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Article

Effect of Surface Treatment of Nano-Magnetite Particles on PLA/PBAT Composites

by
Le Zhang
1,
Wenbo Wang
2,
Kun Li
1,
Jingbo Chen
1,*,
Yunlong Xu
2,
Zhibo Zhao
2,
Yanan Li
1,2 and
Long Yu
1,2,*
1
School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001, China
2
Institute of Chemistry, Henan Academy of Sciences, Zhengzhou 450001, China
*
Authors to whom correspondence should be addressed.
J. Compos. Sci. 2025, 9(11), 592; https://doi.org/10.3390/jcs9110592 (registering DOI)
Submission received: 29 September 2025 / Revised: 27 October 2025 / Accepted: 29 October 2025 / Published: 1 November 2025
(This article belongs to the Section Composites Manufacturing and Processing)
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Abstract

In this work, polylactic acid (PLA)/poly(butylene adipate-coterephthalate) (PBAT) composites containing nanomagnetite particles were developed for electromagnetic shielding. The nanomagnetite particles acted not only as a conductive filler but also as a reinforced agent and compatibilizer for PLA/PBAT blends. The effect of surface treatments by the silicon coupling agent (SCA) under different pH conditions and with other substances (silica and dopamine (DA)) were investigated in particular. The composites were prepared by thermal mixing and characterized by Fourier-transform infrared spectroscopy (FTRI), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transparency electron microscopy (TEM) and tensile testing. The results show that the interface between the PBAT spheres and the PLA matrix was improved after the addition of magnetite particles treated with SCA or PDA. It is interesting to find that under acidic conditions, SCA acted more efficiently due to the chemical reaction of SCA with the hydroxyl groups on the surface of the magnetite particles, which resulted in chemical improvement. Tensile strength increased about 20%, while elongation also increased about 15%. The fracture surface under SEM clearly showed plastic deformation, which contributed to an improvement in mechanical properties, especially toughness.

