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Abstract

This study aims to enhance the electrical, mechanical, and thermal properties of a novel PLA/EPDM/TiO₂/CNT nanocomposite fabricated by selective laser sintering (SLS). For this purpose, the response surface method (RSM) was employed to examine the effect of the process parameters such as laser power, scan rate, CNTs, and TiO₂ nanoparticles on the melting temperature, crystallization temperature, electrical conductivity, tensile stress, and impact resistance of the nanocomposite. Thermal characterization was conducted via TGA and DSC, whereas electrical and microstructural properties were assessed using a four-probe test and SEM imaging. The results indicate that incorporating CNT and TiO₂ nanoparticles significantly enhanced the material’s thermal stability and electrical conductivity. A homogeneous distribution of nanoparticles within the microstructure was achieved with a 2 wt% concentration of CNT and TiO₂. Furthermore, minimal porosity and effective solidification were obtained at a laser power of 18 W and a scan rate of 2500 mm/s. The optimization process using RSM and desirability function analysis determined that the optimal parameters for simultaneously improving tensile stress and impact resistance were: 1.8 wt% CNT, 1.9 wt% TiO₂, a laser power of 16.5 W, and a scan rate of 2624 mm/s.

Keywords

Selective laser sintering (SLS)thermal stability tensile stress impact resistance

Introduction

The application of polymer materials continues to expand across diverse industries such as aerospace, automotive, military, and chemical, primarily due to their exceptional strength-to-weight ratio.^1,2 Among these, polylactic acid (PLA) has recently gained significant attention for applications in various industries, including aerospace, automotive, packaging, medical, etc., due to its high strength, biocompatibility, biodegradability, low energy loss, and resistance to water and fat penetration.^3–5 Although PLA has many benefits, it also has drawbacks, including poor heat resistance, low impact strength, gas permeability, a slow rate of degradation, hydrophobicity, and chemical neutrality.^6,7 To address the issue of impact resistance, researchers have tried blending PLA with rubbers like Ethylene Propylene Diene Monomer (EPDM), High-density polyethylene (HDPE), Polyurethane (PU), etc..^8–12 Additionally, the thermal, electrical, and mechanical performance of PLA is often enhanced through the common use of different nano-fillers.^2,13,14 Carbon nanotubes (CNTs) are among the most popular and extensively studied nano-fillers because they possess remarkable properties such as a large surface area, superb electrical and thermal conductivity, flexibility, chemical stability, and biocompatibility.^15–17 Multiple studies have demonstrated that incorporating CNTs into the PLA matrix considerably improved the thermal, mechanical, rheological, and electrical properties of the resulting composite.^18–21 However, research indicates that while the addition of CNTs enhances certain mechanical properties of PLA composites, it can also diminish others, including impact strength,^22,23 tensile strength,^24,25 and elastic modulus.²⁶ Consequently, the concept of incorporating two nano-fillers into polymer composites has been put forward to improve mechanical properties concurrently. Batakliev et al.²⁷ reported that the addition of both graphene (GPN) and CNTs to PLA led to better hardness and elastic modulus properties than composites loaded with a single CNTs. The stiffness and elastic modulus of PLA were enhanced by Khammassi et al.²⁸ via the addition of silver and GPN nanoparticles. The tensile and flexural strength of a PLA/epoxy composite were also improved by Nimbagal et al.²⁹ through the incorporation of 0.2 wt% GPN and 0.3 wt% CNTs. Kumar et al.³⁰ demonstrated that adding 1.5 wt% CNTs and 0.5 wt% GPN to PLA simultaneously improved its tensile strength, elastic modulus, yield strength, and impact strength. Titanium dioxide (TiO₂) nanoparticles are another nano-filler known to enhance the mechanical, electrical, and thermal properties of polymer nanocomposites. Kumar et al.³¹ demonstrated that the incorporation of TiO₂ nanoparticles enhanced the flexural, wear, and morphological properties of PLA. In a separate study, Leena et al.¹⁴ observed that a hybrid filler system of 1 wt% GPN and 0.5 wt% TiO₂ simultaneously increased tensile strength, critical stress intensity factor, and tensile modulus. Alrawi et al.³² demonstrated that for PLA composites, a 4 wt% clay content optimizes tensile properties, while a 1 wt% TiO₂ content improves the elastic modulus. In another study, Triamnak et al.³³ observed that the addition of TiO₂ nanoparticles into PLA improved the Young’s modulus but decreased tensile strength and elongation at break. However, Sathish et al.³⁴ reported that the tensile strength, thermal stability and biodegradability of PLA improved by addition of 1 wt% TiO₂ and 1 wt% graphene oxide. The positive effect of TiO₂ on the performance of PLA has also been reported in other references 35–38. Building on previous studies which demonstrate that hybrid filler systems improve the thermal, electrical and mechanical performance of polymer composites, this work utilizes a combination of carbon nanotubes (CNT) and titanium dioxide (TiO₂).

Additive manufacturing of polymer-based nanocomposites is gaining increasing attention. Several studies highlight this trend, including the production of PLA/CNT composites via integrated 3D printing and laser cutting,³⁹ the 3D printing of PLA/hydroxyapatite/CNT composites,⁴⁰ and the use of 3D printing to improve the performance of PLA/CNT⁴¹ and GPN/PLA/CNT⁴² nanocomposites. Among additive techniques, Selective Laser Sintering (SLS) is particularly favored for its high production speed and reduced material waste. Within this field, Selective Laser Sintering (SLS) is seeing growing adoption due to advantages such as high production speed, the capability to fabricate parts with complex geometries and robust mechanical properties, minimal waste generation, and no need for molds and accessories. Consequently, the use of the SLS process has expanded into various high-tech industries, such as automotive, aerospace, military, and medical.^43–49 Building on this trend, researchers have employed SLS to develop advanced composites for enhanced properties. For instance, Li et al.⁵⁰ fabricated CaSiO₃/PLA composites to improve compressive strength and modulus, while Xu et al.⁵¹ produced polycaprolactone/polylactic acid/nano hydroxyapatite (PCL/PLA/nHA) ternary composites to investigate their mechanical properties, surface morphology, wettability, and cytocompatibility. Furthermore, Li et al.⁵² used SLS to enhance the mechanical properties of a PLA/poly(butylene adipate-co-terephthalate) composite, while in a separate study, Li et al.⁵³ investigated the mechanical properties and degradation of a PLA/Mg composite. Similarly, Liu et al.⁵⁴ studied the effect of the SLS process on PLA nanoparticles to improve part stability and performance. The versatility of SLS is highlighted by its use in diverse material systems. For specialized functional applications, Ding et al.⁵⁵ fabricated polyether-block-amide elastomer/carbon nanotube (TPAE/CNT) composites, targeting strain sensing and electro-induced shape memory capabilities. Conversely, Kryszak et al.⁵⁶ took a fundamental approach, analyzing the effect of SLS process parameters on enhancing the mechanical properties and controlling the degradation rate of polylactic acid (PLA). Further studies highlight unique material applications for SLS process. Odin et al.⁵⁷ used recycled nylon powder from SLS waste to create parts reinforced with Mg particles. Elsewhere, Idriss et al.⁵⁸ used SLS to create a composite from peanut husk powder (PHP) and polyether sulfone (PES), which showed improved density, impact strength, tensile strength, and bending strength. Further advancing SLS methodologies, Demina et al.⁵⁹ utilized a specialized variant of the process to fabricate polylactide micro-particles stabilized by a chitosan graft-copolymer for scaffolds. Moving beyond fabrication, Shuai et al.⁶⁰ employed thermal post-processing to enhance the surface smoothness of SLS -produced PLA-HA bone scaffolds. In a forward-looking approach, Ulkier⁶¹ integrated artificial intelligence to optimize the thermomechanical properties of PLA/metal composites manufactured via SLS.

