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Article

Study of Thermoplastic Starch/Poly (Butylene Succinate) Blends: The Effect of Reactive Compatibilizers

by
Ke Gong
1,2,*,
Yuanyuan Chen
1,
Yinshi Lu
1,
Zijian Zhao
1,
Alexandre Portela
3,
Han Xu
1,
Mengli Hu
4,
Handai Liu
1 and
Maurice N. Collins
2
1
Polymer, Recycling, Industrial, Sustainability and Manufacturing (PRISM), Athlone Campus, Technological University of Shannon: Midlands Midwest, N37 HD68 Athlone, Ireland
2
Bernal Institute and SFI BiOrbic, University of Limerick, V94 T9PX Limerick, Ireland
3
Department of Environment & Climate Action, Nenagh, Tipperary County Council, E45 YW31 Dublin, Ireland
4
College of Chemistry and Materials, Jiangxi Normal University, Nanchang 330022, China
*
Author to whom correspondence should be addressed.
Macromol 2025, 5(3), 42; https://doi.org/10.3390/macromol5030042
Submission received: 24 June 2025 / Revised: 7 August 2025 / Accepted: 8 September 2025 / Published: 11 September 2025
(This article belongs to the Special Issue Advances in Starch and Lignocellulosic-Based Materials)
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Abstract

Compatibilizers that enhance sustainability and improve the miscibility of polymer blend components have garnered significant attention. This study investigates the difference between the synthetic chain extender Joncryl® ADR 4468 and the natural epoxidized linseed oil (ELO) Merginat 8510100 as compatibilizers for thermoplastic starch/poly (butylene succinate) (TPS/PBS) blends. Blends containing 40% TPS and 60% PBS were prepared with 1, 3, and 5 phr of each compatibilizer, along with a reference with no additives. The properties of these blends were evaluated using tensile testing, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), rheology, and scanning electron microscopy (SEM). The findings indicate that while Joncryl® ADR 4468 significantly improved tensile strength, it also resulted in a brittle fracture. In contrast, ELO batches exhibited greater ductility, albeit with lower tensile strength. These differences are attributed to the chain extension and minor cross-linking effects of Joncryl® ADR 4468, compared to the increased chain mobility arising from ELO’s plasticizing and compatibilizing actions. Supporting evidence for these observations includes increased cold crystallization temperature (Tcc) and melting temperature (Tm), greater storage modulus along with higher complex viscosity, strengthened interfacial adhesion, and fewer morphological defects in Joncryl® ADR 4468 blends. These results highlight the importance of selecting an appropriate compatibilizer based on specific application requirements. Overall, this study addresses the knowledge gap regarding the loadings of Joncryl® ADR 4468 and ELO in TPS/PBS blends and provides a basis for further optimization strategies, such as the incorporation of binary compatibilizers, alternative grafting-based compatibilizers, and twin-screw blending modifications.