1. Introduction

Polylactic acid (PLA) and poly (butylene adipate-coterephthalate) (PBAT) are two of the most popular biodegradable polymers on the market, and their blends offer a balance of mechanical properties [1,2]. PLA/PBAT offers a good balance of performance, since PLA is known for its tensile strength and processability, while PBAT has flexibility and good toughness [3,4]. The addition of conductive materials into PLA/PBAT blends offers a promising route to develop environmentally friendly and effective EMI (electromagnetic interference) shielding materials for various applications, particularly for disposable packaging for sensitive electronic components. Electromagnetic interference shielding/absorbing materials are crucial for protecting equipment from unwanted electromagnetic radiation or interference, ensuring reliable operation across various industries [5,6]. The advantages of polymeric EMI shielding materials include being lightweight, being low-cost, having good processability, and having tunable conductivities over a wide range. The most popular conductive materials used for this popup are carbonic fillers [7], including carbon black (CB) [8], graphite [9], graphene [10], carbon fibers (CFs) [11], carbon nanofibers (CNFs) [12], and carbon nanotubes (CNTs) [13,14,15,16].
To increase mechanical and electrical and thermal properties, a better dispersion of filler in polymer composites is important [17,18,19]. Miks Bleija et al. [20] developed biodegradable poly(butylene succinate-co-adipate) (PBSA) nanocomposites incorporating various carbon nanofillers via solvent casting. The composites, especially those with multi-walled carbon nanotubes and nanostructured carbon black, exhibited significant electrical conductivity and electromagnetic shielding efficiency in microwave and terahertz bands, demonstrating strong potential for sustainable antistatic and EMI shielding applications. Kashi et al. [21] studied the effect of graphene nanoplatelets (GNPs) dispersed in poly lactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT)on the electromagnetic properties and electromagnetic interference shielding effectiveness (SE) via melt mixing. It was found that with a content of more than 6 wt% of GNP, PLA nanocomposites showed significantly higher dielectric loss than PBAT nanocomposites, although pure PLA led to lower dielectric loss than pure PBAT. This was attributed to the dispersion state of GNPs in the two matrices, detected in morphological studies. More recently, Zhang et al. [22] developed conductive composites of PLA/PBAT containing carbon black (CB) prepared by melt blending. They found that compared to PLA/CB and PBAT/CB, the PLA/PBAT/CB composite had a lower percolation threshold, especially when the CB mainly distributed PBAT, which promoted a co-continuous structure and improved conductive pathways and electrical properties. Wang et al. [23] reported PLA/PBAT blends containing carbon nanotubes (CNTs) and epoxy-functionalized ionomer (EFI). It was revealed that EFI can improve the interaction force between PLA and PBAT by inducing the interfacial crosslink reaction. EFI can also refine the dispersion of CNT in composites due to the noncovalent force between EFI and CNT and promote the formation of the filler network inside composites; when the CNT content is 3 wt%, the composite has a tensile strength of 30.4 MPa and an elongation at break of 279.3%, which are 30% and 48% higher than those of the PLA/PBAT blend, and it also exhibits good dielectric properties with a dielectric constant of 25.2 and a dielectric loss of 11.6.
Other substances such as metals [5] and conductive polymers [24] were also used to prepare the EMI materials. The advantages of this kind of EMI shielding materials include their lightweight, low cost, good processability, and tunable conductivities over a wide range [25]. For example, Balakrishnan et al. [26] prepared PLA films loaded with expanded graphite/Fe3O4 through the solution casting process and reported a total EMI SE of around 9 dB. Other studies demonstrated the excellent microwave-absorbing properties of PLA loaded with hybrid materials of GNP/Fe3O4 [27] and FeSiAl/Fe3O4/GNP [28]. Magnetite Fe3O4 particles have an inverse spinel structure with mechanical and thermal stability and lower costs. Applying magnetite to develop biodegradable EMI materials is feasible due to the fact that rigid mineral particles can also reinforce the biodegradable blends because the weaker mechanical properties of these biodegradable materials are well recognized.
Previous research [29] has shown that pH played an important role in the formation of (Fe3O4) nanoparticles. When the pH value was 6 and 9 in a solution containing iron salts, II and III ions produced ε-Fe2O3, while a pH value of 11 produced the magnetite phase (Fe3O4). Due to magnetite (Fe3O4), surfaces have hydroxyl groups (–OH) that can undergo protonation or deprotonation depending on the pH value. The point of zero charge (PZC) of magnetite was found to typically be around pH 6–7. At pH < PZC, the surface is positively charged, while at pH > PZC, the surface is negatively charged. However, when silicon couple agent (SCA) was used to improve the interface between magnetite particles and the polymer matrix, the acidic conditions were able to enhance the dehydration of the SCA, which resulted in an enhancement of the reaction between the SCA and the hydroxyl group on the magnetite surface. Therefore, magnetite added to a polymer matrix under acidic conditions is expected to show a better homogeneous distribution during thermal processing [30,31]. On the other hand, pure magnetite magnetic nanoparticles are prone to aggregation due to their high surface energy and strong magnetic interactions, which significantly impact their dispersibility and subsequent applications. The introduction of polydopamine (PDA) or silica (SiO2) coating layers can effectively enhance the dispersion stability of Fe3O4 nanoparticles. Moreover, the surfaces of PDA and SiO2 are rich in various reactive functional groups, providing convenient opportunities for further surface functionalization modifications. This two-step process ensures the functionalization of magnetite nanoparticles with dopamine for compatibility with the polymer matrix and subsequent silane coupling for further surface modifications.
The aim of this work is to develop PLA/PBAT composites containing nanomagnetite particles used for electromagnetic shielding. The work reported in this paper is particularly focused on the effect of surface treatment by silicon couple agent (SCA) under different pH conditions and in the presence of polydopamine (PDA) on the morphologies and interface between the polymeric matrix and magnetite, as well on the mechanical properties. The composites were prepared by thermal extrusion and characterized by FTRI, DSC, TGA, DMA, SEM and tensile testing.

2. Materials and Methods

2.1. Materials and Pretreatment

Commercially available PLA was purchased from NatureWork (USA) (4032D), and PBAT was from BASF (C1200) (German). Silicon couple agent (KH560, γ-glycidoxy propyl trimethoxy silane), magnetite, ferric chloride hexahydrate, ferrous sulfate heptahydrate, ammonium hydroxide solution, tetraethyl silicate, glacial acetic acid (GA acid), dopamine hydrochloride, and tris (hydroxymethyl) aminoethane (Tri) were purchased from Shanghai Macklin Biochemical (Shanghai, China).
Both PLA and PBAT were dried in a vacuum oven at 60 °C for 12 h before application.

