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Abstract

The composites of polylactic acid (PLA) exhibit improved mechanical strength, biocompatibility, antimicrobial properties, and degradation, making these suitable for biomedical applications. This investigation compares the effect of various reinforcements such as tricalcium phosphate (TCP), magnesium oxide (MgO), zinc oxide (ZnO), and zirconium oxide (ZrO₂) on PLA. Various weight fractions of TCP, MgO, ZnO, and ZrO₂ were used to fabricate the PLA/TCP, PLA/MgO, PLA/ZnO, and PLA/ZrO₂ composites and compared with pure PLA. PLA/TCP, PLA/MgO, PLA/ZnO, and PLA/ZrO₂ nanocomposites exhibit enhanced tensile strength with a significant change in ductility. Further, all the composites exhibit enhanced degradation in terms of weight loss in the phosphate-buffered saline (PBS) solution. The failure analysis of deformed specimens under tensile load confirmed the improved load-carrying capabilities of PLA/ZnO as compared to other composites.

Keywords

PLA composites PLA/MgO composites PLA/ZnO composites PLA/TCP composites

Introduction

Polyester-based biodegradable composites are used in a variety of applications, especially in packaging and the biomedical industry.¹ These composites are sustainable and non-toxic. Further, these composites exhibit improved mechanical properties, making them suitable for applications that require long-lasting material.² The most important concern with using biodegradable composites is their degradation behavior.^3,4 These polymers have the advantage of degrading in a physiological environment after performing their function.⁵ Among these, polylactic acid (PLA) is one of the most used biodegradable polymers because it is biocompatible, biodegradable, low-cost, and easy to process.^6–9 These properties make it suitable for biomedical applications.^10,11 PLA composites are fabricated to achieve improved mechanical and degradation properties.^12,13

Calcium phosphate-based reinforcements such as tricalcium phosphate (TCP) and hydroxyapatite (HA) are the most common reinforcements for improving the bio-restorability, bioactivity, and strength of PLA.^14–22 Zhu et al.²³ used the nanoparticles of HA to prepare the PLA/HA composites. The results showed that PLA/HA nanocomposites exhibit improved biocompatibility and controlled capsaicin release. He et al.²⁴ fabricated the PLA/HA composites by 3D printing technology. PLA/HA composites exhibit 28% increased compressive modulus compared to neat PLA samples. Harb et al.²⁵ fabricated the PLA/TCP composites for enhanced bone regeneration. PLA/TCP filaments were prepared by high melt extrusion and then porous PLA/TCP scaffolds were prepared by 3D printing. Backes et al.²⁶ developed printable PLA/TCP composites and investigated the thermal stability and biocompatibility of these composites. The addition of TCP (25 wt%) decreased thermal stability and increased the bioactivity of composites. The results of the literature confirm that PLA/TCP is one of the promising materials for biomedical applications. Further, PLA/TCP-based composites are widely used for making biomedical devices such as screws, pins plates, etc. Hence, in this study, PLA/TCP was used as a reference material for comparing the properties of other metal-oxide-based composites.

Biodegradable metals such as Mg, Zn, Fe, and their nanoparticles have been proven effective for improving the degradation, and mechanical performance of PLA. Liu et al.²⁷ studied the antibacterial and mechanical properties of PLLA/ZnO nanocomposites. PLLA/ZnO composites with 10 wt% ZnO nanoparticles exhibit 54 times enhanced ductility as compared to pure PLA samples. This significant increase in ductility was attributed to the improved interfacial interaction between the PLA matrix and ZnO nanoparticles. Chong et al.¹¹ summarized the biological characteristics of PLA/ZnO composites. The potential of PLA/ZnO composites in biomedical applications was discussed. This review concluded that the addition of ZnO in PLA improves the degradation and antibacterial properties of PLA. Tammizi et al.²⁸ studied the effect of ZnO on the mechanical properties of PLA. The tensile strength was increased from 21.96 MPa to 23.664 MPa with the addition of ZnO nanoparticles. Zhao et al.²⁹ studied the effect of MgO on the degradability of PLA. The degradation of PLA/MgO was measured in a phosphate-buffered saline (PBS) solution. The presence of MgO increases the water uptake and accelerates the decomposition of PLA. Mr et al.³⁰ fabricated PLA/ZrO₂ composites and found that the addition of ZrO₂ into PLA is beneficial to improve the flexibility of PLA. Petousis et al.³¹ investigated that the addition of ZrO₂ into PLA increased the strength of PLA. The results show the potential of ZrO₂ as a reinforcement in the PLA matrix. Arciniega et al.³² fabricated the PLA/ZrO₂ scaffolds and investigated the biological characteristics of PLA in cell culture. The results showed that PLA/ZrO₂ samples exhibit improved cell proliferation as compared to PLA scaffolds.

