High Solid Content Research Articles

Enhanced anaerobic digestion of freezing and thawing pretreated cow manure with increasing solid content: kinetics and microbial community dynamics

High solid anaerobic digestion has proved the mainstream technology for the treatment of organic wastes. However, the high molecular weight and complex lignocellulosic structure of cow manure (CM) make it indigestible and inefficient, leading to limit the hydrolysis step of anaerobic digestion at high solid content. To mitigate this bottleneck, an improved cost-effective freezing and thawing pretreatment technique was proposed in this study. The freezing and thawing pretreatment of raw CM without any dilution was done for 20 days. The maximum cumulative methane yield (487 mL CH4 g− 1VS) was achieved at a total solid (TS) of 5% followed by TS of 10% and 15%, which was 13%, 20% and 21% higher than obtained from untreated CM, respectively. The kinetic results revealed that the biodegradable materials could be utilized at increasing TS with decreasing hydrolysis rate. The pretreatment significantly enhanced the methylotrophic methanogenic pathway during high solid anaerobic digestion, which was contrary to the general concept that the process is usually dominated by acetoclastic and hydrogenotrophic methanogens. This study is very important to understand the effect of solid content but also important to understand the effect of freezing and thawing pretreatment on process parameters and microbial community dynamics in high solid anaerobic digestion.

Determination of optimal technological conditions for the manufacture of semi-finished products from gooseberry fruit

The quality of pureed berries products is determined by many factors. The purpose of the study was to determine the optimal technological conditions for the manufacture of semi-finished products from gooseberries, providing for the use of equipment with a rotary machine (MAG‑50) and ensuring the required quality characteristics. The objects of research were semi-finished products from gooseberries. The manufacturing technology involved high-temperature processing or the use of the rotary machine MAG‑50. The research methods were standard. It has been found that in order to obtain products with the required quality characteristics, the duration of processing in MAG‑50 had the greatest influence. The optimal technological conditions for the manufacture of products in MAG‑50 have been determined: processing for 14–20 minutes at a temperature of 59–65°C of at least 72% of fresh berries or 58–65°C of at least 66% of quick-frozen ones. It has been established that the technology involving the use of rotary machine MAG‑50, compared with the high-temperature one, made it possible to obtain products with a lower content of mesophilic aerobic and facultative anaerobic microorganisms, molds (by 97.7 and 69.8%, respectively), better appearance characteristics (by 1.7%), color, texture and odor (by 2.3%), taste and aftertaste (by 3.6%). The state of the raw materials had the greatest impact on the content of yeast in semi-finished products — products made from fresh berries contained 48.7% more of them on average than products from quick-frozen ones. Compared with the Senator variety, gooseberry fruits of the Pink 2 variety made it possible to obtain products with a high content of soluble solids, sugars, minerals and ascorbic acid (by 18.2, 58.9, 7.7 and 61.8%, respectively), less titrated acids and dietary fibers (by 21.2 and 20.3%, respectively). The study demonstrates the potential of obtaining semi-finished products from gooseberries, regardless of their variety and condition by using the technology involving the use of MAG‑50.

Cooperation of rhamnolipid and thermophilic bacteria modifies proteinic structure, microbial community, and metabolic traits for efficient solubilization and acidogenesis of mariculture solid wastes

Anaerobic fermentation combined with thermophilic bacteria (TB) pretreatment is a promising method to realize effective waste management and carbon resource recovery. However, undesirable properties of high-strength mariculture solid wastes (MSW) such as high solids concentration, excessive salinity and poor bioavailability limited the overall solubilization and acidogenic efficiency. This study innovatively introduced rhamnolipid (RL) to alleviate this adverse effect, and unveiled its cooperation with TB on enhancing organic matter dissolution and volatile fatty acids (VFAs) production. The results showed that VFAs yield from pretreated MSW was improved by 9.4-15.1 folds with enriched acetate (81.4%-94.4%) in the TB+RL groups. The co-pretreatment of RL and TB disintegrated substrate structure for efficient release of electron shuttles and biodegradable organics. This was because introducing RL reconstructed solid-liquid interfacial charge and molecular arrangement, improved thermophilic enzyme activity, and reduced apoptosis and necrosis cells of TB. Substrate bioavailability was further improved with proteinic structure shifted from α-helix and β-sheet to random coil and aggregated strands, and amide II and carboxyl groups interacted with RL molecules. These changes induced the selective enrichment of hydrolytic and acidogenic bacteria, and the upregulated expression of encoding genes responsible for transmembrane transport, protein hydrolysis, carbohydrate metabolism and acetate biosynthesis. This study provides a new strategy to overcome the bottlenecks of acidogenesis from high-strengthen organic wastes and deciphers the underlying mechanism.

