Low Lignin Research Articles

Overexpression of Bacterial Beta-Ketothiolase Improves Flax (Linum usitatissimum L.) Retting and Changes the Fibre Properties

Beta-ketothiolases are involved in the beta-oxidation of fatty acids and the metabolism of hormones, benzenoids, and hydroxybutyrate. The expression of bacterial beta-ketothiolase in flax (Linum usitatissimum L.) results in an increase in endogenous beta-ketothiolase mRNA levels and beta-hydroxybutyrate content. In the present work, the effect of overexpression of beta-ketothiolase on retting and stem and fibre composition of flax plants is presented. The content of the components was evaluated by high-performance liquid chromatography, gas chromatography-mass spectrometry, Fourier-transform infrared spectroscopy, and biochemical methods. Changes in the stem cell walls, especially in the lower lignin and pectin content, resulted in more efficient retting. The overexpression of beta-ketothiolase reduced the fatty acid and carotenoid contents in flax and affected the distribution of phenolic compounds between free and cell wall-bound components. The obtained fibres were characterized by a slightly lower content of phenolic compounds and changes in the composition of the cell wall. Based on the IR analysis, we concluded that the production of hydroxybutyrate reduced the cellulose crystallinity and led to the formation of shorter but more flexible cellulose chains, while not changing the content of the cell wall components. We speculate that the changes in chemical composition of the stems and fibres are the result of the regulatory properties of hydroxybutyrate. This provides us with a novel way to influence metabolic composition in agriculturally important crops.

Mechanically strong nanopapers based on lignin containing cellulose micro- and nano-hybrid fibrils: Lignin content-fibrils morphology-strengthening mechanism

Lignin-containing cellulose nanopapers are emerging multifunctional materials in the fields of coatings, films, and packaging. However, the forming mechanism and properties of nanopapers with various lignin content have not been thoroughly studied. In this work, a mechanically strong nanopaper was fabricated based on lignin-containing cellulose micro- and nano-hybrid fibrils (LCNFs). The influence of lignin content and fibrils morphology on the formation process of nanopapers was investigated to understand the strengthening mechanism of nanopapers. LCNFs with high lignin content provided nanopapers with intertwined micro- and nano-hybrid fibrils layers with small layer spacing, while LCNFs with low lignin content offered nanopapers interlaced nanofibrils layers with large layer spacing. Although lignin was expected to interfere with hydrogen bonds between fibrils, the uniformly distributed lignin contributed to the stress transfer between fibrils. Due to the good coordination between microfibrils, nanofibrils and lignin (as network skeleton, filler and natural binder, respectively), the well-designed LCNFs nanopapers with lignin content of 14.5 % showed excellent mechanical properties, including tensile strength (183.8 MPa), Young's modulus (5.6 GPa) and elongation (9.2 %). This work deeply reveals the relationship between lignin content, morphology and strengthening mechanism of nanopapers, and providing theoretical guidance for employing LCNFs as structural and reinforcing materials to design robust composites.

Rheological properties and volumetric isothermal expansivity of bamboo kraft black liquor with high solids content and low lignin content

In this study, a certain percentage of lignin in original bamboo kraft black liquor (BKBL) was separated, and the residual BKBL with low lignin content was expected to be fed into the alkali recovery boiler to reduce the heat transfer load of the alkali recovery boiler. With the decrease in lignin content, the rheological properties/volumetric isothermal expansivity (VIE) of BKBL change. When the lignin content was 70% remaining in the original BKBL, the viscosity of BKBL with low lignin content is close to that of the passivated BKBL at the same solids content, the dynamic viscoelasticity is superior, and the VIE decreases by 57.2%. When the amount of desilication agent is 1.5%, the viscosity of BKBL with low lignin content did not change much, and the VIE increased sharply and was 62.7% higher than that of the passivated BKBL. Therefore, the combination of partial lignin separation process and sodium aluminate desilication process can effectively improve the ability of alkali recovery boiler to deal with BKBL and reduce the influence of “silicon interference”.

