Influence of coir,fique,and sisal fibers on the environmental stability of PLA biocomposites

Abstract

Understanding the environmental degradation of biodegradable polymers is essential for expanding their use in sustainable materials applications. This study examines the degradation behavior of polylactic acid (PLA)-based composites reinforced with 5 wt% natural fibers—fique, sisal, and coir—under simulated environmental conditions, including water immersion, industrial composting, and ultraviolet (UV) exposure. The composites were produced via melt mixing and compression molding. Water absorption tests showed that although the incorporation of natural fibers increased moisture uptake compared to neat PLA, the composites retained competitive mechanical properties relative to other bio-based polymers. Under industrial composting conditions, all materials exhibited substantial disintegration, with neat PLA undergoing faster mass loss than the composites. This was attributed to the nucleating effect of the fibers, which enhanced PLA crystallinity and consequently slowed hydrolytic degradation. UV exposure results revealed that fique and sisal fibers improved the UV resistance of PLA by limiting carbonyl group formation and preserving mechanical integrity, while coir fibers offered less protection, likely due to their higher lignin content. Overall, these findings suggest that PLA composites reinforced with fique, sisal, and coir fibers exhibit favorable environmental degradation profiles, presenting a promising alternative to petroleum-derived and commercial bio-based polymers in applications where controlled degradation is desired. These results contribute to the understanding of how different natural fibers influence the environmental stability of PLA-based biocomposites under multiple degradation mechanisms.

Keywords

polylactic acid natural fibers biocomposites environmental degradation biodegradability

Introduction

Currently, due to environmental concerns, there has been a growing interest in developing materials that can substitute petroleum-based polymers. Therefore, the use and study of bio-based green materials, which can be fully degraded under specific conditions after their use, has risen in recent years.^1–4 Among them, polylactic acid (PLA) stands out as one of the most promising and widely used biobased and biodegradable polymers due to its renewable origin, easy processing and compostability under controlled conditions that support the goals of the circular economy. Although it may not match the performance of some conventional plastics, its environmental benefits position it as a valuable solution for addressing plastic pollution and promoting more sustainable material use.⁴ To overcome these limitations, one promising approach involves the incorporation of natural fibers as reinforcement, which has been extensively reviewed as a key strategy for enhancing the performance of polyester-based composites materials.^5,6 These fibers have been reported to preserve PLA’s desirable properties related to disintegration and final disposal, while also contributing to cost reduction, which is a key advantage, as the high price of PLA can limit its broader application. In terms of processing, one widely used strategy involves incorporating natural fibers as discontinuous reinforcements, which facilitates better dispersion and is compatible with conventional processing techniques such as extrusion or injection molding.^7–10

Sisal (Agave sisalana) and coir fibers are the most studied plant-based reinforcements.^11,12 Sisal fibers are known for their high tensile strength and modulus,¹³ while coir fibers exhibit higher lignin content and have a higher microfibrillar angle. These properties result in lower tensile strength and stiffness, but greater elongation at break in comparison to other natural fibers.^14,15

In addition to coir and sisal, fique (also known as cabuya) is a natural fiber native to Colombia and other South American countries. It has emerged as a promising reinforcement in bio-based composites due to its good thermal stability, low density, and favorable mechanical properties although its behavior in PLA matrices remains largely unexplored.^16,17

Several works have reported on the influence of natural fibers on the mechanical and fracture properties of composite materials based on PLA. These studies demonstrated that the incorporation of fibers can modify damage mechanisms and improve toughness compared to pure PLA. For example, Somsuk et al.¹⁸ compared the properties of 3D-Printed PLA composites reinforced with rice husk and rice straw at 5%wt and 10% wt, respectively. The findings include the enhancement in flexural and impact strength. Ramirez et al.¹⁹ compared the influence of coir, fique, and sisal fibers as reinforcement on the mechanical, thermal, and fracture properties of bio-based composites with varying weight fractions. However, most of these studies are focused on mechanical or thermal performance, while the degradation behavior of such compounds remains less systematically investigated, particularly when considering different types of fibers under comparable conditions.

The degradation behavior of bio-based composites represents a key design parameter, complementing their mechanical and thermal properties. It plays a central role in determining both the material’s durability during use and its end-of-life options, including recyclability and proper disposal.⁸ Specifically, PLA-fiber composites can undergo several degradation mechanisms throughout their lifecycle. These include photodegradation, triggered by ultraviolet (UV) exposure, which is particularly relevant in agricultural settings, and hydrolytic degradation, initiated by contact with moisture or water.^8,20–22 A thorough understanding of the degradation mechanisms of bio-based composites may help assess their suitability for future use in outdoor applications.

The inclusion of natural fibers in a PLA matrix increases its moisture absorption and therefore reduces the mechanical properties of the composite, affecting its proper performance under service conditions.^23–26 Then, the study of water uptake and its kinetics have a critical importance in different applications, especially for natural fiber-reinforced bio-based composites. Despite this issue, natural fiber-reinforced polyolefins have been effectively employed in automotive components and product design, indicating that their performance can meet industry requirements under specific conditions.²⁷ This suggests that if, during the design and development stage, bio-based PLA composites reinforced with natural fibers can achieve water absorption properties comparable to those of commodity polymers such as polypropylene (PP), their range of applications could be expanded.²³

Exposure to UV radiation could affect the properties of PLA and its composites during outdoor applications. Several studies of the effect of UV radiation on PLA^28–31 and its composites^32–34 performance have been carried out, suggesting that the incorporation of natural reinforcements can increase the durability of the composites after long exposure to UV light. For example, Jirků et al.³⁵ recently studied the effect of adding 10%wt of natural coffee-ground as filler into a PLA matrix, finding that the filler enhances the material’s UV resistance degradation, extending its service life. Furthermore, Zhang et al.³⁶ showed that the incorporation of laser printing wastepaper fibers in a PLA matrix can maintain the properties of the composites after ultraviolet exposure.

Some authors have reported how the presence of natural fibers affects PLA’s disintegration process under thermophilic conditions. Dong et al.³⁷ studied the biodegradability of bio-composites based on PLA reinforced with macadamia nutshell powder. They found that the introduction of a filler may create a physical barrier, making it harder to microorganisms and enzymes to access the polymer matrix, hence reducing the disintegration process rate. Vitiello et al.³⁸ studied the degradation kinetic of PLA/hemp composites at different fibers content. Their results showed that the incorporation of hemp fibers increased the crystallinity of the composites, inducing a shielding effect that slowed down the degradation kinetic of the matrix.

Despite these advances, comparative studies systematically addressing multiple environmental degradation mechanisms in PLA composites reinforced with different natural fibers remain scarce. Most previous works focus on a single degradation pathway or a single type of reinforcement, which limits the possibility of directly comparing the influence of fiber type on PLA degradation across hydrolytic, composting, and photo-oxidative environments. This work aims to compare the influence of several natural fibers (coir, fique, and sisal) on the degradation behavior of PLA-based bio-composites under different environmental conditions, including water absorption, disintegration under thermophilic conditions, and UV exposure. This study evaluates the performance of these fibers relative to one another, as well as in comparison to more commonly used commercial polymers and biopolymers available in the literature for packaging uses, aiming to obtain a unified comparative assessment under multiple environmental degradation scenarios, which is still lacking. In particular, the degradation behavior of PLA composites reinforced with fique fibers remains unexplored, representing a key knowledge gap addressed in the present work.

