Next Article in Journal
A Year-Long Comparison of Dentin Bond Strength Using the Co-Curing Technique and Conventional Adhesive Application
Previous Article in Journal
Computational Approach for Optimizing Resin Flow Behavior in Resin Transfer Molding with Variations in Injection Pressure, Fiber Permeability, and Resin Sorption
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
J. Compos. Sci.
Volume 9
Issue 3
10.3390/jcs9030130
jcs-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Proving Partial Miscibility in Poly(L-lactic acid)/Ethylene-Vinyl Acetate Copolymer Blends Using the Spherulite Observation Method

by
Rokibul Hasan Rumon
,
Chisato Nara
,
Kai Xu
and
Atsuhiro Fujimori
*
Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
*
Author to whom correspondence should be addressed.
J. Compos. Sci. 2025, 9(3), 130; https://doi.org/10.3390/jcs9030130
Submission received: 11 February 2025 / Revised: 8 March 2025 / Accepted: 9 March 2025 / Published: 11 March 2025
(This article belongs to the Section Polymer Composites)
Browse Figures
Versions Notes

Abstract

:
Poly(L-lactic acid) (PLLA) was blended with an ethylene-vinyl acetate (EVA) copolymer, which is generally recognized as a phase-separated system. The interactions between these polymer species were examined via spherulite observation. The PLLA/EVA blend was concluded to be a partially miscible system. The onset temperature for the crystallization of PLLA, as the crystalline polymer, systematically changed when PLLA was blended with EVA at various ratios. The glass transition behavior of EVA was almost absent in the thermogram when the PLLA:EVA blend ratio was greater than 2:1. The spherulite size distribution of PLLA became finer as the PLLA:EVA ratio was changed from 3:1 to 2:1 to 1:1, and observing spherulites was difficult when the blend ratio was 1:2. Because the nucleation position was different each time during the repeated melting/crystallization of spherulites, this system exhibited homogeneous nucleation. In addition, in a plot of the spherulite size versus the crystallization time, the inclination angle changed between the PLLA/EVA = 3:1 and 2:1 blends, and the critical ratio at which the crystallization behavior changed was estimated.

Graphical Abstract

1. Introduction

Many materials that exist in the world, including industrial and natural materials, are composite materials [1,2,3,4,5,6,7]. In the academic field of “chemistry”, pure substances are synthesized, and the yield is determined. However, composite materials that exist in nature do not separate into their respective components and demonstrate functionality at appropriate ratios and compositions [8]. Elucidating the interactions between the component molecules of composite materials is important [9,10,11]. Some industrial materials may have excellent physical properties owing to compositions and ratios discovered through trial and error. Therefore, evaluating the molecular-level interactions that produce outstanding physical properties may lead to the development of improved functional materials in the future [12].
In the context of polymer blends [13,14,15], including polymer alloys [16] encompassing organic/inorganic hybrid systems [17,18] and polymer/filler composites [19], determining whether the system is optimally mixed or has achieved phase separation is of paramount importance [20]. Ideally, mixed systems [21,22] may produce properties that cannot be achieved using single components. Phase-separated systems [23] may produce patterned materials that can be used in electrical circuits [24,25] and lithography [26,27] and sometimes even materials that mimic biological assemblies [28,29]. In addition, some systems are partially miscible [30,31,32]. Because they are not completely phase-separated but show partial miscibility, new materials that exhibit the properties of both mixed and phase-separated systems are expected to be developed.
Poly(L-lactic acid) (PLLA) [33,34] is a biodegradable crystalline polymer that can form spherulites having a clear crystal habit [35]. Its weakness is that the processed material is “brittle” [36,37], which is thought to be due to the small density difference between the crystalline and amorphous regions and the relatively poor flexibility of the amorphous parts [38,39]. Ethylene-vinyl acetate (EVA) copolymers [40,41] are known as amorphous polymers that exhibit elastomeric properties [42] and generally used with a vinyl acetate proportion of 10–40% [43]. EVA is flexible, crack-resistant, glossy, and transparent [44,45] and could be mixed with PLLA to eliminate the weaknesses and maintain the advantages of PLLA [46] (Figure 1a). However, PLLA/EVA blends are generally recognized as phase-separated systems in which no interactions occur between the two components [47]. In this regard, some reports have indicated partial miscibility of the two components [48]; however, no systematic evidence has been obtained.
In this study, we focused on the versatility and deliberately used mesoscopic higher-order structure analysis, that is, spherulite observation, to verify the miscibility or phase separation of PLLA/EVA blends. To determine whether PLLA and EVA interact with each other, we focused on the melting/crystallization behavior and spherulite size and established a method for determining this type of phase status. In general, miscibility/immiscibility can be determined based on the presence or absence of a shift in the crystallization peak in differential scanning calorimetry (DSC) thermograms at various ratios, indicating an interaction between the two components [49] (Figure 1b). Multiple investigations through Dynamic Mechanical Analysis (DMA) have revealed that PLA/EVA blends exhibit notable phase interactions [50,51]. An analysis of storage modulus and damping parameters was carried out and compared with the rule of mixtures model, where a decline in peak height points to the miscibility of PLLA/EVA blends. PLLA combined with EVA, which has a high vinyl acetate content, exhibits a negative Flory–Huggins interaction parameter, indicating that the resulting blends are thermodynamically stable and miscible [52].
In addition, in a mixed system that can form a monolayer/Langmuir film on the water surface [53,54], the ideal miscibility/phase separation can be determined based on the continuous change in the collapse pressure according to the mixture ratio in the surface-pressure/area isotherm [55]. The miscibility analysis in this study, which mainly focused on spherulite observation, can be used as a derivative of the analysis using DSC thermograms and can add versatility to analytical methods. In addition, we investigated the type of nucleation and the rate at which the crystallization behavior changed as characteristics of the spherulites observed in the PLLA/EVA blend system (Figure 1c). We hope that this study will expand the use of the PLLA/EVA system, which is a crystalline/amorphous polymer blend.

