Development and Characterization of Wheat Flour Byproduct and Poly(butylene adipate-co-terephthalate) Biodegradable Films Enriched with Rosemary Extract via Blown Extrusion

Abstract

Developing sustainable packaging materials has become a global priority in response to environmental concerns associated with conventional plastics. This study used a wheat flour byproduct (glue flour, GF) and poly(butylene adipate-co-terephthalate) (PBAT) to produce films via blown extrusion, incorporating rosemary extract (RE) at 2% (FRE2) and 4% (FRE4) (w/w). A control film (FCO) was formulated without RE. The physicochemical, thermal, mechanical, and biodegradation properties of the films were evaluated. FCO, FRE2, and FRE4 exhibited tensile strength (TS) values between 8.16 and 9.29 MPa and elongation at break (ELO) above 889%. Incorporating 4% RE decreased luminosity (91.38 to 80.89) and increased opacity (41.14 to 50.95%). A thermogravimetric analysis revealed a main degradation stage between 200 °C and 450 °C, with FRE2 showing the highest residual mass (~15% at 600 °C). Sorption isotherms indicated enhanced hydrophobicity with RE, thereby reducing the monolayer moisture content from 5.23% to 3.03%. Biodegradation tests revealed mass losses of 64%, 58%, and 66% for FCO, FRE2, and FRE4, respectively, after 180 days. These findings demonstrate that incorporating RE into GF/PBAT blends via blown extrusion is a promising strategy for developing biodegradable films with enhanced thermal behavior, mechanical integrity, and water resistance, contributing to the advancement of sustainable packaging materials.

1. Introduction

The global food industry continues to expand, driving a significant increase in the demand for effective and sustainable packaging solutions. Traditionally, fossil-based synthetic polymers have been the primary materials used in food packaging due to their durability and versatility. However, the improper disposal and persistence of these materials in the environment have contributed to severe pollution, raising pressing concerns about their long-term sustainability. In response, biopolymers have gained attention as environmentally friendly alternatives, offering biodegradability and a reduced ecological footprint [1].

Among these alternatives, biopolymers derived from agro-industrial resources—such as starches, cellulose, and proteins—are widely used in formulating biodegradable materials, presenting a promising path toward more sustainable packaging [2]. More recently, research efforts have shifted toward valorizing agro-industrial byproducts, aligning with the principles of the circular economy. In Brazil, glue flour (GF)—a starch-rich, low-cost byproduct generated during wheat milling—is typically excluded from the food supply chain because it does not meet food-grade standards or due to expiration. While it is commonly diverted to the glue manufacturing sector, this underutilized material has shown potential for biodegradable film production. However, its use has been sparsely explored, with limited studies employing casting techniques [3,4] or injection molding [5].

Flours are inherently complex matrices composed of starch, proteins, lipids, and fibers, which interact synergistically to yield favorable film-forming properties [3,6,7]. The application of wheat flour in bioplastic production is not new [6,8,9,10,11]. For instance, Leblanc et al. [11] highlighted its potential as a cost-effective and energy-efficient substitute for purified starch, noting its similar film-forming ability despite certain mechanical limitations.

In addition to byproduct valorization, polymer blending represents a practical strategy for enhancing the performance and cost-efficiency of biodegradable films. These blends often incorporate renewable or partially fossil-derived polymers to achieve balanced properties suitable for industrial applications, particularly through scalable techniques such as blown film extrusion. According to Gao et al. [12], such blending approaches optimize mechanical and barrier properties while maintaining competitive production costs and lower environmental impact [13].

Despite the favorable composition of GF (approximately 65% starch, 11% protein, 8% fiber, 2% lipids, and 0.5% ash) for film production [3], its combination with poly(butylene adipate-co-terephthalate) (PBAT) remains unexplored, especially via blown film extrusion. This gap is particularly relevant given the compatibility of the PBAT with thermoplastic starches and its industrial applicability. PBAT is a flexible, biodegradable aliphatic–aromatic copolyester that is synthesized via the polycondensation of butanediol, adipic acid, and terephthalic acid, and it exhibits mechanical properties comparable to those of low-density polyethylene (LDPE) [14].

Concurrently, recent trends in packaging innovation have emphasized the incorporation of natural bioactive compounds, such as rosemary extract (RE), into biodegradable matrices to develop active and intelligent packaging systems [8]. RE is recognized for its antioxidant and antimicrobial activities [4], but its integration into thermoplastic films remains underexplored.

This study aims to fill this gap by producing and characterizing GF/PBAT films, which are processed through blown film extrusion and enriched with RE. The research focuses on evaluating their physicochemical, thermal, mechanical, and biodegradability properties, with particular attention given to the effects of RE incorporation. By combining a low-value industrial byproduct with a commercially available biodegradable polymer and a natural functional additive, this work contributes to the development of innovative, scalable packaging solutions that are aligned with sustainability goals.

Based on these premises, this study addresses the following research question: Can films produced from GF and PBAT and enriched with rosemary extract present adequate physicochemical, thermal, mechanical, and biodegradation properties for sustainable packaging applications?

The hypotheses are as follows: (i) the incorporation of rosemary extract will enhance the hydrophobicity and thermal stability of the films; (ii) the mechanical properties will remain within acceptable ranges for flexible packaging applications; and (iii) the films will retain their biodegradability despite the use of PBAT in the formulation.

2. Materials and Methods

2.1. Materials

Films were produced using glue flour (GF), poly(butylene adipate-co-terephthalate) (PBAT) (Ecoflex^®, BASF, Ludwigshafen, Germany), glycerol (Dinâmica, São Paulo, Brazil), and commercial food-grade rosemary extract (hydroalcoholic, 70%) (HEIDE Natural Ingredients, Pinhais, Brazil).

2.2. Production of GF/PBAT Films via Blown Extrusion

Figure 1 illustrates the steps in producing GF/PBAT films (FCO, FRE2, and FRE4) using blown extrusion. Firstly, glycerol and RE were mixed, after which PBAT and GF were added and manually combined with a spoon (Figure 1a). The ingredients were weighed according to

Table 1. Formulations of GF/PBAT (FCO, FRE2, and FRE4) films.

Ingredients	Formulations
	FCO	FRE2	FRE4
PBAT (g·100 g−1)	60	60	60
GF (g·100 g−1)	24	24	24
Glycerol (g·100 g−1)	16	14	12
RE (g·100 g−1)	0	2	4

PBAT: poly(butylene adipate-co-terephthalate); GF: glue flour; RE: rosemary extract. FCO: control film (without RE); FRE2: film with 2% (w/w) of RE; FRE4: film with 4% (w/w) of RE.