Aquatic biomass as sustainable feedstock for biorefineries

AbstractThe development of biorefineries is a crucial step in the circular economy framework. In biorefineries, research is intensified towards utilizing feedstocks, which do not need arable land or compete with food sources. In this scenario, emerged, submerged and free‐floating aquatic plants are garnering significant attention as potential feedstocks owing to their generation in huge quantities, especially in eutrophic water bodies, similar composition to lignocellulosic biomass with lower lignin content and requirement for only mild pre‐treatments. Therefore, exploring the feasibility of using these aquatic plants for the production of various biocommodities in a biorefinery approach can be of prime importance. In light of this, the current review illustrates the use of some of the major aquatic plants for the production of different biocommodities. The main focus of the study is to shed light on the various biorefinery schemes that could be implemented using these aquatic plants. It also outlines the challenges and prospects of aquatic plant‐based biorefineries. The findings suggest that various biorefinery schemes can be implemented using these aquatic plants and a combination of chemical and biological processes could aid in lowering the cost and achieving better yields. Furthermore, it is also observed that research on large‐scale management and valorization of these aquatic plants also needs to be intensified.

Physico-chemical, Thermal and Micro-structural Characterization of Four Common Banana Pseudo-Stem Fiber Cultivars in Nigeria

ABSTRACT This study explores Banana pseudo-stem fiber (BPSF) derived from BPF cultivars that are common in Nigeria. The four cultivars are known locally as Agbagba, Omini, Panbola, and Paranta. This study characterized these cultivars to gain insight into their physical, thermal and microstructural properties. The BPSFs were obtained after manual BPS retting and treated with a 2 wt. % sodium hydroxide solution to improve the fiber quality. Data from the characterization revealed the agbagba cultivar to give the highest percentage recovery (3%) and thermal stability at elevated temperatures with a residual char of 14%. The percentage of cellulose, lignin, hemicellulose, and ash content were determined by chemical composition analysis. FTIR spectroscopy showed a lower lignin and hemicellulose absorption band in the agbagba cultivar while scanning electron microscopy supported the FTIR results. Agabagba’s crystallinity index (XRD) of 61.7% was higher than other cultivars, and X-ray fluorescence (XRF) and a biodegradation test also showed that only agbagba cultivar contained calcium and had the strongest resilience to microbial attack under simulated soil conditions. Agbagba BPSF may be a viable reinforcement in bio-fiber polymer composites needing high strength due to its balanced qualities that have been demonstrated in comparison to other cultivars.

From nature back to nature: Spectrally modified poplar and its all-day passive radiative cooling

Thermal radiation properties of natural wood are mainly affected by its chemical composition and physical structure. In the atmospheric transparency window (8–13 µm), cellulose, hemicellulose and lignin all have high average emissivity of 95.77%, 96.83% and 97.22%, respectively. This allows wood to continuously transfer radiation heat to outer space without hindrance, according to natural radiative cooling principle. It is so attractive to develop its all-day radiative cooling potential for continuous heat dissipation and energy-saving without energy input and pollutant output. Cooling capacity is directly affected by spectral property, for which delignified wood is prepared to explore the relation between lignin content and thermal radiation properties of wood. Results show that, the lower lignin content of wood would cause the higher average solar reflectivity and daytime radiative cooling power density, without affecting infrared emissivity and nighttime radiative cooling performance. With lignin content of 0.94%, delignified wood achieves all-day radiative cooling performance, obtaining average temperature drop of 2.60 K and 3.81 K at daytime and nighttime. Magically, its surface has a redirecting effect on incident heat, to the credit of the removal of amorphous lignin and inherited cellulose arrangement. Such a light-weight, environment-friendly, low-cost and all-day energy-saving material combining natural wood and natural radiative cooling principle provides a novel option for green products.

