Thermal Stability and Decomposition Mechanism of PLA Nanocomposites with Kraft Lignin and Tannin

Synthesis of novel L-lactic acid-based plasticizers and their effects on the flexibility, crystallinity, and optical transparency of poly(lactic acid)

Using bio-based plasticizers derived from biomass resources to replace traditional phthalates can avoid the biotoxicity and non-biodegradability caused by the migration of plasticizers during the application of plastics. In this study, L-lactic acid and levulinic acid were employed as the major biomass monomer to successfully fabricate L-lactic acid-based plasticizers (LBL-n, n = 1.0, 1.5, 2.0, 2.5) containing a diverse number of lactate groups. The plasticizing mechanism was explained, manifesting that L-lactic acid-based plasticizers containing a substantial number of lactate groups could effectively improve the flexibility of poly (lactic acid) (PLA), and the elongation at break was 590 %-750 %. Compared to LBL-1.5 plasticized-PLA films, the tensile strength and modulus of ketonized-LBL-1.5 (KLBL-1.5) plasticized-PLA films increased to 59 % and 163 %, indicating the ketal functionality of plasticizers enhanced the strength of PLA. Meanwhile, the increment of lactate groups and the introduction of the ketal group in the plasticizer increased the crystallization, migration, and volatilization stability of plasticized-PLA films and also kept their outstanding optical transparency. Besides, the biodegradability of KLBL-1.5 was investigated by active soil and Tenebrio molitor experiments, and its degradation products were characterized. The findings indicated that KLBL-1.5 was fully decomposed. Taken together, this paper offers new promise for developing high-efficiency and biodegradable plasticizers.

Analysis of thermal decomposition kinetics of chicken feather fiber reinforced Poly-lactic acid composites filament

Derivative Thermogravimetric analysis under air was used to observe the thermal decomposition process of Chicken feather fiber (CFF) reinforced Poly-lactic acid (PLA) composite filament of 2.2 mm diameter. The thermal degradation of the sample was initiated at 140 ֯C. Approximately 75 % of the thermal degradation occurred between the temperature of 357 ֯C and 399 ֯C. The composite's activation energy was established using the Coats-Redfern method. The results showed that the activation energy of 112.06 kJ/mol is utilized for the sample throughout the temperature range of 23 ֯C to 398 ֯C. A low activation energy is indicative of rapid chemical reactions between the CFF and PLA molecules. The results from TGA and DTGA indicate that the addition of CFF in the PLA matrix enhanced the thermal stability.

Recycled PLA for 3D Printing: A Comparison of Recycled PLA Filaments from Waste of Different Origins after Repeated Cycles of Extrusion

The objective of this work is to evaluate the reprocessing of PLA 3D printing waste from different origins, into filaments and films, and without the addition of any additive. Two types of waste were considered: a blend of different printing wastes (masks, visors, other components) of personal protective equipment coming from an association of Spanish coronamakers, and PLA waste from a single known commercial source. Both types of materials were subjected to repeated extrusion cycles and processed into films by compression molding. Samples were characterized after each cycle and their mechanical and viscosity properties evaluated. Diffusion-ordered NMR spectroscopy (DOSY) experiments were also carried out to estimate molecular weights. The results show a better performance for the PLA waste from the known origin, capable of withstanding up to three re-extrusion cycles per two for the waste blending, without significant degradation. Additionally, a model to address collection and mechanical recycling cycles under two different scenarios (full traceability and not full traceability) was proposed.

L-Poly(lactic acid) Production by Microwave Irradiation of Lactic Acid Obtained from Lignocellulosic Wastes

L-polylactic acid (PLA), a semi-crystalline aliphatic polyester, is one of the most manufactured biodegradable plastics worldwide. The objective of the study was to obtain L-polylactic acid (PLA) from lignocellulosic plum biomass. Initially, the biomass was processed via pressurized hot water pretreatment at a temperature of 180 °C for 30 min at 10 MPa for carbohydrate separation. Cellulase and the beta-glucosidase enzymes were then added, and the mixture was fermented with Lacticaseibacillus rhamnosus ATCC 7469. The resulting lactic acid was concentrated and purified after ammonium sulphate and n-butanol extraction. The productivity of L-lactic acid was 2.04 ± 0.18 g/L/h. Then, the PLA was synthesized in two stages. Firstly, lactic acid was subjected to azeotropic dehydration at 140 °C for 24 h in the presence of xylene, using SnCl₂ (0.4 wt.%) as a catalyst, resulting in lactide (CPLA). Secondly, microwave-assisted polymerization was carried out at 140 °C for 30 min with 0.4 wt.% SnCl₂. The resulting powder was purified with methanol to produce PLA with 92.1% yield. The obtained PLA was confirmed using electrospray ionization mass spectrometry, nuclear magnetic resonance, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. Overall, the resulting PLA can successfully replace the traditional synthetic polymers used in the packaging industry.