Recent research indicates a growing trend of using additive manufacturing to produce polymer nanocomposites, expanding their industrial applications. Concurrently, studies on multi-component nanocomposites for enhanced properties are rapidly increasing. To address these areas, this study fabricates a novel quaternary PLA/EPDM/TiO₂/CNT nanocomposite via the SLS process to simultaneously improve its mechanical, thermal, and electrical properties. The SLS technique was employed for this study because of its distinct advantages, including the capacity to produce complex components, rapid production rates, compatibility with a wide range of materials, and minimal material waste.^44–47 Furthermore, the PLA/EPDM/TiO₂/CNT nanocomposite leverages a synergistic filler system, where the CNT and TiO₂ nanoparticles serve as a reinforcing agent to improve mechanical strength, electrical conductivity and thermal stability,^{14,18–21,31–38} while the EPDM elastomer contributes fracture toughness and ductility.^8–12 The optimization of the SLS process parameters to attain the target nanocomposite characteristics was conducted by employing the response surface methodology (RSM) coupled with the desirability function approach. Subsequently, the mechanical, thermal, and electrical properties of the fabricated nanocomposite were evaluated through characterization techniques including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and four-point probe electrical testing.

Materials and methods

Raw materials

The polylactic acid (PLA) powder used in this study was PLA-3052D, supplied by Plastika Kritis S.A. in Heraklion, Crete, Greece. This grade possesses a molecular weight of 116,000 g/mol and a melt flow index of 14 g/10 min, as measured by the ASTM D1238 standard. The ethylene-propylene-diene monomer (EPDM) used was a commercial grade (KEP270) from Korea Kumho Polychem Company. This elastomer has a reported density of 0.86 g/cm³ and a composition of 64 wt% ethylene and 8.6 wt% ethylidene norbornene (ENB). Carbon nanotubes (CNTs) and titanium dioxide (TiO₂) nanoparticles were both supplied by INP Corporation. The CNTs had an average length of 1.5 μm, a diameter of 9.5 nm, and a specific surface area of 250-300 m²/g. The TiO₂ nanoparticles had a density of 4.23 g/cm³ and an average particle size of 20 nm.

Selective laser sintering

Specimens were fabricated via a Selective Laser Sintering (SLS) system (Model EOS P395, Germany). Before processing, CNT and TiO₂ nanoparticles were blended with PLA and EPDM matrix powders using a mechanical mixer. The amount of EPDM in the system was 10 wt%. Maleic anhydride (MA-g) was used as a compatibilizer in PLA/EPDM blends. The mixing process was performed in a cylindrical blender for 70 minutes at 90 rpm to achieve a uniform mixture. The SLS process was then carried out using a CO₂ laser (beam diameter: 250 μm) under varying laser power and scan rate parameters. A scan spacing of 125 μm, a layer thickness of 200 μm, and a bed temperature of 80°C were maintained throughout the building process. To identify the optimum bed temperature, a two-step process was employed. The temperature was initially increased from 40°C in 10°C intervals until agglomeration or hardening of the powder cake was observed. Subsequently, the temperature was reduced in 2°C steps to re-establish a uniform, non-caking powder bed. Preheating near the sintering temperature (145°C) is critical to minimize temperature gradients.

Experimental design

To model the influence of key parameters on the mechanical properties, a Central-Composite Design (CCD) in Response Surface Methodology (RSM) was employed. Input variables consisted of laser power (P), scan rate (s), CNT content, and TiO₂ content, while the output responses were tensile stress and impact resistance. The statistical software Minitab® 17 was used for both generating the experimental design matrix and performing the subsequent data analysis. The experimental framework utilized a Central-Composite Design (CCD) with an α coefficient of 0.5, resulting in five distinct levels for each process parameter, as detailed in Table 1. A total of 27 experiments were conducted according to this design matrix, incorporating three center points to assess experimental variance. The results of these experiments are presented in Table 2. To ensure statistical reliability, each experiment was replicated three times, and the average values were recorded for analysis.

Table 1.

Considered levels for each input parameter.

Parameters	Levels
Parameters	Low (−1)	Middle (−0.5)	Middle (0)	Middle (+0.5)	High (+1)
Laser power (W)	12	13.5	15	16.5	18
Scan rate (mm/s)	2200	2350	2500	2650	2800
TiO₂ content (wt%)	0	1	2	3	4
CNT content (wt%)	0	1	2	3	4

Table 2.

Results of tensile stress and impact resistance measurement based on RSM design.