Materials and methods

Materials

Commercial polylactic acid (PLA) resin Grade 4043D, NatureWorks, LLC (Printalot SRL Argentina), with a 1.24 g/cm³ density according to data technical sheet, was used. Commercial sisal fiber (Agave Sisalana) from Argentina, coir fibers from Mexico, and fique fibers (Furcracea Andina) from Colombia were used in strand form, with no additional chemical treatment, to maintain the processing steps at a minimum. Fibers were manually chopped to a nominal length of 3 mm, which corresponds to the critical fiber length estimated according to equation (1). The critical fiber length lc corresponds to the minimum fiber length necessary for the axial stress in the fiber to reach its ultimate tensile strength³⁹ :

l_{c} = \frac{σ_{f} * d}{2 * τ_{c}}

(1)

where $σ_{f}$ denotes the tensile strength of the fiber, d represents the fiber diameter, and $τ_{c}$ corresponds to the interfacial shear strength at the fiber-PLA interface. The complete calculation procedure and input parameters were reported in a previous study.

Table 1 shows the chemical composition and main physical properties of fibers used according to the literature.

Table 1.

Chemical properties of the studied fibers.^12,14,17

Fiber	% Cellulose	% Hemicellulose	% Lignin	Density (g/cm³)	Young’s modulus (GPa)	Tensile strength (MPa)
Coir	46.5	8.4	33.1	1.01–1.43	1.2–6	14.2–59.9
Fique	58.3	14.6	7.2	1.13–1.47	2.7–5.9	73–125
Sisal	52.8	19.6	13.5	1.28–1.59	9–38	2–25

Composites preparation

Short fibers and PLA matrix were dried in a drying oven at 70°C for at least 12 h. The fiber content of the composites was fixed at 5 wt%. This concentration was selected based on previously reported studies, in which PLA composites containing 1, 3, and 5% wt. of the same natural fibers were investigated for additive manufacturing applications. Among these formulations, composites with 5 wt% fiber content exhibited improved fracture-related mechanical properties. The manufacturing procedure consisted of two main stages; first, the fibers and matrix were blended using a mixer (Bravender Labstation Reo 6, Germany) at 175°C for 8 min at 50 rpm; then the mixture was processed by compression molding (Carver 3853). The press was pre-heated to 170°C, then the material was placed in the mold and held at this temperature for 7 min without applying pressure. The pressure was then increased to 800 psi and maintained at 170°C for 7 min. Subsequently, an automatic water-cooling stage was initiated until the temperature decreased to 100°C, while keeping the pressure constant at 800 psi for 5 min. Finally, the mold was removed from the press and allowed to cool to room temperature under a pressure of 30 psi for 10 min. Matrix films were prepared using the same compression molding conditions as composites.

Degradation under varying environmental conditions

Water absorption

To evaluate the water absorption process, dog-bone type specimens 63 mm in length with a narrow section of 3.3 × 15 mm were immersed in distilled water at 25°C. Samples were removed from immersion at different time intervals, their surfaces were dried, and they were weighed using a high precision balance. This procedure was performed for 30 days, and the water uptake at time t was calculated using equation (2)⁴⁰:

M_{t} (%) = (\frac{w_{t} - w_{0}}{w_{0}}) x 100

(2)

Where $w_{0}$ is the initial weight of the sample, and $w_{t}$ is the weight of the wet sample at time t. Two samples were evaluated at each extraction time to overcome the measurement error.

In addition, the diffusion mechanism was studied following Fick’s law of diffusion. This approach assumes that the water uptake follows a Fickian sorption process, in which moisture penetrates the material primarily by molecular diffusion. To assess whether the absorption behavior adheres to this model, the shape of the sorption curve was evaluated using equation (3) as follows:

\frac{M_{t}}{M_{m}} = k * t^{n}

(3)

Where $M_{t}$ is the moisture content at time $t$ , $M_{m}$ is the moisture content at equilibrium; and $k$ and $n$ are constant. The coefficient $n$ provides information about the diffusion mechanism: if $n$ is equal to or near 0.5, the process of water absorption follows Fickian law of diffusion, while deviations from this value suggest anomalous or non-Fickian behavior.^39,40 The determination of the diffusion coefficient, $D$ , was calculated using equation (4)⁴⁰:

D = π {(\frac{θ h}{4 M_{m}})}^{2}

(4)

Where $θ$ is the slope of the linear portion of the sorption curves, $M_{m}$ is the equilibrium water uptake value, and h is the initial sample thickness. Since the specimens have finite rectangular geometry, it is necessary to account for edge effects when estimating the diffusion coefficient. This correction is applied using equation (5) under the assumption that the diffusion rates are the same in all directions⁴⁰:

D_{c} = D {(1 + \frac{d}{l} + \frac{d}{w})}^{- 2}

(5)

Where $D_{c}$ is the corrected diffusion coefficient, and l and w are the sample length and width, respectively. Although tensile specimens are not perfectly rectangular due to the presence of grips that contribute to water absorption, they were approximated as rectangular for simplicity, using dimensions equal to 19 mm in width and 63 mm in length.

Disintegration under industrial compost conditions

The disintegration of the composites was studied under simulated composting conditions at a laboratory scale, following the recommendations of the standard ISO-20200:2004, “Determination of the degree of disintegration of plastic materials under simulated composting conditions in a laboratory-scale test.⁴¹ A 100% industrial compost provided by Hi Soil^® was used, characterized by the following physicochemical composition: pH 7.2–7.5, organic matter 45%, ashes 55%, dry density 470 g/cm³, and porosity 77%.

Films were cut into 25 × 25 mm squares and buried in compost at a depth of 40–60 mm in a perforated glass box. Systems were maintained at 58°C for 67 days in a cultivation stove Faeta IS 2300C (Argentina). Periodic mixing and hydration were performed to maintain aerobic conditions and keep the compost hydrated. At predetermined time intervals, two specimens were withdrawn for each time point, rinsed with distilled water, and dried at 37°C for 24 h before being weighed. The rate of disintegration ( $D_{i s}$ ) was calculated according to equation (6).

D_{i s} = (\frac{m_{0} - m_{r}}{m_{0}}) x 100

(6)

Where $m_{0}$ is the initial weight of the dry samples and $m_{r}$ represents the weight of the mass recovered. Specimens were photographed at selected time intervals throughout the composting process to document visual changes.

It should be noticed that the number of replicates in the water absorption and disintegration tests was limited by material availability; therefore, the results are intended to highlight comparative trends rather than provide a full statistical analysis.

