	WSP	WAP	WPP	WEP
Grade II peeling length (mm)	Complete peeling	0	0	0	12 × 75
Grade I peeling length (mm)	Complete peeling	18 × 75	Complete peeling	23 × 75	Complete peeling

. After the Grade II test, the wood veneer on one side of the blank control group sample completely peeled off the WPVC, while the other side was partially peeled off. Slight peeling occurred on the WEP, with a peeling length of 12 mm. However, there was no peeling phenomenon between the wood veneer and the WPVC for the WSP, WAP, and WPP samples, indicating that the WWPVCs prepared using the silane coupling agent, the aluminate coupling agent, and the MAPE film met the standards of Grade II dipping–peeling strength.

After the Grade I test, the wood veneer and the WPVC of each group of test pieces had peeled off to some extent. More specifically, complete peeling occurred in the Ctrl, WAP, and WEP groups, and the wood veneer on both sides of the Ctrl completely fell off. The WSP and WPP groups produced local peeling, with peeling lengths of 18 and 23 mm, respectively, thereby indicating that these two samples outperformed the others at high temperatures and under damp–heat peeling strengths.

In a high–temperature and high–humidity environment, owing to the hygroscopic expansion of the wood itself and the thermal expansion and cold contraction of the WPVC, the interface between the wood veneer and the WPVC easily produced an interface shear force during the dipping–peeling test, which damaged the interface and led to separation of the two parts. Therefore, when tested at the Grade II dipping–peeling strength, the Ctrl sample exhibited an apparent peeling phenomenon, while none of the treated samples exhibited serious peeling. These observations indicate that the coupling agents significantly enhanced the interfacial properties between the wood veneer and the WPVC.

4. Conclusions

In this study, wood veneer/wood flour–polyvinyl chloride composites (WWPVCs) were prepared using interface modifiers. Based on the use of static mechanics and the characterization of interfacial properties, it was deduced that the samples prepared using a silane coupling agent exhibited superior comprehensive properties compared to those prepared using other modifiers. Compared with the maleic anhydride–grafted polyethylene (MAPE), maleic anhydride–grafted polypropylene (MAPP), and aluminate coupling agents, the silane coupling agent enhanced the interfacial bonding properties between the wood veneer and the wood flour–polyvinyl chloride composite (WPVC) through the creation of new chemical bonds. The interfacial bonding strength of the resulting sample reached 1.22 MPa, which was 122% higher than that of the control sample (without any modifier). In addition, the wood failure ratio of the sample reached 80%, which was higher than those recorded for the specimens based on other interface modifiers. Moreover, no peeling occurred for this sample after the Grade II dipping–peeling strength test, although a short peeling length was observed in the Grade I dipping–peeling strength test. It was also found that the silane–treated material exhibited good moisture and heat–resistance properties. Visualization of the specimens after scanning electron microscopy showed that the wood veneer and the WPVC demonstrated good adhesion to one another when the silane coupling agent was employed. The resulting material surface was rough, a large number of wood fibers were removed from the wood veneer layer, and some wood fibers remained on the WPVC layer. The silane coupling agent appeared to operate efficiently as a solvent modifier, and notably, it is free from formaldehyde and other harmful gases, thereby indicating its importance in the preparation of environmentally friendly wood–plastic composite products. Further research into the creep response and mechanical properties at higher and lower temperatures would be desirable in the future to fully reveal the properties of wood–veneered polymer composites prepared via silane treatment.