Exploring the performance and biodegradability of Edible Biopolymer blends incorporating Pistacia atlantica subsp. Mutica Gum and Plasticized Poly(lactic acid) | Scientific Reports

Scientific Reports volume 14, Article number: 25666 (2024) Cite this article

Metrics details

Blending biopolymer is a key objective in development of innovative materials and effectively enhances the characteristics of the components to achieve tailored properties. This study introduces five eco-friendly blends in different ratios, created by melt-blending polymers, incorporating Pistacia atlantica subsp. mutica gum into plasticized poly (lactic acid) with 16% acetyl tributyl citrate. To perform a comprative analysis of blends ratios, comprehensive techniques were applied, including differential scanning calorimetry, tensile testing, Fourier-transform infrared spectroscopy, scanning electron microscopy, and evaluations of water absorption behavior, chemical resistance, and biodegradability. The 70/30 (plasticized poly (lactic acid)/P. atlantica) blend was mechanically superior, exhibiting the greatest elongation at break and the lowest yield strength and Young’s modulus. FTIR analysis showed consistent spectral patterns across the 3000 to 650 cm− 1 range, with numerous absorption bands. DSC analysis identified the highest and lowest glass transition temperatures for the 90/10 and 70/30 blends, respectively. Scanning electron microscopy highlighted the development of more distinct island-sea structures as the proportion of P. atlantica gum increased. Water absorption tests differentiated the 90/10 blend as the most absorbent, while the 70/30 blend absorbed the least. Chemical resistance testing revealed all blends gained weight in HCl, but only the 90/10 blend lost weight in NaOH. All samples were confirmed to be highly biodegradable, surpassing 50% degradation after 6 months. Overall, the findings suggest that blending plasticized poly (lactic acid) and P. atlantica gum enhances the flexibility and performance of poly (lactic acid), warranting further attention.

Natural polymeric materials are becoming increasingly popular due to reduced use of petroleum resources and growing environmental concerns1. Biodegradable polymers like poly (lactic acid) (PLA) have emerged as a response to the environmental issues caused by non-renewable petroleum-based polymers. PLA, derived from natural and renewable resources, is a biodegradable polymer that has attracted significant attention2. As a commercial thermoplastic polymer, PLA degrades within weeks in soil environments3. However, its fragility, low toughness, and high cost limit its widespread use compared to synthetic plastics. To address these limitations, researches have proposed PLA blends or composites4.

Polymer blending techniques offer an efficient, convenient, and cost-effective approach for developing novel materials with tailored properties, without the need to synthesize entirely new materials1. Polymer blends combine two or more macromolecular substances or polymers, which may be from the same chemical family or different ones, resulting in a material that exhibits a combination of characteristics from the individual polymers5,6. Incorporating plasticizers and other polymers can further enhance the properties of the blend7,8,9. Blending has become a significant modification technique theoretically, economically, and practically, for developing materials with new properties such as high thermal resistance, rigidity, and toughness4,5.

Polysaccharide gums are natural biopolymers that are abundantly present in nature and have extensive industrial applications. Pistacia atlantica subsp. mutica gum (PAG), or Saqqez gum, is an underexplored natural biopolymer and a non-toxic, renewable, and biodegradable oleo-gum resin sourced from Bene trees of the Anacardiaceae family in Iran’s Zagros region7. Blending PLA with PAG could be an effective strategy. Mallegni et al.10 noted that despite ongoing improvement in PLA-based products through additives, there is still a need for cost-effective approaches to enhance PLA properties.

It is important to note that in polymer blending, most polymer blends are inherently incompatible and require compatibilizers to improve adhesion between their components. The energy absorbed during fracture is often linked to the level of interfacial adhesion. For example, strong interfacial interactions enable efficient stress transfer between phases, which is particularly advantageous when the dispersed phase is elastomeric and can absorb more energy than the blend11. Numerous studies have shown that JONCRYL functions effectively and appropriately as a compatibilizer12,13,14.

Our earlier research focused on improving the characteristics of PLA by plasticizing a blend of PLA and PAG in a PLA/PAG ratio of 70/30 and determined that 16% acetyl tributyl citrate (ATBC) was suitable7. Following that, this study explored the appropriate proportion of plasticized PLA (PPLA) and PAG to develop an elastomeric substance suitable for use in the food industry. Therefore, the current study aims to characterize and compare the biodegradable sample blends formulated by incorporating PPLA and PAG in various proportions through polymer melt-blending technique using Fourier transform infrared spectroscopy (FTIR) for blend characterization, differential scanning calorimetry (DSC) to understand structural alterations, scanning electron microscopy (SEM) and tensile testing to analyze blend morphology and mechanical properties. Additionally, this study assessed water absorption behavior, chemical resistance, and biodegradability over six months in soil. Identifying the suitable blend proportion will contribute to introducing a promising elastomeric compound to the edible food industry.

The commercial PLA pellets were obtained from Behzist Danesh Narvan Co., Mashhad, Iran, and sourced as Ingeo™ biopolymer 4043D from Nature Works (Minneapolis, MN, USA). The PAG, containing ≈ 87% polysaccharide7, was obtained from Saqqez production, Van Co. in Kurdistan, Iran. ATBC was purchased from Sigma–Aldrich Co. (St. Louis, MI, USA), and JONCRYL® ADR-4368-C, a reactive compatibilizer, was provided by Behzist Danesh Narvan Co., Mashhad, Iran, and procured from BASF in Germany. All components used in this study were prepared from food-grade ingredients.

