Selective acid precipitation of Kraft lignin: a tool for tailored biobased additives for enhancing PVA films properties for packaging applications

Different lignin fraction extraction by pH fractionation for lignin microspheres preparation as UV-blocking PVA film

Kraft lignin (KL), a major by-product of the pulp and paper industry, has garnered significant research attention due to its abundant availability and distinctive chemical structure, making it a promising candidate for applications such as biofuels, carbon materials, and polymer composites. Despite these advantages, its utilization in fine chemical industries, including nanomaterials, is constrained by its inherent dark color and broad molecular weight distribution. Addressing these limitations has become a central focus in ongoing research efforts aimed at enhancing the functionality and commercial viability of KL. In this study, we fractionated KL from a paper-making enterprise using pH fractionation, and obtained four kinds of lignin with different molecular weights. Following that, lignin microspheres (LMPs) were formed by self-assembly from four sizes of KL. Analyzing the KL and LMP properties, the low molecular weight lignin, such as KL-2, exhibited good antioxidant properties (84.27 %, 5 mg/mL), high brightness (ISO% = 7.6), high L⁎ value (L⁎ = 86.2) and low polydispersity index (PDI = 1.19). The LMP showed a narrow size distribution (1.0-1.4 μm). When the LMP content is 5 %, the 5 % LMP/PVA film maintains high transparency and exhibits excellent UV protection, achieving a UV shielding rate of up to 94.6 %. Therefore, this study offered an effective way for the comprehensive utilization of pulping waste KL.

A dual approach with lignin and nanolignin: Reinforcing UV stability and sustainability in PVA matrices

Kraft lignin (KL) and its acetic acid-fractionated derivatives were evaluated for their antioxidant and ultraviolet C (UV-C)-absorbing properties to mitigate the photooxidative degradation of polyvinyl alcohol (PVA). PVA films were prepared with 4 % (w/w) KL macroparticles - including unfractionated KL and the fractionated forms KL30, KL40, and KL50 - and with 0.4 % (w/w) lignin nanoparticles (NP), derived from the same fractions (named NPKL, NP30, NP40, and NP50). All formulations, including the control (pure PVA), were blended with 10 % (w/w) NPK fertilizer (nitrogen‑phosphorus‑potassium, 10-10-10) and plasticized with glycerol for film casting. After 21 days of UV-C exposure, films containing LNP retained over 90 % transparency, compared to ~70 % for pure PVA. Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirmed reduced photooxidative and thermal degradation in lignin-containing films, especially those with KL30 and NP30. Biodegradation assays using respirometric CO₂ analysis showed accelerated release for NP30 (up to 90 mg after 20 days), reflecting enhanced microbial activity. Leaching assays demonstrated controlled release of NPK ions over 40 days in films with NP. In mulch film application tests with cherry tomato, PVA + NP30 showed seedling development comparable to commercial mulch and superior to control films. These results confirm the potential of NP as sustainable, multifunctional additives for UV stabilization and controlled nutrient delivery in biodegradable agricultural films.

Construction of Multifunctional Composite Films with Biomimetic Bridging and Stress Dissipation Properties

Strategies based on biodegradable polymers to replace traditional petroleum-based plastics have become research hotspots, while designing multifunctional composite films as packaging materials remains a challenging task. Herein, mussel-inspired hollow mesoporous polydopamine (HMPDA) is prepared and used as a secondary reaction platform to immobilize silver nanoparticles (HMPDA@Ag), which are then co-doped into a polyvinyl alcohol (PVA) matrix in combination with naturally derived 2D montmorillonite (MMT). Benefiting from the noncovalent interactions between the composite particles and MMT with the PVA matrix, as well as the synergistic effects between nanofillers, the fabricated films exhibit a great tensile strength of 424.7 MPa, a high toughness of 1093.7 MJ m-3, and a significantly improved water barrier property. HMPDA@Ag nanoparticles endow the film with excellent properties such as a photothermal synergistic antibacterial effect, ultraviolet shielding, and antioxidation. Additionally, the developed films exhibit significantly improved flame retardancy. Compared with pure PVA, the reduction in peak heat release rate (PHRR) and total heat release (THR) reaches 8.2% and 19.5%, respectively, alongside a notable inhibition of smoke release and melt dripping behavior. This work provides a novel idea for manufacturing multifunctional PVA-based composite films to reduce the environmental impact resulting from the excessive use of non-biodegradable, petroleum-based packaging materials worldwide.