. The mixture was then dried in an oven for 1 h at 60 °C. The cylindrical profiles were processed (Figure 1b) using a laboratory single-screw extruder (model EL-25, BGM, São Paulo, Brazil) with a screw speed of 40 rpm and a die with two holes, each 4 mm diameter. The barrel temperature profile was 90/120/120/115 °C across the four zones. The extruded cylindrical profiles were cut into small, uniform pellets (granules) using a pelletizer (BGM, São Paulo, Brazil) (Figure 1c), and the pellets were further extruded to produce films. The barrel temperature profile for film production was 90/120/120/135 °C across the four zones, with the 50 mm film-blowing die set at 130 °C, utilizing internal air to form the film “bubble” (Figure 1d). A screw speed of 35 rpm was maintained during this stage. One batch of each formulation (approximately 5 m in length) was produced, and representative parts of each film were utilized in the subsequent tests.

2.3. Film Characterization

2.3.1. Color and Apparent Opacity

The CIELAB color system parameters (L*, a*, b*, and ΔE*) of the films were determined using a colorimeter MiniScan XE Plus (HunterLab, Reston, VA, USA). The films were placed on a white surface (calibration ceramic), and measurements were taken at random points.

The film’s apparent opacity was determined using a colorimeter (CR-400, Konica Minolta, Osaka, Japan) following the method described by Maria et al. [15]. The illuminant D65 (daylight) and a visual angle of 10° were used. Opacity was calculated as the ratio of the opacity of the sample over a black standard (Opb) to the opacity over a white standard (Opw). Apparent opacity was represented on an arbitrary scale of 0%–100%. The analyses were performed in triplicate.

2.3.2. Thickness, Density, and Grammage

The thickness of the films was determined using a digital micrometer with a resolution of 0.001 mm. Measurements were taken in at least 5 different film positions, with 10 repetitions, to calculate the average thickness.

Film samples (2 × 2 cm) were placed in a desiccator containing silica (0% RH) for 20 days to determine the grammage (G) and density (ρ^s) using Equations (1) and (2).

$$G(g·{cm}^{-2})={\displaystyle \frac{m}{A}}$$

(1)

$${\rho }^S(g·{cm}^{-3})={\displaystyle \frac{m}{A\times \epsilon }}$$

(2)

Here, A is the film area (4 cm²), m is the film weight after 20 days (g), and ε is the film thickness.

2.3.3. Moisture and Solubility in Water

Moisture and solubility determinations were conducted following the methodology described by Peron-Schlosser et al. [3]. Films were cut into disks (∅ 2 cm), weighed (m₀, g), dried in an oven for 24 h at 105 °C, and reweighed (m₁, g). The dried films were then immersed in Erlenmeyer flasks containing distilled water (150 mL) and agitated using a shaker at 25 °C for 24 h. Subsequently, the samples were dried in an oven for 24 h at 105 °C and weighed (m₂, g). The moisture and solubility percentages for each formulation were calculated using Equations (3) and (4), respectively. The analysis was performed in triplicate.

$$Moisture\left(\%\right)={\displaystyle \frac{m_0-m_1}{m_0}}\times 100$$

(3)

$$Solubility(\%)={\displaystyle \frac{m_1-m_2}{m_1}}\times 100$$

(4)

2.3.4. Sorption Isotherm

The moisture sorption isotherms of the films were determined using the dynamic dew point method with the AquaSorp device (Decagon Devices, Pullman, WA, USA). Film samples were cut and pre-dried for 7 days in a desiccator containing anhydrous calcium chloride (CaCl₂). Subsequently, the dry samples (0.5–0.8 g) were individually placed in the AquaSorp isotherm generator. An initial desorption cycle was programmed to achieve the minimum water activity (a_w) at the top of the absorption test. The absorption cycle scanning was maintained between 0.25–0.80 of a_w at 25 °C. After the adsorption, a new desorption cycle was performed to determine the dry sample weight, which was used in the calculation of the equilibrium moisture content of the samples.

The Guggenheim Anderson de Boer (GAB) model (Equation (5)) was applied using Sorptrack 1:14 (Decagon Devices, Pullman, WA, USA).

$$m={\displaystyle \frac{m_0·k·C·a_w}{[(1-k·a_w)·(1-k·a_w+C·k·a_w)]}}$$

(5)

Here, m is the moisture (g·100g_solids⁻¹ or g·g_solids⁻¹); C (monolayer heat of sorption) and k (multilayer heat of sorption) are GAB constants; m₀ is the monolayer value, with the same units as m; and a_w is the water activity in the moisture, m.

2.3.5. Water Vapor Permeability (WVP)

The WVP was performed according to the standard method E96/96M-16 [16], with some modifications. Permeation cells (area of 0.0028 m²) were filled with silica (relative humidity (RH) 0%) and sealed with film specimens. The cells were then placed in desiccators containing a saturated NaCl solution (22 °C, RH 62%). The weight gain of the cells was monitored every 24 h until the water gain reached a constant rate. The experiments were conducted in triplicate. The WVP was calculated using Equation (6).

$$WVP={\displaystyle \frac{G}{t}}·{\displaystyle \frac{\epsilon }{{A·P}_s\left({RH}_1-{RH}_2\right)}}$$

(6)

Here, G·t⁻¹ is the slope of the straight line obtained by the mass gain of the cells over time (g·s⁻¹); $\epsilon$ is the film thickness (m); A is the permeation cell area (m²); P_s is the saturation vapor pressure of water (Pa); RH₁ is the relative humidity in the desiccator; and RH₂ is the relative humidity in the cell.

2.3.6. Coefficients of Solubility and Water Diffusion

The solubility (β) and water diffusion (D_w) coefficients of the films were determined according to Larotonda et al. [17]. The β coefficient was obtained from the first derivative of the film sorption isotherm (GAB model) concerning a_w, which was divided by the water vapor pressure (p_s) at the sorption isotherm temperature. Physically, β is the water partition coefficient between the air and the film, calculated using Equation (7).

$$\beta ={\displaystyle \frac{Ck{m}_0}{p_s}}\left[{\displaystyle \frac{1}{\left(1-k{a}_w\right)\left(1-k{a}_w+Ck{a}_w\right)}}-{\displaystyle \frac{a_w}{\left(1-k{a}_w\right){\left(1-k{a}_w+Ck{a}_w\right)}^2}}\left[-k\left(1-k{a}_w+Ck{a}_w\right)+\left(1-k{a}_w\right)\left(-k+Ck\right)\right]\right]$$

(7)

Here, C, m₀, and k are GAB model-adjusted parameters, and β is expressed in g_water·g_solids⁻¹·Pa⁻¹.