Ultraviolet light exposure

To study the effect of UV light on the degradation process of PLA and its composites, a UV chamber-built ad-hoc was used. The aging was carried out in a chamber equipped with three fluorescent lamps (UVA-340, 15 W each, emission peak at 340 nm). The samples were placed at an approximate distance of 10 cm from the lamps and exposed under these conditions. Dog-bone type samples were maintained at 30°C and 75% relative humidity during the test. Two samples were collected after 0, 14, 21, 42, 65, and 78 days of exposure for further characterization.

Characterization

Fourier transform infrared (FTIR)

Aging UV samples surface analysis was performed before and after UV exposure by attenuated total reflectance (ATR) infrared spectroscopy using a Nicolet 6700 Thermo Scientific device in the range of 4500–400 cm ⁻¹ at room temperature (23 ± 2°C). The degradation process was monitored by calculating a dimensionless parameter, the carbonyl index (CI), which relates the intensity of the carbonyl peak at 1750 cm⁻¹, to that of the methyl stretching band, at 2900 cm⁻¹ and it is defined according to equation (7).

C I = \frac{I_{C = O} (1750 c m^{- 1})}{I_{C - H} (2900 c m^{- 1})}

(7)

Where $I_{C = O}$ represents the peak intensity of carbonyl groups and $I_{C - H}$ is the intensity of the methyl group stretching.⁴²

Differential scanning calorimetry (DSC) measurements

Disintegration film samples and aging UV samples were characterized at predetermined time intervals of extraction using differential scanning calorimetry (DSC) in a Shimadzu DSC-50 instrument. Samples of 3–5 mg were heated from room temperature to 200°C under a nitrogen atmosphere (30 ml/min), at a heating rate of 10°C/min. Onset and peak melting temperatures for the first endothermic peak were obtained from heating thermograms curves. In addition, the crystallinity of PLA within composites was calculated using equation (8).

X_{c} = 100 * \frac{Δ H_{f} - Δ H_{c c}}{Δ H_{f}^{0} (1 - % w t)}

(8)

Where $Δ H_{f}$ is the melting enthalpy of the composite, $Δ H_{c c}$ is the cold crystallization enthalpy of the composite, $Δ H_{f}^{0}$ is the melting enthalpy of 100% crystalline PLA (93 J/g) and $% w t$ is the percentage weight of fiber included in the matrix.⁴³

Mechanical properties

Dog-bone-shaped specimens for water absorption and UV aging tests were subjected to uniaxial tensile testing at different extraction times. Samples were performed using an INSTRON dynamometer 5985 at a crosshead speed of 5 mm/min at room temperature following ASTM standard D638 recommendations.⁴⁴ Duplicate measurements were carried out for each condition. Tensile strength, Young’s modulus, and strain at break values were determined from tensile stress-strain curves, as described in a previous study. The percentage variations of these properties over time were reported. Mechanical performance is discussed in terms of percentage variation relative to the undegraded composites, as this representation provides a more direct assessment of degradation effects. The absolute mechanical properties of the pristine materials are shown in Table 2.

Table 2.

Tensile properties of pristine materials.

Material	Young’s Modulus (GPa)	Tensile resistance (MPa)	Elongation at break (%)
PLA	2.2 ± 0.2	47 ± 5	2.9 ± 0.1
PLACoir	2.5 ± 0.1	44 ± 3	1.7 ± 0.2
PLAFique	2.8 ± 0.4	34 ± 6	1.4 ± 0.3
PLASisal	3.0 ± 0.4	44 ± 3	1.6 ± 0.3

Scanning electron microscopy (SEM)

To evaluate the adhesion between the fiber and matrix, the fracture surface of the composites prior to water immersion was examined by field emission scanning electron microscopy (SEM) using a PHENOM XPRO instrument operated at an accelerating voltage of 5 kV. Prior to analysis, the samples were sputter-coated with a thin chromium layer using a Quorum Q150T ES Plus ion coater to avoid image distortion, enhance electron conductivity, reduce beam-induced damage, and eliminate surface charging effects.

Results and discussion

Water absorption behavior

Figure 1 shows the water uptake of the matrix and composites as a function of t^1/2 (expressed in hours^1/2). As it is shown, all materials exhibited an initial linear relationship between water uptake and the square root of time, followed by a plateau that suggests saturation, in accordance with a predominantly Fickian diffusion behavior during the early stages of water uptake.

Figure 1.

Water absorption curves for PLA and its composites.

The incorporation of natural fibers increases the water uptake of the composites, where PLA reinforced with coir fibers shows the highest values in comparison to other composites. These values are higher than those reported for composites reinforced with synthetic fibers such as glass or carbon fiber.^45,46

Figure 2 expresses the logarithmic form of equation (3) for PLA and its composites. The curve fit showed values of the kinetic parameter n close to 0.5, while the correlation coefficient R² was close to 1 (see Table 2), indicating that the absorption process in all studied materials follows a predominantly Fickian behavior, with slight deviations depending on the system. Therefore, Fickian law can be reasonably applied to analyze the initial water absorption of neat PLA and its composites.⁴⁷

Figure 2.

Water absorption data fitted to diffusion models for PLA and its composites.

The values of kinetic parameters n and k, the correlation coefficient R², equilibrium water absorption M_m, diffusion coefficient D, and corrected diffusion coefficient D_c obtained from the curve fitting and the corresponding calculations are summarized in Table 3. The equilibrium water uptake for PLA at room temperature (25 °C) was 1.29%, and the calculated values of diffusion coefficient and corrected diffusion coefficient were 5.07 × 10⁻³ mm²/h and 4.55 × 10⁻³ mm²/h, respectively. These results agree with those found in the literature.^40,48 For example, Tengsuthiwat et al.⁴⁸ immersed PLA and PLA reinforced with sisal fibers in distilled water at 30°C over 12 days, finding out that the diffusion coefficient for neat PLA was 5.4 × 10⁻³ mm²/h. Orue et al.⁴⁰ immersed samples of PLA at 28°C in distilled water and reported a diffusion coefficient of 2.41 × 10⁻³ mm²/h.

Table 3.

Kinetic parameters of Fickian model, equilibrium water absorption, diffusion coefficient and corrected diffusion coefficient obtained for PLA and composites after water uptake test.

