Oligo(lactic acid)-grafted starch: A compatibilizer for poly(lactic acid)/thermoplastic starch blend

Design strategy for blends of biodegradable polyester and thermoplastic starch based on a molecular dynamics study of the phase-separated interface

Molecular insight into the phase-separated interface formed when biodegradable polyesters and thermoplastic starch (TPS) are melt-blended is valuable for the design of composites. In this study, eight different interfaces combining four major biodegradable polyesters (PLA, PBS, PHB and PBAT) and two TPSs [unmodified TPS (nTPS) and citrate-modified TPS (cTPS)] were investigated by using molecular dynamics (MD) simulations. According to the MD simulation results, PBS, PHB and PBAT diffuse readily into the TPS and form compatible interfaces, whereas PLA is less compatible with the TPS. The results of tensile simulations show that PBS and PBAT adhere well to TPS; in particular, PBS/cTPS and PBAT/cTPS exhibit high interfacial-fracture energy (G). Both PLA and PHB blended with TPS exhibit low G because PLA is less compatible with TPS and PHB and TPS have low electrostatic interaction. The reason for the high G of PBS/cTPS and PBAT/cTPS is thought to be a combination of three factors: (i) formation of a deep compatible interface, (ii) suppression of void growth by electrostatic interactions and (iii) absorption of strain energy by a change in the conformation of the molecular chains. These three interfacial adhesion mechanisms should be considered when designing biodegradable polyester/TPS blends with good mechanical properties.

Thermally-Activated Shape Memory Behavior of Biodegradable Blends Based on Plasticized PLA and Thermoplastic Starch

Biodegradable blends based on plasticized poly(lactic acid) PLA and thermoplastic starch (TPS) have been obtained. The influence of the PLA plasticizer as a compatibility agent has been studied by using two different plasticizers such as neat oligomeric lactic acid (OLA) and functionalized with maleic acid (mOLA). In particular, the morphological, thermal, and mechanical properties have been studied as well as the shape memory ability of the melt-processed materials. Therefore, the influence of the interaction between different plasticizers and the PLA matrix as well as the compatibility between the two polymeric phases on the thermally-activated shape memory properties have been studied. It is very interesting to use the same additive able to act as both plasticizer and compatibilizer, decreasing the glass transition temperature of PLA to a temperature close to the physiological one, obtaining a material suitable for potential biomedical applications. In particular, we obtain that OLA-plasticized blend (oPLA/TPS) show very good thermally-activated capability at 45 °C and 50% deformation, while the blend obtained by using maleic OLA (moPLA/TPS) did not show shape memory behavior at 45 °C and 50% deformation. This fact is due to their morphological changes and the loss of two well-distinguished phases, one acting as fixed phase and the other one acting as switching phase to typically obtain shape memory response. Therefore, the thermally-activated shape memory results show that it is very important to make a balance between plasticizer and compatibilizer, considering the need of two well-established phases to obtain shape memory response.

A natural butter glyceride as a plasticizer for improving thermal, mechanical, and biodegradable properties of poly(lactide acid)

Polylactic acid (PLA) is a biobased and biodegradable thermoplastic polyester with great potential to replace petroleum-based plastics. However, its poor toughness and slow biodegradation rate affect broad applications of PLA in many areas. In this study, a glycerol triester existing in natural butter, glycerol tributyrate, was creatively explored and compared with previously investigated triacetin and tributyl citrate, as potential plasticizers of PLA for achieving improved mechanical and biodegradation performances. The compatibilities of these agents with PLA were assessed quantitively via the Hansen solubility parameter (HSP) and measured by using different testing methods. The incorporation of these compounds with varied contents ranging from 1 to 30 % in PLA altered thermal, mechanical, and biodegradation properties consistently, and the relationship and impacts of chemical structures and properties of these agents were systematically investigated. The results demonstrated that glycerol tributyrate is a novel excellent plasticizer for PLA and the addition of this triester not only effectively reduced the glass transition, cold crystallization, and melting temperatures and Young's modulus, but also led to a significant improvement in the enzymatic degradation rate of the plasticized PLA. This study paves a way for the development of sustainable and eco-friendly food grade plasticized PLA products.