The D_w coefficient can be determined using the film WVP, β, and density (ρ^s) values, as shown in Equation (8).

$$D_w={\displaystyle \frac{WVP}{{\rho }^S\beta }}$$

(8)

2.3.7. Tensile Strength, Young’s Modulus, and Elongation at Break

A universal testing machine (Shimadzu, model AG-I, Tokyo, Japan) equipped with a 10 kN load cell was used to determine the mechanical properties of the films. Tensile strength (TS), Young’s modulus (YM), and elongation at break (ELO) were determined according to the ASTM standard D882-18 [18]. Ten samples of each formulation (100 × 25 mm) were cut in the longitudinal direction. The tests were performed with a crosshead speed of 0.8 mm·s⁻¹ and an initial grip distance of 50 mm. Before testing, the samples were conditioned at 25 °C and RH of 58% for 48 h.

2.3.8. Morphology

A scanning electron microscope (SEM) (JEOL, model JSM 6360-LV, Akishima, Japan) was used to observe the cross-section and surface morphology of the films. Before analysis, the films were fractured using liquid nitrogen (cryogenic fracture) and gold-coated (Balzers Union, model FL 9496, Balzers, Liechtenstein). Images were taken of the cross-section at a magnification of 250× and the surface at a magnification of 1700×.

2.3.9. Fourier-Transform Infrared (FT-IR)

FT-IR analyses were carried out from 4000 to 500 cm⁻¹ with a resolution of 4 cm⁻¹. A Perkin-Elmer Spectrum (model 1000 FT-IR, Shelton, CT, USA) with a Universal Attenuated Total Reflectance (UATR, ZnSe crystal, Santa Clara, CA, USA) module was used. Before the analysis, film samples were conditioned in a silica desiccator for 7 days.

2.3.10. X-Ray Diffraction

The X-ray diffraction analysis of the films was carried out using a Panalytical X’Pert PRO MRD diffractometer (Almelo, The Netherlands) using copper Kα radiation (λ = 1.5418 Å), with a voltage of 30 kV and an operating current of 30 mA. The diffraction intensity measurements were performed in the 2θ range of 2 to 60° at room temperature, with a step size of 0.05° and a scanning speed of 1° s⁻¹. Before the analysis, the films were cut into 20 × 30 mm dimensions and conditioned in a desiccator at 0% RH for 7 days at 25 °C.

The relative crystallinity index (RCI) was estimated using the ratio of the area of the crystalline region (CR) in relation to the total area, which is the sum of the crystalline region (CR) and the amorphous region (AR) (Equation (9)) [19].

$$RCI={\displaystyle \frac{CR}{(CR+AR)}}\times 100$$

(9)

2.3.11. Thermal Properties

A Differential Scanning Calorimeter (DSC) (model DSC 60, Shimadzu Co., Tokyo, Japan) was used to evaluate the thermal properties of the films. The samples (8–10 mg) were packaged in aluminum pans. They were then heated under a nitrogen atmosphere from 25 to 200 °C at a rate of 10 °C·min⁻¹ and cooled from 200 to 40 °C at a rate of 5 °C·min⁻¹. For thermogravimetric analysis (TGA), samples weighing approximately 10 mg were heated at a rate of 10 °C·min⁻¹ from 25 °C to 700 °C, with nitrogen as the purging gas.

2.3.12. Antimicrobial Activity

The disk diffusion method determined the antimicrobial activity of the FCO, FRE2, and FRE4 films [20], according to the methodology described by Peron-Schlosser et al. [4].

2.3.13. Biodegradation Tests

The biodegradation test was performed based on the standard method G160-12 [21], with modifications (Figure 2). The soil used for biodegradation evaluation consisted of a mixture of commercial garden-prepared soil [composition: humus, poultry manure, mineral fertilizer (NKP 10-10-10), charcoal powder, organic compost, and limestone] and coarse sand in a 2:1 ratio with a pH level of around 6.0 and 20% moisture. The films were cut into squares (50 × 50 mm), weighed, fixed onto aluminum screens, and buried in resistant, waterproof containers at a minimum depth of 12.7 cm. The containers were maintained at room temperature for a period of 180 days. At 15, 30, 50, 70, 80, 90, 100, 120, and 180 days, the samples were removed from the soil, rinsed with distilled water, photographed, and then dried in an oven at 50 °C for 24 h until they reached a constant weight. The percentage of weight loss was calculated using Equation (10) as follows:

$$Weightloss(\%)={\displaystyle \frac{m_i-m_f}{m_i}}\times 100$$

(10)

where m_i is the initial mass of the film before burial, and m_f is the dry mass of the film after excavation and washing.

2.4. Statistical Analysis

Analysis of variance (ANOVA) and Tukey’s test were used to evaluate the data obtained at a significance level of 5% (p < 0.05) using Statistica 7.0 software (Statsoft Inc., Tulsa, OK, USA, 2004).

3. Results and Discussion

3.1. Visual Aspects and Color Measurements

The films exhibited an opaque yellowish to greenish coloration, with good homogeneity and handleability. Color and opacity are important properties of biodegradable films, as they contribute to protection and influence consumer purchasing decisions. The color parameters and opacity values of FCO, FRE2, and FRE4 films are presented in

Table 2. Color parameters and opacity of FCO, FRE2, and FRE4 films.

Film	L*	a*	b*	ΔE*	Opacity
FCO	91.38 ± 0.15 a	−1.65 ± 0.05 b	9.40 ± 0.38 c	-	41.14 ± 3.64 b
FRE2	87.31 ± 0.40 b	−1.84 ± 0.22 b	28.51 ± 1.25 b	19.54 ± 1.00 b	35.51 ± 0.78 c
FRE4	80.89 ± 0.70 c	3.59 ± 0.69 a	49.20 ± 0.95 a	41.66 ± 1.19 a	50.95 ± 2.52 a

Different lowercase letters in the same column indicate significant differences (p < 0.05). FCO: control film (without RE); FRE2: film with 2% (w/w) of RE; FRE4: film with 4% (w/w) of RE.