1. Introduction

The increasing emphasis on environmental sustainability within material science has driven extensive research into compatibilizers used in polymer blends, particularly those derived from both synthetic and natural sources. Joncryl® ADR 4468, a chemically synthesized compatibilizer, is widely recognized for its ability to enhance polymer blend performance by promoting crosslinking [1,2] and facilitating the formation of branched molecular structures [3,4]. However, concerns regarding the environmental and health impacts of such chain extenders have limited their applicability. Synthetic polymers, for example, are among the most persistent organic pollutants in marine ecosystems, where they can be ingested by aquatic organisms and accumulate within the food chain [5]. In response to these challenges, naturally derived alternatives, such as epoxidized linseed oil (ELO), have attracted increasing interest due to their environmentally benign characteristics [6,7,8]. These bio-based compatibilizers enhance the properties of polymer blends by acting as plasticizers and improving compatibility, particularly in systems involving immiscible polymers such as thermoplastic starch (TPS), polylactic acid (PLA), and poly (butylene succinate) (PBS) [9,10,11].
TPS is typically produced by disrupting the crystalline nature of native starch in presence of water and/or various plasticizers, including glycerol, sorbitol, and glucose [12,13]. The selection of specific plasticizers allows for the tailoring of TPS properties to suit diverse applications [14,15]. Due to its low cost, abundant availability, and biodegradability, TPS has been considered a promising alternative to conventional petroleum-based plastics [16,17,18]. However, its practical applications are constrained by its poor mechanical strength, low thermal stability, weak water vapor barrier properties, and susceptibility to aging [19,20,21]. To address these limitations while preserving its environmentally friendly nature, various strategies have been explored, including chemical modifications and material reinforcement [22]. Recent research has primarily focused on blending TPS with other biodegradable polymers, such as polylactic acid (PLA) [23]. For instance, Martin et al. [24] found that increasing the TPS content in TPS/PLA blends lowers the glass transition temperature (Tg) due to the poor compatibility between the components. Additionally, Ke et al. [25] further examined the impact of water content and heat treatment on TPS/PLA blends, reporting that higher water content enhances starch gelatinization, thereby reducing the extent to which TPS incorporates into the PLA matrix [26]. Additionally, Li et al. [13] compared the effects of sorbitol and glycerol as plasticizers in TPS/PLA blends, demonstrating that PLA forms the continuous phase while TPS forms the dispersed phase, with sorbitol exhibiting a more pronounced influence than glycerol. Furthermore, previous research has explored the effects of compatibilizers on blends, revealing a significantly finer dispersed phase size via chemical crosslinking [26,27,28,29] enhanced tensile strength [30,31] and improved particle surface morphology through amphiphilic bridging [32]. For example, the Joncryl® chain extender has been shown to enhance viscosity, melt strength, and processability in PLA/TPS blends [22,33]. Similarly, a relatively low content of maleinized linseed oil [34] and epoxidized thistle oil [35] have significantly improved the ductility and interfacial adhesion of TPS/PLA blends, respectively. These enhancements promote greater interfacial adhesion and reduce surface heterogeneity in composite films [36,37]. However, despite these advantages, materials modified with such compatibilizers often exhibit low elongation at break, which remains a challenge for further optimization.
Regarding PBS, this polymer can be blended with TPS to produce a material with enhanced mechanical properties, lower production costs, and an improved degradation rate compared to virgin TPS [9,38,39]. Nevertheless, the direct blending of TPS and PBS does not inherently result in optimal properties due to the strong hydrogen bonding and hydrophilic nature of TPS. To address these challenges, various studies have explored strategies to enhance the performance of TPS/PBS blends. For example, Yin et al. [40] incorporated recycled PBS (rPBS) into TPS/PBS blends, improving tensile strength, elongation at break, and water resistance by enhancing interfacial miscibility. Similarly, Zeng et al. [41] introduced rPBS containing terminal NCO groups into TPS, leading to a tenfold increase in tensile strength with 10 wt% rPBS compared to unmodified TPS. Li et al. [42] investigated the influence of waxy and normal corn starches on TPS/PBS blends, finding that waxy starch resulted in better processability, mechanical properties, and water resistance. Additionally, Li et al. [43] examined the dynamic rheological behavior of TPS/PBS blends, revealing that the TPS phase significantly affected rheological properties, with normal TPS exhibiting higher storage modulus and complex viscosity than waxy TPS. Boonprasith et al. [44] studied the incorporation of different clays into TPS/PBS blends and found that Cloisite 30B improved tensile properties, whereas Cloisite Na enhanced thermal stability. Fahrngruber et al. [45] investigated the role of hydrophilic and hydrophobic compatibilizers in TPS/PBS films, reporting that a TPS-based polyester compatibilizer improved TPS incorporation into the matrix, leading to greater tensile strength and tear resistance. These findings highlight the importance of compatibilization and material selection in optimizing the performance of TPS/PBS blends for various applications.
Despite recent advancements, a recent study focusing on the varied effects of Joncryl® ADR 4468 and epoxidized linseed oil (ELO) on the TPS/PBS blends was conducted and found a positive impact from Joncryl® ADR 4468 on the tensile strength and Young’s Modulus [46]. However, the performances of these blends may be tailored because of the loadings of both compatibilizer. Building on previous studies, this research employs varied loadings of Joncryl® 4468 and ELO 8510100 to compare their effects on the performance of 40%TPS/60%PBS blends. The primary objectives are to enhance compatibilization, address miscibility challenges, and assess the feasibility of using ELO as a sustainable substitute for the synthetic Joncryl® compatibilizer in the formulation of these blends.

2. Materials and Methods

2.1. Materials

The TPS pellets in the tradename of Solanyl® C1201 were purchased from Solanyl Rodenburg Corporation in Oosterhout, The Netherlands. The PBS pellets in the tradename of BioPBSTM (FZ91) were obtained from Mitsubishi Chemical Group Corporation in Tokyo, Japan. Joncryl® ADR 4468 (chain extender chemical) and Merginat epoxidized linseed oil (ELO) 8510100, were purchased from BASF SE Corporation, Ludwigshafen, Germany and HOBUM Oleochemicals GmbH Corporation in Hamburg, Germany, respectively. Their physical characteristics and chemical structures are displayed in Table 1, Table 2, and Figure 1, respectively.

