Enhancing Polylactic Acid Films With Polyethylene Glycol‐Based Plasticizers: A Reactive Extrusion Approach

Abstract

The enhancement of polylactic acid (PLA) films using polyethylene glycol (PEG)‐based plasticizers through reactive extrusion, employing dicumyl peroxide (DCP) as a cross‐linking agent is studied in this work. Incorporating PEG plasticizers into PLA substantially raises its elongation at break, from 12.0% in neat PLA to 61.3%, while preserving satisfactory tensile strength. This improvement broadens the industrial applicability of PLA; however, it should be noted that the plasticizers exhibit a tendency to migrate. The reactive extrusion process reduces plasticizer migration, lowering values from 140.3 mg kg⁻¹ in PLA‐PEG films to 40.8 mg kg⁻¹ in films processed with reactive extrusion (PLA‐PEG‐R). This substantial reduction enables the safe use of these materials in food‐contact applications. Thermal stability is also enhanced, with degradation temperatures rising from 268.7 °C in PLA‐PEG to 333.8 °C in PLA‐DCP systems. Additionally, the glass transition temperature (Tg) decreases to 38.3 °C, enhancing material ductility. The films retain certain transparency despite slight alterations in optical properties, and their increased water vapor permeability can be beneficial for applications in food packaging applications. These findings demonstrate that reactive extrusion (REX) with PEG‐based plasticizers improves PLA's mechanical, thermal, and functional properties, broadening its industrial application while preserving its environmental advantages.

This study explores the enhancement of polylactic acid (PLA) films through reactive extrusion with polyethylene glycol (PEG)‐based plasticizers and dicumyl peroxide (DCP) as a cross‐linking agent. The process improves mechanical strength, ductility, and thermal stability while reducing plasticizer migration, broadening the potential applications of PLA in packaging and high‐performance materials.

1. Introduction

The growing global concern over the environmental impact of the widespread use of traditional petroleum‐based polymers has intensified efforts to develop sustainable and biodegradable alternatives. Conventional petrochemical polymers significantly contribute to waste buildup, ecosystem pollution, and overall environmental degradation.^{[ 1} , ^{2 ]} The durability of plastic debris, coupled with its slow decomposition, underscores the urgent need for materials that can be effortlessly assimilated into the Earth's biological cycles. The introduction of biodegradable polymers not only addresses these environmental issues but also supports the growing demand for environmental sustainability and responsible consumption practices.^{[ 3} , ^{4 ]} Among these materials, polylactic acid (PLA) is one of the most interesting choices. This polymer is derived from renewable agricultural sources such as corn and sugarcane.^{[ 5 ]} This demonstrates the potential of PLA to improve sustainable materials science and reduce dependence on fossil fuels.^{[ 6} , ^{7 ]} PLA's molecular structure imparts qualities like rigidity and transparency, comparable to traditional plastics. These features make PLA exceptionally adaptable and applicable in various sectors including packaging, the textile industry, and biomedical devices.^{[ 8} , ^{9 ]} Its inherent rigidity makes it ideal for products requiring structural integrity, while its glossy finish and transparency are highly valued in packaging and disposable items. Additionally, PLA's compatibility with existing plastic manufacturing infrastructure enables seamless integration into various production processes, further expanding its practical applications.^{[ 10 ]}

PLA is widely used in biodegradable packaging solutions, offering an eco‐friendly alternative to traditional petrochemical plastics. Its applications range from food containers to biodegradable films, driven by growing consumer demand for sustainable packaging options.^{[ 11 ]} In the textile industry, PLA fibers are highly regarded for their biodegradability, providing a sustainable option for fabrics and furnishings. This makes them particularly appealing to environmentally conscious brands and consumers. In the biomedical field, PLA's biocompatibility and degradability are key advantages, enabling its use in surgical sutures, drug delivery systems, and temporary implants. Its ability to safely degrade within the body eliminates the need for post‐treatment removal, offering significant benefits in medical applications.^{[ 12 ]} However, the widespread adoption of PLA as a sustainable alternative is hindered by its limited flexibility and toughness, which are critical for applications requiring resistance to mechanical stress and environmental fluctuations.^{[ 13 ]} Compared to conventional plastics like polyethylene (PE) or polypropylene (PP), PLA's brittleness and lower impact strength pose significant challenges in applications demanding high performance and durability.^{[ 14} , ^{15 ]} The rigidity of PLA, while beneficial in certain applications, limits its use in situations requiring flexibility, as it may lead to cracking or failure under stress. Additionally, PLA's toughness—its ability to absorb energy before breaking—is considerably lower than that of many petroleum‐based plastics, which restricts its suitability for high‐impact applications.^{[ 16 ]}

Efforts to improve PLA's flexibility and toughness are centered on strategies like plasticization, copolymerization, and the incorporation of impact modifiers. These approaches aim to enhance its properties, enabling PLA to compete more effectively with conventional plastics.^{[ 17 ]} Research into PLA modification often involves the use of plasticizers, a widely adopted method to enhance PLA's flexibility and processability. This approach is easily scalable for industrial applications and is critical for improving PLA's performance across diverse uses.^{[ 18 ]} Plasticizers are additives that reduce intermolecular forces within plastics, increasing chain mobility. When incorporated into PLA, they significantly improve its flexibility, making it suitable for applications that require bendable or moldable materials. Additionally, plasticized PLA exhibits enhanced processability, allowing it to be more easily shaped into complex forms.

Selecting the right plasticizers for PLA is essential, as they must improve desired properties without compromising PLA's biodegradability. It is also crucial to ensure the compatibility of plasticizers with PLA, as well as their impact on mechanical properties and degradation rates, during the selection process.^{[ 19 ]}

Commonly used plasticizers for PLA include citrate esters, phthalates (though their use is declining due to health concerns), and polyethylene glycols (PEGs). Each type provides unique benefits in improving flexibility, processability, and influencing biodegradability. The use of plasticizers effectively addresses key limitations of PLA, such as brittleness and limited flexibility. However, at higher plasticizer concentrations, phase separation can occur, potentially leading to the migration phenomenon.^{[ 20} , ^{21 ]} The incorporation of plasticizers into PLA significantly enhances its mechanical properties, broadening its versatility and making it suitable for a wider range of applications. This modification not only preserves PLA's biodegradability but also improves its manufacturability, enabling easier shaping and fabrication into diverse products. The use of plasticizers in PLA is a strategic approach to address the material's inherent stiffness, expanding its utility in industries where flexibility and stress resistance are critical. By reducing intermolecular forces within PLA chains, plasticizers increase chain mobility, thereby improving the material's flexibility and toughness. These advancements unlock new possibilities for PLA in applications such as packaging, biomedical devices, and other fields that demand materials capable of withstanding flexural stress.^{[ 22} , ²³ , ^{24 ]}

