Enhanced Mechanical Properties and Surface Finish of PLA 3D Prints via Combined Heat Annealing and Powder Coating

Abstract

In this study, we investigate a novel post-processing approach combining heat annealing and powder coating to enhance both the mechanical performance and surface finish of polylactic acid (PLA) 3D-printed components. Previous work demonstrated that annealing PLA at temperatures between 100 and 120 °C significantly improves its mechanical properties. Building on this, we explore the effects of applying medium-density fiberboard (MDF) powder coating, which cures at a similar temperature range, to simultaneously improve the material’s surface aesthetics. Test specimens were printed with identical parameters and subjected to heat treatment at 120 °C for varying durations (0 to 15 min, in one-minute intervals). Additional observations included dimensional stability and surface uniformity. The results indicate a clear correlation between post-processing time and improvements in both strength and surface appearance, with optimal outcomes observed between 5 and 8 min of curing. This combined post-processing method provides a cost-effective and accessible way to enhance part performance and aesthetics, thereby expanding the applications of PLA-based additive manufacturing, particularly in functional and design-focused use cases.

1. Introduction

1.1. Background on PLA in 3D Printing

Polylactic acid (PLA) is one of the most widely adopted thermoplastics in material extrusion-based additive manufacturing, particularly in fused deposition modeling (FDM). Derived from renewable resources such as corn starch or sugarcane, PLA is recognized for its biodegradability under industrial composting conditions, ease of use, low warping tendency, and relatively low printing temperature, making it an ideal material for consumer-level and educational 3D printing. However, its biodegradation requires specific conditions, such as elevated temperature, humidity, and microbial activity, which are not typically found in natural environments. Its popularity has grown rapidly due to its accessibility, environmental appeal, and minimal post-processing requirements compared to engineering-grade filaments like ABS, PETG, or nylon.

Despite these advantages, PLA suffers from several limitations that restrict its application in functional or industrial contexts. It is relatively brittle, has low thermal resistance (with a glass transition temperature around 60 °C and a melting temperature near 150–160 °C), and exhibits visible layer lines that detract from its surface quality. As a semi-crystalline thermoplastic, both Tg and Tm play roles in defining its thermal behavior: Tg marks the onset of molecular mobility leading to softening, while Tm represents the point at which crystalline regions melt, affecting dimensional stability under heat. In the context of this study, Tg is particularly relevant, as the applied post-processing temperatures (around 120 °C) are above Tg but below Tm. This enables increased polymer chain mobility and promotes recrystallization without causing melting or deformation. These shortcomings hinder its use in load-bearing or high-temperature environments, as well as in applications where a high-quality surface finish is essential [1].

To expand the usability of PLA beyond prototyping, various enhancement techniques have been explored, including polymer blending, filler integration, and post-processing methods such as chemical smoothing and heat treatment. Among these, heat annealing has emerged as a promising solution to improve mechanical and thermal properties by promoting crystallization and interlayer bonding within the printed structure. However, while annealing improves internal strength, it does not address surface appearance, which remains a barrier in design-oriented applications.

While PLA is easy to print and offers acceptable dimensional accuracy, its mechanical properties and surface quality often fall short for demanding applications. One primary limitation is interlayer adhesion. Due to the layer-by-layer deposition inherent in FDM processes, printed PLA parts exhibit anisotropic behavior—significantly weaker along the Z-axis. This directional weakness arises from insufficient molecular diffusion between layers, resulting in microgaps that act as crack initiation points under mechanical load [2].

Another critical drawback is PLA’s brittleness. Unlike engineering polymers that can withstand substantial deformation before failure, PLA tends to fracture suddenly with limited ductility [3]. Furthermore, its low glass transition temperature (~60 °C) restricts usage in environments with moderate heat exposure, where part deformation can occur even under light loading [4].

From a visual perspective, PLA prints often exhibit visible layer lines, surface roughness, and inconsistent color or texture, particularly at lower infill or layer heights [5]. Although some commercial techniques, such as vapor smoothing, are available for materials like ABS, they are either ineffective or chemically incompatible with PLA.

These mechanical and aesthetic limitations reduce the material’s viability in fields requiring strength, finish, or both—such as product enclosures, decorative components, custom tools, and functional end-use parts. Therefore, a unified post-processing method that strengthens interlayer bonding while improving visual appeal could substantially increase PLA’s application scope.