Run	Laser power (W)	Scan rate (mm/s)	CNT (wt%)	TiO₂ (wt%)	Tensile stress (MPa)	Impact resistance (kJ/m²)	Tensile modulus (MPa)	Strain-at-break (%)	Density (g/cm³)	Porosity (%)
1	12.0	2200	0	0	40.4 ± 2.3	15.4 ± 1.1	2485 ± 12.3	2.56 ± 0.4	1.195 ± 0.02	18.2 ± 1.7
2	18.0	2200	0	0	44.5 ± 3.1	16.5 ± 1.9	2757 ± 14.8	3.07 ± 0.6	1.214 ± 0.01	15.8 ± 1.4
3	12.0	2800	0	0	32.9 ± 2.8	15.8 ± 1.5	2016 ± 15.4	2.54 ± 0.3	1.093 ± 0.01	23.4 ± 1.5
4	18.0	2800	0	0	45.2 ± 3.6	19.9 ± 1.7	2809 ± 21.3	3.32 ± 0.8	1.206 ± 0.04	15.1 ± 1.4
5	12.0	2200	4	0	41.6 ± 3.1	14.1 ± 1.2	2561 ± 13.9	2.35 ± 0.4	1.180 ± 0.03	17.3 ± 1.2
6	18.0	2200	4	0	46.5 ± 3.9	15.0 ± 1.7	2874 ± 12.6	2.88 ± 0.5	1.254 ± 0.05	14.9 ± 1.7
7	12.0	2800	4	0	36.1 ± 2.5	15.3 ± 1.6	2247 ± 18.7	2.51 ± 0.5	1.118 ± 0.02	21.8 ± 1.5
8	18.0	2800	4	0	51.6 ± 4.2	17.9 ± 1.7	3190 ± 16.5	3.04 ± 0.3	1.298 ± 0.05	11.9 ± 1.2
9	12.0	2200	0	4	42.8 ± 3.4	14.8 ± 2.2	2615 ± 15.4	2.26 ± 0.2	1.204 ± 0.03	16.2 ± 2.1
10	18.0	2200	0	4	47.2 ± 3.8	15.9 ± 1.5	2892 ± 16.3	3.21 ± 0.4	1.237 ± 0.03	14.5 ± 1.5
11	12.0	2800	0	4	35.0 ± 2.6	15.4 ± 0.8	2151 ± 22.6	2.57 ± 0.7	1.106 ± 0.02	22.4 ± 1.3
12	18.0	2800	0	4	52.3 ± 3.7	18.7 ± 2.1	3134 ± 24.3	2.82 ± 0.6	1.311 ± 0.04	11.6 ± 1.1
13	12.0	2200	4	4	41.8 ± 3.2	12.8 ± 1.4	2553 ± 17.9	2.08 ± 0.3	1.210 ± 0.03	17.1 ± 1.4
14	18.0	2200	4	4	48.3 ± 3.5	13.4 ± 0.9	2897 ± 16.7	2.24 ± 0.7	1.246 ± 0.05	13.8 ± 0.9
15	12.0	2800	4	4	36.5 ± 2.7	12.1 ± 1.2	2450 ± 14.5	2.10 ± 0.5	1.114 ± 0.03	22.1 ± 1.2
16	18.0	2800	4	4	49.3 ± 4.1	15.2 ± 2.4	3248 ± 13.9	2.55 ± 0.4	1.259 ± 0.02	13.3 ± 2.4
17	13.5	2500	2	2	60.4 ± 4.5	20.4 ± 2.3	3636 ± 11.4	3.58 ± 0.6	1.271 ± 0.04	9.4 ± 1.3
18	16.5	2500	2	2	65.2 ± 4.3	21.7 ± 2.7	4005 ± 16.1	3.72 ± 0.3	1.293 ± 0.04	8.3 ± 1.7
19	15.0	2350	2	2	61.0 ± 3.8	22.2 ± 2.3	3673 ± 19.7	3.80 ± 0.4	1.278 ± 0.05	9.2 ± 1.3
20	15.0	2650	2	2	62.3 ± 4.9	22.1 ± 2.6	3954 ± 18.2	3.23 ± 0.7	1.280 ± 0.04	9.0 ± 1.6
21	15.0	2500	1	2	58.6 ± 4.4	22.6 ± 2.3	3724 ± 13.6	3.12 ± 0.8	1.264 ± 0.04	10.3 ± 2.3
22	15.0	2500	3	2	59.3 ± 4.3	21.0 ± 2.1	3628 ± 15.4	3.30 ± 0.5	1.266 ± 0.05	9.9 ± 2.1
23	15.0	2500	2	1	60.9 ± 3.2	21.7 ± 1.8	3760 ± 16.3	3.36 ± 0.7	1.263 ± 0.04	9.3 ± 1.7
24	15.0	2500	2	3	61.7 ± 3.8	21.6 ± 1.8	3416 ± 12.9	3.61 ± 0.2	1.267 ± 0.05	8.9 ± 1.7
25	15.0	2500	2	2	64.4 ± 3.4	23.2 ± 1.5	3881 ± 18.6	4.06 ± 0.7	1.282 ± 0.03	8.6 ± 1.5
26	15.0	2500	2	2	63.6 ± 4.2	23.4 ± 2.5	3834 ± 17.4	3.91 ± 0.8	1.285 ± 0.04	8.7 ± 1.1
27	15.0	2500	2	2	64.0 ± 4.5	23.1 ± 2.6	3859 ± 16.6	3.98 ± 0.5	1.286 ± 0.05	8.6 ± 1.4

The operating parameters for the process were established from existing literature^50–61 and preliminary feasibility tests. The selected values, specifically a laser power of 12–18 W and a scan rate of 2200–2800 mm/s at a constant scan spacing (125 μm) and layer thickness (200 μm), yielded an energy density between 0.17 and 0.33 J/mm³. The results of the initial feasibility tests demonstrated that deviations from this range were problematic: lower energy densities resulted in insufficient melting and poor densification, whereas higher energies caused thermal degradation of the material.

The density of the samples was measured via the Archimedes principle, employing deionized water and an XS204 analytical balance (Mettler Toledo) fitted with an XPR/XSR density kit. Measurements were conducted at a water temperature of about 22.5°C, using a reference water density of 0.99,768 g/cm³ for calculations. Moreover, the porosity percentage was measured by analyzing SEM images in ImageJ software.

Mechanical properties measurement

SLS process was employed to manufacture specimens for tensile and impact testing. The geometry of the tensile specimens adhered to the ASTM D-638 standard. Tensile tests were conducted using a Zwick/Roell-Z100 universal testing machine, applying a constant cross-head displacement rate of 0.08 mm/s. The stress-strain curves for some of samples were shown in Figure 1. Furthermore, notched Izod impact testing was performed in accordance with the ASTM D-256 standard. The dimensions of a standard specimen for ASTM D-256 are 63.5 × 12.7 × 3.2 mm.

Figure 1.

Stress-strain curves for experimental runs of 1 to 12.

Thermal properties measurement

The melting (T_m) and crystallization (T_c) temperatures of the fabricated samples were determined using differential scanning calorimetry (DSC) analysis. Measurements were performed on a Netzsch 200 F3 Maia instrument using a heating and cooling rate of 10°C/min in a nitrogen environment. The test was performed between 20 and 200°C, by applying a heat-cool-heat cycle. The degree of crystallinity (X_c) was subsequently determined from the thermal data according to equation (1).