Before starting the sample preparation process, the raw materials, including PLA pellets and PAG, were dried in a vacuum oven (Heraeus Vacum therm VT6130P, Borken, Germany) at 80 °C and 45 °C, respectively, to remove moisture. PPLA was created by directly mixing 16% ATBC with PLA through a melt-blending process using an internal mixer (RheoSense, IPPI, Iran) at 160 °C and 60 rpm for 15 min. To produce PPLA/PAG blends, the prepared PPLA was crushed and manually pre-mixed with PAG, as the blending partner, at various ratios, along with JONCRYL (2 phr). Five blends with different mass ratios of PPLA/PAG (90/10, 80/20, 70/30, 60/40, and 50/50) were synthesized. These mixtures were further blended in the internal mixer at 150 °C and 60 rpm for 10 min. Samples designated for mechanical properties evaluation were melted between hot plates at 160 °C for 7 min without pressure to remove air bubbles. They were then pressed at 160 °C under 20 MPa for 5 min using a laboratory mini hot press (Toyosiki Press, Tokyo, Japan), followed by cooling to room temperature to form sheets measuring 100 × 100 × 0.3 mm3. These sheets were conditioned in a desiccator with a saturated solution of magnesium nitrate at 25 °C (53% RH) for a week before testing.

Tensile tests were conducted following ASTM D882-02 guidelines15. Each sample was prepared by punching three rectangular strips from preconditioned sheets, each measuring 50 mm × 13.1 mm × 0.3 mm. Uniaxial tensile strength testing was carried out at room temperature and 60% relative humidity. A SPICO twin-column universal testing machine (Model UTM-S500, Tehran, Iran) equipped with a 5-ton load cell was used to measure yield strength, elongation at break (EB), and Young’s modulus. The test proceeded at a crosshead speed of 5 mm/min until tensile failure. Results reported are the average of three repetitions for each sample, along with the standard error.

Thermal analysis of the PPLA/PAG blends was performed using a differential scanning calorimeter (DSC SL800, SPICO, Wuhan, China). This analysis included determining the glass transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tc). Samples weighing approximately 5 to 15 mg were placed in sample pans, sealed, and introduced into the heating cell of the DSC. They were then heated from 25 to 250 °C at a rate of 5 K/min under a nitrogen atmosphere with a flow rate of 10 mL/min16.

Infrared spectroscopy was conducted utilizing Attenuated Total Reflectance Infrared Spectroscopy (ATR). The FTIR-ATR spectra of the blends were captured using a Thermo Nicolet device (AVATAR 37, USA), equipped with an ATR Smart MIRacle™ adapter with a diamond crystal. The spectral range covered 500–4000 cm− 1, with a resolution of 4 cm− 1, and a total of 32 scans were performed. The collected spectra were analyzed using Omnic 8 software (Thermo Scientific, USA).

The morphology of the fracture surface was inspected using field emission scanning electron microscopy (FESEM) at an acceleration voltage of 10 kV. The examination was conducted on a gold-coated surface in a vacuum. The FESEM instrument used was a TESCAN model MIRA3 from the Czech Republic.

This assessment aimed to investigate the water absorption behavior of PPLA/PAG blends while immersed in distilled water. The process followed the ASTM D 570 − 98 standard for analyzing water absorption kinetics17. Before measuring the weight, the samples were dried in an oven at 100 °C for one day. Following this, the specimens were submerged in distilled water at 25 °C, and their weight was recorded periodically until saturation was reached, which usually occurs between 1 and 10 days. The weight of the samples before and after absorption was measured using a precise electronic scale with an accuracy of 10− 4 g. The percentage of water absorbed (WA) was then calculated using Eq. (1). W0 and Wt represent the weight (in grams) of the samples before and after exposure to water for a certain time (t)18,19.

The percentage of water absorption (%) was calculated at different time intervals and plotted against the square root of immersion time to determine the diffusion coefficient. Evaluation the diffusion coefficient involves using Eq. (2), which requires identifying the slope of the graph relating the percentage of water absorption (%) to the square root of immersion time.

The slope of the linear portion of the sorption graph (m), along with the initial thickness of the sample (t) measured in millimeters, is used to determine the equilibrium sorption coefficients, as illustrated in Eq. (3).

The percentage of water absorption during saturation and at a specific time point is denoted by W∞ and Wt, respectively. The permeability coefficient, a combined measurement of sorption and diffusion coefficients, is determined using Eq. (4) as proposed by Gupta & Singh19.

To evaluate the chemical resistance, the dried specimens were first weighed using an accurate electric balance and then immersed in 100 ml of 1 M NaOH and 1 M HCl as chemical agents for 10 days (240 h). After extracting the treated samples, they were filtered, dried, and weighed to determine the percentage reduction/increase. The percentage of chemical resistance (Pcr) was evaluated by calculating the weight loss using Eq. (5):

Here, Ti represents the original weight, while Waci symbolizes the weight after a certain period of time20.

The assessment of aerobic biodegradability for the formulated specimens was carried out in accordance with ASTM D5988-1821. The purpose was to evaluate the level and rate of aerobic biodegradation of the samples compared to a standard material in contact with soil under controlled laboratory conditions. This approach involved measuring the quantity of carbon dioxide produced from the biological deterioration of the samples by microorganisms within a time frame and temperature range of 20–28 °C. To ensure microbial diversity within the soil matrix, a blend of three soil types (agricultural, forest, and pasture soil) along with a small quantity of vegetable compost served as the matrix soil, following the protocol provided in the standard. Specifically, a single gram of bio-blend powder was used as the test sample, while 1 g of PAG powder served as a positive control. The evaluation was carried out on all samples, including the control sample, with three repetitions.

The sample data was subjected to one-way analysis of variance (ANOVA) and Tukey’s test for comparing mean values and identifying significant differences at a 95% confidence level (p < 0.05) using Minitab 16 software.

The tensile test results for sample blends, including EB, Young’s modulus, and Yield strength, are summarized in Table 1. The data reveals interesting trends: in the 90/10, 80/20, and 70/30 blends, as the PAG content increased, EB progressively increased, which can improve the mechanical characteristics of the blends22. Therefore, the 70/30 blend, due to its highest EB, exhibits superior performance. On the other hand, in the 60/40 and 50/50 blends, EB decreased. The reduction of EB may be attributed to incompatibility and poor interfacial adhesion between PLA and its partner in the blends. The presence of the blend partner appears to act as a nucleating agent, resulting in increased crystallinity, phase separation and reduced EB, as confirmed by previous researches on other PLA-based blends23,24,25.

