Lignin nanoparticles: Eco-friendly and versatile tool for new era

Journal Pre-proof Lignin nanoparticles: Eco-friendly and versatile tool for new era

Prakram Singh Chauhan PII:

S2589-014X(19)30264-6

DOI:

https://doi.org/10.1016/j.biteb.2019.100374

Reference:

BITEB 100374

To appear in:

Bioresource Technology Reports

Received date:

4 November 2019

Revised date:

23 December 2019

Accepted date:

24 December 2019

Please cite this article as: P.S. Chauhan, Lignin nanoparticles: Eco-friendly and versatile tool for new era, Bioresource Technology Reports(2018), https://doi.org/10.1016/ j.biteb.2019.100374

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© 2018 Published by Elsevier.

Journal Pre-proof Lignin nanoparticles: eco-friendly and versatile tool for new era Prakram Singh Chauhan*1 1

College of Basic Sciences and Humanities, Govind Ballabh Pant University of Agriculture

and Technology, Pantnagar-263145, Uttarakhand, India. *Corresponding author Dr. Prakram Singh Chauhan College of Basic Sciences and Humanities, Govind Ballabh Pant University of Agriculture

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and Technology,

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City - Pantnagar-263145,

Country - India.

Tel.: +917727019854

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E-mail: [email protected]

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State - Uttarakhand,

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ORCID No. : 0000-0002-9464-5402

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Journal Pre-proof Abstract Lignin is the second most abundant biopolymer after cellulose and is one of the most intriguing natural materials for utilization across a wide range of applications. It is generated in large quantities as by-products in pulping industries and biorefineries through various processes. Conversion of lignin into nanoparticles exhibit unique properties because of this, recently it gained significant interest among researchers. Therefore this review is providing the proper updated information on the state of the art of different chemical, physical,

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mechanical techniques which are involved in the synthesis of variety of lignin nanoparticles

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and their potential applications in different fields such as antibacterial, UV adsorbent,

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antioxidant, hybrid nanocomposites, drug delivery vehicles, bioremediation and carbon

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precursor etc. have been discussed.

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Keywords : Lignin; Lignin nanoparticle synthesis; Antibacterial; UV absorbent.

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Journal Pre-proof 1.

Introduction

Lignin is the second most abundant biopolymer on earth, after cellulose. According to Sameni (2015) and Schutyser et al (2018), biorefineries and pulping industries produce lignin as a by-product through various processes such as kraft, organosolv, soda, enzymatic hydrolysis and steam explosion. A target of 79 billion litres of second-generation biofuels needs to be produced within the year 2022, as per the U.S. Energy Security and Independence Act regulated in 2007. As per the assumption, 355 L of bioethanol can be produced from one

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generating 62 million tons of lignin (Wang et al, 2019a).

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ton of dry biomass and total of 223 million tons of dry biomass is processed every year thus

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Most of the lignin produced nowadays is used as boiler fuel whereas small portion is used for

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the production of value-added products (Agarwal et al, 2018). The type of plant material as well as its processing methods decides the physico-chemical properties of lignin. Lignin is

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inexpensive and possesses number of excellent features for instance, high thermal stability,

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antioxidant activity, high amount of carbon and favourable stiffness (Kai et al, 2016). However, different types of lignin show distinct variants in terms of functional groups,

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elemental composition and molecular weight (Upton et al, 2016). These advantages increased the interest among researcher for the conversion of lignin into value-added products to be used in different applications (Kai et al, 2016). The lignin produced from kraft process is shown to possess particles in the size range of 10 μm to more than 100 μm however it harms the mechanical properties of the blends (Melro et al, 2018). Lignin Nanoparticles (LNPs) is one of the best strategies to improve the blending properties of lignin since they possess novel characteristics such as high surface area and improved properties compared to original material. Furthermore they can be easily surface modify due to the availability of huge number of functional groups like thiols, aliphatic hydroxyl and phenolic which can be chemical modified thus enhancing their application

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Journal Pre-proof potential (Zhao et al, 2016). Thus, the researchers recently shifted their interest towards the preparation of LNPs and exploring their potential applications (Beisl et al, 2017; Figueiredo et al, 2018). It is expected that LNPs will play a vital role in promoting lignin valorization, similar to synthetic polymer nanoparticles contribute in the polymer industry (Zhao et al, 2016; Ma et al, 2018). Various research articles published so far emphasized the lignin conversion into functional and useful products (Kai et al, 2016; Zhao et al, 2016; Fortunati et al, 2016; Upton

