High toughness and fast home-compost biodegradable packaging films derived from polylactic acid/thermoplastic starch/para-rubber ternary blends | Scientific Reports

Scientific Reports volume 14, Article number: 18603 (2024) Cite this article

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This research aims to formulate biobased and biodegradable packaging films with high toughness and fast home-compost biodegradation using ternary blends of polylactic acid (PLA), Para rubber (NR), and thermoplastic starch (TPS) through blown-film extrusion. The TPS content in this work ranges from 5 to 20 wt%, while the PLA: NR ratio is fixed at 70:30. At this PLA: NR ratio, the blend with 10 wt% TPS (PNT10) exhibited the highest % elongation at break and tensile toughness. Peroxide radical initiator was investigated as a potential additive for improving the properties of the ternary blend. Our binary interaction study indicated that peroxide initiated grafting reactions of PLA–NR and NR–TPS pairs, while no grafting occurred between PLA and TPS. In ternary blends, the highest peroxide content (0.5 wt%) increased the % elongation at break up to 120%, with the tensile toughness reaching 7255 MJ/m3. The improved compatibility induced by peroxide addition was supported by enhanced dispersion of TPS in the PLA/NR matrices. Results from the room-temperature soil burial test indicated that the presence of TPS could significantly accelerate the home-compost degradation of PNT films compared to films produced from neat PLA and PLA/NR. This suggests its potential as both a cost reducer and a biodegradation accelerator.

Due to environmental concerns over accumulated nondegradable plastic waste in landfills and marine environments, biodegradable plastics are considered the most sustainable option for single-use applications. Nevertheless, the use of biodegradable plastics is still not widespread due to their high cost, triggering a very high demand for lower-cost biodegradable plastics.

At present, polylactic acid (PLA) is considered the cheapest bio-based and biodegradable plastics that can be processed into various environmentally friendly products through the same process as conventional plastics. Despite possessing good mechanical strength and chemical properties, PLA still has limitations. It is inherently hard and brittle, making it difficult to process into flexible packages, particularly packaging films1,2,3. Furthermore, its cost remains nearly twice that of conventional plastics, and it degrades slowly in home-compost environments (room temperature).

To increase its toughness, PLA has to be blended with toughening agents, such as tougher plastics or elastomers4,5,6. Examples include thermoplastic polyurethane7, poly(ethylene octene)8, ethylene-co-vinyl acetate9, poly (ethylene-butylacrylate-glycidyl methacrylate)10, and synthetic rubber such as synthetic polyisoprene rubber, silicone rubber, acrylic rubber, acrylic core–shell rubber11,12, and poly(butylene-adipate-co-terephthalate) (PBAT)13,14,15,16. Among these, PBAT is considered the most commonly used toughening agent for PLA as it could effectively provide toughness without losing its biodegradability13,14,15,16,17. Nevertheless, PBAT is much more expensive than PLA, making PBAT-modified PLAs costlier17,18. Furthermore, since PBAT is fossil-based, the carbon footprints of the modified PLAs are unavoidably higher.

Consequently, the use of bio-based polymers that exhibit high elasticity, full biodegradability, and cost-effectiveness presents a promising opportunity for research and development. In this regard, commercial natural rubber (NR), cultivated from Para rubber trees, possesses a high potential for improving the toughness of PLA because it is a cheap bio-elastomer with inherent biodegradability. More importantly, it is low-cost and possesses a very low carbon footprint. Furthermore, NR possesses outstanding elasticity and strength, ideal for improving the toughness of PLA19,20,21,22,23,24,25,26,27,28. Although NR could effectively improve toughness and reduce the carbon footprint and overall cost of PLA/NR blends, the cost of these blends remains relatively high compared to traditional petroleum-based plastics. Efforts to incorporate NR contents above 20% in PLA were not very promising, as they resulted in films that were either too sticky for general-use packaging applications or sometimes even too sticky to blow into film28.