Young’s modulus decreased with increasing PAG weight% in the 90/10, 80/20, and 70/30 blends. Conversely, in the 60/40 and 50/50 blends, Young’s modulus values increased, which generally occurs due to phase separation in PLA-based blends23. The lower Young’s modulus is associated with compounds requiring less force for elastic deformation, leading to superior elastic properties and better performance26. The 70/30 blend exhibited the lowest Young’s modulus value.

Yield strength is another crucial parameter for evaluating tensile properties. According to the results, yield strength values gradually decreased with increasing PAG content in the 90/10, 80/20, and 70/30 samples. The 70/30 blend had the lowest yield strength. In the 60/40 and 50/50 blends, yield strength increased. The increase in yield strength may be attributed to the incompatibility between polar PLA and non-polar components at the sharp boundaries between the two polymeric phases, which prevents the effective transfer of applied stress through the interface of the blended components27. In summary, for the samples without the possibility of phase separation) 90/10, 80/20, and 70/30 samples), the EB of PPLA improved with the incorporation of PAG, while the Young’s modulus decreased concurrently. This suggests that blending PAG with PPLA could be an effective strategy to enhance the toughness of PPLA, making it more suitable for elastomeric applications.

Thermal curves for PPLA/ PAG sample blends in the temperature range of 50 to 250 °C are showen in Fig. 1. The curves of all samples clearly indicate identical thermal events, particularly exo- and endothermic peaks. The reduction in endothermic peaks within the Tg range, as well as peaks corresponding to Tc and Tm, is significant in all curves.

DSC traces of PPLA/ PAG sample blends with the marked transition peak temperatures (Tg, Tc, and Tm).

The findings for Tg, Tc, and Tm are provided in Table 1. In the DSC curves of all sample blends, a single Tg can be observed, demonstrating the miscibility of the blends28,29, regardless of PAG content. However, Tg decreased with increasing PAG content in the 90/10, 80/20, and 70/30 samples. Zha et al. (2024) suggested that PLA blends exhibit partial compatibility, and the activity of PLA chains increases due to the effect of the blending partner on free volume30. The lowest Tg value was recorded for the 70/30 sample at 46.2 °C. While neat PLA typically exhibits a Tg at approximately 60 °C31, the addition of plasticizer and PAG in all samples led to a decrease in Tg. Furthermore, all samples exhibit exothermic crystallization points, with a slight reduction in Tc observed in the 90/10, 80/20, and 70/30 samples. Mutlur (2004) believed that when heated above the Tg, an exothermic crystallization peak may appear, indicating the formation of additional crystals due to increased mobility of the polymers at temperatures above Tg. This crystallization dip will only occur if the polymer has not fully crystallized to its maximum capacity during cooling. The temperature at the tip of this crystallization dip is referred to as the crystallization temperature, Tc32. This means that the percentage of Tc in the DSC curves indicates the semi-crystallinity of the polymer. Hence, all the sample blends are semi- crystalline. Deng et al. (2018) demonstrated that reduced Tc in PLA/Poly (Butylene Adipate-co-Terephthalate) blends facilitates the crystallization process of PLA and PBAT, suggesting PBAT as a nucleating agent for crystallization33. Yu et al. (2020) confirmed the nucleating effect of thermoplastic acetylated starch (TPAS) in PLA/TPAS blends during PLA crystallization. They also highlighted that the crystallization rate of neat PLA is relatively slow, whereas the inclusion of TPAS enables effective control of the crystallization rate31. The Tc of neat PLA was reported to be 120 °C7. In this study, all PLA sample blends showed a significant decrease in Tc, which can be attributed to the nucleating effect of PAG during the crystallization process. Interestingly, in the 60/40 and 50/50 blends, there was an increase in the Tc values. This may indicate a potential link between the change in crystallization peaks and the differing chain flexibility, which affects the ability to form a crystal structure34. Regarding JONCRYL, Baimark and Srihanam (2015)’s study on the thermal properties of stereo-complex PLA indicated that JONCRYL did not influence the Tg or the Tc of the blends35. Meng et al. (2012) demonstrated that JONCRYL, being a multi-functional reactive polymer, alters the molecular structure of PLA blends from linear to branched or cross-linked, depending on the JONCRYL content and processing temperature. This cross-linked structure similarly affects the melting temperature (Tm)36. The neat PLA and neat PAG exhibited Tm values of 160 °C and 102.9 °C, respectively7. The neat PLA and the 60/40 and 50/50 sample blends showed similar Tm values. Meng et al. (2012) also suggested that the reduction in Tm could be attributed to the finer crystal morphology caused by the hindrance effect of the cross-linking points in the PLA/JONCRYL blends36, observed in the 90/10, 80/20, and 70/30 sample blends.

All samples showed an endothermic peak ranging from 152 to 164 °C in their thermograms. Tm, an essential parameter in thermal analysis, decreased in the 90/10, 80/20 and 70/30 samples as the PAG content increased. The 70/30 sample had the lowest temperature at 146.6 °C. Conversely, a notable rise in Tm was observed in the 60/40 and 50/50 samples. Prior research suggested that the endothermic melting temperature is influenced by the molecular movement of polymer chains and structural degradation of molecules. This phenomenon could be attributed to moisture evaporation from the sample or softener breakdown, impacting material properties and applications37. Nishinari (1997) explained that an exothermic peak occurs when the system transitions from a disordered state to an ordered state (e.g., crystallization), while an endothermic peak is observed when the system shifts from an ordered state to a disordered state (e.g., melting of crystals)38. In summary, incorporating PAG into PPLA blends can effectively modify key thermal parameters, including Tg, Tc, and Tm.

FTIR has emerged as a powerful tool for simultaneous identifying organic components, assessing chemical bonding, and qualitatively evaluating interactions between compounds39,40. The spectroscopic results for neat PAG, PPLA, and sample blends with varying proportions of PPLA and neat PAG are depicted in Fig. 2.