2.2. Compounding

Both TPS and PBS pellets were initially dried overnight in an oven set at 40 °C to remove moisture. The Joncryl® ADR 4468 was first weighed in 1, 3 and 5 phr and then manually mixed with the compounded materials for 10 s. For ELO batches, a one-channel syringe pump filled with ELO was utilized to inject the amount in compounding from the vent of zone 5 under 0.7, 1.4, and 2.1 mL/min speed for 1, 3 and 5 phr volume. In addition, the composition of the composites is displayed in Table 3. In addition, both TPS and PBS were dried in the oven under 40 °C for 8 h prior to the processing.
An E-LAB 22 High-Temperature Twin Screw Compounder (EuroTech Extrusion Machinery SRL, Tradate, VA, Italy) was employed for the compounding stage. The temperature employed in zone 1 to zone 8 were 110 °C, 130 °C, 150 °C, 150 °C, 160 °C, 160 °C, 150 °C, and 150 °C, respectively. Following compounding, the raw materials were fed under 2 kg/h and then blended under 200 rpm screw speed. These compounded materials were first pushed out through the two-strand die and then cooled through the water bath and finally pelletized to granule forms.

2.3. Injection Molding

A Babyplast 6/12 Injection Molding Machine (Rambaldi Company, Molteno, Italy) with a 14 mm-diameter piston was employed to fabricate the tensile bars. The temperature set up for the plasticizing zone, chamber, and nozzle were 170 °C, 160 °C, and 150 °C, respectively. All IM parameters were first investigated under the preliminary trials and then carried in the production stage and were displayed as follows: shot size at 39 mm, cooling time at 30 s, injection pressure at 60 bar, injection pressure time at 2 s, holding pressure at 50 bar, holding pressure time at 5 s, holding pressure setting at 4 mm, decompression at 4 mm, injection speed at 50%, holding speed at 40%, and holding point at 4 mm.

2.4. Fourier Transform Infrared Spectroscopy (FTIR)

FTIR tests were conducted using a Thermo Fisher Scientific-ATR Nicolet iZ10 machine (Waltham, MA, USA) with a range scan from 500 cm−1 to 4000 cm−1, the test set up were 16 scans with a resolution of 4 [47].

2.5. Melt Flow Index (MFI)

Melt flow index values for these batches were determined subjective to ASTM D1238-10 [48] using a CEAST Melt Flow Quick Indexer (Instron, Norwood, MA, USA) under the fixed weight of 2.16 kg. The melted materials flowed through a 2.095 mm-diameter orifice and the values were reported in g/10 min. All the batches were tested under 150 °C [49].

2.6. Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) tests were conducted using 214 polyma machine (NETZSCH, Selb, Germany) for the thermal performances of all compounded materials. All specimens weighed ~8 mg were placed in non-perforated aluminum pans, with an empty crimped aluminum pan employed as the reference batch. These tested batches were first heated from 25 °C to 150 °C at the rate of 10 °C/min, kept at 150 °C for 3 min and then cooled to −50 °C at the rate of 5 °C/min. Subsequently, another heating process was carried in from −50 °C to 150 °C under the rate of 10 °C/min. The cold crystallization temperature (Tcc) and the melting temperature (Tm) were obtained during the cooling and second heating stage, respectively, [50]. The degrees of crystallinity of all blends were obtained using the equation below:
Xc (%) = (ΔHm − ΔHcc)/(ΔHm′ × w) × 100
where ΔHm and ΔHcc refer to the melting enthalpy and cold crystallization enthalpy of tested batches, respectively, ΔHm’ (J/g) refers to the melting enthalpy of PBS (110.3 J/g) and w is the weight fraction of PBS [51].

2.7. Rheological Test

A Discovery Hybrid Rheometer (Discovery RH 30, TA instrument, New Castle, DE, USA) with a 25 mm-diameter parallel plate was conducted to determine the linear viscoelastic region, where the following parameters were used: fixed strain amplitude at 1%, angular frequency range from 0.04 to 600 rad/s, printing temperature at 150 °C.

2.8. Tensile Test

The tensile specimens subjective to the ASTM D638-3 standard [52] were tested using a 2.5 kN Lloyd LRX Universal tester (Lloyd Instruments Ltd., Bognor Regis, UK) at the fixed speed of 50 mm/min in room temperature. A vernier caliper was applied to measure the dimensions of tensile bars. All experimental data were calculated using Nexygen Software (Version 15) to determine maximum tensile strength (σ), Young’s Modulus (E), and elongation value.

2.9. Fracture Observation

A scanning electron microscopy (TESCAN VEGA, Kohoutovice, Czech Republic) with the magnitude of X2000 was employed in this study to observe the fractured cross sections of tensile bars. All fractured sections were first gold coated using Agar sputter coater (Agar Scientific Ltd., Rotherham, UK).