Another notable biobased and biodegradable polymer that could potentially be combined with PLA/NR blends is thermoplastic starch (TPS). TPS is produced from starch sources like cassava, corn, and potato by undergoing a plasticization process to form a thermoplastic material29,30. It has gained attention due to its abundance, renewability, and affordability. TPS itself is not suitable as a packaging film due to its high brittleness and significant moisture uptake. As a result, a ternary blend of PLA/NR/TPS (or PNT) offers a promising opportunity to further reduce costs and allows for the addition of higher NR contents in the blends. More importantly, TPS possesses high potential in expediting the biodegradation of PLA/NR films owing to its exceptional biodegradability31,32. To the best of our knowledge, no research has investigated on blown films produced from a ternary blend of PLA/NR/TPS. A systematic review identified only one relevant study focusing on PLA/NR/TPS ternary blends. The study only investigated the impact of nano-precipitated calcium carbonate (NPCC) on the mechanical, thermal, and barrier properties of the blends without addressing specific influences of TPS in the blend or its potential in film blowing applications33.

The key innovation of this study is the development of non-sticky, fully bio-based, and biodegradable packaging films with high NR content, cost efficiency, and rapid room-temperature biodegradation from ternary blends of PLA/NR/TPS. The chosen PLA: NR ratio was determined based on the requirement that it should not make the collapsed PNT blown film too sticky to detach. In the PNT ternary blend, the addition of TPS reduces the film’s stickiness, permitting an increased NR content. This work selected a PLA:NR ratio of 70:30 (corresponding to 27% NR in PNT10) because this high NR content did not induce film stickiness in PNT films. The TPS content was then varied for further investigation. The phase compatibility and dispersion of minor domains in the PLA matrix were enhanced through reactive blending with peroxide. The compounds and films were characterized and analyzed for the changes in mechanical properties, thermal properties, morphology, and gas permeability. The films produced were also pre-screened for home compostability using a soil-burial test for up to 8 months.

PLA grade 4043D with the melt flow index (MFI) and the specific gravity of 6.0 g/10 min and 1.24 g/cc, respectively, was purchased from Natureworks LLC. Thermoplastic starch (TPS) was supplied by Siam Modified Starch Co., Ltd. Standard Thai Rubber grade (STR5L) was purchased from Srijareon Rubber Co., Ltd. Tert-butyl peroxide, an organic peroxide radical initiator, was purchased from Sigma-Aldrich and used as received.

PLA was dried in an oven at 80 °C overnight to remove excess moisture before use. A masterbatch of PLA/NR was prepared at a weight ratio of 70:30 in a twin-screw extruder (LTEM26-56, Labtech Engineering Co., Ltd.) with an L/D ratio of 52 and a screw diameter of 26 mm, at a die head temperature of 185 °C. This high-NR ratio was selected to offset the reduction in toughness due to the addition of high-brittleness TPS. Additionally, increasing the amount of NR is beneficial for reducing the compound cost. After being extruded, the masterbatch was pelletized using a side-cut pelletizer and dried overnight at 80 °C. It was then compounded with TPS to create the PLA/NR/TPS ternary blend under the same conditions as the masterbatch.

In the first part of this study, the PLA/NR/TPS compounds, denoted as PNT, were prepared using TPS contents ranging from 5 to 20 wt% at a fixed PLA/NR ratio of 70:30 to study the effect of TPS in the PLA/NR blend. In the second part, the effect of an organic peroxide in PNT was investigated with contents ranging from 0 to 0.5 wt%. The selected range of peroxide contents was based on our prior studies on the effect of peroxide in PLA34 and PLA/NR28. The compositions of different PNT films in both parts are shown in Table 1.

For the film-blowing process, the neat PLA and PNT compounds were dried in a vacuum oven at 80 °C overnight and blown into films by a film-blowing machine (Labtech Engineering Co., Ltd.). The process temperature range was 180–190 °C (across 4 zones), with a spiral die temperature of 190 °C, and a screw speed of 170 rpm. The speed of the nip rolls and the airflow rates inside and outside the bubble were adjusted to maintain a BUR (Blow-Up Ratio) of 2.8. The nip roll speed was fixed at 7–8 m/min to produce a film sample with an approximate thickness of 0.05–0.06 mm.

Fourier transform infrared spectra of dried film specimens were recorded using a Perkin Elmer Spectrum™ 3 FT–IR spectrometer equipped with a universal attenuated total reflectance (UATR). In this mode, spectra are obtained from the absorption of the wave which is transmitted through an internal reflection element of high refractive index and penetrates a short distance (2 μm) into the sample. The spectra were recorded from the wave numbers of 4000–400 cm−1 at a resolution of 4 cm−1.

