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Abstract

Poly (lactic acid) (PLA) composites can be a sustainable and biodegradable alternative to conventional synthetic plastics. It could be widely used across a range of applications, including trunk liners, door panels, and interior storage compartments, demonstrating its suitability for lightweight and durable interior applications. However, despite its versatility, overcoming the inherent limitations of PLA—particularly its relatively low degradation rate and water absorption —remains a challenge. In this study, the impact of integrating microfibrillated cellulose (MFC) as a reinforcement in PLA composites, specifically at fiber loadings of 0.5 wt% and 1.5 wt%, was comprehensively investigated through soil degradation and water absorption tests, examining their effects on mechanical, thermal, and morphological behavior. The MFC from curaua fibers utilized in the composites was pretreated with NaClO and NaOH solutions to optimize its interfacial properties. Interestingly, the composite with 0.5 wt% MFC showed delayed degradation and superior mechanical performance compared to the 1.5 wt% composite. Before degradation, the 0.5 wt% MCF/PLA composite had a flexural strength of 50.38 ± 2.83 MPa, statistically superior to the 44.09 ± 8.35 MPa of the 1.5 wt% composite. Under dry dynamic mechanical analysis (DMA) conditions (time mode and 1 Hz), the 0.5 wt% composite exhibited the highest storage modulus (3.13 GPa), notably higher than the 2.55 GPa recorded for the 1.5 wt% composite. After 90 days of soil exposure, the 0.5 wt% formulation retained significantly more strength (33.97 MPa) than the 1.5 wt% composite, which dropped to 13.07 MPa. The 0.5 wt% composite also showed the least affected increase in crystallinity after soil degradation (16.18%). Despite the 0.5 wt% composite absorbing slightly more water (nearly 1%) than the 1.5 wt% composite, it maintained a higher storage modulus under wet conditions (0.5% at 1.85 GPa vs 1.5% at 1.77 GPa at 1 Hz). These results revealed the complex interplay between the MFC content and composite characteristics. Furthermore, the intricate balance between degradability and water absorption is paramount when determining the optimal application of these biocomposites.

Keywords

Microfibrillated cellulose curaua fibers polylactic acid soil degradation water absorption

Introduction

The world faces a pressing environmental challenge posed by the ever-increasing accumulation of plastic waste. In response, biodegradable polymers have emerged as promising sustainable alternatives. These materials are uniquely characterized by their capacity to undergo complete degradation and assimilation through microbiological mechanisms, ultimately transforming into harmless elements within the environment.¹

The intricate process of biodegradation relies primarily on the sequential action of microscopic life forms: bacteria and fungi. Fungi, in particular, exhibit greater efficiency in this process due to their superior adhesion, especially when confronted with more resistant polymeric structures.² However, the speed at which these materials breakdown is not uniform; it is intricately influenced by several key factors, including the polymer’s precise chemical composition, its carbon ratio, and even the presence of various additives or plasticizers.³

While polymer degradation is crucial for environmental sustainability, another aspect of polymeric materials is their durability and lifespan in industrial applications. These attributes have significant economic, commercial, and safety implications. However, there is an inherent paradox: many polymers and composites are inherently susceptible to chemical decomposition reactions over time, which inevitably compromise their critical mechanical and chemical properties.⁴ For example, the oxidation of carbonyl groups, followed by random chain scissions, is frequently observed in various biodegradable polymers and stands out as one of the mechanisms underlying their properties over time.⁵

Polymers with hydrophilic characteristics, such as PLA, poly (hydroxybutyrate) (PHB), and starch blends, tend to exhibit a relatively high affinity for water, leading to the hydrolysis of polymer chains and accelerated degradation in humid environments.⁶ This phenomenon becomes even more pronounced when vegetable fibers are incorporated into hydrophobic matrices, reducing fiber-to-matrix adhesion and compromising the mechanical properties of the composites.⁷ Consequently, such materials are subject to significant dimensional variations, particularly in tropical and equatorial conditions, where high temperatures and humidity intensify degradation processes.⁸

Specifically, the degradation time for PLA in the environment can range from 6 months to 2 years, depending on the conditions to which the material is exposed. This process occurs in two main stages. Initially, water penetrates the polymer, promoting the hydrolysis of ester groups, particularly in the amorphous regions, and fragmenting the polymer chains into smaller, more soluble structures. Subsequently, specific enzymes metabolize these fragments, completing the material’s decomposition.⁹

Extensive research has been conducted on the biodegradability of various composites through water absorption and soil degradation tests. However, few studies have investigated the effects of these tests on PLA-based composites reinforced with microfibrillated cellulose at low content in the composites. Behera et al.¹⁰ developed composites reinforced with waste luffa sponge fibers using biodegradable soy resin and poly (vinyl alcohol) (PVA). After water absorption testing, the mechanically optimized formulation exhibited a water uptake of 32.6% and a maximum tensile strength of 46.2 MPa. Behera et al.¹¹ examined the water absorption behavior and limited biodegradation of thermoplastic starch (TPS) reinforced with jute fibers. Results from soil burial and fungal degradation tests confirmed the biodegradability of the composites, while water absorption analysis indicated a moderately hydrophobic nature. Subsequently, in another study by Behera et al.,¹² it was reported that the incorporation of cellulose fillers into the TPS matrix significantly influenced water uptake, with absorption increasing from 6.2% to 42.3% as the cellulose content increased from 0 to 25 wt%. These findings collectively highlight the strong correlation between fiber content, hydrophilicity, and the mechanical performance of biodegradable composites.

Similarly, the degradation of materials directly influences their mechanical properties, which can be monitored and controlled through specific tests, such as compression, tensile, hardness, and fatigue tests.¹³ Pursuing biodegradable polymers that strike a balance between stability during use and efficient degradation after disposal is a scientific and technological priority in this scenario. Among these materials, polyesters such as PLA stand out because of their chemical structure, which facilitates biodegradation through hydrolysis. This feature allows the production of materials ranging from highly crystalline, rigid polymers to more ductile polymers.¹⁴ Nevertheless, implementing polymers such as PLA faces challenges related to structural compatibility, cost, performance under different environmental conditions, and industrial feasibility.

A strategy to overcome these limitations is the addition of microfibrillated cellulose to PLA polymer composites, which has led to significant improvements in mechanical properties, including tensile strength and flexural resistance. For example, microfibrillated cellulose can increase the elongation at break of PLA while modifying its elastic modulus and tensile strength, depending on the fiber concentration and type used.¹⁵ In addition, compared with other biopolymers, such as PHB and PLA, which are produced from the fermentation of renewable raw materials like sugarcane, beets, and corn, PLA has superior mechanical properties.¹⁶ Despite this, its biological degradation is significantly slower than that of PHB, even under ideal conditions.