. As expected, the incorporation of RE affected the optical properties. The FCO film exhibited a yellowish hue, whereas the FRE2 and FRE4 films displayed a greenish tone.

The L* parameter decreased with the addition of RE, indicating reduced brightness. This trend aligns with findings by Peron-Schlosser et al. [4] for GF and RE films, as well as Campos et al. [22], who reported a similar effect when incorporating curcumin into thermoplastic starch (TPS)/PBAT films. The L* value of the FCO film was comparable to the values reported by Silva et al. [23] (L* = 94.84) and Mücke et al. [24] (L* = 90.21) for cassava starch/PBAT (70:30) films produced via blown extrusion. However, Balan et al. [8] reported lower luminosity (L* = 88.61) in wheat flour/PBAT (60:40) films, which they attributed to Maillard reactions between proteins and carbohydrates during extrusion. In the present study, the Maillard reaction likely did not affect film luminosity, possibly due to the higher PBAT content relative to GF in the formulation.

Regarding chromatic parameters, the a* value of the FCO film did not differ significantly (p > 0.05) from that of FRE2. However, FRE4 showed a significant increase in a* compared to FCO, indicating a shift toward red. The b* values increased significantly with RE incorporation, reflecting enhanced yellowness. These changes culminated in perceptible color differences (ΔE*) for both FRE2 and FRE4 relative to the control, with values of 19.54 and 41.66, respectively, confirming a statistically significant alteration in film coloration (p < 0.05).

Opacity, which is a crucial parameter for food packaging applications, was also affected by RE incorporation. As observed in Table 2, the addition of 2% RE (FRE2) significantly reduced (p < 0.05) the opacity of the film compared to the control (FCO), while the incorporation of 4% RE (FRE4) led to a significant increase. This suggests that the impact of RE on optical properties is concentration-dependent. This finding is consistent with the results reported by Balan et al. [8], who observed increased opacity in wheat flour/PBAT films after adding oregano essential oil. According to Galdeano et al. [25], film opacity can be influenced by formulation factors such as film thickness and starch–plasticizer interactions. The higher opacity values observed in FRE4 may be attributed to increased pigment concentration and possible structural modifications induced by RE addition.

In addition to influencing color and opacity, incorporating RE may also have sensory implications for the films, particularly regarding odor. Although it was not evaluated in the present study, the characteristic aroma of rosemary could impact consumer acceptance if the films are used in direct contact with food. Further studies assessing the sensory attributes of the films, including odor and the potential migration of volatile compounds, are recommended to better understand their applicability in food packaging contexts.

3.2. Thickness, Grammage, and Density

Table 3. Thickness, density, grammage, moisture, and water solubility of FCO, FRE2, and FRE4 films.

Film	Thickness (mm)	Density (g·cm−3)	Grammage (g·cm−2)	Moisture (%)	Solubility (%)
FCO	0.175 ± 0.012 b	1.11 ± 0.03 a	0.019 ± 0.002 b	20.70 ± 0.42 a	1.09 ± 0.02 b
FRE2	0.220 ± 0.024 a	1.04 ± 0.03 a	0.022 + 0.003 a	19.17 ± 0.42 b	1.40 ± 0.08 a
FRE4	0.233 ± 0.012 a	1.06 ± 0.06 a	0.023 ± 0.004 a	17.07 ± 0.09 c	1.42 ± 0.13 a

Different lowercase letters in the same column indicate a significant difference (p < 0.05). FCO: control film (without RE); FRE2: film with 2% (w/w) of RE; FRE4: film with 4% (w/w) of RE.

presents the results for the thickness, density, grammage, moisture, and water solubility of FCO, FRE2, and FRE4 films.

The thickness of the films ranged from 0.175 mm (FCO) to 0.233 mm (FRE4). Although the FRE2 and FRE4 films did not differ statistically from each other (p > 0.05), both differed significantly from the FCO film. In blown film extrusion, thickness is primarily influenced by processing parameters such as winder speed and the airflow within the film bubble [8]. According to Kraus et al. [26], variation in formulation and processing conditions can also significantly affect film thickness. In the present study, it was not feasible to standardize the thickness across all formulations; notably, the airflow had to be reduced during the extrusion of the FRE4 film to prevent rupture, which likely contributed to its increased thickness.

The density of FCO, FRE2, and FRE4 films ranged from 1.04 to 1.11 g·cm⁻³, with no statistically significant differences among the formulations (p > 0.05). These values are comparable to those of conventional food packaging materials, such as polystyrene (1.04–1.12 g·cm⁻³) and polyamide (1.05–1.14 g·cm⁻³), but higher than those typically reported for low- and high-density polyethylene (0.915–0.935 g·cm⁻³, 0.945–0.964 g·cm⁻³, respectively) [27]. Compared to starch/PBAT blends, GF/PBAT films exhibited lower density. For instance, Santos et al. [28] reported densities between 1.14 and 1.23 g·cm⁻³ for starch/PBAT/montmorillonite films. The lower density observed in this study may be attributed to the high PBAT content in the formulations. This difference may be attributed to the higher PBAT content in the current formulations, as increased PBAT content has been associated with reduced film density [29].

Grammage values ranged from 0.019 to 0.023 g·cm⁻², with the FCO formulation differing significantly (p < 0.05) from the others. According to Almeida et al. [30], grammage is directly related to both mechanical and barrier properties of films, implying that films with higher grammage may offer improved structural integrity and performance under stress.

3.3. Moisture and Solubility

The moisture content of FCO, FRE2, and FRE4 films ranged from 20.70% to 17.07%, with statistically significant differences among formulations (p < 0.05) (Table 3). The incorporation of RE led to a reduction in moisture content of approximately 17.5% compared to the control (FCO). This reduction in moisture upon RE addition may be attributed to hydrophobic compounds present in the extract, which can interfere with water retention in the polymer matrix. The moisture level of the FCO film was comparable to that reported by Gallo-García et al. [31] (21.70%) but higher than the 6.99% observed by Mücke et al. [24] in TPS/PBAT blend films.

Although all formulations exhibited low water solubility, adding RE increased solubility by approximately 30%. FRE2 and FRE4 showed statistically higher solubility values than the FCO (p < 0.05). After 24 h of immersion in water, none of the films showed visible structural degradation, confirming their resistance to aqueous environments. A similar trend was reported by Gallo-García et al. [31] in TPS/PBAT films.