Exploration on ability of printable modified papers for the application in heat sublimation transfer printing of polyester fabric

In this work heat transfer papers were loaded with a new core-shell pigment based on precipitating thin shell of titanium dioxide on a core of rice husk silica ash TiO₂/RHSA to be applied in dye sublimation printing of textile fabrics. Besides, 0.1% (w/w) cationic polyacrylamide (CPAM) and 1% (w/w) bentonite (Bt) were also added sequentially to improve drainage and filler retention of the paper hand-sheets made from bleached kraft bagasse pulps. The effect of the new core-shell pigment on the mechanical and barrier properties, thermal stability and surface morphology of modified paper sheets were investigated. In addition, the study of transfer printability and ease of dye release from paper to fabric in this heat transfer printing of polyester fabrics using silk-screen printing under different transfer parameters were studied. Also, fastness measurements including washing, light and perspiration of printing polyester fabric were also estimated.

Recent Advances in the Investigation of Poly(lactic acid) (PLA) Nanocomposites: Incorporation of Various Nanofillers and their Properties and Applications

Poly(lactic acid) (PLA) is considered the most promising biobased substitute for fossil-derived polymers due to its compostability, biocompatibility, renewability, and good thermomechanical properties. However, PLA suffers from several shortcomings, such as low heat distortion temperature, thermal resistance, and rate of crystallization, whereas some other specific properties, i.e., flame retardancy, anti-UV, antibacterial or barrier properties, antistatic to conductive electrical characteristics, etc., are required by different end-use sectors. The addition of different nanofillers represents an attractive way to develop and enhance the properties of neat PLA. Numerous nanofillers with different architectures and properties have been investigated, with satisfactory achievements, in the design of PLA nanocomposites. This review paper overviews the current advances in the synthetic routes of PLA nanocomposites, the imparted properties of each nano-additive, as well as the numerous applications of PLA nanocomposites in various industrial fields.

Evaluating the Stability of PLA-Lignin Filament Produced by Bench-Top Extruder for Sustainable 3D Printing

As additive manufacturing continues to evolve, there is ongoing discussion about ways to improve the layer-by-layer printing process and increase the mechanical strength of printed objects compared to those produced by traditional techniques such as injection molding. To achieve this, researchers are exploring ways of enhancing the interaction between the matrix and filler by introducing lignin in the 3D printing filament processing. In this work, research has been conducted on using biodegradable fillers of organosolv lignin, as a reinforcement for the filament layers in order to enhance interlayer adhesion by using a bench-top filament extruder. Briefly, it was found that organosolv lignin fillers have the potential to improve the properties of polylactic acid (PLA) filament for fused deposition modeling (FDM) 3D printing. By incorporating different formulations of lignin with PLA, it was found that using 3 to 5% lignin in the filament leads to an improvement in the Young's modulus and interlayer adhesion in 3D printing. However, an increment of up to 10% also results in a decrease in the composite tensile strength due to the lack of bonding between the lignin and PLA and the limited mixing capability of the small extruder.

Synthesis and Characterization of Poly(lactic acid) Composites with Organosolv Lignin