Representative FTIR spectra for the neat PAG, PPLA, and PPLA/ PAG blends.

Neat PAG and PPLA exhibited a sharp absorption band in the 3667–3500 cm–1 region, indicative of hydrogen bonding. This confirms the presence of hydrate (H2O), hydroxyl (-OH), ammonium, or amino groups41. However, these absorption bands were absent in the sample blends, suggesting rearrangements such as alcohol formation (OH out-of-plane bend at 720–590 cm− 1), primary amine, or primary amine, CN stretch (1090–1020 cm− 1), which were demonstrated in all sample blends. PPLA and neat PAG illustrated 3500, and 3445 cm− 1, related to the presence of dimeric OH stretch, which are characteristics absorption bonds.

Both neat PAG and PPLA showed sharp absorption bands in the 2996 –2946 cm− 1 range, corresponding to methyl C-H asymmetric groups. In the sample blends, these bands were less intense, indicating disruption of hydrogen-saturated methyl bonding and the formation of unsaturated compounds in the double and triple regions of the sample blends’ spectra. Chieng et al. (2014) identified the presence of symmetric and asymmetric methyl groups at wavelengths of 2995 cm− 1 and 2946 cm− 1 in the PLA sample42. The current investigation on PLA-based blends revealed a reduction in these values to the range of 2920–2940 cm− 1 across various samples, potentially attributable to the existence of weaker linkages or elongated chains compared to neat PLA. Moreover, the plasticization of the samples with ATBC might explain the decrease in absorption levels in the peaks compared to neat PLA. Yu et al. (2008) previously demonstrated that ATBC could lower the wavenumber or absorption levels in specific peaks while enhancing interactions within the blend40.

PPLA, compared to the blends and neat PAG, had two characteristic absorption bands at 3657 and 2996 cm− 1, representing the nonbonded hydroxy group, (OH stretch)41. Neat PAG displayed characteristic absorption bands at 1246 and 1204 cm− 1, representing tertiary amine (C-N stretch) according to Coates, (2000)43.

Both compounds exhibited amides or carboxylates functional groups below 1700 cm–1, consistently observed in all sample blends. The FTIR spectrum of all sample blends depicted absorption bands at 1759, 1183, 1131 and 1087 cm− 1, which represent the backbone ester group of PPLA and PAG. Xu et al. (2009) revealed the backbone of ester group presence in PLA1.

PPLA, neat PAG, 60/40, and 50/50 blends indicated absorption bands at 2877, 2872, 2864, and 2864 cm− 1, related to the presence of methylamino, N-CH3, and C-H stretch41.These functional groups rearranged as the proportion of neat PAG increased in the blends.

Notably, PPLA and 60/40 blends showed one and two characteristics absorption bands, respectively, in the range of 1625–1680 cm− 1, representing the aryl-and alkenyl C = C stretch41.

The resulting graphs of the sample blends showed nearly similar spectra within the range of 3000 to 650 cm–1. Absorptions below 3000 cm–1 typically suggest the presence of aliphatic compounds43, confirming the dominance of PLA as an aliphatic compound44 in the blends. Moreover, significant absorptions around 2935 and 2860 cm–1, along with absorptions at 1470 and 720 cm–1, indicate the presence of a long linear aliphatic structure43. Based on the results, it can be anticipated that the 60/40 sample, followed by the 50/50 sample, meets these conditions. The absorption range between 2000 and 1500 cm–1 is related to double bonds and is present in all samples in this study. Conversely, absorption in the higher range of 1750 to 1700 cm–1 suggests the presence of simple carbonyl compounds such as ketones, aldehydes, esters, or carboxylic acids, aligning with the properties of the blend components under investigation41.

According to the FTIR spectra, obviously, with the increase of neat PAG and decrease of PPLA in the blends, the relative strength of peak at 1759 cm− 1 which belongs to carbonyl group in PLA was decreased. On the other hand, the relative strength of peak at 2946 cm− 1 which represent the methylene C-H asymmetric absorption band of PPLA, with the increase of neat PAG in the blends, was decreased.

The peaks position of certain spectra in both PPLA and neat PAG remained nearly unchanged across all sample blends. For instance, the peaks at 1475, 1385, 1177, 1125, 1070, and 660 cm− 1, correspond specific molecular vibrations: methylene C-H bending, gem-dimethyl or iso methyl (− CH3), aliphatic fluoro- compounds (C-F stretching), alkyl-substituted ether (C-O stretching), primary amine (C-N stretching) in saturated aliphatic compounds, and acetylenic (alkyne C-H bending) respectively43. This lack of significant peak shifts suggests that the molecular interactions between neat PAG and PPLA were not strong enough to cause structural rearrangements.

In summary, the molecular interfacial interactions between PLA and neat PAG are characterized by the presence of aliphatic and carbonyl compounds. Specific absorption peaks provide insights into the nature of the chemical bonds and interactions within the blends. Additionally, the polysaccharide nature of PAG may contribute to unique interactions, particularly through the formation of hydrogen bonds and other polysaccharide-specific interactions. When PAG, initially a saturated compound, is blended with PPLA, new double bonds form in all sample blends. The presence of simple carbonyl compounds in all sample blends such as ketones, aldehydes, esters, or carboxylic acids, indicates residues of these functional groups in PAG. Since the nature of PAG and PPLA are amides or carboxylates (carboxylic acid salts) all samples meet these criteria.

Additionally, Karsli (2017) observed that the JONCRYL spectra exhibited a peak at 758 cm− 1, attributed to the C-O stretching vibrations of epoxy groups. In contrast, this peak was not present in the spectra of any sample blends. Karsli (2017) inferred that the epoxy groups in JONCRYL were entirely consumed during the compounding process. When epoxy-based chain extenders are used, both esterification and etherification reactions occur between the carboxyl and hydroxyl end groups of PLA, as a polyester. It is hypothesized that epoxy groups initially react preferentially with carboxyl groups rather than hydroxyl groups during the initial stages of blending45.