The solubility values obtained in this study were lower than those reported for other starch-based blends with added bioactive compounds. For instance, Gallo-García et al. [31] observed solubility values between 4.55% and 6.25% in TPS/PBAT films containing Chlorella pyrenoidosa biomass. Balan et al. [8] reported solubility ranging from 3.71% to 14.30% in wheat flour/PBAT films with oregano essential oil (3.71%–14.30%), while Silva et al. [23] and Mücke et al. [24] reported even higher solubility values for TPS/PBAT films containing Araucaria angustifolia extract (24.68%–28.15%) and soluble curcumin (20.45%–24.14%).

The relatively low solubility observed in GF/PBAT films in the present study is likely due to the high PBAT content (60%) in the formulation. Given the hydrophobic nature of PBAT, its presence limits water uptake and dissolution, thus enhancing the resistance of the films to aqueous environments.

3.4. Sorption Isotherms in Biodegradable Films

The sorption isotherms of the FCO, FRE2, and FRE4 films are shown in Figure 3. All samples exhibited Type II–III isotherm profiles, which is consistent with previous studies on starch-based and biodegradable films [32,33]. In all formulations, moisture content increased sharply at a_w levels between 0.6 and 0.9, which can be attributed to the progressive replacement of starch–starch and starch–glycerol hydrogen bonds by starch–water and water–glycerol interactions [32,34]. This behavior is commonly associated with the “pool of water” phenomenon, where excess water does not integrate into the polymer matrix. Instead, it remains free water on the surface or in capillary structures [35].

The GAB model was applied to fit the experimental data, and the corresponding parameters are presented in

Table 4. GAB model parameters adjusted for sorption isotherms of FCO, FRE2, and FRE4 films.

Film	GAB Model Parameters			R2
	m0 *	k *	C
FCO	5.2257	0.8266	10,000	0.990
FRE2	5.2709	0.8072	10,000	0.995
FRE4	3.0256	0.9288	10,000	0.991

* Significant parameters (p < 0.05); m₀: monolayer moisture content. FCO: control film (without RE); FRE2: film with 2% (w/w) of RE; FRE4: film with 4% (w/w) of RE.

. Among the model parameters, only C showed no statistically significant difference among the formulations (p > 0.05). The model demonstrated excellent goodness of fit (R² > 0.99) across all samples, confirming its suitability for describing the water sorption behavior of biodegradable films. This outcome agrees with other studies on bioplastics and active packaging systems [2,35,36].

The films FCO and FRE2 exhibited monolayer moisture values (m₀) of approximately 5.2 g of water·100 g⁻¹ of dry solid, whereas FRE4 showed a notably lower value of around 3 g of water·100 g⁻¹ of dry solid. This reduction suggests that the incorporation of 4% RE decreased the hydrophilicity of the film, rendering FRE4 more hydrophobic compared to FCO and FRE2. The observed decrease in m₀ indicates a reduction in high-energy binding sites for water molecules. This is consistent with incorporating hydrophobic bioactive compounds, as evidenced by the reduced m₀ (from 5.2257 to 3.0256, Table 4) and the lower coefficient β observed in FRE4 (

Table 5. Water vapor permeability (WVP), solubility (β), and diffusion coefficients (D_w) of FCO, FRE2, and FRE4 films.

Film	ΔRH (%)	WVP (×10−11 g·m−1·s−1·Pa−1)	β (×10−5 g·g−1·Pa−1)	Dw (×10−11 m2·s−1)
FCO	0–62	9.03 ± 1.35 a	2.46	3.34 ± 0.49 b
FRE2	0–62	8.95 ± 1.14 a	2.39	3.62 ± 0.06 b
FRE4	0–62	8.88 ± 0.26 a	1.75	4.72 ± 0.51 a

Different lowercase letters in the same column indicate a significant difference (p < 0.05). ΔRH represents the gradient of relative humidity; FCO: control film (without RE); FRE2: film with 2% (w/w) of RE; FRE4: film with 4% (w/w) of RE.

).

According to Labuza and Altunakar [37], the GAB k parameter reflects the energy of sorption in multilayer regions. When k ≈ 1, it suggests either an absence of specific interactions between water molecules and the material in the multilayer domain or a uniform sorption energy, characteristic of a more homogeneous solid structure. All films exhibited k values close to 1. FCO and FRE2 exhibited values near 0.8, while FRE4 exhibited a notably higher value of approximately 0.9. This increase may indicate a more ordered or compact microstructure in FRE4, possibly resulting from interactions between RE constituents and the polymer matrix, which could enhance the barrier properties of the films. This hypothesis is supported by the sorption isotherms (Figure 3) and the reduced β value (Table 5), which indicate decreased water affinity, as well as by the SEM micrographs (Figure 4), which show a slightly more cohesive internal structure in FRE4 compared to FCO and FRE2, despite the presence of some fissures.

3.5. Water Vapor Permeability (WVP), Solubility (β), and Diffusion Coefficient (D_w)

Table 5 presents the WVP, β, and D_w values for the FCO, FRE2, and FRE4 films. No statistically significant differences (p > 0.05) in WVP were observed among the formulations, which may be attributed to morphological similarities in the film structures. The WVP values observed were slightly higher than those reported by Balan et al. [8] for wheat flour/PBAT films (5.33–6.06 × 10⁻¹¹ g·m⁻¹·s⁻¹·Pa⁻¹) and by Gallo-García et al. [31] for TPS/PBAT films (4.53 × 10⁻¹¹ g·m⁻¹·s⁻¹·Pa⁻¹), suggesting that the GF-based matrix exhibits slightly lower barrier performance under the tested conditions.

The incorporation of RE resulted in a decrease in β and a concurrent increase in D_w. Brandelero et al. [38] reported that higher β values indicate greater water affinity, whereas lower D_w values suggest better compatibility between starch and PBAT. Therefore, the observed decrease in β suggests that RE reduced the affinity for water of the films, possibly due to its hydrophobic constituents. Conversely, the increase in D_w implies reduced compatibility between the GF starch and PBAT phases, likely caused by phase separation or altered molecular interactions induced by the extract. This dual effect highlights the role of RE not only as a bioactive additive but also as a structural modifier of the polymer matrix.

3.6. Mechanical Properties

Table 6. Mechanical properties of FCO, FRE2, and FRE4 films.