Microwave Frequency Analysis of Dielectric Properties in Biological Tissues: Insights into Dielectric Constant, Conductivity, and Resistivity at 9.4 GHz

This study investigates the dielectric properties of various biological tissues at microwave frequencies, specifically focusing on their dielectric constant, conductivity, resistivity, and loss tangent. Using methods such as Von Hippel’s and Yadav Gandhi’s techniques, the dielectric characteristics of heart, liver, brain, and muscle of chicken tissues were analysed at 9.4 GHz. It is found that tissues with higher water content exhibit greater dielectric constants and conductivities, while those with higher solid content, like liver, display higher resistivity. It has also been observed that tissues with lower dielectric constants and conductivities are those with greater absorption indices, which are typically associated with increased energy dissipation as heat. An increasing amount of energy dissipation may result from tissues with higher absorption rates being less effective at transferring microwave energy, as suggested by this inverse connection, which also emphasizes the complexity of electromagnetic wave interaction within tissues. This work provides critical insights into the interaction of electromagnetic waves with biological tissues, which is essential for applications in medical diagnostics, therapeutic technologies, and electromagnetic exposure safety standards.

Insight into the mechanism of alkali-thermal pretreatment of food-waste solid residue through fluorescence spectroscopy coupled with parallel factor analysis

Food-waste solid residue is the remaining solid after food waste treatment, with high yield, high solid content, high protein and fiber content. Effective pretreatment is necessary to improve the efficiency of hydrolysis and acidification for anaerobic digestion of food-waste solid residue. In this study, fluorescence spectroscopy coupled with parallel factor analysis were used to insight into the mechanism of food-waste solid residue during three pretreatments (alkali, thermal and alkali-thermal). Pretreatments increased the solubility of lignocellulosic substrate and destroyed structure of starch, while lignocellulosic analogs were effectively cracked, changing the composition and improving the degradability. Soluble chemical oxygen demand, soluble protein and soluble polysaccharide concentrations were increased by 144.60%, 350.57% and 138.72% after pretreatment under the condition of 120 °C + 2% CaO, respectively. Three-dimensional fluorescence spectra showed the region of maximum fluorescence intensity under alkali-thermal pretreatments, indicating chemical bonds (such as OC–C) were easier broken and the solubility of organic substances were increased. Three main fluorescence components were obtained by parallel factor analysis, which were humic acid-like, lignocellulose-like and protein-like, respectively, while the lignocellulose-like had the maximum Fmax value. The fluorescence intensity of samples under alkali-thermal pretreatment varied in the range from 59.48 × 105 to 13.18 × 106, which was an increase of 174.27%–507.74% over the control (21.68 × 105), indicating that alkali-thermal pretreatment observably accelerated the breaking of chemical bonds, and thus promoted the dissolution of organic matter. This study deeply revealed the mechanism of alkali-thermal pretreatment of food-waste solid residue, which is of great significance for efficient resource utilization of food waste and food-waste solid residue.

