Manufacturing of Thermally Remoldable Blends from Epoxidized Soybean Oil and Poly(lactic acid) via Dynamic Cross-Linking in a Twin-Screw Extruder

Crosslinking-induced compatibility and toughness enhancement in poly(lactic acid)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blends with epoxidized soybean oil

Polylactide (PLA) is inherently brittle and lacks ductility, which greatly restricts its range of applications. In order to address these issues, we blended PLA with biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)), and introduced epoxidized soybean oil (ESBO) as a reactive modifier to enhance the properties of the PLA/P(3HB-co-4HB) blends. Furthermore, we used theoretical calculations, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Soxhlet extraction, differential scanning calorimetry (DSC), polarising optical microscopy (POM), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and mechanical testing to investigate the compatibility, crystallization behavior, microstructure, thermal and mechanical properties of the PLA/P(3HB-co-4HB)/ESBO blends. The mechanisms underlying these properties were analyzed in detail. ESBO was found to form cross-linking grafts between PLA and P(3HB-co-4HB), strengthening interfacial bonding and thereby enhancing compatibility. The in situ formation of graft copolymers resulted in finer, more uniform dispersion of P(3HB-co-4HB) and ESBO droplets within the PLA matrix, further improving interfacial adhesion and overall material compatibility. With the addition of 5 wt% ESBO, the tensile strain at break of PLA/P(3HB-co-4HB)/ESBO films increased from 114.6 % to 453.3 %, while the notched impact strength improved from 3.75 kJ∙m-2 to 8.75 kJ∙m-2, compared to PLA/P(3HB-co-4HB) films. However, excessive ESBO slightly decreases the mechanical performance of the material.

Fluorescent Polylactic acid composite incorporating lignin-based carbon quantum dots for sustainable 4D printing applications

Fluorescent 4D printing materials, as innovative materials that combine fluorescent characteristics with 4D printing technology, have attracted widespread interest and research. In this study, green lignin-derived carbon quantum dots (CQDs) were used as the fluorescent module, and renewable poly(propylene carbonate) polyurethane (PPCU) was used for toughening. A new low-cost fluorescent polylactic acid (PLA) composite filament for 4D printing was developed using a simple melt extrusion method. The strength of the prepared composite was maintained at 32 MPa, while the elongation at break increased 8-fold (34 % increase), demonstrating excellent shape fixed ratio (∼99 %), recovery ratio (∼92 %), and rapid shape memory recovery speed. The presence of PPCU prevented fluorescence quenching of the CQDs in the PLA matrix, allowing the composite to emit bright green fluorescence under 365 nm ultraviolet light. The composite exhibited shear thinning behavior and had an ideal melt viscosity for 3D printing. The results obtained demonstrated the versatility of these easy-to-manufacture and low-cost filaments, opening up a novel and convenient method for the preparation of strong, tough, and multifunctional PLA materials, increasing their potential application value.

Epoxidized Soybean Oil Toughened Poly(lactic acid)/Lignin-g-Poly(lauryl methacrylate) Bio-Composite Films with Potential Food Packaging Application

The application of lignin as a filler for poly (lactic acid) (PLA) is limited by their poor interfacial adhesion. To address this challenge, lignin-graft-poly(lauryl methacrylate) (LG-g-PLMA) was first blended with poly (lactic acid), and then epoxidized soybean oil (ESO) was also added to prepare PLA/LG-g-PLMA/ESO composite, which was subsequently hot pressed to prepare the composite films. The effect of ESO as a plasticizer on the thermal, mechanical, and rheological properties, as well as the fracture surface morphology of the PLA/LG-g-PLMA composite films, were investigated. It was found that the compatibility and toughness of the composites were improved by the addition of ESO. The elongation at break of the composites with an ESO content of 5 phr was increased from 5.6% to 104.6%, and the tensile toughness was increased from 4.1 MJ/m3 to 44.7 MJ/m3, as compared with the PLA/LG-g-PLMA composite without ESO addition. The toughening effect of ESO on composites is generally attributed to the plasticization effect of ESO, and the interaction between the epoxy groups of ESO and the terminal carboxyl groups of PLA. Furthermore, PLA/LG-g-PLMA/ESO composite films exhibited excellent UV barrier properties and an overall migration value below the permitted limit (10 mg/dm2), indicating that the thus-prepared biocomposite films might potentially be applied to environmentally friendly food packaging.