Hussain et al.³³ prepared the PLA/ZnO and PLA/TCP composites and investigated the effect of ZnO and TCP on the mechanical and degradation properties of PLA. The results showed that the addition of ZnO is effective in improving the tensile strength and ductility of PLA, while the addition of TCP enhances the strength by decreasing the ductility of PLA. Further, both nanoparticles accelerate the degradation of PLA. Hussain et al.^1,34 summarized that the TCP, MgO, ZnO, and ZrO₂ nanoparticles are the most important reinforcements for the PLA matrix for improving the performance of biodegradable PLA for biomedical applications. This study is the extension of Hussain et al.³³ research work, in which the effect of MgO and ZrO₂ on PLA was investigated, and the comparison was performed between the PLA/ZnO, PLA/TCP, PLA/MgO, and PLA/ZrO₂ composites under the same conditions. Further, the failure behavior of these composites was analyzed under tensile load.

Materials and methods

Materials

Biodegradable PLA granules with a molecular weight of 55000 g/mole and a density of 1.25 g/cm³ were purchased from Xiamen Keyyuan Plastic Co., Ltd (Fujian China). This PLA exhibits a flow index of 9 g/10 min with a glass transition temperature of 50°C, and a melting temperature of 148°C. The reinforcement materials used for the fabrication of PLA nanocomposite consist of TCP, ZnO, MgO, and ZrO₂. TCP was purchased from DUKSAN Pure Chemicals Co., Ltd. Korea. ZnO, MgO, and ZrO₂ nanoparticles were purchased from Guangzhou Hongwu Material Technology Co., Ltd, China. Chloroform with a purity of 99.9% was purchased from Sigma-Aldrich US. All the characteristics of reinforcements are presented in Table 1.

Table 1.

Technical data sheet/certificate of analysis of various reinforcements provided by Guangzhou Hongwu Material Technology Co., Ltd, China, and DUKSAN Pure Chemicals Co., Ltd Korea.

Nano-grade magnesium oxide powder		Nano-grade zinc oxide powder
Color	White	Color	White
Particle size	30 – 50 nm	Particle size	20 – 30 nm
Purity	99.9%	Purity	99.9%
Ph Value	6 – 8	Loss on dry	0.4%
Chloride	0.028%	Sulfated assay	3.5
CaO	0.01%	MnO	0.0008%
Inhale iodine value	60 mg/g	PbO	0.0009%

Nano-grade zirconium dioxide powder		Tricalcium phosphate
Color	White	Particle size	20 µm
Particle size	50 nm	Purity	98%
Purity	99.9%	Chemical formula	Ca₃(PO₄)₂
Na₂O	0.003	Melting point	1000°C
Fe₂O₃	0.003	Specific gravity	3.14
Al₂O₃	0.010	Vapor Density	10.7 (air = 1)
SiO₂	0.019	Molecular weight	310.19
TiO₂	0.0008	Particle size	20 µm
CaO	0.0025