Improving hydrolysis and acidification by regulating the oxygen status and solid content of lignocellulosic waste: Emphasis on the unsealed environment and harnessing the potential of microbial communities

The recalcitrant nature of lignocellulosic raw materials poses a challenge for current biogas plant operations, where hydrolysis and acidification (HA) are the rate-determining steps. To explore the HA balance and microbial mechanisms according to oxygen status and in conditions with relatively high solid content, we made a simple change to build an unsealed reactor. We found that the hemicellulose degradation rate increased by 149.3 % under unsealed conditions. Under microaerobic conditions (Mi), HA with more than 10 % total solid (TS) content exhibited a carbon loss rate of < 10 % in the first 7 days. In the 15 % TS Mi treatment, the organic acid conversion coefficient was 0.04, and the concentration increased to 7.4 g/L within 2 days. A high solid content was the key factor for ensuring efficient organic acid production in the early stage, whereas Mi affected the middle stage. Multiple methods revealed that abundant Prevotella and Clostridium, as well as rare Bifidobacterium, Sporacetigenium, and specific bacteria, had substantial effects on efficient organic acid production and HA balance. The correlation with Mi was 0.57–0.83. The abundance of hemicellulase genes increased by 18.41 %, and the abundance of pyruvate kinase in Mi increased by 15.55 % compared with the sealed condition, demonstrating that Mi can provide complementary advantages in the HA process. The findings in this study improved the operational quality of conventional HA and anaerobic digestion.

Metagenomic Analysis during Co-Digestion Buffalo Sludge and Tomato Pomace Post Thermal Stress: A Case Study

The tomato industry and buffalo farming generate waste, including sludge (BS) and tomato pomace (TP), which can significantly impact their economic and environmental sustainability. The case study tracked changes in microflora composition after a thermal shock during anaerobic co-digestion. The inoculum-to-substrate ratio was 0.5 based on volatile solid content under mesophilic conditions. An Automatic Methane Potential Test System was used to monitor the process before and after thermal stress (50°C) occurred for three days. Next-generation sequencing analyzed the bacterial and archaeal communities. The pH decreased, and methane production plateaued due to the high volatile solid content (87 g/L). After thermal stress, the pH returned to neutral, and the batch resumed biogas production. The cumulative CH4 production reached 3,115 Nml. The biogas had a maximum methane peak of 78.5% compared to 58.4% in BS. The taxonomic classification showed that Firmicutes (51.7%) and Bacteroidetes (29.9%) represented 81.6% of the total OTUs among the bacteria. Fonticella, the most abundant Clostridiaceae (average 4.3%), was absent in BS and increased (up to 17.1%) in TP during methane production. Methanocorpusculum was the most abundant in the archaeal community. However, Metanosarcina showed a stronger correlation with methane production. Brief thermal stress significantly altered bacterial and archaeal populations and allowed to resume biogas production.

Effects of high solid content and straw proportion on volatile fatty acids production from straw, sludge and food wastes: performance and microbial community characteristics

Anaerobic digestion (AD) is an efficient technology for treating organic solid wastes, and the volatile fatty acids (VFAs) produced during AD have significant value due to their wide range of applications and higher added value compared to methane. This study investigated the long-term effects of high solid content and straw proportion in mixed substrates (straw, sludge, and food wastes) on VFAs production through semi-continuous reactors under thermophilic and mesophilic conditions. Results showed that both reactors achieved a maximum VFAs concentration of ~ 22 g/L as the straw proportion increased to 50%. Acetate (48.3 – 64.5%) was the main component of produced VFAs in both reactors, while butyrate and propionate production in thermophilic temperature were superior compared to mesophilic conditions. Microbial community analysis revealed that Defluviitoga plays a pivotal role in acidogenesis within both reactors; besides, unclassified Hungateiclostridiaceae and Caproiciproducen were found to be dominant in thermophilic reactor, while Lachnospiraceae_NK3A20_group and Rikenellaceae_RC9_gut_group were essential for VFAs production under mesophilic conditions. These findings provide valuable insights for the biotechnological exploration of acidogenic fermentation for large-scale mechanized production of VFAs from agricultural wastes.

Low voltage electrostatic field combined with ice-temperature to improve the quality of litchi during storage

Litchi is popular among consumers due to its delicious taste, however, the extremely short shelf life limits its commercial value. Few studies have been conducted to develop new technologies to extend the shelf life of litchi. Therefore, this study applied a novel technique (low voltage electrostatic field, LVEF) combined with ice-temperature (0 °C) treatment on litchi and evaluated its quality characteristics during storage. The results demonstrated that low voltage electrostatic field with ice-temperature storage (LVEF-IT) decreased malondialdehyde content, relative electrolyte leakage, and polyphenol oxidase and peroxidase activities, successfully delayed the start of peel browning. Additionally, it preserved the fruit pulp’s excellent quality, which included high concentrations of soluble solids, ascorbic acid, and soluble protein. These findings imply that LVEF-IT treatment may be a novel technique for extending the storage time of litchi.