In this context, Jesus et al.¹⁷ conducted flexural, indentation, impact, and tensile tests combined with digital image correlation (DIC) to highlight the role of microfibrillated cellulose (MFC) in the PLA matrix. Thermal, morphological, and dynamic mechanical analyses confirmed these results. However, a gap still exists in the scientific literature regarding the evaluation of these composites under soil degradation conditions and after water absorption. Few studies have investigated how the interactions between the polymer matrix and the reinforcement change throughout the material’s life cycle. The integration of these analyses represents an innovative approach that can enhance the understanding of the functional and environmental performance of composites, particularly in applications where both mechanical strength and controlled degradation are essential requirements. Therefore, the development of PLA-based composites reinforced with microfibrillated cellulose represents a significant step toward advancing technological and sustainable solutions for biodegradable polymers. By carefully evaluating properties such as weight loss after soil and water uptake, mechanical performance, thermal behavior, and morphological characteristics, this research aims to understand the interactions between the matrix and the reinforcement, as well as the impacts of degradation on these materials.

Experimental section

Preparation of materials

The curaua fibers are supplied by CEAPAC (Centro de Apoio a Projetos de Ação Comunitária) from Santarém, Brazil. Initially, the fibers had an average natural length of approximately 80 cm. Before processing, the fibers were cut into segments of 5–6 cm to facilitate their incorporation into the composites. Microfibrillated cellulose (MFC): The cellulose used in this work was extracted from curaua fibers as described in detail in our previous study.¹⁷ The fibers were treated in a 2% v/v NaClO solution, followed by mercerization in a 5% w/v NaOH solution. The NaOH-treated fibers were obtained using a Masuko Sangyo Masscollider grinder (MKCA6-2J). PLA was obtained from GoodFellow, USA, and included granules with a diameter of approximately 3 mm, a natural appearance, a density of 1.24 g/cm³, an elongation at break of 6%, a tensile modulus of 3.5 GPa, an Izod impact strength of 16 Jm⁻¹, and a tensile strength of 53 MPa.

Composite MFC/PLA manufacturing: The procedure is described in 17. Initially, MFC microfibers suspended in water were replaced with chloroform (99.5% pure; Merck) in the aqueous suspension until the entire MFC was covered. The water was then replaced with chloroform through centrifugation. Chloroform was used to replace water in the MFC suspension because it is chemically compatible with PLA. Separately, PLA powder was dissolved in chloroform (300 mL per 100 g) by incubation for 24 h, followed by stirring for 1 h. The concentrated MFC suspension was blended with the solubilized PLA and then dried at 80°C for 24 h. The resulting mixture, along with pure PLA, was ground, extruded at 120–185°C and 150 r/min, and injection molded to produce flexural test samples with 0.5 wt% and 1.5 wt% MFC content.

Water Absorption tests

Water absorption tests were conducted in accordance with ASTM D 570.¹⁸ The samples were measured, weighed, and immersed in pure water at room temperature. At predetermined intervals, they were removed from the water, dried with a paper towel, weighed on a precision balance (with a precision of ±0.1 mg), and then placed back in the water. This procedure was repeated for approximately 50 days until the materials reached their water absorption saturation point. At the end of the test, a curve of water absorption (%) versus immersion time (days) was obtained, as specified by the standard. The percentage of water absorbed in the composites and polymers was calculated using equation (1):

{Δ W}_{a} (%) = \frac{W_{f} ‐ W_{i}}{W_{i}} x 100

(1)

where

{Δ W}_{a}

is the variation in water absorption and W_i and W_f correspond to the weights of the samples before and after water immersion, respectively.

Soil degradation tests

The composites and pure PLA in the soil were degraded in accordance with ASTM G160-03.¹⁹ The soil comprises three equal parts of soil, sand, and horse manure, totaling 12 kg. Initially, the sand and soil were sieved using a 10-mesh sieve, and the manure was manually shredded due to its high moisture content. The materials were then placed in a concrete mixer and mixed for 30 min until they were fully homogenized.

The soil was placed in a maturation chamber consisting of a wooden box lined with plastic sheeting, elevated 1.5 m above the ground, and covered with transparent plastic. The soil underwent maturation for 3 months, during which its temperature was monitored daily using thermometers, and its moisture content and pH were checked every 15 days. In accordance with the specified standard, the soil moisture content was maintained at 20–30%, and its pH ranged from 6.5 to 7.5. After maturation, the effectiveness of soil degradation was evaluated using tests with cotton fabric samples. The fabric used was 100% virgin cotton, weighing 460 g/m². The cotton samples were buried in the soil for 5 days and then dried in an oven at 70°C for 3 h. Afterward, tensile strength tests were conducted. According to ASTM G160-03, the soil is considered suitable for degradability testing if the indicated fabric loses 50% or more of its mechanical properties after exposure to the soil.

Once the soil conditions were confirmed after maturation, five samples of each MCF/PLA composite and neat PLA were buried in the soil for 30, 60, and 90 days. Flexural test samples were used for this purpose. During the test period, the soil temperature was monitored daily, while the moisture content and pH were checked biweekly, as required by the standard.

The samples removed from the soil at specified intervals were washed with distilled water to remove excess soil adhering to the surface and then placed in a desiccator for 96 h before further characterization.

The samples were preweighed before they were placed in the soil. After removal from the soil, the samples were washed with distilled water and stored in a desiccator for 5 days. The samples were subsequently weighed again. The percentage weight loss after exposure to the soil ( ${Δ W}_{S}$ ) was calculated using equation (2), where W_i is the initial weight of the sample (g) and W_f is the final weight (g).

{Δ W}_{S} (%) = \frac{W_{f} ‐ W_{i}}{W_{i}} x 100

(2)

Flexural tests

Three-point bending testing was performed on the samples according to the ASTM D 790²⁰ standard using an Instron 8801 test machine (Instron, Glenview, IL, USA) [±100 kN (22,500 lbf)] with a 2620-601 dynamic gauge extensometer (Instron, Glenview, IL, USA). Tests were performed on the polymers and composites before and after degradation in the soil. The results from “before” were previously shown by Jesus et al..¹⁷ The test speed was 1.5 mm/min. The arithmetic means of the numerical results of the tests performed on the composites and the polymers were calculated for five (5) samples. Specimens with dimensions of 130 × 15 × 3 mm were used for testing. Statistical analysis was performed using SPSS 20.0 and applied to the flexural test results to determine whether there were significant differences between the samples.

Scanning electron microscopy (SEM) characterization

The surfaces of the polymers and composites, both before and after degradation in soil, were investigated using SEM. The samples were metalized in gold. SEM analysis was performed using a SHIMADZU Superscan SS-500 scanning electron microscope at 15 kV with magnifications of 500×, 1000×, and 2000×.

Degree of crystallinity determination by DSC

The samples were analyzed from 50 to 600°C at a heating rate of 10°C/min in a simultaneous (TGA‒DSC) thermal analyzer (Q600 SDT, TA Instruments, USA) under a nitrogen atmosphere at a flow rate of 100 mL/min. The analyses were performed in an alumina pan with approximately 10 mg of sample. The polymers and composites were tested before and after degradation in the soil and water absorption tests. The results from “before” were previously shown by Jesus et al.¹⁷

The degree of crystallinity of the polymers was determined using equation (3). The calculation compares the enthalpy of fusion of 100% crystalline PLA, 93.1 J/g, obtained in the samples according to equation (3).

