The effect of gum arabic addition on lignosulfonate/polyvinyl alcohol composite films

Erişir, E. (2026). "The effect of gum arabic addition on lignosulfonate/polyvinyl alcohol composite films," BioResources 21(2), 3688–3717.

Abstract

The effectiveness of Gum Arabic (GA) as a compatibilizer was evaluated in sodium lignosulfonate (LS)/polyvinyl alcohol (PVOH) composite film systems. This study aimed to improve the morphological integrity and mechanical stability of films, while achieving sustainability objectives. The goal was to obtain mechanically reinforced and morphologically homogeneous biodegradable films through GA-assisted phase stabilization. The structural, morphological, and mechanical properties, as well as the water interaction performance, of films were investigated. Fourier transform infrared analysis showed that the band intensity attributed to hydrogen bonding increased with the addition of GA, indicating enhanced molecular interactions. Scanning electron microscopy revealed that GA increased morphological defects such as microphase separation and aggregation, especially at low concentrations. While 25% GA helped fill the pores, it did not completely eliminate structural defects. Mechanical tests showed a decrease in tensile strength of up to 63% associated with such defects. Water sorption and dissolution tests showed that mass loss in aqueous media reached 75% due to the solubility of LS and GA. However, higher GA content moderately reduced this loss by minimizing defect sites. GA failed to act as a compatibilizer under tested formulation and processing parameters but contributed to the film’s surface homogeneity as a physical filler.

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The Effect of Gum Arabic Addition on Lignosulfonate/ Polyvinyl Alcohol Composite Films

Emir Erişir

DOI: 10.15376/biores.21.2.3688-3717

Keywords: Gum arabic; Sodium lignosulfonate; Polyvinyl alcohol; Biodegradable polymers; Film production

Contact information: Department of Paper Technology, Sakarya University of Applied Sciences, Esentepe Kampüsü T4 Binası – SAYEM Sakarya, Turkiye; Email: emirerisir@subu.edu.tr

INTRODUCTION

With increasing awareness of sustainability, petroleum-based materials are losing their market share. Especially, because of their low biodegradability, this shift is being pushed along by various laws. For example, the European Union recently launched a Circular Economy Action Plan. According to the plan, new regulations regarding single-use plastics will be introduced by 2030 and 2040, limiting the use of these types of plastics and to use a certain percentage of recycled materials in their production. As a result, the reduction of certain plastics is expected to increase interest in natural polymers such as cellulose, starch, and lignin.

It is estimated that plants produce between 150 to 180 billion tons of biomass each year, with around 20% of that being lignin (Kropat et al. 2021). Approximately 20 billion tons of lignin are synthesized annually, and the total mass of lignin in the biosphere is around 300 billion tons (Gonçalves et al. 2021). This enormous amount makes it the second most abundant biopolymer in nature after cellulose (Su and Fang 2014; Fuentalba et al. 2025).

The bulk of lignin generated in industries is produced by the separation of polysaccharides from the biomass during the processes employed in the pulping industries. During the pulping process, annually 50 to 70 billion kg of lignin and its derivatives are produced (Hu et al. 2018). Current processes result in approximately 95% of produced lignin being burned for energy generation and chemical recovery (Grossman and Vermerris 2019), a method reported to yield about $80 USD per ton (Luo and Abu-Omar 2017). It is clear that this valuable by-product has not received sufficient attention. However, a forecast on the development of the global lignin market predicts that its market size could reach US $1.12 billion by 2027 (Kropat et al. 2021).

Lignosulfonate (LS) is the most commercially available type of lignin. It is used in diverse areas, from the construction industry to agricultural applications and differs from kraft, soda, and organosolv lignin in its molecular structure and properties (Kropat et al. 2021). Changing the molecular structure and properties increases its potential value and applicability (Lin et al. 2014). However, LS, like other types of natural lignin, has certain limitations. To increase its versatility, modification techniques are applied, or it is combined with other substances that can complement its deficiencies.