2.10. Statistical Analysis

The experimental data obtained from tensile tests were analyzed using Minitab 22 software (Minitab LLC, State College, PA, USA) based on the analysis of variance (ANOVA) method. The p-value was employed here to determine the degree of significance of material variations. Differences were considered significant if a p value under 0.05 is obtained [53].

3. Results and Discussion

3.1. Fourier Transform Infrared Spectroscopy

The FTIR spectra of these blends loaded with different compatibilizers are presented in Figure 2. Notably, the absorption bands around 915 cm−1 correspond to the presence of epoxy groups [54,55]. Additionally, the wavenumber ranges from 1715.5 cm−1 to 1725.6 cm−1 and from 2944.8 cm−1 to 2948.9 cm−1 indicate the stretching vibrations of C=O and C–H (alkane) functional groups, respectively [15,56].
The addition of Joncryl® ADR 4468 and ELO notably influences the FTIR spectra of the finalized materials due to the differences in their chemical structures [46]. Joncryl® ADR 4468 is a multifunctional epoxy-functionalized oligomer designed specifically for reactive extrusion. Its relatively high epoxy functionality allows it to interact effectively with the terminal carboxyl and hydroxyl groups of polyesters, promoting chain extension and branching. This typically leads to increased molecular weight, enhanced melt strength, and improved mechanical properties [56,57]. In contrast, ELO is a natural, triglyceride-based epoxy compound with a lower epoxy functionality and less structural rigidity. While it does contain epoxy groups, its primary effect under our processing conditions appears to be plasticization rather than significant chemical compatibilization or chain extension. This is supported by the observed increase in MFI and decrease in tensile strength, which aligns with behavior typical of low-reactivity plasticizers [34]. For instance, indirect evidence of epoxy reactivity and its influence on the matrix can still be inferred from the spectral shifts and accompanying changes in material properties. For instance, the slight downshift of the epoxy group peak from 919.0 cm−1 to 913.6 cm−1, along with a minor C–H stretching shift, as the Joncryl® content increases from 0 to 5 phr, suggests chemical interaction and incorporation into the polymer network. In contrast, an increase in wavenumber can be observed in the ELO-modified blends, where it rises from 2944.8 cm−1 to 2948.9 cm−1, which is consistent with a stronger interaction in the molecular structure for the peak appearing at a lower wavenumber [58,59]. This difference can be attributed to the aliphatic chains in ELO, which introduce a plasticizing effect that enhances polymer matrix flexibility [46]. Regarding the interaction between ELO and the carboxyl group, an increase in wavenumber from 1715.5 cm−1 to 1724.3 cm−1 was expected [60], likely due to the formation of new ester linkages resulting from the reaction between epoxy and carboxyl groups [61].

3.2. Morphological Observation

Figure 3 illustrates the microstructure and interfacial adhesion of all blend formulations, highlighting the strong dependence of blend properties on phase morphology [41]. A comparison between Figure 3a–d reveals a progressive roughening of the fracture surface. This morphological change suggests improved interfacial interaction and enhanced phase compatibility, attributed to the increasing concentration of Joncryl® ADR 4468 [46,62,63]. Similar observations were reported by Zeng et al. [41], where the incorporation of NCO groups into PBS promoted stronger interfacial bonding. In contrast, Figure 3e–g show a transition from rough surfaces with visible voids and moderate phase separation to relatively smoother surfaces. Despite this, the presence of persistent voids and reduced cohesion between phases suggests weaker interfacial interaction [60]. These results indicate that increasing the concentration of ELO enhances its plasticizing effect and provides a slight improvement in interfacial adhesion. This is likely due to interactions between the hydroxyl groups in TPS and the terminal chain ends of PBS [34]. Moreover, the absence of brittle fracture features in the ELO-containing blends if compared to those with Joncryl® ADR 4468 further supports the notion of relatively improved interfacial adhesion in the presence of ELO [64]. However, at higher ELO concentrations (e.g., 5 phr), plasticizer saturation may occur, significantly increasing chain mobility. This results in greater intermolecular distances and diminished polymer–polymer interactions, ultimately reducing mechanical integrity [34,65]. In comparison, Joncryl® ADR 4468 promotes compatibilization through reactive interactions with PBS chain ends and hydroxyl groups in TPS, without inducing a lubricating or gel-like effect, thus maintaining a more structurally integrated interface.

