Heavy metal contamination in water systems driven by industrialization and urbanization is a primary concern for society. The development of efficient remediation methods to reduce heavy metal contamination in water is necessary. Biochar has emerged as a promising adsorbent for heavy metals due to its unique physicochemical properties. This study investigated the effect of biochars manufactured from 12 different wood species on lead ion (Pb(Ⅱ)) removal capacity in aqueous solutions. The 12 different wood species include two softwoods and 10 hardwoods. The physicochemical properties and the lead ion adsorption capacity of biochars were characterized. The Pb(Ⅱ) removal capacity of biochars derived from hardwoods was significantly higher than that of softwood-derived biochars. Among the hardwoods, aspen biochar exhibited the highest removal capacity (42.7 mg·g-1), which can be attributed to its higher CaCO3 content compared to softwood feedstocks. These results indicate that feedstock type plays a critical role in determining the physicochemical properties of biochar and its performance in Pb(Ⅱ) removal. Overall, hardwoods are more suitable feedstocks for producing biochars intended for lead-contaminated water treatment.

Biochar, a carbon-rich material that can be produced from forest byproducts and waste, is emerging as a valuable material for removing heavy metal ions from aqueous solutions. Biochar can be produced by many processes and equipment. Among these, mobile air curtain burners, developed to achieve lower levels of particulate matter and smoke than open pile burning, can be deployed in the field where biomass feedstocks are located. To elucidate lead metal ion (Pb2+) removal mechanisms, this study characterized seven biochars generated by a novel mobile curtain burner, representing the first such investigation of materials produced by this platform. The Pb2+ removal capacities ranged from 35 to 224 mg·g-1 of biochar. To understand the factors influencing this removal capacity, various physicochemical properties of the biochars were characterized, including the specific surface area, electrical conductivity, zeta potential, and pH. The mineral content, particularly calcium carbonate (CaCO3), was determined by analyzing the X-ray diffraction (XRD) patterns of the biochar samples using the Rietveld refinement method. Quantitative analysis showed that CaCO3 was the primary driver in Pb2+ removal. Precipitates of cerussite and hydrocerussite crystals were observed in the biochar XRD patterns after Pb2+ removal. A linear correlation was observed between the Pb2+ removal capacities of these biochars and the CaCO3 contents. The results indicate that the Pb2+ removal capacities of these biochar samples were predominantly determined by the CaCO3 contents through the chemical precipitation mechanism.

Direct mechanical recycling of multilayer plastic packaging (MPP) leads to downcycling, as the costly barrier layer loses economic value and often degrades the quality of the recycled blend. In this study, a five-layer MPP film consisting of low-density polyethylene (LDPE) structural layers, maleic anhydride-grafted linear LDPE (MA-g-LLDPE) tie layers, and an ethylene vinyl alcohol (EVOH) barrier layer was treated with formic acid to selectively extract the EVOH. The effects of the solvent concentration, temperature, sample size, and solvent-to-sample ratio on dissolution efficiency were evaluated, and optimal conditions were identified and scaled in a pilot setup. The polyolefins reclaimed after EVOH extraction were reprocessed into a blend through a conventional mechanical recycling process. Mechanical testing showed that the reclaimed polyolefin blend exhibited enhanced performance compared to the MPP film blend obtained via direct mechanical recycling and demonstrated properties comparable to those of virgin LDPE. Analysis of the chemical structure and rheological behavior revealed that chemical changes of the MA-g-LLDPE tie layer via hydrolysis and ring-opening reactions played a key role in affecting intermolecular interactions and consequently the mechanical performance of the reclaimed polyolefin blend. Moreover, the thermal properties of the reclaimed polyolefin blend remained largely consistent with those of the LDPE/MA-g-LLDPE blend without dissolution treatment. These findings demonstrate that solvent-based selective dissolution is a practical and scalable method for extracting EVOH and reclaiming polyolefins, enabling subsequent mechanical recycling with satisfactory results.