Polyvinyl alcohol (PVOH), a semi-synthetic material, is an alternative for matrix production due to its low toxicity and biodegradability. Its high film-forming ability, satisfactory mechanical properties, transparency, and biocompatibility contribute to its importance in various applications (Korbag et al. 2018). Due to the strong hydrogen bonding network facilitated by its hydroxyl groups (Li et al. 2022), it is utilized in a variety of applications, ranging from packaging materials to wound dressings and even in the production of graphene. Nonetheless, its affinity for water complicates its application in environments where moisture is prevalent (Zhang et al. 2020). Consequently, it finds application in combinations with different natural polymers.

Lignin is preferred for PVOH matrices in composite production due to its biocompatibility, biodegradability, thermal stability, and UV-shielding properties (Ramadhan et al. 2024). The studies using various types of lignin as additives for the production of PVOH films provide examples. These studies have shown improvements in both the mechanical and barrier properties of lignin (Phansamarng et al. 2024; Ramadhan et al. 2024). There are also studies that establish a relationship between lignin content and the thermal properties of PVOH composites (Xu et al. 2023). The observed increase in the performance properties of LS/PVOH matrices is generally attributed to the strong intramolecular and intermolecular hydrogen bonds between the polymers and the abundance of OH groups, which provide effective interfacial adhesion (Nair et al. 2014). However, 5% is considered the critical concentration limit for lignin concentration in the lignin/PVOH matrix. Using higher concentration, aggregate formation occurs being negative impact on mechanical performance properties (Ye et al. 2016, Zhang et al. 2020). To increase the lignin concentration in LS/PVOH matrices, it is necessary to improve the compatibility between polymers and prevent the formation of polymer aggregates, and the additives are used for this purpose.

Gum Arabic (GA), with a complex chemical structure, is an important natural-based polysaccharide. Its main chain consists of β-D-galactopyranosyl units interconnected by 1,3-linkages, and side branches containing functional groups such as L-arabinose, L-rhamnose, and D-glucuronic acid. Its solubility in water has led to its utilization in various fields including food, medicine, hydrogels, biomaterials, cosmetics, textiles, paper, ink, printing, paint, and adhesives (Patel and Goyal 2015; Rostamabadi et al. 2024).

GA is also used for film production and as an emulsifying agent. Both of these properties help distribute polymer phases evenly in mixed biopolymer systems, even when GA is used in small amounts (Rostamabadi et al. 2024). However, the films made only from GA tend to be brittle, which limits their use and processing without other polymers such as polylactic acid to create films that are mechanically stronger and more stable (Onyari et al. 2008). Beyond its structural function, numerous investigations have revealed GA’s ability to interact with lignin via substantial hydrogen bonding, and under specific circumstances, it may even establish partial covalent bonds (Gorish et al. 2025). Furthermore, GA has been employed to facilitate a more uniform polymer distribution within nanocellulose-reinforced starch film matrices, leading to reduced vapor permeability and increased tensile strength (Vigneshwaran et al. 2011).

Numerous comprehensive studies have been conducted on the LS/PVOH, GA/PVOH and GA/LS binary systems. However, it has not yet been determined how GA will function within the LS/PVOH system. In this study, it was hypothesized that GA may create the homogeneous dispersion of polymers in the LS/PVOH system and thereby yield uniform films with improved mechanical strength. The primary objective of this study was to reduce or eliminate the effects of phase separation problems arising from the use of high concentrations of LS in LS/PVOH films. To determine these effects, several analytical test methods were applied to the parent polymers and the resulting films, and the results were evaluated comparatively.

EXPERIMENTAL

Materials

Sodium lignosulfonate (LS, Sigma Aldrich, CAS No: 8061-51-6, M_w: ~52000 g/mol, M_n: ~7000), polyvinyl alcohol (PVOH, Merck, ≥ 98% hydrolyzed, M_w: 60000 g/mol), Gum Arabic (GA, kordofan Gum Arabic, CAS No: 9000-01-5, food grade, purity ≥ 98%), glycerol (Balmumcu Kimya, USP grade, M_w: 92.09 g/mol), and urea (Merck, M_w: 60.06 g/mol, purity ≥ 99%) were procured and utilized without further purification. Deionized (DI) water was used in all production and characterization steps.