Fabrication of composite films

A solution containing 100 mL of chloroform and 4 g of PLA granules was prepared in a glass bottle. The magnetic stirrer made by VELP Scientific was used for stirring the solution at 25°C. The stirring operation was performed 24 h using the digital magnetic stirrer. Then a universal ultrasonic cleaner DSA50-Sk1 with a capacity of 1.8 L and a frequency of up to 45 kHz was used for the sonication of the mixture. This chloroform/PLA solution was poured into Petri dishes for the evaporation of chloroform. The solution poured in Petri dishes was placed at room temperature for 24 h. Then the dry samples were packed. For the fabrication of composites, various additives such as TCP, ZnO, MgO and ZrO₂ were added in the chloroform/PLA solution. Then the same process was used for the fabrication of composites. For this purpose, reinforcements in powder form were added in Chloroform/PLA solution. Then the mixture was poured in bottle and placed in water bath for sonication. After this the suspension was poured in petri dishes and dried to obtain nanocomposite films. The weight fraction of various samples is presented in Table 2. For preparation of composites Figure 1 presents the steps for fabricating composite films, which are described in detail with a schematic in published work.³³ Table 2 presents the details of samples prepared by solution casting.

Table 2.

List of samples prepared by solution casting.

Sample code	PLA	TCP	ZnO	MgO	ZrO₂
Sample code	Grams	wt.%	wt.%	wt.%	wt.%
PLA	4
PLA/10TCP	4	10
PLA/20TCP	4	20
PLA/30TCP	4	30
PLA/1ZnO	4		1
PLA/2ZnO	4		2
PLA/3ZnO	4		3
PLA/1MgO	4			1
PLA/2MgO	4			2
PLA/3MgO	4			3
PLA/1ZrO₂	4				1
PLA/2ZrO₂	4				2
PLA/3ZrO₂	4				3

Figure 1.

Schematic for the preparation of composite films.

Testing of composite films

A Fourier transform infrared (FTIR) spectroscope (IR Prestige, SHIMADZU, China), equipped with IR Solution software was used to record the infrared spectrum of composite films. Scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX) was used for the elemental and surface analysis. The interfacing binding was verified by SEM analysis. A universal testing machine (UTM) connected with a Trapezium X data acquisition system was used for tensile tests. Using the ASTM standard D882 a strip of 100 × 10 mm² was cut from each sample and tested at 2 mm/min feed rate. Stress-strain data was collected for comparison and analysis. At least 3 samples of each material were characterized and the results were reported based on average value. Material degradation in PBS was conducted following the ISO 13781 guidelines. Rectangular strips of the material having a width of 10 mm and length of 100 mm were cut and placed in Eppendorf tubes, which were then filled with PBS to maintain a ratio of at least 30 mL to 1 g of the sample. Before the immersion in PBS solution, all the samples were cleaned twice by immersion in ethanol for 10 min to remove contaminants like water drops and others. The tubes were stored in a water bath at 37°C for up to 120 days. The weight of all the samples was examined every 2 weeks.

Results and discussion

FTIR results

Figure 2 shows the FTIR spectra of various composites. The peak at 3736 cm⁻¹ is common in all composites and pure PLA. It is associated with the O-H stretching vibration, likely due to the presence of moisture, surface hydroxyl groups, or residual unreacted molecules in PLA or the additives. The peak at 2314 cm⁻¹ can be attributed to the absorption of CO₂ from the atmosphere, which is a common occurrence in FTIR spectra. The peak at 1745 cm⁻¹ represents the C = O stretching vibration of the ester carbonyl group, a characteristic peak of PLA. The peak at 1182 cm⁻¹ corresponds to the C-O stretching vibration of the ester bond in PLA. The peaks in the 700–752 cm⁻¹ range are associated with the CH₃ vibrations in the PLA chain. The similar results were presented by Zhu et al.²³

Figure 2.

FTIR spectra for pure PLA, PLA/TCP, PLA/ZnO, PLA/MgO, and PLA/ZrO₂ composite.