Subsequently, after establishing the overall composition of the samples, the absorption peaks characteristic of each sample were identified based on earlier researches42,46, as outlined in Table 2.

The samples were analyzed using a scanning electron microscope (SEM), and Fig. 3 display images at three different magnifications for each sample. Most of the polymers are immiscible, resulting in blends with various structures such as island-sea and co-continuous phases, influenced by the polymer ratio, interfacial properties, and processing conditions. The island-sea structure, where a minor phase is spread within a major continuous phase, is common in the morphology of polymer blends. Factors like processing parameters and blend composition affect the morphology of the dispersed phase47. Upon examining the images of the samples, it is evident that island-sea structures are present in all of them, indicating the distribution of PAG in PPLA. By increasing the amount of PAG in the treatments, the island-sea structures with sharper edges take on more elliptical and ribbon-like shapes. Specifically, at 30k× magnification of the 50/50 sample, a significant number of these structures are distinctly visible compared to the other samples. It is stated that brittle fractures may indicate poor miscibility48,49, that is in agree with tensile test results. Previous studies on the surface fractures of neat PLA have shown a flat structure without any distinctive features33,50. When PLA is perceived as a continuous phase, it becomes more pronounced in treatments with lower PAG ratios. However, as the PAG ratios increase, the uniformity gradually diminishes, leading to the formation of larger particles from the dispersed components within the continuous phase. Deng et al. (2018) suggested that these large particles detach from the matrix, creating cracks and flaws at the interface, ultimately resulting in poor mechanical properties33, as confirmed by the tensile test results in the samples with a higher content of PAG in this study. Most of the sample blends exhibit a two-phase system as a mix of ductile and brittle characteristics. Some studies suggest that this variation may indicate differing levels of compatibility among the materials48,49. During analysis of the blends, aggregates with sharp edges—likely due to the presence of a nucleating agent—are occasionally observed. Furthermore, aggregates exhibiting edges that vary from smooth to sharp are particularly noted in blends containing higher amounts of PAG. Some studies have linked these observations to the presence of a nucleating agent10 .

Moreover, a higher fractal dimension is frequently associated with increased toughness, as it indicates more intricate crack paths and enhanced energy absorption mechanisms49. This effect appears to be intensified by the increasing PAG ratio in the sample blends. Such analysis can provide quantitative insights into the degree of blending at the microscopic level.

SEM micrographs of the PPLA/ PAG blends with different weight ratios at the indicated magnification.

Table 3 presents the results regarding the water absorption, sorption, diffusion and permeability coefficients of the samples after 10 days (240 h). Additionally, Fig. 4 illustrates the absorption behavior across all samples. The increase in PAG content in the 90/10, 80/20, and 70/30 samples led to a gradual decrease in water absorption. The highest and lowest water absorption values during the saturation stage (%) belong to the 90/10 and 70/30 samples, respectively. It can be concluded that the 70/30 sample demonstrates the highest resistance to environmental moisture and stronger structural cohesion compared to other treatments. Conversely, the 90/10 sample can be considered a less coherent structure, as confirmed by other test results in this study. Additionally, this sample is suggested to have a higher water absorption capacity.

The evaluation of water absorption in materials determines their quantity of water absorption, while water sorption refers to their ability to attract and retain water molecules, both reflecting the interaction between water and the material. Water sorption directly impacts a material’s water absorption capacity. The sorption coefficient (S) signifies a substance’s ability to sorb or adsorb water, with higher values indicating a greater sorption capacity. The findings reveal that all samples exhibit relatively similar values, with the 70/30 sample showing the lowest value, alike to water absorption. Similarly, the highest and lowest diffusion coefficient (D) and permeability coefficient (P) values are associated with the 90/10 and 70/30 samples, respectively. These coefficients indicate the rate at which water molecules penetrate the samples and the ease of water flow through them. Notably, the 50/50 sample also shows a highwater penetration rate, following the 90/10 sample. Immiscible PLA blends that cause phase separation increase water absorption and play a crucial role in determining the biodegradability rate51.

The study confirms that samples with higher water absorption capacities tend to have elevated sorption, diffusion, and permeability coefficients. Kamaludin et al., (2021) explored the water absorption kinetics of PLA/chitosan composites and noted that the increase of chitosan increased water uptake, indicating a stronger interaction between water and filler, consequently diminishing tensile properties52.

According to Gaikwad et al. (2019), suggested some insightful potential applications based on the water absorption values: materials with low water absorption, (like the 70/30 sample), are ideal for food packaging as they help maintain the integrity of the packaging and protect the food from moisture, which is crucial for products like dry snacks, cereals, and powdered foods. For high water activity foods such as fresh produce and raw meat, materials with higher water absorption (like the 90/10 sample), can be used as moisture absorbers to control moisture levels inside the packaging, thereby extending the shelf life of the food. Incorporating materials with specific water absorption properties into active packaging can help maintain desired humidity levels, which is particularly useful for products sensitive to moisture, such as baked goods and confectionery. Immiscible PLA blends with higher water absorption can influence biodegradability that mentioned earlier, making them beneficial for creating biodegradable food packaging, an eco-friendly option for the food industry. Materials with controlled water absorption can also be used in storage environments to manage humidity levels, important for maintaining the quality of stored food products, especially those that are hygroscopic53.

In summary, the 70/30 sample, with its lowest water absorption and the highest resistance to environmental moisture, is a strong candidate for food packaging applications where moisture resistance is crucial, while the 90/10 sample, with its higher water absorption capacity, is more appropriate for moisture absorbers inside packaging.

Water absorption (%) of PPLA/ PAG sample blends versus time.