3.3. Melt Flow Index

The melt flow index (MFI) results of blends incorporating different loadings of Joncryl® ADR 4468 and ELO exhibit significant variations in Table 4, reflecting the distinct compatibilization mechanisms of these additives. The 40-60-N/A displayed an MFI of 2.79 ± 0.25 g/10 min, serving as a baseline. With increasing Joncryl® content (1, 3, and 5 phr), the MFI decreased progressively to 1.93 ± 0.05, 1.67 ± 0.12, and 0.82 ± 0.03 g/10 min, respectively. This reduction suggests enhanced chain extension and possible branching reactions between Joncryl® ADR 4468’s epoxy groups and the hydroxyl or carboxyl terminals of TPS and PBS, leading to increased molecular weight and melt viscosity. Similar trends have been reported in prior studies, where multifunctional epoxies reduced MFI and improved interfacial adhesion in polyester-based blends [66,67].
Conversely, the incorporation of ELO resulted in increased MFI values: 4.15 ± 0.08, 5.19 ± 0.19, and 7.24 ± 0.46 g/10 min for 1, 3, and 5 phr, respectively. This behavior is attributed to the plasticizing effect of ELO, which decreases the melt viscosity by increasing polymer chain mobility and reducing intermolecular interactions [34,46,60]. Previous reports have demonstrated similar effects where vegetable oil-based epoxies, due to their flexible aliphatic chains, acted primarily as plasticizers in some starch-based materials [8,68]. Therefore, the opposite MFI trends observed with Joncryl® ADR 4468 and ELO indicate their distinct roles—chain extender versus plasticizer—within the TPS/PBS blend system. These results have implications for tailoring processing behavior and final mechanical properties depending on the compatibilizer used [69].

3.4. Differential Scanning Calorimetry

Table 5 presents the thermal performances for all blends, finding the crystalline structure of starch commonly exists in an amorphous state and the Tcc of all blends are highly related to PBS, which are in line with a previous study [70]. In addition, an increasing trend of Tcc and Tm values can be noticed in the Joncryl® ADR 4468 batches in comparison to the negative impact from ELO based on the increasing content, which is in line with the phenomena in the Joncryl® studies [63,71] and the linseed oil studies [34,60]. This increasing Tcc behavior shown in Joncryl® ADR 4468 batches can be explained from the branched chains after chain extension, which reduces the crystallization ability and results in the cold crystallization [71]. Regarding the decreasing trend of Tcc in ELO batches, this behavior can be attributed to the increasing chain mobility due to the plasticization effect, which leads to the crystallization under lower energy content and therefore results in a lower crystallization temperature [26]. As for the Tm values, a similar behavior can be noticed, where an increasing 0.6 °C difference can be found in Joncryl® ADR 4468 batches but a decreasing 0.5 °C trend finds in ELO batches. However, a Tm threshold (165.66 °C) can be noticed in the virgin PLA loaded with 0.8% Joncryl® ADR 4468, which is above 164.58 °C for 1% Joncryl® ADR 4468 batch and 164.55 °C for 1.2% Joncryl® ADR 4468 batch [71], which reveals attention for the further loading of Joncryl® ADR 4468 in the TPS-PBS blends.
Regarding the crystallinity of these blends, a positive effect can be noticed in function of the increasing loading of Joncryl® ADR 4468, from 14.28 to 19.90%. In addition, a tiny difference of Xc value for 40-60-N/A and 40-60-1CE can be observed in comparison with the next two levels (2.01% difference between 40-60-1CE and 40-60-3CE or 3.10% difference between 40-60-3CE and 40-60-5CE), which can be explained from the heterogeneous nucleation due to the chain extension effect from Joncryl® ADR 4468 [71]. As for the ELO batches, the degree of crystallinity finds an increasing trend in function of the improved chain mobility (ELO loadings). For example, the Xc value in 40-60-5ELO finds a 71.8% increase in comparison with the 40-60-N/A batch, which indicates a greater impact on the TPS/PBS blend in comparison to the virgin PLA (31.3% increase in degree of crystallinity for the batch loaded 5wt% ELO) [60].