For the composites (PLA/MgO, PLA/ZnO, PLA/TCP), the peaks at 1745 cm⁻¹ remain prominent, indicating that the carbonyl group of PLA remains largely unchanged. ZnO seems to cause more distinct shifts in the spectrum, particularly in the 1182 cm⁻¹ and 750 cm⁻¹ regions, suggesting stronger interaction between ZnO and PLA, likely through physical or weak chemical interactions. The addition of TCP shows similar effects to ZnO, with a noticeable shift in the peak at 748 cm⁻¹. TCP may interact more with the PLA matrix, as seen by the slight changes in the vibrational modes used the nanoparticles of HA to prepare the PLA/HA composites. The results showed that PLA/HA nanocomposites exhibit improved biocompatibility and controlled capsaicin release. He et al.²⁴ presented the similar spectrum for PLA/TCP composites. Hussain et al.³³ prepared the PLA/ZnO and PLA/TCP composites and reported the same spectra for PLA. PLA/ZnO and PLA/TCP. The addition of ZrO₂ does not introduce many new peaks but causes subtle changes in the lower wavenumber region (below 1000 cm⁻¹). The peak at 700 cm⁻¹ may be associated with ZrO₂ interactions with the polymer matrix, although the interactions are not strongly visible in the higher wavenumber regions. Similar to the ZrO₂ composite, MgO leads to minor shifts in the peaks, particularly in the lower wavenumber region, with a slightly stronger peak at 752 cm⁻¹. MgO may weakly interact with PLA, causing only slight alterations to the polymer structure. The diminished peaks in the PLA/ZrO₂ composite spectrum are likely due to ZrO₂’s inert nature and lack of significant chemical interaction with PLA. ZrO₂ does not contribute much to the vibrational changes in the molecular structure of PLA, leading to a flatter spectrum without introducing new prominent peaks.

EDX results

The EDX analysis of the PLA-based nanocomposite films shown in Figures 3 and 4 shows a consistent presence of carbon and oxygen across all samples, as these elements are characteristic of the PLA matrix. Figure 3(a) represents pure PLA, carbon (C), and oxygen (O) are the predominant elements, as expected from the polymer structure of PLA, which consists of lactic acid monomers. Small traces of chlorine (Cl) are detected (1.63%), which could be attributed to contamination during sample preparation or external impurities. The presence of gold (Au, 3.23%) is due to the gold coating applied to the sample to enhance conductivity and improve the quality of the EDX measurement, as PLA is a non-conductive material. In Figure 3(b), the incorporation of TCP into the PLA matrix is evident from the detection of phosphorus (P, 9.68%) and calcium (Ca, 16.13%), the key constituents of TCP. These elements are absent in the pure PLA spectrum, clearly indicating the successful integration of TCP into the composite. The lower carbon content (32.36%) compared to pure PLA suggests that TCP replaces part of the PLA matrix. Oxygen remains significant (35.53%), reflecting both the oxygen in the PLA and the phosphate groups in TCP. As with the pure PLA sample, chlorine is present in small amounts (0.99%), likely due to contamination, and gold (5.31%) is used for coating. Figure 3(c) (Spectrum 6) highlights the incorporation of ZnO into the PLA matrix, which is evident from the presence of zinc (Zn, 0.86%). Zinc oxide is often added to PLA composites for its degradation properties and to improve mechanical strength. Interestingly, silver (Ag, 2.8%) is also detected, which suggests the possibility of silver being doped into ZnO, enhancing the antimicrobial effectiveness of ZnO. Carbon (49.32%) and oxygen (35.96%) are still major components, indicating the PLA matrix remains dominant in the composite. Chlorine (3.37%) is detected in a higher amount, possibly due to sample contamination, and gold (7.69%) is again used as a coating for EDX analysis.

Figure 3.

EDX results (a) pure PLA (spectrum 1), (b) PLA/30TCP (spectrum 4), and (c) PLA/2ZnO (spectrum 6) composite films.

Figure 4.

EDX results (a) PLA/MgO (spectrum 8) and (b) PLA/ZrO₂ (spectrum 9) composite films.