Table 3 presents the reactions of PPLA/PAG polymer blends to chemicals after immersion in 1 mol/liter NaOH and 1 mol/liter HCL for 240 h, as indicated by weight percentages changes (+ or gain weight/- or lose weight). Notably, no weight reduction was observed in terms of HCL and NaOH resistance. It is important to note that the weight increase in all polymer blends become more pronounced with higher PAG content. These blends did not lose weight; instead, they exhibited swelling rather than erosion. However, an increase in weight due to swelling in the samples does not indicate an increase in chemical resistance. Instead, it reflects a higher capacity to accept and absorb these chemicals. Observations during the testing process revealed that as the amount of absorption and subsequent swelling in the samples increased, the samples became more brittle and fragile. Therefore, samples with the lowest swelling were more resistant, while those with greater swelling were more fragile. Consequently, the most chemically resistant samples were those with the least weight gain, which corresponded to the samples with the lowest ratio of PEG, specifically the 90/10 sample. Wahit et al. (2015) demonstrated that the chemical resistance of PLA decreases with an increased content of epoxidized natural rubber54.

In Fig. 5, the biodegradability test process is depicted, highlighting the sample blends. Figure 6 illustrates the results consist of sample blends and neat PAG as a positive control. On the 40th day of analysis, it was evident that the biodegradability of PAG exceeded the target value set by the standard, while the other bio-blends exhibited biodegradability ranging from 61.73 to 24.88%. According to the results, all the sample blends achieved biodegradability levels ranging from 81.98 to 54.87% over six months. In general, an increase in the PAG content of the blends led to the increased biodegradability. Moghaddam et al., (2023) highlighted that corn starch and its optimal formulation containing biopolymer blend of corn starch and wheat straw exhibited a biodegradability of 71.1% in the 5th month55.

Biodegradability test process: A A sealed container of test containing distilled water, KOH 0.5 N dish, soil blend matrix, and powdered sample; B Sample buried in the soil blend matrix; C Sealed container prepared for 5 treatments under test; and D Test containers maintained in a dark incubator at a constant temperature of 25 °C for the duration of the six-month experimental period.

Biodegradability of neat PAG and sample blends under aerobic conditions at 25 °C over 6 months.

This study highlights the strategic significance of biopolymer blending in creating innovative polymer blends, aimed at improving component features to meet specific functional criteria. Tensile testing revealed that the 70/30 blend displayed the highest EB and the lowest Young’s modulus, indicating superior elastic properties and improved performance due to its reduced force requirement for elastic deformation. According to FTIR results, all samples displayed absorption peaks, indicating a reduction in the 1700–1750 range, which suggests a transition from carboxylic acid to salt formation from 90/10 to 50/50 blends. The DSC data reveal that introducing PAG into PLA blends can effectively modify main thermal properties, such as Tg, Tc, and Tm. Morphology analysis showed alterations in the uniformity and size of dispersed phases. Moreover, all the sample blends achieved biodegradability levels ranging from 81.98 to 54.87% over six months. Notably, the 50/50 blend exhibited the highest biodegradability (following the positive control). Overall, investigating the potential of novel edible and biodegradable polymer blends in functional food products may open up promising paths for future research and development. Considering the substantial potential of the blends evaluated in this study regarding flexibility, thermal characteristics, and biodegradability, forthcoming research will concentrate on utilizing this emerging and promising blend in the food and packaging industries as a thermoplastic elastomer. In conclusion, this research highlights the potential of using natural biopolymers to improve the properties of PLA blends, offering sustainable alternatives to conventional petroleum-based polymers.

All data generated or analysed during this study are included in this published article.

Xu, C., Luo, X., Lin, X., Zhuo, X. & Liang, L. Preparation and characterization of polylactide/thermoplastic konjac glucomannan blends. Polym. (Guildf). 50, 3698–3705 (2009).

CAS Google Scholar

Maroufkhani, M., Katbab, A., Liu, W. & Zhang, J. Polylactide (PLA) and acrylonitrile butadiene rubber (NBR) blends: the effect of ACN content on morphology, compatibility and mechanical properties. Polym. (Guildf). 115, 37–44 (2017).

CAS Google Scholar

Wu, C. S. & Liao, H. T. A new biodegradable blends prepared from polylactide and hyaluronic acid. Polym. (Guildf). 46, 10017–10026 (2005).

CAS Google Scholar

Markovic, G. & Visakh, P. M. Polymer blends: state of art. Recent. Dev. Polym. Macro, Micro and Nano Blends 1–15 (2017).

Mao, Z., Zhang, X., Jiang, G. & Zhang, J. Fabricating sea-island structure and co-continuous structure in PMMA/ASA and PMMA/CPE blends: correlation between impact property and phase morphology. Polym. Test. 73, 21–30 (2019).

CAS Google Scholar

Utracki, L. A. Characterization methods for high temperature polymer blends. in High Temperature Polymer Blends 14–69 Elsevier, (2014).

Kaveh, M., Yeganehzad, S., Hesarinejad, M. A., Kiumarsi, M. & Abdollahi Moghaddam, M. R. Polylactic Acid/Saqqez gum blends for chewing gum applications: impact of plasticizers on Thermo-Mechanical and Morphological properties. Polym. (Basel). 16, 1469 (2024).

CAS Google Scholar

Cai, K. et al. Preparation of biodegradable PLA/PBAT blends with balanced toughness and strength by dynamic vulcanization process. Polym. (Guildf). 291, 126587 (2024).

CAS Google Scholar

Courgneau, C., Domenek, S., Guinault, A., Avérous, L. & Ducruet, V. Analysis of the structure-properties relationships of different multiphase systems based on plasticized poly (lactic acid). J. Polym. Environ. 19, 362–371 (2011).

CAS Google Scholar

Mallegni, N., Phuong, T. V., Coltelli, M. B., Cinelli, P. & Lazzeri, A. Poly (lactic acid)(PLA) based tear resistant and biodegradable flexible films by blown film extrusion. Mater. (Basel). 11, 148 (2018).

ADS Google Scholar

Smith, M. J. & Verbeek, C. J. R. Compatibilization effects in thermoplastic protein/polyester blends. J. Appl. Polym. Sci. 135, 45808 (2018).

Google Scholar

de Nunes, C. D., de Souza, E. & Rosa, S. A. G.dos D. Effect of the Joncryl® ADR Compatibilizing Agent in Blends of Poly (butylene adipate-co‐terephthalate)/Poly (lactic acid). in Macromolecular Symposia vol. 383 1800035Wiley Online Library, (2019).