X c (%) = \frac{{Δ H}_{m} - {Δ H}_{c c}}{w \times Δ H_{m}^{o}} \times 100

(3)

where Xc (%) is the percentage of polymer crystallinity; ΔH_m is the enthalpy of melting of the sample; ΔH_cc is the enthalpy of cold crystallization peak;

Δ H_{m}^{o}

is the theoretical melting enthalpy of the polymer with 100% crystallinity; and w is the weight percentage of the matrix in the composite.

DMA tests

The DMA test was conducted on samples with dimensions of 25 × 5 × 4.05 mm. The samples were tested using a Perkin Elmer instrument at the University of Alberta, Canada. It operated in single cantilever mode under multifrequency conditions at 1 and 10 Hz, either dry or in a water bath, at room temperature (20°C) for 60 min, in time-scan mode.

Results and discussion

Effects of water absorption on the properties of polymers and composites

Figure 1 shows the water absorption percentages for the polymers and composites before and after the water absorption test. Figure 1 shows that the PLA samples exhibited the lowest water absorption values, which can be attributed to the absence of microfibrillated cellulose and stress concentrators, as confirmed by SEM analysis (see Figure 3). After 41 days, the PLA absorbed only 0.65% of the water. Among the composites, the PLA with 0.5 wt% microfibrillated cellulose exhibited the highest water absorption, at nearly 1%, followed by the composite with 1.5 wt% microfibrillated cellulose, which absorbed approximately 0.8% water.

Figure 1.

Water absorption versus time curves for pure PLA and the composites (A) and images of the samples subjected to water absorption before (B) and after the tests (C). Pure PLA (a), 0.5 wt% microfibrillated cellulose/PLA composite (b), and 1.5 wt% microfibrillated cellulose/PLA composite (c).

In the present study, the microfibrillated cellulose content in the PLA matrix ranged from 0.5 wt% to 1.5 wt%. Water absorption was relatively low at these low loading levels compared with that of neat PLA. Owing to its affinity for PLA (both are polar), water can hydrolyze the polymer chains in the matrix, further diminishing the mechanical properties. Other factors, such as microstructure and crystallinity, can also influence the water absorption properties of biodegradable polymers.

Prashantha et al.²¹ reported a similar effect in their studies, noting that the number of free hydroxyl groups and effective interactions directly influence the water absorption of materials. Furthermore, the water absorption properties of biodegradable composites made from a Mater-Bi-Y matrix, a commercial blend of starch, cellulose derivatives, and additives combined with jute fibers, show that water absorption decreases with decreasing fiber content.

To corroborate the data obtained from the water absorption test, water contact angle measurements are commonly used to assess the wetting behavior of polymeric surfaces. In general, hydrophilic materials exhibit contact angles below 90°, while hydrophobic surfaces typically exhibit contact angles above this threshold.²² PLA is widely recognized as a hydrophobic polymer due to its high water contact angle, which ranges from 120 to 139°,²³ reflecting its low moisture affinity, as observed in Figure 1 for the neat PLA sample.

The shelf life of PLA-based compounds is complex to determine, as it is strongly influenced by the environmental conditions to which the material is exposed throughout its shelf life. Among the key mechanisms involved in performance deterioration, hydrolytic degradation plays a predominant role. The susceptibility of PLA to hydrolysis is directly associated with the presence of ester linkages in its structure, which are progressively cleaved in the presence of moisture. Therefore, high-humidity environments significantly accelerate molecular chain scission, resulting in reduced molecular weight and, consequently, decreased mechanical properties.³

Temperature is another factor that intensifies degradation. As the material temperature increases, the mobility of polymer chains increases, facilitating water penetration and accelerating hydrolysis kinetics.²⁴ This combined effect makes PLA particularly vulnerable in applications subjected to fluctuating or elevated temperatures, such as automotive components or outdoor-use products. Additionally, the incorporation of reinforcing fillers or fibers can also influence the degradation mechanism. While these additives may improve mechanical performance, they may also hinder chain mobility and restrict water diffusion into the matrix, delaying the onset of hydrolysis.²⁵ Thus, establishing or fixing a shelf life for PLA materials is challenging. The literature consistently demonstrates that PLA longevity results from a complex interaction between intrinsic properties (e.g., crystallinity, molecular weight, additives) and external environmental conditions.³

Effects of soil degradation on the mechanical and morphological properties of PLA and MCF/PLA

Table 1 presents the weight loss results for the samples before and after exposure to soil degradation. According to the data, compared with the original materials (i.e., before exposure to soil degradation), the composites showed no significant weight change after 30, 60, or 90 days.

Table 1.

Weights of the samples before and after exposure to soil degradation.

Samples	Weight (g)
Samples	Before	30 days	60 days	90 days
PLA	7.24 ± 0.21	7.23 ± 0.21	7.24 ± 0.23	7.21 ± 0.11
Microfibrillated cellulose 0.5 wt%/PLA	7.33 ± 0.09	7.25 ± 0.07	7.29 ± 0.09	7.21 ± 0.05
Microfibrillated cellulose 1.5 wt%/PLA	7.29 ± 0.11	7.26 ± 0.01	7.32 ± 0.11	7.25 ± 0.05

In accordance with ASTM G160-03,¹⁹ the soil moisture content must be maintained between 20% and 30%. The controlled moisture of the degraded soil enables water diffusion into the materials, initiating the degradation of PLA and its composites through hydrolysis. The degradation of PLA occurs in two stages: the initial hydrolysis of the material, followed by microbial attack of the resulting lactic acid oligomers. The degradation process in soil can take anywhere from 6 months to 2 years. During this process, the polymer chains breakdown into smaller, soluble fragments, resulting in gradual weight loss over time.^26,27

Furthermore, ASTM G160-03¹⁹ requires monitoring the soil moisture index. An increase in weight occurred due to water absorption by the polymers and composites. Costa et al.²⁸ emphasized that hydrolysis is particularly critical for the degradation of polymers such as polyethylene terephthalate (PET), PLA and its copolymers, poly (α-glutamic acid), and polydimethylsiloxanes (silicones). According to the findings, the synthetic polymers most susceptible to enzymatic hydrolysis are polyurethanes and polyesters, where hydrolysis occurs at ester bonds mediated by hydrolases.

The addition of natural fibers to polymeric composites can enhance degradation by increasing hydrophilicity, facilitating moisture penetration into the material, disrupting the PLA crystalline regions, and accelerating hydrolytic chain scission. Although this mechanism accelerates degradation, the overall decomposition rate remains relatively moderate.⁴

PLA, which can trigger hydrolytic degradation through the cleavage of its ester linkages, resulting in a progressive reduction of molecular weight. The prolonged exposure to soil is particularly accelerated at temperatures above approximately 30°C, where the fibers’ insertion enhances chain mobility, facilitating water diffusion along the polymer backbone. This process generates oligomers and lactic acid monomers that may contribute to localized pH changes in the surrounding soil environment.²⁹

According to the analysis in Table 1, virtually no weight loss occurred. However, significant reductions in flexural properties were evident. The results for the flexural strength of the samples after degradation testing in soil for 30 to 90 days are shown in Table 2.