Material	n (-)	k (h⁻ⁿ)	R ²	θ (%/h^1/2)	M_m (%)	D (mm²/h)	D_c (mm²/h)
PLA	0.59 ± 0.03	0.15 ± 0.01	0.99	0.25913	1.29 ± 0.03	5.07E-03	4.55E-03
PLACoir	0.44 ± 0.06	0.20 ± 0.03	0.97	0.78088	3.07 ± 0.03	8.13E-03	7.43E-03
PLAFique	0.46 ± 0.02	0.17 ± 0.01	0.99	0.5041	2.32 ± 0.02	5.93E-03	5.37E-03
PLASisal	0.55 ± 0.07	0.14 ± 0.02	0.96	0.49805	2.13 ± 0.01	6.87E-03	6.23E-03

According to Table 3, all composite materials exhibit higher equilibrium water uptake and diffusion coefficients compared to neat PLA. Moreover, the diffusion coefficients of the composites also are in agreement with literature. For example, Ratna et al.⁴⁹ studied the influence of the incorporation in different proportions (10; 20; and 30 %wt) of sisal fibers in a PLA matrix, on water absorption behavior. Their results indicate that at 30% wt. of reinforcement, the diffusion coefficient is 6.33 × 10⁻³ mm²/h after 35 days of immersion in distilled water. Orue et al.⁴⁰ reported a diffusion coefficient of 1.93 × 10⁻³ mm²/h for composites based on PLA reinforced with sisal fibers at 10% wt. and immersed in distilled water at 28°C. Jiang et al.⁵⁰ reported the diffusion coefficient for PLA and jute biocomposites at 10% wt. as 4.31 × 10⁻³ mm²/h at 23 °C in distilled water. In the case of PLAFique, PLASisal and PLACoir, although the differences are not substantial, a progressive increase in the diffusion coefficient (D) of approximately 17%, 35%, and 60%, respectively, is observed with respect to PLA. A similar trend is observed for the corrected diffusion coefficient (D_c), suggesting that the addition of natural fibers influences the water transport properties of the composites. This moderate enhancement in diffusion behavior may be attributed to their chemical compositions, which are very similar (see Table 1). In addition, the hydrophilic nature of the fibers may promote water molecule penetration within the composite, thereby enhancing the diffusion rate.^40,51,52 However, it should be noted that water transport in these composites is also influenced by processing-induced porosity, interfacial voids, and degree of crystallinity, which may partially mask the effect of fiber chemical composition alone.

For neat PLA, the kinetic exponent n = 0.59 indicates a weak anomalous diffusion behavior, which is commonly reported for PLA and attributed to the coupling between water diffusion and polymer chain relaxation.^53,54 However, given its proximity to the ideal Fickian value (n = 0.5), the overall water uptake behavior can still be reasonably described using Fickian-based diffusion models. In contrast, fiber-reinforced composites exhibit $n$ values closer to 0.5, suggesting a diffusion behavior closer to ideal Fickian transport during the initial absorption stage. At longer immersion times, deviations from ideal Fickian predictions become more evident, suggesting the contribution of additional transport mechanisms as saturation is approached.

It was expected that composites with fibers containing a higher content of lignin would present lower values of water uptake due to the hydrophobic nature of the lignin. However, this trend was not clearly reflected in the experimental results, despite the chemical composition data shown in Table 1. This apparent discrepancy suggests that lignin content alone is not sufficient to explain the water uptake behavior of the composites. Processing-induced porosity and interfacial voids formed during melt mixing and compression molding may contribute to the initial water uptake by acting as preferential filling sites. However, once filled, these features do not necessarily facilitate further diffusion toward the bulk material. In addition, composite crystallinity may further influence the effective diffusion pathway.⁵²

The macroscopic appearance of samples at different times of soaking in distilled water at room temperature are shown in Figure 3. Initially, both PLA and its composites were transparent; however, after 30 days of soaking, an increase in the opacity of the samples was observed. Opacity can be attributed to a degradation process of the sample. This phenomenon could be possible due to different mechanisms, such as the presence of micro voids, water, and/or degradation products formed during the hydrolytic process. In general, there is no macroscopic damage for the samples after 30 days of soaking.

Figure 3.

Macroscopic appearance of water-soaked samples for PLA and its composites at different times of extraction.

Figure 4 shows the percentual variation of mechanical properties for all evaluated materials. Two distinct behaviors can be identified. In the case of neat PLA, the strain at break increases with the immersion time in comparison to day 0, reaching a maximum at day 7. This could indicate that water molecules act as a plasticizer. In contrast, it can be appreciated that the tensile strength and Young’s modulus variation decrease in comparison to day 0, indicating that there is a degradation in the polymer due to the presence of water. Similar results were reported by Deroiné et al., who studied the degradation mechanism in neat PLA at different temperatures. They found that there is an influence of the temperature of soaking on the degradation mechanisms. At room temperature (near 25°C), the degradation and plasticization of PLA is reversible, and it is possible to recover its mechanical properties after drying the samples.⁵³

Figure 4.

Percentual variation of tensile properties for all materials studied after water immersion test: (a) percentual variation of Young’s Modulus, (b) percentual variation of tensile strength, and (c) percentual variation of strain at break.

On the other hand, there is an important reduction in tensile strength and strain at break for all composites, along with a slight increase in Young’s Modulus. These trends suggest a degradation mechanism driven by water absorption. The diffusion of water into the composites is facilitated by the free volume within the polymer. In addition, it is favored by the weak adhesion between fiber and matrix, as demonstrated in the literature¹⁹ and also evidenced by SEM micrographs for the composites tested before water immersion (Figure 5(a)). It is possible to observe interfacial gaps and fiber pull out after breaking the samples. This poor adhesion that creates interfacial gaps and micro-voids at the fiber–matrix boundary, could serve as preferential pathways for water ingress. These defects not only accelerate moisture uptake but also act as initiation sites for microcrack formation, ultimately compromising the mechanical integrity of the composite. As water is absorbed, the fibers swell, generating internal stresses, creating microcracks, and promoting the fiber matrix debonding, as reported in the literature.⁵⁵ For instance, Avci et al.⁵⁵ studied the incorporation of flax fiber into a matrix of PLA and reported that there is a decrease in mechanical properties of the composites due to the formation of microcracks around the fibers that act as a stress concentrator. Also, the diffusion of water through these cracks eliminates the interface between the matrix and fibers. Kassegn et al. study the influence of water absorption on the mechanical properties of PLA-based composites reinforced with sisal fibers⁵⁶ and found that after water aging of the composites, the tensile and flexural strength diminished due to the absorption of water, which leads to fiber swelling that causes debonding of the fibers and matrix. This degradation mechanism, which we assume is acting in our composites, is schematized in Figure 5(b).

Figure 5.

(a) SEM micrographs of composites before water immersion test and (b) absorption water mechanism in fiber reinforced composites materials studied.

Disintegration tests under composting conditions

Figure 6 shows the visual appearance and weight loss of PLA and its composites as a function of exposure time to composting conditions. In contrast to the samples immersed in distilled water at room temperature, it was observed for all samples (Figure 6(a)) that after only 5 days of incubation in compost, the color and appearance of the samples changed from transparent to white, and this color intensified over time. This color variation could be directly related to how light diffuses through the samples, which results from structural modifications induced by water absorption, hydrolytic degradation, increased crystallinity, the formation of pores during the degradation process, and the biotic environment and higher temperature during composting.^21,38 It was extensively reported that the disintegration process primarily takes place in amorphous regions of the polymer structure. Since the PLA matrix is almost 100% amorphous, the whitening in the surface was higher than that occurring in composite materials.^21,57 As the days of incubation passed by, it was possible to observe a progressive loss in sample integrity through a decrease in thickness, increased fragility, formation of superficial cracks, visual fragmentation, and macroscopic surface fungi.

Figure 6.

Macroscopic appearance changes and weight mass loss in PLA and PLA composites during disintegration in industrial compost test: (a) visual appearance (b) weight loss % at different days of incubation in compost.