2. Materials and Methods

2.1. Materials

PLLA (Mw = 780,000, Tm: 194.5 °C, and density: 1.248 g·cm−3) was purchased from BMG Inc., Kyoto, Japan and EVA copolymer (vinyl acetate content: 42 wt%, and melt index: 70 g·10 min−1) was purchased from the TOSOH Corporation, Tokyo, Japan (Figure 2a).

2.2. Preparation of Polymer Blends

Polymer blends were prepared using the melt-compounding method. For this process, a melt-kneader (TDR60-3M, Toshin Co., Ltd., Gifu, Japan) was used, and the temperature was set to 195 °C, which is near the melting point of PLLA. After PLLA and EVA were added to the kneader, the rotation speed and kneading time were set to 50 rpm and 5 min, respectively (Figure 2b). Before kneading was started, nitrogen gas was introduced to replace the air in the apparatus.
To observe the spherulite structure, film-like samples were prepared as follows: a hot-press apparatus (Toyo Seiki Seisaku-sho, Ltd., Tokyo, Japan Mini testpress-10) was used to sandwich the neat or blend polymer between two sheets of heat-resistant polyimide film, and the molding temperature and pressure were set to 195 °C and 20 MPa, respectively. After pressure was applied for 2 min, the samples were quenched in water. The average thickness of the obtained film was ~30 µm.

2.3. Characterization

The melting and crystallization behaviors of the neat and blend polymers were evaluated using DSC (DSC 214 Polymer, NETZSCH Japan K.K., Kanagawa, Japan). The heating and cooling rates for the DSC were set to 10 °Cꞏmin−1, and nitrogen gas (purity: 99.99%) was introduced. An aluminum pan was used for the measurements.
Polarized optical microscopy (POM; Olympus BX51, Olympus Corporation, Tokyo, Japan) was used to observe the spherulite structure. A heating and cooling device for the microscope (Linkam TH-600RMS, Japan High Tech Co., Ltd., Fukuoka, Japan) was used to control the temperature during the observation. The sample was first heated from room temperature to 200 °C at 10 °Cꞏmin−1 and then cooled to 125 °C and held at that temperature for 30 min before the observation. The positive and negative orientations of the spherulites were confirmed by employing a sensitive color detection plate (U-TAD, Olympus Corporation, Tokyo, Japan).

3. Results and Discussion

3.1. Thermal Behavior of PLLA:EVA Polymer Blends

Figure 3 shows the DSC thermograms of the PLLA:EVA blend during the first heating and cooling processes. The onset temperature for the melting of neat PLLA, a crystalline polymer, is 180.2 °C. The thermal behavior is complex: during the heating process, a small signal that appears to be an endothermic peak at first glance appears at ~60 °C, and a broad exothermic peak appears at temperatures ≥90 °C. The former strictly corresponds to the glass transition temperature [56], and the latter is close to the region of the crystallization peak appearing during the cooling process. Therefore, the broad exothermic peak starting at ~90 °C is believed to indicate the behavior of molecular chains that are not completely crystallized realigning/crystallizing during the heating process [57]. The glass transition behavior of EVA, an amorphous polymer, is observed at ~30 °C during the cooling process. This behavior also results in a transition curve with an overshoot that initially appears to be an exothermic peak. The second heating process has been included in Figure S1.
In the evaluation of polymer blend miscibility, if the previously mentioned transition curves remain largely unchanged, the blend is regarded as phase-separated [23]. However, if the melting/crystallization behavior of PLLA changes depending on the EVA proportion, the blend can be considered to be a miscible system [58]. As mentioned previously, because a blend of a crystalline polymer and an amorphous polymer is studied, behavior similar to that of a phase-separated system is predicted; however, in reality, a slight mutual influence is confirmed. The onset temperature for melting during the heating process decreases to 174–179 °C when the blend ratio is in the range of 3:1 to 1:2. The PLLA:EVA = 1:3 blend does not crystallize.
During the cooling process, the onset temperature for the crystallization of neat PLLA is 113.5 °C and of the PLLA:EVA = 3:1, 2:1, 1:1, and 1:2 blends are 121.3, 120.2, 117.1, and 114.1 °C, respectively. Table S1 in the Supporting Information presents the composition-dependent variations in onset temperatures, peak positions, and peak areas for the first heating and cooling curves of PLLA/EVA blends. The blends’ crystallization temperature, which increases upon blending, approaches the crystallization temperature of neat PLLA as the EVA proportion increases. The glass transition behavior of EVA during the cooling process is considered to be equivalent within the error level of the blend data. Thus, the effect of blending with EVA on the melting/crystallization behavior of PLLA cannot be ignored, even though the dependency is unclear. The results indicate that the PLLA:EVA system is partially miscible.