Light-colored lignin extraction by ultrafiltration membrane fractionation for lignin nanoparticles preparation as UV-blocking sunscreen

A wide range of applications are available for kraft lignin (KL). However, the dark color and wide size distribution of KL make it challenging to use in cosmetics and nanoparticle preparation. In this study, we fractionated KL from a paper-making enterprise using ultrafiltration membrane fractionation, and obtained four kinds of lignin with different molecular weights, namely ultrafiltration lignin (UL). Following that, lignin nanoparticles (ULNPs) were formed by self-assembly from four types of UL. Analyzing the UL and ULNP properties, the low molecular weight lignin, such as ULA, exhibited good antioxidant properties (89.47 %, 5 mg/mL), high brightness (ISO% = 7.55), high L⁎ value (L⁎ = 72.3) and low polydispersity index (PDI = 1.41). The ULNP showed a narrow size distribution (0.8–1.4 m) and high dispersibility in sunscreen. When ULNP was added to sunscreen with 5 % load, its sun protection factor (SPF) value increased from 14.93 to 63.74. Therefore, this study offered an effective way for the comprehensive utilization of pulping waste KL.

Selection of kraft lignin fractions as a partial substitute for phenol in synthesis of phenolic resins: Structure-property correlation

In this work, a strategy was proposed aiming to describe an efficient kraft lignin (KL) fractionation method to extract large amounts of low molar mass lignin to partially replace non-renewable phenol with the KL fractions in the synthesis of phenolic resins. KL from Eucalyptus urograndis wood was refined by a fractionation process in ethyl acetate (EtAc). The lignin-phenol-formaldehyde (LPF) resins were formulated by replacing 25% and 50% of phenol with the fractionated lignin. The lignin employed were KL, fraction of KL insoluble in EtAc (LFIns) and fraction of KL soluble in EtAc (LFSol). The LFSol and LFIns fractions were analyzed for composition, functional group content, and thermal properties. Gel Permeation Chromatography (GPC) results indicated that the lower molar mass lignin fractions (LFSol) showed higher solubility in EtAc. The total hydroxyl groups content (by 31 P NMR) of the soluble EtAc fraction increased to 4.73 mmol.g −1 after fractionation. The phenolic resin based on monomers derived from LFSol showed adhesion strength, glass transition temperature and thermal stability with values close to commercial phenolic resins. The better homogeneity of the LPF resin produced from LFSol at 25% phenol substitution resulted in adhesion properties similar to the control resin. On the other hand, LFSol could successfully directly replace 15% of the commercial PF resin (corresponding to > 30% phenol replacement) showing the performance similar to the commercial PF control and significantly higher than the LFIns and non-fractionated KL. • Extraction method of low molar mass kraft lignin. • Structure-performance correlation of selection of kraft lignin fractions. • Partial replacement of non-renewable phenol by lignin fractions. • Improved performance of the soluble lignin fraction as an adhesive.

Anaerobic Fermentation of Kepok Banana (Musa Paradisiaca) Peels with Different Levels of Tapioca for Reducing Their Fiber Components

Banana peel is restricted to use as feedstuffs because it has a high crude fiber content. The reduction of crude fiber can be done by anaerobic fermentation such as silage making. Soluble carbohydrates are needed as an energy source for microorganisms in ensilage process. Tapioca is one of soluble carbohydrates that can be used to improve silage quality. The objective of this study was to evaluate effect of tapioca levels on the fiber fraction of kepok banana peel silage (Musa paradisiaca). A completely randomized design was used in this study, with 4 treatments and 5 replications, namely T0: without tapioca, T5: 5% tapioca, T10: 10% tapioca, T15: 15% tapioca. Variables observed were the content of NDF (%), ADF (%), hemicellulose (%), cellulose (%), and lignin (%).Collected data was analyzed by analysis of variance and if it had a significant effect, it was continued with Duncan's multiple range test. The results of analysis of variance showed that the level of tapioca had a highly significant effect (P<0.01) on NDF, ADF, hemicellulose, cellulose, and lignin. DMRT showed that the lowest NDF content was at T15 with an average of 48.06%, the lowest ADF was found at T15 with an average of 20.20%, the lowest hemicellulose was found at T15 with an average of 27.46%, the lowest cellulose was found at T10 with an average of 7.98% and the lowest lignin against T15 with an average of 12.09%. In conclusions, 1) Different levels of tapioca was can reduce ADF, NDF, hemicellulose, cellulose, and lignin in kepok banana peel silage, 2) The use of 10% tapioca reduced the highest kepok banana peel silage fiber fraction.