Figure 6(b) shows the weight loss curves for all samples. It can be observed that there is no significant change in mass loss at the beginning of the test for all materials studied. This behavior could be attributed to the early stages of PLA degradation, which are governed by non-enzymatic hydrolysis. As reported by Iglesias-Montes et al.²¹ PLA degradation follows a two-step mechanism; first, hydrolytic cleavage of the ester bonds reduces the molecular weight, and then, once it falls below a critical threshold, microbial assimilation begins. At this point, the significant changes in mass loss are noticeable once the enzymatic degradation of the polymer starts, since microorganisms would start to metabolize the organic compound (oligomers and lactic acid). Our observations are in agreement with studies such as those by Fabri et al. and Iglesias-Montes et al., which confirmed that there is a decrease in molecular weight of PLA during hydrolytic degradation experiments, but did not register any weight loss during the first steps of the experiment.^21,58 These factors can explain the behavior observed during the first 2 weeks of the experiment. However, on day 21, it was observed that the weight loss of all samples increased exponentially.

After 21 days of incubation, the mass loss of neat PLA is higher than that of the composites. This could be attributed to the incorporation of natural fibers that can act as nucleating agents and increase the crystallinity of the composites in comparison to neat PLA, as observed in the initial crystallinity values obtained from DSC (Table 4).^19,21,59,60 The effect of the degradation process on the crystallinity of PLA and composites was investigated using DSC. The thermograms corresponding to the first heating scans are shown in Figure 7. Also, the thermal parameters obtained from these curves are presented in Table 4. Higher crystallinity is known to hinder the penetration of water molecules into the polymer matrix, thereby reducing the extent of hydrolytic chain scission. Since hydrolysis preferentially occurs in amorphous regions, an increased crystalline fraction leads to slower degradation rates. Consequently, the more crystalline composite samples exhibit lower mass loss compared to the more amorphous neat PLA. According to Figure 6(b), the weight loss percentage for PLA was about 80% at 67 days of incubation, while for the composites, the weight loss percentage was around 70% for the same period. PLAcoir composites seem to show lower degradation rates in comparison to fique and sisal composites. This behavior could be correlated with its chemical composition: among the three fibers, coir fibers have the highest content of lignin, as it was shown in Table 1. It was reported in literature that a high content of lignin can reduce the biodegradation process of composite materials, since lignin can inhibit prolonged microbial activity necessary for complete mineralization.^61,62 On the other hand, composites with fique and sisal fibers exhibited similar disintegration curves. Both fibers have higher content of cellulose and hemicellulose than coir fibers, which can enhance the hydrolytic degradation in comparison to PLAcoir materials.⁶³

Figure 7.

DSC thermograms (first heating scan) during disintegration in industrial compost tests for PLA and its composites at different times of extraction (0, 21, and 44 days): (a) PLA, (b) PLACoir, (c) PLAFique, and (d) PLASisal.

Table 4.

Thermal properties obtained from DSC curves during disintegration in industrial compost test for PLA and PLA composites.

Material	Time (d)	Tg (°C)	Tm (°C) peak 1	Tm (°C) peak 2	Xcr (%)
PLA	0	55.3	150.5	n.d	0.08
	21	n.d	137.6	n.d	42
	44	n.d	142.7	n.d	47
PLACoir	0	58.8	148.5	154.2	7
	21	n.d	143.5	n.d	28
	44	n.d	140.1	n.d	48
PLAFique	0	58.8	147.7	152.0	8
	21	n.d	140.5	n.d	42
	44	n.d	142.5	n.d	44
PLASisal	0	58.9	148.1	153.9	7
	21	n.d	139.5	n.d	41
	44	n.d	142.3	n.d	40

Neat PLA (Figure 7(a), day 0) exhibited a clear shift in heat flow at 55°C associated with the glass transition temperature (Tg) of the sample, followed by a flat exothermic cold crystallization peak and a small endothermic melting peak. The degree of crystallinity on day 0 of incubation was very low (0.08%), indicating a predominantly amorphous structure at the beginning of the experiment. On days 21, and 44, Tg was no longer detectable in the thermograms, and the cold crystallization peak had disappeared. Additionally, a notable increase in crystallinity was observed, reaching 42% at day 21 and 47% at day 44. The melting peak also shifted to lower temperatures when compared to day 0. This behavior could be attributed to the polymer hydrolysis process, which causes random cleavage of polymer chains and a consequent reduction in molecular weight, as was reported by Iglesias-Montes et al.²¹ As polymer chains become shorter, their mobility increases, requiring less energy to start moving (lower Tg).⁶⁴ This increased mobility facilitates the reorganization of polymer segments into more ordered structures, even in regions that were initially amorphous, which is reflected in the increase in crystallinity. Moreover, since amorphous domains are generally more susceptible to hydrolytic attack, their preferential degradation may also contribute to an apparent increase in the relative proportion of crystalline regions. The shift of the melting peak to lower temperatures was reported in previous literature and is often associated with the formation of crystalline domains composed of shorter chains. It has been claimed that although thermal degradation promotes chain mobility and facilitates the crystallization of amorphous regions, the hydrolysis process leads to the formation of less perfect and less homogeneous crystalline structures, as evidenced by a broad melting peak.²¹

DSC thermograms of PLA-based composites (Figure 7(b)–(d)) exhibited similar behavior to neat PLA, showing a clear heat flow shift associated with the Tg of the samples (at day 0), but at higher temperatures than in the matrix. Both the cold crystallization peak and the endothermic melting peak were larger than in neat PLA and showed a double melting peak in the samples. The crystallization degree of composites was nearly 8%, indicating that the fibers promoted the crystallization of the composites as a nucleating agent. As incubation progressed, the cold crystallization peaks of the composites disappeared, while the melting peaks became broader and increased in intensity. This could be attributed to the melting of the crystalline phase initially present in samples, and the formation of a new crystalline domain based on the oligomeric fractions formed during composting.³⁸ For coir composites at day 21, their crystallization degree was lower than the corresponding sisal and fique composites and the PLA matrix. This could be correlated with its higher lignin content, which can inhibit the growth of microbial agents that attack the amorphous regions of the material.^61,62

Figure 8 shows a clear correlation between mass loss and the apparent increase in crystallinity degree (%Xc) for all systems. This trend was reported for PLA during disintegration process in industrial compost and is attributed to the preferential degradation of amorphous regions, which results in a relative increase in the crystalline fraction as mass loss progresses.^21,65,66 Consequently, the increase in %Xc with degradation should be interpreted as a structural evolution effect rather than as evidence of enhanced crystallization. Regarding the effect of crystallinity on biodegradation, higher initial crystallinity is generally associated with slower degradation kinetics due to the reduced accessibility of crystalline domains to water diffusion and enzymatic attack. In the present results, samples with higher initial %Xc tend to exhibit slightly reduced mass loss compared to neat PLA at comparable exposure times, indicating that crystallinity plays a secondary, modulatory role. However, within the studied degradation window, the overall biodegradation process appears to be mainly governed by the preferential erosion of amorphous regions rather than by the absolute crystalline content.

Figure 8.

Mass loss (%) versus Xcr (%) for PLA and its composites after disintegration test.