Tensile testing of blown films was carried out according to ASTM D882 at room temperature by a Universal Testing Machine (UTM) model UTB9251-ACHiTech from Narin Instruments. The film samples, cut into sizes of 10 mm wide and 200 mm long, were measured in the machine direction using a 0.98-kN load cell at a cross-head speed of 20 mm/min and a gauge length of 100 mm. Five specimens were measured for each sample. The Young’s modulus, tensile strength, elongation at break, and tensile toughness were calculated for each measurement.

The microscopic surface morphologies of PLA, PLA/NR, PLA/TPS, and PNT films were recorded with a JEOL JSM-7800F scanning electron microscope operated at 3 kV. Before SEM observation, the specimens were sputtered with gold under vacuum. In addition, the macroscopic appearance of the films was monitored and photographed using a Dino-Lite™ digital microscope and a digital camera.

The changes in glass transition temperature (Tg), percent crystallinity (%Xc), and crystalline melting temperature (Tm) after degradation were examined through a Discovery DSC 2500 differential scanning calorimeter from the TA instrument. For the first heating scan, a sample of about 8 mg was heated from 25 to 190 °C and held for 3 min to erase the thermal history. The sample then underwent a cooling scan down to 25 °C followed by a second heating scan to 190 °C, all steps at the rate of 10 °C min−1. The experiments were performed in a nitrogen atmosphere. The %Xc was calculated by Eq. (1),

where ∆Hm and ∆Hc are the melting and cold crystallization enthalpies of the compounds, respectively. xPLA is the weight fraction of PLA in the blends and ∆Hf is the reference melting enthalpy for PLA crystals, which is 93.6 J/g35,36.

The PNT compounds were dried overnight in a vacuum oven at 80 °C and then formed into discs with a diameter of 25 mm through compression molding at 170 °C. The dynamic rheological properties of samples were assessed at 190 °C using a modular compact rheometer (MCR102) equipped with a 25-mm parallel plate geometry from Anton Paar GmbH. The gap distance was set at 1 mm, and frequency sweep tests were conducted within the linear viscoelastic limit.

An oxygen permeability (OP) test was conducted to determine the rate at which oxygen gas permeates through the film. The test was conducted by the Illinois Oxygen Permeation Analysis Model 8501 apparatus following the ASTM D3985 standard at 23 ± 2 °C and 0%RH.

In this study, we employed commercial organic planting soil to assess the biodegradability of PLA and PNT blown films. The films were submerged in the soil at a depth of approximately 8 cm inside a closed plastic container. The composting conditions included an average daytime temperature of 34–35 °C and a water feed rate of 150 ml/week. The composting process continued for up to 8 months. The surface disintegration of the films was examined using a Dino-lite™ digital microscope with a magnification of 150 × .

Figure 1 displays the distinct FTIR fingerprints of TPS, PLA, and NR, illustrating the differences in their chemical structures. As can be seen, the fingerprint of TPS includes a broad peak of the –OH group at 3402–3667 cm−1, –CH2 stretching at 1346 cm−1, C–O–C stretching at 1077 cm−1, and pyranose ring at 995 cm−1. The fingerprint of PLA includes the peaks at 2995 cm−1 and 2945 cm−1 (–CH3 stretching), 1747 cm−1 (C = O), 1452 cm−1and 1376 cm−1 (C–H bending), 1127 cm−1 (CH3 bending), 1080 cm−1 (C–O–C), 1043 cm−1 (C–CH3 stretching), and 867 cm−1 (C–COO stretching). The reference spectrum of NR includes the characteristic peaks at 2961 cm−1 (–CH3 stretching), 2925 and 2852 cm−1 (–CH2 stretching), 1662 cm–1 (C = C stretching), 1452 cm−1 and 1367 cm−1 (C–H bending), 834 cm–1 (= C–H bending). The FTIR spectrum of the PNT ternary blend comprising 10 wt% TPS (PNT10) shows the characteristic peaks of PLA, NR, and TPS as expected. In Fig. 2, the overlay spectra of PNT films with TPS contents ranging from 5 to 20 wt% indicate an increase in the intensity of TPS peaks with higher TPS contents.