Integrating reactive extrusion (REX) with dicumyl peroxide (DCP) as a cross‐linking agent represents an advanced approach to modifying PLA. This technique facilitates a chemical reaction between PLA and other components, enhancing their compatibility and overall effectiveness,^{[ 25} , ²⁶ , ^{27 ]} while preventing plasticizer migration. As a radical initiator, DCP promotes the formation of covalent bonds between PLA polymer chains and plasticizer molecules, thereby improving the mechanical stability and properties of the modified PLA. Reactive extrusion with DCP involves the controlled thermal decomposition of DCP to generate free radicals, which initiate cross‐linking reactions within the PLA structure.^{[ 28} , ^{29 ]} This method not only ensures a more uniform distribution of plasticizers throughout PLA but also achieves a stable integration with the polymer chains. The result is a material with enhanced flexibility, toughness, and thermal stability. The process is carefully controlled under specific temperature and shear conditions to optimize the reaction and achieve the desired material characteristics.^{[ 30} , ^{31 ]}

Several studies have investigated the enhancement of the interaction between plasticizers and PLA by reactive and conventional extrusion processes with the addition of anhydride groups. Hassouna et al. analyzed the chemical grafting of tributyl citrate (TbC) onto maleic anhydride‐modified PLA (MAG‐PLA) by reactive extrusion. This strategy allowed reducing plasticizer migration and maintaining long‐term thermal stability, evidenced by the absence of phase separation after six months of aging. In addition, a shift of Tg towards higher values was observed, indicating a higher interaction between the plasticizer and the polymer matrix.^{[ 32 ]} Other work from Hassouna et al. explored the plasticization of PLA by PEG grafting through reactive extrusion with MAG‐PLA. This technique favored the compatibility between PEG and PLA, increasing the ductility of the material and significantly reducing the Tg compared to physical blends. In addition, the integrity of the polymeric structure was maintained without drastically affecting its molecular weight.^{[ 33 ]} On the other hand, Brüster et al. investigated the efficacy of limonene (LM) and myrcene (My) as bio‐based plasticizers for PLA, comparing conventional and reactive extrusion. They found that reactive extrusion, using a free radical initiator, improved the crystallinity and mechanical properties of the material, due to the formation of branched and cross‐linked regions. However, in the case of myrcene, reactive extrusion was detrimental, causing polymerization of the plasticizer and decreasing the ductile capacity.^{[ 34 ]} Finally, Gómez‐Caturla et al. developed PLA formulations plasticized with linalyl acetate (LAc) and geranyl acetate (GAc), both bio‐based terpenoids, by conventional and reactive extrusion. The formulations plasticized with 20% terpenoids showed a significant increase in ductility, increasing the elongation at the break by over 230%. In addition, reactive extrusion with DCP allowed plasticizers to be anchored to the polymer chain, improving thermal and mechanical stability.^{[ 35 ]} When employing peroxides, only one extrusion process is required, whereas the use of anhydride‐based compatibilizers necessitates an additional extrusion step to obtain the compatibilizer. Consequently, from both a scale‐up and cost‐efficiency perspective, the DCP strategy is more advantageous for the industry, as it involves fewer processing steps and reduces overall production costs.

The use of reactive extrusion with DCP addresses limitations associated with traditional plasticization methods, such as phase separation and plasticizer migration. These issues can lead to inconsistent material properties, reduced performance over time, and potential contamination of products in contact with the material (e.g., food, pharmaceuticals, and medical devices).^{[ 36 ]} By chemically bonding plasticizer molecules to PLA, this approach ensures a more consistent material profile and long‐term stability under varying environmental conditions. This reactive extrusion technique broadens PLA's potential applications, ranging from high‐performance engineering materials to flexible packaging solutions. The improved interaction between PLA and plasticizers through reactive extrusion enables the development of materials with tailored mechanical properties, enhanced durability, and greater usability, meeting the demands of various industries seeking sustainable material solutions.^{[ 22} , ^{37 ]}

In this study, the development of PLA enhanced with polyethylene glycol (PEG)‐based plasticizers was explored using reactive extrusion. The primary materials used were PLA and PEG‐based plasticizers, chosen for their ability to improve the flexibility and mechanical properties of PLA films. Reactive extrusion facilitates the cross‐linking of PEG plasticizers with PLA, improving the general properties of the developed films. The primary interest in using these additives lies in their potential to advance polymer engineering by modifying the physical properties of polylactide to meet specific performance criteria. To evaluate the effectiveness of these modifications, various characterization techniques were employed. These included mechanical testing to assess tensile strength and elongation at break, thermal analysis using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA), and other relevant methods to determine the structural and functional properties of the modified films. These techniques provided insights into the interactions between the polymer matrix and the incorporated plasticizers, highlighting the potential of PEG‐based plasticizers in creating more adaptable and robust PLA materials.

2. Experimental Section

2.1. Materials

Poly(lactic acid) (PLA) grade LL 712 procured from ErcrosBio in Barcelona, Spain, and characterized by a melt flow index of 4 g/10 min (measured according to ISO 1133‐A at 190 °C with a 2.16 kg load) was used in this research. To facilitate plasticization, various formulations of poly(ethylene glycol) (PEG) sourced from Sigma–Aldrich in Schnelldorf, Germany, were integrated at a concentration of 10 wt.%. The chemical structures of the employed plasticizers are shown in Figure 1 . PEG with a molecular weight of 600 g mol⁻¹ served as the control. Additionally, poly(ethylene glycol) monooleate and poly(ethylene glycol) dioleate, with molecular weights of 816 g mol⁻¹ and 914 g mol⁻¹ respectively, were included in the study. Moreover, for the purpose of reactive extrusion, dicumyl peroxide (DCP) with the CAS number 80‐43‐3, sourced from Sigma‐Aldrich in Lyon, France, was utilized at a rate of 1 part per hundred resin (phr).

Figure 1.

Chemical structure of the employed plasticizers.

2.2. Film Processing

Prior to commencing film production, PLA underwent a drying process at 85 °C for 6 h within a dehumidifying oven from Industrial Marsé S.A. in Barcelona, Spain. Material blending was performed using a micro extruder provided by Xplore in Sittard, The Netherlands. Here, the specific amount of PLA was processed for 6 min at a temperature of 180 °C and a rotational speed of 100 revolutions per minute. These conditions were meticulously selected to enable the desired reactive extrusion with DCP, ensuring uniformity in all experimental batches. During the film extrusion phase, the temperature of the extruder die was held steady at 170 °C. The utilized die measured 65 mm in width and had a thickness of 0.1 mm. To achieve the specified film thickness, the speed of the chill‐roll system was adjusted to 3000 mm min⁻¹.

2.3. Mechanical Characterization

The mechanical properties of the films were assessed through tensile tests conducted on a universal testing machine, model ELIB 30, produced by S.A.E. Ibertest in Madrid, Spain. These tests adhered to the protocols outlined in ISO 527‐3:2019 and involved rectangular samples measuring 160 mm by 10 mm. For these experiments, a 100 N load cell was utilized, and the cross‐head speed was set at 5 mm min⁻¹. Each film formulation was represented by six individual specimens, which were tested under standard room conditions. The key data recorded during these tests included tensile strength (σ), strain at failure (ε), and tensile modulus (E).

