Utilization of bamboo biochar as a multi-functional filler of flexible poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) bioplastic

Biodegradable poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) triblock copolymer could potentially be used in bioplastic applications because it is more flexible than PLLA. However, investigations into modifying PLLA-PEG-PLLA with effective fillers are still required. In this work, bamboo biochar (BC) was used as an eco-friendly and cost-effective filler for the flexible PLLA-PEG-PLLA. The influences of BC addition on crystallization properties, thermal stability, hydrophilicity, and mechanical properties of the PLLA-PEG-PLLA were explored and compared to those of the PLLA. The PLLA-PEG-PLLA matrix and BC filler were found to have strong interfacial adhesion and good phase compatibility, while the PLLA/BC composites displayed weak interfacial adhesion and poor phase compatibility. For the PLLA-PEG-PLLA, the addition of BC induced a nucleation effect that was characterized by a decrease in the cold crystallization temperature from 76 to 71-75 °C and an increase in the crystallinity from 18.6 to 21.8-24.0%; however, this effect was not observed for the PLLA. When compared to pure PLLA-PEG-PLLA, the PLLA-PEG-PLLA/BC composites displayed greater thermal stability, tensile stress, and Young's modulus. Temperature at maximum decomposition rate (Td,max) of PLLA end-blocks increased from 315 to 319-342 °C. Ultimate tensile stress of PLLA-PEG-PLLA matrix improved from 14.5 to 16.2-22.6 MPa and Young's modulus increased from 220 to 280-340 MPa. Based on the findings, the crystallizability, thermal stability, and mechanical properties of the flexible PLLA-PEG-PLLA bioplastic were all enhanced by the use of BC as a multi-functional filler.

Thermal, Morphological, Mechanical, and Biodegradation Properties of Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide)/High-Density Polyethylene Blends

Polymer blends of poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) and high-density polyethylene (HDPE) with different blend ratios were prepared by a melt blending method. The thermal, morphological, mechanical, opacity, and biodegradation properties of the PLLA-PEG-PLLA/HDPE blends were investigated and compared to the PLLA/HDPE blends. The blending of HDPE improved the crystallization ability and thermal stability of the PLLA-PEG-PLLA; however, these properties were not improved for the PLLA. The morphology of the blended films showed that the PLLA-PEG-PLLA/HDPE blends had smaller dispersed phases compared to the PLLA/HDPE blends. The PLLA-PEG-PLLA/HDPE blends exhibited higher flexibility, lower opacity, and faster biodegradation and bioerosion in soil than the PLLA/HDPE blends. Therefore, these PLLA-PEG-PLLA/HDPE blends have a good potential for use as flexible and partially biodegradable materials.

Preparation of Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide)/Zinc Oxide Nanocomposite Bioplastics for Potential Use as Flexible and Antibacterial Food Packaging

High-molecular-weight poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) is a flexible and biodegradable bioplastic that has promising potential in flexible food packaging but it has no antibacterial ability. Thus, in this work, the effect of zinc oxide nanoparticles (nano-ZnOs) which have antimicrobial activity on various properties of PLLA-PEG-PLLA was determined. The addition of nano-ZnOs enhanced the crystallization, tensile, UV-barrier, and antibacterial properties of PLLA-PEG-PLLA. However, the crystallization and tensile properties of nanocomposite films decreased again as the nano-ZnO increased beyond 2 wt%. The nano-ZnO was well distributed in the PLLA-PEG-PLLA matrix when the nano-ZnO content did not exceed 2 wt% and exhibited some nano-ZnO agglomerates when the nano-ZnO content was higher than 2 wt%. The thermal stability and moisture uptake of the PLLA-PEG-PLLA matrix decreased and the film's opacity increased as the nano-ZnO content increased. The PLLA-PEG-PLLA/ZnO nanocomposite films showed good antibacterial activity against bacteria such as Escherichia coli and Staphylococcus aureus. It can be concluded that nano-ZnOs can be used as a multi-functional filler of the flexible PLLA-PEG-PLLA. As a result, the addition of nano-ZnOs as a nucleating, reinforcing, UV-screening, and antibacterial agent in the flexible PLLA-PEG-PLLA matrix may provide protection for both the food and the packaging during transportation and storage.