Heat-Induced Actuator Fibers: Starch-Containing Biopolyamide Composites for Functional Textiles

This study introduces the development of a thermally responsive shape-morphing fabric using low-melting-point polyamide shape memory actuators. To facilitate the blending of biomaterials, we report the synthesis and characterization of a biopolyamide with a relatively low melting point. Additionally, we present a straightforward and solvent-free method for the compatibilization of starch particles with the synthesized biopolyamide, aiming to enhance the sustainability of polyamide and customize the actuation temperature. Subsequently, homogeneous dispersion of up to 70 wt % compatibilized starch particles into the matrix is achieved. The resulting composites exhibit excellent mechanical properties comparable to those reported for soft and tough materials, making them well suited for textile integration. Furthermore, cyclic thermomechanical tests were conducted to evaluate the shape memory and shape recovery of both plain polyamide and composites. The results confirmed their remarkable shape recovery properties. To demonstrate the potential application of biocomposites in textiles, a heat-responsive fabric was created using thermoresponsive shape memory polymer actuators composed of a biocomposite containing 50 wt % compatibilized starch. This fabric demonstrates the ability to repeatedly undergo significant heat-induced deformations by opening and closing pores, thereby exposing hidden functionalities through heat stimulation. This innovative approach provides a convenient pathway for designing heat-responsive textiles, adding value to state-of-the-art smart textiles.

Molecular insight into toughening induced by core-shell structure formation in starch-blended bioplastic composites

Binary and ternary blends with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and thermoplastic starch (TPS) were prepared by a melt process to produce biodegradable biomass plastics with both economical and good mechanical properties. The mechanical and structural properties of each blend were evaluated. Molecular dynamics (MD) simulations were also conducted to examine the mechanisms underlying the mechanical and structural properties. PLA/PBS/TPS blends showed improved mechanical properties compared with PLA/TPS blends. The PLA/PBS/TPS blends with a TPS ratio of 25-40 wt% showed higher impact strength than PLA/PBS blends. Morphology observations showed that in the PLA/PBS/TPS blends, a structure similar to that of core-shell particles with TPS as the embedding phase and PBS as the coating phase was formed, and that the trends in morphology and impact strength changes were consistent. The MD simulations suggested that PBS and TPS tightly adhered to each other in a stable structure at a specific intermolecular distance. From these results, it is clear that PLA/PBS/TPS blends are toughened by the formation of a core-shell structure in which the TPS core and the PBS shell adhered well together and stress concentration and energy absorption occurred in the vicinity of the core-shell structure.

Property improvement of a thermoplastic starch/poly(butylene adipate-co-terephthalate) blown film by the addition of sodium nitrite

Recently, global awareness of the adverse environmental impacts of single-use plastics has risen due to their nonbiodegradability and likelihood of ending up in the ocean. Thermoplastic starch (TPS) is an alternative material employed for manufacturing single-use products because of its high biodegradability, nontoxicity, and low cost. However, TPS is moisture sensitive and has poor mechanical properties and processability. Blending TPS with biodegradable polyesters, including poly(butylene adipate-co-terephthalate) (PBAT), can expand its practical applications. This research aims to improve the performance of TPS/PBAT blends by adding sodium nitrite, a food additive, and considering its effect on the morphological characteristics and properties of TPS/PBAT blends. TPS/PBAT/sodium nitrite (TPS/PBAT/N) blends with a TPS:PBAT weight ratio of 40:60 and sodium nitrite concentrations of 0.5, 1, 1.5, and 2 wt% were prepared by extrusion and then blown into films. The acids generated from the sodium nitrite during extrusion led to the molecular weight reduction of starch and PBAT polymers, causing the increased melt flow ability of the TPS/PBAT/N blends. The incorporation of sodium nitrite improved the blends' homogeneity and the compatibility between the TPS and PBAT phases, resulting in the increased tensile strength, extensibility, impact strength, and oxygen barrier properties of the TPS/PBAT blend film.