Study on performance regulation of electro-mechanical properties 3D printed BaTiO3/HA porous structure composite ceramic

BaTiO3/Ca10(PO4)6(OH)2 composite ceramic is an outstanding representative of piezoelectric biomaterials, with excellent biocompatibility and piezoelectric effect, and has potential applications in the field of bone tissue repair. In this work, vat photopolymerization 3D printing technology was used to fabricate triply periodic minimal surface structure BaTiO3/Ca10(PO4)6(OH)2 composite ceramic bone tissue scaffolds with different pore sizes and porosity, and their mechanical and electrical properties were studied. First, the ceramic slurry configuration process was optimized to obtain a ceramic slurry with high solid content (45 vol%) and excellent rheological properties. Then the effect of sintering temperature on microstructure, relative density, mechanical properties, and electrical properties is discussed. The results show that when sintering at 1300 °C, the BaTiO3/Ca10(PO4)6(OH)2 composite ceramic has the highest relative density (99.18 %), the highest compressive strength (44 MPa), large relative dielectric constant (379–389), and low dielectric loss. The polarization electric field strength of the BaTiO3/Ca10(PO4)6(OH)2 composite ceramic was set to 15 kV/cm through the test of the hysteresis loop. Finally, based on multi-physics coupled finite element simulation, the effects of different porosity and different pore sizes on stress distribution and piezoelectric potential were analyzed, and the relationship between them was explored through experiments. The results show that as the porosity increases and the pore size decreases, the mechanical properties of the scaffold decrease significantly, and its compressive strength ranges between 1.67 and 4.26 MPa; as the porosity increases and the pore size increases, the piezoelectric coefficient (d33) of the scaffold showed a decreasing trend, and its d33 ranged between 2 and 9 pC/N. The mechanical and electrical properties of the scaffold meet the performance requirements of cancellous bone. In summary, this work provides a strategy for the application of customized BaTiO3/Ca10(PO4)6(OH)2 composite ceramic scaffolds in new-generation orthopedic implants.

Direct ink writing of WC-Co composite with flexible green bodies

Direct ink writing of 3D WC-Co with conformable green bodies was achieved benefiting from the highly flexible WC-Co paste with high solid loading. Rheology properties of the paste, microstructure of the 3D structure was investigated. Organic-based paste of WC-8Co with a high solid content of 91 wt% were prepared, which exhibited shear thinning behavior and had a high storage modulus, two key parameters for ensuring the smooth printing. After secondary molding, 3D WC-Co green bodies with overhanging structure and no cracks were confirmed through secondary treatment of twisting or bending. Sound 3D structures with uniform and dense microstructure were obtained after debinding and sintering in vacuum. This work showed a facile route for the fabrication of 3D bone cemented carbides by direct ink writing with flexible green bodies.

High-solid digestion – A comparison of completely stirred and plug-flow reactor systems

High-solid digestion (HSD) for biogas production is a resource-efficient and sustainable method to treat organic wastes with high total solids content and obtain renewable energy and an organic fertiliser, using a lower dilution rate than in the more common wet digestion process. This study examined the effect of reactor type on the performance of an HSD process, comparing plug-flow (PFR) type reactors developed for continuous HSD processes, and completely stirred-tank reactors (CSTRs) commonly used for wet digestion. The HSD process was operated in thermophilic conditions (52 °C), with a mixture of household waste, garden waste and agricultural residues (total solids content 27–28 %). The PFRs showed slightly better performance, with higher specific methane production and nitrogen mineralisation than the CSTRs, while the reduction of volatile solids was the same in both reactor types. Results from 16S rRNA gene sequencing showed a significant difference in the microbial population, potentially related to large differences in stirring speed between the reactor types (1 rpm in PFRs and 70–150 rpm in CSTRs, respectively). The bacterial community was dominated by the genus Defluviitoga in the PFRs and order MBA03 in the CSTRs. For the archaeal community, there was a predominance of the genus Methanoculleus in the PFRs, and of the genera Methanosarcina and Methanothermobacter in the CSTRs. Despite these shifts in microbiology, the results showed that stable digestion of substrates with high total solids content can be achieved in both reactor types, indicating flexibility in the choice of technique for HSD processes.