X_{c} = (\frac{{Δ H}_{m} - {Δ H}_{c}}{{Δ H}_{0} \times W_{p}}) \times 100 %

(1)In this equation,

{Δ H}_{m}

is the melting enthalpy,

{Δ H}_{c}

is the crystallization enthalpy, W_p is the weight fraction of PLA in the composite, and

{Δ H}_{0}

is the melting enthalpy for 100% crystalline PLA (93 J/g).

Electrical properties measurement

A four-point probe electrical conductivity meter (Suragus, Germany) was employed to measure the electrical resistance of the fabricated samples under ambient conditions (25°C, 55% RH). Electrical resistance (R) was converted to electrical resistivity (ρ) using the equation ρ = R/k = V/(Ik), where k is a geometrical factor determined by the probe spacing.⁶² In this equation, V is the measured potential difference and I is the circuit current. To ensure result accuracy, the electrical resistivity (ρ) was calculated from the measured resistance (R) using the standard formula ρ = RA/L, where A is the cross-sectional area and L is the sample thickness, following the method in 63. To ensure electrical continuity, an adhesive hydrogel with a volume resistivity of approximately 10 Ω.m was placed between the probe and the specimen.

Microstructure examination

Sample microstructure was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) on a VEGA-TESCAN-XMU instrument. Prior to imaging, the specimens were prepared by cryofracturing in liquid nitrogen to expose a clean fracture surface. To ensure electrical conductivity and prevent charging, the fractured surfaces were sputter-coated with a gold layer employing an Agar Scientific B7340 system (United Kingdom).

Results and discussion

Thermal analysis

Differential Scanning Calorimetry (DSC) was employed to investigate the thermal characteristics of the PLA/EPDM/TiO₂/CNT nanocomposite. The resulting DSC thermogram is displayed in Figure 2. The derived data including crystallization temperature, melting temperature, and degree of crystallinity are compiled in Table 3. The DSC thermogram in Figure 2 reveals a single endothermic melting peak at 168.1°C for PLA, which indicates an α-crystalline structure. This unimodal peak that indicates the formation of exclusively stable crystals via homogeneous nucleation during cold crystallization,⁵⁹ is also observed in the PLA/EPDM/TiO₂/CNT nanocomposite. The persistence of a single peak in the nanocomposite is attributed to the role of CNT and TiO₂ nanoparticles in facilitating the formation of PLA crystals with uniform thickness.⁶⁴

Figure 2.

Results of DSC analysis for PLA/EPDM/TiO₂/CNT at different TiO₂/CNT contents.

Table 3.

Thermal properties of PLA/EPDM/TiO₂/CNT nanocomposites obtained by DSC test.

Thermal properties	PLA/EPDM +0 wt% CNT +0 wt% TiO₂	PLA/EPDM +2 wt% CNT +2 wt% TiO₂	PLA/EPDM +4 wt% CNT +4 wt% TiO₂
Melting temperature (°C)	168.1	170.8	174.1
Crystallization temperature (°C)	127.8	132.3	135.4
Crystallinity (%)	38.4	41.6	45.2

Data presented in Table 3 demonstrate that the incorporation of CNT and TiO₂ nanoparticles into PLA enhances the melting and crystallization temperatures of the resulting PLA/EPDM/TiO₂/CNT nanocomposite. This thermal enhancement is attributed to two primary factors: the nucleation effect of the nanoparticles, which leads to smaller and more stable crystal nuclei,⁶⁴ and their partial absorption of heat. The shift in melting temperatures signifies improved thermal stability without affecting PLA’s molecular weight, confirming the efficacy of CNT and TiO₂ as nucleating agents. This role is further evidenced by a measured increase in the material’s percentage crystallinity.

The thermal properties of the PLA/EPDM/TiO₂/CNT nanocomposite were further investigated using thermogravimetric analysis (TGA) and difference thermogravimetry (DTG) from 0 to 600°C (Figure 3). The results demonstrate that adding CNT and TiO₂ nanoparticles enhanced the thermal stability of PLA. Specifically, the onset decomposition temperature increased from 324°C for neat PLA to 363°C for the nanocomposite. This improvement is attributed to nanoparticles restricting polymer chain mobility and creating a barrier effect. This barrier impedes the diffusion of volatile degradation products by prolonging their escape path, thereby increasing the decomposition temperature.²⁴

Figure 3.

Effect of TiO₂ and CNT contents on (a) TGA and (b) DTG results.

Thermal behavior of PLA/EPDM/TiO₂/CNT nanocomposite was characterized by its degradation temperatures at 10%, 50%, and 90% mass loss, as shown in Table 4. It can be deduced from Table 4 that the increase of CNT and TiO₂ content improved PLA’s thermal stability. This enhancement occurs as the nanoparticles inhibit the dominant degradation pathway: intramolecular transesterification within the PLA polymer chains. Moreover, the residue mass of the PLA nanocomposites was found to be close to the added filler content due to the fact that the fillers do not fully decompose until 600°C.

Table 4.

Weight loss temperature at 10, 50 and 90 %, and residual mass at 600°C.

Temperature	PLA/EPDM +0 wt% CNT +0 wt% TiO₂	PLA/EPDM +2 wt% CNT +2 wt% TiO₂	PLA/EPDM +4 wt% CNT +4 wt% TiO₂
T₁₀ (°C)	376 ± 4	398 ± 9	423 ± 12
T₅₀ (°C)	418 ± 6	446 ± 12	462 ± 11
T₉₀ (°C)	471 ± 7	489 ± 8	507 ± 14
Residual mass at 600°C	0.9 ± 0.03	1.6 ± 0.04	2.8 ± 0.06

Microstructural evolutions

An analysis of the sintered parts’ microstructure was conducted to evaluate the distribution of nanoparticles in the PLA/EPDM/TiO₂/CNT nanocomposite and to determine the quality of the manufacturing process. The fracture surfaces of tensile specimens with different CNT and TiO₂ loadings are presented in Figure 4. As shown in Figure 4(a), the fracture surface of pure PLA exhibits a smooth and uniform microstructure. In contrast, Figure 4(b) demonstrates that with a 2 wt% loading of CNT and TiO₂, the nanoparticles are well-dispersed throughout the PLA/EPDM/TiO₂/CNT nanocomposite. This effective dispersion strengthened the interfacial interaction between the nanoparticles and the PLA matrix, which resulted in enhanced mechanical properties of the nanocomposite. A high interfacial surface area, resulting from the small size of the CNT and TiO₂ nanoparticles, enables effective stress transfer from the PLA matrix to the reinforcing nanoparticles, thereby increasing the nanocomposite’s strength.^65,66 At higher loadings of 4 wt%, however, nanoparticle agglomeration was observed (Figure 4(c)). These aggregates cause inhomogeneous dispersion, which acts as a defect site and is detrimental to the mechanical performance of the nanocomposite.