2.4. Thermal Characterization

The thermal properties of the cured materials were assessed using Differential Scanning Calorimetry (DSC), utilizing a DSC 25 device from TA Instruments located in New Castle, United States. Thermal analysis was initiated at −10 °C and extended up to 200 °C, with a controlled heating rate of 5 °C min⁻¹, under a constant flow of nitrogen at 50 mL min⁻¹. The samples maintained a mass between 5 and 6 mg. Important thermal transitions measured included the glass transition temperature (T_g), cold crystallization temperature (T_cc), melting temperature (T_m), and melt crystallization temperature (T_mc). Enthalpies associated with these transitions during the DSC scan encompassed the cold crystallization process (∆h_mc) and melting process (∆h_m). The degree of crystallinity was calculated using a specific formula, with calculations based on data from the second heating cycle, where $\mathrm{\Delta }{H}_m^0$ is the theoretical fully crystalline enthalpy of PLA which is 93 J g⁻¹.^{[ 2 ]}

$$X_c\left(\%\right)=\frac{\mathrm{\Delta }{H}_m-\mathrm{\Delta }{H}_{cc}}{\mathrm{\Delta }{H}_m^0·\left(1-w\right)}·100$$ (1)

Thermogravimetric analysis (TGA) was employed to assess the thermal degradation properties of the materials using a TG‐DSC2 thermobalance from Mettler‐Toledo in Columbus, USA. The analysis involved a heating protocol that ranged from 30 °C to 700 °C at a rate of 10 °C min⁻¹, conducted in an air atmosphere. The parameters evaluated during this analysis included the temperature at which a 5% mass loss occurred (T₅), the peak rate of degradation (T_max), and the residual char content at 700 °C.

2.5. Thermo‐Mechanical Characterization

Dynamic mechanical thermal analysis (DMTA) was performed using a DMA1 instrument from Mettler‐Toledo (Columbus, USA). The analysis was carried out in tensile mode with specimens sized 20×6 mm². The DMTA protocol included setting the maximum dynamic deformation to 10 µm and applying a sinusoidal deformation at a frequency of 1 Hz. The temperature profile for the analysis encompassed a sweep from −50 °C to 80 °C at a heating rate of 2 °C min⁻¹.

2.6. Migration Characterization

Migration tests on films were conducted in accordance with Commission Regulation EU No 10/2011, employing simulant A (ethanol 10% (v/v)). Rectangular film strips with a total surface area of 10 cm² were immersed in 10 mL of the simulant within glass tubes. These assemblies were then placed in a controlled environment maintained at 40 °C for a period of 10 days, consistent with the EN‐1186 standard protocol. After incubation, the films were removed, and the simulants were allowed to evaporate until dry. The residual mass was measured using an analytical balance to determine the overall migration values, with each film type undergoing three repeated measurements to ensure accuracy.

2.7. Theoretical Approach to Solubility

The solubility parameter (δ) is essential for achieving proper dispersion of the additive within the polymeric matrix. The solubility parameters of the PEG‐based plasticizer and PLA were calculated using the Hoftyzer‐Van Krevelen group contribution method. The solubility parameter comprises various contributions: dispersive forces (${\delta }_d$), polar forces (${\delta }_p$) and hydrogen bonding (${\delta }_h$). These parameters were derived from the molecular group contributions as detailed by D.W. van Krevelen et al. and K. te Nijenhuis et al.^{[ 38 ]} Additionally, the molar volume ($V_m$) was calculated using the ratio of molar mass ($M_m$) and density ($\rho$).

The degree of miscibility with PLA is determined by the radius of a sphere, established as $R_0$= 10.7 MJ m⁻³ as reported by Brüster et al. and Auras et al.^{[ 34} , ^{39 ]} Plasticizers within this sphere are miscible with PLA, while those outside are not. To quantify the distance between the base polymer and the plasticizer, the parameter Ra is defined according to the Hansen Solubility Parameters (HSP) theory.

The ratio between $R_a$ and $R_0$ allows the determination of the relative energy difference (RED) as per Equation (2). Values close to zero indicate optimal compatibility. Values greater than 1 indicate that the plasticizer is outside the sphere defined by the PLA, resulting in an immiscible blend.

$$RED=\frac{R_a}{R_0}$$ (2)

2.8. Water Vapor Permeability Characterization

The water vapor transmission rate (WVTR) of films was measured using a gravimetric method in compliance with ISO 2525. This process involved filling permeability cups with 2 g of dry silica gel, which were then sealed with film samples. The sealed cups were placed in a desiccator maintained at 90% relative humidity and 23 °C. The mass of these cups was recorded hourly for a duration of 7 h. Changes in mass overtime were plotted, and the water vapor transmission rate was determined from the slope obtained through a linear regression analysis. Equation (3) was used for the calculation of the water vapor transmission rate.

$$WVTR=\frac{n·l}{S}·100$$ (3)

where n represents the slope derived from the linear regression of weight change over time. The variable l denotes the thickness of the film, while S signifies the film's exposed surface area.

2.9. Wetting Characterization

Alterations in the wetting characteristics were assessed using contact angle measurements performed on an EasyDrop Standard goniometer, model FM140 from KRÜSS in Hamburg, Germany. This instrument is equipped with a video capture kit and analysis software, providing a measurement range from 1 to 180 °C with a precision of ±0.1 °C. Double distilled water was used for these measurements. To ensure both accuracy and reproducibility, ten measurements were conducted on each sample.

2.10. Optical Characterization

The absorption spectra of the films were analyzed using a Cary Series UV–vis–NIR spectrophotometer from Agilent Technologies, (Santa Clara, USA). The analysis spanned a wavelength range from 200 to 800 nm, and all samples were tested in their thin film configuration. To ensure both accuracy and reproducibility, three replicates of each sample were examined.

2.11. Gel Permeation Chromatography

Gel permeation chromatography (GPC) was employed to assess the number average molecular weight (Mn) and the polydispersity index (PDI). For each analysis, ≈5 mg of sample was dissolved in 3 mL of tetrahydrofuran (THF). The measurements were conducted using a Waters 2414 refractive index (RI) detector. Chromatographic separation was performed with THF as the mobile phase, maintained at a constant flow rate of 1.0 mL min⁻¹. Calibration of the GPC columns was carried out using polystyrene standards, and data processing was performed using the EMPOWER Chromatography software.

2.12. Statistical Differences

Statistical differences among the samples were assessed using a one‐way analysis of variance (ANOVA) followed by Tukey's post‐hoc test, with a significance threshold set at p ≤ 0.05, corresponding to a 95% confidence level. All analyses were conducted using the open‐source R software.

3. Results

3.1. Expected Reaction Mechanism

During the reactive extrusion process, thermal energy applied to DCP promotes its decomposition, leading to the formation of alkoxy radicals (RO·). According to DSC characterization, this process starts at 110 °C and extends up to 192 °C.^{[ 40 ]} The decomposition of DCP proceeds at different rates depending on the temperature; it has been proposed that at 175 °C the reaction occurs in only 1 minute.^{[ 41 ]} The resulting structure from this reaction is presented in Figure 2a. Figure 2b shows the effect on PLA chains, where these radicals promote hydrogen abstraction from PLA. Certain overlapping phenomena can recombine and form C‐C bonds, including branching or cross‐linking with adjacent chains.^{[ 28} , ^{42 ]} In addition, the plasticizer employed can also react with the free radical initiator via hydrogen abstraction. Figure 2c proposes the possible sites for hydrogen abstraction. In the literature, PEG is reported to react with anhydride groups via esterification.^{[ 33 ]} In this work, a different methodology is proposed by adding DCP to improve the properties of plasticized PLA formulations, such as migration or thermal stability, while preserving acceptable ductility.