The effect of polyethylene glycol sorbitan monostearate on the morphological characteristics and performance of thermoplastic starch/biodegradable polyester blend films

Although thermoplastic starch (TPS) has been developed to mitigate greenhouse gas emissions and environmental and health-related impacts from plastics, high moisture sensitivity and poor mechanical properties limited its practical applications. Blending TPS with biodegradable polyesters, i.e., poly(lactic acid) (PLA) and poly(butylene succinate-co-butylene adipate) (PBSA), is an alternative approach; however, the compatibility among polymer phases needs to be improved. Here, polyethylene glycol sorbitan monostearate (Tween 60), an amphiphilic surfactant, was proposed to improve the compatibility and performance of the TPS/PLA/PBSA 40/30/30 blend. The concentration of Tween 60 varied in the range of 0.5-2.5 wt%. The blends were fabricated using an extruder through two different melt-mixing routes, i.e., direct mixing and masterbatch mixing, and then converted to film using a blown film extrusion line. Tween 60 could improve compatibility between TPS dispersed phase and PLA/PBSA matrix, resulting in increased tensile strength, extensibility, impact strength, thermal stability, and water vapor and oxygen barrier properties of the ternary blend. In addition, better performance of the blend was obtained from the direct mixing route. Tween 60 could thus be considered a potential compatibilizer for the TPS/PLA/PBSA blend film, which can be further used as a biodegradable packaging material.

Preparation of flexible poly(l-lactide)-b-poly(ethylene glycol)-b-poly(l-lactide)/talcum/thermoplastic starch ternary composites for use as heat-resistant and single-use bioplastics

Poly(l-lactide)-b-poly(ethylene glycol)-b-poly(l-lactide) block copolymer (PLLA-PEG-PLLA) is a highly flexible bioplastic, yet its use in practical applications is limited due to its poor heat resistance and high production cost. In this study, talcum was used as a nucleating agent to improve the heat resistance, and thermoplastic starch (TPS) was used as a low-cost filler to reduce the cost of production. PLLA-PEG-PLLA/talcum/TPS and PLLA/talcum/TPS ternary composites with 4 wt% talcum and various TPS contents were prepared by melt blending before injection molding and were then evaluated. When PEG middle-blocks were present, the PLLA-PEG-PLLA-based composites showed a higher crystallinity, more flexibility, and a higher heat resistance than the PLLA-based composites. Although the addition of TPS decreased the heat resistance of all the composites, the PLLA-PEG-PLLA/talcum/TPS composites still had high Vicat softening temperatures (VST, 113-131 °C) and demonstrated a good dimensional stability to heat by maintaining their original shapes upon heat exposure. The biodegradation test in soil suggested that the synergistic effect of the PEG middle-blocks and TPS significantly increased the biodegradability of the PLLA-PEG-PLLA/talcum/TPS composites. This improved heat resistance, lower cost, and accelerated biodegradation make PLLA-PEG-PLLA/talcum/TPS composites a promising material to be used as heat-resistant and single-use bioplastic products.

Polymorphic Crystallization Behavior of a Poly(butylene adipate) Midblock within a Poly(L-lactide-butylene adipate-L-lactide) Triblock Copolymer

New biodegradable aliphatic PLLA-PBA-PLLA copolymers with soft poly(butylene adipate) (PBA) and hard poly(l-lactide) (PLLA) building blocks were synthesized via ring-opening polymerization (ROP). Proton nuclear magnetic resonance (¹HNMR) was utilized to confirm the volume fraction of PBA (f_PBA) within PLLA-PBA-PLLA. It was found that a PBA midblock (PBA-mid) within PLLA-PBA-PLLA-s (PLLA-PBA-PLLA triblock copolymer with a short PLLA block length) might display lamellar domain structure. However, PBA-mid within PLLA-PBA-PLLA-l (PLLA-PBA-PLLA triblock copolymer with a long PLLA block length) might locate itself as a nanoscale cylindrical domain surrounded by a PLLA continuous phase. Polymorphic crystals of PBA-mid within the PLLA-PBA-PLLA copolymers were formed after melt crystallization at the given temperatures, which were studied by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analysis. According to the WAXD and DSC analyses, it was interesting to find that the α-type crystal of PBA-mid was favorable to develop in the lower temperature region regardless of the state (crystallization or amorphous) of the PLLA component. Additionally, when the PLLA component was held in its amorphous state, it was easier for PBA-mid within the PLLA-PBA-PLLA copolymers to transform from the metastable β-form crystal to the stable α-form crystal. Furthermore, polarized optical microscopy (POM) photos provided direct evidence of the polymorphic crystals of PBA-mid within PLLA-PBA-PLLAs.