3.2. Spherulite Formation and Size Distribution in PLLA:EVA Polymer Blends

Figure 4 shows the POM images of the spherulites observed in the neat PLLA and PLLA:EVA blends. Neat PLLA forms negative spherulites, suggesting that the refractive index in the direction of the molecular chain is higher than that in the direction perpendicular to the molecular chain [59]. As shown in Figure S2 in the Supporting Information, EVA cannot form spherulites under any of the conditions. Although PLLA is blended with EVA in the system, negative spherulites are observed in the PLLA:EVA = 1:3, 2:1, and 1:1 blends. The crystal size and habit of the PLLA:EVA = 3:1 blend are comparable to those of neat PLLA. The average spherulite size is slightly smaller in the PLLA:EVA = 2:1 blend than in neat PLLA, and this tendency is more pronounced in the case of the PLLA:EVA = 1:1 blend. No spherulites are observed in the POM image of the PLLA:EVA = 1:2 blend.
Because the PLLA:EVA = 1:3, 2:1, and 1:1 blends form negative spherulites, similar to neat PLLA, we confirmed the difference in the size distribution. Figure 5 shows the spherulite size distribution of neat PLLA and the PLLA:EVA = 1:3, 2:1, and 1:1 blends based on the POM images. Holding the sample at the isothermal crystallization temperature for 30 min, we proceeded to acquire 30 images of distinct samples utilizing polarized optical microscopy from various positions. Following this imaging process, we analyzed the microscopy scale to compute the radius of the spherulite. In neat PLLA, spherulites having a diameter of 17 μm are the most abundant, followed by spherulites having a diameter of 19 μm. In the PLLA:EVA = 3:1 blend, spherulites having a diameter of 15 μm are the most abundant, followed by spherulites having diameters of 13 and 17 μm (approximately half the number of spherulites having a diameter of 15 μm). In the PLLA:EVA = 2:1 and 1:1 blends, the numbers of spherulites having diameters of 13 and 7 μm, respectively, are approximately twice those in the surrounding size distribution regions. Thus, the spherulite size distribution systematically becomes finer with an increasing EVA proportion. In a completely phase-separated system, predicting a systematic change in the spherulite size with respect to the blend ratio is difficult, indicating a certain degree of miscibility/interaction between the two components.

3.3. Characterization of Spherulite Formation/Growth Behavior in PLLA:EVA Polymer Blends

Figure 6 depicts the nucleation of each spherulite. The formed spherulites were subjected to a melting/crystallization process, and the observation area was under the same conditions. Heterogeneous nucleation was considered if the nucleation position was the same each time, and homogeneous nucleation was considered if the nucleation position changed each time. For observations, the temperature was increased from 25 to 200 °C once and then decreased to 125 °C to perform isothermal crystallization. After microscopic observations, the temperature was increased again to 200 °C, and the same thermal history was used. The figure reveals that the nucleation position changes in all the neat PLLA and blend samples at each ratio, suggesting homogeneous nucleation. In other words, crystal nuclei are generated through density fluctuations between the melt and crystals, instead of via nucleating agents or impurities, and grow slowly. This result supports the clear size distribution shown in Figure 5. If the nucleation process were heterogeneous, the spherulites would collide with each other and growth would stop; thus, a clear size distribution would not have been obtained. The crowded appearance of the images is primarily due to the high density of spherulites formed during the isothermal crystallization process. This is an inherent characteristic of the system, as the nucleation and growth of spherulites are highly dependent on the composition and crystallization conditions. The high density of spherulites reflects the actual behavior of the material under the conditions studied.
Figure 7 displays a plot of the crystallization time (the horizontal axis) versus the spherulite radius (the vertical axis). The crystallization time was set to 2 h, and the average spherulite size was measured at 25, 50, 70, and 110 min. The figure shows that neat PLLA and the PLLA:EVA = 3:1 blend result in almost similar slopes, and the PLLA:EVA = 2:1 and 1:1 blends lead to gentler slopes. Thus, a clear transition in the spherulite growth behavior occurs between the PLLA:EVA = 3:1 and 2:1 blends. This result indicates a change not only in the size of the spherulites finally formed (Figure 5) but also in the spherulite growth rate. Thus, in the PLLA:EVA = 2:1 and 1:1 blends, the EVA component is not simply pushed out from the PLLA crystalline phase but is incorporated into the spherulites, affecting the crystallization behavior.
The results are presented in Figure 8. The spherulite formation behavior is used to evaluate the miscibility of the PLLA:EVA system, which is a blend of crystalline and amorphous polymers. The PLLA:EVA system used in this study is a homogeneous nucleation system; therefore, comparing growth patterns based on the spherulite size is easy. Whether the blend is completely phase-separated or an ideal mixture can be assessed by referring to the shift in the crystallization peak obtained from thermal analysis, as in the past. All the spherulites obtained in this study are negative, but the size distribution in the homogeneous nucleation is clear. As the EVA proportion increases, the spherulite size distribution becomes finer. In addition, the slope of the plot of the average radius of the spherulites versus the crystallization time changes when the PLLA:EVA = 2:1 blend is used; thus, the EVA component clearly affects the crystallization of PLLA.