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et al, 2016; Roopan et al, 2017; Melro et al, 2018; Agarwal et al, 2018; Ma et al, 2018;

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Figueiredo et al, 2018; Wang et al, 2019a). However, none of the comprehensive review is

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available which specifically focus on lignin nanoparticle synthesis and their applications

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together. Therefore, In the present review, I summarized all the information in two section, first section deals with different preparation methods of LNPs synthesis and second section

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deals with their potential applications in various field. The article is intended to gain wide

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range of attention from the targeted audience towards leveraging the LNPs for value-added applications.

Different methods of lignin nanoparticles synthesis

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2.

Recently various kinds of LNPs are being synthesized from different resources using a combination of chemical and physical methods. Different approaches such as polymerization, acid precipitation, solvent exchange, ultrasonication, self-assembly, interfacial crosslinking and emulsion, antisolvent precipitation, microbial and enzyme mediated, freeze-drying and thermal stabilization, homogenization and alkaline precipitation has been discovered by which lignin can be converted into lignin nanoparticles (Table 1). 2.1. Polymerization In a first of its kind, the coniferyl alcohol was polymerized to synthesize the arabinoxylandehydrogenation polymers (synthetic lignin polymer) nanoparticles. During this process, a

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Journal Pre-proof combination of coniferyl alcohol/sinapyl alcohol was used with two structurally-related heteroxylans (HX). The nanoparticles produced in this process were characterized by the help of Light Scattering (LS), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and fluorescent probes (Barakat et al, 2007; Barakat et al, 2008). Qian et al, (2014) synthesized N,N-diethylaminoethyl methacrylate (DEAEMA)-grafted LNPs via Atom transfer radical polymerization (ATRP), which had size range of 237 to 404 nm. The produced nanoparticles were utilized in the CO2/N2-switchability pickering emulsions as a

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surfactant which was in correlation with graft density as well as the DEAEMA’s chain

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length.

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2.2. Acid precipitation

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A unique acid preparation method was developed by Frangville et al, (2012) in order to produce novel LNPs that remain non-toxic for yeasts as well as microalgae. In this research,

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two different methods were compared to synthesize the nanoparticles that have variations in

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its stability upon change in pH. In the first method, low-sulfonated lignin gets precipitated by ethylene glycol solution in the presence of diluted acidic aqueous solutions. In this way, the

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LNPs can be retrieved and their stability is high in different pH ranges. In the second method, the lignin gets acid-precipitated from high pH aqueous solution thus resulting in the formation of LNPs that has stability only at acidic range (Fig. 1). Gupta et al, (2014) also explored the use of acid precipitation technology and synthesized the LNPs. The particle size was measured using TEM and Dynamic Light Scattering (DLS) and it was observed that particles do not get aggregated and they are uniformly distributed which allows to upscaling of this process. Gilca et al, (2014) reported a chemical method to synthesize nanoparticles using hydroxymethylated lignin and optimized the conditions for particle size point of view. The LNPs produced from this process contained high number of hydroxyl groups due to which they can replace the phenol in the synthesis of

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Journal Pre-proof phenolformaldehyde resin, composites, biocides etc.. Furthermore, Richter et al, (2015; 2016) also synthesized the LNPs with the precipitation method discussed above, additionally silver ions were infused in the LNPs and coated with poly(diallyldimethylammonium chloride) (PDAC). Another unique method for the synthesis of high amount of spherical LNPs was developed by Rahman et al, (2018) using different media such as Water (W), Ethylene Glycol (EG) and Castor Oil (CO) through acid precipitation technology and nanoparticles were characterized by TEM, DLS and Scanning Electron Microscopy (SEM). Azimvand et al,

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(2018a;b;c) synthesize the LNPs using alkali lignin as a raw substrate after modification by

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EG characterized by DLS, SEM, Fourier-transform infrared spectroscopy (FTIR),

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Thermogravimetric analysis (TGA-DTG). Yang et al, (2019) investigated the role of EG on

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solution structure of lignin before the reduction in pH thus enabling the assessment of the

2.3. Solvent exchange method

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solvent quality, the conformation of lignin subunits and their aggregation in EG.