1.2. Overview of Post-Processing Techniques

Post-processing methods for 3D-printed components are typically employed to address deficiencies in mechanical properties, surface finish, or both. The choice of technique depends on the base material, desired properties, and end-use application. For PLA, common post-processing strategies include heat treatment, sanding and polishing, chemical smoothing, painting, and composite reinforcement [6].

Heat annealing is widely used to improve the thermal and mechanical behavior of PLA. By exposing printed parts to temperatures above the glass transition point but below the melting point (typically 100–120 °C), molecular chains are allowed to reorganize into more crystalline structures [7,8]. This results in enhanced interlayer bonding, improved tensile and flexural strength, and an increased heat deflection temperature. However, uncontrolled annealing can introduce warping or dimensional instability if parts are not properly supported during the heating process.

Surface finishing methods, such as sanding and painting, are labor-intensive and limited in precision, particularly for complex geometries. Chemical smoothing is effective for materials like ABS, which can be treated with acetone, but PLA lacks an easy-to-apply solvent-based technique due to its distinct chemical nature. Additionally, some solutions for PLA (e.g., ethyl acetate) are less accessible or pose safety concerns in a home or small laboratory setting.

Powder coating, although rarely explored for plastics like PLA, is well-established in the finishing of metals and MDF. It offers an efficient way to apply a durable, aesthetically pleasing surface in a single curing step. Traditional thermoset powder coatings require high temperatures (160–200 °C), which exceed the tolerance of PLA. However, specialized MDF-targeted powder coatings cure at ~120 °C, making them compatible with PLA’s annealing window.

This convergence in temperature profiles opens up the possibility for a combined annealing and coating process, minimizing post-processing time while simultaneously achieving both structural and aesthetic improvements [9].

1.3. Rationale for Combining Heat Annealing and Powder Coating

Heat annealing and powder coating, though traditionally separate processes, present a compelling synergy when applied to PLA 3D-printed components. Annealing enhances internal material properties by promoting crystallization and reducing residual stresses, while powder coating improves external surface characteristics through a uniform, high-gloss finish. The overlapping temperature window—approximately 100–120 °C for both PLA crystallization and MDF-grade powder coat curing—makes it feasible to carry out both treatments in a single thermal cycle [10].

This dual-purpose approach addresses two of PLA’s most prominent weaknesses simultaneously: low mechanical strength and poor surface finish. While annealing improves mechanical performance, it typically has little effect on addressing the visible layer lines or roughness inherent to FDM-printed surfaces. Conversely, powder coating alone does not alter the material’s internal structure. By combining the two, a printed PLA part can be structurally reinforced and visually upgraded in a single, controlled oven process.

Furthermore, the powder coating process may offer additional mechanical reinforcement by filling surface gaps and forming a continuous external shell, which could contribute to improved load distribution and minor impact resistance. This could also enhance environmental protection (e.g., against moisture or UV exposure), depending on the properties of the powder used [11].

This method is particularly attractive because it is scalable, cost-effective, and can be implemented using readily accessible equipment, such as a convection oven and an electrostatic spray gun. For designers, engineers, and small manufacturers, this represents a promising post-processing route that improves performance and presentation without requiring material changes or complex machinery.

1.4. Objectives of the Study

The primary objective of this study is to evaluate the combined effect of heat annealing and powder coating on the mechanical and visual properties of PLA 3D-printed specimens. This study investigates the combination of annealing with powder coating, a finishing method traditionally used in wood and metal fabrication, to simultaneously enhance PLA’s structural integrity and visual aesthetics—two key parameters for expanding the functional capabilities of 3D printed parts [12]. By leveraging the overlapping processing temperatures of PLA crystallization and MDF-targeted powder coating, this research aims to develop a streamlined post-processing method that can be applied in a single step.

A total of 20 specimens per time group were evaluated. Mechanical properties were assessed through tensile strength testing, while surface quality was analyzed via subjective visual grading by multiple evaluators, using a defined scoring system

To systematically assess this combined treatment, the following specific goals are defined:

• To determine the optimal curing duration at 120 °C that yields the greatest mechanical improvement without causing deformation or loss of dimensional accuracy
• To evaluate surface appearance improvements through both subjective human assessment and optional objective roughness characterization.
• To compare the strength characteristics of treated and untreated specimens across multiple curing durations, identifying trends and thresholds of benefit.
• To propose a repeatable workflow that can be adopted for functional and aesthetic enhancement of PLA prints in design, engineering, and prototyping applications.
• The outcomes of this study are expected to provide a novel and practical contribution to post-processing strategies for FDM 3D printing, expanding the usability of PLA into domains traditionally limited by its material properties and appearance [13].