Pristine crawfish shell waste and shell-derived biochars produced at 500, 650, and 800 degrees C were evaluated as calcium-rich sustainable biosorbents for Nd(III) immobilization from aqueous solution. Batch experiments were conducted at 23 degrees C using 50 mL of 1000 mg L-1 Nd(III) solution and sorbent mass of 25-100 mg to investigate removal behavior, kinetics, and mechanisms. The 800 degrees C biochar exhibited the highest apparent Nd(III) removal capacity (1200 mg g(-1)), which was attributed to instantaneous alkaline precipitation and the formation of Nd (OH)(3). In contrast, pristine crawfish shell and the 500 and 650 degrees C biochars immobilized Nd(III) primarily through a dissolution-precipitation mechanism, yielding amorphous and crystalline Nd-containing carbonate phases. Among these sorbents, pristine crawfish shell showed the highest removal capacity at a sorbent mass of 25 mg (574.8 mg g-1), followed by the 500 degrees C biochar (490.1 mg g-1), whereas the 650 degrees C biochar exhibited substantially lower performance (291.4 mg g-1). Except for the 800 degrees C biochar, for which removal was instantaneous, the Elovich model provided the best fit to the kinetic data across pristine shell, 500 degrees C, and 650 degrees C sorbent types, regardless of the sorbent mass. The strong correlation between Ca(II) release and Nd(III) removal, supported by XRD, FTIR, and SEM-EDS analyses, indicates that Nd(III) immobilization is governed by phasedependent dissolution of calcium carbonate substrates followed by reprecipitation of Nd phases. These findings demonstrate that crawfish shell waste can serve as a highly efficient sacrificial biogenic calcium carbonate precursor for Nd(III) immobilization, even under ambient conditions.

This study introduces a systematic approach to optimize methyltrimethoxysilane (MTMS) modification of alkali (Alk), kraft (Kl), and organosolv (Org) lignin at varying MTMS loadings of 0.5, 1, and 2.5 mol/g. The objective was to determine how lignin type, hydroxyl (-OH) composition, and MTMS loading influence lignin functionalization and, in turn, the barrier and mechanical performance of thermoformed lignin-coated sheets. By correlating lignin type, hydroxyl (-OH) composition, and MTMS loading, critical hydroxyl content ranges were identified (4 < OH < 5 mmol/g for Alk, Org, and Kl), establishing direct links between hydroxyl chemistry and water and oil repellency of the coated sheets. Optimal lignin functionalization was achieved at 0.5 mol/g MTMS for Alk lignin, 2.5 mol/g for Kl lignin, and 0.5-1 mol/g for Org lignin. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and phosphorus-31 nuclear magnetic resonance (31P NMR) confirmed successful silanization and reduction of accessible hydroxyl groups. Thermogravimetric analysis (TGA) revealed enhanced thermal stability attributed to siloxane (Si-O-Si) network formation. These functionalized lignins were then applied as a coating on thermoformed fiber sheets, producing high water contact angle (97°-120°) and improved oil contact angle (58°-75°). The coated sheets also showed substantial improvements in strength and stiffness, with Young's modulus increase from 1,770 ± 2.3 MPa to 3,170 ± 1.6 MPa and tensile strength from 67 ± 3.7 MPa to 125 ± 1.2 MPa. These findings advance the chemistry of lignin functionalization for sustainable packaging applications.

Lignin-carbohydrate complexes, in which lignin and polysaccharides are directly connected, have been identified and extensively analyzed. To date, however, the origin of these structures has not been unequivocally established. That notwithstanding, it has been found that delignification, whether by conventional pulping and bleaching processes or in the biorefinery context, is effected by the presence of lignin-carbohydrate complexes. Using density functional theory calculations, the current work has evaluated the thermodynamics of bond dissociation as a function of structure and chemical composition. Among the lignin-carbohydrate complexes that have been identified, the homolytic bond dissociation energy is highest for the α-benzyl ethers and γ-ester, with phenyl glycosides being markedly less endothermic. This is consistent with observations on the recalcitrance of these compounds. Heterolytic cleavage reactions of the α-benzyl ethers are less endothermic, due to water solvation of the ions. The latter observation may provide support for the proposed homolytic cleavage reaction, since if heterolysis were operative, the α-benzyl ethers would not exhibit the level of recalcitrance that is observed experimentally.