Production of LS-PVOH-GA Films

In this study, a final weight for each film was set at 2.00 g. The composite film matrix ultimately consists of a mixture of 1.00 g of GA (a%) and PVOH (100% – a%) with 1.00 g of LS. The proportions of PVOH, a semi-synthetic polymer, and GA, a natural polysaccharide, were methodically adjusted (0, 1, 5, 10, or 25%). During the preparation of the film solutions, calculations were made for the production of two films.

The evaporation time of the solvent was considered an essential factor in the formulation of the film solutions. To investigate the potential effect of this stage on film morphology and thus the final properties, two different pre-evaporation times, 60 and 90 min, were applied. Through extending the evaporation time, it was expected that the total solid concentration in the solution would increase, which would, in turn, affect the interactions between the polymers and phase separation. This approach made it possible to better understand the dynamics of the film formation process and to determine the role of this parameter in the formation of structural defects. Film production was carried out using the processes described below:

The preparation of the PVOH solution: To achieve a final polymer matrix weight of 2.00 g, PVOH at the concentration defined above was dissolved in 20 mL of DI water in an oil bath operating at 85 to 90 °C under continuous magnetic stirring at a constant speed of 500 rpm.
The preparation of LS-GA solution: The specified amount of GA, determined according to its desired percentage (0, 1, 5, 10, 25% based on PVOH amount) in the total polymer matrix of 2.00 g, was combined with around 2.00 g of LS, 0.20 g of urea, and 4.00 mL of a 25 wt% glycerol solution. This mixture was then dissolved in 20 mL of deionized water at room temperature at a constant speed of 500 rpm and heated after completed dissolution.
The preparation of the final film formation solution: After preparing the LS-GA and PVOH solutions separately, these solutions were combined in the same reaction vessel. The reaction vessel lid was closed and stirred for 60 min using a magnetic stirrer at 500 rpm to obtain a homogeneous final solution. The reaction vessel was kept in an oil bath at 85 to 90 °C.
Pre-evaporation process: To increase the concentration of the film solution, the lid was opened to allow some solvent (DI water) to evaporate. Pre-evaporation was performed for 60 or 90 min.
Film casting and storage: The film-forming solution was carefully poured into two silicone molds with an inner diameter of 100 mm and left to dry in a controlled environment at 28 °C for 12 to 16 h in a climate-controlled environment.

At the end of the drying process, the films were carefully removed from the molds and securely placed in zippered plastic bags for storage.

Methods

The lignin and ash content of LS were determined using TAPPI T222 om-11 (2011) and TAPPI T211 om-02 (2002) standards, respectively. The other methods and equipment used in the study are described below.

Analytical methods

The instrumental analyses included Nuclear Magnetic Resonance (¹³C-NMR), Fourier Transform Infrared Spectroscopy (FTIR), tensile testing, and Scanning Electron Microscopy (SEM). ¹³C-NMR analysis was conducted to identify the structure of LS using a Bruker Ascend 500 MHz spectrometer, with DMSO-d₆ as solvent at a working concentration of 20 g/L. The FTIR spectra were recorded with a Bruker Alpha I instrument for the structural characterization of films and neat polymers. Measurements for films were taken at multiple points on both surfaces to confirm the layered structure. The spectra were obtained in the 4000 to 400 cm⁻¹ range with a resolution of 4 cm⁻¹. Tensile testing was performed with an Instron Model 3345 to determine film strength. Film samples (90 × 10 mm²) with thicknesses of 1.226 to 1.567 mm (Table S1) were tested at a speed of 20 mm/min and a maximum load of 5 kN. Each test was performed in triplicate. The SEM imaging (Thermo Scientific Asia) was employed to examine film morphology. Images were taken from both the open (exposed) and closed (mold-contact) surfaces. Samples were coated with gold–palladium and imaged at magnifications of 100×, 1000×, 2500×, and 5000×, under 15 kV accelerating voltage and vacuum.

Water absorption and dissolution

The samples (10 x 10 mm²) were subjected to the immersion method to determine water absorption and dissolution in the films. Prior to the tests, the samples were dehydrated in an oven at 60 °C for 24 h until a stable weight was attained. This procedure guarantees full removal of all moisture from the samples. The dry samples were immersed in water at the room temperature. After determining the initial dry weights of the samples, measurements were repeated at 1, 2, 3, 6, 24, 48, and 72 h. The percentage (%) of water absorption of the samples was calculated using the weight measurements. The percentage of water absorption (%WA) was determined using Eq. 1,

WA% = (W₂–W₁) × 100 / W₁ (1)

where W₁ represents the oven-dried weight (g) of the sample, and W₂ represents the weight (g) of the sample subsequent to immersion in water.