Film	TS (MPa)	ELO (%)	YM (MPa)
FCO	9.29 ± 0.61 a	889.61 ± 81.00 a	25.64 ± 1.96 a
FRE2	8.16 ± 0.49 b	889.34 ± 99.64 a	25.43 ± 2.94 a
FRE4	9.07 ± 0.40 a	901.68 ± 93.72 a	27.16 ± 1.95 a

Different lowercase letters in the same column indicate a significant difference (p < 0.05). TS: tensile strength; ELO: elongation at break; YM: Young’s modulus. FCO: control film (without RE); FRE2: film with 2% (w/w) of RE; FRE4: film with 4% (w/w) of RE.

presents the mechanical properties of FCO, FRE2, and FRE4 films. The TS ranged from 8.16 MPa (FRE2) to 9.29 MPa (FCO), with FRE2 showing a statistically significant difference (p < 0.05) compared to the other formulations. The lower TS observed in FRE2 compared to FCO and FRE4 may be attributed to partial plasticizing effects of the RE at 2% (w/w), which could disrupt the starch–PBAT matrix without promoting sufficient intermolecular reinforcement. In contrast, the higher RE concentration in FRE4 may have led to additional molecular interactions or microstructural reorganization that counterbalanced this effect, resulting in TS values similar to those of the FCO. These TS values fall within the typical range reported in the literature for LDPE films (7–25 MPa), which are a conventional material used in food packaging [27]. Furthermore, the TS values observed in this study were higher than those reported for TPS/PBAT films incorporating microalgae biomass [31], pomegranate peel extract [32], curcumin [24], and wheat flour with oregano essential oil [8] but slightly lower than the TS values observed in TPS/PBAT (20:80) blends [12,39,40].

The ELO ranged from 889.34% to 901.68%, indicating high flexibility, with no statistically significant differences among the formulations (p > 0.05). These values are consistent with those reported by Gao et al. [12] (~800%) and Liu et al. [39] (1264.3%) for TPS/PBAT films, suggesting that the incorporation of RE did not compromise the extensibility of the films.

The YM, which reflects the stiffness of the materials, ranged from 25.43 to 27.16 MPa, with no significant differences among the formulations (p > 0.05). These values indicate low rigidity, which is characteristic of ductile materials. The YM values of the FCO, FRE2, and FRE4 films were lower than those reported by Liu et al. [39] (30.80 MPa), Mücke et al. [24] (37.19 MPa), and Gallo-García et al. [31] (37.06 MPa) but slightly higher than those observed in wheat flour/PBAT films (19.16 MPa) by Balan et al. [8].

The mechanical properties obtained in this study were comparable to those of TPS/PBAT films reported by Geralde et al. [41] and significantly higher than those of blown wheat flour/PBAT films (TS: 3.87 MPa, ELO: 296.67%) described by Balan et al. (2021) [8] and those of wheat flour-only films developed by Benincasa et al. [6] (TS: 0.72–1.75 MPa, ELO: 38.33%–115.82%) and Puglia et al. [42] (TS: 0.7–1.4 MPa, ELO: 36%–72%).

This significant enhancement is primarily attributed to the presence of PBAT, a polymer known for its excellent mechanical properties, in the formulations. According to Jian et al. [43], PBAT exhibits a TS of 21 MPa and an ELO of 670%, improving the strength and flexibility of biopolymer blends. Zhai et al. [44] further emphasized that the mechanical performance of composite films improves considerably when the PBAT content exceeds 30%, as observed in the present study.

Although glycerol was included as a plasticizer and its concentration decreased across formulations (FCO: 16%, FRE2: 14%, FRE4: 12%), no statistically significant differences were observed in ELO or YM among the films. This suggests that within the tested range, the reduction in glycerol content did not markedly affect the flexibility or stiffness of the material. It is possible that the plasticizing effect of glycerol was counterbalanced by interactions among the other components, particularly the incorporation of RE and the high PBAT content, which contributed to the maintenance of mechanical performance.

Additionally, Balan et al. [8] reported that the mechanical reinforcement of wheat flour-based films is facilitated by intermolecular interactions between starch, proteins, and PBAT during extrusion, thereby enhancing the polymer matrix’s cohesion. These combined effects—PBAT’s intrinsic mechanical performance, its concentration in the blend, and molecular-level interactions—likely explain the superior mechanical behavior observed in the GF/PBAT films developed in this study.

Overall, the mechanical performance of the films indicates adequate strength and flexibility for potential application in flexible food packaging, with minimal impact from RE incorporation on elasticity and stiffness.

3.7. Surface Morphology and Microstructure

Figure 4 shows the SEM micrographs of the surface and cross-sections of the control film (FCO) and those incorporated with RE (FRE2 and FRE4). The control film exhibited a slightly rough surface with pores and non-gelatinized or partially fused starch granules, which is a common feature in starch-based systems [22,45].

The incorporation of RE modified the surface morphology of the films, promoting increased homogeneity. Nevertheless, more prominent pores and cracks were observed, particularly in the film with the highest extract content (FRE4). This may be associated with reduced interfacial compatibility between the components, possibly due to phase separation or limited interaction between the hydrophilic and hydrophobic domains of the system.

Additionally, it is important to note that the glycerol content, a hydrophilic plasticizer known to enhance miscibility between GF (hydrophilic) and PBAT (hydrophobic), is reduced in the RE-containing formulations (from 16% in FCO to 12% in FRE4). This reduction may have negatively affected interfacial compatibility by limiting the molecular mobility and the interaction between the polymer phases, potentially contributing to the incomplete fusion of starch granules and the formation of distinct microdomains observed in the SEM images.

All films containing RE also exhibited visible starch granules, suggesting that during the extrusion process, multiple chemical and physical transformations—such as granule swelling, gelatinization, degradation, fusion, and crystallization—may co-occur. Insufficient energy input or suboptimal processing conditions during extrusion can lead to incomplete granule fusion, resulting in the persistence of partially intact starch structures [44].

Similar morphological patterns have been reported in wheat flour/PBAT films containing oregano oil microparticles [8] and starch/PBAT systems [46], both of which are processed using blown film extrusion. A cross-sectional analysis revealed a slightly more cohesive internal structure in the films that contained RE, although discontinuities such as pores and fissures remained evident along the fracture paths.

Overall, despite the microstructural modifications observed, the incorporation of RE did not significantly affect the mechanical performance of the films. These findings suggest that the visual and morphological changes resulting from extract addition did not compromise the mechanical integrity of the starch-based polymeric blends. The morphologies observed in the present study are similar to those of wheat flour/PBAT [8] and TPS/PBAT films [24,31].

