Self-Formation of Lignin Particles Through Melt-Extrusion for Active Biodegradable Food Packaging.

This study presents a method for the self-formation of lignin particles within a polylactic acid (PLA) matrix during melt-extrusion, eliminating the need for separation and drying steps typically associated with submicro-size lignin particles. This method effectively mitigates the problem of agglomeration often associated with the drying step. Softwood kraft lignin, guaiacyl lignin (GL-lignin), was dissolved in low-molecular-weight poly(ethylene glycol) (PEG) and was introduced into a twin-screw extruder using a liquid feeder. Lignin particles within a particle size range of 200-500 nm were observed in the extrudate of the PLA/PEG/GL-lignin composites. PLA/PEG/GL-lignin composite films were produced through blown film extrusion. These composite films demonstrated superior ultraviolet (UV)-barrier and antioxidant properties compared to neat PLA films, with optical and mechanical characteristics comparable to those of neat PLA. Moreover, migration values of the composite films in various food simulants were below regulatory limits, suggesting their potential for food packaging applications. This self-formation process offers a promising approach for utilizing lignin for PLA applications.

Preparation of High-Toughness Cellulose Nanofiber/Polylactic Acid Bionanocomposite Films via Gel-like Cellulose Nanofibers.

This study demonstrates a procedure for preparing gel-like cellulose nanofibers (CNFs) in polyethylene glycol (PEG) to toughen polylactic acid (PLA) nanocomposite films. A well-dispersed solution of CNFs in ethanol was produced from microcrystalline cellulose by using a high-pressure microfluidizer. The fiber diameter of CNFs was found to be in the range of 80-100 nm. Ethanol was replaced by PEG using a rotary evaporator to obtain gel-like CNFs/PEG. PLA/PEG/CNF films were prepared using the solvent casting method, with the CNF content varying from 0.15 to 5 phr. The effect of CNFs on the mechanical, morphological, and thermal properties of PLA nanocomposite films was investigated. The results demonstrate that the addition of CNFs improved Young's modulus and toughness of PLA/PEG films. In contrast, a slight decrease in mechanical properties was observed when the content of CNFs reached 0.83 phr. Considère's constructions are used to explain the neck phenomena and cold drawing of nanocomposite films. The crystallization and thermal stability of PLA nanocomposite films were enhanced, with a slight decrease in cold-crystalline temperature (T cc) and an increase in decomposition temperature (T d).

Enhanced antifungal properties of poly(butylene succinate) film with lignin nanoparticles and trans-cinnamaldehyde for mango packaging.

Sustainable poly(butylene succinate) (PBS) films incorporating lignin nanoparticles (LN) and trans-cinnamaldehyde (CN) have been developed to preserve mango freshness and provide food safety. PBS/LN, PBS/CN, and PBS/LN/CN composite films were produced by blown film melt extrusion. This study investigated the effect of CN-LN on the CN remaining content, thermal, mechanical, and barrier properties, diffusion coefficient, and antifungal activity of PBS films both in vitro and in vivo. Results showed that LN in the PBS/LN/CN composite film contained more CN than in the PBS/CN film. The compatibility of CN-LN with PBS produced homogeneous surfaces with enhanced barrier properties. PBS/LN/CN composite films demonstrated superior antifungal efficacy, inhibiting the growth of Colletotrichum gloeosporioides and preserving mango quality during storage. Results suggested that incorporating LN into PBS composite films prolonged the sustained release of antifungal agents, thereby inhibiting microbial growth and extending the shelf life of mangoes. Development of PBS/LN/CN composite films is a beneficial step toward reducing food waste and enhancing food safety.

Identification of a plastic-degrading enzyme from Cryptococcus nemorosus and its use in self-degradable plastics.

For decades, plastic waste management has been one of the major ecological challenges of our society. Despite the introduction of biodegradable alternatives such as polylactic acid (PLA), their beneficial environmental impact is limited by the requirement of specific compost facility as biodegradation of PLA in natural environment occurs at a very slow rate. In this work, a plastic-degrading enzyme was utilized to facilitate degradation process. Genomic and proteomic tools were employed to identify a new biodegradable plastic-degrading enzyme from Cryptococcus nemorosus TBRC2959. The new enzyme, Cr14CLE, functions optimally under mild conditions with temperature range of 30 to 40 °C and suffers no significant loss of enzymatic activity at pH ranging from 6 to 8. In addition to PLA, Cr14CLE is capable to degrade other types of biodegradable plastic such as polybutylene succinate (PBS) and polybutylene adipate terephthalate (PBAT) as well as composite bioplastic. Applications of Cr14CLE have been demonstrated through the preparation of enzyme-coated PLA film and laminated PLA film with enzyme layer. PLA films prepared by both approaches exhibited capability to self-degrade in water. KEY POINTS: • Novel plastic-degrading enzyme (Cr14CLE) was identified and characterized. • Cr14CLE can degrade multiple types of biodegradable plastics under mild conditions. • Applications of Cr14CLE on self-degradable plastic were demonstrated.

Fiber Melt Spinning and Thermo-Stabilization of Para-Rubber Wood Lignin: An Approach for Fully Biomass Precursor Preparation.