Assessment of the Biochemical Methane Potential of Wastewater and Sludge Cake from a Poultry Slaughterhouse

Objectives : This study evaluates the potential for resource recovery through anaerobic digestion of organic waste generated in a poultry slaughterhouse, specifically focusing on poultry slaughterhouse wastewater and sludge cake obtained from in-house wastewater treatment.Methods : Basic characteristics (total solids, alkalinity, etc.), total nitrogen/ammonia nitrogen, and elemental analysis (macro and trace elements) were performed to determine the properties of the samples and calculate theoretical methane potential. Experimental methane potential was determined through BMP tests, with parameters such as lag period (λ) and maximum methane production rate (CH 4 mL/g VS/d) obtained using the modified Gompertz equation.Results and Discussion : The wastewater exhibited low organic matter concentration (1.79 g VS/kg; 3.74 g COD/L), while the sludge cake showed high total solids content (TS 170.8 g/kg) and organic matter concentration (131.5 g VS/kg; 220 g COD/L). Elemental analysis revealed that the C/N ratio was 9.17 for the sludge cake and 8.24 for the wastewater, indicating high nitrogen content. Methane production modeling using the modified Gompertz equation revealed a lag period of 7.5 days and T80 (time to produce 80% of total methane) of 21 days for wastewater, and a lag period of 2.4 days and T80 of 14 days for sludge cake.Conclusion : Wastewater and sludge cake from poultry slaughterhouses show significant potential as substrates for anaerobic digestion. However, the wastewater has low organic matter content, and the sludge cake, while high in organic matter, has low moisture and high ammonia levels. Therefore, it may be appropriate to co-digest these two substrates, or to co-digest the sludge cake with other substrates that have low nitrogen content and high water content. These findings provide fundamental data for the anaerobic digestion of slaughterhouse waste and highlight the need for further research on co-digestion and continuous processes.

Microstructural evolution, enhanced mechanical properties, and complex shapes design in high solid content alumina ceramics through additive manufacturing

Manufacturing industrially profitable high solid-loading ceramic materials with finely designed complex shapes is an exciting yet challenging in sustainable additive manufacturing. Here, we propose a resin strategy to achieve a high solid-loading content of 62 vol% alumina slurry for 3D printing high-quality complex shapes using digital light processing (DLP) technology. Remarkably, both high solid-loading content and tuned sintering temperature emerge as key factors in ensuring optimal print quality and mechanical performance. With this strategy, the ceramic slurry containing 62 vol% exhibits lower shear rate and improved layer adhesion. The burnout treatment was designed based on the DSC-TGA results, followed by sintering in an air atmosphere. Comprehensive physical measurements were achieved, alongside precise structural characterization at multilength scales in situ. In depth exploration of post-sintering analysis revealed no changes in phase composition or chemical bonding. The optimum overall performance of sintered specimen exhibited shrinkage of 8.3 %, 8.8 %, and 11.5 % in the X, Y, and Z directions, with a bulk density of 3.76 g/cm3. Mechanical testing demonstrated superior flexural strength of 247.23 MPa, nanoindentation hardness of 30.9 GPa, and modulus of 428.35 GPa. This high-precision printing strategy may significantly contribute to understanding the structure-property relationship of DLP-3D printed Al2O3 ceramic and opening avenue for the applications of high-strength parts in demanding environments.