Figure 4 shows the EDX results for PLA/MgO and PLA/ZrO₂ composites. In the case of the PLA/2MgO nanocomposite, as shown in Figure 4(a) magnesium is detected at 2.37 wt%, confirming the incorporation of MgO nanoparticles into the polymer matrix. The presence of chlorine at 3.49 wt% might be a residual from the synthesis process, though its role in the composite appears minor. Gold peaks observed in the spectrum are likely due to the thin gold coating applied to improve the conductivity of the sample during EDX analysis. For the PLA/2ZrO₂ nanocomposite as shown in Figure 4(b), zirconium is present at 2.08 wt%, indicating the successful inclusion of ZrO₂ particles within the PLA matrix. Similar to the MgO sample, the carbon and oxygen levels remain almost identical, emphasizing the consistency of the PLA content. Chlorine is again detected at around 3.45 wt%, though it is not a significant component of the composite. The EDX data further confirms the overall composition, with gold peaks also present, again attributed to the coating applied during fabrication.

XRD results

XRD spectra for PLA and PLA/TCP are shown in Figure 5. The XRD peaks at 16.42° and 18.79° confirm the crystallinity of pure PLA. The sharp, well-defined peaks indicate the semi-crystalline structure of PLA, which is typical for this polymer at room temperature. The addition of TCP into PLA results in multiple diffraction peaks at specific 2θ angles (25.9°, 26.40°, 30.25°, 31.82°, 32.23°, 32.95°, 34.11°, 39.78°, 46.75°, 49.58°, 53.26°, and 63.13°). These peaks correspond to the crystalline phases of TCP, indicating its presence and successful incorporation into the PLA matrix. The wide range of peaks suggests a complex crystalline structure for the TCP within the PLA matrix.

Figure 5.

XRD results of pure PLA and PLA/TCP composite films.

In the case of PLA/ZnO nanocomposite, the XRD pattern as shown in Figure 6 shows characteristic peaks at 31.47°, 34.26°, 36.02°, 56.35°, and 62.65°. These peaks are associated with ZnO, confirming the successful incorporation of ZnO into the PLA matrix. The XRD pattern for PLA/MgO shows significant diffraction peaks at 42.9° and 62.3°, which are characteristic of MgO. These peaks confirm the crystalline nature of MgO in the PLA composite. The presence of MgO as shown in Figure 6 is further confirmed by additional peaks at 42.68°, 62.4°, 74.28°, and 78.62°, corresponding to the (200), (220), and (311) planes of the MgO structure. PLA/ZrO₂ exhibits diffraction peaks at 24.02°, 28.03°, and 31.43°, consistent with the tetragonal phase of ZrO₂. These peaks reveal the crystalline structure of ZrO₂ in the composite. The peak at 30° (2θ) corresponds to the (111) plane of ZrO₂, supporting the tetragonal structure of the incorporated ZrO₂ nanoparticles.

Figure 6.

XRD results of PLA/ZnO, PLA/MgO, and PLA/ZrO₂ composite films.

Tensile test results

The tensile test results provide valuable information about the effect of different additives influence on the mechanical properties of PLA. Pure PLA, with a tensile strength of 19.78 MPa and elongation at a break of 42.22%, demonstrates its limited ductility. When TCP is added to PLA, a significant improvement in tensile strength is observed, especially at 30 wt% tensile strength reaches 28.43 MPa. However, this comes at the expense of flexibility, as elongation drops drastically to 3.17%. For example, PLA/30TCP exhibits a very low elongation at a break of 3.166%, compared to 42.22% for pure PLA. This indicates that while TCP can reinforce the PLA matrix, it makes the material more brittle and prone to fracture under stress. This stiffening effect of TCP is typical of ceramics, which increase the strength but also induce brittleness in the composite. The stress-strain curves of various PLA/TCP composites are presented in Figure 7.

Figure 7.

Tensile test behavior of pure PLA and PLA/TCP composites.

Deformed tensile-tested specimens are shown in Figure 8. The images indicate that significant deformation occurs in the gauge length. However, some PLA specimens do not break in the mid-section. Load is concentrated close to the grip of machine jaws and finally specimen failed within this region. It means after carrying the load in gauge length, the fracture appears at the top of this portion close to the top grip. Both axial and lateral strains appear at the upper portion of the specimen and the bottom portion of the specimen remains unchanged.