Figure 4.

Fracture surface of nanocomposite for (a) CNT = 0 wt%, TiO₂ = 0 wt%, (b) CNT = 2 wt%, TiO₂ = 2 wt%, (c) CNT = 4 wt%, TiO₂ = 4 wt%. Laser power and scan rate are at middle levels.

The EDX analysis in Figure 4 reveals the elemental composition of the nanocomposites. The base PLA/EPDM material is comprised of carbon and oxygen (Figure 4(a)). With the incorporation of CNT and TiO₂, titanium is also detected (Figure 4(b)). The uniform weight percentage of these elements at various points signifies a homogeneous dispersion of nanoparticles within the microstructure. Conversely, Figure 4(c) demonstrates that agglomerates of CNT and TiO₂ lead to localized elevations in carbon and titanium/oxygen weight percentages, respectively, revealing regions of heterogeneous nanoparticle distribution.

The particle size distribution was also measured by analyzing SEM images in ImageJ software, as shown in Figure 5. According to Figure 5, increasing the CNT and TiO₂ content from 2 wt% to 4 wt% results in a significant increase in the average nanoparticle size, from about 280 nm to 390 nm. This suggests that the higher concentration promotes agglomeration, leading to a less uniform distribution.

Figure 5.

Particle size distribution for (a) CNT = 2 wt%, TiO₂ = 2 wt%, (b) CNT = 4 wt%, TiO₂ = 4 wt%. Laser power and scan rate are at middle levels.

The influence of laser power and scan rate on the density and porosity percentage was shown in Figure 6. It can be observed from Figure 6 that an increase in the laser power up to 18 W significantly reduced the porosity percentage and consequently improved the density of sintered samples. Moreover, Figure 6 shows that minimum porosity percentage and thus the highest density were obtained at scan rates between 2350 and 2500 mm/s. The influence of varying laser power on the microstructure of PLA/EPDM/TiO₂/CNT nanocomposite is depicted in Figure 7. It can be seen from Figure 7(a) that a laser power of 12 W provides inadequate thermal energy, resulting in partially unmelted powder within the microstructure of PLA/EPDM/TiO₂/CNT nanocomposite. This energy deficit prevents full densification and, as a consequence, induces the formation of cracks. These defects are expected to compromise the material’s mechanical properties. At a higher laser power of 15 W, the increased thermal energy reduced the prevalence of unmelted PLA/EPDM particles and improved the densification of the nanocomposite, as evidenced in Figure 7(b). Optimal results were achieved at 18 W (Figure 7(c)), where the microstructure was completely free of unmelted particles and cracks. This elimination of defects culminated in excellent densification and strong particle adhesion.

Figure 6.

Influence of laser power and scan rate on (a) porosity percentage, (b) density. TiO₂ and CNT contents are at middle levels.

Figure 7.

Fracture surface of nanocomposites for laser power of (a) 12 W, (b) 15 W, (c) 18 W. TiO₂ and CNT contents are at middle levels.

The influence of the laser scanning rate on microstructure is presented in Figure 8. A low rate of 2200 mm/s results in a high cavity content, compromising densification (Figure 8(a)). An optimal rate of 2500 mm/s minimizes these cavities and maximizes densification (Figure 8(b)). Conversely, an excessively high rate of 2800 mm/s provides insufficient energy input, leading to unmelted powder and cavity formation, which consequently reduces densification (Figure 8(c)).

Figure 8.

Fracture surface of nanocomposites for scan rate of (a) 2200 mm/s, (b) 2500 mm/s, (c) 2800 mm/s. TiO₂ and CNT contents are at middle levels.

The interaction between laser power and scanning rate is critical for optimal microstructure, as shown in Figure 9. The combination of low laser power (12 W) and high scanning rate (2800 mm/s) delivers inadequate energy, leading to high porosity, unmelted particles, and consequently, severely compromised solidification (Figure 9(a)). In contrast, the high energy input from a high laser power (18 W) and low scanning rate (2200 mm/s) causes excessive heat, resulting in thermal deterioration and crack formation (Figure 9(b)).

Figure 9.

Fracture surface of nanocomposites for (a) laser power = 12 W, scan rate = 2800 mm/s, (b) laser power = 18 W, scan rate = 2200 mm/s. TiO₂ and CNT contents are at middle levels.

Electrical analysis

Figure 10 presents the volume conductivity of sintered nanocomposites with varying nanoparticle content. The base PLA/EPDM composite exhibited low electrical conductivity (0.23 S/m), characteristic of an insulating material. The incorporation of CNT and TiO₂ nanoparticles significantly enhanced this property, with a 2 wt% loading increasing conductivity to 0.48 S/m. However, a further increase to 4 wt% yielded only a marginal improvement to 0.54 S/m, indicating diminishing returns in conductivity enhancement at higher nanoparticle concentrations.

Figure 10.

Volume conductivity of sintered samples at different TiO₂ and CNT contents.

The increase in volume conductivity originates from the high electrical conductivity of the CNT and TiO₂ nanoparticles. These particles created a percolating network throughout the insulating PLA matrix, establishing stable conductive pathways that meet the requirements for functional applications. The diminished returns observed at the higher loading (4 wt%) can be attributed to agglomeration effects. This agglomeration leads to inhomogeneous dispersion of nanoparticles that compromised interfacial adhesion with the polymer matrix and prevented optimal network formation.^67,68

Mechanical properties analysis

Analysis of variance

To quantify the influence of the process parameters on tensile stress and impact resistance, an analysis of variance (ANOVA) was conducted. This analysis also served to derive regression models for each response. The ANOVA results were presented in Tables 5 and 6 for tensile stress and impact resistance, respectively. The ANOVA results were interpreted using P-values and F-values. Parameters with a P-value below 0.05 were deemed statistically significant at a 95% confidence level, and a larger F-value denoted a greater influence. The results indicate that scan rate, laser power, CNT content, and TiO₂ content are all significant parameters. Their effects are mathematically expressed in regression equations (2) and (3) based on uncoded units.