Recent Advances in Starch-Based Blends and Composites for Bioplastics Applications

Environmental pollution by synthetic polymers is a global problem and investigating substitutes for synthetic polymers is a major research area. Starch can be used in formulating bioplastic materials, mainly as blends or composites with other polymers. The major drawbacks of using starch in such applications are water sensitivity and poor mechanical properties. Attempts have been made to improve the mechanical properties of starch-based blends and composites, by e.g., starch modification or plasticization, matrix reinforcement, and polymer blending. Polymer blending can bring synergetic benefits to blends and composites, but necessary precautions must be taken to ensure the compatibility of hydrophobic polymers and hydrophilic starch. Genetic engineering offers new possibilities to modify starch inplanta in a manner favorable for bioplastics applications, while the incorporation of antibacterial and/or antioxidant agents into starch-based food packaging materials brings additional advantages. In conclusion, starch is a promising material for bioplastic production, with great potential for further improvements. This review summarizes the recent advances in starch-based blends and composites and highlights the potential strategies for overcoming the major drawbacks of using starch in bioplastics applications.

Effect of surfactant content on rheological, thermal, morphological and surface properties of thermoplastic starch (TPS) and polylactic acid (PLA) blends

Miscibility in biopolymeric blends is a critical process that requires evaluation of the effect of surfactants or coupling agents under conditions similar to processing. Different mixtures in the molten state of plasticized starch and polylactic acid in the presence of a surfactant (Tween 20) at different concentrations were studied. This allowed knowing the rheological, thermal and surface behavior of the mixtures. The results of the dynamic rheological analysis showed increases in viscosity in the presence of the surfactant, in which strong interactions were produced at high shear rates that reflect possible crosslinking between the polymer chains, in addition to intermolecular interactions that were evidenced in the infrared spectrum. Likewise, the storage and loss modulus showed transitions mainly from viscous to elastic typical for thermoplastics. The thermogravimetric analysis did not show significant changes between the mixtures. However, the calorimetric analysis showed changes in the crystallinity of the mixtures, the tensoactive promotes greater freedom of movement and rearrangements in the microstructure with decrease of interface between polymers, and less compaction of the material induced by the emulsion. Analysis derived from biopolymeric films against contact with water shows significant changes. Interaction with water in short times (in the order of minutes) according to the sessile drop technique, favors hydrophilicity by increasing the concentration of Tween 20. However, interaction with water for prolonged times (in the order of hours), shows that the absorption reaches saturation in samples a stabilization in the absorption is observed. The results demonstrate that the miscibility of PLA in AS was achieved in the presence of the tween, under conventional processing conditions. The stability of the different formulations allows the production of films for packaging and biomedical applications.

Improvement in Thermal Stability of Flexible Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastic by Blending with Native Cassava Starch

High-molecular-weight poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) triblock copolymer (PLLA-PEG-PLLA) is a promising candidate for use as a biodegradable bioplastic because of its high flexibility. However, the applications of PLLA-PEG-PLLA have been limited due to its high cost and poor thermal stability compared to PLLA. In this work, native cassava starch was blended to reduce the production cost and to improve the thermal stability of PLLA-PEG-PLLA. The starch interacted with PEG middle blocks to increase the thermal stability of the PLLA-PEG-PLLA matrix and to enhance phase adhesion between the PLLA-PEG-PLLA matrix and dispersed starch particles. Tensile stress and strain at break of PLLA-PEG-PLLA films decreased and the hydrophilicity increased as the starch content increased. However, all the PLLA-PEG-PLLA/starch films remained more flexible than the pure PLLA film, representing a promising candidate in biomedical, packaging and agricultural applications.