Improvement in Crystallization, Thermal, and Mechanical Properties of Flexible Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastic with Zinc Phenylphosphate

Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) shows promise for use in bioplastic applications due to its greater flexibility over PLLA. However, further research is needed to improve PLLA-PEG-PLLA's properties with appropriate fillers. This study employed zinc phenylphosphate (PPZn) as a multi-functional filler for PLLA-PEG-PLLA. The effects of PPZn addition on PLLA-PEG-PLLA characteristics, such as crystallization and thermal and mechanical properties, were investigated. There was good phase compatibility between the PPZn and PLLA-PEG-PLLA. The addition of PPZn improved PLLA-PEG-PLLA's crystallization properties, as evidenced by the disappearance of the cold crystallization temperature, an increase in the crystallinity, an increase in the crystallization temperature, and a decrease in the crystallization half-time. The PLLA-PEG-PLLA's thermal stability and heat resistance were enhanced by the addition of PPZn. The PPZn addition also enhanced the mechanical properties of the PLLA-PEG-PLLA, as demonstrated by the rise in ultimate tensile stress and Young's modulus. We can conclude that the PPZn has potential for use as a multi-functional filler for the PLLA-PEG-PLLA composite due to its nucleating-enhancing, thermal-stabilizing, and reinforcing ability.

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.

Improvement in Phase Compatibility and Mechanical Properties of Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide)/thermoplastic Starch Blends with Citric Acid

Flexible poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) block copolymer (PLLA-PEG-PLLA) bioplastic has been blended with low-cost thermoplastic starch (TPS) to prepare fully biodegradable bioplastics. However, the mechanical properties of PLLA-PEG-PLLA matrix decrease after the addition of TPS. In this work, citric acid (CA) was used as a compatibilizer to improve the phase compatibility and mechanical properties of PLLA-PEG-PLLA/TPS blends. TPS was first modified with CA (1.5 %wt, 3 %wt, and 4.5%wt) before melt blending with PLLA-PEG-PLLA. The PLLA-PEG-PLLA/modified TPS ratio was constant at 60/40 by weight. CA modification of TPS suppressed the crystallinity and enhanced the thermal stability of the PLLA-PEG-PLLA matrix, as determined through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The compatibility between the dispersed TPS and PLLA-PEG-PLLA phases was improved through modification of TPS with CA, as revealed by the smaller size of the co-continuous TPS phase from scanning electron microscopy (SEM) analysis. Increasing the hydrophilicity of the blends containing modified TPS confirmed the improvement in phase compatibility of the components. From the tensile test, the ultimate tensile strength, elongation at break, and Young's modulus of the blends increased with the CA content. In conclusion, CA showed a promising behavior in improving the phase compatibility and mechanical properties of PLLA-PEG-PLLA/TPS blends. These PLLA-PEG-PLLA/modified TPS blends have potential to be used as flexible bioplastic products.

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.

Renewable Polymers Derived from Limonene

Renewable natural and synthetic basic substances can be used to produce biodegradable polymers. Several methods of the polymerization of terpene limonene have been evaluated. The polymerization methods evaluated are radical polymerization, cationic polymerization and thiol-ene polymerization. The free-radical polymerization of limonene with azobisisobutyronitrile (AIBN) as an initiator was carried out. The cationic polymerization of limonene was carried out using AlCl3 as a catalyst. The copolymerization of limonene with mercaptoethanol, 2-mercaptoethyl ether without an initiator and with an AIBN initiator was studied and it was also shown that polymerization can proceed spontaneously. The resulting compounds were investigated by NMR and FTIR spectroscopy. The values of the molecular weight characteristics of the samples obtained are presented, such as: number-average molecular weight, hydrodynamic radius and characteristic viscosity, depending on the method of production. The coefficients α (molecular shape) in the Mark–Kuhn–Houwink equation are determined according to the established values of the characteristic viscosity. According to the values obtained, the AC molecules in solution have parameters α 0.14 to 0.26, which corresponds to a good solvent and the molecular shape-dense coil.