2. Materials and Methods

2.1. Materials Used

PLA Filament Specifications—The base material used in this study was PLA Original Black Filament from AzureFilm (Slovenia), a commercially available PLA filament widely used for FDM 3D printing applications. The filament has a nominal diameter of 1.75 mm, with a manufacturer-specified diameter tolerance of ±0.02 mm. AzureFilm PLA is recognized for its low shrinkage and excellent printability, with recommended print temperatures ranging from 200 °C to 220 °C and a glass transition temperature of approximately 60 °C. The mechanical properties as specified by the manufacturer include a tensile strength of ~65 MPa and an elongation at break of ~6%, making it suitable for non-load-bearing and prototyping applications [14].

Powder Coating Material—For the powder coating process, a specialized low-temperature curing powder was selected, designed specifically for MDF substrates. The coating material used was TIGER Drylac^® Series 14, RAL 9010 Pure White, developed by TIGER Coatings GmbH & Co. KG (Wels, Austria). This powder is formulated to cure at lower temperatures compared to conventional metal-targeted powders, with an optimal curing range of 120 °C to 130 °C for 10 min, aligning well with the thermal window required for PLA annealing. The powder provides a high-gloss, durable finish and is applied using standard electrostatic spraying equipment. Its compatibility with PLA was a key factor in selecting this material, allowing a combined post-processing step without exceeding the polymer’s thermal degradation threshold. The powder formulation typically comprises 45–55 wt % organic binder—primarily polyester (often epoxy-polyester hybrid ratios of 50–70: 30–50 resin to curing agent)—~25 wt % inorganic pigments such as titanium dioxide (TiO₂) for whiteness, and up to ~25 wt % inorganic fillers (e.g., calcium carbonate, barium sulfate) to improve durability and film structure. Minor additives (below ~5 wt %) such as flow modifiers, degassing agents (e.g., benzoin), and adhesion promoters are also present [15,16]. These components cure into a hard, continuous film at low temperatures, making them suitable for PLA substrates.

2.2. 3D Printing Parameters

For this study, all 3D printing was performed using an Ender 3 FDM printer. G-code was generated using Creality Print software [17], as shown in Figure 1, with optimized settings to ensure high-quality and consistent PLA parts for post-processing treatments. The general setup is as follows:

2.2.1. 3D Printing Parameters

The 3D printing parameters used in this study were set on an Ender 3 printer. A layer height of 0.2 mm was selected, representing a standard resolution that strikes a balance between strength and printability. The infill density was set at 20%, providing an effective compromise between material usage and mechanical strength. A rectilinear infill pattern was chosen to ensure good mechanical strength primarily along the X-Y plane. Printing was performed at a temperature of 210 °C, which falls within the recommended range for the AzureFilm PLA filament. The print bed was maintained at 60 °C to ensure proper adhesion of the PLA to the surface. Cooling was set to 100% fan speed to minimize overheating of layers and enhance surface finish quality. Finally, a print speed of 50 mm/s was applied to achieve an optimal balance between print quality and time efficiency.

2.2.2. Specimen Geometry

Test specimens were designed for mechanical testing and evaluation of visual layer adhesion. The primary specimen geometry consists of a 10 mm × 10 mm × 50 mm rectangular bar, with an additional postument (or base) of 20 mm × 20 mm × 5 mm at the bottom. The part also features a 90° angle at the junction of the postument, creating a critical geometry that allows for the evaluation of how the combined heat annealing and powder coating react to this transition and critical edge [18].

This specific design was chosen to test the layer adhesion and structural integrity at the point where the postument and main body meet, as this is a common failure point for FDM-printed parts, particularly when subjected to thermal post-processing treatments.

2.2.3. Number of Specimens

A total of 10 specimens were printed for each curing time group (ranging from 0 to 15 min), with each specimen being individually processed and tested for both mechanical strength and surface finish.

2.3. Post-Processing Procedures

The post-processing procedure integrated both powder coating and heat annealing in a single thermal step to enhance both the mechanical and aesthetic properties of the PLA specimens. The following subsections describe the setup and method in detail.