Table 2.

Strength and flexural modulus of the polymers and composites before and after soil degradation.

Sample	Before¹⁷	30 days	60 days	90 days
Flexural strength (MPa)
PLA	42.84 ± 4.74^a	28.28 ± 8.96^a	23.33 ± 9.33^a	29.81 ± 3.54^a
Microfibrillated cellulose 0.5 wt%/PLA	50.38 ± 2.83^b	38.55 ± 4.64^b	43.48 ± 4.64^b	33.97 ± 1.84^a
Microfibrillated cellulose 1.5 wt%/PLA	44.09 ± 8.35^a	34.59 ± 10.27^b	24.23 ± 13.89^a	13.07 ± 13.96^b
Flexural modulus (GPa)
PLA	2.58 ± 0.06^a	3.95 ± 0.46^a	3.08 ± 0.67^a	3.53 ± 0.25^a
Microfibrillated cellulose 0.5 wt%/PLA	2.88 ± 0.04^a	3.78 ± 0.23^a	3.68 ± 0.12^a	3.47 ± 0.13^a
Microfibrillated cellulose 1.5 wt%/PLA	2.49 ± 0.18^a	3.91 ± 0.31^a	2.81 ± 0.59^b	2.07 ± 1.75^b

a–c Letters indicate significant differences between samples by Tukey’s test.

As shown in Table 2, the data reported by Jesus et al.,¹⁷ a previous work, indicate that the microfibrillated cellulose 1.5 wt%/PLA composite exhibited lower flexural strength and modulus than the microfibrillated cellulose 0.5 wt%/PLA composite. This reduction in flexural performance is due to more effective reinforcement dispersion at lower filler content. According to Digital Image Correlation (DIC) analysis, the microfibrillated cellulose (MFC) 0.5 wt%/PLA composite exhibited a more homogeneous distribution of cellulose within the PLA matrix, thereby promoting stronger interfacial interactions. This uniform dispersion decreased the intermolecular spacing and restricted molecular mobility, ultimately resulting in higher flexural strength.

Figure 2 shows a possible molecular interaction between poly (lactic acid) and cellulose. Poly (lactic acid) consists of repeating units of lactic acid monomers, which contain methyl (–CH₃), carboxyl (–COOH), and hydroxyl (–OH) terminal groups. Cellulose, in turn, is composed of anhydroglucose units linked by β-(1→4)-glycosidic bonds. Each monomeric unit contains three hydroxyl (–OH) groups, which form extensive intra- and intermolecular hydrogen-bonding networks that provide rigidity and crystallinity to the structure.³⁰ The interaction between PLA and cellulose mainly occurs through hydrogen bonds formed between the hydroxyl groups of cellulose and the carbonyl (C = O) and terminal hydroxyl groups of PLA. These interactions can promote a more efficient interfacial adhesion between the polymeric phases.

Figure 2.

Probable interaction between poly (lactic acid) and cellulose.³⁰

Tukey’s statistical analysis was used to compare the flexural strength and modulus of all samples (PLA, 0.5 wt% MFC/PLA, and 1.5 wt% MFC/PLA) before soil degradation. Although variations were observed in both flexural strength and modulus among the samples before soil degradation, the statistical analysis confirmed that these differences were significant only for the samples microfibrillated cellulose 0.5 wt%/PLA (group “b”), as samples PLA and microfibrillated cellulose 1.5 wt%/PLA were classified within the same group “a”. According to Table 2, the flexural strength decreased after the samples were subjected to soil degradation. However, an increase in the flexural modulus was observed after 30 days of exposure. The likely cause is water absorption and the hydrolysis of the ester groups present in PLA, followed by microbial attack of the amorphous regions of the material. A similar study²⁷ investigated the biodegradation of PLA/kenaf composites after exposure to the fungus Pleurotus ostreatus for 30 to 180 days. After 180 days, more than 45% of the composites were degraded, and a reduction in mechanical properties was observed due to fungal activity. It was proposed that enzymatic activity from the fungus disrupted the interaction between the PLA matrix and microfibrillated cellulose, leading to the degradation of the cellulose. This degradation subsequently reduced the material’s flexural strength while increasing its modulus.

The duration of soil exposure significantly influences mechanical strength and flexural modulus. In their studies on biodegradable composites, Luo et al.³¹ reported substantial variations in mechanical properties over time, attributed to surface defects induced by biodegradation. Similarly, Hermida et al.³² reported that during biodegradation of the polymeric matrix, the sizes of pores and surface microcracks increased until a critical size was reached, leading to failure points. Under mechanical stress, these cracks accumulate stress, leading to failure with reduced plastic deformation.

Water likely penetrated the amorphous regions of the PLA matrix, where hydrophilic groups caused swelling. This swelling created stress on the polymer chains and reduced the interfacial interaction forces within the composites, thereby decreasing the flexural strength. In another study, Karaduman et al.³³ examined the degradation of composites reinforced with carpet and jute waste. They reported a reduction in flexural strength and an increase in flexural modulus, attributing these changes to the plasticizing effect of water.

Additionally, Tukey’s test was applied in this study to identify significant differences in flexural test results following soil degradation. After 30 days of soil degradation, statistically significant differences were observed between neat PLA (group “a”) and the MFC-reinforced composites (group “b”). At 60 days, the statistical analysis indicated no significant difference between neat PLA and the 1.5 wt% MFC/PLA composite; however, the 0.5 wt% MFC/PLA composite remained significantly different. Finally, after 90 days, Tukey’s test confirmed statistically significant differences among microfibrillated cellulose 1.5 wt%/PLA (group “b”) and both the neat PLA and the 0.5 wt% MFC/PLA samples (group “a”). Figure 3 shows the SEM morphology of the cross-sections of fractured samples from flexural tests after different periods of exposure to degradation in soil. The morphology of the PLA material did not change significantly during the 90-day exposure period. The same observations were made for the other materials exposed to the soil. Some microorganisms adhered to the surfaces of PLA, microfibrillated cellulose, and the composites after 60 days of exposure (indicated by the red circles).

Figure 3.

SEM micrographs of materials subjected to degradation in soil: PLA after (A) 30 days, (B) 60 days, (C) 90 days of exposure; PLA composite reinforced with 0.5% microfibrillated cellulose after (D) 30 days, (E) 60 days, (F) 90 days of exposure; and PLA composite reinforced with 1.5% microfibrillated cellulose after (G) 30 days, (H) 60 days, and (I) 90 days of exposure.

In the analysis of the composite morphology, cracks were observed (indicated by red circles), which likely made the material more brittle, as evidenced by the flexural mechanical tests. As shown in Figure 3(F), 3(H), and 3I, greater exposure of the microfibrillated cellulose relative to the matrix was noted after 60 days of soil exposure. This phenomenon is attributed to the moisture absorption by microfibrillated cellulose, which allows it to access the matrix. This suggests that hydrolysis products near the surface were dissolved in the medium and assimilated. Similar effects have been reported in studies involving low-cost polymeric composites manufactured from jute residues and carpet fibers.³³

SEM images of the degraded samples, along with weight loss analysis, revealed that degradation occurred primarily in the neat polymer. Azevedo et al.²⁶ reported similar phenomena in their studies on the degradation of composites reinforced with natural fibers. In their research, the authors identified carbon dioxide production and material weight loss. Therefore, with the addition of microfibrillated cellulose, the composites exhibited lower weight loss, even though biodegradation was enhanced.