T e n s i l e s t r e s s = - 41 - 10.4 L a s e r p o w e r + 0.124 S c a n r a t e + 13.11 C N T + 4.59 {T i O}_{2} + 0.177 L a s e r p o w e r \times L a s e r p o w e r - 0.000, 033 S c a n r a t e \times S c a n r a t e - 3.451 C N T \times C N T - 1.101 {T i O}_{2} \times {T i O}_{2} + 0.002, 639 L a s e r p o w e r \times S c a n r a t e + 0.0167 L a s e r p o w e r \times C N T + 0.0437 L a s e r p o w e r \times {T i O}_{2} + 0.000, 500 S c a n r a t e \times C N T + 0.000, 021 S c a n r a t e \times {T i O}_{2} - 0.2219 C N T \times {T i O}_{2}

(2)

I m p a c t r e s i s t a n c e = - 59.1 + 12.71 L a s e r p o w e r - 0.0184 S c a n r a t e + 1.74 C N T + 2.59 {T i O}_{2} - 0.464 L a s e r p o w e r \times L a s e r p o w e r - 0.000, 002 S c a n r a t e \times S c a n r a t e - 0.295 C N T \times C N T - 445 {T i O}_{2} \times {T i O}_{2} + 0.000, 653 L a s e r p o w e r \times S c a n r a t e - 0.0250 L a s e r p o w e r \times C N T - 0.0063 L a s e r p o w e r \times {T i O}_{2} - 0.000, 208 S c a n r a t e \times C N T - 0.000, 354 S c a n r a t e \times {T i O}_{2} - 0.0938 C N T \times {T i O}_{2}

(3)

Table 5.

ANOVA results for tensile stress.

Source	DF	SS	MS	F-value	P-value
Model	14	2833.99	202.428	115.86	0.000
Linear	4	422.59	105.648	60.47	0.000
Laser power	1	389.82	389.821	223.12	0.000
Scan rate	1	11.13	11.127	6.37	0.027
CNT	1	8.37	8.367	4.79	0.049
TiO₂	1	13.28	13.275	7.60	0.017
Square	4	2305.85	576.462	329.95	0.000
Laser power × Laser power	1	0.42	0.423	0.240	0.632
Scan rate × Scan rate	1	1.50	1.503	0.860	0.372
CNT × CNT	1	31.71	31.710	18.15	0.001
TiO₂×TiO₂	1	3.23	3.229	1.85	0.199
2-Way interaction	6	105.56	17.593	10.07	0.000
Laser power × Scan rate	1	90.25	90.250	51.660	0.000
Laser power × CNT	1	12.60	12.603	7.21	0.020
Laser power × TiO₂	1	1.10	1.102	0.63	0.442
Scan rate × CNT	1	1.44	1.440	0.82	0.382
Scan rate × TiO₂	1	0.00	0.003	0.00	0.970
CNT × TiO₂	1	0.16	0.160	0.09	0.767
Error	12	20.97	1.747
Lack-of-Fit	10	20.65	2.065	12.90	0.074
Pure error	2	0.32	0.160
Total	26	2854.96
R² = 99.27%	R²_Adj = 98.41%		R²_Pred = 94.93%	Standard error = 0.8184

Table 6.

ANOVA results for impact resistance.

Source	DF	SS	MS	F-value	P-value
Model	14	349.308	24.9506	69.14	0.000
Linear	4	54.273	13.5683	37.60	0.000
Laser power	1	18.455	18.4547	51.14	0.000
Scan rate	1	9.244	9.2438	25.62	0.000
CNT	1	18.349	18.3491	50.85	0.000
TiO₂	1	8.226	8.2256	22.79	0.000
Square	4	285.907	71.4769	198.07	0.000
Laser power × Laser power	1	2.906	2.9062	8.050	0.015
Scan rate × Scan rate	1	0.008	0.0081	0.020	0.883
CNT × CNT	1	0.231	0.2314	0.64	0.439
TiO₂×TiO₂	1	0.527	0.5268	1.46	0.250
2-Way interaction	6	9.127	1.5212	4.22	0.016
Laser power × Scan rate	1	5.522	5.5225	15.300	0.002
Laser power × CNT	1	0.360	0.3600	1.00	0.338
Laser power × TiO₂	1	0.023	0.0225	0.06	0.807
Scan rate × CNT	1	0.250	0.2500	0.69	0.421
Scan rate × TiO₂	1	0.722	0.7225	2.00	0.183
CNT × TiO₂	1	2.250	2.2500	4.23	0.058
Error	12	4.330	0.3609
Lack-of-Fit	10	4.284	0.4284	18.36	0.053
Pure error	2	0.047	0.0233
Total	26	353.639
R² = 98.78%	R²_Adj = 97.35%		R²_Pred = 95.65%	Standard error = 0.2844

The model’s accuracy was validated by the R², R²_Adj and R²_Pred values presented in the ANOVA tables. Values for these metrics near 100% indicate a model with excellent predictive power. The high values reported in Tables 5 and 6 demonstrate that the models for tensile stress and impact resistance are both accurate and reliable for predicting the responses. The standard errors of the ANOVA models were also given in Tables 5 and 6 The adequacy of the models was assessed using normal probability plots (Figure 11) and predicted versus actual plots (Figure 12). According to Figure 11, the proximity of the residuals to the normal distribution line demonstrates the models’ high predictive accuracy and confirms that the assumption of normality was met. Moreover, Figure 12 shows that the model-predicted values for tensile stress and impact strength are close to the actual values.

Figure 11.

Normal probability plots for (a) tensile stress and (b) impact resistance.

Figure 12.

Predicted versus actual plots for (a) tensile stress and (b) impact resistance.

Single effect of parameters on the mechanical properties

Figure 13 illustrates the single effect of parameters on tensile stress and impact resistance. As shown in Figure 13(a), increasing the laser power from 12 to 18 W enhanced tensile stress by approximately 16%. This improvement aligns with microstructural observations in Figure 7, where incomplete melting at 12 W, evidenced by residual polymer particles on fracture surfaces, led to poor densification due to insufficient energy input. Consequently, the lower tensile stress at 12 W is attributed to inadequate densification from low laser power. In contrast, at 18 W, improved densification resulted in higher tensile stress, consistent with findings in prior studies.^50,51,69,70 The influence of scan rate on tensile stress is non-linear, as shown in Figure 13(a). An increase from 2200 to 2500 mm/s yielded a modest 3.5% improvement, but a further increase to 2800 mm/s caused a 6.5% reduction. This trend is explained by the microstructural analysis in Figure 8. The scan rate of 2500 mm/s produced a well-densified microstructure with minimal defects (Figure 8(b)), leading to higher strength. Deviating from this optimum, either to a slower 2200 mm/s or a faster 2800 mm/s, resulted in incomplete densification and a proliferation of defects such as cracks and cavities (Figure 8(a) and (c)), which consequently impaired the tensile stress. The results obtained are consistent with those reported in 69–72. In the case of nanoparticle effects in Figure 13(a), a 2 wt% loading represents the optimum concentration for both CNT and TiO₂ nanoparticles, resulting in tensile stress improvements of 30% and 10.5%, respectively. This significant enhancement is attributed to the homogeneous dispersion of nanoparticles observed in the SEM micrographs (Figure 4(b)). A uniform distribution is critical as it enables efficient load transfer from the softer PLA/EPDM matrix to the stronger, stiffer nanoparticles. The enhancement of mechanical properties with nanoparticle addition can be explained by critical percolation theory. At concentrations up to 2 wt%, a flexible and percolating network of nanoparticles forms, bridged by polymer chains.⁷³ This structure facilitates efficient stress transfer from the PLA matrix to the nanoparticles, thereby improving mechanical performance. However, at 4 wt%, the concentration exceeds the percolation threshold, leading to nanoparticle aggregation. These aggregates hinder interaction with the PLA matrix, immobilizing both the nanoparticles and the surrounding polymer chains.⁷³ Consequently, the diffusive motion of PLA is restricted, and the mechanical properties deteriorate. Literature confirms that nanofillers substantially improve the tensile stress of PLA. Single fillers like TiO₂³⁵ or CNTs^20,74 typically provide improvements of ∼30%, whereas hybrid systems are more effective, boosting tensile strength by 71% (CNTs/GPN),³⁰ 52% (TiO₂/GO),¹⁴ and 35% (TiO₂/GPN).³⁴