2.3.1. Powder Coating

Powder coating was applied using an E-COAT PRO V2 electrostatic spray gun. This model is designed for precise application of powder on complex geometries, making it well-suited for coating the layered surfaces of FDM-printed PLA.

The coating material used was TIGER Drylac^® Series 14, RAL 9010 Pure White, a low-temperature powder formulated specifically for wood and MDF substrates [19]. It was selected due to its 120 °C curing temperature, which aligns with the thermal annealing window of PLA. A thin, uniform layer of powder was electrostatically applied to the specimens, ensuring good surface coverage without obscuring fine surface features or creating excessive buildup, as shown in the procedure in Figure 2 [19].

2.3.2. Heat Annealing and Powder Coating Curing

After application, the coated specimens were transferred to a custom powder coating oven featuring a hybrid electrical and gas-based heating system. The oven operates without active airflow, reducing the risk of powder displacement before melting and ensuring gentle, uniform heating suitable for thermoplastics like PLA [20]. The curing temperature was maintained at a constant 120 °C. Specimens were cured for varying durations ranging from 0 min (control) up to 15 min in one-minute increments, with 10 specimens tested per time group.

The process began by preheating the oven to 120 °C before inserting the samples to ensure a stable thermal environment. Each specimen was then exposed to the controlled temperature for its assigned duration, ranging from 0 to 15 min. After removal from the oven, the samples underwent passive cooling at room temperature, allowing the powder coating to fully cure and the PLA to stabilize without thermal shock or deformation. This carefully controlled thermal cycle was designed to achieve two key outcomes simultaneously. First, it promoted crystallization and layer fusion within the PLA material, which enhances its mechanical strength and dimensional stability. Second, it enabled curing of the powder coating, resulting in a smooth, high-gloss, and durable surface finish as illustrated in Figure 2. Together, these effects contribute to improved functional and aesthetic performance of the 3D-printed parts.

2.3.3. Post-Processing Notes

Due to the absence of airflow in the oven, powder displacement was minimized and temperature uniformity was maintained, reducing the risk of surface defects or inconsistent annealing. Specimens were placed on a non-stick, heat-resistant surface to prevent deformation or fusing with the oven tray.

2.4. Mechanical Testing Methods

To assess the impact of combined heat annealing and powder coating on the structural properties of PLA specimens, a strength evaluation was conducted across all time-based curing groups. The testing focused on flexural and stiffness characteristics, which are most relevant to real-world applications of PLA parts in non-load-bearing but mechanically sensitive use cases [21].

Test Method

Given the dimensions and geometry of the specimens (10 × 10 × 50 mm with a 20 × 20 × 5 mm postument), a three-point bending test was selected as the primary mechanical testing method to evaluate flexural strength, stiffness (elastic modulus), and layer adhesion performance, including delamination or crack propagation.

The specimens were placed on two support points, with the postument section aligned centrally under the loading pin to simulate stress concentrations. The force was applied until the point of failure or significant deformation, as shown in Figure 3.

Each of the 10 specimens per curing time group was individually tested. The test captured the maximum load before fracture or yield.

2.5. Failure Observation

A visual inspection was conducted post-test to identify failure modes, such as cracking between layers, surface delamination, and brittle fracture or ductile deformation. These observations helped correlate mechanical behavior with curing duration and powder coverage, providing insight into how the treatments affect interlayer bonding. The evaluation was performed under standardized lighting conditions and involved subjective scoring by a panel of reviewers. Focus areas included surface smoothness, layer visibility, coating coverage and adhesion, deformation or warping, and gloss uniformity.

Reviewers compared each specimen visually and tactilely, assigning qualitative notes supported by photographic documentation. Specimens representing key curing stages (0, 11, and 15 min) were selected for detailed comparison.

The observation revealed pronounced layer delamination upon fracture [22], characterized by a ductile tearing mode between printed layers. The surface quality exhibited visible layer lines, even under the powder coating, and the coating was poorly adhered in some areas. The specimen shown in Figure 4 represents the behavior of untreated PLA, exhibiting weak interlayer bonding and insufficient heat exposure to initiate annealing or achieve proper coating fusion.

The specimen shown in Figure 5 demonstrated a balanced performance between mechanical strength and visual quality. The fracture mode exhibited brittle failure on the exterior, with ductile characteristics internally. Surface quality revealed good layer adhesion, although a mild layering texture was still visible beneath the coating. It is noted that applying a second powder coating layer could completely mask the remaining texture. Overall, this specimen represents an ideal curing duration, showing no significant dimensional changes while achieving strong aesthetics and improved strength.