Effect of solid content, particle size, and deflocculant on rheological properties of kaolin suspensions

In this research, two different particle sizes of kaolin were selected, and their rheological properties were characterized by steady-state and dynamic rheological tests. Stress relaxation in the flow curves was a novel finding; redefinition and interpretation of flow curves were the focus of our research. Two methods were used and compared for determining the yield stress. The results showed that suspensions with higher solid content and smaller particle size showed more compact inter-particle interactions, exerting multiple stress relaxation and a strong yield and viscoelastic characteristic. The thixotropic properties were also strongly affected by solid content and particle size, and the differences were reflected in the structural recovery capability. Finally, the effects on rheological properties by introducing deflocculant were studied; the stress relaxation disappeared gradually, and storage modulus and yield stress increased.Moreover, kaolin suspensions with smaller particle sizes required more deflocculant for adsorption and electrical neutralization, confirming that more positively charged edges were exposed after fragmentation. This study has provided an excellent approach to control and adjust the rheological properties of kaolin suspensions in industrial applications.

Efficient electrochemical removal of ammoniacal nitrogen from livestock wastewater: The role of the electrode material

Wastewater from livestock farms contains high concentrations of suspended solids, organic contaminants, and nitrogen compounds, such as ammoniacal nitrogen. Discharging livestock effluents into water bodies without appropriate treatment leads to severe environmental pollution. Compared to conventional treatment methods, electrochemical oxidation exhibits higher nitrogen removal efficiencies. In the present work, the electrochemical removal of ammoniacal nitrogen from real livestock wastewater was investigated through a lab-scale reactor. Preliminary experiments were carried out to investigate the effects of different anode materials, including boron-doped diamond and iridium/ruthenium-coated titanium, on the total nitrogen removal efficiency using synthetic wastewater. Boron-doped diamond, a well-known non-active electrode, allowed to obtain 63.7 ± 1.21 % of total nitrogen degradation efficiency. However, the iridium/ruthenium-coated titanium electrode, belonging to the class of active anodes, showed a higher performance, achieving 78.8 ± 0.76 % contaminant degradation. Coupling iridium/ruthenium-coated titanium anode with a stainless-steel cathode improved the performance of the system, achieving even 96.2 ± 2.73 % of total nitrogen removal. The optimized cell configuration was used to treat livestock wastewater, resulting in the degradation of 67.0 ± 2.25 % of total nitrogen and 37.3 ± 0.68 % of total organic carbon when sodium chloride was added. At the end of the process, the ammonium content was completely removed, and only 17.7 ± 0.51 % of the initial nitrogen turned into nitrate. The results show that the proposed system is a promising approach to treating livestock wastewater by coupling high contaminant removal efficiencies with low operational costs. Anyway, further studies on process optimization with an emphasis on power requirements and electrode costs need to be carried out.

A scalable, chromatography-free, biocatalytic method to produce the xyloglucan heptasaccharide XXXG

Xyloglucan oligosaccharides (XyGOs) are highly branched, complex carbohydrates with a variety of chemical and biotechnological applications. Due to the regular repeating pattern of sidechain substitution of the xyloglucan backbone, well-defined XyGOs are readily accessed for analytical and preparative purposes by specific hydrolysis of the polysaccharide with endo-glucanases. To broaden the application potential of XyGOs, we present here an optimized, scalable method to access large quantities of galactosylated XyGOs by treatment of the bulk agricultural by-product, tamarind kernel powder (TKP), with a highly specific endo-xyloglucanase at high-solids content. Subsequent β-galactosidase treatment reduced XyGO complexity to produce exclusively the branched heptasaccharide XXXG (Xyl3Glc4: [α-D-Xylp-(1 → 6)]-β-D-Glcp-(1 → 4)-[α-D-Xylp-(1 → 6)]-β-D-Glcp-(1 → 4)-[α-D-Xylp-(1 → 6)]-β-D-Glcp-(1 → 4)-D-Glcp). The challenge of removing the co-product galactose was overcome by fermentation with baker’s yeast, thereby avoiding chromatography and other fractionation steps to yield highly pure XXXG. This simplified approach employs many of the core concepts of green chemistry and engineering, enables facile production of 100 g quantities of XyGOs and XXXG for laboratory use, and serves as a guide to further production scale-up for applications, including as prebiotics, plant growth effectors and elicitors, and building blocks for glycoconjugate synthesis.