2.2. Sample Preparations

2.2.1. Nano-Magnetite Particle Preparation

First, we weighed 32.436 g of iron chloride hexahydrate (FeCl3·6H2O) and 16.681 g of iron (II) sulfate heptahydrate (FeSO4·7H2O), and then dissolved them in 450 mL of deionized water in a three-neck flask. The solution was purged with nitrogen gas to remove dissolved oxygen. We slowly added 40 mL of ammonia solution (NH3·H2O) and adjusted the pH to 9–10 using an additional amount of ammonia solution. We maintained the reaction at 70 °C for 10 min under nitrogen protection. Finally, the obtained precipitate was washed with deionized water, the product was collected using a magnetic separator and the product was dried under vacuum or in an oven.

2.2.2. Surface Treatment of Magnetite Particle

Figure 1 shows the scheme for the surface modifications of magnetite particle:
  • Surface treatment with KH560: An amount of 1 g of Fe3O4 particles was added to a mixed solution of 300 mL of water and 300 mL of anhydrous ethanol, followed by stirring and ultrasonication for 10 min under nitrogen protection. An amount of 3.5 mL of KH560 was added and the mixture was ultrasonicated for 30 min at 50 °C for 6.5 h to achieve surface modification. The pH of the solution was adjusted to an acidic condition by adding 60 mL of glacial acetic acid, and the subsequent steps (stirring, ultrasonication, reaction, and drying) were performed identically to the above procedure. The product was collected using a magnet, washed and dried under a vacuum at 60 °C for 2 h.
  • Surface treatment with KH560 and dopamine: An amount of 1.0 g of Fe3O4 nanoparticles was dispersed in 250 mL of deionized water containing 10 mM Tris under stirring and ultrasonic treatment for 30 min. Subsequently, 1.0 g of dopamine was added to the suspension and the reaction was allowed to proceed for 4 h under stirring. The resulting dopamine-coated Fe3O4 nanoparticles were collected using a magnet, thoroughly washed and dried. Finally, the nanoparticles were treated with KH560, and this was repeated after the procedure.
  • Surface treatment with KH560 and silica: We weighed 1 g of Fe3O4 nanoparticles and dispersed them in a mixture of 280 mL of anhydrous ethanol and 70 mL of deionized water. The mixture was subjected to ultrasonic agitation for 30 min to ensure homogeneous dispersion. The pH of the suspension was adjusted to 9 using an ammonia solution (NH4OH) under stirring. Then, 2 mL of tetraethyl silicate was added dropwise to the solution. The reaction was allowed to proceed with continuous stirring at room temperature for 12 h to facilitate silica deposition on the Fe3O4 surface. The resulting core–shell nanoparticles (Fe3O4@SiO2) were collected using a magnet, separated from the supernatant, and washed several times with ethanol and deionized water to remove unreacted species. The purified product is dried in an oven, resulting in a yellowish–brown powder. Finally, the nanoparticles were treated with KH560, and this was repeated after the procedure.

2.2.3. Mixing and Specimen Preparation

The PLA/PBAT blends and composites containing the nanomagnetite particles treated in different ways were thermally prepared in an internal mixer (Shanghai Kaichang Electromechanical Technology Co) (Shanghai, China). The specimen (size: 25 × 5 × 1) used for the tensile tests was compressed into a dumbbell sample using a hot compressor (Craftsman Mechanical Equipment K14L20VHE, Zhengzhou, China) at 180 °C with 1000 kg pressure for 60 s. All the samples were about 2.0 mm. Table 1 lists sample cords and formulations.