Towards phosphorylated lignin-based epoxy resins: An integrated technological route to obtain a macromonomer with enhanced thermal and potential flame-retardant properties

The growing search to replace petrochemical derivatives with materials having renewable origin has increased the prospection for biomolecules from lignocellulosic biomass. The aim of this work was to develop epoxy resins based on kraft lignin (KL) with flame retardant properties by phosphorylation of this lignin followed by its glycidylation. The phosphorylation of KL was carried out using 85 % wt. H3PO4 in THF at 40 °C for 30 min, yielding phosphorylated KL (PKL). Glycidylation of KL and PKL were carried out using epichlorohydrin in an alkaline medium without and with TBAB at room temperature for 24 h, obtaining glycidylated KL (GKL) and PKL (GPKL), respectively. Lignins were characterized by FTIR, 1H, 31P and HSQC NMR, TGA, DSC, MCC and wet analyses. Spectral analyses showed that the grafting of phosphorous occurred in the form of monoester phosphate groups and that the use of TBAB significantly increased the quantity of grafted glycidyl groups. GPKL presented enhanced thermal, thermo-oxidative, and solubility properties in comparison with KL. The results of the proposed integrated route showed it was possible to develop bio-based material with enhanced thermal and flame-retardant properties, having great potential for use in various technological applications.

Fabrication of biodegradable polyvinyl alcohol-based plastics toward technical lignin valorization

The fabrication of composite materials from lignin has attracted increasing attention to reducing the dependence of petrochemical-based resources on carbon neutrality. However, the low content of lignin in the biocomposites remains a challenge. Herein, industrial lignin is fractionated by an organic solvent to reduce its structural heterogeneity. Subsequently, the fractionated lignin samples are integrated with polyvinyl alcohol (PVA) to fabricate plastics characterized by uniform thickness and smooth surfaces. The resultant composite films exhibit tensile strength and strain up to 75 MPa and 1050%, respectively, which surpass state-of-the-art lignin-based bioplastics. The mechanism investigations reveal that the enhanced mechanical properties are due to the internal non-covalent interactions derived from the hydroxyl groups of lignin and PVA. Notably, the PVA/lignin films are biodegradable after 92 days' burial in soil. This study paves the way for the rational design of lignin-based biodegradable polymers as sustainable alternatives to conventional plastics.

Kappa-carrageenan and sodium alginate-based pH-responsive hydrogels for controlled release of methotrexate

Despite remarkable progress in medical sciences, modern man is still fighting the battle against cancer. In 2022, only in the USA, 640 000 deaths and 2 370 000 patients were reported because of cancer. Chemotherapy is the most widely used for cancer treatments. However, chemotherapeutics have severe physicochemical side effects. Therefore, we have prepared poly(amididoamine) dendrimeric carrageenan (CG), sodium alginate (SA) and poly(vinyl alcohol) (PVA) hydrogels by using solution casting methodology. The constituents of hydrogels were cross-linked by mutable quantity of 3-aminopropyl(diethoxy)methyl silane (APDMS). Hydrogels were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscope and atomic force microscopy. Hydrogels exhibited higher swelling volumes in 5-7 pH range. In vitro biodegradation in ribonuclease-A solution and cytocompatibility analysis against DF-1 fibroblasts established their biodegradable and non-toxic nature, which enables them as a suitable carrier for chemotherapeutic compounds. Hence, methotrexate (MTX) as a model drug was loaded on CAP-8 hydrogel and its release was detected by the UV-visible spectrophotometer in phosphate-buffered saline (PBS) solution. In 13.5 h, 81.25% and 77.23% of MTX were released at pH 7.4 (blood pH) and 5.3 (tumour pH) in PBS, respectively. MTX was released by super case II mechanism and best fitted to zero-order and Korsmeyer-Peppas model. The synthesized APDMS cross-linked CG/SA/PVA dendrimeric hydrogels could be an efficient model platform for the effective delivery of MTX in cancer treatments.