Determination of the crystallinity of the MCF/PLA composites by DSC after degradation in soil and water absorption

The DSC curves for PLA, the composite reinforced with 0.5% microfibrillated cellulose, and the composite reinforced with 1.5% microfibrillated cellulose after degradation in soil for 0, 30, 60, and 90 days are shown in Figure 4. Figure 4 also presents the DSC curves of the polymers and composites before (C) and after (D) the water absorption test. The calculated crystallization enthalpies and crystallinity values (Xc%) for all the samples are listed in Table 3.

Figure 4.

Comparative DSC curves of PLA (A) and microfibrillated cellulose 1.5 wt%/PLA (B) after degradation in soil for 0, 30, 60 and 90 days and DSC curves of polymers and composites before (C) and after (D) the water absorption test.

Table 3.

Crystallization enthalpies and degrees of crystallinity of the PLA and composites before and after soil degradation (90 days) and water absorption tests.

Period	Specimen	T_g (°C)	T_m (°C)	T_cc (°C)	ΔH_cc (J/g)	ΔH_m (J/g)	Xc%
Before soil degradation and water absorption¹⁷	PLA	58.67	170.03	96.60	34.90	44.67	10.49
	Microfibrillated cellulose 0.5 wt%/PLA	56.04	170.36	85.85	8.73	49.33	5.90
	Microfibrillated cellulose 1.5 wt%/PLA	58.37	170.85	93.57	29.40	37.35	8.67
After soil degradation	PLA	55.97	168.23	93.96	28.78	40.35	12.42
	Microfibrillated cellulose 0.5 wt%/PLA	56.15	170.24	92.84	27.15	41.46	16.18
	Microfibrillated cellulose 1.5 wt%/PLA	55.33	168.08	91.86	30.21	41.93	12.78
After water absorption	PLA	57.91	169.03	94.62	29.51	38.49	9.64
	Microfibrillated cellulose 0.5 wt%/PLA	57.02	169.85	92.36	29.48	41.44	13.52
	Microfibrillated cellulose 1.5 wt%/PLA	56.17	167.94	92.46	30.98	43.69	13.86

T_g: glass transition temperature peak; T_m: melting temperature peak; T_cc: cold crystallization peak; ΔH_m: enthalpy of melting; ΔH_cc: enthalpy of cold crystallization.

During the first 30 days, all the materials experienced an increase in crystallinity, as shown in Table 3. The materials produced from the PLA matrix did not experience thermal degradation events, such as a decrease in the thermal degradation temperature, within the first 30 days, as observed in Figure 4. After 60 days, the crystallinity of PLA increased by more than 78%, whereas that of the composites slightly increased, approximately 45%, compared with that of the unexposed material. At 90 days, the materials maintained crystallinity levels similar to those observed after 30 and 60 days.

All the DSC curves presented in Figure 4 revealed the occurrence of cold crystallization during heating. It was observed that neat PLA showed a higher cold crystallization temperature (Tcc), (Table 3). This behavior is generally attributed to the plasticizing effect of the polymer itself.³⁴ With the incorporation of 0.5% microfibrillated cellulose, there was a reduction of approximately 10°C in Tcc, while for the composite containing 1.5% microfibrillated cellulose the decrease was around 3°C.

According to Melillo et al.,³⁴ the presence of the reinforcing material in the composites can reduce the free energy required for the formation of new crystalline nuclei. As a result, the polymer tends to crystallize more readily during heating, as reflected in its lower cold crystallization temperature (T_cc).

The weight loss of PLA and its derivatives has been linked to the surface of the matrix cracking, which is attributed to the delamination and shrinkage of the polymeric phase caused by increased crystallization after degradation in soil. Hydrolysis then occurs in the amorphous regions, which are more susceptible to microbial attack due to their weaker molecular interaction and looser packing, ultimately leading to degradation of the crystalline phase.³⁵

Increased crystallinity in the polymer and composites was observed after 60 days of exposure. This phenomenon is likely linked to water absorption and microbial colonization in the amorphous regions, leading to chain scission by hydrolysis into smaller chains, eventually affecting the crystalline regions.³⁶ Furthermore, DSC curve analysis revealed that all the samples subjected to degradation in soil experienced two thermal events before the melting temperature of the PLA polymer matrix was reached. The first event is associated with the moisture present in PLA and the composites, which is due to soil moisture. The second event is related to the crystallization temperature of the materials, which corresponds to the rearrangement of amorphous regions into a crystalline phase.³⁷

According to Hidayat et al.,²⁷ the environmental degradation time for PLA and its composites ranges from 6 months to 2 years, depending on the conditions to which the material is exposed. In terms of material crystallinity, a nonlinear trend was observed. However, for the composites, a gradual reduction in crystallinity was noted, particularly in the material reinforced with 0.5% microfibrillated cellulose after 90 days of exposure, compared with that of PLA. These reductions in crystallinity may be attributed to microbial attack of the amorphous regions of the composite, which is facilitated by the presence of microfibrillated cellulose or the formation of microvoids.

Solarski et al.³⁸ reported that the increase in crystallinity of PLA after degradation in soil is related to two factors: semicrystalline polymeric materials are preferentially attacked in their amorphous regions because of their increased susceptibility to water and oxygen penetration, resulting in hydrolysis. Consequently, the percentage of crystalline regions increases over time as degradation progresses. However, after 90 days or more of soil degradation, the crystallinity decreases, which may be attributed to hydrolysis becoming the predominant mechanism.

The biological degradation of PLA and its composites is slower than that of other biodegradable polymers, such as PHB or starch-based materials. However, the presence of microfibrillated cellulose led to increased crystallinity in all the composites and a loss of mechanical properties, indicating that microfibrillated cellulose accelerated the degradation process, even under ideal conditions (e.g., temperature, pH, moisture).³⁹

The soil moisture content influences the structural evolution of cellulose in polymer composites, altering its crystalline lattice parameters and inducing expansion, contraction, and changes in the monoclinic angle of its unit cell.⁴⁰ Additionally, changes in the hydroxyl (–OH) and carbonyl (–CO) functional groups reflect ongoing molecular degradation and restructuring within the composite. Consequently, intramolecular interactions contribute to a more ordered organization of cellulose chains, thereby increasing crystallite size and the overall degree of crystallinity. Together with microorganisms, they preferentially attack the amorphous regions, leading to a progressive reorganization of cellulose chains into larger, more ordered crystalline domains. This reduces molecular mobility, thereby decreasing flexibility and promoting breakage. This structural evolution corresponds to an increase in crystallinity and fiber stiffness.⁴¹ Such microstructural and molecular transformations can account for the initial increase in flexural strength, followed by an increase in brittleness, as observed in the current study (Table 2). The interplay among soil–moisture interactions, crystalline rearrangement, crystallite growth, and the degradation of amorphous regions can elucidate the mechanisms underlying the mechanical and chemical changes in microfibrillated cellulose/PLA composites during environmental exposure.