At the end of the 72-h water immersion period, the samples were removed and dried to determine their final mass. To determine the amount of dissolved material, the containers used in the water immersion experiments were dried at 40 °C until completely dry, and residual material was calculated.

RESULTS AND DISCUSSION

Structural Characterization of Na-Lignosulfonate

Wet analyses showed the LS was composed of 94.6% lignin and 7.26% ash. ¹³C-NMR spectrum (Fig. S1 in Appendix) showed no distinct signals in the 90 to 102 ppm range (Yang et al. 2017), indicating high purity with minimal polysaccharide content. Both results allow focusing on lignin-based interactions. A resonance of dimethyl sulfoxide-d6 (DMSO-d₆), used as a solvent, was detected in the 39.5 ppm band, confirming that the sample was effectively dissolved. The signals observed in the range of 112.2 to 159.0 ppm clearly reveal the aromatic structure of lignin (Xia et al. 2001; Korbag and Saleh 2016; Phansamarng et al. 2024). The major signal at 158.5 ppm corresponds to the C-4 atom in the p-coumaric acid ester framework (Yang et al. 2017), while C-5 aromatic C-H bonds were observed at 115.6 ppm (Nasef et al. 2024). However, signals observed at 112.2 and 119.1 ppm, respectively, correspond to the C-2 and C-6 aromatic C-H bonds (Nasef et al. 2024) in the same region, exhibit a lower intensity compared to the previous signals. The absence of signals for aliphatic oxygen-containing groups (C-O) or methoxy (-OCH₃) groups indicates that these functional groups were below the detectable levels in the stock lignin or may have previously modified.

Fourier Transform Infrared Spectroscopy (FTIR) Analysis

The FTIR spectra from both film surfaces and neat polymers were analyzed to assess structural characteristics. In Fig. 1, the spectra for explaining these interactions are displayed separately.

Characteristic properties of neat polymers

The bands showing the characteristic vibrations determined for each polymer are presented in Fig. S2 in the Appendix. The PVOH showed a strong and broad band between 3000 to 3700 cm⁻¹, which is linked to O–H stretching vibrations resulting from both intramolecular and intermolecular hydrogen bonds (Bhargav et al. 2007). A distinct peak at 1142 cm⁻¹ is attributed to crystalline PVOH (Su and Fang 2014). Another notable signal appears in the 1700 to 1750 cm⁻¹ range, indicating C=O stretching vibration. Furthermore, there were two distinct signals at 839 and 912 cm⁻¹ corresponding to C=C bonds (Phansamarng et al. 2024).

Fig. 1. FTIR spectra of films without GA are illustrated in A (60 min) and B (90 min), while spectra of GA-containing films are given in C (60 min) and D (90 min). In A and B, spectra were recorded from both surfaces of the films, with the bottom surface represented in black and the top surface in red. For GA-containing films (C and D), mean spectra were generated by averaging measurements from the top and bottom surfaces.

GA exhibited typical glycosidic C–O–C stretching at 1021 cm⁻¹, carbonyl-related bands at 1415 to 1600 cm⁻¹, and a weak O–H/C–H stretching region between 3600 and 2800 cm⁻¹ (Vigneshwaran et al. 2011; Mudgil et al. 2012; Pereira et al. 2021; Thombare et al. 2023; Gorish et al. 2025).

The LS showed sulfonic (-SO₃⁻) signals at 618 and 1048 cm⁻¹ (Abdelrahman et al. 2024) and aromatic bands at 1105, 1433, and 1590 cm⁻¹ (Klapiszewski et al. 2016; Ou and Zhao 2017; Ysulat et al. 2023). The hypothesis that this value is largely due to the presence of Na⁺ ions (Tables S1 and 2 in Appendix) is supported by the vibrations observed at 488 cm⁻¹, which are attributed to these ions in the literature (Abdelghany et al. 2014).