Figure 13.

Single effect of parameters on (a) tensile stress and (b) impact resistance.

Figure 13(b) shows that the optimal impact resistance for the nanocomposite occurred within a laser power range of 15 to 16.5 W, resulting in a 17% increase compared to the value at 12 W. The subsequent reduction in impact resistance observed at the higher power of 18 W is likely caused by thermal degradation mechanisms, such as the development of microcracks or residual stresses, due to the excessive thermal energy input. Similar results were also reported in 50,51,69,70. As also evidenced in Figure 13(b), impact resistance improved by 8% as the scan rate increased from 2200 to 2650 mm/s but declined slightly (1%) at 2800 mm/s. The optimal performance observed at intermediate scan rates (2500-2650 mm/s) is attributed to superior densification and a reduction in crack formation within the microstructure. As illustrated in Figure 13(b), impact resistance peaks at a CNT concentration of 1 to 2 wt%, a result of the nanoparticles’ optimal dispersion within this range (Figure 4(b)). A further increase to 4 wt%, however, leads to a significant decline in impact resistance. This reduction is attributed to CNT agglomeration (Figure 4(c)), which creates stress concentration sites. A TiO₂ content of 2 wt% resulted in the highest impact resistance due to its superior nanoparticle dispersion (Figure 4(b)). Conversely, the decline in impact resistance observed at 4 wt% was attributed to the agglomeration of TiO₂ nanoparticles (Figure 4(c)).

Interaction effect of parameters on the mechanical properties

Statistical analysis of variance (Tables 5 and 6) indicates that the interaction between laser power and scan rate significantly influences both tensile stress and impact resistance (p < .05). Furthermore, the interaction between laser power and CNT content significantly affects tensile stress. Given their significance, these interaction effects were investigated using the response surface plots, as presented in Figure 14.

Figure 14.

Interaction effect of parameters on (a, b) tensile stress and (c) impact resistance.

It can be observed from Figure 14(a) that tensile stress responds differently to scan rate depending on the laser power. At 12 W, increasing the scan rate from 2200 to 2800 mm/s consistently reduced tensile stress. Conversely, at 18 W, the same increase in scan rate initially improved tensile stress before causing a reduction, resulting in a maximum value at a mid-level scan rate of 2500 mm/s. The decline at the high power (18 W) and low scan rate (2200 mm/s) is attributed to thermal degradation from excessive heat input, as evident from SEM images in Figure 9(b). According to Figure 14(b), the effect of laser power on tensile stress is highly dependent on CNT content. While increasing laser power from 12 to 18 W only slightly improved tensile stress at 0 wt% CNT, it caused a significant improvement at 4 wt% CNT. Therefore, higher CNT loadings require higher laser power to achieve optimal tensile stress. This is because CNT nanoparticles absorb a portion of the laser energy, which reduces the overall sintering rate of the nanocomposite. Figure 14(c) reveals that the effect of laser power on impact resistance is contingent on the scan rate. At a low scan rate (2200 mm/s), impact resistance initially improved then declined as laser power increased to 18 W. Conversely, at a high scan rate (2800 mm/s), impact resistance improved continuously over the same power range. The decline observed at high laser power and low scan rate is attributed to excessive heat input causing thermal degradation, as confirmed by the SEM images in Figure 9(b). Consequently, optimal impact resistance is achieved by combining high laser power with a high scan rate to avoid detrimental heat accumulation.

Simultaneous optimization of the mechanical properties

Research into the mechanical properties of SLS-produced PLA/EPDM/TiO₂/CNT nanocomposites revealed that process parameters often affect tensile stress and impact resistance in opposing ways. Consequently, optimizing these properties simultaneously requires finding a parameter balance. The desirability function technique is well-suited for this type of multi-response optimization. It works by first translating the predictive model for each response into an individual desirability function (d), which are then combined into an overall composite desirability function (D). This function yields a value between 0 (representing an unacceptable result) and 1 (representing the ideal outcome). The single desirability functions (d) can be computed based on the intended purpose; 1- A higher response is better, 2- A lower response is better, and 3- A desired value of response is better.²⁴ For this study, where the objective was to maximize all responses, the “A higher response is better” option was selected for calculating each individual desirability function (equation (4)).

{\begin{cases} 0 y < L \\ {(\frac{y - L}{T - L})}^{r} L \leq y \leq T \\ 1 y > T \end{cases}

(4)

In this equation, L and T correspond to the response’s lower limit and target value, respectively, while the exponent r defines its importance. The overall composite desirability (D) is determined by calculating the geometric mean of all individual desirability scores (d). For this study, this method was applied to combine the tensile stress and impact resistance responses into a composite desirability function, labeled as equation (5).

D = \sqrt[2]{d_{1} (T e n s i l e s t r e s s) \times d_{2} (I m p a c t r e s i s t a n c e)}

(5)

In this equation, D represents the composite desirability function and d_n indicates the single desirability function corresponding to the each response.²⁴ An equal weighting factor was assigned to both tensile stress and impact strength. This reflects their equivalent importance for the nanocomposite’s application in key industries such as medical, automotive, and aerospace, where its enhanced mechanical and thermal properties are valuable. The composite and single desirability functions were calculate using Minitab®17 software. The optimization results were presented in Figure 15. The optimization analysis yielded a high composite desirability of 0.95 (Figure 15), indicating that the predicted results are very close to the optimal response values. The model determined that the mechanical properties are optimized at a laser power of 16.5 W, a scanning speed of 2624 mm/s, 1.8 wt% CNT, and 1.9 wt% TiO₂. At these settings, regression Equations (2) and (3) predict a tensile stress of 65 MPa and an impact resistance of 22.5 kJ/m². The individual desirability for tensile stress is higher than that for impact resistance. This indicates that the optimal conditions are more suitable for improving tensile stress.