A generalizable reactive blending strategy to construct flame-retardant, mechanically-strong and toughened poly(L-lactic acid) bioplastics

Poly(L-lactic acid) (PLA) is an environmentally-friendly bioplastic with high mechanical strength, but suffers from inherent flammability and poor toughness. Many tougheners have been reported for PLA, but their synthesis usually involves organic solvents, and they tend to dramatically reduce the mechanical strength and cannot settle the flammability matter. Herein, we develop strong, tough, and flame-retardant PLA composites by reactive blending PLA, 6-((double (2-hydroxyethyl) amino) methyl) dibenzo [c, e] [1,2] oxyphosphate acid 6-oxide (DHDP) and diphenylmethane diisocyanate (MDI) and define it PLA/xGH, where x indicates that the molar ratio of -NCO group in MDI to -OH group in PLA and DHDP is 1.0x: 1. This fabrication requires no solvents. PLA/2GH with a -NCO/-OH molar ratio of 1.02: 1 maintains high tensile strength of 63.0 MPa and achieves a 23.4 % increase in impact strength compared to PLA due to the incorporation of rigid polyurethane chain segment. The vertical combustion (UL-94) classification and limiting oxygen index (LOI) of PLA/2GH reaches V-0 and 29.8 %, respectively, because DHDP and MDI function in gas and condensed phases. This study displays a generalizable strategy to create flame-retardant bioplastics with great mechanical performances by the in-situ formation of P/N-containing polyurethane segment within PLA.

Recent Approaches to the Plasticization of Poly(lactic Acid) (PLA) (A Review)

Poly(lactic acid) (PLA) is a polyester attracting growing interest every year in different application fields, such as packaging, cosmetics, food, medicine, etc. Despite its significant advantages, it has low elasticity that may hinder further development and a corresponding rise in volume of consumption. This review opens a discussion of basic approaches to PLA plasticization. These considerations include copolymerization and blending with flexible polymers, introducing oligomers and low-molecular additives, as well as structural modification. It was demonstrated that each approach has its advantages, such as simplicity and low cost, but with disadvantages, including complex processing and the need for additional reagents. According to the analysis of different approaches, it was concluded that the optimal option is the application of copolymers as the additives obtained via reactive mixing to PLA and its blends with other polymers.

Preparation of degradable chemically cross-linked polylactic acid films and its application on disposable straws

The semi-rigidity of the polylactic acid (PLA) molecular chain makes it brittle, poor impact resistance and barrier properties, which severely limits its practical applications. In this paper, a bio-based reactive plasticizer epoxy soybean oil (ESO) was used to improve the mechanical and barrier properties of maleic anhydride grafted polylactic acid (MAPLA) by the chemical reaction between the epoxy and anhydride group. Firstly, the optimum curing conditions were 93.5 °C, 100 °C, and 110.8 °C for 2 h. The effects of different mass fractions of ESO on the properties of MAPLA-ESO (ME) films were systematically investigated. It was found that when the content of ESO was 10 wt%, the tensile properties of the resulting ME films were the best, with a tensile strength of 35.2 MPa. And it had an elongation at break of 20.0 % and toughness of 5.4 MJ/m3, which increased to 690 % and 675 %, respectively, compared with pure MAPLA films. The chemically crosslinked ME films also displayed excellent water resistance, well degradation, low migration properties, and better performance than that of commercial paper straws and PLA straws, exhibiting great application potential as degradable disposable straws. Therefore, this work provides an effective way to develop high-performance, green, and degradable PLA films and products.

Grafting Polymerization of Long-Chain Hydrophobic Acrylic Monomer onto Lignin and Its Application in Poly(Lactic Acid)-Based Wholly Green UV Barrier Composite Films

The development of low-cost and high-performance bio-based composites derived from forestry waste lignin and polylactic acid has emerged as a topic of central attention. However, the weak compatibility between lignin and polylactic acid often resulted in high brittleness of the composites. Graft copolymerization is not only the most effective way to modify lignin but also can significantly improve the compatibility of lignin and polylactic acid. In this study, bio-based monomer lauryl methacrylate was grafted onto lignin by feasible radical polymerization to prepare lignin graft copolymers with excellent thermal stability and hydrophobicity, which are expected to improve the compatibility with polylactic acid. Wholly bio-based composites were prepared by compounding this graft copolymer with polylactic acid. The results showed that the crystallization ability of the composite was improved, and the highest crystallinity was increased from 6.42% to 17.46%. With addition of LG-g-PLMA lower than 9%, the thermal stability of the composites was slightly improved. At 5% copolymer addition, the elongation at break and tensile toughness of the composites increased by 42% and 36%, respectively. Observation of the frozen fracture surface of the composite by SEM found that wire drawing and ductile deformation appeared when a small amount of LG-g-PLMA was added. The thus prepared composites also showed excellent UV barrier properties. This approach provides a new idea for the high-value application of lignin.

In situ formation of PLA-grafted alkoxysilanes for toughening a biodegradable PLA stereocomplex thin film

Current work provides a synergistic approach to prepare super tough PLA without any significant loss of its excellent intrinsic mechanical properties.