Interactions and morphological consequences of polymers

It was confirmed by the spectra that strong physical interactions (H-bonds, van der Waals, electrostatic, hydrophobic) between PVOH and LS (Ye et al. 2016; Kazzaz and Fatehi 2020; Zhang et al. 2020; Nouh et al. 2023) play a crucial role for films, not chemical bonds. These interactions may result in alterations in the spectra. The broad -OH band suggested an intensified hydrogen-bonding network (Ye et al. 2016), consistent with physical cross-linking between LS and PVOH phases (Zhang et al. 2020).

The casting process revealed noticeable phase separation, pointing to limited integration of the components. In the films without GA, the C=O signal at 1741 cm⁻¹ for PVOH was distinct on the top surface but nearly absent on the bottom, a result attributed to lignin aggregation and poor miscibility (Zhang et al. 2020; Zhou et al. 2022), as further confirmed by SEM. On the top surfaces, a clear band broadening was observed in the spectral region associated with LS, pointing a higher concentration of lignin.

Extending the pre-evaporation time led to a clearer phase separation. This observation highlights that the degree of separation is shaped by the specific process variables. The greater signal intensity at 610 to 620 cm⁻¹ on top surfaces and the appearance of a PVOH-specific C-C stretch at 1230 to 1240 cm⁻¹ (Bhargav et al. 2007) on bottom surfaces validated an LS-rich upper structure and a PVOH-rich lower structure.

The addition of GA created differences in the density of C-O-C and S-O bands, indicating that LS became increasingly dominant in the film structure (Fig. 1). The addition of GA intensified the -OH band, indicating a reinforced hydrogen bond system (Gorish et al. 2025). The signal for GA-specific glycosidic bonds became stronger as the GA concentration was increased (from 0 to 25%), while the signal showing the semi-crystalline structure of PVOH was weakened by a reduction of its concentration.

In addition, a consistent downward shift was observed in the broad O–H stretching band (from about 3350–3370 cm⁻¹ to 3310–3330 cm⁻¹) with increasing GA concentration. Similar redshift phenomena, a sign of stronger hydrogen bonding, have been observed in PVOH–lignin composites (Ye et al. 2016; Korbag and Saleh 2016) and PVOH–polysaccharide systems (El-Nemr et al. 2020; Gui et al. 2024). Furthermore, the C=O stretching band, located between 1700 and 1740 cm⁻¹, exhibited a slight upshift, approximately 5 to 10 cm⁻¹, which is attributed to the reorganization of carbonyl groups involved in hydrogen bonding interactions. These spectral alterations provide evidence that the incorporation of GA enhanced the hydrogen-bonding network within the LS/PVOH matrix, thereby promoting molecular association and mitigating phase heterogeneity.

Mechanical Properties of Composite Films

The mechanical properties of the films were evaluated by tensile strength (Fig. 2). A notable reduction in the mechanical properties of the films was found with higher GA concentration. Increasing polysaccharide content while diminishing PVOH concentration resulted in a reduction of tensile strength by as much as 63%.

Fig. 2. The effect of GA concentration on tensile strength in LS/PVOH films (A for 60 min and B for 90 min)

Research demonstrates that elevating the LS concentration to an optimal level (Ye et al. 2016; Zhang et al. 2020; Li et al. 2022; Baite et al. 2023; Xu et al. 2023; Phansamarng et al. 2024; Ramadhan et al. 2024) enhances tensile strength via mechanisms including hydrogen bond formation, the rigidity of lignin, and superior interfacial adhesion.

However, the use of high LS concentrations has been shown to lead to lower tensile strength values. It is thought that as LS concentration increases, the dispersion bonding percentage increases (Ramadhan et al. 2024), interfacial adhesion decreases (Phansamarng et al. 2024), and lignin particles aggregate within the PVOH matrix, leading to microphase separation (Yang et al. 2024). As a result of this assumption, irregular LS-PVOH bonds are thought to occur, causing lignin to act solely as a filler. The results of Xu et al. (2013) are similar, and they found similar reductions in mechanical properties.

Scanning Electron Microscope

As shown in the SEM images (Figs. 3 through 7), changes in GA content (0 to 25%) together with differences in pre-evaporation time (60 or 90 min) altered the morphology of the films. Variations were also evident in porosity and surface roughness. The control sample (0% GA) showed a heterogeneous structure with phase separation and polymer aggregates due to poor LS/PVOH compatibility (Kubo and Kadla 2003; Wang et al. 2020), corroborated by FTIR findings.