In summary, the slightly lower degradation kinetics observed in reinforced materials may be partially attributed to a shielding effect of fibers, as suggested by the thermograms and the higher initial crystallinity of composites in comparison to the neat matrix. The induced crystallinity may contribute to limiting water diffusion and reducing the hydrolysis of amorphous regions.³⁸

Degradation under UV conditions

Figure 9 exhibits FTIR results for materials exposed to UV at different times. In FTIR spectra, it is possible to identify the main absorption peaks corresponding to PLA and its composites. The absorption band at 1748 cm⁻¹ corresponds to the stretching vibration of carbonyl groups C=O. The absorption peak at 1452 cm⁻¹ corresponds to the deformation vibration of -CH₃. The peaks at 1382 cm⁻¹ and 1360 cm⁻¹ correspond to the symmetric and asymmetric deformation vibration of C-H. The peaks at 1182 cm⁻¹, 1128 cm⁻¹, 1080 cm⁻¹, and 1042 cm⁻¹ correspond to the stretching vibration of C-O. Finally, the peak at 865 cm⁻¹ corresponds to the stretching vibration of C-COO.^67–69 It is observed that there is no significant difference between the spectra of composites and PLA. This is due to an overlapping image of PLA and fibers, since there is no big difference in the chemical nature of the components of the composites. Besides, the concentration of fibers in composites is not enough to see big changes in FTIR spectra.¹⁹

Figure 9.

FTIR spectra and Carbonyl index for PLA and its composites at different UV exposure times: (a) PLA, (b) PLACoir, (c) PLAFique, (d) PLASisal, and (e) Carbonyl index.

As shown in Figure 9, the characteristic peak positions remained unchanged throughout UV exposure, suggesting no major structural shifts in terms of bond vibrations. On the right side of the figure, a closer view of the evolution of the peak at 1748 cm⁻¹ is shown for each material, providing insight into degradation. The carbonyl indexes (CI) calculated from these spectra and normalized to their value at day 0 are shown in Figure 9(e). From these results, two distinct behaviors can be identified: one corresponding to neat PLA and PLACoir composites, and the other to PLAFique and PLASisal composites. These groups exhibit markedly different responses to UV exposure.

In the first group, which includes neat PLA and PLACoir composites, the carbonyl index increases progressively over time, particularly pronounced for the PLA matrix as it is observed in Figure 9(e). This behavior is associated with the photodegradation process of the material, mainly through Norrish type II mechanism, which occurs preferentially in the amorphous regions of the polymer (Figure 10). This process involves the absorption of photons by the ester carbonyl group along the PLA backbone, promoting them to an excited triplet state. This excitation facilitates cleavage of the adjacent carbon–oxygen (C-O) bond in the ester group. This generates radical intermediates that rearrange to form diketones. These diketones act as secondary chromophores that can absorb UV radiation more efficiently, accelerating the photodegradation process. Then, the photolysis of diketone groups leads to the hemolytic cleavage of the C-C bonds between two carbonyl groups. This leads to the formation of terminal carboxylic acid groups and additional free radicals, which in turn propagate further chain scission reactions.^42,69 In the presence of oxygen, the photoexcited species or resulting radicals can also react with molecular oxygen to generate peroxyl radicals or hydroperoxides, through hydrogen abstraction reactions. These unstable intermediates decompose into reactive species that promote further chain cleavage and can also lead to the formation of anhydride and carboxylic acid groups. This photooxidative degradation pathway may act synergistically with Norrish type II reactions under ambient conditions, accelerating the overall degradation process. These combined processes ultimately lead to a reduction in the molecular weight of the polymer and an increase in the intensity of the carbonyl band at 1748 cm⁻¹ in FTIR spectra.^61,68

Figure 10.

Degradation mechanism of photo-degradation of PLA (via Norrish II), adapted from González-López et al. (2020) and González-López et al. (2020).

In addition, the formation of carbon–carbon double bonds (C=C) has been proposed in some studies as a possible product of this degradation pathway; these bands are typically of low intensity and not clearly resolved in the FTIR spectra due to their low concentration. PLACoir composites follow a similar trend; the increase in CI is less pronounced than that observed for the PLA matrix, which directly correlates with a lower increase in absorbance peak at 1748 cm⁻¹ in FTIR spectra (Figure 9(b)). This result suggests that the incorporation of coir fibers partially mitigates the degradation caused by UV radiation, possibly from the light-absorbing properties of lignin, light scattering by the fibrous phase, or scavenging free radicals.^61,69

In contrast, the second group, represented by fique and sisal composites, shows a stable CI for the UV exposure period. The intensity of the 1748 cm⁻¹ band remains nearly constant over the exposure time, and no significant spectral changes are observed. This stability suggests that fewer carbonyl groups are being formed because of UV exposure, indicating limited progression of photodegradation reactions. Therefore, the incorporation of fique and sisal fibers appears to provide a more effective protective effect, likely by absorbing or scattering UV radiation, or by stabilizing the polymer matrix through interactions that inhibit the formation of degradation products such as carboxylic acids and diketones. This could be clearly checked by observing the close-ups in Figure 9(d) and (e), where the increment of the absorbance peak is almost null.

Comparing the behavior of coir, fique, and sisal PLA composites, the UV protection provided by coir fibers is lower than fique and sisal fibers. This could be attributed to the ability of lignin to absorb UV radiation. Coir fibers are known to contain a higher lignin content compared to fique and sisal fiber (see Table 1). Lignin is known to absorb a broad range of UV radiation due to its chromophoric structures, such as α-carbonyl, biphenyl, and ring conjugated groups. In addition, lignin degrades more rapidly than cellulose and other fiber components, leading to the UV-induced degradation of the composite. In the case of PLACoir composites, the higher lignin content of the fibers may promote preferential absorption of UV radiation by the fibrous phase, leading to photodegradation of the fibers themselves rather than providing uniform shielding of the PLA matrix. In this context, coir fibers may act as sacrificial UV absorbers, limiting direct UV exposure of the matrix while simultaneously generating lignin-derived degradation products that can contribute to secondary photo-oxidative processes in the surrounding polymer. By contrast, the low concentration of lignin of fique and sisal fibers results in an improved UV resistance of the composites.^42,61,70,71

In addition to the increase in carbonyl index, the absorbance peak at 1748 cm⁻¹ for neat PLA exhibits a significant broadening and an increase in absolute intensity over time, ranging approximately from 4.8 to 9.5 absorbance units. This marked increase reflects not only the accumulation of carbonyl-containing degradation products but also a broader distribution of chemical species, indicating structural heterogeneity due to random scission mechanisms. PLACoir composites show a similar but less pronounced trend, with a moderate widening and a lower absorbance range at this wavenumber (4.5 to 6.87 absorbance units). In contrast, the spectra for PLAFique and PLASisal composites maintain a relatively narrow and stable band centered at 1748 cm⁻¹ throughout UV exposure. This suggests that these fibers confer a more effective protective effect by limiting the extent and variety of carbonyl-containing degradation products. The lower intensity and lack of broadening in the carbonyl band further support their role in mitigating UV-induced structural breakdown.