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In the solvent shifting method, a solution of an organic compound in a water miscible organic solvent, which is mixed with an excess of water, and nanoparticles are generated due to their

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decreasing solubility. There is a vast range of application available for this process and it show a straightforward system. But the major disadvantage in this process is the amount of low solid content i.e., approximately 1 wt% (Beisl et al, 2017). For the first time, Qian et al, (2014b), produced the colloidal lignin spheres of 110 nm based on self-assembly method in which acetylated lignin was dissolved in Tetrahydrofuran (THF) and the water (67%) was added gradually to the solution. This caused the lignin molecules to associate with one another because of hydrophobic interactions. Yearla and Padmasree (2016) study focused on the generation of spherical dioxane lignin nanoparticles (DLNP) and alkali lignin nanoparticles (ALNP) from two lignin sources such as softwood alkali lignin (AL) and hardwood dioxane lignin (DL) that was extracted from the

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Journal Pre-proof stem region of subabul. Kai et al, (2015) produced lignin nanoparticles of controllable size using acetylated lignin dissolved in THF and water was added gradually to the solution. Similarly, Li et al, (2016) prepared nanocapsules of 10-100 nm range by dissolving the kraft lignin solution into the ethanol and drop by drop addition of water. The nanocapsules are preferred for different applications due to its distinct characteristics such as cheap preparation cost, easy preparation methods and environment-friendly features. Lievonen et al, (2016) introduced a direct method for the production of LNPs from the waste lignin obtained from

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kraft pulping. When the softwood kraft lignin was dissolved in THF, the spherical-shaped

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LNPs were obtained after which the water was introduced in the system via dialysis. There

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was no need to chemically modify the lignin in this case... The nanoparticles’ final size is

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decided on the basis of pre-dialysis concentration of the dissolved lignin. This study also investigated the firmness of the nanoparticle dispersion in terms of pH, salt concentration and

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time. The stability of the lignin nanoparticle was above two months in both pure water as

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well as in room temperature, but in case of low pH or high salt concentration, it increased the aggregation of LNPs. Figueiredo et al, (2017a;b) developed three types of spherical LNPs

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that had been prepared by solvent exchange. These three types were pure lignin nanoparticles (pLNPs), iron(III)-complexed lignin nanoparticles (Fe-LNPs), and iron oxide (Fe3O4) nanoparticle infused lignin nanoparticles (Fe3O4-LNPs). When a lignin solution was mixed with oleic acid-coated Fe3O4 nanoparticles in THF (50:50 w/w) followed by a water dialysis, it resulted in the formation of Fe3O4- LNPs. Since it possesses excellent paramagnetic behaviour, it is considered as the best choice for diagnosis and treatment of cancer. Tian et al, (2017b) developed a thin film through the amalgamation of polyvinyl alcohol with dual kinds of LNPs namely DLNP and ALNP on the basis of lignin isolation technical method. To achieve full utilization of lignocellulosic biomass and easy integration of LNPs production into current biorefinery concept, a two-step pretreatment strategy, mild steam pretreatment

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Journal Pre-proof followed by solvent extraction, was employed to produce Deep eutectic solvent (DES) and organosolv technical lignins from raw hardwood poplar. Both the technical lignin dissolved in dimethylsulfoxide (DMSO) and underwent micellization with the help of dialysis process resulting in the production of evenly distributed LNPs often mentioned as DLNPs and OLNPs, respectively. The LNPs thus produced were spherical in shape with novel core-shell nanostructure. Sipponen et al, (2017, 2018) synthesized Colloidal Lignin Particles (CLPs) by dissolving the

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softwood kraft lignin in THF : water ratio of 5:1 v/v over a period of 3 h and then

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precipitating by rapid pouring of the solution into 380 g of vigorously stirred deionized water.

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Various weight proportions of cationic lignin were then coated onto the CLPs in soluble

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fraction. In comparison, the cationic CLPs were able to stabilize a wide range of long-lasting pickering emulsions than its counterpart i.e., irregular kraft lignin particles or otherwise the

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regular CLPs. Wang et al, (2019b) proposed a very simple, yet unique and green technique to

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produce regular LNPs of high quantity. Lignin was first modified through a microwave acetylation process without any catalysts and solvents other than acetic anhydride, which

