limited by feedstock variability. This study provides a controlled comparison of neat recycled PVC and WPC (PVC +

20 wt.% wood flour) processed under identical extrusion and compression-molding conditions. Tensile, flexural and

hardness tests were conducted according to ASTM standards, and results are reported as mean ± standard deviation (n

feedstock variability and identifies the need for future microstructural characterization to confirm the hypothesized

deformation and failure mechanisms.

Keywords: wood–plastic composite, recycled PVC, tensile tests, flexural tests, hardness, ASTM standards,

mechanical properties, sustainability.

(*) Corresponding author.

Among commonly recycled thermoplastics, polyvinyl chloride (PVC) stands out due to its extensive use in

construction, packaging, and consumer goods. PVC exhibits desirable characteristics such as flame retardancy,

corrosion resistance, and dimensional stability. However, its recycling is complicated by the presence of additives like

plasticizers, stabilizers, and residual contaminants that can hinder reprocessing and reduce mechanical integrity [7],

[8]. Still, the abundance of post-consumer PVC waste, particularly from pipes, cables, and siding, offers a valuable

feedstock for secondary applications if properly reformulated [9].

[11], [12].

WPCs are increasingly used in decking, fencing, automotive interiors, and furniture [13]. However, their mechanical

performance is influenced by many factors, including wood particle size and morphology, polymer–filler ratio,

processing conditions (like mixing methods and temperature profiles), and interfacial adhesion [10], [14], [15].

Generally, adding wood flour increases composite stiffness and hardness but can impact ductility and strength

depending on the specific formulation and interface quality. This performance balance is often attributed to the inherent

incompatibility between hydrophobic polymer matrices (like PVC) and hydrophilic cellulosic fillers, potentially

leading to stress concentrations and microvoids at the interface [16], [17], [18]. The quality of the recycled matrix itself

can also influence final composite properties [8], [19].

Despite numerous studies on WPCs (often based on polyolefins) and recycled PVC separately [10], [19], [25], few

have offered a systematic mechanical comparison between recycled PVC and its corresponding WPC variant under

identical processing and testing protocols. This study aims to address this gap by presenting a controlled, comparative

investigation of key mechanical properties – specifically tensile, flexural, and Shore D hardness of recycled PVC and

its 20% wood-filled composite under consistent, ambient conditions.

were precisely laser cut according to ASTM D638 Type I (tensile), ASTM D790 (flexural), and ASTM D2240

(hardness) dimensions [26], [27], [28].

maintained at 23 ± 2°C and 50 ± 5% Relative Humidity (RH), logged using an environmental chamber compliant with

ISO 291 [31]. For each material condition (PVC and WPC), five tensile specimens (n = 5), five flexural specimens (n

= 5), and five hardness specimens (n = 5) were tested in accordance with the respective ASTM standards. All specimens

Tensile tests: Performed according to ASTM D638 (Type I specimens) using a universal testing machine at a crosshead

and elongation at break were determined.

Flexural tests: Conducted according to ASTM D790 using a three-point bending setup [27]. The support span-to-depth

ratio was maintained at 16:1, and the crosshead speed was 2 mm/min [18]. Flexural modulus and flexural strength were

calculated.

Hardness tests: Measured according to ASTM D2240 using a Shore D durometer mounted on an operating stand to

ensure perpendicularity and consistent load application [28]. Measurements were taken after a dwell time of 15 seconds.

Figure 1. The stress vs strain curve of PVC is illustrated with a solid blue line whereas that of WPC is illustrated with

a dashed red line. The tensile stress–strain curves in Figure 1 show a typical elastic region followed by a short yield-

like transition without a well-defined plateau for both materials, indicating semi-ductile behavior. Neither PVC nor

WPC exhibited classical strain hardening; instead, both curves rose monotonically until reaching their respective

maximum stresses, followed by an abrupt load drop, characteristic of polymer composites with limited plastic

deformation. The PVC curve shows a smoother transition to failure, while the WPC curve displays a slightly steeper

post-yield slope, consistent with modest reinforcement from wood flour.

The tensile properties are reported as mean ± standard deviation for n = 5 specimens per material. PVC exhibited an

elastic modulus of 395 ± 32 MPa. Its ultimate tensile strength was measured at 8.2 ± 0.85 MPa, with an elongation at

break of 6.2 ± 0.13%.