Natural Cellulose from Ziziphus jujuba Fibers: Extraction and Characterization.

Nowadays, due to their natural availability, renewability, biodegradability, nontoxicity, light weight and relatively low cost, natural fibers, especially lignocellulosic fibers, present attractive potential to substitute non-eco-friendly synthetic fibers. In this study, Ziziphus jujuba fibers were used, thanks to their low lignin content, as an alternative of renewable resource for the production of cellulosic fibers with suitable characteristics and minimal time and energy consumption. In fact, due to their valuable chemical composition, it was possible to remove the amorphous fractions and impurities from the fiber surface by applying ultrasounds coupled with alkaline treatment (80 °C, 5 wt.% NaOH), followed by a bleaching step. The efficient dissolution of the noncellulosic compounds was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The resulted increase in the crystallinity index (from 35.7% to 57.5%), occurred without impacting the crystalline structure of the fibers. The morphological analysis of the fibers evidences the higher surface area of the obtained fibers. Based on the obtained results, Ziziphus jujuba fibers were found to present a suitable sustainable source for the production of cellulosic fibers.

Comparative Physiological Analysis of Lignification, Anthocyanin Metabolism and Correlated Gene Expression in Red Toona sinensis Buds during Cold Storage

The characteristics of anthocyanin and lignin are important parameters in evaluating the quality of red Toona sinensis buds. Red T. sinensis buds are prone to senescence during postharvest storage, which subsequently affects their quality and sales. However, the mechanism of senescence in red T. sinensis buds under low-temperature conditions remains unclear. In this study, red T. sinensis buds were stored at 4 °C, and their anthocyanin and lignin contents as well as the enzyme activities of PAL (phenylalanine ammonia lyase), 4CL (4-coumarate-CoA ligase), CAD (cinnamyl alcohol dehydrogenase) and POD (peroxidase) were determined at 0, 1, 2 and 3 d after handing. Meanwhile, the cellular structure of postharvest red T. sinensis buds was observed by microscopy. The relative expression of lignin-related and anthocyanin-related genes was analyzed using qRT-PCR. The results show that the anthocyanin content of the leaves was higher than that of the petioles. After 3 d of storage, the anthocyanin content of the leaves was 4.66 times that of the petioles. Moreover, the lignin content of the red T. sinensis buds gradually increased. Compared with 0 d, the lignin content of the leaves and petioles increased by 331.8 and 94.14 mg·g−1, respectively. The enzyme activities of PAL, 4CL, CAD and POD increased during cold storage. The intercellular space and the arrangement of the palisade tissue and sponge tissue in the mesophyll of red T. sinensis buds became smaller and closer, respectively. The secondary cell wall of xylem cells thickened, the number of xylem cells increased, and the arrangement number of the xylem cells became closed in the leaf vein and petioles during red T. sinensis bud storage. The expression levels of anthocyanin-related (Except for TsCHS and TsANS) and lignin-related genes increased during red T. sinensis bud storage and are highly consistent with the accumulation patterns of anthocyanins and lignin. This study may serve as a reference for exploring the molecular mechanisms of senescence, regulating the quality and cultivating new varieties of red T. sinensis buds that have low lignin content but high anthocyanin content after harvest.

Lignin-Containing Cellulose Nanofibrils from TEMPO-Mediated Oxidation of Date Palm Waste: Preparation, Characterization, and Reinforcing Potential.