Figure 8.

Failed PLA samples under tensile load.

Most of the PLA/TCP samples were deformed at the center of the specimen. It means a complete PLA/TCP sample carries the load. However, these PLA/TCP samples show less ductility as compared to pure PLA samples. Figure 9 shows the failed PLA/TCP samples.

Figure 9.

Failed PLA/TCP samples under tensile load.

ZnO as an additive, produces an interesting combination of increased tensile strength and improved elongation at break. The incorporation of ZnO in PLA/ZnO composites results in improved tensile strength in PLA/1ZnO, PLA/2ZnO, and PLA/3ZnO composites. At 2 wt%, the tensile strength peaks at 25.20 MPa while elongation reaches to 114.9%, and at 3 wt%, elongation reaches 183.87%. Notably, PLA/3ZnO exhibits a slight reduction in tensile strength. This indicates that ZnO acts as a toughening agent, allowing PLA to deform more before failure, likely due to its fine dispersion within the polymer matrix, which prevents stress concentration points from forming. The stress-strain curves of various PLA/ZnO composites is presented in Figure 10.

Figure 10.

Tensile test behavior of pure PLA and PLA/ZnO composites.

At low ZnO concentrations (1-2%), the tensile strength improves to 25.20 MPa (PLA/2ZnO), indicating a reinforcing effect. However, at higher concentrations (3%), the tensile strength slightly decreases, suggesting that excess ZnO may lead to agglomeration or limit further reinforcement. More notably, ZnO significantly increases the strain and elongation at break. This is seen in Figure 11, where the ZnO composites sustain high levels of strain before failure. The addition of ZnO allows PLA to become more ductile and able to absorb greater amounts of energy before breaking, making it more suitable for applications requiring flexibility and toughness. Each portion of these samples carries the load and these samples showed deformation after the 2 to 3 times increase in length.

Figure 11.

Failed PLA/ZnO samples under tensile load.

MgO also enhances both tensile strength and ductility. At 2 wt%, it achieves a tensile strength of 25.62 MPa with an elongation of 54.90%. The stress-strain curves of various PLA/MgO composites are presented in Figure 12. The addition of MgO nanoparticles improves the tensile strength of PLA to a lesser extent than TCP or ZnO. However, the mechanical behavior of the PLA/MgO composites is more balanced compared to the other nanoparticle types. While MgO does not enhance the ductility as dramatically as ZnO, it still leads to an improved elongation at break, reaching 62.99% for PLA/3MgO. This suggests that MgO nanoparticles provide a moderate increase in toughness without the severe reduction in ductility observed with TCP. PLA/MgO samples shown in Figure 13 showed improved load-carrying abilities as compared to pure PLA samples. The whole PLA/MgO sample carried the load and failed in the middle of the specimen.

Figure 12.

Tensile test behavior of pure PLA and PLA/MgO composites.

Figure 13.

Failed PLA/MgO samples under tensile load.

The tensile strength of the PLA/ZrO₂ composites does not exhibit a significant enhancement with the addition of ZrO₂ as shown in Figure 14. PLA/1ZrO₂, PLA/2ZrO_2, and PLA/3ZrO₂ exhibit similar or slightly lower tensile strengths compared to pure PLA. At 1% ZrO₂ (PLA/1ZrO₂), the tensile strength is 19.32 MPa, which is even slightly lower than pure PLA (19.78 MPa). As the ZrO₂ content increases to 2%, the tensile strength improves modestly to 20.17 MPa, showing a slight reinforcing effect. However, at 3% ZrO₂, the tensile strength decreases again to 19.02 MPa. This trend indicates that ZrO₂ does not significantly strengthen the PLA matrix, and higher concentrations may even reduce the reinforcing efficiency, possibly due to particle agglomeration or poor interfacial bonding between the ZrO₂ and PLA matrix. The maximum strain values for the PLA/ZrO₂ composites increase with ZrO₂ content, suggesting a slight improvement in the material’s ability to undergo deformation before failure. For PLA/2ZrO₂, the strain reaches 7.40%, which is higher than the 3.31% for PLA/1ZrO₂. However, the strain decreases slightly to 6.53% for PLA/3ZrO₂. While ZrO₂ slightly improves the strain capacity, the changes are moderate, and the overall strain values remain lower than those observed for other nanoparticle additives like ZnO. The elongation at break for the PLA/ZrO₂ composites remains relatively consistent across different ZrO₂ concentrations, with values around 19.46% to 22.25%. The elongation slightly increases as the ZrO₂ content rises, indicating a minor improvement in ductility. For PLA/3ZrO₂, the elongation at break is 22.25%, which is a marginal improvement compared to 19.46% for PLA/1ZrO₂. PLA/ZrO₂ samples shown in Figure 15 showed brittle behaviour.