2.3. Characterizations

Fourier transform infrared (FTIR) spectroscopy: Possible chemical interactions between magnetite and SCA were detected by FTIR (Vertex-70, Bruck, German). FTIR spectra were collected with 64 scans, and the spectral range and spectral resolution were 4000-600 cm−1 and 4 cm−1, respectively.
Scanning electronic microscopy (SEM): The cryofracture and fracture surfaces of the samples were examined using a scanning electron microscope (TM4000Plus, Hitachi, Japan) at 10 kV. The test bar was coated with gold for one minute by magnetron sputtering (MSP-1S, Shinkuu, Japan) prior to observation. The fracture surfaces were prepared by broking the samples after immersion in liquid nitrogen.
Transparency electronic microscopy (TEM): A TEM (FEI/Talos F200S, USA) with EDM was used to study the distribution of Fe in the polymer. The samples were cut by ultramicrotome (Leica EM UC7 FC7) (German) under frozen conditions.
Differential scanning calorimetry (DSC): The thermal properties of the starch-grafted copolymer were measured using a differential scanning calorimeter (PerkinElment 8500, The Netherlands). Amounts of approximately 8 mg of the samples were sealed in aluminum pans, and their thermal history was removed by first heating them to 200 °C, keeping them at that temperature for 3 min and then subjecting them to a colder temperature of 30 °C at 15 °C/min. The glass transition temperature (Tg), the cold crystallization temperature (Tcc), and the melting temperature (Tm) were measured during heating from 30 °C to 200 °C at 15 °C/min.
Thermal–Gravimetric Analysis (TGA): The thermal stability of PLA/PBAT mixtures containing magnetite treated in different ways was measured via thermogravimetric analysis (STA8000, Perkin Elmer, The Netherlands). The samples were heated at a rate of 15 °C/min from 30 °C to 800 °C under nitrogen gas.
Tensile Testing: Mechanical Properties were evaluated with a tensile testing apparatus (Sansi UTM6104, Shenzhen, China) following the ASTM D648-23 standard with a crosshead speed of 2 mm/min. The dumbbell-shaped specimen is compatible with the ASTM D638 Type V standard. Seven specimens were repeatedly tested to obtain average values.

2.4. Statistical Analysis

According to the test standard, the measurements of the particle size of the PBAT phase in the blends were repeated three times, and the results were expressed as means ± SDs. Mechanical properties were assessed using seven specimens and variance analysis was performed using SPSS 25 software at a significance level of p < 0.05. When p > 0.005, the p > 0.005, results are presented as a, b, c, etc.

3. Results

3.1. Surface Chemistry

The magnetite samples with and without SCA (KH560) surface treatment were studied by FTIR and TGA. Figure 2a shows the FTIR spectra of magnetite with and without SCA (KH560) treatment. According to the literature [32,33], the magnetite FTIR spectrum exhibits two strong infrared absorption bands at 570 and 390 cm−1. These bands can be assigned to the Fe–O stretching mode of the tetrahedral and octahedral sites (the band at 570 cm−1) and to the Fe–O stretching mode of the octahedral sites (the band at 390 cm−1). The new peaks include one appearing at 1100 cm−1, which is the antisymmetric absorption peak of the Si-O-Si bond, and one near 800 cm−1, which is the symmetrical contraction vibration of the Si-O-Si bond [34]. These new peaks are contributed by SCA KH560, indicating that the magnetite was successfully coated by SCA. Figure 2b shows the TGA curves of magnetite with and without SCA (KH560) surface treatment. The weigh loss of pure magnetite particles is about 6.78%, which then increased to about 10.09%. The weight loss for the sample treated later on with PDA was increased to about 15.41%. The amount of weight loss could be indicate the amount of the component adhered onto the Fe3O4 surface.