Ucpinar Durmaz, B., Atılgan, M. G. & Aytac, A. Evaluation of the morphological, rheological, dynamic mechanical and mechanical characteristics of compatibilized graphene oxide/poly (ethylene terephthalate)/poly (butylene terephthalate) nanocomposites. Polym. Compos. 42, 6941–6951 (2021).

CAS Google Scholar

Kahraman, Y., Özdemir, B., Gümüş, B. E. & Nofar, M. Morphological, rheological, and mechanical properties of PLA/TPU/nanoclay blends compatibilized with epoxy-based Joncryl chain extender. Colloid Polym. Sci. 301, 51–62 (2023).

CAS Google Scholar

ASTM D882-12. ASTM D882-12, Standard test Method for Tensile Properties of thin Plastic Sheeting (ASTM International, 2012).

McKeen, L. W. 11-Elastomers and Rubbers. Eff. Long Term Therm. Expo. Plast. Elastomers, ed. LW McKeen (Oxford William Andrew Publ. 239–271 (2014).

ASTM D570-22. Standard Test Method for Water Absorption of Plastics. in ASTM Committee D-20 on Plastics. Subcommittee D20. 50 on (American Society for Testing and Materials), (1995).

Chen, R. S., Ghani, A., Salleh, M. H., Ahmad, M. N. & Tarawneh, M. A. S. Mechanical, water absorption, and morphology of recycled polymer blend rice husk flour biocomposites. J. Appl. Polym. Sci. 132, 41494 (2015).

Gupta, M. K. & Singh, R. PLA-coated sisal fibre-reinforced polyester composite: water absorption, static and dynamic mechanical properties. J. Compos. Mater. 53, 65–72 (2019).

ADS CAS Google Scholar

Thakur, V. K. & Singha, A. S. Physico-chemical and mechanical characterization of natural fibre reinforced polymer composites. (2010).

ASTM D5988-18. Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under High-Solids Anaerobic‐Digestion Conditions. in. ASTM West Conshohocken, PA, (2018).

Atnurkar, V., Schuster, J. & Shaik, Y. P. Increased elongation at breaking point with improved mechanical characteristics in PLA. Open. J. Compos. Mater. 13, 13–28 (2023).

CAS Google Scholar

Pivsa-Art, W., Chaiyasat, A., Pivsa-Art, S., Yamane, H. & Ohara, H. Preparation of Polymer blends between poly (lactic acid) and poly (butylene adipate-co-terephthalate) and biodegradable polymers as compatibilizers. Energy Procedia. 34, 549–554 (2013).

CAS Google Scholar

Nazrin, A. et al. Nanocellulose reinforced thermoplastic starch (TPS), polylactic acid (PLA), and polybutylene succinate (PBS) for food packaging applications. Front. Chem. 8, 213 (2020).

ADS CAS PubMed PubMed Central Google Scholar

Ko, H. S., Lee, S., Lee, D. & Jho, J. Y. Mechanical properties and Bioactivity of Poly (Lactic Acid) composites containing poly (glycolic acid) fiber and hydroxyapatite particles. Nanomaterials. 11, 249 (2021).

CAS PubMed PubMed Central Google Scholar

Lim, H. & Hoag, S. W. Plasticizer effects on physical–mechanical properties of solvent cast Soluplus® films. Aaps Pharmscitech. 14, 903–910 (2013).

CAS PubMed PubMed Central Google Scholar

Ploypetchara, N., Suppakul, P., Atong, D. & Pechyen, C. Blend of polypropylene/poly (lactic acid) for medical packaging application: physicochemical, thermal, mechanical, and barrier properties. Energy Procedia. 56, 201–210 (2014).

CAS Google Scholar

Mehrabi Mazidi, M., Edalat, A., Berahman, R. & Hosseini, F. S. Highly-toughened polylactide-(PLA-) based ternary blends with significantly enhanced glass transition and melt strength: tailoring the interfacial interactions, phase morphology, and performance. Macromolecules. 51, 4298–4314 (2018).

ADS CAS Google Scholar

Su, S. Prediction of the miscibility of PBAT/PLA blends. Polym. (Basel). 13, 2339 (2021).

CAS Google Scholar

Zhao, T. et al. Thermal, crystallization, and mechanical properties of polylactic acid (PLA)/poly (butylene succinate)(PBS) blends. Polym. Bull. 81, 2481–2504 (2024).

CAS Google Scholar

Yu, M., Zheng, Y. & Tian, J. Study on the biodegradability of modified starch/polylactic acid (PLA) composite materials. RSC Adv. 10, 26298–26307 (2020).

ADS CAS PubMed PubMed Central Google Scholar

Mutlur, S. Thermal analysis of composites using DSC. Adv. Top. Charact. Compos. 13, 11–33 (2004).

Deng, Y., Yu, C., Wongwiwattana, P. & Thomas, N. L. Optimising ductility of poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends through co-continuous phase morphology. J. Polym. Environ. 26, 3802–3816 (2018).

CAS Google Scholar

Abdelwahab, M. A. et al. Thermal, mechanical and morphological characterization of plasticized PLA–PHB blends. Polym. Degrad. Stab. 97, 1822–1828 (2012).

CAS Google Scholar

Baimark, Y. & Srihanam, P. Influence of chain extender on thermal properties and melt flow index of stereocomplex PLA. Polym. Test. 45, 52–57 (2015).

CAS Google Scholar

Meng, Q., Heuzey, M. C. & Carreau, P. J. Control of thermal degradation of polylactide/clay nanocomposites during melt processing by chain extension reaction. Polym. Degrad. Stab. 97, 2010–2020 (2012).

CAS Google Scholar

Ghaderi, J., Hosseini, S. F., Shabazadeh, I. & Gómez-Guillén, M. C. Fabrication and characterization of biocomposite films based on carboxymethyl cellulose/polyvinyl alcohol/fish gelatin for food packaging exploits. Innov. Food Technol. 8, 383–398 (2021).