Valorization of Starch to Biobased Materials: A Review

Many concerns are being expressed about the biodegradability, biocompatibility, and long-term viability of polymer-based substances. This prompted the quest for an alternative source of material that could be utilized for various purposes. Starch is widely used as a thickener, emulsifier, and binder in many food and non-food sectors, but research focuses on increasing its application beyond these areas. Due to its biodegradability, low cost, renewability, and abundance, starch is considered a "green path" raw material for generating porous substances such as aerogels, biofoams, and bioplastics, which have sparked an academic interest. Existing research has focused on strategies for developing biomaterials from organic polymers (e.g., cellulose), but there has been little research on its polysaccharide counterpart (starch). This review paper highlighted the structure of starch, the context of amylose and amylopectin, and the extraction and modification of starch with their processes and limitations. Moreover, this paper describes nanofillers, intelligent pH-sensitive films, biofoams, aerogels of various types, bioplastics, and their precursors, including drying and manufacturing. The perspectives reveal the great potential of starch-based biomaterials in food, pharmaceuticals, biomedicine, and non-food applications.

Green starch/graphene oxide hydrogel nanocomposites for sustained release applications

Green nanocomposite hydrogels (ST-PHEMA/GO) comprised of starch and 2-Hydroxyethyl methacrylate (HEMA) reinforced with different ratios of graphene oxide (GO) were prepared via gamma radiation induced crosslinking polymerization. The chemical structure and morphology and the crystallinity were studied by FTIR FE-SEM, AFM, TEM and XRD, respectively. The swelling behavior of the claimed hydrogels was verified versus time and the pH-dependent swelling at three different irradiation dose:10, 20 and 30 kGy was also investigated. The results of the swelling study showed that the swelling capacity of the hydrogel networks varied with the changes of the pH of the solution, the GO content and the irradiation doses. Moreover, the swelling isotherm of all the prepared hydrogels followed a Fickian diffusion mechanism n < 0.5.

Graphical abstract

Development and Characterization of Polylactide Blends with Improved Toughness by Reactive Extrusion with Lactic Acid Oligomers

In this work, we report the development and characterization of polylactide (PLA) blends with improved toughness by the addition of 10 wt.% lactic acid oligomers (OLA) and assess the feasibility of reactive extrusion (REX) and injection moulding to obtain high impact resistant injection moulded parts. To improve PLA/OLA interactions, two approaches are carried out. On the one hand, reactive extrusion of PLA/OLA with different dicumyl peroxide (DCP) concentrations is evaluated and, on the other hand, the effect of maleinized linseed oil (MLO) is studied. The effect of DCP and MLO content used in the reactive extrusion process is evaluated in terms of mechanical, thermal, dynamic mechanical, wetting and colour properties, as well as the morphology of the obtained materials. The impact strength of neat PLA (39.3 kJ/m2) was slightly improved up to 42.4 kJ/m2 with 10 wt.% OLA. Nevertheless, reactive extrusion with 0.3 phr DCP (parts by weight of DCP per 100 parts by weight of PLA–OLA base blend 90:10) led to a noticeable higher impact strength of 51.7 kJ/m2, while the reactive extrusion with 6 phr MLO gave an even higher impact strength of 59.5 kJ/m2, thus giving evidence of the feasibility of these two approaches to overcome the intrinsic brittleness of PLA. Therefore, despite MLO being able to provide the highest impact strength, reactive extrusion with DCP led to high transparency, which could be an interesting feature in food packaging, for example. In any case, these two approaches represent environmentally friendly strategies to improve PLA toughness.

In Situ Chemical Modification of Thermoplastic Starch with Poly(L-lactide) and Poly(butylene succinate) for an Effectively Miscible Ternary Blend

Thermoplastic starch (TPS) is in situ ring-opening polymerized with L-lactide (L-LA) and directly condensed with a poly(butylene succinate) (PBS) prepolymer in an extruder using two different production pathways to demonstrate the concept “like dissolves like” in a miscible poly(lactide)/TPS/PBS (PLA/TPS/PBS) ternary blend. The TPS crystalline pattern changes from a V_H-type to an E_H-type after TPS modification with a hydrophobic-PLLA segment. Heteronuclear multiple-bond correlation confirmed the successful formation of PLLA-TPS-PBS copolymers via two different in situ chemical modification pathways (i.e., (I) step-by-step modification and (II) one-pot reaction). All obtained PLLA-TPS-PBS copolymers functioned as the miscible phase, enhancing PLA/PLLA-TPS-PBS/PBS ternary blend miscibility, especially the random structural PLLA-TPS-PBS-II copolymers created in an in situ one-pot reaction. However, the PLLA-TPS-PBS-I copolymers can enhance PBS crystallization only. While the random PLLA-TPS-PBS-II copolymers exhibit a homogeneous multi-phase dispersion and crystallization acceleration in both the PLA and PBS chains. Moreover, the storage modulus level of the PLA/PLLA-TPS-PBS-II/PBS ternary blend remains high with a downward temperature shift in the glass transition region, indicating a stronger and more flexible system. The practical achievement of in situ modified TPS and, consequently, a miscible PLA/PLLA-TPS-PBS/PBS ternary blend with favorable physical properties, reveal its potential application in both compostable and food contact packaging.

Poly(lactic acid)/thermoplastic cassava starch blends filled with duckweed biomass

Duckweed (DW) is a highly small, free-floating aquatic plant. It grows and reproduces rapidly, comprises mainly protein and carbohydrate, and has substantial potential as a feedstock to produce bioplastics due to its renewability and having very little impact on the food chain. The aim of this work was to analyze the effect of DW biomass on the characteristics and properties of bio-based and biodegradable plastics based on a poly(lactic acid)/thermoplastic cassava starch (PLA/TPS) blend. Various amounts of DW biomass were compounded with PLA and TPS in a twin-screw extruder and then converted into dumbbell-shaped specimens using an injection molding machine. The obtained PLA/TPS blends filled with DW biomass exhibited a lower melt flow ability, higher moisture content, and increased surface hydrophilicity than the neat PLA/TPS blend. Incorporation of DW with low concentrations of 2.3 and 4.6 wt% increased the tensile strength, Young's modulus, and hardness of the PLA/TPS blend. Moisture and glycerol from DW and TPS played important roles in reducing the T_g, T_cc, T_m, and T_d of PLA in the blends. The current work demonstrated that DW could be used as a biofiller for PLA/TPS blends, and the resulting PLA/TPS blends filled with DW biomass have potential in manufacturing injection-molded articles for sustainable, biodegradable, and short-term use.

Crystallization, Structure and Significantly Improved Mechanical Properties of PLA/PPC Blends Compatibilized with PLA-PPC Copolymers Produced by Reactions Initiated with TBT or TDI

Poly (lactic acid) (PLA)-Poly (propylene carbonate) (PPC) block copolymer compatibilizers are produced in incompatible 70wt%PLA/PPC blend by initiating transesterification with addition of 1% of tetra butyl titanate (TBT) or by chain extension with addition of 2% of 2,4-toluene diisocyanate (TDI). The above blends can have much better mechanical properties than the blend without TBT and TDI. The elongation at break is dramatically larger (114% with 2% of TDI and 60% with 1% of TBT) than the blend without TDI and TBT, with a slightly lower mechanical strength. A small fraction of the copolymer is likely formed in the PLA/PPC blend with addition of TBT, and a significant amount of the copolymer can be made with addition of TDI. The copolymer produced with TDI has PPC as a major content (~70 wt%) and forms a miscible interphase with its own Tg. The crystallinity of the blend with TDI is significantly lower than the blend without TDI, as the PLA blocks of the copolymer in the interphase is hardly to crystallize. The average molecular weight increases significantly with addition of TDI, likely compensating the lower mechanical strength due to lower crystallinity. Material degradation can occur with addition of TBT, but it is very limited with 1% of TBT. However, compared with the blends without TBT, the PLA crystallinity of the blend with 1%TBT increases sharply during the cooling process, which likely compensates the loss of mechanical strength due to the slightly material degradation. The added TDI does not have any significant impact on PLA lamellar packing, but the addition of TBT can make PLA lamellar packing much less ordered, presumably resulted from much smaller PPC domains formed in the blend due to better compatibility.

Comprehensive exploration of natural degradation of poly(lactic acid) blends in various degradation media: A review

Poly(lactic acid) (PLA), a bio-based polyester, has been extensively investigated in the recent past owing to its excellent mechanical properties. Several studies have been conducted on PLA blends, with a focus on improving the brittleness of PLA to ensure its suitability for various applications. However, the increasing use of PLA has increased the contamination of PLA-based products in the environment because PLA remains intact even after three years at sea or in soil. This review focuses on analyzing studies that have worked on improving the degradation properties of PLA blends and studies how other additives affect degradation by considering different degradation media. Factors affecting the degradation properties, such as surface morphology, water uptake, and crystallinity of PLA blends, are highlighted. In natural, biotic, and abiotic media, water uptake plays a crucial role in determining biodegradation rates. Immiscible blends of PLA with other polymer matrices cause phase separation, increasing the water absorption. The susceptibility of PLA to hydrolytic and enzymatic degradation is high in the amorphous region because it can be easily penetrated by water. It is essential to study the morphology, water absorption, and structural properties of PLA blends to predict the biodegradation properties of PLA in the blends.

Melt-processed poly (vinyl alcohol)/corn starch/nanocellulose composites with improved mechanical properties

Corn starch (CS) and cellulose nanofibrils (CNFs) were incorporated into biodegradable poly (vinyl alcohol) (PVA) to prepare mechanically robust and sustainable composites through melt-processing. Based on the regulation and control of hydrogen bonding network, CS and CNFs can extend the processing window and improve the thermoplasticity of PVA composites. Fourier transform infrared spectroscopy and Raman spectra analysis indicate that the intra- and inter-molecular hydrogen bonds of PVA are broken, accompanied by the formation of new hydrogen bonds among PVA, CS and CNFs during the melt-processing treatment. Thermal analysis shows that the processing window of PVA composite is significantly broadened to 131.46 °C. The tensile strength, modulus and elongation at break of the composites reach to 28.19 MPa, 1572.54 MPa and 10.72% by the incorporation of 10 wt% CS and 10 wt% CNFs. This strategy is not only expected to provide a direction for preparing complex three-dimensional products of PVA by melt-processing, but also provide a method to enhance the mechanical properties of other biodegradable plastics.

Structure and properties of in situ reactive blend of polylactide and thermoplastic starch

In this study, in situ reactive extrusion of polylactide and thermoplastic starch modified with chloropropyl trimethoxysilane coupling agent (PLA/mTPS) is proposed. The success of covalent bond formation between PLA matrix and mTPS phase is clarified by two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy with ¹H¹H TOCSY mode. This chemically bound PLA with starch gives the remarkable compatibility in the PLA/mTPS film, with not only a decreased glass transition temperature (47 °C) but also an increased crystallinity of PLA (Χ_c of 50%). It consequently increases oxygen barrier significantly and also enhances the film flexibility as observed from the drastic increase of elongation at break (from 3% to 50%). Moreover, the PLA/mTPS 60/40 (w/w) film exhibits the accelerated degradation as compared with pure PLA film.

High-Toughness Poly(Lactic Acid)/Starch Blends Prepared through Reactive Blending Plasticization and Compatibilization

In this study, poly(lactic acid) (PLA)/starch blends were prepared through reactive melt blending by using PLA and starch as raw materials and vegetable oil polyols, polyethylene glycol (PEG), and citric acid (CA) as additives. The effects of CA and PEG on the toughness of PLA/starch blends were analyzed using a mechanical performance test, scanning electron microscope analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray diffraction, rheological analysis, and hydrophilicity test. Results showed that the elongation at break and impact strength of the PLA/premixed starch (PSt)/PEG/CA blend were 140.51% and 3.56 kJ·m-2, which were 13.4 and 1.8 times higher than those of pure PLA, respectively. The essence of the improvement in the toughness of the PLA/PSt/PEG/CA blend was the esterification reaction among CA, PEG, and starch. During the melt-blending process, the CA with abundant carboxyl groups reacted in the amorphous region of the starch. The shape and crystal form of the starch did not change, but the surface activity of the starch improved and consequently increased the adhesion between starch and PLA. As a plasticizer for PLA and starch, PEG effectively enhanced the mobility of the molecular chains. After PEG was dispersed, it participated in the esterification reaction of CA and starch at the interface and formed a branched/crosslinked copolymer that was embedded in the interface of PLA and starch. This copolymer further improved the compatibility of the PLA/starch blends. PEGs with small molecules and CA were used as compatibilizers to reduce the effect on PLA biodegradability. The esterification reaction on the starch surface improved the compatibilization and toughness of the PLA/starch blend materials and broadens their application prospects in the fields of medicine and high-fill packaging.