3.2. Morphologies and Fracture Surfaces

Figure 3 shows the morphologies of the cryofractured surfaces of PLA 70/PBAT 30 mixes either containing or not containing magnetite with various surface treatments. It can be seen that PLA is presented as a continuous matrix, while PBAT is a separation phase in the form of spherite domain particles distributed in the matrix, exhibiting typical sea-island morphologies. The particle size of the PBAT domains is about 3–5 µm. The phase separation and the gaps between the PBAT particles and PLA matrix are clearly visible in the blends, which is expected since they are immiscible and incompatible. In particular, the blend of PLA/PBAT without filler showed many holes (marked by the dish line with arrow), i.e. caves, as a result of the PBAT domains being separated from the PLA matrix. Almost none of these kinds of holes appeared on the surface of PLA/PBAT blends containing magnetite treated with polydopamine (PDA), indicating an improvement in the interface. There are many plastic deformations (see the white line with an arrow) on the surface of the mixture containing PDA. It can be explained that PDA could act as a plasticizer for the PLA matrix. It was observed that the blends containing magnetite treated with silicon coupler (SCA) decreased the number of holes, particularly due to the higher magnetite content. It is interesting to find that there were also some plastic deformations observed on the surface containing a higher magnetite content. These phenomena confirm that magnetite treated with both PDA and SCA under acidic conditions improved the interface between PLA and PBAT. It should be noted that there were no magnetite particles identified under SEM, probably due to the lower concentration (1%) and smaller particle size, which meant that they could not be distinguished from smaller PBAT particles.
The distribution of Fe particles in the PLA/PBAT blends was investigated by TEM (see Figure 4a,b). In the blend without magnetite, the PLA presented as a continuous matrix, while PBAT was a separation phase distributed in the matrix, exhibiting typical sea-island morphologies with a particle size of about 3 µm. These phenomena are similar to the ones observed under SEM (see Figure 3). The Fe particles, especially those aggregated together, were clearly identified in the blends containing magnetite. The well-distributed particles in are hard to be observed at the nano-scale in this work. It is interesting to find the Fe particles were mainly distributed in the PBAT phase. A possible explanation is that PBAT has a lower melting point; thus, the Fe particles were likely firstly distributed in it, and then PBAT had better compatibility with the Fe particles. Similar phenomena have been reported for different systems [35,36]. Further investigation will be carried out to confirm this.
Figure 5 shows the EDM images of the PLA 70/PBAT 30 blends containing magnetite with surface treatment using KH and PDA, in which the green points are Si elements and the red points are Fe elements. As expected, Si particles are homogeneously distributed in the polymer matrix. Fe particles can also clearly be identified in the polymer matrix in even smaller sizes. The densities of the Fe particles distributed in the polymer matrix in the different ranges are different since the Fe distributions in PLA and PBAT are different (see Figure 3). Some aggregated Fe can be found in the blends containing magnetite with surface treatment using KH and PDA.

3.3. Thermal Properties

The thermal behaviors of PLA/PBAT blends containing magnetite treated in different ways were studied by DSC (see Figure 6). The DSC thermograms of the various blends present thermal characteristics similar to those of pure PLA since the thermal signals of PBAT were very weak. Specifically, the glass transition temperature (Tg), the cold crystallization temperature (Tcc) and the melting temperature (Tm) were in the range of approximately 50~55 °C, 90~95 °C, and 169~172 °C, respectively. Table 2 summarizes the thermal properties of PLA/PBAT blends containing magnetite treated in different ways. It can be seen that the Tg values of various PLAs remained largely unchanged after adding magnetite. A decrease in Tc was observed after additional magnetite addition, and the amount of Tc gradually further decreased with increasing magnetite content, suggesting that magnetite may act as a nucleating agent. It is interesting to find that the magnetite treated tolerated the acidic conditions with greater efficiency to enhance the Tc content, indicating that the interface was further improved. There is no observable difference between the two PLA melting points (a and b). The melting peak of PBAT at approximately 120 °C was offset or inhibited by the cold crystallization of PLA in the blends.
The TGA results (Figure 7) show the effect of additional magnetite with various surface treatments on the thermal stability of PLA. It can be seen that the decomposition temperature of polymers decreased with additional magnetite. Similar results have previously been reported [37,38] due to the several stages of the thermal decomposition process and the significant reduction in the thermal stability of polymer matrix under the influence of magnetite. Table 2 also provides the onset temperatures of the various composites and residue. Generally, with increasing magnetite content, the decomposition temperatures were decreased. All the surface modifications reduced the trend of decrease, indicating that surface modification improved the stability of the polymers. As expected, the amoubt of residue was increased slightly with the addition of magnetite.

3.4. Mechanical Properties

The effect of magnetite with and without surface treatment on the mechanical properties of the PLA/PBAT mixture is shown in Figure 8. It can be seen that the modulus slightly decreased after the addition of magnetite which was unexpected. Further investigation will be carried out. There was no observable difference in the tensile properties of the blend after the native magnetite was added without any surface treatment. It can observed that all surface treatments increased both tensile strength and elongation, which was expected due to the contribution of the surface improvement. It is interesting to find that the mixture containing magnetite with surface treatment under acid conditions showed the highest tensile strength and elongation. These phenomena can be explained by the fact that the acidic conditions enhanced the dehydration of the SCA, which resulted in an enhancement in the reaction between the SCA and the hydroxyl group on the magnetite surface. The PDA also showed better elongation since lower-molecular-weight PDA can act as a toughness agent. The results corresponded with those of the SEM observation (see Figure 3).