4. Conclusions

The properties of spherulites, which are characteristic higher-order structures in crystalline polymers, may have many applications. In particular, in homogeneous nucleation, which is not affected by impurities, spherulites can be used to evaluate the inherent properties of polymers [60]. In this study, we focused on a PLLA:EVA blend, which is a blend of crystalline and amorphous polymers and not a completely phase-separated system. Differences were confirmed in the spherulite size distribution and the ratio of spherulite growth to crystallization time, and interactions between the two components were observed. Thus, a PLLA:EVA blend cannot be considered to be a completely phase-separated system; however, it is not miscible. Hence, it is a partially miscible system with slight interactions. Even in the DSC thermograms, the shift in the crystallization peak in the blend system is weak and easy to overlook. However, the miscibility can be investigated via only mesoscopic spherulite observations by carefully evaluating the size and growth rate of the spherulites. Partially mixing EVA, a material that is resistant to elongation, with the spherulites of PLLA, which is a mechanically fragile polymer material, may lead to the development of useful materials involving biodegradable polymers; this may mitigate certain growing concerns regarding marine plastic pollution in today’s world. We hope that this blend material, its analogs, and a method for evaluating compatibility using spherulite observations will become more widely used in the future.

Supplementary Materials

The following Supporting Information can be downloaded at: https://www.mdpi.com/article/10.3390/jcs9030130/s1, Table S1: Dependence of onset temperatures, peak positions, and peak areas on composition; Figure S1: DSC thermograms of neat PLLA, neat EVA, and PLLA/EVA blends with various ratios (scanning rate is 10 °C·min−1; second heating process); Figure S2: POM observation of crystallization behavior of neat EVA.

Author Contributions

Methodology, C.N., K.X. and A.F.; formal analysis, A.F.; investigation, A.F.; data curation, R.H.R. and A.F.; writing—original draft, A.F.; writing—review and editing, A.F.; supervision, A.F.; project administration, A.F.; funding acquisition, A.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by JSPS KAKENHI Grant Number (C) JP 24K08538 and the KOSE Cosmetology Research Foundation (J-23-7).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

This study was supported by JSPS KAKENHI Grant Number (C) JP 24K08538 and the KOSE Cosmetology Research Foundation (J-23-7).