Figure 14.

Tensile test behavior of pure PLA, PLA/ZnO, PLA/MgO, and PLA/ZrO₂ composites.

Figure 15.

Failed PLA/ZrO₂ samples under tensile load.

In summary, the addition of TCP generally improves tensile strength at the expense of ductility. ZnO and MgO additions result in enhanced tensile strength and increased ductility, with ZnO notably showing a notable increment in elongation at break. The impact of ZrO₂ on tensile strength is negligible. Mr et al.³⁰ reported that the addition of ZrO₂ into PLA is beneficial to improve the flexibility of PLA. Petousis et al.³¹ reported that the addition of ZrO₂ into PLA increased the strength of PLA. All the tensile test results are summarized in Table 3.

Table 3.

Tensile test results of PLA, PLA/MgO, PLA/ZnO, PLA/TCP, and PLA/ZrO₂ composites.

Sample name	Additive (wt.%)	Tensile strength (MPa)	Max % strain at the entire area	% Elongation at break
Pure PLA	–	19.78	9.51	42.22
PLA/10TCP	10	21.96	3.91	13.99
PLA/20TCP	20	24.12	6.23	8.700
PLA/30TCP	30	28.43	2.953	3.166
PLA/1ZnO	1	23.59	8.326	82.38
PLA/2ZnO	2	25.20	13.43	114.9
PLA/3ZnO	3	23.29	12.17	183.87
PLA/1MgO	1	22.95	10.32	43.92
PLA/2MgO	2	25.62	10.05	54.90
PLA/3MgO	3	24.27	4.55	62.99
PLA/1ZrO₂	1	19.32	3.31	19.46
PLA/2ZrO₂	2	20.17	7.40	19.58
PLA/3ZrO₂	3	19.02	6.53	22.25

Degradation test results

The degradation behavior in terms of weight loss % is presented in Figure 16. PLA/ZnO composites exhibit an escalating trend in weight loss with increasing ZnO content. PLA/2ZnO demonstrates the highest weight loss among the ZnO composites, suggesting a significant influence of ZnO on accelerating PLA degradation. PLA/MgO composites exhibit substantial weight loss, with higher MgO content correlating with higher degradation rates. These composites show even higher weight loss compared to pure PLA, emphasizing the potential of MgO to accelerate degradation. Zhao et al.²⁹ reported the degradability of PLA and PLA/MgO. The degradation of PLA/MgO was measured in a PBS solution. The presence of MgO increases the water uptake and accelerates the decomposition of PLA. PLA/ZrO₂ composites display moderate weight loss, with higher ZrO₂ content leading to slightly increased degradation rates. These composites occupy an intermediate position in terms of weight loss between pure PLA and the other PLA composites. All the results are summarized in Table 4.

Figure 16.

Weight loss versus time plot of pure PLA and composites.

Table 4.

Weight loss (%) of PLA, PLA/MgO, PLA/ZnO, PLA/ZrO₂ and PLA/TCP, composites.