3.5. Tensile Result

The mean values and standard deviations for tensile strength and Young’s Modulus are summarized in Table 6 for all the TPS-PBS blends. A comparison between the highest and lowest average values indicates that tensile strength is observed between 25.46 MPa and 32.64 MPa, with Young’s Modulus ranging from 541.21 MPa to 724.13 MPa, which depends on the compatibilizer strategies. These results highlight the differing influences of Joncryl® ADR 4468 and ELO on the mechanical properties of the blends. For example, the tensile strength of 40-60-N/A is 30.62 ± 0.16 MPa and the elongation at break is 68.82%. These values are then turning to 32.64 ± 0.17 MPa (6.6% increase) and 61.03% (11.3% decrease), respectively, under the loading of 5 phr Joncryl® ADR 4468. The results (Table 6 and Figure 4) reveal an increasing tendency of tensile strength based on the greater amount of Joncryl® ADR 4468 due to the crosslinking [72,73], and the elongation at break changes less [71]. The low standard deviations in tensile strength across the compatibilized blends suggest improved repeatability and consistency. Moreover, these results align with ANOVA findings, where the p-values for compatibilizer type and concentration are 0 and 0.024, respectively, confirming their statistically significant effects.
This decrease in elongation at break can be explained from the lamellar structure shown in Figure 3b–d, where a rougher interface of the composite can be obtained based on the increasing Joncryl® ADR 4468 loadings. Meanwhile, the increasing Young’s Modulus values in function of the increasing Joncryl® ADR 4468 loading (from 651.29 ± 27.23 to 724.13 ± 14.33 MPa) is attributed to the large dispersion of molecular weight, which offers closer contact between molecular chains and the enhanced resistance to external forces [71,74]. The ANOVA analysis for Young’s Modulus further supports these observations, with p-values of 0 and 0.009 for compatibilizer type and concentration, respectively, indicating their statistically significant influence.
In addition, an improved ductile performance can be noticed in the ELO-loaded blends, even though a lower tensile strength and Young’s Modulus can be expected. For example, 40-60-5ELO finds a decrease in tensile strength of 16.9% with regard to 40-60-N/A. Similar phenomenon can be noticed by Silverajah et al. [64], where a 36.3% decrease in tensile strength can be observed in 5 wt% epoxidized palm olein with regard to the neat PLA. Nevertheless, the enhanced ductile properties by ELO loadings (from 68.82% elongation at break for 40-60-N/A to 91.42% for 40-60-3ELO) are consistent with Ferri et al. [75], where a 5 phr octyl epoxy stearate (OES) triggers to the highest elongation at break in the range of 5–20 phr. This behavior can be explained from the phase separation shown in Figure 3g compared with (e) and (f), where an increased chain mobility and intermolecular mobility can be obtained due to the lubricant effect and free volume from ELO [76,77].

3.6. Rheological Result

Rheological tests were conducted to determine the storage modulus (G’) and complex viscosity (η*) of all blends, as shown in Figure 5a,b. Storage modulus indicates elastic behavior or the stored energy in the material. Figure 5a finds an increasing addition of Joncryl® ADR 4468 results in a greater storage modulus for these blends. Nevertheless, a negative impact of ELO can be observed in Figure 5a, with a lower storage modulus observed as ELO content rises. These phenomena agree with the aforementioned tensile performances that the addition of Joncryl® ADR 4468 can improve the tensile strength and Young’s Modulus of blended materials, whereas a negative impact on both terms can be expected under the addition of ELO.
In case of complex viscosity, results indicate shear-thinning behaviors across all batches, characterized by a decrease in viscosity under high shear rates and an increase during the cooling and solidification stages of injection molding, which can be expected to enhance the mechanical performance of these blends [78]. All blended materials exhibit a reduction in complex viscosity with increasing angular frequency in Figure 5b. In addition, a more noticeable tendency can be obtained here, where the complex viscosity can be increased with the addition of more Joncryl® ADR 4468 and shows a decrease with higher ELO content. This phenomenon is consistent with the tensile performance, indicating that a high concentration of Joncryl® ADR 4468 can effectively act as a compatibilizer to achieve the chain extension and therefore improve the processability [66]. Regarding the ELO batches, a reduced viscosity can be observed, indicating an improved flow property of finalized material. This phenomenon can be explained from two claims: (a) the Joncryl® ADR 4468 results in a stronger molecular interaction and less mobile polymer chains and (b) the addition of ELO increases the chain mobility since it acts as a typical plasticizer with a lubricant effect.