Hurricanes generate a large volume of downed timber in the southeastern United States each year. Utilizing this timber as a source of wood fibers (WFs) for reinforcing polypropylene (PP) could help mitigate landowners' economic losses. This study investigated the effects of tree age and environmental exposure on the sizes, morphologies, and surface properties of WFs from downed timber, as well as the mechanical and rheological behaviors of PP composites reinforced with these WFs at different loading levels. Tree age emerged as the dominant factor affecting strength, while loading level played a key role in enhancing stiffness, and exposure duration had a relatively minor influence. The major findings discovered that fibers with high maturity contributed to enhanced mechanical performance, while fibers from older trees, containing high extractive content, were more prone to degradation under extended exposure durations. Overall, all composite exhibited significantly higher tensile, flexural, and impact strengths than neat PP. The rheological study further explored fiber-matrix interactions, providing critical insights into the fiber quality and the processability of the composites. The WFs derived from downed timber harvested within 12 months demonstrate great potential for use as reinforcement in PP.

Understanding the correlation between morphology and the fundamental behavior of blends is crucial for tailoring their properties. This study investigated the effects of phase morphology on mechanical performance, rheology, and non-isothermal crystallization kinetics of immiscible polypropylene (PP)/high-density polyethylene (HDPE) blends. Nanometer-scale HDPE phases dispersed within PP, co-continuous phases, and micrometer-scale PP phases dispersed within HDPE were formed at 75/25, 50/50, and 25/75 PP/HDPE weight ratios, respectively. Mechanical results indicated that the co-continuous morphology dissipated energy more efficiently than the matrix-dispersed morphology. Rheological results showed that nanometer-scale dispersion significantly enhanced the blend elastic modulus through the restriction effect at the interfaces. Non-isothermal crystallization kinetics were analyzed using Jeziorny-modified Avrami, Ozawa, Mo, and Kissinger models. Due to HDPE's heterogeneous nucleation effect, the crystallization temperature of PP was elevated, and the crystallization rate of the blend also increased with higher HDPE content. Furthermore, the blend with the 25/75 PP/HDPE exhibited a higher crystallization rate than neat HDPE, as the interfacial boundaries facilitated the alignment of HDPE chains. The higher crystallization activation energy calculated in the 75/25 PP/HDPE blend suggested that nanometer-scale dispersion imposed a more significant restriction on crystal growth compared to micrometer-scale dispersion.

Enhancing the performance of polypropylene (PP)/high-density polyethylene (HDPE) blends is crucial for valorizing mixed plastic waste. This study incorporated microcrystalline cellulose (MCC), combined with maleic anhydride grafted polyethylene (MAPE), into a PP/HDPE blend to enhance its performance. Mechanical results showed that the addition of MCC increased strength, stiffness, and toughness of the PP/HDPE blend, with further enhancement achieved through adding MAPE. Morphological observations and thermal analyses revealed that the enhanced mechanical properties were attributed to the formation of core-shell structured particles, with MCC as the core and MAPE, miscible with HDPE, acting as the shell at the interface. Rheological behaviors provided insights into processability and MCC-polymer matrix interactions of the composites, highlighting percolation effects at high MCC content. These MCC-based core-shell particles demonstrated great potential for improving the PP/HDPE blend performance.

Amidst declining fossil-based resources and environmental challenges, the focus on biobased materials has intensified. Carboxymethylation is one way to introduce reactive functionality to enhance the reactivity of lignin for a specified application. This research investigates the carboxymethylation of four lignin sources: eucalyptus kraft lignin, spruce kraft lignin, birch cyclic extracted organosolv lignin, and spruce cyclic extracted organosolv lignin. Our aim is to elucidate the role of the lignin structure in its reactivity. Using the advanced analytical techniques NMR spectroscopy, Fourier transform infrared spectroscopy, density functional theory, and size-exclusion chromatography, we provide a comprehensive characterization of the modified lignin. The findings offer valuable insights into how the chemical and physical properties of molecular lignin affect the selectivity and efficiency of the carboxymethylation reaction. These fundamental findings hold great potential for guiding considerations on the selection of lignin sources for specific applications based on their molecular properties.