Para-rubber wood (PRW) lignin, extracted from agricultural waste, was successfully melt-spun to fibers and thermo-stabilized without employing auxiliary additives. 31P NMR analysis revealed that PRW-lignin contained mainly a syringyl unit of phenolic C5-substituted OH group, which enabled melt flow during fiber spinning, as well as a guaiacyl unit which offered the ability to cross-link during thermo-stabilization. Thermo-stabilized fibers with no fusion were achieved at 250 °C with the heating rate of 0.1 °C/min. Structural changes in the fibers during stabilization were systematically investigated using FTIR and XPS analyses. From the results, changes in the intensities of characteristic bands relating to C-H stretching, aromatic C-H stretching, and C=O stretching indicated structural changes of lignin toward aromaticity via oxidation reactions. XPS analysis of the fibers carbonized at 900, 1000, and 1200 °C revealed an increase in carbon content from 72 to 87 wt %. and a decrease in oxygen content from 28 to 13 wt %. with the increasing carbonization temperature. The weight loss of carbonized fibers was in the range of 73.6 to 88.7%. The high weight loss of fibers carbonized at 1200 °C was explained partly due to the thermal decomposition of disordered carbon. The tensile strength and modulus of carbonized fibers were 163.0 and 275.1 MPa, respectively. This study demonstrates an approach to prepare a fully biomass precursor fiber and contributes to the exploration of the potential use of lignin from biomass waste.

Single-Solvent Fractionation and Electro-Spinning Neat Softwood Kraft Lignin.

This paper reports on the production of electro-spun nanofibers from softwood Kraft lignin without the need for polymer blending and/or chemical modification. Commercially available softwood Kraft lignin was fractionated using acetone. The acetone-soluble lignin (AcSL) had an ash content of 0.06 wt %, a weight average molecular weight of 4250 g·mol-1 along with the polydispersity index of 1.73. The corresponding values for as-received lignin (ARL) were 1.20 wt %, 6000 g·mol-1, and 2.22, respectively. The AcS was dissolved in a binary solvent consisting of acetone, and dimethyl sulfoxide (2:1, v/v) was selected for dissolving the AcSL. Conventional and custom-designed grounded electrode configurations were used to produce electro-spun neat lignin fibers that were randomly oriented or highly aligned, respectively. The diameter of the electro-spun fibers ranged from 1.12 to 1.46 µm. After vacuum drying at 140 °C for 6 h to remove the solvents and oxidation at 250 °C, the fibers were carbonized at 1000, 1200, and 1500 °C for 1 h. The carbonized fibers were unfused and void-free with an average diameter of 500 nm. Raman spectroscopy, scanning electron microscopy, and image analysis were used to characterize the carbonized fibers.

Lignin Nanoparticles for Enhancing Physicochemical and Antimicrobial Properties of Polybutylene Succinate/Thymol Composite Film for Active Packaging.

The natural abundance, polymer stability, biodegradability, and natural antimicrobial properties of lignin open a wide range of potential applications aiming for sustainability. In this work, the effects of 1% (w/w) softwood kraft lignin nanoparticles (SLNPs) on the physicochemical properties of polybutylene succinate (PBS) composite films were investigated. Incorporation of SLNPs into neat PBS enhanced Td from 354.1 °C to 364.7 °C, determined through TGA, whereas Tg increased from -39.1 °C to -35.7 °C while no significant change was observed in Tm and crystallinity, analyzed through DSC. The tensile strength of neat PBS increased, to 35.6 MPa, when SLNPs were added to it. Oxygen and water vapor permeabilities of PBS with SLNPs decreased equating to enhanced barrier properties. The good interactions among SLNPs, thymol, and PBS matrix, and the high homogeneity of the resultant PBS composite films, were determined through FTIR and FE-SEM analyses. This work revealed that, among the PBS composite films tested, PBS + 1% SLNPs + 10% thymol showed the strongest microbial growth inhibition against Colletotrichum gloeosporioides and Lasiodiplodia theobromae, both in vitro, through a diffusion method assay, and in actual testing on active packaging of mango fruit (cultivar "Nam Dok Mai Si Thong"). SLNPs could be an attractive replacement for synthetic substances for enhancing polymer properties without compromising the biodegradability of the resultant material, and for providing antimicrobial functions for active packaging applications.

Physicochemical properties of lignin nanoparticles from softwood and their potential application in sustainable pre-harvest bagging as transparent UV-shielding films.