3.8. ATR-FTIR

The ATR-FTIR spectra of FCO, FRE2, and FRE4 films are shown in Figure 5. A broad absorption band observed around 3331 cm⁻¹ can be attributed to the stretching vibrations of hydrogen-bonded hydroxyl groups (–OH), including free, intramolecular, and intermolecular bonds [22], which are indicative of hydroxyl groups from both the starch-rich matrix (GF) and phenolic compounds in the RE. The absorption near 2980 cm⁻¹ is attributed to C–H stretching vibrations of aliphatic chains, which were present in all formulations.

The band near 1710 cm⁻¹ corresponds to C=O stretching vibrations of ester groups that are primarily associated with PBAT [22,40,43]. The bands between 1015 and 1017 cm⁻¹ are assigned to C–O stretching in glycosidic C–O–C linkages [44].

Except for the bands at 3331 and 1017 cm⁻¹, no notable visual differences in band position or appearance were observed between the films, indicating no new chemical interactions. The RE-containing films showed less prominent features at 3331 cm⁻¹, suggesting a lower availability of free hydroxyl groups, possibly due to interactions between the bioactive compounds in RE and the polymer matrix [47]. Similarly, the features near 1017 cm⁻¹ appeared less defined in FRE2 and FRE4, potentially indicating changes in the polysaccharide-related structure. The lower moisture content observed in FRE2 (19.17%) and FRE4 (17.07%) compared to FCO (20.70%) may be associated with a reduced availability of free hydroxyl groups, which are known to affect water affinity and sorption capacity.

The spectra observed in this study are consistent with those reported in the literature for starch/PBAT films [22,40,44]. Thus, it can be concluded that the incorporation of RE did not induce the formation of new chemical bonds or alter the functional groups in the films. Similar results were obtained by Gallo-García et al. [31] for TPS/PBAT films containing microalgae biomass.

3.9. Crystallinity

A qualitative analysis of crystallinity was carried out via X-ray diffraction (XRD), and the diffractograms of FCO, FRE2, and FRE4 are shown in Figure 6. All samples exhibited diffraction peaks near 16.4°, 17.5°, 20.0°, 23.3°, and 24.8°, indicating that the incorporation of RE did not significantly alter the overall crystalline pattern of the films. These peaks are characteristic of type A crystalline structures, which are typically found in native starches, as reported by Gao et al. [12]. Similarly, PBAT displays peaks at approximately 16.3°, 17.6°, 20.3°, 23.1°, and 25.0°, confirming its semi-crystalline nature [48].

During extrusion, native starch disrupts its crystalline structure due to plasticization and thermal energy. However, depending on the processing conditions and formulation, amylose can recrystallize into V-amylose hydrated (VH), V-amylose with alcohol (VA), or ethanol–amylose (EH) crystalline formations [45].

The calculated relative crystallinity of the films was 15.41% for FCO, 15.84% for FRE2, and 13.21% for FRE4, indicating generally low crystallinity levels. Such values are commonly associated with extensive starch gelatinization, which disrupts the native crystalline regions and enhances polymer dispersion within the matrix [49]. The slight reduction in crystallinity for FRE4 suggests that higher concentrations of RE may interfere with crystal formation, possibly due to phase separation or restricted chain mobility during cooling.

Crystallinity directly influences film properties, including mechanical strength, optical clarity, and water solubility. More crystalline films tend to be more opaque and less soluble [45,50]. Therefore, the moderate crystallinity observed here likely contributed to the balanced mechanical and barrier properties demonstrated by the GF/PBAT films.

3.10. Characterization of Thermal Properties

Figure 7 shows the DSC curves of the FCO, FRE2, and FRE4 films. All formulations exhibited an endothermic peak near 121 °C and an exothermic peak between 80 °C and 90 °C, indicating that RE incorporation at 2% and 4% did not significantly affect the thermal transitions (T_m or T_c).

Garalde et al. [41] reported two endothermic peaks in PBAT at 46 °C and 115 °C, which were attributed to the poly(butylene adipate) (PBA) and poly(butylene terephthalate) (PBT) segments, respectively. In their study, the addition of TPS raised the T_c from 77 °C to 83 °C. Jian, Xiangbin, and Xianbo [43] found a T_m near 123 °C and a T_c of 60 °C for PBAT, while Mohanty and Nayak [51] observed a T_m of approximately 111.3 °C and a T_c of 75.3 °C in TPS/PBAT blends. Liu et al. [39] identified two melting points (110 °C and 125 °C) in PBAT/TPS films, with the Tc increasing from 55 °C to 84 °C. These findings are consistent with the present study, in which the T_m of GF/PBAT (FCO, FRE2, and FRE4) films closely resembled that of pure PBAT, and the incorporation of GF likely contributed to the T_c shift to approximately 80 °C, as observed in the DSC thermograms.

Figure 8 presents the TGA thermograms of the FCO, FRE2, and FRE4 films. The thermal degradation of the samples occurred in four distinct stages of mass loss. Initially, all materials exhibited a modest weight loss up to approximately 200 °C, attributed to eliminating physically adsorbed moisture and low-molecular weight compounds. The main thermal degradation stage occurred between 200 °C and 450 °C, corresponding to the decomposition of the constituent macromolecules. Up to around 230 °C, the observed mass loss is probably associated with the evaporation of volatile compounds and glycerol [52,53]. The third degradation stage, ranging from 230 °C to approximately 320 °C, may correspond to the thermal decomposition of starch and gluten components [54]. The fourth stage, between 320 °C and 530 °C, is presumably related to the degradation of polymeric chains present in PBAT [45,52,55].

The weight loss rate was similar among the samples; however, a significant variation was observed in the residual mass at 600 °C. FRE2 retained a higher residue than FRE4 and FCO, suggesting the presence of more thermally stable materials or promoting greater carbonaceous residue formation. These results indicate that the FRE2 formulation exhibited enhanced thermal stability compared to the base material, FCO, particularly at temperatures above 400 °C, possibly due to enhanced interactions between RE constituents and the polymer matrix at the 2% concentration. However, the thermal stability of the FRE4 film appeared to be comparable to or slightly lower than that of the FCO film, possibly due to the reduced glycerol content or structural disruptions associated with higher RE concentration.

Similar thermal behavior was reported by Silva et al. [9], who investigated the production of biodegradable films composed of PBAT, malt bagasse, and wheat flour. Despite slight differences in formulation—approximately 44% wheat flour, 38.5% PBAT, 13.5% glycerol, 4% malt bagasse, and 0.2% citric acid—the degradation profile of the blends exhibited comparable characteristics to those observed in the present study.