Modeling copper leaching from non-pulverized printed circuit boards at high concentrations of bioregenerated ferric sulfate

This work studies the leaching of copper contained in waste printed circuit boards (PCB) with ferric sulfate, with the aim of improving the results found in the literature for an industrial application of the process. For this purpose, temperatures and concentrations of ferric ion higher than those of previous works (up to 60 °C and 40 g/L) are used. Furthermore, ferric sulfate can be continuously regenerated by ferro-oxidizing bacteria immobilized in a bioreactor, avoiding physical contact between waste and microorganisms to optimize independently operation conditions. A kinetic model was developed for the interpretation of the experimental results validated at different conditions. The model was based on a shrinking core model limited by mass transfer inside the PCB where the geometry and structure of the PCB has been considered and an excellent fit of the model to the experimental data was obtained. The connection with the bioreactor for biooxidation of the generated ferrous ion allows maintaining high concentrations of ferric when operating at high solid concentrations (5–10 %). In all the cases studied, more than 99 % of the copper contained in the non-pulverized PCB parts was dissolved in less than 24 h, with an average copper extraction rate of 0.6 g/L·h higher than those found in previous works.

Mechano-chemical, high-consistency activation of kraft pulp in deep eutectic solvent of choline chloride and urea

Deep eutectic solvents (DESs) offer an appealing green medium for the activation of cellulose fibres to promote their swelling, reactivity, hydrolysis, disintegration, and solubility for further processing. Typically, DES treatments are carried out below 5 wt% consistency even though a higher solids content could enhance the fibre activation and reduce the solvent consumption. In this work, a high-consistency (HC) mechano-chemical activation of bleached softwood kraft pulp was elucidated using a simultaneous fibre treatment with DES of choline chloride-urea and a sigma-type kneader or a twin-screw extruder at a solids content of 15–35 wt% and 30 wt%, respectively. Both HC treatments efficiently triggered fibre swelling, which was indicated by an increase in the fibre width, and loosened the cell wall structure which was indicated by an increase in the mesopore volume. Mechano-chemical HC processing generated fibre fines and external fibrillation, while the molecular-level structural alteration or changes in chemical composition were minor; the intrinsic viscosity and the crystallinity of the pulp remained at their initial level and only a small amount of xylan was dissolved. Overall, HC treatment in a twin-screw extruder caused notably more severe morphological changes in the fibres than batch treatment in a sigma-type kneader. Thus, the mechano-chemical HC treatment with DES provides an industrially relevant technology for cellulose modification and opens possibilities to enhance heterogeneous cellulose modification processes in which the highly available surface area of pulp is a key parameter.

Crystalline Nanoflowers Derived from the Intramolecular Cyclization-Induced Self-Assembly of an Amorphous Poly(amic acid) at High Solid Content.

The investigation of the amorphous to crystalline transformation and the corresponding influence on the self-assembly behavior of amphiphilic polymers are of significant interest in this field. Herein, we propose the concept of intramolecular cyclization-induced self-assembly (ICISA) to prepare crystalline nanoflowers at a high solid content of 15% on the basis of the amorphous to crystalline transformation of poly(amic acid) (PAA). Taking advantage of the reactive property of the PAA, rigid and crystalline polyimide (PI) segments are introduced to the backbone of the PAA to give P(AA-stat-I) induced by the intramolecular cyclization reaction upon thermal treatment, leading to the in situ formation of crystalline nanoflowers. Revealing the formation mechanism of the nanoflowers, we found that the nanosheets are formed at the early stage and then stacked to form the nanoflowers at high concentrations. The relationship between the degree of imidization and incubation temperature is quantitatively analyzed, and the effects of temperature on the morphology, degree of imidization, and crystallinity of the assemblies are also investigated. Furthermore, computer simulations demonstrate the optimized temperature of ICISA of 160 °C, which ensures the match between the intramolecular cyclization reaction rate, the self-assembly process, and the lowest energy state of the self-assembly system, resulting in the formation of nanoflowers with high crystallinity. Overall, a facile one-step strategy is proposed to prepare crystalline nanoflowers based on the in situ thermally triggered intramolecular cyclization reaction of a PAA, which may bring fresh insights into the dynamic amorphous to the crystalline transformation of polymers.