Fourier transform infrared analysis is very useful for understanding the chemical effects on the PLA structure.⁴² When comparing the material exposed to soil for 3 months with the PLA at day zero, a reduction in the intensity of the band at 1748 cm⁻¹, corresponding to the stretching of carbonyl groups, is observed, suggesting the onset of ester bond cleavage. After 8 months of degradation, the disappearance of the bands at 2995 cm⁻¹ and 2945 cm⁻¹, attributed to –CH₃ stretching vibrations, indicates a more advanced breakdown of amorphous regions in the polymer.⁴³ These results confirm the progressive structural deterioration of PLA over time, demonstrating that the soil environment accelerates the chemical degradation process of the material.

From the DSC curves of the polymers and composites before (C) and after (D) the water absorption test, and from the data in Table 3, a slight shift in the melting temperature (T_m) was observed, likely due to hydrolysis of the amorphous regions in the PLA matrix. This shift is associated with the breakdown of PLA polymer macromolecules caused by exposure to an aqueous environment, as water preferentially attacks amorphous or low-crystallinity regions.³⁶

The crystallinity of the material, as well as that of its composites, was calculated for PLA before and after exposure, as shown in Table 3. The crystallinity of PLA increased by 15% compared with the samples after soil degradation. Similarly, compared with the unexposed material, the polymer composites exhibited a 63% increase in crystallinity for the composite with 0.5% microfibrillated cellulose and a nearly 32% increase for the composite with 1.5% microfibrillated cellulose after soil degradation. This increase was attributed to the hydrolysis of the amorphous fraction of PLA, which increased the crystalline fraction, a phenomenon similar to that occurring in materials degraded in soil.

A similar effect has been attributed to an increase in crystallinity caused by the plasticizing effect of lactic acid oligomers formed during the degradation process, which enhances chain mobility.⁴⁴ Similarly, this increase in crystallinity may be linked to the rapid relaxation of lower-molecular-weight chains resulting from hydrolytic degradation.⁴⁵

According to Zimmermann et al.,³⁶ the crystallization temperature (T_cc) decreases during the hydrolytic degradation process. This decrease is attributed to the formation of PLA oligomers resulting from chain scission during hydrolysis, as well as the degradation of amorphous regions within the matrix, which leads to increased mobility and relaxation of the polymer chains. Chains with lower molecular weights crystallize more easily because of their more efficient packing and lower crystallization temperatures.

Dynamic mechanical analysis (DMA) properties of the polymers and composites

In the first part of this study,¹⁷ DMA analyses were performed as a function of temperature, considering that the physical, chemical, and mechanical behavior of polymer composites is strongly affected by thermal conditions. The results demonstrated that incorporating MFC into the PLA matrix increased the stiffness of the matrix. Specifically, the storage modulus (E′) of the composite containing 0.5 wt% of MFC increased by approximately 16% compared to neat PLA, indicating efficient stress transfer between the reinforcement and the polymer matrix. Additionally, the addition of MFC promoted a more rigid structure, attributed to enhanced interfacial interactions and improved fiber dispersion within the PLA matrix.

Figure 5 shows the storage modulus (E′) and damping factor (Tan δ) behavior of the polymers and composites under dry conditions at room temperature (20°C), and the extracted data are presented in Table 4. Table 4 compares the storage modulus (E′), loss modulus (E''), and damping factor (Tan δ) for the polymers and composites under 1 and 10 Hz, as well as dry and wet conditions (water bath), as a function of time. For the PLA polymer, the wet environment significantly affected the dynamic moduli, particularly the loss modulus (E″). This resulted in proportional increases in both E′ and E″, maintaining a constant Tan δ. Compared with the composite with 0.5% microfibrillated cellulose and the composite with 1.5% microfibrillated cellulose, the neat PLA in a wet medium presented the highest storage modulus (E′). Despite the presence of microfibrillated cellulose, which can impose molecular restrictions and potentially improve interfacial adhesion with the PLA matrix, the wet medium appears to have compromised these interactions. As a result, the expected improvements in macromolecular packing and decrease in the number of stress concentrators were not effectively maintained under wet conditions.

Figure 5.

Storage modulus (A) and Tan δ (B) for polymers and composites at a frequency of 1 Hz in dry media at room temperature (20°C).

Table 4.

Dynamic mechanical properties of the polymers and composites under dry and wet conditions.

Condition		Dry			Wet
Frequency	Sample	E´_30 min (GPa)	E´´ _30 min (MPa)	Tan δ	E´_30 min (GPa)	E´´_30 min (MPa)	Tan δ
1 Hz	PLA	2.77	57.88	0.02	3.01	60.81	0.018
	Microfibrillated cellulose 0.5 wt%/PLA	3.13	36.55	0.01	1.85	35.01	0.021
	Microfibrillated cellulose 1.5 wt%/PLA	2.55	33.74	0.01	1.77	31.55	0.019
10 Hz	PLA	2.81	49.95	0.02	3.05	57.83	0.021
	Microfibrillated cellulose 0.5. wt%/PLA	3.16	33.88	0.01	1.83	31.68	0.018
	Microfibrillated cellulose 1.5 wt%/PLA	2.58	29.38	0.01	1.81	27.2	0.016

The wet environment had a pronounced effect on the composites, especially on E'. A reduction of more than 40% was observed for the composite reinforced with 0.5% microfibrillated cellulose, and a reduction of more than 30% was observed for the composite reinforced with 1.5% microfibrillated cellulose. This reduction in E′ under wet conditions was consistent across all tested frequencies compared to that of neat PLA. At 1 Hz, neat PLA exhibited an E′ of 3.01 GPa, whereas the composites with 0.5 wt% and 1.5 wt% microfibrillated cellulose presented lower values of 1.85 GPa and 1.77 GPa, respectively. A similar trend was observed at 10 Hz (see Table 4). Similar effects were reported by Qin et al.,⁴⁵ attributing these changes to the rapid relaxation of low-molecular-weight chains caused by hydrolytic degradation. Additionally, reasonable fiber‒matrix adhesion, as confirmed by flexural mechanical tests, and the hydrolytic degradation of amorphous regions, followed by the degradation of crystalline components, further contributed to this behavior.

The frequency had no significant influence on the composite behavior. An additional expected effect for the composite with 0.5% microfibrillated cellulose was the restriction of macromolecular mobility, likely caused by the percolation effect between the fibers and the polymer matrix. Furthermore, Table 4 shows that the frequency did not affect the behavior of the materials in a wet environment. Adding 0.5% microfibrillated cellulose to the composite resulted in the anticipated impact, particularly on the storage modulus (E′), although this effect was not evident in the Tan δ values. Both the composites and the polymers maintained relatively constant Tan δ values across all the materials.