3.11. Assessment of Antimicrobial Activity

The antimicrobial activity of RE has been widely studied and reported in the literature. A previous study by Peron-Schlosser et al. [4] demonstrated its antimicrobial activity against Staphylococcus aureus and Aspergillus brasiliensis, including when it was incorporated into GF films produced by casting [4]. The present study used the same commercial RE in 2% and 4% (w/w) concentrations to produce films via blown film extrusion.

However, when tested using the disk diffusion method, no inhibition zones were observed for any RE-containing formulations (FRE2 and FRE4), indicating an apparent loss of antimicrobial activity following the extrusion process (Figure 9). This result suggests that the bioactive compounds in RE were likely degraded or deactivated during extrusion, which involved high temperatures exceeding 90 °C.

Several factors may have contributed to the loss of activity: (i) the thermal degradation of phenolic compounds in RE during processing; (ii) chemical interactions between the extract and components of the polymer matrix, such as starch or PBAT; and (iii) physical entrapment of the active compounds, limiting their diffusion and bioavailability on the film surface. Other studies have reported these effects involving bioactive compounds in thermoplastic matrices [56,57].

Alternative incorporation strategies should be considered to overcome this limitation and preserve bioactivity in future applications. One approach is the microencapsulation of RE before extrusion, which may protect sensitive compounds from thermal degradation by creating a physical barrier (e.g., with biopolymers or lipids). Another possibility is post-extrusion coating or spraying techniques, where RE is applied to the film surface after processing, avoiding exposure to high temperatures. Additionally, encapsulation techniques may allow for controlled release, enhancing the effectiveness of the film as active packaging.

Combined with selecting more stable bioactive sources or synergistic compounds, these strategies could improve the functional performance of GF/PBAT films intended for food contact applications.

3.12. Biodegradability in Simulated Soil

This study evaluated biodegradation under simulated soil conditions—one of the most used approaches for plastic biodegradation—by monitoring weight loss over time. Figure 10 presents the weight loss of the FCO, FRE2, and FRE4 films over 180 days. The visual and physical alterations observed on the film surfaces during simulated soil exposure are shown in Figure 11. A gradual degradation and progressive fragmentation of the films was observed, and after 180 days, only small fragments remained. Within the first 15 days, all films exhibited significant changes in color and structural integrity, indicating the onset of degradation. At this point, mass loss exceeded 30% for all formulations.

As shown in Figure 10, between 15 and 90 days, the biodegradation rate remained relatively constant. By the end of 180 days, the FCO, FRE2, and FRE4 films exhibited mass loss values of approximately 64%, 58%, and 66%, respectively. Notably, the FRE2 film showed a lower biodegradation rate than the control and FRE4 films. This result may be associated with its more compact and homogeneous morphology (as observed in Figure 4), which could reduce microbial access. In addition, FTIR analysis (Figure 5) showed a less pronounced hydroxyl absorption band (~3331 cm⁻¹) in FRE2, suggesting decreased hydrophilicity, possibly limiting water uptake and enzymatic attack. Despite the biodegradable composition, these structural and chemical characteristics may have delayed the degradation process.

Although all components of the film matrix (PBAT, GF, glycerol, and RE) are of biodegradable origin and complete degradation was expected within the study period, other factors influence the biodegradation process. These include polymer structure and morphology, temperature, humidity, pH, and the enzymatic activity of microorganisms [58].

These experiments were conducted under ambient temperature and RH conditions. Therefore, it is likely that such environmental factors influenced the biodegradation rate. The low temperatures in Curitiba during the testing period may have slowed microbial activity, thereby retarding film degradation. However, based on the results obtained, it can be inferred that if the tests were performed under controlled conditions, the biodegradation rate would increase, and complete mass loss could be achieved within 180 days. This would be in accordance with regulatory requirements for biodegradable materials.

Dammak et al. [59] conducted biodegradation tests on TPS/PBAT blends following [60] and observed similar behavior: gradual degradation, discoloration, and fragmentation, with only a few material remnants after eight weeks.

3.13. Study Limitations

Although the findings of this study are promising, several limitations should be acknowledged. First, only two concentrations of rosemary extract (2% and 4%) were investigated, which may not fully capture the potential dose–response relationship regarding bioactivity and film performance. Second, the extrusion processing conditions—particularly high temperatures—may have compromised the functional properties of the bioactive compounds, thereby limiting the expression of antioxidant and antimicrobial activity. Third, biodegradability tests were performed under ambient simulated soil conditions without standardized temperature or humidity control, which may have affected microbial activity and degradation kinetics. Lastly, this study focused on physicochemical and structural characterization; real-world packaging performance (e.g., in contact with food systems) and shelf-life implications were not evaluated.

4. Conclusions

This study demonstrated the feasibility of producing biodegradable films via blown extrusion using GF and PBAT, incorporating RE at 2% (w/w) and 4% (w/w). The films exhibited good mechanical properties, with tensile strength ranging from 8.16 to 9.29 MPa and elongation at break above 889%, which is comparable to conventional packaging materials. The addition of RE reduced luminosity (L* from 91.38 to 80.89) and increased opacity while improving the hydrophobicity of the films, as indicated by a reduction in m₀. A thermal analysis revealed a major degradation stage between 200 °C and 450 °C, with FRE2 retaining approximately 15% residue at 600 °C, indicating enhanced thermal stability. Biodegradation assays under simulated soil conditions confirmed substantial mass losses of 64% (FCO), 58% (FRE2), and 66% (FRE4) after 180 days, thereby validating the environmental degradability of the films.

Although study limitations are presented in Section 3.12, this study provides a scalable and cost-effective solution for valorizing wheat flour byproducts into sustainable packaging materials. For industries seeking to reduce environmental impact, the GF/PBAT films offer a viable alternative to fossil-based plastics, particularly for applications that require high flexibility and moderate barrier properties.

Future research should explore a broader range of rosemary extract (RE) concentrations to better understand its effects on film structure and performance. Alternative incorporation strategies—such as microencapsulation, coating, lamination, or post-extrusion surface functionalization—should be considered to preserve the bioactive properties of RE and enhance the functional characteristics of the films. Additionally, improving the compatibility between GF and PBAT and promoting greater matrix homogeneity may enable reductions in PBAT content without compromising material performance. Further investigations should also include controlled biodegradation assessments based on international standards and the validation of packaging performance under real storage and usage conditions. Altogether, these approaches can foster the development of innovative, scalable, and environmentally responsible packaging materials that align with circular economy principles.