The specimen shown in Figure 6 exhibited high visual quality, excellent coating coverage, and a glossy finish. The fracture mode was brittle, with consistent layer adhesion throughout. Surface quality was smooth, with layer lines fully masked by the coating. However, dimensional deformation began to appear due to the softening and flow of PLA under prolonged heat exposure. While visually excellent, this specimen illustrates how excessive heat can compromise dimensional stability.

These images and their corresponding failure modes help illustrate the trade-off between visual enhancement and material distortion. Specimen 7 clearly demonstrates the optimal post-processing window where both structural and aesthetic improvements peak without introducing dimensional issues.

2.6. Visual and Surface Analysis

A comparative image was prepared to highlight the visual development of powder coating across varying curing durations. Specimen 0 (S0) showed a distinct black PLA filament with clearly defined layer lines, representing the purely as-printed surface with no post-processing applied. Specimen 5 (S5) exhibited partial melting of the white powder coating over the black PLA base; the coating appeared uneven with globular artifacts, indicating incomplete curing. This mid-range heating reflects the onset of surface smoothing but lacks full powder flow, resulting in inconsistent aesthetics. Specimen 9 (S9) displayed a fully cured powder coating with a uniform, glossy white surface that entirely masked the original print layers. At this stage, the coating material had completely melted and bonded, providing an excellent surface finish, although some signs of dimensional softening may begin to appear.

This visual summary (see Figure 7) illustrates the transformation from raw print to a high-quality finished surface, providing a visual reference for assessing surface quality at each stage of thermal treatment.

3. Results

3.1. Mechanical Strength Comparison

Figure 8 shows the relationship between curing time and flexural strength, indicating a plateau in strength at longer durations. To provide a quantitative description of this behavior, the experimental data were fitted using a logistic growth model, which captures the initial slow increase, the rapid strengthening phase, and the final asymptotic behavior. The resulting empirical equation is

$$Strength\left(x\right)={\displaystyle \frac{243.29}{\left(1+\mathit{exp}\left(-0.529 \ast \left(x-7.83\right)\right)\right)}}+245.08$$

where x is the curing time in minutes and strength is the maximum force at failure (N). This model offers a more accurate representation of the curing kinetics compared to simple point-to-point connections.

Initial specimens (0–2 min of curing) exhibited low mechanical strength, ranging from 250 N to 264 N, primarily due to insufficient adhesion between layers. As the curing time increased, the annealing effect significantly enhanced interlayer bonding, resulting in improved mechanical properties. Between 3 and 6 min, the force at failure increased steadily, reaching 420 N.

A notable performance plateau begins around specimen 7 (approximately 11.7 min), where the strength reaches near-optimal values. Specimens 7, 8, and 9 displayed only marginal improvements in strength, stabilizing around 470–478 N. This suggests that the material reaches a saturation point in terms of annealing benefits, beyond which further heat exposure yields diminishing returns in mechanical performance. This plateau indicates an ideal curing window for maximizing mechanical strength while minimizing the risk of dimensional distortion or thermal degradation.

3.2. Surface Quality Assessment

The visual appearance of the specimens was evaluated by a panel of human observers who rated surface smoothness, gloss, and overall aesthetic quality on a scale from 1 to 10. The results, indicate that specimen number 7 consistently received the highest scores, reflecting the optimal balance between heat treatment and powder coating curing.

The distribution of scores resembles a normal (Gaussian) curve centered around specimen 7, with ratings decreasing for both shorter and longer curing times. Early specimens (0–3 min) showed visible layer lines and uneven powder coating, resulting in lower visual scores. Specimens cured for more than 10 min exhibited signs of surface deformation or loss of dimensional accuracy, which negatively affected appearance ratings. These findings suggest that curing times around specimen 7 (approximately 11 min) produce the most visually appealing and physically stable coated PLA prints, reinforcing the mechanical strength results observed in the previous section. To quantitatively describe this trend, the surface quality was modeled using a Gaussian function:

$$Quality\left(x\right)= 8.749 \ast \mathit{exp}\left( -{\displaystyle \frac{{\left(x - 12.453\right)}^2}{\left(2 \ast {1.703}^2\right)}}\right)+ 1.090$$

where x is the curing time in minutes and quality represents the visual surface score on a 1–10 scale.