Technical lignin can be mainly obtained as a waste by-product from pulp industry, and it exhibits unique properties including ultraviolet adsorption, biodegradable, antibacterial, and antioxidant which can be utilized for bioplastic applications. However, common limitations of technical lignin for plastic applications are compatibility mainly due to poor interfacial adhesion, relatively large particle size and impurity. In this study lignin nanoparticles from softwood (S-LNPs) were successfully produced through a continuous-green-scalable antisolvent precipitation and the suitability of S-LNPs for fabrication of bio-composite polybutylene succinate (PBS) films using conventional blown film extrusion was examined. The attained S-LNPs showed lower ash content, higher phenolic content and higher lignin content compared to pristine softwood kraft lignin (S-lignin). Rheological property including shear viscosity and melt-flow index was determined. The obtained PBS/S-LNP composite films showed improved tensile modulus, higher water vapor transmission rate and excellent UV-shielding ability compared to neat PBS and PBS/S-lignin films. Accelerated weathering testing was conducted to replicate outdoor conditions. Degradation indices including carbonyl, vinyl and hydroxyl of the weathered PBS/lignin composites were evaluated for photo-oxidative stability. The S-LNPs as multifunctional bio-additives in biodegradable composite film exhibited superior performances of transparency, UV-absorption and stiffness with high photo-oxidative stability suitable for outdoor applications.

Development of Bioactive Opuntia ficus-indica Edible Films Containing Probiotics as a Coating for Fresh-Cut Fruit.

Bioactive edible films have received more attention in recent years as a method for food preservation with value-added functions. The aim of this study was to develop a bioactive edible film containing mucilage of cactus (Opuntia ficus-indica) and incorporating the probiotic strain Enterococcus faecium FM11-2 as an active component to promote consumer health benefits. Opuntia ficus-indica is rich in nutritional and bioactive compounds and the abundance of this cactus makes it attractive for food applications. Mucilage of Opuntia ficus-indica contained 0.47 ± 0.06 mg/g total sugar, 0.33 ± 0.06 mg AGE/mL phenolic content, 0.14 mg/ mL vitamin C, and possessed 35.51 ± 1.88% DPPH scavenging activity. The edible film that was developed exhibited the following characteristics: thickness of 0.02-0.11 mm, percent moisture content 0.19-0.24%, water solubility 30.66-59.41% and water vapor permeability of 0.15-1.5 g·mm/m2·min·kpa, while the range of the variation depended on the type of plasticizer used (either sorbitol or glycerol). The addition of sorbitol in the film provided the maximum mechanical strength based on the evaluation of tensile strength, Young's modulus and elongation at break (44.71 ± 0.78 MPa, 113.22 ± 0.23 MPa and 39.47 ± 0.61%, respectively). The optimal formulation of the edible film, according to the physicochemical, physical and maintenance of fresh-cut apple slices, contained cactus mucilage, gelatin, glycerol and a probiotic. The incorporation of a probiotic into the cactus film created a bioactive edible film that could provide a health benefit. While improvement is needed to maintain the survival rate of the probiotic, this work presents an exciting method for furthering the study of food preservation with edible films.

Physicochemical characteristics of organosolv lignins from different lignocellulosic agricultural wastes.

Lignin is a promising alternative to petrochemical precursors for conversion to industrial-needed products. Organosolv lignins were extracted from different agricultural wastes including sugarcane bagasse (BG) and trash (ST), corncob (CC), eucalyptus wood (EW), pararubber woodchip (PRW), and palm wastes (palm kernel cake (PKC), palm fiber (PF), and palm kernel shell (PKS), representing different groups of lignin origins. Physicochemical characteristics of lignins were analyzed by several principal techniques. Most recovered lignin showed high purity of >90 % with trace sugar contamination, while lower purities were found for lignin from palm wastes. Hardwood lignins (EW and PRW) mainly contained guaiacyl (G) and syringyl (S) units with a minor fraction of p-hydroxyphenyl units (H) with high molecular weight, glass transition temperature, phenolic hydroxy group and low aliphatic hydroxy group. Grass-type lignins (BG, ST, CC) and palm lignins (PKC, PF, and PKS) contained three monolignols of H, G, and S units with lower molecular weights and C5-substituted hydroxy of S unit. Among the grass-type lignins, PKC lignin contained the highest nitrogen and lipophilic components with the lowest molecular weight, thermal stability, and glass transition temperature. This provides insights into properties of organosolv lignin as basis for their further applications in chemical, polymer and material industries.

Improved procedure for electro-spinning and carbonisation of neat solvent-fractionated softwood Kraft lignin.

In general, the electro-spinning of lignin requires it to be functionalised and/or blended with synthetic or natural polymers. This paper reports on the use of solvent fractionated lignin-lignin blend to electro-spin BioChoice softwood Kraft lignin. The blend consisted of acetone-soluble and ethanol-soluble lignin in a binary solvent of acetone and DMSO. Solvent fractionation was used to purify lignin where the ash content was reduced in the soluble lignin fractions from 1.24 to ~ 0.1%. The corresponding value after conventional acid-washing in sulphuric acid was 0.34%. A custom-made electro-spinning apparatus was used to produce the nano-fibres. Heat treatment procedures were developed for drying the electro-spun fibres prior to oxidation and carbonisation; this was done to prevent fibre fusion. The lignin fibres were oxidised at 250 °C, carbonised at 1000 °C, 1200 °C and 1500 °C. The cross-section of the fibres was circular and they were observed to be void-free. The longitudinal sections showed that the fibres were not fused. Thus, this procedure demonstrated that solvent fractionated lignin can be electro-spun without using plasticisers or polymer blends using common laboratory solvents and subsequently carbonised to produce carbon fibres with a circular cross-section.