Lignin-containing cellulose nanofibrils (LCNFs) have emerged as a new class of nanocelluloses where the presence of residual lignin is expected to impart additional attributes such as hydrophobicity or UV-absorption. In the present work, LCNFs with a lignin content between 7 and 15 wt% were prepared via a TEMPO-mediated oxidation as chemical pretreatment followed by high-pressure homogenization. The impact of the carboxyl content (CC) on the properties of the resulting LCNF gel, in terms of lignin content, colloidal properties, morphology, crystallinity, and thermal stability, were investigated. It was found that lignin content was significantly decreased at increasing CC. In addition, CC had a positive effect on colloidal stability and water contact angle, as well as resulting in smaller fibrils. This lower size, together with the lower lignin content, resulted in a slightly lower thermal stability. The reinforcing potential of the LCNFs when incorporated into a ductile polymer matrix was also explored by preparing nanocomposite films with different LCNF contents that were mechanically tested under linear and non-linear regimes by dynamic mechanical analysis (DMA) and tensile tests. For comparison purposes, the reinforcing effect of the LCNFs with lignin-free CNFs was also reported based on literature data. It was found that lignin hinders the network-forming capacity of LCNFs, as literature data shows a higher reinforcing potential of lignin-free CNFs. Nonetheless, the tensile strength of the acrylic matrix was enhanced by 10-fold at 10 wt% of LCNF content.

Brown midrib mutant and genome-wide association analysis uncover lignin genes for disease resistance in maize.

Brown midrib (BMR) maize (Zea mays L.) harbors mutations that result in lower lignin levels and higher feed digestibility, making it a desirable silage market class for ruminant nutrition. Northern leaf blight (NLB) epidemics in upstate New York highlighted the disease susceptibility of commercially grown BMR maize hybrids. We found the bm1, bm2, bm3, and bm4 mutants in a W64A genetic background to be more susceptible to foliar fungal (NLB, gray leaf spot [GLS], and anthracnose leaf blight [ALB]) and bacterial (Stewart's wilt) diseases. The bm1, bm2, and bm3 mutants showed enhanced susceptibility to anthracnose stalk rot (ASR), and the bm1 and bm3 mutants were more susceptible to Gibberella ear rot (GER). Colocalization of quantitative trait loci (QTL) and correlations between stalk strength and disease traits in recombinant inbred line families suggest possible pleiotropies. The role of lignin in plant defense was explored using high-resolution, genome-wide association analysis for resistance to NLB in the Goodman diversity panel. Association analysis identified 100 single and clustered single-nucleotide polymorphism (SNP) associations for resistance to NLB but did not implicate natural functional variation at bm1-bm5. Strong associations implicated a suite of diverse candidate genes including lignin-related genes such as a β-glucosidase gene cluster, hct11, knox1, knox2, zim36, lbd35, CASP-like protein 8, and xat3. The candidate genes are targets for breeding quantitative resistance to NLB in maize for use in silage and nonsilage purposes.

Lignin-Derived Oil Palm Biomass Using Deep Eutectic Solvent

Deep Eutectic Solvent (DES) are eutectic mixes of hydrogen bond acceptors (HBA) and donors (HBD) with melting points significantly lower than their constituents. Choline chloride (ChCl) and glycerol were chosen as HBA and HBD because they are simple to prepare, have low toxicity, are biodegradable, and are environmentally friendly. As a result, the study aims to determine the feasibility of extracting lignin from oil palm fronds (OPF) and empty fruit bunches (EFB) using DES. The molar ratios of DESs were investigated to determine their effect on OPF solubility and lignin yield. The reaction is carried out at a solid loading ratio of 1:10, 150°C, and 6 hours. Because the DES medium induces homogeneous swelling and breakdown of small fibre fragments but not dissolution, both OPF and EFB are insoluble in DES. Small fragment disintegration suggests rapid dissolution, which will be easily dissolved in the DESs. The lignin yield and solubility of EFB and OPF in DESs are significantly reduced when the molar concentration of glycerol is increased. The highest lignin yields, 27.6% (EFB) and 16.1% (OPF) were obtained with a ChCl/glycerol molar ratio of 1:3. The comparatively low lignin yield achieved for both OPF and EFB is ascribed to the poor hydrogen bonding between the chloride ion and the hydroxyl group of the DES due to the low acidity of the DES. Despite this, lignin is extracted successfully due to the presence of chloride ions in ChCl, which target β-O-4 bonds and successfully cleave the ether bonds present in the lignin-carbohydrate linkage.