3.3. Optimal Processing Time Identification

Based on the combined analysis of mechanical strength and surface quality, specimen number 7, corresponding to approximately 11 min of curing time, was identified as the optimal processing condition for heat annealing and powder coating of PLA 3D prints.

The mechanical strength data (see Figure 8) demonstrated a significant increase in flexural strength up to specimen 7, after which strength gains plateaued, indicating minimal benefit from longer curing durations. Simultaneously, the visual surface quality evaluation (refer to Figure 9) revealed that specimen 7 achieved the highest aesthetic rating, with a smooth, glossy, and defect-free powder-coated surface.

Specimens cured for shorter durations (0–6 min) exhibited poor layer adhesion and suboptimal coating, resulting in reduced strength and surface quality. Conversely, specimens subjected to extended curing beyond 11 min exhibited minor surface deformation and dimensional instability, which adversely affected their visual appearance without providing substantial mechanical improvement.

Therefore, specimen 7 offers an optimal balance between mechanical enhancement and aesthetic finish, maximizing performance while minimizing processing time and potential thermal damage. This processing window provides a practical guideline for post-processing PLA 3D-printed parts with powder coating to improve durability and appearance.

4. Discussion

4.1. Interpretation of Results

4.1.1. Material Behavior Under Thermal Treatment

The heat annealing process applied to PLA specimens induces molecular rearrangement and partial recrystallization within the polymer matrix. This thermal treatment enhances interlayer adhesion by promoting polymer chain diffusion across printed layers, which is typically limited in FDM-printed parts. As a result, the mechanical strength significantly improves up to an optimal annealing duration. However, excessive heat exposure beyond this window can lead to softening and deformation, causing dimensional instability and loss of part fidelity.

4.1.2. Synergistic Effect of Heat and Powder Coating

The integration of powder coating curing at temperatures overlapping with the annealing range presents a synergistic effect. While the heat annealing improves mechanical properties by strengthening interlayer bonds, the powder coating simultaneously melts and cures on the surface, filling microvoids and creating a continuous, glossy finish. This dual action not only improves the physical appearance but also contributes to surface protection and added stiffness.

The powder coating’s ability to fuse with the annealed PLA surface reduces the visibility of layer lines and enhances durability, expanding the range of potential applications for 3D-printed PLA components. The combined thermal and coating treatment thus provides a practical post-processing approach that maximizes both structural integrity and aesthetic quality.

4.2. Comparison to Literature

Traditional post-processing techniques for PLA 3D prints primarily focus on mechanical strengthening or aesthetic improvements separately. Common methods include solvent smoothing, chemical treatments, sanding, and standalone annealing. While these approaches can enhance either surface finish or mechanical properties, they often involve trade-offs such as dimensional distortion, environmental concerns, or limited effectiveness in simultaneously improving strength and appearance.

The combined heat annealing and powder coating method presented in this study introduces a novel, integrated post-processing approach that leverages the overlap in curing temperatures to synergistically improve both the mechanical performance and surface aesthetics of PLA prints. To the best of our knowledge, this dual treatment has not been previously reported or systematically studied in the literature [23].

This innovative method opens new possibilities for producing high-quality, durable PLA components with enhanced visual appeal, potentially widening the scope of PLA’s industrial and consumer applications. However, further research is necessary to validate this approach across a wider range of PLA formulations, filament colors, and powder coating types. Additionally, long-term durability, environmental stability, and scalability should be investigated to fully establish the technique’s practical viability.

Continued exploration in this direction could lead to standardized post-processing protocols, promoting wider adoption in additive manufacturing workflows.

4.3. Practical Implications—Business Models and Economic Perspectives

The combined post-processing technique introduces a transformative improvement in the utility of PLA for functional and market-ready applications. Beyond its technical benefits, this dual treatment method presents several practical implications with substantial relevance for consumer markets, sustainable product development, and small-scale manufacturing, all of which are relevant for business positioning. Four relevant business and market positioning implications are described in the following text.