4. Discussions

Figure 9 is a schematic representation of the surface reaction of SCA with hydroxyl groups on the magnetite surface under acidic conditions. Ferric tetroxide and the silane coupling agent KH560 reacted in a mixed solution of water and ethanol under a nitrogen atmosphere. The silane coupling agent was hydrolyzed and reacted with the hydroxyl groups on the surface of ferric tetroxide, resulting in ferric tetroxide particles with epoxy functional groups on their surface.

5. Conclusions

PLA/PBAT composites containing nanomagnetite particles were thermally prepared. The nanomagnetite particles acted not only as a conductive filler but also as a reinforced agent and compatibilizer for PLA/PBAT blends. The interface between PBAT spheres and the PLA matrix was improved after the addition of magnetite particles treated with SCA and PDA. It was interesting to find that under acidic conditions, SCA acted more efficiently to improve the interface and performance of the PLA/PBAT blends as a result of the chemical reaction of SCA with the hydroxyl groups on the surface of magnetite particles, which resulted in the chemical improvement. There were many plastic deformations on the surface of the mixture for the PLA 70/PBAT 30 blends containing magnetite with various surface treatments, especially for the one containing PDA. Tensile strength increased by about 20%, while elongation also increased about by 15%. The fracture surface, observed under SEMm clearly showed plastic deformation, which contributed to the improvement in mechanical properties, especially toughness. The silane coupling agent was hydrolyzed and reacted with the hydroxyl groups on the surface of ferric tetroxide, resulting in ferric tetroxide particles with epoxy functional groups on their surface, especially under acidic conditions. The distribution of Fe particles in the PLA/PBAT blends was clearly identified by TEM and EDM. The densities of the Fe particles distributed in the polymer matrix in the different ranges were different since the Fe distributions in PLA and PBAT were different.

Author Contributions

Conceptualization, L.Z., J.C. and L.Y.; methodology, L.Z., W.W. and K.L.; validation, Z.Z. and Y.L.; formal analysis, L.Z. and L.Y.; resources, K.L. and J.C.; data curation, L.Z. and Y.X.; writing—original draft preparation, L.Z. and L.Y.; writing—review and editing, L.Z. and L.Y.; supervision, J.C. and L.Y.; project administration, K.L.; funding acquisition, Y.X. and L.Y. All authors have read and agreed to the published version of the manuscript.