Understanding the percolation threshold is essential for determining the performance of particle-reinforced polymer composites. Spray-dried cellulose nanocrystals (SDCNC) of micrometer size reinforced homopolymer polypropylene (HPP) composites at 20, 30, 40, and 50 wt.% were prepared to investigate the percolation threshold of SDCNC particles in HPP. The effect of a compatibilizer (maleic anhydride polypropylene (MAPP)) at 3, 5, and 7 wt.%, on the SDCNC percolation networks and composites performance were also studied. The results indicated that SDCNC particle percolation networks in HPP were established between 30 and40 wt.%. For composites without MAPP, the impact strength significantly increased by up to 23% below the percolation threshold and declined beyond it. The peak crystallization temperature of HPP was steadily increased until 30 wt.% SDCNC particles were added due to the SDCNC saturated nucleation function at the threshold. Introducing MAPP significantly improved tensile strength (58%), tensile strain (61%), flexural strength (45%), and impact strength (91%) compared with the corresponding composites without MAPP, attributed to the enhanced interfacial adhesion between the SDCNC particles and HPP. Water absorption results indicated that adding MAPP changed the SDCNC particle distribution networks within the matrix above the percolation threshold but did not change it below the threshold. The distribution of spray-dried cellulose nanocrystal particles in polypropylene can be probed by water absorption and the crystallization behaviors of the composites. image

Multilayer plastic packaging (MPP) has attracted extensive attention due to its functionality and inherent difficulty in reclamation. One primary concern is the performance of reprocessed MPP since it inherently consists of many dissimilar polymers. This study aims to assess the effect of multiple thermomechanical reprocessing cycles on the properties of a MPP blend. Low density polyethylene (LDPE)/maleic anhydride grafted linear LDPE (LLDPE-g-MA)/ethylene vinyl alcohol (EVOH) blend was manufactured and subjected to thermomechanical reprocessing, including thermal compounding, grinding, and injection molding for six cycles to characterize the impact of thermomechanical reprocessing on the blend's mechanical, morphological, thermal, and rheological properties. The tensile strength and modulus of the reprocessed blend remained consistent throughout six cycles. A pronounced decline in elongation at break was observed after four cycles of reprocessing. Toughness, as represented by the essential work of fracture, increased steadily up to three cycles of processing, followed by a decline in the following reprocessing cycles. The main property change is possibly caused by the gelling of the EVOH in the reprocessed blend, as demonstrated by larger EVOH agglomerates in the LDPE matrix. Differential scanning calorimetry results indicated that the degree of crystallization of the EVOH phase changed with increasing reprocessing cycles, suggesting EVOH degradation. Rheological behavior in the linear viscoelastic region indicated enhanced interfacial interaction between LDPE and EVOH due to the cross-linking of LLDPE-g-MA and rigid EVOH in the early reprocessing stages. After four cycles of reprocessing, decreases in storage and loss moduli were observed, indicating the possibility of phase separation caused by gelling of EVOH. Using polymer blending to reclaim LDPE-based EVOH multilayer is promising for up to four cycles of reprocessing as shown by mechanical, thermal, and rheological behaviors.

The intrinsic fragility and inferior processibility of metal-organic frameworks (MOFs) particles often restrict their functional application despite their high surface area and porous structure. We investigated the feasibility of sulfonated cellulose nanofibrils (SCNF) as a biopolymer template to hybridize MOFs. SCNF was synthesized through periodate oxidation followed by bisulfite sulfonation. The sulfonate groups increased electronegativity and enhanced the dispersibility of the cellulose fibers. More importantly, the negatively charged sulfonates could serve as anchors for metal ions to initiate the in situ growth of MOFs along the surface of cellulose fibers. We have achieved the synthesis of three types of SCNF/MOF hybrids, namely, SCNF/ZIF-8, SCNF/ZIF-67, and SCNF/HKUST-1. These hybrids can be formed as free-standing aerogels, exhibiting remarkably high surface areas and flexibility for applications. The assessment of the adsorptive efficiency of the SCNF/ZIF-8 hybrid indicates that the hybrid material exhibited a notably higher adsorption capacity for methylene blue versus the SCNF control. DFT calculation provides further insights into the underlying adsorption mechanisms, revealing that the sulfonates on the SCNF and the nitrogen atoms in the ZIF-8 ligands primarily contributed to the affinity for methylene blue. SCNF offers a versatile and robust biopolymer substrate for templating a wide array of MOFs with promising applications as adsorbents and beyond.