4. Conclusions

This study investigates the effects of two compatibilizers, Joncryl® ADR 4468 and epoxidized linseed oil (ELO), on the TPS 40%–PBS 60% blend under three conditions: (a) without compatibilizer, (b) with Joncryl® ADR 4468 at concentrations of 1, 3, and 5 phr, and (c) with ELO at concentrations of 1, 3, and 5 phr. All formulations were processed using a twin-screw extruder. The properties of the resulting blends were evaluated through Fourier Transform Infrared Spectroscopy (FTIR), morphological characterization, Melt Flow Index (MFI), differential scanning calorimetry (DSC), tensile testing, and rheological analysis.
Tensile testing revealed that Joncryl® ADR 4468 induced enhanced tensile strength, increasing from 30.6 to 32.6 MPa. Conversely, ELO incorporation led to moderate reductions in strength from 30.6 to 25.5 MPa. A comparable trend was observed in Young’s Modulus, with Joncryl® 4468 blends exhibiting incremental increases, whereas ELO blends displayed declining values. Fracture behavior analysis indicated brittle failure in uncompatibilized and Joncryl® 4468 blends, contrasted by ductile deformation in ELO ones. DSC analysis demonstrated suppressed cold crystallization (Tcc) and melting temperatures (Tm) with higher ELO loading, alongside elevated crystallinity for both additives. Rheological assessments revealed enhanced storage moduli in Joncryl® 4468 blends, potentially attributable to chain extension or entanglement effects. In contrast, ELO-modified blends exhibited improved chain mobility, promoting elongation and toughness, likely due to polar interactions enhancing flexibility—a finding corroborated by fracture surface morphology.
In conclusion, both compatibilizers improved interfacial compatibility in TPS/PBS blends, albeit through distinct mechanisms. Joncryl® ADR 4468 enhanced mechanical rigidity and strength, while ELO favored ductility and toughness. Synergistic applications of these compatibilizers may optimize blend performance. Future investigations could explore binary compatibilizer systems, graft-based compatibilization strategies, or advanced extrusion protocols to further refine blend properties.

Author Contributions

Conceptualization, K.G., Y.C. and M.N.C.; methodology, K.G., Y.L., Z.Z., A.P. and H.X.; software, K.G., Y.L. and A.P.; validation, K.G., Y.L. and H.L.; formal analysis, K.G., M.H. and H.L.; investigation, K.G., Y.C. and M.N.C.; resources, K.G., Y.C. and M.N.C.; data curation, K.G. and M.H.; writing—original draft preparation, K.G., Y.C. and M.N.C.; writing—review and editing, K.G., Y.C. and M.N.C.; visualization, K.G., H.X. and M.H.; supervision, K.G., Y.C. and M.N.C.; project administration, K.G., Y.C. and M.N.C.; funding acquisition, Y.C. and M.N.C. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by Research Ireland (SFI22/NCF/HE/1142) and MAGICBIOMAT (HE101181381).

Data Availability Statement

The data presented in this study are available on request from the corresponding author since the data are part of an ongoing research.

Acknowledgments

The authors would like to acknowledge the support they received from the staff in Applied Polymer Technology and Centre for Industrial Services and Design in Technological University of Shannon: Midlands and Midwest.

Conflicts of Interest

The authors declare no conflicts of interest.