FTIR fingerprints of TPS, PLA, NR, and PNT films.

FTIR spectra of PNT films at TPS contents of 5, 10, 15, and 20 wt%.

The rheological properties of PNT ternary blends are expressed in terms of complex viscosity (η*) and storage modulus (Gʹ) to indicate the resistance to flow and the solid-like behavior, respectively. Figure 3 illustrates that TPS led to sharp upturns in Gʹ and η* in the terminal region (low frequency), with the rise being more pronounced at a higher TPS content. This observation suggests the presence of branched or gel-like structures in TPS. Based on the Cox–Merz rule37, the relationship between η* and angular frequency (ω) corresponds to the relationship between shear viscosity and shear rate. The stronger shear-thinning effect and the lower viscosities of PNTs at high frequencies compared to the unmodified PLA/NR blend (PNT0) imply lower torques during processing at high shear rates. This phenomenon is attributed to the plasticizing effect of a plasticizer present in TPS. The effect of plasticizers in lowering the Gʹand η* of PLA was consistently found in other studies38,39.

Complex viscosity (η*) and storage modulus (Gʹ) of PLA/NR and the PNT blends at various TPS contents.

To observe the microscopic changes of PNT films at higher TPS contents, their SEM micrographs were compared with a reference PLA/NR film in Fig. 4. As can be seen, the presence of TPS in the films resulted in rougher surfaces than the PLA/NR film. At higher TPS contents (corresponding to lower NR contents), the NR domains become smaller and the TPS phase becomes more dispersed, especially at the highest TPS content (20 wt%). Other studies on the PLA/TPS system did not directly report the effect of TPS content on the dispersed domain size but emphasized the impact of compatibilizers and peroxide on improving dispersion40. In this study, a fixed small amount of peroxide (0.05 wt%) was also used. Therefore, the smaller dispersed domain size observed at higher TPS content might be attributed to the combined effects of peroxide and the inherent compatibilizers present in TPS.

Film surface morphology of PLA/NR film (a), and PNT films at increasing TPS contents: 5 wt% (b), 10 wt% (c), 15 wt% (d), and 20 wt% (e).

DSC first-heating scans of neat TPS, neat PLA, PLA/NR, and PNTs at various TPS contents, along with the percent crystallinity of the PLA phase (%Xc), are presented in Fig. 5. In Fig. 5a, TPS exhibits a virtually amorphous nature, characterized by the absence of a crystalline melting peak, indicating effective plasticization of starch. Conversely, PLA shows a cold crystallization peak (Tc) at 125.50 °C and a crystalline melting peak (Tm) at 149.43 °C. With the addition of NR, the Tc was shifted down to 118.15 °C, probably due to increased chain mobility41. Notably, the incorporation of TPS into the PLA/NR system not only further reduced Tc but also decreased the Tg and Tm of PLA, potentially due to the nucleating effect of smaller dispersed domain size and the plasticizing effect of plasticizers present in TPS40,42. Figure 5b indicates that the incorporation of NR (PLA/NR) and NR plus 5 wt% TPS (PNT5) does not yield a significant change in the %Xc of PLA. However, at higher TPS contents, there is an almost proportional increase in the %Xc. This observation suggests that TPS contents at 10 wt% and above may function as effective crystallization promoters for PLA/NR. A similar effect of TPS in promoting crystallization was previously reported in a PLA/TPS system, where 20% TPS similarly increased the %Xc of PLA from 1.6 to 9.1%, even in the absence of NR42.

(a) DSC thermograms (first heating) of neat PLA, neat TPS, and PNTs at various TPS contents (5, 10, 15, 20 wt%) and (b) their %Xc.

Tensile strength, Young’s modulus, %elongation at break, and tensile toughness of PLA and PNT films having TPS contents of 5, 10, 15, and 20 wt% were compared to those of the referenced neat PLA and PLA/NR films as shown in Fig. 6. The referenced PLA/NR film used for comparison here consisted of 15 wt% NR. As can be seen, the PNT films possessed lower tensile strengths than the reference PLA and PLA/NR films due to the presence of plasticizers in TPS. However, the PNT films tended to have higher tensile toughness and % elongation at break, with the highest toughness achieved at a TPS content of 10 wt% (PNT10). As a result, the formula containing 10 wt% TPS was selected for further investigation.