Phase Morphology, Mechanical, and Thermal Properties of Calcium Carbonate-Reinforced Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastics

Poly(L-lactide) (PLLA) is a promising candidate as a bioplastic because of its non-toxicity and biodegradability. However, the low flexibility of PLLA limits its use in many applications. Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-b-PEG-b-PLLA) block copolymer is of interest for bioplastic applications due to its superior flexibility compared to PLLA. The aim of this work is to modify PLLA-b-PEG-b-PLLA using a low-cost calcium carbonate (CaCO₃) filler to improve material properties compared to PLLA/CaCO₃ composites. The addition of CaCO₃ enhanced the crystallinity and thermal stability for the PLLA-b-PEG-b-PLLA matrix but not for the PLLA matrix, as determined by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). Phase morphology investigation using scanning electron microscopy (SEM) revealed that the interfacial adhesion between PLLA-b-PEG-b-PLLA and CaCO₃ was stronger than between PLLA and CaCO₃. Additionally, tensile testing was carried out to determine the mechanical properties of the composites. With the addition of CaCO₃, the tensile stress and Young's modulus of the PLLA-b-PEG-b-PLLA matrix were increased, whereas these properties of the PLLA matrix were significantly decreased. Thus, CaCO₃ shows great promise as an inexpensive filler that can induce nucleation and reinforcing effects for PLLA-b-PEG-b-PLLA bioplastics.

Synergistic effects of PEG middle-blocks and talcum on crystallizability and thermomechanical properties of flexible PLLA-b-PEG-b-PLLA bioplastic

In this study, talcum was melt-blended with a flexible poly(l-lactide)-b-polyethylene glycol-b-poly(l-lactide) triblock copolymer (PLLA-PEG-PLLA) with 1, 2, 4, and 8 wt% talcum, for improvement of the crystallization and thermomechanical properties of PLLA-PEG-PLLA compared with PLLA. The crystallizability of PLLA-PEG-PLLA/talcum composites was better than that of PLLA/talcum composites as determined from differential scanning calorimetry. X-ray diffractometry showed that the PLLA-PEG-PLLA/talcum films had a higher degree of crystallinity than the PLLA/talcum films. PEG middle-blocks and talcum showed a synergistic effect for crystallization of PLLA end-blocks. The PLLA-PEG-PLLA/talcum films showed better thermomechanical properties than those of the PLLA/talcum films as determined from dynamic mechanical analysis. This was confirmed from the results of dimensional stability to heat. In summary, the PLLA-PEG-PLLA/talcum composites have potential for use as flexible bioplastics with good dimensional stability to heat.

Electrically conductive and light-weight branched polylactic acid-based carbon nanotube foams

In spite of the high electrical conductivity of carbon nanotube (CNT), its tendency to aggregate and expensive cost in fabricating aerogel, foams, and porous materials remains a problem. Therefore, we described a simple and feasible way to design light-weight, high electrically conductive, and cost-efficient polylactic acid (PLA)/CNT foams. The branched PLA (BPLA) resin with excellent melt elasticity and foamability was induced by nucleophilic ring-opening reaction of epoxy-based acrylic/styrene copolymer and PLA. After that, BPLA/CNT composites and foams were prepared by melt-mixing and supercritical carbon dioxide foaming technology, respectively. The thermal, electrical, and foaming properties were studied. The resultant BPLA/CNT foam possessed a low density of 0.174 g/cm3 and high crystallinity of 3.03%. An improvement of the oriented structure of CNT induced by cell growth in BPLA matrix increased the conductivity of the foam up to 3.51 × 104 Ω/m. The proposed foaming materials provided a way for designing and preparing high performance CNT products.

Sustainable block copolymers of poly(limonene carbonate)

Ring-opening copolymerization of lactide/lactide derivatives and trans-limonene oxide is used for the synthesis of sustainable block copolymers. The method alters the properties of bio-based, non-food-based poly(limonene carbonate).