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Huang, W.; Shishehbor, M.; Guarín-Zapata, N.; Kirchhofer, N.D.; Li, J.; Cruz, L.; Wang, T.; Bhowmick, S.; Stauffer, D.; Manimunda, P.; et al. A natural impact-resistant bicontinuous composite nanoparticle coating. Nat. Mater. 2020, 19, 1236–1243. [Google Scholar] [CrossRef] [PubMed]
  2. Wang, X.; Yang, Y.; Li, Z.; Li, T.; Niu, C.; Wang, R. Natural composite hydrogel regulated interface polymerization to prepare high performance nanofiltration membranes with wrinkled structure. J. Membr. Sci. 2025, 717, 123567. [Google Scholar] [CrossRef]
  3. Stankovich, S.; Dikin, D.A.; Dommett, G.H.B.; Kohlhaas, K.M.; Zimney, E.J.; Stach, E.A.; Piner, R.D.; Nguyen, S.T.; Ruoff, R.S. Graphene-based composite materials. Nature 2006, 442, 282–286. [Google Scholar] [CrossRef]
  4. Clyne, T.W.; Hull, D. An Introduction to Composite Materials, 3rd ed.; Cambridge University Press: Cambridge, UK, 2019. [Google Scholar]
  5. Christensen, R.M. Mechanics of Composite Materials; Wiley: New York, NY, USA, 1979. [Google Scholar]
  6. Chawla, K.K. Composite Materials: Science and Engineering, 4th ed.; Springer: New York, NY, USA, 2019. [Google Scholar]
  7. Kelly, A. A Concise Encyclopedia of Composite Materials; Pergamon Press: Oxford, UK, 1989. [Google Scholar]
  8. Vincent, J.F.V. Structural Biomaterials, 3rd ed.; Princeton University Press: Princeton, NJ, USA, 2012. [Google Scholar]
  9. Noe, M.M.; Sugawara, A.; Asoh, T.A.; Takashima, Y.; Harada, A.; Uyama, H. Composite hydrogels with host–guest interaction using cellulose nanocrystal as supramolecular filler. Polymer 2023, 277, 125979. [Google Scholar] [CrossRef]
  10. Li, H.; Dai, X.; Han, X.; Wang, J. Molecular Orientation-Regulated Bioinspired Multilayer Composites with Largely Enhanced Mechanical Properties. ACS Appl. Mater. Interfaces 2023, 15, 21467–21475. [Google Scholar] [CrossRef]
  11. Ehrburger, P.; Ubbelohde, A.R.J.P.; Scott, R.A.M.; Johnson, J.W.; Richardson, M.O.W.; Watt, W.; Harris, B.; Ham, A.C. Interface in composite materials. Philos. Trans. R. Soc. Lond. A 1980, 294, 495–505. [Google Scholar] [CrossRef]
  12. Evans, D.F.; Wennerström, H. The Colloidal Domain: Where Physics, Chemistry, Biology, and Technology Meet, 2nd ed.; Wiley-VCH: New York, NY, USA, 1999. [Google Scholar]
  13. Lee, J.H.; Lyu, J.; Kim, M.; Ahn, H.; Lim, S.; Jang, H.W.; Chung, H.-J.; Lee, J.H. Quantitative Determination of Charge Transport Interface at Vertically Phase Separated Soluble Acene/Polymer Blends. Adv. Funct. Mater. 2023, 33, 2215221. [Google Scholar] [CrossRef]
  14. Xu, J.; Luo, T. Unlocking enhanced thermal conductivity in polymer blends through active learning. npj Comput. Mater. 2024, 10, 74. [Google Scholar] [CrossRef]
  15. Jayarathna, S.; Andersson, M.; Andersson, R. Recent Advances in Starch-Based Blends and Composites for Bioplastics Applications. Polymers 2022, 14, 4557. [Google Scholar] [CrossRef]
  16. Uramatsu, T.; Morinaga, S.; Shibatsuka, T.; Kawauchi, T. Polymer alloys with high thermal properties consisting of polyfunctional benzoxazine derived from an oligonuclear phenolic compound and bismaleimide. Polym. J. 2024, 56, 1223–1230. [Google Scholar] [CrossRef]
  17. Sango, T.; Koubaa, A.; Ragoubi, M.; Yemele, M.C.N.; Leblanc, N. Insights into the functionalities of cellulose acetate and microcrystalline cellulose on water absorption, crystallization, and thermal degradation kinetics of a ternary polybutylene succinate-based hybrid composite. Ind. Crops Prod. 2024, 222, 119572. [Google Scholar] [CrossRef]
  18. Guzel, M.; Torlak, Y.; Choi, H.; Ak, M. Designed hybrid organic−inorganic nanocomposite film based on synergistic effect of conducting polymer and keggin type polyoxometalate clusters. Mater. Res. Bull. 2023, 167, 112406. [Google Scholar] [CrossRef]
  19. Vargo, E.; Ma, L.; Li, H.; Zhang, Q.; Kwon, J.; Evans, K.M.; Tang, X.; Tovmasyan, V.L.; Jan, J.; Arias, A.C.; et al. Functional composites by programming entropy-driven nanosheet growth. Nature 2023, 623, 724–731. [Google Scholar] [CrossRef] [PubMed]
  20. Moore, W.J. Physical Chemistry, 5th ed.; Prentice-Hall: Englewood Cliffs, NJ, USA, 1972. [Google Scholar]
  21. Agarwal, B.D.; Broutman, L.J. Analysis and Performance of Fiber Composites, 2nd ed.; Wiley: New York, NY, USA, 1990. [Google Scholar]
  22. Guo, Y.; Deng, J.; Yu, H.; Huang, Y.; He, B. Preparation and properties of self-reinforced polypropylene composites modified with β-nucleating agents. Polymer 2024, 313, 127723. [Google Scholar] [CrossRef]