Fig. 3. Electron microscope images of the films without gum addition are shown after 60 min of pre-evaporation. The bottom surface is shown in A at 100× and in B at 1000× magnifications. The top surface is displayed in C at 100× and in D at 1000× magnifications.

Even low GA concentrations (1% and 5%) increased morphological defects (Figs. 4 and 5) leading to greater porosity. The structural changes became more apparent by the concentration of GA to 10%. This was shown by the appearance of distinct micro-pores and polymer aggregates, which were visible on a millimeter scale (Fig. 6). These morphological defects are also the main reason for the decrease in the mechanical strength of the films.

Fig. 4. Electron microscope images of films with 1% gum addition after 60 min of pre-evaporation are presented. The bottom surface is shown in A at 100× and in B at 1000× magnifications. The top surface is displayed in C at 2500× and in D at 5000× magnifications.

Fig. 5. Electron microscope images of films with 5% gum addition after 60 min of pre-evaporation are presented. The bottom surface is shown in A at 100× and in B at 2500× magnifications. The top surface is displayed in C at 70× and in D at 1000× magnifications.

Fig. 6. Electron microscope images of films with 10% gum addition after 60 min of pre-evaporation are presented. The bottom surface is shown in A at 70× and in B at 1000× magnifications. The top surface is displayed in C at 70× and in D at 2500× magnifications.

Fig. 7. Electron microscope images of films with 25% gum addition after 60 min of pre-evaporation are presented. The bottom surface is shown in A at 70× and in B at 1000× magnifications. The top surface is displayed in C at 70× and in D at 1000× magnifications.

Conversely, elevating the polysaccharide concentration to 25% yielded a favorable outcome, with GA functioning as a filler, addressing morphological defects and pores (Fig. 7A, C, and D). Nonetheless, the general heterogeneous structure and the creation of aggregates continued. This conclusion aligns with existing work indicating that some LS functions merely as a filler rather than forming a binding with PVOH (Xu et al. 2013). Extending the pre-evaporation time to 90 min results in the polymer clusters (Fig. 8B), an increase in both the quantity and dimensions of pores (Fig. 8C), and the emergence of white patches (Fig. 8D) on the film surfaces as the gum concentration rises relative to films with 0% GA additive.

Fig. 8. SEM images of films containing 1% (A, B) and 10% (C, D) GA after 90 min pre-evaporation, shown at 70× and 1000× magnifications

Elemental mapping results (Tables S1 and S2) showed that Na⁺ and –SO₃⁻, representing the LS phase, were mainly concentrated at the film surface in 60-min pre-evaporated samples, while shifting toward the bottom in 90-min samples. This inversion indicates phase separation between LS and PVOH domains. Consistent with FTIR results, the higher oxygen content in LS-rich regions indicates that GA primarily interacts with LS. It was reported that similar compositional redistribution occurred in lignin–PVOH films under extended drying or humidity cycling conditions (Gui et al. 2024; Wang et al. 2024; Li et al. 2022).

The findings from Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses indicate that the phase separation observed in LS/PVOH/GA films primarily originated from the poor miscibility of lignosulfonate (LS) within the polyvinyl alcohol (PVOH)-rich matrix. This theory is supported by the differences between the upper and lower film surfaces, as well as the absence of the C=O stretching band on the lower side. Similarly separated morphologies have been reported in other PVOH–lignin systems; in these cases, the hydrophilic PVOH tends to migrate toward the aqueous phase during solvent evaporation, whereas the less soluble aromatic lignosulfonate accumulates near the air interface (Xu et al. 2023; Tian et al. 2024; Erişir 2025). These studies indicate that the hydrophilic groups of PVOH are moved by the hydrophobic surface of lignin particles, thereby facilitating phase separation.