Figure 2.

Graphical representation of the effect of free radical initiator on the materials employed: a) free radical initiator, b) PLA, and c) plasticizers.

Hydrogen abstraction in the employed plasticizers and PLA chains can induce different cross‐linking phenomena. PLA can react with PEG‐based plasticizers, promoting the desired reaction that preserves ductile properties while reducing migration. During the extrusion process, overlapping phenomena such as unbranched plasticizers may also occur. Also chains of the same type can react to form bonds between plasticizer chains or between PLA‐PLA bonds, resulting in a blend of materials.^{[ 28} , ³⁵ , ^{43 ]} The properties obtained after the proposed process are presented in this work and the expected mechanism of interaction between the system is represented in Figure 3 .

Figure 3.

Expected reaction mechanism during the reactive extrusion of the plasticized PLA films.

3.2. Mechanical Characterization of Plasticized Films

The main mechanical properties of plasticized PLA films are presented in Table 1 . PLA exhibits fragile behavior that limits its application in the industry. In this study, films made with PLA exhibited a tensile strength of 48.1 MPa and an elongation at break of 12.0%. In comparison, PLA manufactured by injection molding achieves up to 70 MPa with an elongation of 3% or lower.^{[ 44 ]} The film manufacturing process tends to align the polymer chains due to the shear induced by the extrusion process and the stretching applied to adjust the thickness of the film. This alignment of the chains is retained due to the rapid cooling of the film, as PLA tends to relax quickly if cooled slowly. Injection molding shear stress does not induce chain alignment due to a relaxation process that dilutes the alignment and also promotes a slower cooling process.^{[ 45 ]} Stretching a sample can significantly change its behavior, provoking changes in tensile strength and elongation at break depending on the conditions employed in the process. Mortalo et al. produced extruded PLA films with a maximum tensile strength of 42 MPa and 19% elongation at break, in a range similar to the films developed in this study.^{[ 46 ]} For laboratory‐scale production, other techniques beyond the extrusion process employed here have been reported. For instance, Ordoñez et al. utilized a thermocompression approach to develop neat PLA and cast films. The properties of these samples depend on the chosen method: the thermoformed films reached a tensile strength of 33 MPa and 3% elongation at break, while cast films achieved 21 MPa in tensile strength and 67% elongation. These differences reflect the organization of the chains within the structure, which influences the cohesiveness of the matrix.^{[ 47 ]}

Table 1.

Mechanical properties of plasticized PLA films.

	Elongation at break [%]	Tensile strength [MPa]	Tensile modulus [MPa]
PLA	12.0 ± 1.4 a)	48.1 ± 1.8 a)	1432 ± 131 a)
PLA‐PEG	33.7 ± 0.8 a)	29.2 ± 1.6 a)	766 ± 28 a)
PLA‐PEG‐R	22.6 ± 4.6 a)	30.1 ± 1.1 a)	775 ± 70
PLA‐MON	12.1 ± 1.9 a)	47.1 ± 1.9 a)	823 ± 64 a)
PLA‐MON‐R	6.1 ± 2.1 a)	50.1 ± 7.2 a)	996 ± 18 a)
PLA‐DI	61.3 ± 3.6 a)	41.5 ± 4.7	936 ± 63 a)
PLA‐DI‐R	29.8 ± 5.6 a)	46.6 ± 3.1 a)	950 ± 12 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

The addition of PEG‐based additives was intended to improve the ductility of PLA. The most common effect of adding plasticizers to films is the enhancement of elongation at break values, as reported by many authors.^{[ 9} , ^{48 ]} As a result of the modifications introduced in this study, significant differences are observed among the samples in terms of their elongation at break values. At the same time, due to the plasticization effect that enhances the sample's ductility, a reduction in tensile strength is observed. Chains tend to slide more easily, promoting both changes.^{[ 49 ]} In this work, some samples exhibited similar results to neat PLA despite including the PEG‐based plasticizer. Due to the changes catalyzed by the plasticizer, the best outcome in terms of flexibility is the composition with dioleate, exhibiting an elongation at break of 61.3%. The plasticization of PLA is complex, sometimes promoting an anti‐plasticization effect that reduces elongation or does not significantly change the value.^{[ 14 ]} This effect likely occurred with the monoleate plasticizer, which revealed elongation at break values similar to or even lower than neat PLA. Brdlik et al. investigated PLA films plasticized with conventional agents such as PEG (400 g mol⁻¹) and acetyl tributyl citrate (ATBC). The ATBC‐based materials reached nearly 80% elongation at break, with a tensile strength of about 35 MPa. In contrast, the PEG‐based films exhibited elongation values close to 55% and a tensile strength below 20 MPa.^{[ 50 ]} In this work, the tensile strength achieved was similar to or higher than the values reported by Brdlik et al. In terms of elongation at break, the highest results obtained also fell within the range presented in the cited manuscript.

In this study, the reactive extrusion process led to an increase in tensile strength and a reduction in elongation at break. This outcome suggests the formation of a cross‐linked network during reactive extrusion, where the plasticizer forms bonds with PLA chains. This effect is confirmed by the increase in the molecular weight measured by GPC. These bonds limit the improvement in elongation at break but contribute to enhanced tensile strength. Significant differences in tensile strength values arise upon the incorporation of DCP, particularly in the monoleate and dioleate samples, where the reactive extrusion process proves more effective due to the chemical structure of the plasticizers. In these REX samples, GPC analysis confirms that the most pronounced changes occur with monoleate and dioleate plasticizers, indicating enhanced cross‐linking and corresponding improvements in mechanical performance. As a result, a balance between ductility and improved tensile strength can be achieved. This effect is more pronounced in plasticizers containing double bonds, as peroxides tend to break these bonds, creating active sites for the formation of a cross‐linked network.^{[ 51 ]} Finally, concerning the tensile modulus, a clear trend of reduction is observed with the addition of PEG‐based plasticizers. This result is expected, as plasticizers enhance chain mobility, thereby decreasing the stiffness of the samples.^{[ 52} , ^{53 ]} This reduction is more pronounced in the PEG samples due to the lower molecular weight of the plasticizer, which enhances the efficiency of the plasticization effect. The comparison of the tensile modulus among the plasticized samples revealed that the presence of the plasticizer induces significant variations. Moreover, the addition of DCP led to a notable difference only in the sample containing the monooleate plasticizer. An improvement in ductility combined with reduced plasticizer migration is of considerable interest in food packaging. In this sector, ductile films play a crucial role in preserving the packaging's durability and integrity, thereby providing prolonged protection for food products.^{[ 9} , ^{54 ]}

3.3. Thermal Characterization of Plasticized Films

The thermal characterization of the sample was assessed using DSC and TGA techniques. Table 2 presents the main thermal parameters of DSC characterization, while Figures 4 and  5 show the DSC thermograms for the different materials developed here. Additionally, the thermal stability tested using TGA provided the main results shown in Table 3 , and Figure 6 presents the thermogravimetric curves.

Table 2.

DSC main properties of plasticized PLA films.