Tensile properties of neat PLA, PLA/NR, and PNT films at various TPS contents (5, 10, 15, and 20 wt%).

In this section, the properties of PNT compounds were enhanced through reactive compounding with peroxide. The impact of peroxide on binary interactions among components within the PNT ternary blends was examined by introducing peroxide into three pairs of binary blends: PLA/NR, PLA/TPS, and NR/TPS. The changes in their FTIR spectra were subsequently analyzed. For the PLA/NR pair, the overlay spectra of PLA/NR with and without 0.05 wt% peroxide in Fig. 7 revealed that peroxide led to the reduction of –CH2 peaks of NR at 2852 cm−1 and 2925 cm−1 indicating that peroxide-induced grafting between PLA and NR, potentially at the NR allylic carbon, where the proposed mechanism is illustrated in Fig. 10a28,43.

FTIR spectra of PLA/NR and peroxide-treated PLA/NR.

For the NR/TPS binary blend, the unreacted portion of NR in the NR/TPS films was extracted using chloroform (CHCl3) before conducting the FTIR test to intensify the grafted portion of the films (Fig. 8). As observed, the peaks of NR were significantly stronger in the peroxide-treated film compared to the untreated film. Since chloroform dissolved only the NR phase while leaving the TPS phase intact, the increased peak intensity of NR after the reactive compounding with peroxide suggests that peroxide potentially induced grafting or crosslinking of NR in the NR/TPS blends. While most peaks were inherently present in unreacted NR or TPS, a new small ester peak at 1128 cm−1 (R–CO–R stretching) appeared, indicating a possible grafting reaction between NR and TPS by a condensation reaction between NR and –OH sites of TPS as illustrated in Fig. 10b.

FTIR spectra of NR/TPS and modified NR/TPS.

On the other hand, for the PLA/TPS blend (Fig. 9), the reaction with peroxide did not cause any peak differences in the FTIR spectra. Even after acetone extraction to eliminate the unreacted PLA component, the characteristic peaks of PLA/TPS with and without peroxide remained almost identical, indicating no evident chemical reaction between PLA and TPS. The binary interaction mapping of PLA–NR, NR–TPS, and PLA–TPS could be represented as shown in Fig. 10c.

FTIR spectra of PLA/TPS and modified PLA/TPS.

Possible reaction mechanisms of peroxide with PLA/NR (a) and NR/TPS (b), and infographic of possible peroxide-induced interaction between PLA, NR, and TPS (c).

In the ternary blend of PLA/NR/TPS, the FTIR spectra of peroxide-treated films at peroxide contents ranging from 0 to 0.5 wt% are shown in Fig. 11. Since PLA, NR, and TPS contents were fixed, the peak changes were attributed to the reaction that occurred at increasing peroxide content. Note that the original peroxide fingerprint was absent due to its rapid decomposition into reactive species that induce grafting and crosslinking of other components upon heating during the compounding step. Obviously, the higher peroxide content led to the decrease in intensity of the broad O–H stretching at 3667–3402 cm−1 and O–H bending at 1645 cm−1 of TPS. The C = C peak of NR at 1662 cm−1 also decreased in intensity. This indicates that peroxide might induce a reaction between the double bonds of NR and the –OH groups of TPS as proposed in Fig. 10b.

FTIR spectra of PNT films at peroxide contents of 0, 0.02, 0.05, 0.2, 0.5 wt%.

The effect of peroxide on the changes in rheological properties of PNT films was investigated in terms of the complex viscosity (\(\eta\)*) and storage modulus (Gʹ) by using the dynamic frequency sweep and time sweep tests as shown in Figs. 12 and 13, respectively. In Fig. 12, \(\eta\)* and Gʹ of PNT gradually increased with increasing peroxide content, indicating the structural change into more solid-like structures. This is consistent with the earlier work on the effect of peroxide in PLA/NR blends28. The time sweep test at 190 °C in Fig. 13 reveals a rapid reduction in the complex viscosity over time implying severe thermal degradation of the blends at this temperature. However, the blends with higher peroxide concentration could maintain higher viscosity throughout the 20-min testing time.

Complex viscosity (η*) and storage modulus (Gʹ) at 190 °C of the peroxide-treated PNT10 at various peroxide contents.