Antioxidant and UV-blocking activity of PVA/tannin-based bioplastics in food packaging application

In this study, bioplastics with antioxidant and UV protection properties based on tannin and PVA were created for packaging uses. Using a hot water extraction method at various extraction temperatures (60-100 °C), tannins were removed from the bark of Acacia mangium. Tannins with the best antioxidant activity were extracted at 80 °C. In order to create bioplastic formulations (PVA/Tannins), the extract is then employed. The non-heating bioplastic method's preparation (M3) stage produced the highest levels of antioxidant activity. Therefore, subsequent tests were conducted using the non-heating method (M3). On the opacity, UV protective activity, antioxidant capacity, mechanical strength, thermal stability, and water vapor permeability of the resultant bioplastics, the impact of tannin concentration (0.1-0.5 g) was examined. The findings of the experiments demonstrate that PVA/Tannin bioplastics are less transparent than pure PVA. The PVA/tannin bioplastics that are formed, on the whole, show strong antioxidant and UV protection action. Comparing PVA/Tannin bioplastics to pure PVA also revealed a small improvement in thermal stability and tensile strength. In PVA bioplastics with resistant tannins, moisture content was marginally greater even at low tannin concentrations (0.1 g). Based on the findings, bioplastics made from PVA and the tannin A. mangium have the potential to be used to create packaging that is UV and active antioxidant resistant. It can be applied as the second (inner) layer of the primary packaging to protect food freshness and nutrition due to their antioxidant activity.

High value valorization of lignin as environmental benign antimicrobial

Lignin is a natural aromatic polymer of p-hydroxyphenylpropanoids with various biological activities. Noticeably, plants have made use of lignin as biocides to defend themselves from pathogen microbial invasions. Thus, the use of isolated lignin as environmentally benign antimicrobial is believed to be a promising high value approach for lignin valorization. On the other hand, as green and sustainable product of plant photosynthesis, lignin should be beneficial to reduce the carbon footprint of antimicrobial industry. There have been many reports that make use of lignin to prepare antimicrobials for different applications. However, lignin is highly heterogeneous polymers different in their monomers, linkages, molecular weight, and functional groups. The structure and property relationship, and the mechanism of action of lignin as antimicrobial remains ambiguous. To show light on these issues, we reviewed the publications on lignin chemistry, antimicrobial activity of lignin models and isolated lignin and associated mechanism of actions, approaches in synthesis of lignin with improved antimicrobial activity, and the applications of lignin as antimicrobial in different fields. Hopefully, this review will help and inspire researchers in the preparation of lignin antimicrobial for their applications.

Unraveling the adsorption mechanism of methylene blue onto selective pH precipitated Kraft lignins: Kinetic, equilibrium and thermodynamic aspects