Lignin, being one of the main structural components of lignocellulosic biomass, is considered the most abundant natural source of phenolics and aromatics. Efforts for its valorisation were recently explored as it is mostly treated as waste from heat/energy production via combustion. Among them, polymer-based lignin composites are a promising approach to both valorise lignin and to fine tune the properties of polymers. In this work, organosolv lignin, from beech wood, was used as fillers in a poly (lactic acid) (PLA) matrix. The PLA/lignin composites were prepared using melt mixing of masterbatches with neat PLA in three different lignin contents: 0.5, 1.0 and 2.5 wt%. Lignin was used as-isolated, via the organosolv biomass pretreatment/fractionation process and after 8 h of ball milling. The composites were characterised with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, X-ray Diffraction (XRD), and Differential Scanning Calorimetry (DSC). Additionally, their antioxidant activity was assessed with the 2,2-Diphenyil-1-picrylhydrazyl (DPPH) method, the colour was measured with a colorimeter and the mechanical properties were evaluated with tensile testing. Ball milling, at least under the conditions applied in this study, did not induce a further substantial decrease in the already relatively small organosolv lignin primary particles of ~1 μm. All the produced PLA/lignin composites had a uniform dispersion of lignin. Compression-moulded films were successfully prepared, and they were coloured brown, with ball-milled lignin, giving a slightly lighter colour in comparison with the as-received lignin. Hydrogen bonding was detected between the components of the composites, and crystallization of the PLA was suppressed by both lignin, with the suppression being less pronounced by the ball-milled lignin. All composites showed a significantly improved antioxidant activity, and their mechanical properties were maintained for filler content 1 wt%.

Do poly(lactic acid) microplastics instigate a threat? A perception for their dynamic towards environmental pollution and toxicity

Fears concerning microplastics (MPs) environmental fate and persistence are progressively expanding on a global basis, with the emphasis given to manufacturing bioplastics for substituting petro-derived plastics extensively growing. Among them, poly(lactic acid) (PLA) holds a pioneering role towards the replacement of conventional polymeric materials, owing to its multifunctional properties, enclosing superior mechanical properties, low cost, renewability, great biocompatibility, transparency, and thermoplasticity launching many fields of application. Due to the wide applicability of PLA in several sectors of everyday life, its waste to be released into the environment is expected to follow a growing tendency during the upcoming years. Even though PLA is a biodegradable polyester, it actually degrades under specific composting environments, including a rich oxygen environment with high temperatures (58-80 °C), high humidity (>60% moisture) as well as the presence of micro-organisms (thermophilic bacteria). Additionally, in various studies it has been implied that PLA displays slower degradation performance when found in blends with other conventional polymers, underlining the unspecified effects on PLA degradation profile, keeping thus the information about PLA degradation from a blur standpoint. Therefore, a deepened understanding of the fate and dynamic effects of PLA MPs is of primary importance. Nevertheless, the current examination of the effects of PLA MPs in terms of sorption capacities and toxicity is so far limited and broadly unexplored since the current scientific emphasis has been merely centered on the conventional MPs' behavior. In this light, the present review provides an inclusive overview of the ongoing research of poly(lactic acid) in the framework of microplastics' pollution, while the future trends and missing points in this context are highlighted.

Kraft Lignin/Tannin as a Potential Accelerator of Antioxidant and Antibacterial Properties in an Active Thermoplastic Polyester-Based Multifunctional Material

This research focuses on key priorities in the field of sustainable plastic composites that will lead to a reduction in CO₂ pollution and support the EU’s goal of becoming carbon neutral by 2050. The main challenge is to develop high-performance polyphenol-reinforced thermoplastic composites, where the use of natural fillers replaces the usual chemical additives with non-toxic ones, not only to improve the final performance but also to increase the desired multifunctionalities (structural, antioxidant, and antibacterial). Therefore, poly (lactic acid) (PLA) composites based on Kraft lignin (KL) and tannin (TANN) were investigated. Two series of PLA composites, PLA-KL and PLA-TANN, which contained natural fillers (0.5%, 1.0%, and 2.5% (w/w)) were prepared by hot melt extrusion. The effects of KL and TANN on the PLA matrices were investigated, especially the surface physicochemical properties, mechanical properties, and antioxidant/antimicrobial activity. The surface physicochemical properties were evaluated by measuring the contact angle (CA), roughness, zeta potential, and nanoindentation. The results of the water contact angle showed that neither KL nor TANN caused a significant change in the wettability, but only a slight increase in the hydrophilicity of the PLA composites. The filler loading, the size of the particles with their available functional groups on the surfaces of the PLA composites, and the interaction between the filler and the PLA polymer depend on the roughness and zeta potential behavior of the PLA-KL and PLA-TANN composites and ultimately improve the surface mechanical properties. The antioxidant properties of the PLA-KL and PLA-TANN composites were determined using the DPPH (2,2′-diphenyl-1-picrylhydrazyl) test. The results show an efficient antioxidant behavior of all PLA-KL and PLA-TANN composites, which increases with the filler content. Finally, the KL- and PLA-based TANN have shown resistance to the Gram-negative bacteria, E. coli, but without a correlation trend between polyphenol filler content and structure.