  23. Sato, K.; Oaki, Y.; Imai, H. Phase separation of composite materials through simultaneous polymerization and crystallization. NPG Asia Mater. 2017, 9, e377. [Google Scholar] [CrossRef]
  24. Shang, S.A.; Wang, L.; Yao, J.; Lv, X.; Xu, Y.; Dou, W.; Zhang, H.; Ye, J.; Chen, Y.-C. Characterizing microstructural patterns within the cortico-striato-thalamo-cortical circuit in Parkinson’s disease. Prog. Neuropsychopharmacol. Biol. Psychiatry 2024, 135, 111116. [Google Scholar] [CrossRef]
  25. Strobl, G. The Physics of Polymers: Concepts for Understanding Their Structures and Behavior; Springer: Berlin, Germany, 1997. [Google Scholar]
  26. Liu, M.; Yang, R.; Guo, Z.; Chen, K.; Feng, H.; Lu, H.; Huang, S.; Zhang, M.; Ye, H.; Shui, L. Dynamic photomask directed lithography based on electrically stimulated nematic liquid crystal architectures. Nat. Commun. 2024, 15, 9389. [Google Scholar] [CrossRef]
  27. Reichmanis, E.; Nalamasu, O.; Houlihan, F.M. Materials Challenges and Alternatives for Advanced Photolithographic Patterning: From 193 to 157 nm and Beyond. MRS Online Proc. Libr. 2000, 636, 521. [Google Scholar] [CrossRef]
  28. Deng, B.; Wan, G. Technologies for studying phase-separated biomolecular condensates. Adv. Biotechnol. 2024, 2, 10. [Google Scholar] [CrossRef]
  29. Meyers, M.A.; Sarikaya, M.; Ritchie, R.O. Nano- and Microstructural Design of Advanced Materials; Elsevier: Amsterdam, The Netherlands, 2003. [Google Scholar]
  30. Harada, K.; Chu, P.; Xu, K.; Fujimori, A. Polypropylene-based nanocomposite with improved mechanical properties: Effect of cellulose nanofiber and polyrotaxane with partial miscibility. Polym. Compos. 2023, 44, 2977–2987. [Google Scholar] [CrossRef]
  31. Mokoena, L.S.; Mofokeng, J.P. Morphology and thermal properties of poly(lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/graphene oxide polymeric composites. Polym. Eng. Sci. 2024, 64, 5329–5350. [Google Scholar] [CrossRef]
  32. Prausnitz, J.M.; Lichtenthaler, R.N.; de Azevedo, E.G. Molecular Thermodynamics of Fluid-Phase Equilibria, 3rd ed.; Prentice-Hall: Upper Saddle River, NJ, USA, 1998. [Google Scholar]
  33. Xie, Y.; Tan, J.; Fang, S.; Li, T.; Chen, Y.; Li, L.; Chen, N. A biodegradable, osteo-regenerative and biomechanically robust polylactide bone screw for clinical orthopedic surgery. Int. J. Biol. Macromol. 2024, 283, 137477. [Google Scholar] [CrossRef] [PubMed]
  34. Zhao, X.; Yu, J.; Liang, X.; Huang, Z.; Li, J.; Peng, S. Crystallization behaviors regulations and mechanical performances enhancement approaches of polylactic acid (PLA) biodegradable materials modified by organic nucleating agents. Int. J. Biol. Macromol. 2023, 233, 123581. [Google Scholar] [CrossRef] [PubMed]
  35. Banpean, A.; Sakurai, S. Confined crystallization of Poly(ethylene glycol) in spherulites of Poly(L-lactic acid) in a PLLA/PEG blend. Polymer 2021, 215, 123370. [Google Scholar] [CrossRef]
  36. Xu, K.; Chu, P.; Rumon, R.H.; Fujimori, A. Enhancing in-plane elasticity of carbon fiber reinforced thermoplastic multilayer films with polyrotaxane and nanocellulose composites. Polym. Compos. 2025, 46, 1–14. [Google Scholar] [CrossRef]
  37. Jaziri, M.; Kossentini Kallel, T.; Mbarek, S.; Elleuch, B. Morphology development in polyethylene/polystyrene blends: The influence of processing conditions and interfacial modification. Polym. Int. 2005, 54, 1384–1391. [Google Scholar] [CrossRef]
  38. Yun, X.; Li, X.; Eerdunbayaer; Cheng, P.; Pan, P.; Dong, T. Controllable Poly(L-lactic acid) Soft Film with Respirability and Its Effect on Strawberry Preservation. Polym. Sci. Ser. A 2021, 63, 77–90. [Google Scholar] [CrossRef]
  39. Righetti, M.C.; Gazzano, M.; Delpouve, N.; Saiter, A. Contribution of the rigid amorphous fraction to physical ageing of semi-crystalline PLLA. Polymer 2017, 125, 241. [Google Scholar] [CrossRef]
  40. Watson, M.D.; Wagener, K.B. Ethylene/Vinyl Acetate Copolymers via Acyclic Diene Metathesis Polymerization. Examining the Effect of “Long” Precise Ethylene Run Lengths. Macromolecules 2000, 33, 5411–5417. [Google Scholar] [CrossRef]
  41. Ali, S.J.A.; Rahmatabadi, D.; Baghani, M.; Baniassadi, M. Experimental Evaluation of Mechanical Properties, Thermal Analysis, Morphology, Printability, and Shape Memory Performance of the Novel 3D Printed PETG-EVA Blends. Macromol. Mater. Eng. 2024, 309, 2400069. [Google Scholar] [CrossRef]
  42. Qi, X.; Dong, Y.; Islam, M.Z.; Zhu, Y.; Fu, Y.; Fu, S.Y. Excellent triple-shape memory effect and superior recovery stress of ethylene-vinyl acetate copolymer fiber. Compos. Sci. Technol. 2021, 203, 108609. [Google Scholar] [CrossRef]