Figure 15.

Results of optimization using the desirability function.

The precision of the optimization results was confirmed through three validation tests performed at the optimal parameters, as the results were given in Table 7. The strong correlation between the experimental and predicted results validates the developed models. This successful outcome is attributed to the role of CNTs and TiO₂ nanoparticles, which strengthen the PLA/EPDM matrix and restrict the intermolecular motion of polymer chains under the optimal SLS parameters. In this state, the nanoparticles effectively adhere to the powder surface via a facilitated latex technique and integrate with the polymer chains during melting and solidification.⁷²

Table 7.

Results of validation experiments and prediction at optimal values of parameters.

Response	Predicted results	Validation experiments	Percentage error
Tensile stress (MPa)	65	66.8 ± 2.4	2.7 %
Impact resistance (kJ/m²)	22.5	21.2 ± 1.2	5.7 %

Although all fabrication occurred in the XY plane, three samples were produced at 0°, 45°, and 90° angles to evaluate the material’s anisotropy under optimal condition of parameters, as shown in Table 8. According to Table 8, the mechanical properties of the samples were consistent across different fabrication angles, confirming their isotropic nature and the absence of significant anisotropy.

Table 8.

Results of measurement of tensile stress and impact resistance at different angles.

Response	0°	45°	90°
Tensile stress (MPa)	65.6 ± 2.4	63.4 ± 2.5	62.1 ± 1.8
Impact resistance (kJ/m²)	22.4 ± 2.1	23.7 ± 2.3	22.9 ± 2.4

The optimization results were validated through confirmation experiments conducted near the predicted optimum (Table 9). These tests confirmed that the best combination of tensile stress and impact strength occurred only at the optimized condition. For instance, while a slight increase of laser power up to 17 W could slightly improve the tensile stress, it compromised the impact resistance. Conversely, when the laser power was reduced to 16 W, the impact strength was slightly improved but the tensile stress was reduced. Similarly, varying the scan rate or nanoparticle amount from their optimums led to a decrease in both tensile stress and impact strength.

Table 9.

Results of validation experiments with confidence interval close to the optimal condition.

Laser power (W)	Scan rate (mm/s)	CNT (wt%)	TiO₂ (wt%)	Tensile stress (MPa)	Impact resistance (kJ/m²)
16.5	2624	1.8	1.9	66.8 ± 2.4	21.2 ± 1.2
17	2624	1.8	1.9	67.3 ± 2.1	19.5 ± 0.9
16	2624	1.8	1.9	63.5 ± 1.8	21.8 ± 1.1
16.5	2630	1.8	1.9	65.7 ± 2.1	20.4 ± 1.2
16.5	2620	1.8	1.9	66.3 ± 2.2	19.9 ± 1.3
16.5	2624	1.9	1.9	65.1 ± 2.4	21.0 ± 0.8
16.5	2624	1.7	1.9	64.8 ± 2.3	20.7 ± 1.1
16.5	2624	1.8	2	62.6 ± 2.0	21.2 ± 1.2
16.5	2624	1.8	1.8	64.9 ± 2.2	20.3 ± 1.0

Conclusions

This study optimized the thermal, electrical, and mechanical properties of PLA/EPDM/TiO₂/CNT nanocomposites by integrating response surface methodology (RSM) with a desirability function approach. Thermal analysis revealed that adding CNT and TiO₂ nanoparticles to the PLA/EPDM blend increased its melting temperature, crystallization temperature, and percent crystallinity. This enhancement is attributed to the nanoparticles’ nucleating effect and their ability to partially absorb heat. The electrical conductivity of the PLA/EPDM/TiO₂/CNT nanocomposites was also significantly enhanced by the addition of 2 wt% CNT and TiO₂. Beyond this concentration, increasing the loading to 4 wt% resulted in only a marginal improvement, which is attributed to agglomeration effects. The laser power and scan rate have a complex interaction. While increasing laser power from 12 to 18 W improved densification of the nanocomposite and thus enhanced its tensile stress and impact resistance, a laser power of 18 W combined with a low scan rate of 2200 mm/s induced thermal degradation, leading to a reduction in those same properties. An enhancement in tensile stress and impact resistance was also observed at CNT and TiO₂ loadings of up to 2 wt%, which is attributed to the successful dispersion of the nanoparticles. Conversely, a further increase to 4 wt% degraded the mechanical properties as a consequence of agglomeration. Finally, the optimal tensile stress and impact resistance for the nanocomposites were achieved at a laser power of 16.5 W, a scan rate of 2624 mm/s, a CNT content of 1.8 wt%, and a TiO₂ content of 1.9 wt%. Under these conditions, the tensile stress and impact resistance were predicted to reach 65 MPa and 22.5 kJ/m², respectively.

Supplemental Material

Supplemental Material - Comprehensive investigation of a novel PLA/EPDM/TiO₂/CNT nanocomposite produced by selective laser sintering

Supplemental Material for Comprehensive investigation of a novel PLA/EPDM/TiO₂/CNT nanocomposite produced by selective laser sintering by Ishraga Galal-Eldin Abdalla Awad in Journal of Thermoplastic Composite Materials

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Ishraga Galal-Eldin Abdalla Awad

Data Availability Statement

The data supporting the findings of this study are available within the article.*

Supplemental Material

Supplemental material for this article is available online

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Supplementary Material

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Comprehensive investigation of a novel PLA/EPDM/TiO 2 /CNT nanocomposite produced by selective laser sintering

Abstract

Keywords

Introduction

Materials and methods

Raw materials

Selective laser sintering

Experimental design

Mechanical properties measurement

Thermal properties measurement

Electrical properties measurement

Microstructure examination

Results and discussion

Thermal analysis

Microstructural evolutions

Electrical analysis

Mechanical properties analysis

Analysis of variance

Single effect of parameters on the mechanical properties

Interaction effect of parameters on the mechanical properties

Simultaneous optimization of the mechanical properties

Conclusions

Supplemental Material

Supplemental Material - Comprehensive investigation of a novel PLA/EPDM/TiO2/CNT nanocomposite produced by selective laser sintering

Footnotes

Declaration of conflicting interests

Funding

ORCID iD

Data Availability Statement

Supplemental Material

References

Supplementary Material

Supplemental Material - Comprehensive investigation of a novel PLA/EPDM/TiO₂/CNT nanocomposite produced by selective laser sintering