DSC thermograms at different UV exposure times are shown in Figure 11, while obtained thermal properties are depicted in Table 5. On day 0, it is possible to distinguish different characteristics of PLA and its composites, as it was explained in previous sections.¹⁹ After UV exposition, Tg values increase in comparison to day 0 for all evaluated materials, moving from 55°C to 60°C for PLA, and approximately from 58°C to 61°C for composites. This phenomenon was reported before,^69,72 and was attributed to the relaxation and rearrangement of the polymer chains that were exposed to UV light, reducing their free volume. This densification limits chain mobility and increases their glass transition temperature.⁶⁹ For PLA composites it can be seen that even though the cold crystallization peak temperature and melting temperature remains almost unchanged, the crystallization of the polymer increase after 78 days of exposure to UV light, indicating that there is a degradation of the material after the exposure due to chain scission that promotes rearrangements in the amorphous zones of the polymer, and correlate well with the result observed in FTIR spectra discussed before.^42,73

Figure 11.

DSC thermograms (first heating scan) for PLA and its composites after UV exposure at different times of extraction (0, 14, 21, 42, 65 and 78 days): (a) PLA, (b) PLACoir, (c) PLAFique, and (d) PLASisal.

Table 5.

Thermal properties obtained from DSC curves for PLA and PLA composites materials exposed to UV light.

Material	Time (d)	Tg (°C)	Tcc (°C)	Tm (°C) peak 1	Tm (°C) peak 2	Xcr (%)
PLA	0	55.3	123.0	150.5	n.d	0.08%
	14	60.1	120.5	150.0	n.d	1.3%
	21	60.8	120.6	151.1	n.d	2.7%
	42	62.0	121.4	150.0	n.d	2.5%
	65	60.9	123.9	149.7	n.d	2.4%
	78	61.7	121.5	150.8	n.d	4.6%
PLACoir	0	58.8	115.6	148.5	154.2	7%
	14	60.3	115.8	148.6	154.1	8%
	21	60.1	119.4	149.6	n.d	8%
	42	60.2	118.7	150.6	n.d	7%
	65	61.5	121.9	151.5	n.d	8%
	78	60.9	113.8	148.8	154.2	10%
PLAFique	0	58.8	111.9	147.7	152.0	8%
	14	60.9	118.1	150.4	n.d	9%
	42	60.6	118.5	150.1	n.d	9%
	65	58.7	106.7	145.2	152.3	8%
	78	58.7	115.2	149.4	153.4	15%
PLASisal	0	58.9	113.8	148.1	153.9	7%
	14	61.7	114.7	148.6	152.5	7%
	21	60.1	117.3	148.8	n.d	8%
	42	60.9	116.8	149.3	n.d	8%
	65	62.2	118.9	149.7	n.d	8%
	78	61.2	117.0	149.7	n.d	11%

For composite materials, two different behaviors were observed. In PLACoir composites, the Tcc tends to increase at day 21, remains unchanged, and then decreases at day 78. The initial increase could be attributed to crosslinks of the polymer chains and the fiber degradation products, particularly those induced by lignin degradation products. The following decrease on day 78 may be due to enhanced molecular chain mobility caused by chain scission.⁶⁹ The degree of crystallinity in PLACoir composites remains constant in comparison to day 0, except at day 78, where a marked increase to 10% was observed. This result is consistent with a higher extent of chain scission, which promotes polymer chain reorganization and enhances crystallization. In contrast, for PLAFique and PLASisal composites, the Tcc remains constant over the exposure time, and the crystallinity of the composites also shows no significant variation in comparison to day 0, with the exception of day 78, where a slight increase was observed for both composites (same as PLAcoir fibers). As with PLACoir this is attributed to the chain scission within the amorphous regions and structural reorganization of polymeric chains that induce the crystallinity of the polymer.^61,69

Summarizing, DSC and FTIR results indicate that natural fibers indeed induce protection of the composite to UV exposure compared to neat PLA.

Figure 12 shows the percentual variation of tensile mechanical properties (Young’s Modulus and strain at break) for all composites at different UV radiation times. Young’s modulus of neat PLA decreases by up to 50% compared to day 0, even after short exposure times, such as 14 days of radiation. In contrast, the decrease in Young’s modulus for composites is slower than that of neat PLA, reaching the same loss of property only after long periods of UV exposure (day 78). Figure 12(b) shows that on day 14, all the materials (PLA and composites) reach a maximum in strain at break. After this point, a decrease in its variation is observed, with composites exhibiting values closer to those at day 0 than in neat PLA.

Figure 12.

(a) Young’s modulus and (b) strain at break variation for PLA and its composites after UV exposure at different times.

According to these results, Young’s modulus and strain at break appear to be highly sensitive to UV radiation. After 14 days of radiation exposure, neat PLA exhibits an important decrease in Young’s modulus and a significant increase in strain at break in comparison to composites materials. This could be attributed to the formation of short length polymeric chains of PLA due to the UV radiation. These chains serve as lubricants to longer polymeric chains, helping them to flow under tensile stress. For composites, this effect is attenuated due to the incorporation of fibers, that could serve as protector for UV radiation as was discussed above. After day 42, it is possible to see that the strain at break variation for PLA and composites decreases because of high intensity UV light energy, where the chains are broken and then the properties decrease. Similar results were found by Yu et al., who studied modified starch and PLA composites materials under UV radiation light and found that for short periods of time the elongation at break of the PLA increased and then decreased with the exposure time. This result indicates that UV light radiation can cause a rearrangement or change of the crystal structure to increase its elongation at break.⁷⁴

Results discussion

After all the analysis of how different environments impact on properties of the studied materials, it seems important to summarize all results in order to be able to distinguish if the developed materials can be applied to a specific application. Table 6 shows the change in properties for all the environments simulated on the final day of every test.

Table 6.

Summary of properties of biobased composites materials evaluated under different simulated environments (water soak, disintegration in industrial compost, and UV radiation).

	Simulated environment
	Distilled water (after 30 days of immersion)				Industrial compost (after 67 days)	UV exposure (after 78 days)
	Property
Material	Water absorption (%)	Tensile modulus variation (%)	Tensile strength variation (%)	Tensile elongation variation (%)	Disintegration degree	Carbonil Index	Crystallinity	Tensile modulus variation (%)	Tensile elongation variation (%)
PLA	1.29	−19	−20	−3	82	1.7	5	−57	60
PLACoir	3.07	−3	−34	−31	71	1.4	10	−53	15
PLAFique	2.32	7	−44	−50	70	1.2	15	−48	30
PLASisal	2.13	7	−30	−38	70	1.1	10	−54	76

It can be concluded that the incorporation of natural fibers contributes to enhancing the disintegration process of the material while extending its shelf life. Additionally, the fibers provide a degree of UV protection compared to neat PLA, suggesting potential for outdoor applications where exposure to UV radiation is a critical factor. However, the inherent hydrophilicity of natural fibers, combined with their poor interfacial adhesion to the PLA matrix, imposes limitations in applications involving prolonged exposure to moisture. Under such conditions, composites tend to absorb more water and exhibit a faster decline in mechanical properties compared to neat PLA, which is inherently hydrophobic. Future research will focus on improving the interfacial adhesion between the matrix and the fibers to mitigate water absorption and enhance the performance of the composites relative to 100% PLA.