Massive amount of downed timber is generated by hurricanes and tornados. This research studied the properties of wood fibers (WFs) generated from downed loblolly pine (Pinus taeda L.) trees at different maturity (ages 15, 30, and 39 years) with various natural environmental exposure periods (0, 6, and 12 months) for wood polymer composite (WPC) manufacturing. The wood fiber critical properties for WPC manufacturing, including particle size and morphologies, physical and chemical properties, and thermal stability, were characterized. Prolonged environmental exposure increased WF surface roughness. The density and 1% sodium hydroxide solubility of WFs for the 15 - and 30-year-old tree decreased after 12 months of environmental exposure. The WFs generated from the 39-year-old tree contain extractives due to heartwood development, resulting in significantly less moisture absorption. Thermogravimetric analysis results showed no significant change in the thermal stability of WFs generated from the 15 - and 30-year-old trees after natural environmental exposure because of the loss of degraded wood components. The cellulose and lignin thermal degradation peak temperatures decreased by up to 9 and 6 degrees C for WFs extracted from the 39-year-old tree. The degraded wood components were fixed within WFs due to extractives, causing thermal degradation peak temperatures to decrease.

Methyl parathion is a typical organophosphorus pesticide that poses threats to the global environment and human health. In this study, we developed a portable 2D sensing pad for monitoring methyl parathion based on aggregation-induced emission (AIE) properties of innovated hybrid material that integrates cellulose nanofibers (CNFs) with luminescent metal-organic frameworks (LMOFs). The hybrid material enhanced the flexibility and moldability of the LMOFs and significantly improved scalability of the sensing material. The resulting CNF/LMOF material was shaped into a 2D pad, exhibiting fluorescent properties under UV exposure. The fluorescence of the hybrid pad was quenchable upon exposure to methyl parathion. This host-guest interaction enabled the precise quantification of the pesticide’s concentration by monitoring the intensity variation of the fluorescence at 405nm wavelength. We further engineered these hybrid pad prototypes into a user-friendly and portable sensing kit, and then validated them with real sample testing. Time-dependent Density Functional Theory (TD-DFT) calculations were employed to elucidate the underlying fluorescence quenching mechanism triggered by methyl parathion. This work introduces a practical and sustainable sensing platform for pesticide detection.

Downed timber is valuable for manufacturing biochar in environmental remediation applications due to the low cost of raw materials and low-temperature manufacturing process. Loblolly pine (Pinus taeda L.) trees at different maturities (15-, 30-, and 39-year-old) with 0, 6, and 12 months of local environmental exposure in the southeastern region of the US were collected for biochar manufacturing. The biochar samples were characterized for their physicochemical properties, including morphologies, elemental compositions, surface functional groups, carbon structure, pH, electrical conductivity, and specific surface area. The Pb2+ adsorption isotherms were measured. The results indicated that the biochar physicochemical properties, affected by the tree maturities and the environmental exposure periods, significantly impacted the Pb2+ adsorption capacity. The Pb2+ adsorption capacity of biochar increased with the environmental exposure of wood for 6 months, followed by a decrease for biochar made from wood with an environmental exposure of 12 months. A recommendation can be made that downed timber collected up to a 6-month environmental exposure period can manufacture biochar with superior performance regarding adsorbing Pb2+ in water systems. The research outcome offered insights for the biochar manufacturing community to prepare forest feedstock for biochar production with better performance in Pb2+ adsorption.

Polypropylene (PP) and polyethylene (PE) are widely used polymers but significantly contribute to plastic waste. Effective recycling of PP and PE is essential for reducing plastic pollution and enhancing sustainability. Collection of post-consumer PP and PE wastes forming comingled mixtures is routinely done due to the difficulty of sorting. While polymer blending offers a cost-effective way to recycle these mixtures, their inherent immiscibility limits the development of high-performance blends. This review provides an overview of recent advances in compatibilization strategies aimed at enhancing the PP/PE blend performance, with a focus on using bio-derived fillers as sustainable compatibilizers. Mechanical properties of the PP/PE blends compatibilized by various approaches, including non-reactive, reactive, and bio-derived filler compatibilizations are summarized and discussed in terms of their advantages and weaknesses. Simultaneous incorporation of bio-derived fillers and commercial compatibilizers potentially provides PP/PE blends with more desirable mechanical performance. Furthermore, the review summarizes the rheological and crystallization behaviors of compatibilized blends, emphasizing the significant impact of compatibilization on the processing-structure-property relationships within the blends. Current challenges and future directions in using bio-derived fillers to enhance PP/HDPE compatibilization are discussed. This review provides insight into a sustainable future by endowing plastic waste with desirable properties for broader applications.