Complex viscosity (\(\upeta\)*) at 195 °C and angular frequency of 10 s−1 of PNT10 using peroxide contents of 0, 0.02, 0.05, 0.2, and 0.5 wt%.

Peroxide treatment also affects the surface morphology of the PNT films as illustrated in Fig. 14. As can be seen, distinct domains of TPS and NR are observable all over the surface. With the presence of peroxide, interphase compatibility improved, leading to smaller domain sizes, and higher peroxide content resulted in even smaller granules. The effect of peroxide on better dispersion of disperse domains in the blends is consistent with those found in PLA/NR systems28. Notably, the film with the highest peroxide content (0.5 wt%) exhibited the smallest granules, implying the highest phase compatibility. This result supports the film’s highest tensile toughness. To locate the TPS position on the film surfaces, the PNT films were submerged in distilled water for 24 h to remove TPS domains before taking SEM micrographs (Fig. 15). The black holes on the micrographs indicate the position of TPS on the films. As can be seen, big holes are evident on the surface of untreated PNT film, suggesting poor dispersion of TPS. With increasing peroxide contents, the holes on the film surfaces became smaller with better distribution. Moreover, the size of NR domains also decreased, affirming that peroxide improved the dispersion of both TPS and NR within the PLA matrix.

SEM morphology of peroxide-modified PNT films at the peroxide contents of 0 (a), 0.02 (b),0.05 (c),0.2 (d), and 0.5 (e) wt%, respectively, at 300X magnification.

SEM micrographs of water-extracted PNT films with varying peroxide content: 0 wt% (a), 0.02 wt% (b), 0.05 wt% (c), 0.2 wt% (d), and 0.5 wt% (e) at 1000 × magnification.

Interestingly, peroxide treatment also contributed to a remarkable decrease in Tc and higher %Xc of the PNT compounds as shown in the DSC first heating scans in Fig. 16a with the %Xc illustrated in Fig. 16b. In a peroxide-treated PLA system, low peroxide contents (≤ 0.2%) resulted in a reduction in %Xc, whereas a sufficiently high peroxide content (0.5 wt%) significantly increased %Xc44. However, in PLA/NR blends, even low peroxide contents could induce a greater %Xc24,44, similar to the case of PNT blends in this study. This increase in %Xc in the blends probably results from peroxide acting as a compatibilizer, which creates smaller dispersed domains that enhance nucleation in the blend systems.

(a) DSC thermograms (first heating) and (b) the %crystallinity of PNT10 at peroxide contents of 0, 0.02, 0.05, 0.2, and 0.5 wt%.

The peroxide-treated PNT films also possess improved mechanical properties as illustrated in Fig. 17. From the figure, even though their tensile strength and Young’s modulus were comparably lower than those of the rigid PLA film, an increase in peroxide content resulted in higher %elongation at break and tensile toughness. In this work, the maximum % elongation at break and tensile toughness reached 119.8% and 7254.86 MJ/m3, respectively, at the highest peroxide content of 0.5 wt%.

Tensile strength, Young’s modulus, %elongation at break, and tensile toughness of PLA and PNT10 films at peroxide contents of 0.02, 0.05, 0.2, and 0.5 wt%.

Oxygen permeability (OP) of PNT films was analyzed to assess their suitability for permeability control applications, as depicted in Fig. 18. The OP exhibited a decreasing trend with increasing TPS and peroxide contents. This result corresponds to the smoother film surfaces and higher %Xc observed at higher TPS and peroxide contents, as shown in the SEM micrographs (Figs. 4 and 14) and the %Xc (Figs. 5b and 16b). According to the OP of our in-house prepared films, neat PLA and PLA/NR with 25% NR films exhibited oxygen permeabilities of 16.77 and 32.93 cc mm/(m2 day atm), respectively. These OPs were lower than those of PNT films, indicating that TPS could be employed to further increase the OP beyond that of PLA/NR blends, where the optimal TPS and peroxide contents can be utilized to adjust the OP of the films.

Oxygen permeability of (a) PNT films at various TPS contents and (b) PNT10 at various peroxide contents.