  43. Lee, J.H.; Ryu, H.J.; Rejinold, N.S.; Choi, J.Y.; Long, Y.-Z.; Choi, G.; Choy, J.-H. Nano-enhanced thermo-mechanical properties of ethylene vinyl acetate with intumescent agent and organoclays. Appl. Clay Sci. 2024, 262, 107608. [Google Scholar] [CrossRef]
  44. Ercan, N.; Korkmaz, E. Structural, thermal, mechanical and viscoelastic properties of ethylene vinyl acetate (EVA)/olefin block copolymer (OBC) blends. Mater. Today Commun. 2021, 28, 102634. [Google Scholar] [CrossRef]
  45. Zhang, H.; Zhang, F.; Liu, C.; Chen, M.; Che, Q.; Bai, Y.; Zhou, C.; Xu, K. A novel ethylene-vinyl acetate-impact hardening polymers composite with impact-resistance ability, strain-rate sensitivity and enhanced mechanical performance. Mater. Today Commun. 2025, 42, 111423. [Google Scholar] [CrossRef]
  46. Han, D.H.; Choi, M.C.; Nagappan, S.; Kim, Y.M.; Kim, H.S. Ethylene vinyl acetate (EVA)/poly(lactic acid) (PLA) blends and their foams. Mol. Cryst. Liq. Cryst. 2020, 707, 38–45. [Google Scholar] [CrossRef]
  47. Sangeetha, V.H.; Valapa, R.B.; Nayak, S.K.; Varghese, T.O. Investigation on the Influence of EVA Content on the Mechanical and Thermal Characteristics of Poly(lactic acid) Blends. J. Polym. Environ. 2018, 26, 1–14. [Google Scholar] [CrossRef]
  48. El-Taweel, S.H. Synergistic effect of TiO2 nanoparticles and poly (ethylene-co-vinyl acetate) on the morphology and crystallization behavior of polylactic acid. Sci. Rep. 2024, 14, 18142. [Google Scholar] [CrossRef]
  49. Chu, P.; Nara, C.; Rumon, R.H.; Xu, K.; Fujimori, A. Introduction of organo-modified carbon nanotubes into fluoropolymer-based hybrids containing polyrotaxane and cellulose nanofibers as organic fillers and their drawn orientation effects. Polym. Compos. 2025, 46, 1–13. [Google Scholar] [CrossRef]
  50. Singla, R.K.; Zafar, M.T.; Maiti, S.N.; Ghosh, A.K. Physical blends of PLA with high vinyl acetate containing EVA and their rheological, thermo-mechanical and morphological responses. Polym. Test. 2017, 63, 398–406. [Google Scholar] [CrossRef]
  51. Mendoza-Duarte, M.E.; Estrada-Moreno, I.A.; García-Casillas, P.E.; Vega-Rios, A. Stiff-Elongated Balance of PLA-Based Polymer Blends. Polymers 2021, 13, 4279. [Google Scholar] [CrossRef]
  52. Yoon, J.S.; Oh, S.H.; Kim, M.N.; Chin, I.J.; Kim, Y.H. Thermal and mechanical properties of poly(l-lactic acid)–poly (ethylene-co-vinyl acetate) blends. Polymer 1999, 40, 2303–2312. [Google Scholar] [CrossRef]
  53. Maeda, M.; Shioda, Y.; Fujimori, A. Creation of Quasi-DNA Origami at the Air/Water Interface Using the Collapsed Mechanism of Langmuir Monolayer. ChemistrySelect 2024, 9, e202400063. [Google Scholar] [CrossRef]
  54. Yamagishi, Y.; Sakamoto, S.; Hasunuma, Y.; Fujimori, A. Characterization of Langmuir Monolayers for Nanodiamonds Surface-Modified with 12-Hydroxystearyl Chains and the Occurrence of Structural Colors. ChemistrySelect 2024, 9, e202403262. [Google Scholar] [CrossRef]
  55. Hasunuma, Y.; Sakamoto, S.; Yamagishi, Y.; Fujimori, A. Preparation and Structural Properties of Gel Coating Films Containing Lipophilized Nanocarbon Particles Functionalized with Thixotropic Chains. J. Oleo Sci. 2025, 74, 107–121. [Google Scholar] [CrossRef]
  56. Singla, R.K.; Maiti, S.N.; Ghosh, A.K. Mechanical, morphological, and solid-state viscoelastic responses of poly(lactic acid)/ethylene-co-vinyl-acetate super-tough blend reinforced with halloysite nanotubes. J. Mater. Sci. 2016, 51, 10278–10292. [Google Scholar] [CrossRef]
  57. Tábi, T. The application of the synergistic effect between the crystal structure of poly(lactic acid) (PLA) and the presence of ethylene vinyl acetate copolymer (EVA) to produce highly ductile PLA/EVA blends. J. Therm. Anal. Calorim. 2019, 138, 1287–1297. [Google Scholar] [CrossRef]
  58. Abdel-Kader, M.H.; Alharby, T.S.; Alamri, S.N. Enhancement of structural, morphological, thermal, optical and mechanical characteristics of PVA/PEO blends based on acetate fillers and infrared laser irradiation. Radiat. Phys. Chem. 2025, 229, 112488. [Google Scholar] [CrossRef]
  59. Otsuki, Y.; Terui, R.; Hoshino, Y.; Suzuki, T.; Shibasaki, Y.; Fujimori, A. Spherulitic Characterization and Hierarchical Structural Evaluation of Azacalixarene-Polyethylene Glycol Copolymers Containing s-Triazine Rings. Macromol. Chem. Phys. 2023, 224, 2300117. [Google Scholar] [CrossRef]