Funding

The authors of Institute of Chemistry would like to acknowledge the financial support provided by Henan Academy of Sciences High Level Talent Research Start-up Project Funding (No. 232018005, 231818054), Joint Fund of Henan Province Science and Technology R&D Program (No. 225200810010), Key Scientific and Technological Project of Henan Province (No. 242102231055), and Fundamental Research Fund of Henan Academy of Sciences (No. 240618055).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Scheme of surface modifications of magnetite particle.
Figure 1. Scheme of surface modifications of magnetite particle.
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Figure 2. FTIR spectra (a) and TGA curves (b) of magnetite with and without SCA (KH560) treatment.
Figure 2. FTIR spectra (a) and TGA curves (b) of magnetite with and without SCA (KH560) treatment.
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Figure 3. Morphologies of cryofracture surfaces of PLA 70/PBAT 30 blends containing no magnetite or magnetite with various surface treatments: (a) PLA/PBAT blend; (b) blend/Fe-PDA, (c) blend/Fe-KH0.5, and (d) blend/Fe-KH3.
Figure 3. Morphologies of cryofracture surfaces of PLA 70/PBAT 30 blends containing no magnetite or magnetite with various surface treatments: (a) PLA/PBAT blend; (b) blend/Fe-PDA, (c) blend/Fe-KH0.5, and (d) blend/Fe-KH3.
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Figure 4. TEM images of PLA 70/PBAT 30 blends either containing no magnetite (a,b) or containing magnetite with surface treatment using KH ((c) Blend/Fe-KH1) and PDA ((d) blend/Fe-PDA).
Figure 4. TEM images of PLA 70/PBAT 30 blends either containing no magnetite (a,b) or containing magnetite with surface treatment using KH ((c) Blend/Fe-KH1) and PDA ((d) blend/Fe-PDA).
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Figure 5. EDM images of PLA 70/PBAT 30 blends containing magnetite with surface treatment using KH and PDA: the green points are Si elements and the red points are Fe elements.
Figure 5. EDM images of PLA 70/PBAT 30 blends containing magnetite with surface treatment using KH and PDA: the green points are Si elements and the red points are Fe elements.
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Figure 6. Effect of magnetite with various surface treatments on the thermal behaviors of PLA.
Figure 6. Effect of magnetite with various surface treatments on the thermal behaviors of PLA.
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Figure 7. Effect of magnetite with various surface treatments on the thermal stability of PLA.
Figure 7. Effect of magnetite with various surface treatments on the thermal stability of PLA.
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Figure 8. Tensile strength and elongation of PLA 70/PBAT 30 blend either not containing magnetite or containing magnetite with or without various surface treatments. When p > 0.005, results are presented as a, b, c.
Figure 8. Tensile strength and elongation of PLA 70/PBAT 30 blend either not containing magnetite or containing magnetite with or without various surface treatments. When p > 0.005, results are presented as a, b, c.
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Figure 9. Schematic representation of the surface reaction of SCA with hydroxyl groups on the surface of magnetite under acid conditions.
Figure 9. Schematic representation of the surface reaction of SCA with hydroxyl groups on the surface of magnetite under acid conditions.
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Table 1. Sample codes and formations.
Table 1. Sample codes and formations.
Sample CodePLA/PBAT
(Ratio)		Fe3O4
(Adding %)		KH560
(Ratio) *		GA Acid
(pH Value)		SiO2
(Ratio) *		DA
(Ratio) *
PLA/PBAT70/3000000
Blend/Fe-KH370/3033.54.500
Blend/Fe-KHSiO270/3013.5020
Blend/Fe-KHPDA70/3013.5001
* Ratios of added substances (KH, SiO2, DA) to the Fe3O4 content (Fe3O4/-).
Table 2. Effect of magnetite with various surface treatments on the thermal behaviors (DSC) and stability (TGA) of PLA.
Table 2. Effect of magnetite with various surface treatments on the thermal behaviors (DSC) and stability (TGA) of PLA.
Sample CodeTg
°C		Tcc
°C		Tm
°C		Ton
°C		Residue
%
PLA/PBAT63111.55168.91317.412.12
Blend/Fe62.55112.55169.57272.463.42
Blend/Fe-KH62.75112.59169.22-3.52
Blend/Fe-KH0.562.25112.83169.04311.523.40
Blend/Fe-KH162.11110.98168.38262.435.64
Blend/Fe-KH362.25110.52168.72325.173.44
Blend/Fe-KHSiO262.85111.18168.61270.536.21
Blend/Fe-KHPDA62.85110.49168.51268.833.42
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MDPI and ACS Style

Zhang, L.; Wang, W.; Li, K.; Chen, J.; Xu, Y.; Zhao, Z.; Li, Y.; Yu, L. Effect of Surface Treatment of Nano-Magnetite Particles on PLA/PBAT Composites. J. Compos. Sci. 2025, 9, 592. https://doi.org/10.3390/jcs9110592

AMA Style

Zhang L, Wang W, Li K, Chen J, Xu Y, Zhao Z, Li Y, Yu L. Effect of Surface Treatment of Nano-Magnetite Particles on PLA/PBAT Composites. Journal of Composites Science. 2025; 9(11):592. https://doi.org/10.3390/jcs9110592

Chicago/Turabian Style

Zhang, Le, Wenbo Wang, Kun Li, Jingbo Chen, Yunlong Xu, Zhibo Zhao, Yanan Li, and Long Yu. 2025. "Effect of Surface Treatment of Nano-Magnetite Particles on PLA/PBAT Composites" Journal of Composites Science 9, no. 11: 592. https://doi.org/10.3390/jcs9110592

APA Style

Zhang, L., Wang, W., Li, K., Chen, J., Xu, Y., Zhao, Z., Li, Y., & Yu, L. (2025). Effect of Surface Treatment of Nano-Magnetite Particles on PLA/PBAT Composites. Journal of Composites Science, 9(11), 592. https://doi.org/10.3390/jcs9110592

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