Spray-dried cellulose nanocrystal (SDCNC) particles have attracted intense interest as reinforcements in polymer composites because of their unique physical and mechanical properties. This work aims to develop homopolymer polypropylene (HPP) composites with different loading levels of SDCNC particles (5, 10, 15, and 30 wt%) to understand their impact on composite mechanical, morphological, and thermal properties. The SDCNC-reinforced HPP composites were manufactured using a C.W. Brabender bowl internal mixer with a masterbatch concept and an injection molding process. The mechanical, morphological, and thermal properties of the composites were investigated. Compared to pure HPP, the tensile, and flexural modulus of elasticity (MOE) of composites with 30 wt% SDCNC significantly increased by up to 67% and 49%. The impact strength of the composites with the absence of a compatibilizer significantly increased by up to 19%, which was attributed to the mechanical interlocking network established between SDCNC particles and HPP. Additionally, increasing SDCNC loading in the composites led to higher crystallization peak temperatures and increased the degree of crystallinity (especially at 30 wt% SDCNC content), indicating that the SDCNC particles can act as heterogeneous nucleating agents during the crystallization process. The thermal stability of the composite was slightly improved upon SDCNC introduction.HighlightsWith the incorporation of spray-dried cellulose nanocrystal (SDCNC), the tensile modulus of elasticity (MOE), flexural MOE, and impact strength of filled homopolymer polypropylene (HPP) composites were significantly improved by up to 67%, 49%, and 19%, respectively.Mechanical interlocking network established between SDCNC and HPP contributed to the enhanced the impact strength.SDCNC particles can act as heterogeneous nucleating agents to promote the crystallization process of HPP.SDCNC particles slightly enhanced the thermal stability of HPP composite. The impact strength of SDCNC-reinforced HPP composites significantly improved because of the formation of mechanical interlocking network between SDCNC particles and matrix. SDCNC particles can act as heterogeneous nucleating agents to promote the crystallization process of HPP.image

Nanocellulose is a promising and sustainable feedstock for developing advanced and functional materials. However, the characteristics of nanocellulose, such as crystallinity, surface energy, and aspect ratio, can vary depending on biomass source and pretreatment methods, leading to variable performance of the nanocellu-lose-based materials. In this study, cellulose nanocrystals (CNCs) were isolated from hemp and poplar using totally chlorine free (TCF) peracetic acid and sodium chlorite delignification and bleaching pretreatments to probe the influences of biomass source and treatment methods on the isolation and characteristics of CNCs. Our results showed that hemp and poplar were almost completely delignified by peracetic acid treatment, whereas sodium chlorite treatment left 5%–6% lignin in the pulp. The yields of CNCs from raw hemp and poplar biomass ranged from 9.8% to 21.9% and 10.9% to 28.3%, respectively, depending on the treatment methods. The dimensions of CNCs from TCF-treated biomass generally maintained a larger width and aspect ratio than those from sodium chlorite-treated biomass. The poplar-derived CNCs exhibited slightly higher crystallinity of 53%–58% than hemp-derived CNCs of 49%–54%. The zeta potential of the CNCs, ranging from -20.1 mV to -31.1 mV, ensured a well-dispersed aqueous solution. The surface energy (dispersive energy of 40–80 mJ/m2 and specific energy of 2–10 mJ/m2), water interaction, and thermal stability of the CNCs were comparable, regardless of the biomass source and pretreatment methods. Our finding suggests that the TCF technique with peracetic acid treatment is a promising delignification and bleaching approach to obtain cellulose-rich pulps from herbaceous and hardwood biomass for nanocellulose isolation.