At 1 Hz, the composite containing 0.5% microfibrillated cellulose demonstrated a greater than 12% increase in E′ compared with that of neat PLA under dry conditions. Similar behavior was also observed for the same composite and condition at 10 Hz. However, as shown in Table 4, this improvement was not reflected in damping, likely due to the presence of microvoids in the polymer matrix or hydrolysis of the matrix caused by water diffusion into the PLA. On the other hand, the composite reinforced with 1.5% microfibrillated cellulose presented a lower E′ than did all the other materials. This is likely due to the agglomeration of microfibrillated cellulose and the presence of stress concentrators in the PLA matrix, which facilitates water diffusion into the microstructure of the material. This phenomenon can be explained by chain relaxation involving lower-molecular-weight chains, which results from the breakdown of macromolecules caused by hydrolysis.⁴⁵

The variation in tan δ over time for the polymers and composites is presented in Table 4. The frequency did not influence the behavior of the materials in a moist environment. The addition of microfibrillated cellulose did not produce the expected effect on the composites. Tan δ remained nearly unchanged for the PLA polymers, at 0.018 for PLA. The reduction in the height of the tan δ peak may be linked to the increased crystallinity of PLA.³⁸ This is supported by the results of thermal and mechanical tests, as semicrystalline polymers degrade preferentially in amorphous regions, where water and oxygen penetration is easier, resulting in hydrolysis. Consequently, hydrolytic degradation over time increases the relative proportion of crystalline regions. The second reason is associated with polymer chain scission, resulting in the formation of lower-molecular-weight chains.

The DMA analysis conducted under both wet and dry conditions revealed that microfibrillated cellulose contributes to the degradation of the material by increasing its crystallinity, as confirmed by DSC tests. Additionally, it increases the flexural modulus of elasticity.

Conclusions

Degradation in soil has proven to be an effective accelerated process, providing an optimal environment for microorganism activity. Similarly, degradation in an aqueous medium is a practical and straightforward process. The weight loss of the composites reinforced with microfibrillated cellulose was similar to that of neat PLA after soil exposure. Morphological analysis using SEM revealed no significant structural changes in the simulated soil after 90 days, although microbial colonization was observed on the PLA and composite surfaces after 60 days.

The 1.5 wt% microfibrillated cellulose (MFC)/PLA composite is considered the least optimal formulation, particularly in mechanical performance, because the higher filler content led to MFC agglomeration and the formation of stress concentrators within the PLA matrix. Before soil degradation, the 1.5 wt% MFC/PLA composite exhibited lower flexural strength and modulus than the 0.5 wt% composite. Tukey’s statistical analysis confirmed that the results for the 1.5 wt% composite and neat PLA were grouped (“a”), while the 0.5 wt% composite was statistically superior (“b”). After 90 days of soil degradation, the 1.5 wt% composite displayed the lowest flexural strength (13.07 ± 13.96 MPa) and the lowest flexural modulus (2.07 ± 1.75 GPa) compared to all other materials.

The dynamic mechanical tests under dry conditions (1 Hz) and time mode at 20°C, the 1.5 wt% composite had a storage modulus (E' = 2.55 GPa) that was lower than that of both neat PLA (2.77 GPa) and the 0.5 wt% composite (3.13 GPa). When tested in a wet environment (1 Hz), the 1.5 wt% composite showed the lowest storage modulus (E' = 1.77 GPa) among all samples. This reduction in E′ was attributed to the agglomeration of MFC and the presence of stress concentrators facilitating water diffusion into the microstructure.

After soil degradation, the 0.5 wt% composite formulation maintained better structural stability, with the least affected increase in crystallinity (16.18%). The inferior flexural strength of the 1.5 wt% composite, compared to the 0.5 wt% composite, is linked to the dispersion quality. The 0.5 wt% MFC/PLA composite exhibited a more homogeneous cellulose distribution, leading to stronger interfacial interactions and higher flexural strength.

Overall, the 0.5% MFC composite modulates PLA biodegradability and is a promising solution for technological and sustainable applications, such as disposable household items.

Footnotes

Declaration of conflicting interests

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

Funding

The authors would like to acknowledge the support of the Brazilian Research Agencies, CNPq, Capes, FAPDF and DPG-UnB.

ORCID iD

Linconl A. Teixeira

References

Çevik

Yıldırım

Kanbur

. Examining the mechanical and biodegradable characteristics of hemp fiber added PLA bio-composites with various modifications. J Thermoplast Compos Mater 2025; 38: 3535–3558.

Khanoonkon

Kongsin

Jampanit

, et al. Effect of steam explosion and silanization of hemp fibers on polylactic acid biocomposites; analysis of mechanical-thermal properties and fungal biodegradation. J Thermoplast Compos Mater 2024; 37: 2858–2879.

Momeni

Craplewe

Safder

, et al. Accelerating the biodegradation of poly (lactic acid) through the inclusion of plant fibers: a review of recent advances. ACS Sustainable Chem Eng 2023; 11: 15146–15170.

Hussain

Khan

Shafiq

, et al. A review on PLA-based biodegradable materials for biomedical applications. Giant 2024; 18: 100261.

Liu

Hua

, et al. Thermal-oxidation degradation of polylactic acid/cellulose nanocrystal composites: effects of surface chemistry. Ind Crops Prod 2023; 202: 117008.

Rogovina

Zhorina

Yakhina

, et al. Hydrolysis, biodegradation and ion sorption in binary biocomposites of chitosan with polyesters: polylactide and Poly(3-Hydroxybutyrate). Polymers 2023; 15: 645.

Sethy

Sahoo

. A comprehensive review on different leaf fiber loading on PLA polymer matrix composite. J Thermoplast Compos Mater 2025; 38: 1231–1256.

Velghe

Buffel

Vandeginste

, et al. Review on the degradation of poly (lactic acid) during melt processing. Polymers 2023; 15: 2047.

Zhao

, et al. Research progress of five biodegradable plastics reinforced with different plant fillers. J Thermoplast Compos Mater 2025: 08927057251361020.

10.

Behera

Pattnaik

Mishra

, et al. Fabrication and characterization of industrial biocomposite from cellulosic fibers of Luffa cylindrica in a protein based natural matrix. Ind Crops Prod 2024; 212: 118328.

11.

Behera

Mohanty

Pradhan

, et al. Assessment of soil and fungal degradability of thermoplastic starch reinforced natural fiber composite. J Polym Environ 2021; 29: 1031–1039.

12.

Behera

Manna

Das

. Effect of soy waste/cellulose on mechanical, water sorption, and biodegradation properties of thermoplastic starch composites. Starch Starke 2022; 74: 2100123.

13.

Sun

Zheng

Wang

, et al. PLA composites reinforced with rice residues or glass fiber—a review of mechanical properties, thermal properties, and biodegradation properties. J Polym Res 2022; 29: 422.

14.

Gorrasi

Pantani

. In: Di Lorenzo

Androsch

(eds). Hydrolysis and Biodegradation of Poly(lactic acid). Cham: Springer International Publishing, 2017, pp. 119–151.

15.