As TPS is expected to improve the biodegradability and degradation rate of the PNT films, this section explores the effect of TPS content on the soil burial degradation of PNT films in a home-compost environment. The appearance of the disintegrated PLA and PNT films before the test (day 0) and after 5- and 8-month test periods is illustrated in Fig. 19. Initially, both PLA and PNT films exhibited smooth surfaces. After the test, all films displayed increased roughness and wrinkles, particularly at higher TPS contents. These films revealed degradation of the film surface with high porosity within the 240-day timeframe, surpassing the degradation rate observed in the PLA film. These findings strongly suggest that PNT films have the potential to be biodegradable, even in a home compost (low-temperature) environment. The rapid degradation in the presence of TPS is potentially attributed to its hydrophilic nature, which facilitates soil water penetration into the film, thereby accelerating hydrolytic degradation and microbial assimilation. Additionally, the early degradation of TPS further exposes the film surface to soil, water, and microbes, maintaining a high rate of hydrolytic degradation45. The effect of TPS on faster biodegradation in this work is consistent with that found in the PLA/TPS system32, where Palai et al.32 reported a weight loss seven times higher for the PLA/20% TPS film (40.6%) compared to neat PLA film (5.8%) within three months at room temperature. The fast biodegradation of PNT films even in a home compost (low-temperature) environment shows promise as an environmentally friendly alternative for various packaging applications.

Surface appearance of neat PLA and PNT films before (day 0) and after 5-month and 8-month soil burial tests at room temperature.

This study systematically investigated the influence of TPS and peroxide treatment on the multifaceted properties of biodegradable PLA/NR/TPS (or PNT) films, focusing on surface morphology, mechanical properties, gas permeability, and biodegradability. The incorporation of TPS into the PLA/NR masterbatch (70:30 by weight) resulted in a reduction in tensile strength but an increase in % elongation at break and tensile toughness. The optimal TPS content for achieving the desired mechanical properties was found to be 10 wt%. The introduction of organic peroxide played a pivotal role in enhancing compatibility among the three phases by inducing chemical grafting between NR–PLA and NR–TPS interfaces. This chemical modification not only improved mechanical properties but also resulted in a smoother surface and lower oxygen permeability. The blend of PLA/NR masterbatch (70:30) with 10 wt% TPS and 0.5 wt% peroxide yielded the highest tensile toughness (7254.86 MJ/m3) and elongation at break (119.8%), along with good dispersion of TPS in PNT blends. Furthermore, the presence of TPS resulted in a significantly faster degradation of the PNT films in a home-compost environment. The developed PNT film has high potential as a low-cost, biobased, and biodegradable packaging film with a fast biodegradation rate in a home-compost environment.

Data sets generated during the current study are available from the corresponding author upon reasonable request.

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This work is financially supported by the Fundamental Fund (FF2567), Thailand Science Research and Innovation (TSRI), Thailand, 2024. The additional financial support from the research unit in polymer rheology and processing at Thammasat University. In addition, this study was supported by Thammasat Postdoctoral Fellowship.

Research Unit in Polymer Rheology and Processing, Department of Chemical Engineering, Thammasat School of Engineering, Faculty of Engineering, Thammasat University, Klong Luang, Pathumthani, Thailand

Tuchathum Tosakul, Peerapong Chanthot & Cattaleeya Pattamaprom

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Tuchathum Tosakul designed and conducted formulation, compounding, and film blowing experiments, collected and characterized data, prepared tables and figures, drafted the manuscript; Peerapong Chanthot designed and conducted biodegradation and gas permeation study, collected and characterized data, contributed in writing, reviewing and preparing figures and tables for the manuscript; Cattaleeya Pattamaprom formulated research ideas, analyzed the data, reviewed, edited, and finalized this manuscript. All authors read and approved the final manuscript.

Correspondence to Cattaleeya Pattamaprom.

The authors declare no competing interests.

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Tosakul, T., Chanthot, P. & Pattamaprom, C. High toughness and fast home-compost biodegradable packaging films derived from polylactic acid/thermoplastic starch/para-rubber ternary blends. Sci Rep 14, 18603 (2024). https://doi.org/10.1038/s41598-024-69508-y

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Received: 20 April 2024

Accepted: 06 August 2024

Published: 10 August 2024

DOI: https://doi.org/10.1038/s41598-024-69508-y

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