	First heat cycle						Cooling
	Tg) [°C]	Tcc) [°C]	Tm) [°C]	ΔHcc) [J g−1]	ΔHm) [J g−1]	Xc) [%]	Tmc) [°C]	ΔHmc) [J g−1]
PLA	57.2 ± 0.3 a)	80.8 ± 0.4 a)	153.5 ± 0.5 a)	18.0 ± 0.3 a)	31.6 ± 0.6 a)	14.6 ± 0.2 a)	–	–
PLA‐PEG	38.8 ± 0.2	79.1 ± 0.5 a)	151.7 ± 0.6 a)	18.3 ± 0.3 a)	28.3 ± 0.5 a)	11.9 ± 0.3 a)	–	–
PLA‐PEG‐R	38.3 ± 0.3 a)	69.5 ± 0.6 a)	146.3 ± 0.4 a)	16.8 ± 0.2 a)	28.1 ± 0.4 a)	13.5 ± 0.3 a)	–	–
PLA‐MON	44.2 ± 0.4 a)	68.8 ± 0.5	151.8 ± 0.3 a)	19.5 ± 0.4 a)	33.4 ± 0.5 a)	16.6 ± 0.2 a)	–	–
PLA‐MON‐R	43.7 ± 0.3 a)	77.3 ± 0.4 a)	148.7 ± 0.6 a)	17.1 ± 0.3 a)	26.1 ± 0.5 a)	10.8 ± 0.2 a)	101.4 ± 0.3 a)	26.0 ± 0.7 a)
PLA‐DI	44.9 ± 0.2 a)	79.4 ± 0.5 a)	151.5 ± 0.7 a)	11.5 ± 0.1 a)	28.2 ± 0.7 a)	20.0 ± 0.4	–	–
PLA‐DI‐R	43.7 ± 0.4 a)	73.6 ± 0.4 a)	149.2 ± 0.6 a)	13.2 ± 0.1 a)	25.2 ± 0.6 a)	14.3 ± 0.3 a)	104.5 ± 0.2 a)	22.6 ± 0.6 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

Figure 4.

DSC scan for the first heating of plasticized PLA films. Red region represents the T_m, in green T_cc, and blue highlights the T_g.

Figure 5.

DSC scan for the cooling of plasticized PLA films. Green region highlights the T_mc region.

Table 3.

TGA properties of plasticized PLA films.

	T5 [°C]	Tmax [°C]	Residue
PLA	297.2 ± 1.2 a)	366.7 ± 0.7 a)	3.5 ± 0.2 a)
PLA‐PEG	268.7 ± 1.4 a)	312.5 ± 0.8 a)	1.2 ± 0.3 a)
PLA‐PEG‐R	288.7 ± 1.3 a)	372.4 ± 0.9 a)	0.3 ± 0.2 a)
PLA‐MON	293.4 ± 0.9 a)	373.9 ± 1.2 a)	0.8 ± 0.4
PLA‐MON‐R	303.8 ± 1.7 a)	371.3 ± 1.3 a)	0.8 ± 0.2 a)
PLA‐DI	311.4 ± 1.2	372.6 ± 1.5 a)	1.0 ± 0.3 a)
PLA‐DI‐R	333.8 ± 1.5 a)	376.7 ± 0.9 a)	0.2 ± 0.1 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

Figure 6.

TGA curves of plasticized PLA films.

The DSC characterization shows results from the first heating cycle immediately after the film was manufactured. This characterization reveals the crystallization achieved during the manufacturing process, which is representative of the properties of the film during its use. A clear plasticization effect was observed with the addition of PEGs, regardless of their molecular weights or the processing method used. All plasticized samples exhibited lower T_g compared to neat PLA, demonstrating the ability of PEGs to increase the free volume between PLA polymer chains. The glass transition phenomenon is highlighted in blue in Figure 4. As observed, the reduction in T_g was more pronounced in PLA‐PEG and PLA‐PEG‐R samples than in those with higher molecular weight PEGs (MON and DI). This finding aligns with the fact that plasticizers with lower molecular weights are generally more effective at reducing T_g.^{[ 20 ]} Furthermore, the decrease in T_g values corresponds well with the improvement in material flexibility, as evidenced by the increase in elongation at break. Additionally, the T_g values follow the same trend as tensile modulus and tensile strength, while showing the opposite trend to elongation at break. Among the observed differences, the most prominent variation depends on the specific plasticizer used, primarily due to the influence of the molecular weight of the plasticizer used. In this context, for a given plasticizer, the incorporation of DCP does not result in significant changes.

PLA exhibits a low crystallization rate,^{[ 55} , ^{56 ]} corroborated by a cold crystallization process during the heating program in DSC, where the chains rearrange to achieve higher crystallinity. This process is highlighted with a green region in Figure 4. It should be noted that the film's manufacturing process provokes the film to rapidly cool due to the film's low thickness, affecting the degree of crystallization. For example, Ma et al. studied different isothermal crystallization conditions, showing that the highest tensile and impact strength are obtained for samples cooled faster.^{[ 57 ]} This indicates that the fast‐cooling conditions characteristic of the film's manufacturing process provide the best mechanical properties for the material used. Since the cooling process was conducted identically for all samples, no significant differences in melting temperature were detected, as confirmed by the statistical analysis. However, variations in the crystalline structure may lead to the appearance of distinct melting peaks, as less stable crystalline arrangements can develop when crystallization occurs at lower temperatures.^{[ 58 ]}

With the modifications in PLA by adding plasticizers and processing by REX, there is no consistent trend in the measured cold crystallization enthalpy. In general, the melting enthalpy is reduced in plasticized films compared to neat PLA. However, this trend is not observed in the monoleate film, likely because some plasticizers promote a nucleation effect, aiding the formation of nuclei from which crystals grow.^{[ 59 ]} With more nuclei, samples achieve a higher degree of crystallinity. In addition, in Figure 5 some exothermic peaks related to the melt crystallization of the sample are observed. In general, PLA has a low crystallization ability that can be managed by the addition of nucleating agents. In this context, the addition of peroxides is reported to act as a nucleating agent promoting this phenomenon.^{[ 60 ]} As a result of the modifications introduced through the addition of PEG‐based plasticizers and the incorporation of DCP, significant differences were observed among the samples, as confirmed by the statistical analysis.

The melting process involves the fusion of PLA crystals formed during sample manufacturing. The melting behavior of the films is marked with a red region in Figure 4. As the composition of each formulation changes with the addition of PEG‐based plasticizers and DCP, crystallinity is analyzed by calculating the degree of crystallinity using the equation provided in the experimental section. The addition of PEG reduces the degree of crystallinity in the samples, likely due to the disruptive effect caused by the incorporation of PEG into the PLA chains, despite the increased mobility of PLA during the manufacturing process.