Positioning PLA as a viable material for consumer-grade functional products. Traditionally perceived as a material suitable primarily for prototyping or aesthetic-only applications, PLA has been limited by its brittleness, low thermal resistance, and visible layer lines. However, the demonstrated mechanical improvements through annealing, together with the refined, high-gloss finish achieved via powder coating, mark a significant shift in how PLA can be positioned in the marketplace. The enhanced strength and surface uniformity allow PLA components to perform reliably in consumer-facing products, including housings, wearables, desktop accessories, and modular assemblies. This functional upgrade enables designers and small manufacturers to market PLA prints not as placeholders or mockups, but as final-use products, expanding the role of additive manufacturing in low-volume production runs and direct-to-consumer sales.

Eco-friendly, durable alternatives to conventional plastics. PLA’s bio-based origin and biodegradability have long made it an environmentally attractive material. However, its lack of durability has traditionally limited its applicability in use cases where longevity and strength are most relevant. The integration of mechanical reinforcement and surface sealing through this thermal-powder coating process addresses this gap, resulting in PLA components that are both sustainably sourced as well as structurally robust. In addition, unlike many chemical finishing methods, the powder coating process applied here is solvent-free and conducted at relatively low temperatures, minimizing environmental impact. This synergy between ecological value and enhanced functionality positions the treated PLA components as viable, eco-friendly substitutes for petroleum-based plastics in a range of consumer and industrial products, particularly those seeking to meet rising sustainability standards.

New product lines for customized end-use parts. The high-quality surface finish afforded by the powder coating process effectively masks layer lines and yields a consistent, visually polished appearance—qualities previously unattainable with standard PLA printing. This aesthetic enhancement significantly widens the design envelope for small producers and 3D printing entrepreneurs, enabling the creation of market-ready and customizable product lines. With the additional benefit of mechanical performance, treated PLA parts can now serve as functional, end-use items in applications such as personalized decor, tech accessories, promotional merchandise, and boutique consumer products. This development supports business models based on mass customization, where short production runs tailored to individual customer specifications can now be fulfilled with greater confidence in quality, durability, and visual appeal.

Cost and time efficiency as competitive advantages. This procedure, completed in a single thermal cycle, presents clear economic and operational benefits. By combining two distinct post-processing steps into one, production time is reduced and equipment utilization is streamlined, making the technique particularly suitable for small- to medium-scale fabrication environments. Material usage can also be optimized: the improvement in mechanical strength may allow reduced infill percentages during printing without compromising structural integrity, thereby saving filament and reducing print duration. These efficiencies directly translate into lower costs per unit and faster turnaround times, which enable competitive pricing and agile manufacturing workflows. As a consequence, this process offers a scalable and cost-effective approach for producing high-performance PLA parts with commercial viability.

4.4. Limitations and Considerations

Despite the promising results, the combined heat annealing and powder coating process presents several limitations that must be carefully managed. One of the primary challenges is the risk of warping and dimensional deformation during prolonged thermal exposure. PLA’s relatively low glass transition temperature makes it susceptible to softening, which can cause parts to lose dimensional accuracy if annealed beyond optimal timeframes.

Consistency in the powder coating application is another crucial factor that influences the quality of the final product. Uneven powder distribution or incomplete curing can lead to surface defects such as “globing”, reduced gloss, or compromised adhesion between the coating and the substrate. Ensuring uniform coating thickness and controlled curing conditions is crucial for achieving repeatable results.

Additionally, variability in filament formulations, printer calibration, and part geometry can affect the reproducibility of mechanical and aesthetic improvements. These factors highlight the need for standardized protocols and further testing across diverse conditions to better understand and mitigate these challenges.

Future research should also explore alternative powder coating materials and curing profiles to optimize compatibility with different PLA grades and colorants.

5. Conclusions

This study demonstrates that combining heat annealing and powder coating significantly enhances both the mechanical strength and surface aesthetics of PLA 3D-printed parts. The dual treatment enhances interlayer adhesion and produces a smooth, glossy finish, broadening the potential applications of PLA components in lightweight structural and industrial design fields. Specimen 7, corresponding to approximately 11 min of curing, was identified as the optimal processing time, as it balances strength and visual quality.

While the results are promising, limitations such as warping, deformation, and coating consistency must be addressed to ensure reliable, reproducible outcomes. The method represents a novel and practical approach for PLA post-processing, yet further validation is needed across a broader range of PLA formulations and powder coating materials.

Future work should focus on testing various part geometries and wall thicknesses to better simulate real-world applications. Additionally, exploring different powder coating types and colors will be essential to optimize the process for diverse industrial needs and aesthetic preferences. Such investigations will help refine the technique and facilitate its integration into mainstream additive manufacturing workflows.