The incorporation of 20% wood flour into PVC to create the WPC resulted in notable changes. The elastic modulus

after the PVC matrix yields, enhancing the composite's overall strength before fracture. The effect on ductility requires

careful consideration of failure modes.

illustrated in Figure 2. The stress vs strain curve of PVC is illustrated with a solid blue line whereas that of WPC is

illustrated with a dashed red line. The flexural stress–strain curves in Figure 2 show a linear elastic region up to

approximately 2–2.5% strain for both materials, after which the curves begin to deviate due to matrix microcracking

and the onset of tensile-side yielding typical of thermoplastic composites under bending. Neither material exhibited a

distinct yield plateau; instead, the curves increased steadily to a peak flexural stress before showing a sharp drop

associated with catastrophic failure. The WPC curve demonstrates slightly higher peak stress and marginally improved

Flexural properties (n = 5 per material) are presented as mean ± standard deviation. Both PVC and WPC showed similar

The strain at which failure or substantial load drop occurred in bending was approximately 0.035 ± 0.009 for PVC and

slightly higher, around 0.038 ± 0.011, for WPC. This suggests the WPC could withstand slightly more bending

deformation before failure compared to PVC under these test conditions.

The tensile and flexural test results indicate that while the incorporation of 20% wood flour does not alter the stiffness

(Young's/Flexural Modulus) compared to PVC, it enhances both the tensile and flexural strength. This improvement is

the quality of interfacial adhesion between the relatively hydrophobic PVC matrix and the hydrophilic wood filler [10],

unstressed. As a consequence, the measured stiffness is governed primarily by the behavior of the surface layers, which

respond more rigidly than the bulk polymer under uniform tensile loading. Additionally, bending constrains lateral

contraction more strongly than tension, reducing Poisson expansion and further increasing the apparent modulus. From

a microstructural standpoint, the wood flour present in the WPC improves surface stiffness under bending because

fibers located near outer surfaces engage more effectively in load transfer. In contrast, tensile testing probes the entire

cross-section uniformly, including regions containing micro-voids, imperfect filler dispersion or weak polymer–filler

adhesion, which collectively reduce the effective tensile modulus.

of the wood flour also play a significant role in determining the reinforcing efficiency [14], [15]. Although these tests

were conducted in a controlled dry state, the inherent hydrophilicity of wood fillers could introduce variability or affect

long-term performance under ambient humidity due to moisture sorption at the interface, potentially degrading both

the filler and the interface itself [32], [33], [34].

The slightly higher strain at failure observed in bending for the WPC, compared to PVC, is not contradictory to the

tensile ductility trends. This difference arises because tensile and flexural failures are governed by different

mechanisms. In bending, failure initiates in the highly stressed outer surface while the neutral axis remains relatively

unstressed, allowing limited redistribution of strain before catastrophic fracture. Local microcrack blunting or fiber-

bridging effects in the WPC can delay surface crack propagation, permitting a slightly greater strain before failure.

When interpreting the magnitude of the observed strength improvements, approximately 12% in tensile strength and

8% in flexural strength, it is important to consider their relevance within the context of typical design safety factors and

target application domains. For many structural or semi-structural applications involving PVC and WPCs such as

decking boards, facade components, low-load automotive interior panels, safety factors typically range from 2 to 4.

Within this framework, strength increments of the order reported here may be viewed as modest in absolute terms and,

in some cases, comparable to batch-to-batch variation commonly observed in recycled polymer composites.

Nonetheless, these improvements remain meaningful for several reasons. First, the increases in strength occurred

without compromising stiffness or hardness and without the use of coupling agents, indicating that even unmodified

wood flour can contribute positively to load-bearing capacity. Second, for high-volume applications where material

cost and environmental impact are key considerations, incremental gains in strength can translate to reductions in

It is important to emphasize that the discussion regarding micro-void formation, interfacial debonding, and potential

This study provides comparative mechanical benchmarks that are relevant for industrial quality control and materials

selection, particularly in applications such as automotive components, façade panels, and construction elements where

recycled or resource-efficient materials are increasingly considered [13], [19]. Rather than making explicit

environmental claims, the present work should be viewed as contributing to material substitution strategies that are

broadly consistent with circular economy principles and supportive of Sustainable Development Goals (SDGs) 9 and

12, which emphasize responsible production and sustainable infrastructure development [9], [35]. Achieving enhanced

chloride (PVC) and a wood–plastic composite (WPC) containing 20 wt.% wood flour, processed via extrusion and

compression molding. The results demonstrated that incorporating wood flour achieved performance enhancements

consistent with a reinforcing effect:

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