Characterization of lodging variation of weedy rice.

Weedy rice (Oryza spp.), one of the most notorious weeds of cultivated rice, evades eradication through stem lodging and seed shattering. Many studies have focused on seed shattering, whereas variations in lodging have received less attention and the underlying mechanisms that cause the differences in lodging between weedy and cultivated rice have not been studied in detail. Here, we compared lodging variation among diverse Chinese weedy rice strains and between weedy rice and co-occurring cultivated rice. The chemical composition of basal stems was determined, and transcriptome and methylome sequencing were used to assess the variation in expression of lodging-related genes. The results showed that the degree of lodging varied between indica-derived weed strains with high lodging levels, which occurred predominantly in southern China, and japonica-derived strains with lower lodging levels, which were found primarily in the north. The more lodging-prone indica weedy rice had a smaller bending stress and lower lignin content than non-lodging accessions. In comparison to co-occurring cultivated rice, there was a lower ratio of cellulose to lignin content in the lodging-prone weedy rice. Variation in DNA methylation of lignin synthesis-related OsSWN1, OsMYBX9, OsPAL1, and Os4CL3 mediated the differences in their expression levels and affected the ratio of cellulose to lignin content. Taken together, our results show that DNA methylation in lignin-related genes regulates variations in stem strength and lodging in weedy rice, and between weed strains and co-occurring cultivated rice.

A New Insight into the Composition and Physical Characteristics of Corncob—Substantiating Its Potential for Tailored Biorefinery Objectives

Corncobs of four different corn varieties were physically segregated into two different anatomical portions, namely the corncob outer (CO) and corncob pith (CP). The biomass composition analysis of both the CO and CP was performed by four different methods. The CP showed a higher carbohydrate and lower lignin content (83.32% and 13.58%, respectively) compared with the CO (79.93% and 17.12%, respectively) in all of the methods. The syringyl/guaiacyl (S/G) ratio was observed to be higher in the CP (1.34) than in the CO (1.28). The comprehensive physical characterization of both samples substantiated the lower crystallinity and lower thermal stability that was observed in the CP compared to the CO. These properties make the CP more susceptible to glycanases, as evident from the enzymatic saccharification of CP carried out with a commercial cellulase and xylanase in this work. The yields obtained were 70.57% and 88.70% of the respective theoretical yields and were found to be equal to that of pure cellulose and xylan substrates. These results support the feasibility of the tailored valorization of corncob anatomical portions, such as enzymatic production of xylooligosaccharides from CP without pretreatment combined with the bioethanol production from pretreated CO to achieve an economical biorefinery output from corncob feedstock.

Valorisation of Underutilized Grass Fibre (Stem) as a Potential Material for Paper Production.

An integrated and feasible approach was proposed using the underutilized grass fibre (stem) derived from Napier grass and sugarcane for paper production in this study. To enhance paper strength, pre-hydrolysis and beating techniques have been used to improve the chemical pulps and mechanical pulping process, respectively. Napier grass and sugarcane are promising non-wood sources for pulp production, owing to their high cellulose and low lignin and extractive content. With the additional mild alkaline pre-treatment to the mechanical pulping process, the lignin content was greatly reduced. The results reveal that the mechanical pulping with alkaline pre-treatment may indeed potentially replace the most prevalent pulping process (chemical pulping). As evidenced by the paper strength properties, mechanical pulping is far more suitable for grass-type biomass, particularly Napier grass, which had a folding endurance capability five times greater than chemical pulping. Furthermore, the remaining high hemicellulose content from mechanical pulping contributed to a high pulp yield, while also facilitating the fibrillation on the sugarcane's laboratory paper handsheet. The findings also demonstrated that the additional beating process from chemical pulping causes the fibres to be drawn toward each other, resulting in a more robust fibre network that contributes to good paper strength. Consequently, this work sheds new light on the development of advanced paper derived from grass fibre.