Sample name	Solution	Immersion time (days)	Initial weight (grams)	Final weight (grams)	Weight loss (%)
PLA	PBS	120	0.3601	0.3493	2.999
PLA/10TCP	PBS	120	0.4001	0.3832	4.224
PLA/20TCP	PBS	120	0.5930	0.5635	4.975
PLA/30TCP	PBS	120	0.5570	0.5261	5.546
PLA/1ZnO	PBS	120	0.5430	0.4952	8.803
PLA/2ZnO	PBS	120	0.5790	0.5009	13.49
PLA/3ZnO	PBS	120	0.5150	0.4689	8.951
PLA/1MgO	PBS	120	0.6120	0.5280	13.72
PLA/2MgO	PBS	120	0.5830	0.4823	17.27
PLA/3MgO	PBS	120	0.5880	0.4625	21.34
PLA/1ZrO₂	PBS	120	0.5230	0.4905	6.214
PLA/2ZrO₂	PBS	120	0.5420	0.5034	7.121
PLA/3ZrO₂	PBS	120	0.5670	0.5126	9.594

SEM results

The SEM images of various composites are shown in Figure 17(a)–(e). Neat PLA polymeric film exhibits smooth, homogenous, and compact surfaces, while other composite surfaces indicate the presence of nanoparticles in the polymeric matrix. TCP films exhibit more roughness and less uniform dispersion of particles into the PLA matrix due to the high weight fraction (30 wt%) of nanoparticles. Other PLA/ZnO, PLA/MgO, and PLA/ZrO₂ samples exhibit smooth and homogenous surfaces due to the low weight fraction of ZnO, MgO, and ZrO₂ films. However, the results indicate that the ZnO, MgO, and ZrO₂ nanoparticles are compatible additives for the PLA matrix.

Figure 17.

(a-e): SEM images of pure PLA, PLA/30TCP, PLA/2ZnO, PLA/2MgO, and PLA/2ZrO₂ composite films.

Conclusion

This study compares the mechanical and degradation properties of various PLA composites with TCP, MgO, ZnO, and ZrO₂. FTIR results confirm the presence of ester functional groups in PLA molecules. SEM with EDX results confirm the presence of various reinforcements in the PLA matrix. Incorporating TCP, ZnO, and MgO into PLA matrix in improved tensile strength. The following mechanical and degradation results in comparison to PLA were summarized:

• PLA/30TCP shows the highest improvement in tensile strength (43.7%) as compared to pure PLA. PLA/2MgO and PLA/2ZnO show significant improvements of 29.5% and 27.4%, respectively. PLA/2ZrO₂ shows a small increase (2%) in tensile strength compared to pure PLA.

• PLA/3ZnO exhibits the most significant improvement in elongation at break, with a 335.4% increase compared to pure PLA. PLA/2ZnO and PLA/1ZnO also show major improvements of 172.1% and 95.1%, respectively. PLA/10TCP, PLA/20TCP, and PLA/30TCP show significant decreases in elongation.

• PLA/3MgO exhibits the highest degradation with a 611.9% increase in weight loss compared to pure PLA. PLA/2MgO and PLA/2ZnO also show significant increases in degradation, with improvements of 476.0% and 349.8%, respectively. PLA/30TCP exhibits an 85.0% increase in weight loss.

• PLA/2MgO and PLA/2ZnO offer superior mechanical and degradation properties, making them the best materials for applications requiring both enhanced mechanical properties and faster degradation.

Footnotes

Declaration of conflicting interests

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

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2025R41), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. The authors extend their appreciation to the Deanship of Scientific Research at Northern Border University, Arar, KSA for funding this research work through the project number “NBU-FFR-2025-2505-07”.

ORCID iD

Sami Ullah Khan

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Comparative analysis of mechanical properties and degradation behavior in PLA composites with TCP,ZnO,MgO,and ZrO 2

Abstract

Keywords

Introduction

Materials and methods

Materials

Fabrication of composite films

Testing of composite films

Results and discussion

FTIR results

EDX results

XRD results

Tensile test results

Degradation test results

SEM results

Conclusion

Footnotes

Declaration of conflicting interests

Funding

ORCID iD

References