Shi

Wang

Sun

, et al. Morphology and properties of polyolefin elastomer/polyamide 6/Poly (lactic acid) in situ special-shaped microfibrillar composites: influence of viscosity ratio. Polymers 2022; 14: 4556.

16.

Trivedi

Gupta

Singh

. PLA based biocomposites for sustainable products: a review. Adv Ind Eng Polym Res 2023; 6: 382–395.

17.

Jesus

LCC

Oliveira

Leão

, et al. Tensile behavior analysis combined with digital image correlation and mechanical and thermal properties of microfibrillated cellulose fiber/polylactic acid composites. Polym Test 2022; 113: 107665.

18.

ASTM D570 . Standard test method for water absorption of plastics. ASTM Stand 2014; 98: 25–28.

19.

American Society for Testing and Materials - ASTM . Standard practice for evaluating microbial susceptibility of nonmetallic materials by laboratory soil burial. ASTM Stand 2019; i: 2–4.

20.

ASTM . Flexural properties of unreinforced and reinforced plastics and electrical insulating materials. ASTM Stand 2017; i: 12.

21.

Prashantha

Vasanth Kumar Pai

Sherigara

, et al. Interpenetrating polymer networks based on polyol modified Castor oil polyurethane and poly (2-hydroxyethylmethacrylate): Synthesis, chemical, mechanical and thermal properties. Bull Mater Sci 2001; 24: 535–538.

22.

Mukaila

Adeniyi

Bello

, et al. Optimizing film mechanical and water contact angle properties via PLA/starch/lecithin concentrations. Clean Circ Bioeconomy 2024; 8: 100095.

23.

Tümer

Erbil

Akdoǧan

. Wetting of superhydrophobic polylactic acid micropillared patterns. Langmuir 2022; 38: 10052–10064.

24.

Gorrasi

Pantani

. Effect of PLA grades and morphologies on hydrolytic degradation at composting temperature: assessment of structural modification and kinetic parameters. Polym Degrad Stabil 2013; 98: 1006–1014.

25.

Jiang

, et al. Effect of short jute fibers on the hydrolytic degradation behavior of poly(lactic acid). Polym Degrad Stabil 2020; 178: 109214.

26.

Azevedo J

Carvalho L

Canedo

, et al. Biodegradation evaluation of composites with natural fiber by weight loss and CO2 production. Rev Virtual Química 2016; 8: 1115–1129.

27.

Hidayat

Tachibana

. Characterization of polylactic acid (PLA)/Kenaf composite degradation by immobilized mycelia of Pleurotus ostreatus. Int Biodeterior Biodegrad 2012; 71: 50–54.

28.

Costa

Albuquerque

MCC

Brum

, et al. Microbial and enzymatic degradation of polymers: a review. Quim Nova 2014; 38: 259–267.

29.

Dissanayake

Withana

Sang

, et al. Effects of biodegradable poly (butylene adipate‐co‐terephthalate) and poly (lactic acid) plastic degradation on soil ecosystems. Soil Use Manag 2024; 40: e13055.

30.

Wan Ishak

Rosli

Ahmad

. Influence of amorphous cellulose on mechanical, thermal, and hydrolytic degradation of poly (lactic acid) biocomposites. Sci Rep 2020; 10: 11342.

31.

Luo

Netravali

. A study of physical and mechanical properties of poly (hydroxybutyrate-co-hydroxyvalerate) during composting. Polym Degrad Stabil 2003; 80: 59–66.

32.

Hermida

ÉB

Yashchuk

Miyazaki

. Changes in the mechanical properties of compression moulded samples of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) degraded by Streptomyces omiyaensis SSM 5670. Polym Degrad Stabil 2009; 94: 267–271.

33.

Karaduman

Onal

. Water absorption behavior of carpet waste jute-reinforced polymer composites. J Compos Mater 2011; 45: 1559–1571.

34.

Melillo

JMA

Pereira

Mottin

, et al. Modification of poly (lactic acid) filament with expandable graphite for additive manufacturing using fused filament fabrication (FFF): effect on thermal and mechanical properties. Polímeros 2021; 31: e2021024.

35.

Krawczyk-Walach

Gzyra-Jagieła

Milczarek

, et al. Characterization of potential pollutants from poly (lactic acid) after the degradation process in soil under simulated environmental conditions. AppliedChem 2021; 1: 156–172.

36.

Zimmermann

MVG

Brambilla

Brandalise

, et al. Observations of the effects of different chemical blowing agents on the degradation of poly (lactic acid) foams in simulated soil. Mat Res 2013; 16: 1266–1273.

37.

Pereira

Morales

. Estudo do comportamento térmico e mecânico do PLA modificado com aditivo nucleante e modificador de impacto. Polimeros 2014; 24: 198–202.

38.

Solarski

Ferreira

Devaux

. Characterization of the thermal properties of PLA fibers by modulated differential scanning calorimetry. Polymer (Guildf) 2005; 46: 11187–11192.

39.

Lopera-Valle

Caputo

Leão

, et al. Influence of epoxidized canola oil (eCO) and cellulose nanocrystals (CNCs) on the mechanical and thermal properties of polyhydroxybutyrate (PHB)—Poly (lactic acid) (PLA) blends. Polymers 2019; 11: 933.

40.

Zabler

Paris

Burgert

, et al. Moisture changes in the plant cell wall force cellulose crystallites to deform. J Struct Biol 2010; 171: 133–141.

41.

Marasović

Puchalski

Kopitar

. Effects of field conditions on the degradation of cellulose-based and PLA nonwoven mulches. Sci Rep 2025; 15: 11986.

42.

Benhami

VML

Longatti

SMO

Moreira

FMS

, et al. Biodegradation of poly (lactic acid) waste from 3D printing. Polímeros 2024; 34: e20240013–e20240019.

43.

Udayakumar

Zsoldos

Kollár

. Study on effect of degradation of poly(lactic acid) on its properties. In: Publ. MultiScience - XXXI. MicroCAD Int. Sci. Conf, Hungary, 20–21 April 2017, University of Miskolc.

44.

Fukushima

Abbate

Tabuani

, et al. Biodegradation of poly (lactic acid) and its nanocomposites. Polym Degrad Stabil 2009; 94: 1646–1655.

45.

Qin

Qiu

Liu

, et al. Mechanical and thermal properties of poly (lactic acid) composites with rice straw fiber modified by poly (butyl acrylate). Chem Eng J 2011; 166: 772–778.

Microfibrillated cellulose for enhanced performance of PLA composites after soil degradation and water absorption

Abstract

Keywords

Introduction

Experimental section

Preparation of materials

Water Absorption tests

Soil degradation tests

Flexural tests

Scanning electron microscopy (SEM) characterization

Degree of crystallinity determination by DSC

DMA tests

Results and discussion

Effects of water absorption on the properties of polymers and composites

Effects of soil degradation on the mechanical and morphological properties of PLA and MCF/PLA

Determination of the crystallinity of the MCF/PLA composites by DSC after degradation in soil and water absorption

Dynamic mechanical analysis (DMA) properties of the polymers and composites

Conclusions

Footnotes

Declaration of conflicting interests

Funding

ORCID iD

References