The addition of GA, an amphiphilic polysaccharide, led to a partial reduction in interfacial tension; however, complete separation reduction was not achieved, a result of its characteristic solubility limitations and competition for hydrogen-bonding sites. This phenomenon aligns with findings in PVOH–guar gum (Shaikh et al. 2022) and PVOH–tamarind gum (Rawooth et al. 2022) systems, where dual-phase microstructures were similarly observed at elevated gum concentrations. Consequently, the phase separation observed in this study indicates a thermodynamic incompatibility between LS and the PVOH/GA matrix, a condition that is exacerbated under prolonged pre-evaporation conditions.

Water Absorption and Dissolution

All samples reached water absorption equilibrium within the first hour (Fig. 9). The control group absorbed 76.1% water. Absorption increased to 85.4% with 1% GA but decreased to 58.2% with 5% GA, maintaining ~75% at 10% and higher concentrations. Over time, film mass decreased due to polymer dissolution (Raj and Bajpai 2020), with dissolution rate exceeding absorption.

Fig. 9. The effects of GA concentration on the water absorption of LS/PVOH films are shown. Graph A presents the results for films pre-evaporated for 60 min, while Graph B displays those obtained after 90 min.

A slight drop noted around the third hour (Fig. 9/b) was not due to a measurement error. Instead, it stemmed from a brief release of moisture and internal reorganization within the LS-, PVOH-, and GA-rich domains. Temporary changes in water distribution have also been observed in PVOH–lignin and other lignin-containing biopolymer systems when subjected to alternating humidity or hydrothermal conditions (Jain et al. 2017; Hu et al. 2023; Gui et al. 2024; Wang et al. 2024; Singh et al. 2024).

GA, LS and PVOH are polymers with high hydrophilicity (Banegas et al. 2013; Rahman et al. 2021; Li et al. 2022; Phansamarng et al. 2024), but after 72 h immersion (Fig. 10) the control group showed minimal mass loss. Despite the reduction in PVOH content within the sample, the overall weight of the films exhibited an increase with the higher GA concentration. This phenomenon can be attributed to the covering and filling effects of GA of film surfaces mentioned before.

The highest mass loss (66% to 74%) was observed in the 1% GA-added LS/PVOH matrix. This finding is consistent with the fact that films containing 1% GA had the highest water absorption values. A general decrease in water absorption performance was observed at GA concentrations higher than 1%. These results indicate that the effect of GA on film structure varies with concentration, and that there is an optimum equilibrium point.

Fig. 10. The effect of GA concentration and pre-evaporation time on the residual material (%) of LS/PVOH films after 72 h of immersion in water

CONCLUSIONS

In contrast to the initial hypothesis, gum Arabic (GA) did not effectively interact with the lignosulfonate/poly(vinyl alcohol) (LS/PVOH) system under tested conditions. Lower GA concentrations (1% and 5%) led to microphase separation and aggregation, caused surface cracks and pores to form.
In the evaluated conditions, GA worked more as a filler than as a compensatory agent, especially at higher concentrations (25%).
The 1:1 LS/PVOH ratio used in this study was not optimal for maintaining the material’s morphological stability. This composition caused phase heterogeneity and a noticeable decrease in mechanical strength. Evaluating GA performance at different LS/PVOH ratios would provide clearer insights into composition-dependent behavior.
GA concentration increment resulted in a decline in film strength, with tensile strength decreasing by more than 60% at higher GA levels. This reduction appears to be related to the increased aggregation tendency as the PVOH fraction decreases.
The concentration of GA also influenced by water absorption and dissolution in it. At lower concentrations, GA had little effect on how much water was taken up. However, higher concentrations of GA, specifically 25%, reduced mass loss. This was because GA decreased surface defects and limited water penetration. These findings were also supported by the differences in shape seen in the scanning electron microscope (SEM) images.

ACKNOWLEDGMENTS

The author gratefully acknowledges Mert Kaban (Sakarya University of Applied Sciences) for the SEM measurements and Rumeysa Yildirim (Kocaeli University) for Tensile testing measurements.

Conflict of Interest

The author declares that there is no conflict of interest regarding the publication of this manuscript. No personal, financial, or professional relationships exist that could have influenced the research or conclusions presented in this work.

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Article submitted: September 5, 2025; Peer review completed: November 1, 2025; Revised version received: January 13, 2026; Accepted: February 20, 2026; Published: March 2, 2026.

DOI: 10.15376/biores.21.2.3688-3717