Regarding the TGA properties of the manufactured films (Figure 6), the weight loss curves of all the tested samples exhibit a single step degradation process. PLA begins its degradation at 297.2 °C. The addition of PEG reduces this temperature, as plasticizers with low molecular weight tend to volatilize at lower temperatures.^{[ 61 ]} Despite this, degradation of the PLA‐PEG sample starts at 268.7 °C, still above the temperatures used during the manufacturing process and/or the materials' intended uses. As molecular weight increases, this parameter rises to 311.4 °C in the PLA‐DI sample, which exceeds that of neat PLA. This stabilization effect, suggesting that the employed plasticizer can enhance structural stability by extending thermal stability, is supported by other studies.^{[ 62 ]} Furthermore, it is important to note that reactive extrusion also raises the initial degradation temperature. In the REX process, the interaction between the plasticizers and PLA chains intensifies due to bond formation among the chains in all plasticized samples, elevating this parameter to 333.8 °C for the PLA‐DI‐R.^{[ 28 ]} Achieving a higher initial weight loss temperature helps minimize plasticizer loss during manufacturing. Plasticizers typically exhibit low initial degradation temperatures owing to their low molecular weight. Although processing temperatures generally remain below the boiling point, some volatilization still occurs, leading to plasticizer loss.^{[ 14 ]} Enhancing the initial weight loss temperature broadens the processing window, which allows these materials to be applied in additional contexts while avoiding excessive plasticizer volatilization. Statistical differences in the onset degradation temperature were identified among certain samples. The increase in this parameter is attributed to changes in the molecular weight of the polymer network induced by REX process following DCP addition. This effect was particularly evident in samples plasticized with PEG and DI.

This trend is evident in the T_max parameter, which indicates the temperature at which degradation rate is maximum. For PLA, T_max is 366.7 °C, while PEG tends to lower this parameter. Similar to the initial degradation temperature, higher molecular weight plasticizers and the application of reactive extrusion contribute to a rise in T_max, enhancing the values over those of neat PLA. At the end of the process, the residue remains minimal across all tested formulations. During the scheduled heating program, both polymer and plasticizer chains disintegrate, leading to almost zero residue at the end of the test.^{[ 63 ]} Significant differences in this parameter were observed for the PEG and PEG‐R samples. PEG, being the plasticizer with the lowest molecular weight employed in this study, led to a reduction in the thermal stability of the material. In contrast, the use of plasticizers with higher molecular weight resulted in increased T_max values.

3.4. Thermo‐Mechanical Characterization of Plasticized Films

The behavior of the films under dynamic temperature conditions was assessed using DMTA. The main results are presented in Table 4 , and the curves obtained for the storage modulus (E’) during the test are shown in Figure 7a,b shows the tan (δ) curves. The modification of PLA led to a decrease in the E' from −30 °C for all samples. In this study, only PLA‐PEG‐R reported a slightly lower E’ compared to neat PLA. Above this temperature, the plasticizer caused a further reduction in storage modulus. As observed in the mechanical characterization, PEG‐based plasticizers increase the mobility of polymer chains, enhancing ductility and reducing the stiffness of the samples. The lowest E’ value at −50 °C was recorded for PLA‐PEG samples, at 1269 MPa. The PEG plasticizer used in this sample, has the lowest molecular weight in the study, demonstrating the highest plasticization efficiency, resulting in the greatest reduction in E’ and the lowest T_g.^{[ 64 ]} The reactive extrusion process led to a slight increase in E’ compared to the analogous sample without reactive extrusion. In the work by Kfoury et al., different methods of performing reactive extrusion on PLA plasticized materials resulted in variations in the final E’ properties. The incorporation of the plasticizer led to statistically significant differences in the E′ values, as demonstrated by the conducted statistical analysis. The cross‐linked network formed during reactive extrusion produced samples with an increased storage modulus while maintaining ductile behavior.^{[ 65 ]} As a result of the modification in the E′ induced by the REX process, significant differences were observed between samples containing the same plasticizer, with the exception of the dioleate‐based formulation, in which the observed differences were not statistically significant.

Table 4.

Thermomechanical properties of plasticized PLA films.

	E’ at −50 °C [MPa]	E’ at 20 °C [MPa]	Tg [°C]
PLA	1856 ± 33 a)	1616 ± 25 a)	63.9 ± 1.2 a)
PLA‐PEG	1269 ± 37 a)	976 ± 18	47.1 ± 1.5 a)
PLA‐PEG‐R	1930 ± 41 a)	1432 ± 31 a)	48.1 ± 1.3 a)
PLA‐MON	1488 ± 43 a)	1222 ± 24 a)	50.1 ± 0.8 a)
PLA‐MON‐R	1835 ± 35 a)	1467 ± 23 a)	49.6 ± 0.9 a)
PLA‐DI	1682 ± 32 a)	1288 ± 37 a)	48.0 ± 1.4
PLA‐DI‐R	1755 ± 27 a)	1293 ± 33 a)	54.3 ± 1.4 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

Figure 7.

Thermomechanical curves of plasticized PLA films.

As previously noted in the DSC results, a significant improvement from the addition of plasticizers to PLA is the reduction in T_g. This reduction enhances ductile properties at room temperature. The tan δ curves of plasticized PLA samples show that the peaks shifted to lower temperatures compared to neat PLA, further confirming the improvement in ductile properties, as observed in the mechanical properties. The incorporation of the plasticizer resulted in a reduction of the Tg, leading to statistically significant differences compared to neat PLA. However, the Tg values of the plasticized samples remained within a relatively narrow range, with the exception of the PLA‐DI‐R formulation, which exhibited a higher Tg that differed significantly from the other plasticized samples.

3.5. Migration and Solubility Characterization of Plasticized Films

The efficiency of a plasticizer is highly correlated with its molecular weight. In this context, low molecular weight plasticizers promote a better outcome of the blend but tend to migrate more. Migration can be problematic in applications such as the food preservation industry, where plasticizers can come into contact with food, potentially leading to toxicity issues.^{[ 66 ]} Migration is not solely dependent on plasticizer molecular weight; factors such as miscibility also play a significant role. Highly miscible plasticizers with the polymer matrix tend to migrate less than those with low miscibility, as low miscibility promotes weak interactions with the polymer, leading to rapid phase separation.^{[ 67} , ^{68 ]} In this study, the efficiency of various PEG‐based plasticizers processed through two different extrusion methods was evaluated, and the results of migration tests are presented in Table 5 .

Table 5.

Migration properties of plasticized PLA films in aqueous solution with simulant type A.

	Migration [mg kg−1]
PLA	8.0 ± 2.6 a)
PLA‐PEG	140.3 ± 7.2
PLA‐PEG‐R	40.8 ± 2.4 a)
PLA‐MON	60.7 ± 3.6 a)
PLA‐MON‐R	48.1 ± 3.2 a)
PLA‐DI	42.2 ± 2.2
PLA‐DI‐R	32.4 ± 1.7 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

To better understand the behavior of these plasticizers, miscibility parameters with PLA were calculated according to the numerical method proposed by Hoftyzer‐Van Krevelen based on the energetical contribution of each chemical group.^{[ 38 ]} All plasticizers used in this study appear to be miscible with PLA, as indicated by the Relative Energy Difference (RED) presented in Table 6 . The solubility parameters of all materials were calculated, and the corresponding distances in a 3D space were determined to evaluate the gap between the polymer and the plasticizer. This gap was compared with the solubility region of the polymer. When the distance between the polymer and the plasticizer remained below this solubility region, the RED parameter fell within the proposed limit for PLA, with values below 1. This result implies a theoretical solubility of the system, which suggests favorable long‐term performance. As expected, PEG is highly miscible with PLA, which is why it is widely used in the plasticization of PLA, demonstrating excellent results in enhancing ductile properties.^{[ 69} , ^{70 ]} The RED parameter for PEG is 0.55, while it increases to 0.72 for dioleate, indicating that the incorporation of two oleic acid chains reduces miscibility. Despite this increase in the RED parameter, the addition of PEG‐based plasticizers improved the performance of the manufactured films, as evidenced by all the characterization techniques employed. With respect to the solubility parameters, all plasticizers employed exhibited statistically significant differences among themselves, despite all values falling within the solubility range established for neat PLA.