  60. Zhang, J.; Duan, Y.; Sato, H.; Tsuji, H.; Ozaki, Y. Crystal modifications and thermal behavior of poly(L-lactic acid) revealed by infrared spectroscopy. Macromolecules 2005, 38, 8012–8021. [Google Scholar] [CrossRef]
Jcs 09 00130 g001
Figure 1. Background and research strategy of this study: schematic illustrations of (a) material properties that were previously expected for the PLLA:EVA system, (b) a conventional method for determining miscible/immiscible systems using DSC thermograms, and (c) the research strategy used in this study.
Figure 1. Background and research strategy of this study: schematic illustrations of (a) material properties that were previously expected for the PLLA:EVA system, (b) a conventional method for determining miscible/immiscible systems using DSC thermograms, and (c) the research strategy used in this study.
Jcs 09 00130 g001
Jcs 09 00130 g002
Figure 2. Materials and experimental methods used in this study: chemical formulas and 3D models of (a) PLLA and EVA; (b) method of preparing polymer blends using melt-compounding method.
Figure 2. Materials and experimental methods used in this study: chemical formulas and 3D models of (a) PLLA and EVA; (b) method of preparing polymer blends using melt-compounding method.
Jcs 09 00130 g002
Jcs 09 00130 g003
Figure 3. DSC thermograms of neat PLLA, neat EVA, and PLLA/EVA blends with various ratios (scanning rate is 10 °C·min−1; first heating and cooling process).
Figure 3. DSC thermograms of neat PLLA, neat EVA, and PLLA/EVA blends with various ratios (scanning rate is 10 °C·min−1; first heating and cooling process).
Jcs 09 00130 g003
Jcs 09 00130 g004
Figure 4. POM observation of spherulites for (a) neat PLLA, (b) PLLA:EVA = 3:1, (c) PLLA:EVA = 2:1, (d) PLLA:EVA = 1:1, and (e) PLLA:EVA = 1:2 blends.
Figure 4. POM observation of spherulites for (a) neat PLLA, (b) PLLA:EVA = 3:1, (c) PLLA:EVA = 2:1, (d) PLLA:EVA = 1:1, and (e) PLLA:EVA = 1:2 blends.
Jcs 09 00130 g004
Jcs 09 00130 g005
Figure 5. Distribution of spherulite size for neat PLLA and PLLA:EVA = 3:1, 2:1, and 1:1 blends. The red numbers denote the most abundant spherulite radius and the red arrows indicate changes in diameter.
Figure 5. Distribution of spherulite size for neat PLLA and PLLA:EVA = 3:1, 2:1, and 1:1 blends. The red numbers denote the most abundant spherulite radius and the red arrows indicate changes in diameter.
Jcs 09 00130 g005
Jcs 09 00130 g006
Figure 6. Evaluation of the nucleation process of each spherulite using POM images for the heat-melting, cooling, and isothermal crystallization process (a) neat PLLA, (b) PLLA:EVA = 3:1, (c) PLLA:EVA = 2:1, (d) PLLA:EVA = 1:1. The red dashed lines indicate changes in the position of spherulite formation.
Figure 6. Evaluation of the nucleation process of each spherulite using POM images for the heat-melting, cooling, and isothermal crystallization process (a) neat PLLA, (b) PLLA:EVA = 3:1, (c) PLLA:EVA = 2:1, (d) PLLA:EVA = 1:1. The red dashed lines indicate changes in the position of spherulite formation.
Jcs 09 00130 g006
Jcs 09 00130 g007
Figure 7. Plot of spherulite radius versus crystallization time for neat PLLA and PLLA:EVA = 3:1, 2:1, and 1:1 blends.
Figure 7. Plot of spherulite radius versus crystallization time for neat PLLA and PLLA:EVA = 3:1, 2:1, and 1:1 blends.
Jcs 09 00130 g007
Jcs 09 00130 g008
Figure 8. Overall conclusions and discussion.
Figure 8. Overall conclusions and discussion.
Jcs 09 00130 g008
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Rumon, R.H.; Nara, C.; Xu, K.; Fujimori, A. Proving Partial Miscibility in Poly(L-lactic acid)/Ethylene-Vinyl Acetate Copolymer Blends Using the Spherulite Observation Method. J. Compos. Sci. 2025, 9, 130. https://doi.org/10.3390/jcs9030130

AMA Style

Rumon RH, Nara C, Xu K, Fujimori A. Proving Partial Miscibility in Poly(L-lactic acid)/Ethylene-Vinyl Acetate Copolymer Blends Using the Spherulite Observation Method. Journal of Composites Science. 2025; 9(3):130. https://doi.org/10.3390/jcs9030130

Chicago/Turabian Style

Rumon, Rokibul Hasan, Chisato Nara, Kai Xu, and Atsuhiro Fujimori. 2025. "Proving Partial Miscibility in Poly(L-lactic acid)/Ethylene-Vinyl Acetate Copolymer Blends Using the Spherulite Observation Method" Journal of Composites Science 9, no. 3: 130. https://doi.org/10.3390/jcs9030130

APA Style

Rumon, R. H., Nara, C., Xu, K., & Fujimori, A. (2025). Proving Partial Miscibility in Poly(L-lactic acid)/Ethylene-Vinyl Acetate Copolymer Blends Using the Spherulite Observation Method. Journal of Composites Science, 9(3), 130. https://doi.org/10.3390/jcs9030130

Article Metrics

Back to TopTop