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Macromol 05 00042 g001
Figure 1. Chemical structures of (a) Joncryl® ADR 4468 and (b) ELO.
Figure 1. Chemical structures of (a) Joncryl® ADR 4468 and (b) ELO.
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Figure 2. FTIR spectra of TPS 40%–PBS 60% blends in function of compatibilizers.
Figure 2. FTIR spectra of TPS 40%–PBS 60% blends in function of compatibilizers.
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Figure 3. SEM observations for the fractured cross sections of batches under varied conditions at 2000× magnification: (a) without compatibilizer, (b) 1 phr Joncryl® ADR 4468, (c) 3 phr Joncryl® ADR 4468, (d) 5 phr Joncryl® ADR 4468, (e) 1 phr ELO, (f) 3 phr ELO, and (g) 5 phr ELO.
Figure 3. SEM observations for the fractured cross sections of batches under varied conditions at 2000× magnification: (a) without compatibilizer, (b) 1 phr Joncryl® ADR 4468, (c) 3 phr Joncryl® ADR 4468, (d) 5 phr Joncryl® ADR 4468, (e) 1 phr ELO, (f) 3 phr ELO, and (g) 5 phr ELO.
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Figure 4. Stress–strain curves for the blends in function of compatibilizers.
Figure 4. Stress–strain curves for the blends in function of compatibilizers.
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Figure 5. Rheology performances of TPS-PBS blends in function of added compatibilizers: (a) storage modulus and (b) complex viscosity.
Figure 5. Rheology performances of TPS-PBS blends in function of added compatibilizers: (a) storage modulus and (b) complex viscosity.
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Table 1. Characteristics of Joncryl® ADR 4468.
Table 1. Characteristics of Joncryl® ADR 4468.
CharacteristicsValues
Specific Gravity, 25 °C (g/cm3)1.08
MW (Ave)7300
Tg (°C)59
Non-volatile by GC (%)>99
Epoxy equivalent weight (g/mol)310
Table 2. Characteristics of Merginat epoxidized linseed oil (ELO) 8510100.
Table 2. Characteristics of Merginat epoxidized linseed oil (ELO) 8510100.
CharacteristicsValues
Melting Point (°C)−5–1
Viscosity, 25 °C (mPa·s)899–1200
Water Solubility, 20 °C (mg/L)0.421–1.780
Density, 25 °C (g/cm3)1.031–1.038
Vapor Pressure, 25 °C, (Pa)≤0.000017
Table 3. Blended TPS/PBS compositions.
Table 3. Blended TPS/PBS compositions.
BatchComponent CompositionCompatibilizer
TPS (%)PBS (%)
40-60-N/A4060No Compatibilizer
40-60-1CE40601 phr Joncryl® ADR 4468
40-60-3CE40603 phr Joncryl® ADR 4468
40-60-5CE40605 phr Joncryl® ADR 4468
40-60-1ELO40601 phr Epoxidized Linseed Oil
40-60-3ELO40603 phr Epoxidized Linseed Oil
40-60-5ELO40605 phr Epoxidized Linseed Oil
Table 4. MFI results for all blends.
Table 4. MFI results for all blends.
BatchMFI (g/10 min)
40-60-N/A2.79 ± 0.25
40-60-1CE1.93 ± 0.05
40-60-3CE1.67 ± 0.12
40-60-5CE0.82 ± 0.03
40-60-1ELO4.15 ± 0.08
40-60-3ELO5.19 ± 0.19
40-60-5ELO7.24 ± 0.46
Table 5. DSC results of blends in function of cold crystallization temperature (Tcc), melting temperature (Tm), melting enthalpy (ΔHm), cold crystallization enthalpy (ΔHcc), and degree of crystallinity (Xc).
Table 5. DSC results of blends in function of cold crystallization temperature (Tcc), melting temperature (Tm), melting enthalpy (ΔHm), cold crystallization enthalpy (ΔHcc), and degree of crystallinity (Xc).
BatchTcc (°C)Tm (°C)ΔHm (J/g)ΔHcc (J/g)Xc (%)
40-60-N/A88.1115.145.5836.1314.28
40-60-1CE88.3115.446.2136.4214.79
40-60-3CE88.6115.647.3536.2316.80
40-60-5CE88.7115.748.4135.2419.90
40-60-1ELO8811543.2332.7415.85
40-60-3ELO87.7114.847.1133.1321.12
40-60-5ELO87.6114.651.7535.5124.54
Table 6. Tensile results for all TPS-PBS blends.
Table 6. Tensile results for all TPS-PBS blends.
BatchTensile Strength (MPa)Young’s Modulus (MPa)Elongation at Break (%)
40-60-N/A30.6 ± 0.2651.3 ± 27.268.8
40-60-1CE31.3 ± 0.3688.2 ± 19.365.8
40-60-3CE32.1 ± 0.1701.2 ± 16.563.0
40-60-5CE32.6 ± 0.2724.1 ± 14.361.0
40-60-1ELO29.7 ± 0.4627.6 ± 12.985.9
40-60-3ELO27.8 ± 0.3584.2 ± 14.291.4
40-60-5ELO25.5 ± 0.3541.2 ± 11.078.5
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Gong, K.; Chen, Y.; Lu, Y.; Zhao, Z.; Portela, A.; Xu, H.; Hu, M.; Liu, H.; Collins, M.N. Study of Thermoplastic Starch/Poly (Butylene Succinate) Blends: The Effect of Reactive Compatibilizers. Macromol 2025, 5, 42. https://doi.org/10.3390/macromol5030042

AMA Style

Gong K, Chen Y, Lu Y, Zhao Z, Portela A, Xu H, Hu M, Liu H, Collins MN. Study of Thermoplastic Starch/Poly (Butylene Succinate) Blends: The Effect of Reactive Compatibilizers. Macromol. 2025; 5(3):42. https://doi.org/10.3390/macromol5030042

Chicago/Turabian Style

Gong, Ke, Yuanyuan Chen, Yinshi Lu, Zijian Zhao, Alexandre Portela, Han Xu, Mengli Hu, Handai Liu, and Maurice N. Collins. 2025. "Study of Thermoplastic Starch/Poly (Butylene Succinate) Blends: The Effect of Reactive Compatibilizers" Macromol 5, no. 3: 42. https://doi.org/10.3390/macromol5030042

APA Style

Gong, K., Chen, Y., Lu, Y., Zhao, Z., Portela, A., Xu, H., Hu, M., Liu, H., & Collins, M. N. (2025). Study of Thermoplastic Starch/Poly (Butylene Succinate) Blends: The Effect of Reactive Compatibilizers. Macromol, 5(3), 42. https://doi.org/10.3390/macromol5030042

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