Lignin has been used on its crude or modified forms for adsorption purposes. This work evaluated the influence of selective pH precipitation of Kraft lignins (KLs) on their adsorptive performance for removing methylene blue (MB). The alkaline and acid KLs (KL A and KLB, respectively) were characterized by FTIR, ³¹P NMR, GPC and pH_PZC analyses. The effects of biosorbent and adsorbate concentrations, pH, ionic strength, contact time and temperature on the MB adsorption were evaluated. The equilibrium, kinetic and thermodynamic parameters were calculated by Langmuir and Freundlich isotherms, pseudo-first and second order and Van't Hoff and Gibbs models, respectively. KL A and KL B presented peculiar structural features, mainly hydroxyls concentration and M_w values, which have influenced on the removal efficiency of MB and the adsorptive capacities of KL A (>80 %; ≥80 mg g^-1) and KL B (>90 %; ≥20 mg g^-1), respectively. The equilibrium, kinetic and thermodynamic parameters have shown that MB adsorption presented different mechanisms for each KL, but it only has driven by chemisorption for KL B. Therefore, KL A and KL B can be considered as potential novel biosorbents obtained through a clean, fast and simple route for textile wastewater treatment.

A review on lignin antioxidants: Their sources, isolations, antioxidant activities and various applications

Lignin, a biopolymer obtained from agricultural/forestry residues or paper pulping wastewater, is rich in aromatic structure, which is central to its adoption as a candidate to natural antioxidants. Through insight into its structural features from biomass, different functional groups would influence lignin antioxidant activity, wherein phenolic content is the most important factor, hence massive studies have focused on its improvement via different pretreatments and post-processing methods. Besides, lignin nanoparticles and chemical modifications are also efficient methods to improve antioxidant activity via increasing free content and decreasing bond dissociation enthalpy of phenolic hydroxyl. Lignin samples exhibit comparable radicals scavenging ability to commercial ones, showing their potential as renewable alternatives of synthesized antioxidants. Besides, their applications have also been discussed, which demonstrates lignin potential as an inexpensive antioxidant additive and consequent improvements on multiple functionalities. This review is dedicated to summarize lignin antioxidants extracted from biomass resources, methods to improve their antioxidant activity and their applications, which is beneficial for realizing lignin valorization.

Effect of Two-Step Formosolv Fractionation on the Structural Properties and Antioxidant Activity of Lignin

The formosolv fractionation process has been demonstrated to be an effective approach toward lignin recovery as an antioxidant from lignocellulosic biomass. In this study, four lignin fractions, FL-88%, FSL-70%, FIL-70% and FL-EtAc, were isolated from Phragmites australis biomass through two-step formosolv fractionation (88% formic acid delignification followed by 70% aqueous formic acid fractionation). To better understand the structural properties of the lignin obtained from this fractionation process, four isolated lignins were successfully characterized by gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) spectroscopy, thermogravimetric analysis (TGA) and gas chromatograph-mass spectroscopy (GC/MS). It was found that lignin depolymerization via β-O-4 cleavage occurred via a formylation, elimination and hydrolysis mechanism, accompanied by a competitive condensation reaction. Noteworthily, two-step formosolv fractionation can produce specific lignin fractions with different ABTS and DPPH radical scavenging activities. The FL-EtAc fraction with low molecular weight (M_w = 2748 Da) and good homogeneity (PDI = 1.5) showed excellent antioxidant activity, compared with the other three isolated lignin fractions, even equal to that of commercial antioxidant BHT at the same concentration of 2.0 mg·mL⁻¹. These findings are of great help for specific lignin from biomass as a natural antioxidant in the future.

Green solvents-based molecular weight controllable fractionation process for industrial alkali lignin at room temperature

The molecular weight is one of the most important factors influencing the utilization of industrial lignin obtained from chemical pulping process. In this paper, a facile operative green solvent system was successfully developed for molecular weight-controllable fractionation of industrial alkali lignin (IAL) at room temperature. The results showed that through adjusting the ratio of water, ethanol and γ-Valerolactone (GVL), the industrial lignin was fractionated into six levels with molecular weight stepwise controllable from low to high. The fractionation is a physical process according to FTIR and 2D-HSQC NMR analysis, and the chemical structure of lignin has not changed. Additionally, the polydispersity of fractionated lignin with higher molecular weight tends to be narrower. The content of hydroxyl and carboxyl group is higher for the fractionated lignin with lower molecular weight, which would be beneficial for the chemical reactivity in the down-stream application.