Another important issue that should be addressed is whether the developed materials are competitive with conventional polymers that are usually used in the packaging industry. Previous studies have shown that such composites can exhibit similar properties to PS but with improved fracture toughness, and better tensile parameters and fracture toughness than commercial biodegradable polymers.¹⁹ Therefore, the key question here is whether they are competitive in terms of degradation rate and durability. Table 7 shows the evolution of properties after degradation in different environments of petroleum-based polymers and bio-based polymers commonly used in packaging applications, alongside the results obtained for the developed composites (highlighted in gray).

Table 7.

Comparison of properties after degradation in different environments of petroleum-based polymers and bio-based polymers commonly used in packaging applications, with composites developed within this work (highlighted in grey in this table).

		Simulated environment
		Distilled water				Specific enviroments	UV exposure
		Property
		Water absorption (%)	Tensile modulus variation (%)	Tensile strength variation (%)	Tensile elongation variation (%)	Mass loss (%)	Crystallinity (%)	Tensile modulus variation (%)	Tensile elongation variation (%)
Petroleum based polymers	PE	0.2 after 240 days⁷⁵	−15 after 240 days⁷⁶	−2 after 240 days⁷⁶	No data	It takes 250 years to degrade 50% of the initial mass in land⁷⁵	10% after 10 days⁷⁷		−80% after 4 days⁷⁷
	PP	0.03 after 30 days⁷⁸	−7 after 7 month⁷⁹	−2 after 7 month⁷⁹	No data	It takes 780 years to degrade 50% of the initial mass in land⁷⁵	12% after 6 weeks⁷⁷	No data	No data
	PS foam	1.9 after 7 days⁷⁸	No data	No data	No data	It takes more than 2500 years to degrade 50% of the initial mass in land⁷⁵	No data	No data	No data
	PET	0.5 after 14 days	No data	No data	No data	It takes more than 2500 years to degrade 50% of the initial in land⁷⁵	20% after 120 days⁸⁰		75% after 2 h⁸¹
Bio-based polymers	PLA	1.29	−19	−20	−3	82	5	−57	60%
	Wheat gluten	45–341^82–84	No data	No data	No data	87 after 4 days⁸⁵	No data	314 (after 15 days)⁸⁵	−66% (after 15 days)⁸⁶
	Cellophane	7 after 24 h⁸⁷	No data	No data	No data	100 after 2 days⁸⁸
	TPS	10–50^89,90	No data	No data	No data	100 after 56 days⁹¹	127 after 6 days⁹²	900 (after 11 days)⁹³	−97% (after 11 days)⁹³
Developed composites	PLACoir	3.07	−3	−34	−31	71	10	−53	15%
	PLAFique	2.32	7	−44	−50	70	15	−48	30%
	PLASisal	2.13	7	−30	−38	70	10	−54	76%

The composites developed and studied in this work exhibited competitive performance in water-absorption environments when compared to other bio-based polymers. Specifically, they demonstrate lower water uptake, highlighting their potential as viable alternatives to conventional bio-based materials. This advantage is further supported by their superior mechanical properties before immersion, as reported in previous studies.¹⁹ When compared to petroleum-based polymers, our composites exhibited an increase in tensile modulus after immersion, which may indicate a tendency toward increased brittleness.

Regarding the disintegration process, the composites developed in this study demonstrate a clear advantage over petroleum-based polymers, which show virtually no disintegration even after prolonged degradation periods. Furthermore, after UV exposure, our composites displayed improved elongation compared to those reinforced with other types of fibers. These findings suggest that the incorporation of natural fibers as reinforcement not only enhances the UV degradation behavior of the matrix but also positions these composites as a promising alternative to conventional polymers.

It should be noted that this study presents some limitations. Microstructural and molecular-level changes were inferred from thermal behavior and mass loss analyses, and no direct measurements of molecular weight or crystalline structure evolution through XRD were performed. Therefore, the proposed degradation mechanisms are supported by indirect evidence and consistency with previous literature.

Further studies combining longer degradation times and complementary analytical approaches would help to refine the interpretation of the structural changes occurring during the disintegration of PLA-based composites in industrial compost.

In summary, from a materials design perspective, the comparative results summarized in Tables 5 and 6 provide clear guidelines for the selection of natural fibers in PLA-based biocomposites depending on the targeted application and service environment. For packaging applications with limited exposure to moisture, all three fiber-reinforced systems demonstrate adequate mechanical stability while offering enhanced end-of-life performance through accelerated disintegration under industrial composting conditions. In this context, the incorporation of natural fibers represents a suitable strategy to balance functional performance during use with improved degradability after disposal. In contrast, for applications involving prolonged contact with water or high humidity, the results indicate that fiber-reinforced PLA composites may experience accelerated mechanical degradation due to fiber swelling and increased water uptake. These findings suggest that, in such cases, additional strategies—such as fiber surface treatments or improved interfacial adhesion—would be required to ensure long-term mechanical stability. Regarding outdoor or UV-exposed applications, the incorporation of natural fibers proved beneficial, as all fiber-reinforced composites exhibited improved retention of mechanical properties compared to neat PLA. Among the studied systems, differences in elongation retention after UV exposure suggest that fiber type can be used as a design parameter to tailor ductility and durability under photodegradation conditions.

Conclusions

Biobased PLA films reinforced with 5 wt% natural fibers (coir, fique, and sisal) were successfully developed and systematically evaluated under different degradation environments relevant to packaging and outdoor applications. The results show that environmental exposure plays a key role in determining the mechanical stability and degradation pathways of PLA-based biocomposites.

From an application-oriented perspective, the incorporation of natural fibers improves UV resistance and enhances compostability, making these materials particularly attractive for products requiring limited service life and controlled end-of-life disintegration. In contrast, prolonged exposure to moisture remains a critical limitation, as water uptake by the fibers accelerates mechanical degradation, highlighting the need for interfacial optimization in moisture-sensitive applications.

The comparative analysis among coir, fique, and sisal fibers shows that fiber selection can be used as a design parameter to tailor degradation behavior, mechanical retention, and durability depending on the targeted service environment.

Overall, the findings of this work provide practical guidelines for the design of PLA-based biocomposites intended for packaging and outdoor use, showing that natural fiber reinforcement enables a tunable balance between service and end-of-life degradation.

The results reported here correspond to composites containing 5 wt% fiber and should therefore be interpreted within this compositional range. Future work will explore higher fiber loadings to evaluate the influence of fiber content on the degradation behavior.

Footnotes

ORCID iDs

Carlos Ramirez

Federico Morales

Eliana Agaliotis

Valeria Pettarin

Funding

Authors would like to thank CONICET, Universidad de Buenos Aires and Universidad Nacional de Mar del Plata for finalcial support.

Declaration of conflicting interests

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

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