Solvent-free synthesis of high-performance polyurethane elastomer based on low-molecular-weight alkali lignin

Using cheap and green lignin as a partial substitute for petroleum-based polyols is highly attractive for sustainable development of polyurethane elastomers (LPUes). However, the traditional synthesis process of LPUes inevitably uses toxic solvents that are difficult to remove or carcinogenic. Here, we reported a solvent-free synthesis method to prepare lignin-containing polyurethane elastomers (SF-LPUes) with high strength, high toughness and high elasticity. Most of the hydroxyl groups of lignin reacted with isocyanates to form a strong chemical cross-linking network, while the unreacted ones formed a dynamic hydrogen bond network with polyurethane matrix, contributing to the in-situ formation of lignin nanoparticles to build a nano-micro phase separation structure. Consequently, a dual-crosslinking network structure was formed and endowed SF-LPUes with excellent mechanical properties. Especially, the SF-LPUes prepared from low molecular alkali lignin possessed a tensile strength as high as 38.2 MPa, a maximum elongation at break of 1108 %, and an elastic recovery ratio of up to 98.7 %. Moreover, SF-LPUes showed impressing reprocessing performance and aging resistance. This work provides an industrial application prospect for the synthesis of lignin-containing polyurethane elastomers via a solvent-free synthesis process.

Revealing the relationship between molecular weight of lignin and its color, UV-protecting property

Lignin has great potential as a natural, green, and sustainable broad-spectrum sunscreen active ingredient. However, the coexistence of dark color and sunscreen properties hinders its application in cosmetics. In this study, we focus on the effects of the molecular weight of lignin on tis UV-protecting property and color in order to prepare lignin-based sunscreen with high performance. A prepared sunscreen containing low molecular weight lignin (F5, <1000 g/mol) exhibits good UV-protecting property (sun protection factor (SPF) = 7.14) and light color advantages (ΔE = 46.2). Moreover, a strong synergistic effect on UV-protecting property exists between low molecular weight lignin and ethylhexyl methoxycinnamate (EHMC), resulting in high SPF of F5@EHMC-based sunscreen (55.56). Additionally, added TiO2 can efficiently mitigate the dark color of lignin-based sunscreens due to prominent covering power of TiO2. Moreover, lignin-based sunscreens have good biocompatibility with HaCaT cells. This work is useful for understanding the mechanism of the UV-protecting property and dark color of lignin, and for designing an efficient and safe lignin-based sunscreen.

The Separation Mechanism of Bamboo Bundles at Cellular Level

Bamboo bundles with linear cracks were produced using mechanical treatments that were more environmentally friendly and more efficient than chemical decomposition and steam explosion. This study presented the separation mechanism by analyzing the structure, micro-mechanical properties and chemical constituent of bamboo bundles at the cellular level. The micro X-ray tomography technology (u-CT) morphology of bamboo and bamboo bundles presented that the separation of bamboo bundles was caused by crack propagation, which was related to the structure of the cell types in bamboo. Field emission scanning microscopy (SEM) was performed to observe the appearance of bamboo bundles at the cellular level, which illustrated that the cracks were prone to grow in the middle lamella (ML) in fiber cells and parenchymal cells. The nanoindentation technique and Raman microscopy was used to illustrate that the middle lamella (ML)with low indentation moduli and high lignin content was the weak structure in bamboo. This is interpreted as how the structure and mechanical properties contributed to the separation of the bamboo.