Table 6.

Solubility parameter for PEG based plasticizers with PLA.

	${\delta }_d$	${\delta }_p$	${\delta }_h$	$\delta$	Ra	RED
PLA	15.3 a)	8.4 a)	11.0 a)	20.7 a)	–	–
PEG	16.6	3.2 a)	12.1	20.8 a)	5.9 a)	0.55 a)
MON	15.8 a)	2.0 a)	9.7 a)	18.7 a)	6.6 a)	0.62
DI	17.0 a)	1.8	9.0	19.3	7.7	0.72 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

Regarding migration, PLA exhibited a migration of 8.0 mg kg⁻¹ during the testing period. PLA is known for its ability to disintegrate in different media, leading to some weight loss during the test.^{[ 71 ]} Some migration tests show that neat PLA exhibited some weight loss during the testing period.^{[ 72 ]} As expected, the weight loss increases with the addition of plasticizers, which tend to migrate due to their lower molecular weight compared to the polymer's molecular weight. The trend exhibited by the employed plasticizers shows a reduction in weight loss with increasing molecular weight.^{[ 73 ]} Additionally, a reduction in weight loss is also observed with the reactive extrusion process. The new bonds formed during this process promote the formation of new bonds between the polymer and the plasticizer, which hinders the migration of the plasticizer. This phenomenon has also been observed by other authors, such as Yang et al., who noted an improvement in migration with the reactive extrusion process.^{[ 74 ]} It is important to bear in mind that the plasticizer migration limit stabilized by the Commission Directive 2006/141/EC, shall not exceed 60 mg of weight loss per each kg of food simulant employed.^{[ 75 ]} The results herein, only the PLA‐PEG exceeds the limit proposed. The other manufactured films are applicable in the food industry for packaging applications, making really interesting the modifications proposed by means of reactive extrusion and also the introduction of modified PEG plasticizers. Employing plasticizers with a higher molecular weight may help to reduce weight loss during testing, thus aligning with regulatory migration limits. However, such plasticizers generally lead to lower ductility because they are less efficient in enhancing flexibility. The approach proposed in this work, which combines the use of selected plasticizers with reactive extrusion, could achieve balanced mechanical performance and minimal migration, offering a sustainable option for food packaging applications. As each sample exhibited distinct migration behavior, the statistical analysis revealed significant differences among them.

3.6. Water Vapor Permeability Characterization of Plasticized Films

The integrity of protective films is closely tied to their atmospheric permeability, a critical factor considering their widespread use in food preservation. The primary goal of these films is to prevent the exchange of the protective atmosphere surrounding the food packaging. This is essential for maintaining the food's freshness and extending its shelf life.^{[ 76 ]} High water vapor permeability is desirable for fresh, breathing foods, as it helps to avoid condensation and proliferation of microorganisms; in contrast, low permeability is preferred for products that require dry environments to prevent undesired reactions. Therefore, the choice of material depends on the sensitivity of the food to moisture, the desired internal atmosphere, and storage conditions.^{[ 77 ]}

Table 7 methodically elucidates the properties of PLA films, providing an in‐depth view of their characteristics. As expected, the infusion of a plasticizer into these films results in a notable increase in permeability. This is attributable to plasticizers augmenting the free volume within the film's matrix. In the work of Chaos et al., an exhaustive characterization of PLA‐PEG samples was undertaken. Beyond the influence of free volume, the crystallinity of films plays a significant role. The crystalline regions create a complex, labyrinthine pathway that hinders gas transmission, thereby affecting the film's overall permeability.^{[ 78 ]}

Table 7.

WVP properties of plasticized PLA films.

	Thickness [µm]	WVP [g µm m−2 d−1)
PLA	20.3 ± 0.6 a)	4384 ± 132 a)
PLA‐PEG	14.7 ± 0.8 a)	5697 ± 114 a)
PLA‐PEG‐R	13.6 ± 0.7	6045 ± 121 a)
PLA‐MON	19.2 ± 0.6 a)	5346 ± 134 a)
PLA‐MON‐R	19.6 ± 0.5 a)	5452 ± 55 a)
PLA‐DI	11.0 ± 0.9 a)	6008 ± 180 a)
PLA‐DI‐R	18.5 ± 0.8	7066 ± 212 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

In this context, it can be argued that the incorporation of PEG‐based plasticizers plays a crucial role in increasing the free volume. This expansion is demonstrated through changes in both mechanical and thermal properties, highlighting the impact of the plasticizing effect. This effect is further emphasized by variations in the crystallinity of films. A marked decrease in crystallinity, denoted as X_c, facilitates an enlargement of the amorphous regions within the films, thereby simplifying the gas permeation process. As a consequence of the various modifications introduced in the plasticized films, statistically significant differences were observed among the samples, as confirmed by the conducted analysis. Additionally, variations in film thickness were identified, attributed to changes in the rheological behavior of the material induced by the plasticizer incorporation, which also led to significant differences in this parameter.

Moreover, additional phenomena significantly impact the materials' permeability. Notably, the polymorphism inherent in the PLA crystal structure promotes the development of various crystal forms, which arise from the material's differing crystallization capacities depending on the modifications introduced. Also, the molecular orientation of the samples during their fabrication emerges as a crucial element affecting the permeability. These factors underscore the intricate interplay between various parameters in determining the films' efficacy as protective barriers in food packaging applications.^{[ 79 ]}

3.7. Wetting Characterization of Plasticized Films

The wettability of the films was characterized by water contact angle measurements, with the results presented in Table 8 in which a reduction of the water contact angle with the plasticizer addition is observed. According to the criterion proposed by Vogler et al., water contact angles above 65° indicate materials with hydrophobic behavior.^{[ 80 ]} The characterized PLA film in this study exhibited a contact angle of 66.1°, confirming its hydrophobic nature, as supported by other authors.^{[ 81} , ^{82 ]} The use of PEG‐based plasticizers resulted in a reduction in water contact angles, indicating that the films adopt hydrophilic behavior. PEG is characterized by the presence of numerous hydrophilic hydroxyl groups, which promote changes in wetting properties.^{[ 69} , ^{83 ]} Additionally, the reaction extrusion process further reduced the water contact angle. This reduction could be related to changes in crystallinity, as lower crystallinity promotes a surface that facilitates water penetration into the internal structure, resulting in higher affinity with water.^{[ 84 ]} According to the statistical analysis, the most significant differences among the samples arise from the type of plasticizer used. The incorporation of DCP led to statistically significant differences only in the samples plasticized with dioleate.

Table 8.

Wetting properties of plasticized PLA films.