Google Scholar

Nishinari, K. Rheological and DSC study of sol-gel transition in aqueous dispersions of industrially important polymers and colloids. Colloid Polym. Sci. 275, 1093–1107 (1997).

CAS Google Scholar

Julinová, M. et al. Effect of different fillers on the biodegradation rate of thermoplastic starch in water and soil environments. J. Polym. Environ. 28, 566–583 (2020).

Google Scholar

Yu, J., Wang, N. & Ma, X. Fabrication and characterization of poly (lactic acid)/acetyl tributyl citrate/carbon black as conductive polymer composites. Biomacromolecules. 9, 1050–1057 (2008).

CAS PubMed Google Scholar

Nandiyanto, A. B. D., Oktiani, R. & Ragadhita, R. How to read and interpret FTIR spectroscope of organic material. Indones J. Sci. Technol. 4, 97–118 (2019).

Google Scholar

Chieng, B. W., Ibrahim, N. A., Then, Y. Y. & Loo, Y. Y. Epoxidized vegetable oils plasticized poly (lactic acid) biocomposites: mechanical, thermal and morphology properties. Molecules. 19, 16024–16038 (2014).

PubMed PubMed Central Google Scholar

Coates, J. Interpretation of infrared spectra, a practical approach. at (2000).

Ranakoti, L. et al. Critical review on polylactic acid: properties, structure, processing, biocomposites, and nanocomposites. Mater. (Basel). 15, 4312 (2022).

ADS CAS Google Scholar

Karsli, N. G. A study on the fracture, mechanical and thermal properties of chain extended recycled poly (ethylene terephthalate). J. Thermoplast Compos. Mater. 30, 1157–1172 (2017).

CAS Google Scholar

Kaavessina, M., Distantina, S., Chafidz, A., Utama, A. & Anggraeni, V. M. P. Blends of low molecular weight of poly lactic acid (PLA) with gondorukem (gum rosin). in AIP Conference Proceedings vol. 30006 (AIP Publishing LLC, 2018). (1931).

Wei, X. F., Nilsson, F., Yin, H. & Hedenqvist, M. S. Microplastics originating from Polymer blends: an emerging threat? Environ. Sci. Technol. 55, 4190–4193 (2021).

ADS CAS PubMed PubMed Central Google Scholar

Torrado Perez, A. R., Roberson, D. A. & Wicker, R. B. Fracture surface analysis of 3D-printed tensile specimens of novel ABS-based materials. J. Fail. Anal. Prev. 14, 343–353 (2014).

Google Scholar

Gao, H. & Qiang, T. Fracture surface morphology and impact strength of cellulose/PLA composites. Mater. (Basel). 10, 624 (2017).

ADS Google Scholar

Ertiletskaya, N. et al. EDP Sciences,. Comparative study of physical and chemical properties of PLA-based films obtained by solution casting and flat-slot die melt extrusion. in BIO Web of Conferences vol. 67 3015 (2023).

Rosli, N. A., Karamanlioglu, M., Kargarzadeh, H. & Ahmad, I. Comprehensive exploration of natural degradation of poly (lactic acid) blends in various degradation media: a review. Int. J. Biol. Macromol. 187, 732–741 (2021).

CAS PubMed Google Scholar

Kamaludin, N. H. I., Ismail, H., Rusli, A. & Ting, S. S. Thermal behavior and water absorption kinetics of polylactic acid/chitosan biocomposites. Iran. Polym. J. 30, 135–147 (2021).

CAS Google Scholar

Gaikwad, K. K., Singh, S. & Ajji, A. Moisture absorbers for food packaging applications. Environ. Chem. Lett. 17, 609–628 (2019).

CAS Google Scholar

Wahit, M. U., Hassan, A., Ibrahim, A. N., Zawawi, N. A. & Kunasegeran, K. Mechanical, thermal and chemical resistance of epoxidized natural rubber toughened polylactic acid blends. Sains Malaysiana. 44, 1615–1623 (2015).

CAS Google Scholar

Moghaddam, M. R. A., Hesarinejad, M. A. & Javidi, F. Characterization and optimization of polylactic acid and polybutylene succinate blend/starch/wheat straw biocomposite by optimal custom mixture design. Polym. Test. 121, 108000 (2023).

Google Scholar

Download references

The authors gratefully acknowledge the Research Institute of Food Science & Technology (RIFST) for their support in funding this research. Also, they appreciate the collaborative efforts of Dr. Mohammadreza Abdollahi Moghaddam and Dr. Moslem Jahani and the generous contribution of materials and laboratory equipments from Behzist Danesh Narvan Co., Mashhad, Iran, which were essential for the successful completion of this work.

Department of Food Sensory and Cognitive Science, Research Institute of Food Science and Technology (RIFST), Mashhad, Iran

Mona Kaveh, Samira Yeganehzad, Mohammad Ali Hesarinejad & Maryam Kiumarsi

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

Conceptualization, SY and MAH; methodology, MKa; software, MKa; investigation, MKa; data curation, SY, MAH, MKi; writing—original draft preparation, MKa; writing—review and editing, SY and MAH; supervision, SY and MAH; funding acquisition, SY and MAH. All authors have read and agreed to the published version of the manuscript. All authors read and approved the final manuscript.

Correspondence to Samira Yeganehzad or Mohammad Ali Hesarinejad.

The authors declare no competing interests.

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.

Reprints and permissions

Kaveh, M., Yeganehzad, S., Hesarinejad, M.A. et al. Exploring the performance and biodegradability of Edible Biopolymer blends incorporating Pistacia atlantica subsp. Mutica Gum and Plasticized Poly(lactic acid). Sci Rep 14, 25666 (2024). https://doi.org/10.1038/s41598-024-77709-8

Download citation

Received: 14 July 2024

Accepted: 24 October 2024

Published: 27 October 2024

DOI: https://doi.org/10.1038/s41598-024-77709-8

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative