Poly( l -lactide- b -butylene succinate- b - l -lactide) triblock copolymer: A multi-functional additive for PLA/PBS blend with a key performance on film clarity

Crystallinity, Rheology, and Mechanical Properties of Low-/High-Molecular-Weight PLA Blended Systems

As semi-crystalline polyester (lactic acid) (PLA) is combined with other reinforcing materials, challenges such as phase separation, environmental pollution, and manufacturing difficulties could hinder the benefits of PLA, including complete biodegradability and strong mechanical properties. In the present investigation, melt blending is utilized to establish a mixture of low- and high-molecular-weight polylactic acids (LPLA and HPLA). The crystallinity, rheology, and mechanical properties of the combination were analyzed using rotational rheometry, differential scanning calorimetry, X-ray diffraction, polarized optical microscopy, scanning electron microscopy, and universal testing equipment. The results demonstrate compatibility between LPLA and HPLA. Moreover, an increase in LPLA concentration leads to a decrease in the crystallization rate, spherulite size, fractional crystallinity, and XRD peak intensity during isothermal crystallization. LPLA acts as a diluent during isothermal crystallization, whereas HPLA functions as a nucleating agent in the non-isothermal crystallization process, promoting the growth of LPLA crystals and leading to co-crystallization. The blended system with a 5% LPLA mass fraction exhibits the highest tensile strength and enhances rheological characteristics. By effectively leveraging the relationship between various molecular weights of PLA's mechanical, rheological, and crystallization behavior, this scrutiny improves the physical and mechanical characteristics of the material, opening up new opportunities.

Molecular dynamics simulations of copolymer compatibilizers for polylactide/poly(butylene succinate) blends

The effects of the molecular architecture of polylactide (PLA)-poly(butylene succinate) (PBS) copolymers on their compatibilization efficiency in immiscible PLA/PBS blends were studied using atomistic molecular-dynamics simulations. The results showed that the diblock copolymer is the most efficient at mixing with PLA and PBS homopolymers and reducing the interfacial tension of the blend. Tensile properties of the compatibilized blends were examined using uniaxial deformation simulations. Deformation behaviours of the blends at the molecular level were revealed. Both the structure (i.e. linear and branch) and the monomer sequence of the copolymers were found to affect the tensile performance. The system with a diblock copolymer showed a much greater tensile strength and elastic modulus than the other compatibilized blends. Comparing between triblock and graft copolymers, the former yielded the blends with better tensile performance than the latter. Our results suggest that copolymers with a linear structure, especially the diblock one, could be good candidates for the compatibilizer of PLA/PBS blends.

Poly(lactic acid)/Poly(butylene succinate) (PLA/PBS) Layered Composite Gas Barrier Membranes by Anisotropic Janus Nanosheets Compartibilizers

Poly(lactic acid) (PLA), one of the most promising biodegradable polymer products, has achieved wide applications for its relatively good mechanical properties and moderate degradability. Here we report an environment-friendly filler, the organic-inorganic composite Janus nanosheets (PLA/PBS JNs), which can jam at the interface of the PLA/PBS blend with a low threshold as the compatibilizer and can simultaneously toughen the composites and improve the gas barrier performance due to better interfacial interaction and tortuous path effect. With 0.3 wt % of PLA/PBS JNs added, the tensile strength and elongation at break of the PLA/PBS blend can be improved by 37% and 224%, respectively. After a further hot-pressing process, the barrier performance of the PLA/PBS composite membranes can be significantly enhanced since PLA, PLA/PBS JNs, and PBS are arranged in a nearly lamellar structure with oxygen permeability of 0.63 × 10^-15 cm³ cm·cm^-2 s^-1 Pa^-1 with only 0.5 wt % of PLA/PBS JNs.

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.

Synthesis, Properties, and Enzymatic Hydrolysis of Poly(lactic acid)-co-Poly(propylene adipate) Block Copolymers Prepared by Reactive Extrusion

Poly(lactic acid) (PLA) is a biobased polyester with ever-growing applications in the fields of packaging and medicine. Despite its popularity, it suffers from inherent brittleness, a very slow degradation rate and a high production cost. To tune the properties of PLA, block copolymers with poly(propylene adipate) (PPAd) prepolymer were prepared by polymerizing L-lactide and PPAd oligomers via reactive extrusion (REX) in a torque rheometer. The effect of reaction temperature and composition on the molecular weight, chemical structure, and physicochemical properties of the copolymers was studied. The introduction of PPAd successfully increased the elongation and the biodegradation rate of PLA. REX is an efficient and economical alternative method for the fast and continuous synthesis of PLA-based copolymers with tunable properties.

Recent advances in compatibility and toughness of poly(lactic acid)/poly(butylene succinate) blends

Poly(butylene succinate) (PBS) has good impact strength and high elongation at break. It is used to toughen biodegradable poly(lactic acid) (PLA) materials because it can considerably improve the toughness of PLA without changing the biodegradability of the materials. Therefore, this approach has become a hotspot in the field of biodegradable materials. A review of the physical and chemical modification methods that are applied to improve the performance of PLA/PBS blends based on recent studies is presented in this article. The improvement effect of PLA/PBS blends and the addition of some common fillers on the physical properties and crystallization properties of blends in the physical modification method are summarized briefly. The compatibilizing effects of nanofillers and compatibilizing agents necessary to improve the compatibility and toughness of PLA/PBS blends are described in detail. The chemical modification method involving the addition of reactive polymers and low-molecular-weight compounds to form cross-linked/branched structures at the phase interface during in situ reactions was introduced clearly. The addition of reactive compatibilizing components is an effective strategy to improve the compatibility between PLA and PBS components and further improve the mechanical properties and processing properties of the materials. It has high research value and wide application prospects in the modification of PLA. In addition, the degradation performance of PLA/PBS blends and the methods to improve the degradation performance were briefly summarized, and the development direction of PLA/PBS blends biodegradation performance research was prospected.

Poly(lactic acid) (PLA)/Poly(butylene succinate-co-adipate) (PBSA) Compatibilized Binary Biobased Blends: Melt Fluidity, Morphological, Thermo-Mechanical and Micromechanical Analysis

In this work poly(lactic) acid (PLA)/poly(butylene succinate-co-adipate) (PBSA) biobased binary blends were investigated. PLA/PBSA mixtures with different compositions of PBSA (from 15 up to 40 wt.%) were produced by twin screw-extrusion. A first screening study was performed on these blends that were characterized from the melt fluidity, morphological and thermo-mechanical point of view. Starting from the obtained results, the effect of an epoxy oligomer (EO) (added at 2 wt.%) was further investigated. In this case a novel approach was introduced studying the micromechanical deformation processes by dilatometric uniaxial tensile tests, carried out with a videoextensometer. The characterization was then completed adopting the elasto-plastic fracture approach, by the measurement of the capability of the selected blends to absorb energy at a slow rate. The obtained results showed that EO acts as a good compatibilizer, improving the compatibility of the rubber phase into the PLA matrix. Dilatometric results showed different micromechanical responses for the 80–20 and 60–40 blends (probably linked to the different morphology). The 80–20 showed a cavitational behavior while the 60–40 a deviatoric one. It has been observed that while the addition of EO does not alter the micromechanical response of the 60–40 blend, it profoundly changes the response of the 80–20, that passed to a deviatoric behavior with the EO addition.

Polylactide (PLA) and Its Blends with Poly(butylene succinate) (PBS): A Brief Review

Polylactide (PLA), poly(butylene succinate) (PBS) and blends thereof have been researched in the last two decades due to their commercial availability and the upcoming requirements for using bio-based chemical building blocks. Blends consisting of PLA and PBS offer specific material properties. However, their thermodynamically favored biphasic composition often restricts their applications. Many approaches have been taken to achieve better compatibility for tailored and improved material properties. This review focuses on the modification of PLA/PBS blends in the timeframe from 2007 to early 2019. Firstly, neat polymers of PLA and PBS are introduced in respect of their origin, their chemical structure, thermal and mechanical properties. Secondly, recent studies for improving blend properties are reviewed mainly under the focus of the toughness modification using methods including simple blending, plasticization, reactive compatibilization, and copolymerization. Thirdly, we follow up by reviewing the effect of PBS addition, stereocomplexation, nucleation, and processing parameters on the crystallization of PLA. Next, the biodegradation and disintegration of PLA/PBS blends are summarized regarding the European and International Standards, influencing factors, and degradation mechanisms. Furthermore, the recycling and application potential of the blends are outlined.

Effect of stereocomplex crystal and flexible segments on the crystallization and tensile behavior of poly(l-lactide)

Effect of stereocomplex crystal and PEG segments in blends on the crystallization and tensile behavior of PLLA.

Crystallization and Stereocomplexation of PLA-mb-PBS Multi-Block Copolymers

The crystallization and morphology of PLA-mb-PBS copolymers and their corresponding stereocomplexes were studied. The effect of flexible blocks (i.e., polybutylene succinate, PBS) on the crystallization of the copolymers and stereocomplex formation were investigated using polarized light optical microscopy (PLOM), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), and carbon-13 nuclear magnetic resonance spectroscopy (¹³C-NMR). The PLA and PBS multiple blocks were miscible in the melt and in the glassy state. When the PLA-mb-PBS copolymers are cooled from the melt, the PLA component crystallizes first creating superstructures, such as spherulites or axialites, which constitute a template within which the PBS component has to crystallize when the sample is further cooled down. The Avrami theory was able to fit the overall crystallization kinetics of both semi-crystalline components, and the n values for both blocks in all the samples had a correspondence with the superstructural morphology observed by PLOM. Solution mixtures of PLLA-mb-PBS and PLDA-mb-PBS copolymers were prepared, as well as copolymer/homopolymer blends with the aim to study the stereocomplexation of PLLA and PDLA chain segments. A lower amount of stereocomplex formation was observed in copolymer mixtures as compared to neat L₁₀₀/D₁₀₀ stereocomplexes. The results show that PBS chain segments perturb the formation of stereocomplexes and this perturbation increases with the amount of PBS in the samples. However, when relatively low amounts of PBS in the copolymer blends are present, the rate of stereocomplex formation is enhanced. This effect dissappears when higher amounts of PBS are present. The stereocomplexation was confirmed by FTIR and solid state ¹³C-NMR analyses.

Manufacturing and Characterization of Toughened Poly(lactic acid) (PLA) Formulations by Ternary Blends with Biopolyesters

Ternary blends with a constant poly(lactic acid) (PLA) content (60 wt %) and varying amounts of poly(3-hydroxybutyrate) (PHB) and poly(ε-caprolactone) (PCL) were manufactured by one step melt blending process followed by injection moulding, with the main aim of improving the low intrinsic toughness of PLA. Mechanical properties were obtained from tensile and Charpy impact tests. The miscibility and morphology of the system was studied by thermal analysis and field emission scanning electron microscopy (FESEM). The obtained results showed a clear phase separation, thus indicating poor miscibility between these three biopolyesters, i.e., PLA, the continuous component with dispersed PHB and PCL domains in the form of different sphere size. Nevertheless, the high fragility of PLA was remarkably reduced, as detected by the Charpy impact test. In accordance with the decrease in brittleness, a remarkable increase in elongation at break is achieved, with increasing PCL load due to its flexibility; in addition, increasing PCL load provides thermal stability at high temperatures. Thus, tailored materials can be manufactured by melt blending PLA, PHB, and PCL in different percentages to offer a wide range of biodegradable polymer blends.

Environmentally Friendly Compatibilizers from Soybean Oil for Ternary Blends of Poly(lactic acid)-PLA, Poly(ε-caprolactone)-PCL and Poly(3-hydroxybutyrate)-PHB

Ternary blends of poly(lactic acid) (PLA), poly(3-hydroxybutyrate) (PHB) and poly(ε-caprolactone) (PCL) with a constant weight percentage of 60%, 10% and 30% respectively were compatibilized with soybean oil derivatives epoxidized soybean oil (ESO), maleinized soybean oil (MSO) and acrylated epoxidized soybean oil (AESO). The potential compatibilization effects of the soybean oil-derivatives was characterized in terms of mechanical, thermal and thermomechanical properties. The effects on morphology were studied by field emission scanning electron microscopy (FESEM). All three soybean oil-based compatibilizers led to a noticeable increase in toughness with a remarkable improvement in elongation at break. On the other hand, both the tensile modulus and strength decreased, but in a lower extent to a typical plasticization effect. Although phase separation occurred, all three soybean oil derivatives led somewhat to compatibilization through reaction between terminal hydroxyl groups in all three biopolyesters (PLA, PHB and PCL) and the readily reactive groups in the soybean oil derivatives, that is, epoxy, maleic anhydride and acrylic/epoxy functionalities. In particular, the addition of 5 parts per hundred parts of the blend (phr) of ESO gave the maximum elongation at break while the same amount of MSO and AESO gave the maximum toughness, measured through Charpy’s impact tests. In general, the herein-developed materials widen the potential of ternary PLA formulations by a cost effective blending method with PHB and PCL and compatibilization with vegetable oil-based additives.