	Water contact angle [°]
PLA	66.1 ± 1.2 a)
PLA‐PEG	58.2 ± 1.3 a)
PLA‐PEG‐R	55.6 ± 1.2 a)
PLA‐MON	60.8 ± 0.8 a)
PLA‐MON‐R	60.0 ± 1.1 a)
PLA‐DI	55.9 ± 0.9 a)
PLA‐DI‐R	51.9 ± 0.8 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

3.8. Optical Characterization of Plasticized Films

The examination of the UV–vis characteristics of the film was meticulously conducted within the spectrum range of 200–800 nm, delineating two distinct segments: 200–400 nm as the ultraviolet (UV) range and 400–800 nm as the visible spectrum. In the field of food packaging manufacturing, film transparency is a critical attribute. High transparency not only allows consumers to visually inspect the product but also enhances the packaging's aesthetic appeal.^{[ 85} , ^{86 ]} However, it is important to note that within the wavelength range of 400–800 nm, food products are vulnerable to photochemical degradation. This necessitates careful consideration in the design and selection of packaging materials.^{[ 87 ]}

The UV–vis characterization results are shown in Figures  8 and 9 illustrates the optical clarity achieved. The PLA films reached approximately 90% transmittance between 350 nm and 800 nm, although a notable drop was detected below 350 nm. This behavior aligns with prior research on PLA‐based materials, as reported by Merino et al., indicating a similar trend across diverse formulations.^{[ 88 ]} Regarding transparency, 600 nm is frequently chosen as a reference wavelength, and different mathematical models have been suggested to define this property. It is commonly described as the capacity to see through.^{[ 89 ]} In Figure 9, the visibility of logos beneath the samples confirms the clarity of the tested specimens.

Figure 8.

UV scan for plasticized PLA films.

Figure 9.

Optical transparency for plasticized PLA film.

Introducing plasticizers lowered transmittance (Figure 8), but the resulting materials still allowed logos beneath each sample to remain discernible (Figure 9). This characteristic is valuable for food packaging, as it enables consumers to view the protected product. Meanwhile, reduced transmittance can inadvertently enhance UV shielding, thus assisting in product preservation. To further improve this effect, various additives, including inorganic nanoparticles such as titanium dioxide and organic compounds like lignin or cellulose, have been incorporated in similar systems, leading to superior UV resistance.^{[ 90 ]}

The addition of plasticizers, while compromising the barrier properties of the films, improves their protection against visible light (400‐800 nm), a phenomenon articulated by Stoll et al.^{[ 91 ]} This enhancement is particularly evident in films containing monooleate processed through reactive extrusion. Similarly, films treated with dioleate via reactive extrusion exhibited lower transmittance compared to their PLA counterparts. The reactive extrusion technique facilitates the modification of chemical groups within the material, engendering new configurations that bolster UV absorption and, consequently, elevate the level of protection offered against UV radiation.^{[ 92 ]}

3.9. Gel Permeation Chromatography Characterization of Plasticized Films

The molecular weight of the samples was determined using gel permeation chromatography (GPC) to evaluate the changes induced during the manufacturing process involving DCP. Neat PLA was employed as a reference, exhibiting a molecular weight of 158,877 g mol⁻¹. The incorporation of plasticizers led to a notable decrease in molecular weight, with PLA–PEG samples presenting the lowest value, at 103,003 g mol⁻¹. This reduction is consistent with previous findings indicating that additives, particularly plasticizers, can facilitate molecular weight degradation.^{[ 93 ]} Correspondingly, thermogravimetric analysis (TGA) revealed that plasticized samples experienced weight loss at lower temperatures, suggesting diminished thermal stability. This behavior is attributed to random chain scission events occurring during processing, primarily due to elevated temperatures and shear forces applied to the polymer matrix.^{[ 94 ]} Conversely, the inclusion of DCP favored cross‐linking reactions, which enhanced the molecular weight of plasticized PLA samples beyond that of neat PLA. This effect was particularly pronounced in the monoleate and dioleate formulations, likely due to their greater reactivity and capacity to establish additional covalent bonds upon DCP activation. The observed molecular weight increase following reactive extrusion aligns with previously reported trends in literature, where cross‐linking is known to significantly influence the structural integrity and molecular architecture of PLA‐based systems.^{[ 95 ]} With regard to the significant differences, these were evident among most of the samples. However, no statistically significant variation was observed between PEG and PEG‐R, as the effect of reactive extrusion in this case was minimal. This limited change aligns with the expected reaction mechanism, which suggests a low degree of modification for this particular formulation (Table 9 ).

Table 9.

GPC properties of plasticized PLA films.

	Mn [g mol−1]	PDI
PLA	158 877 ± 4766 a)	1.74 ± 0.05 a)
PLA‐PEG	103 003 ± 2060 a)	2.07 ± 0.04 a)
PLA‐PEG‐R	103 912 ± 4156	1.87 ± 0.07 a)
PLA‐MON	113 104 ± 3955 a)	1.57 ± 0.08
PLA‐MON‐R	186 297 ± 6515 a)	2.34 ± 0.12 a)
PLA‐DI	128 172 ± 3845 a)	1.57 ± 0.05 a)
PLA‐DI‐R	189 248 ± 3785 a)	2.18 ± 0.04 a)

^a) Distinct letters within the same column denote statistically significant differences between the samples at a confidence level of p < 0.05.

4. Conclusion

This study demonstrates that incorporating PEG‐based plasticizers into PLA films through reactive extrusion with DCP as a cross‐linking agent significantly enhances the material's mechanical and thermal properties. The inherent rigidity and brittleness of PLA are mitigated by robust chemical interactions formed during reactive extrusion, establishing covalent bonds between PLA chains and plasticizer molecules. This process reduces plasticizer migration and results in an increased tensile modulus while maintaining flexibility, as evidenced by consistent elongation at break values. GPC results indicate that the incorporation of DCP led to an increase in the molecular weight of the manufactured films, confirming the occurrence of a cross‐linking effect. This effect was most pronounced in samples plasticized with monoleate and dioleate. The observed increase in molecular weight is consistent with the differences identified in the properties of the plasticized films.

Thermal analyses, including TGA, DSC, and DMA, reveal that the modified PLA films exhibit high thermal stability while maintaining glass transition temperatures close to room temperature, improving ductility of the films at ambient conditions and expanding the usability of PLA films in applications requiring higher processing and operating temperatures. Assessments of optical properties and water vapor permeability indicate a slight reduction in transparency, which remains acceptable for practical use, and an increased permeability, beneficial for moisture‐sensitive applications such as food packaging.

These enhancements broaden the application potential of PLA by improving mechanical strength, thermal stability, ductility, and functional characteristics while preserving its biodegradability. The findings suggest that reactive extrusion with PEG‐based plasticizers is an effective method to produce more versatile and sustainable PLA materials suitable for a wider range of industrial applications. The proposed blending process can be efficiently scaled up. During the blending of the plasticizer with PLA, reactive extrusion is performed, enabling a cost‐effective solution for the industry avoiding the addition of complex process that increase costs.

Conflict of Interest

The authors declare no conflict of interest.

Lazaro‐Hdez C., Gomez‐Carturla J., Arrieta M. P., Boronat T., Ivorra‐Martinez J., Enhancing Polylactic Acid Films With Polyethylene Glycol‐Based Plasticizers: A Reactive Extrusion Approach. Macromol. Rapid Commun. 2025, 46, 2401130. 10.1002/marc.202401130

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.;