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acted as both reaction reagent and dispersion solvent. Consequently, high yielding regular LNPs were produced through a combination of solvent shifting and ultrasound process. The produced LNPs can be easily separated through centrifugation and used THF can be recycled and reused which simply reduce the cost of the process. Interestingly, upon increasing the concentration of lignin content and ultrasound intensity, yield of LNPs has also been increased. Xing et al, (2019) produced LNPs by dissolving soda lignin in acetone and water, filtered and filtrate added rapidly in deionized water. Through rotary evaporation, acetone was removed after which the solution was centrifuged to obtain LNPs. For the first time, the study implemented a bioinspired melanin-like polydopamine thin layer in the LNPs which increases their biocompatibility. Recently Zikeli et al, (2019) separated the lignin from wood

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Journal Pre-proof wastes which consisted of Iroko sawdust (IR) as well as mixed sawdust from Iroko and Norway Spruce (IRNS) and nanoparticles were produced via solvent exchange method by first dissolving lignin in DMSO and dialysis with excess water. 2.4. Ultrasonication Dry and wet milling techniques as well as other such mechanical treatments are generally utilized to reduce the particle size to nanometre scale. However, it has few disadvantages such as non-uniformity in the size and broad particle size distributions. In spite of these, it is

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still preferred because it is a simple method to produce nanoparticles (Beisl et al, 2017). Gilca

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et al, (2015) used the sonication process in order to reduce the size of lignin extracted from

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wheat straw and sarkanda grass. The synthesized nanoparticles were in the range of 10 to 50

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nm and they were characterized both morphologically and dimensionally to evaluate any abnormal changes in its composition and structure. Results confirmed that there was no

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significant relationship between the applied intensity and the compositional and structural

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changes of nanoparticles. This is an even more attracting method for future applications since none of the solvents used in this process are hazardous. Gonzalez et al, (2017) produced

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LNPs by the ultrasonic treatment for different time periods and oscillation amplitude was 95% in order to get the lignin-water dispersions having superior colloidal stability. Yin et al, (2018) also produced LNPs through the ultrasonic-assisted alkali method using switch grass as a lignin source by dissolving into sodium hydroxide and then sonicated at about 600 W for 1 h to obtain LNPs of 220 nm average size. 2.5. Self-assembly Self-assembly is a process in which an incoherent system of the pre-existing components generates a pattern or an organized structure because of the specific interactions in the absence of any external direction. A self-assembly method was made use for the preparation of lignin reverse micelles (Qian et al, 2015a). In this method, cyclohexane was added into

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Journal Pre-proof alkali lignin solution that was pre-dissolved in dioxane. With further addition of cyclohexane, there may be possible flocculation and precipitation of lignin micelles occur. The size of the nanoparticles rendered, was the range of 120 nm to few micrometers on the basis of cyclohexane content. Li et al, (2017) proposed an easy and practical method in the preparation of lignin-based complex spherical micelles in green solvents that possess pHresponsive features. After quaternization, the alkali lignin (AL) was left to self-assembly so as to form the lignin-based complex micelles along with sodium dodecyl benzenesulfonate

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(SDBS) in ethanol/water mixture with increasing amount of water i.e. 0 to above 86%.

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Dai et al, (2017) created a first-of-its-kind green nanoparticle platform using lignin in the

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absence of chemical alterations. The corn cob was utilized as a source of AL in the

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preparation of spherical-shaped nanoparticles that possess good dispersion characteristic. In this preparation process, a simple self-assembly method was followed in which the water was

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added with methanol solution of AL. Mattinen et al, (2018a;b) prepared small-sized colloidal

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lignin particles (CLPs) including bilayer polypeptide alterations from KL utilizing selfassembly so as to make the CNF surfaces adapt to the heat treatment. Liu et al, (2019)

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produced LNPs on the basis of Sequential Organosolv Fragmentation Approach (SOFA) using ethanol as well as various stages of catalysts were explored for selective-dissolution of lignin from corn stover. This was performed to generate multiple uniform lignin streams and alter its chemical characteristics as well as its reactivity so that the LNPs can be fabricated using expected quality features through self-assembly. The effective diameter more or less was in the footsteps of stage 1 (50% ethanol + 1% sulphuric acid), stage 3 (50% ethanol), and stage 2 (50% ethanol + 1% formic acid) in every SOFA. The smallest effective diameter was 130 nm approximately from SOFA that utilized ethanol as well as sulphuric acid. 2.6. Interfacial cross linking and emulsion

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Journal Pre-proof Emulsification and cross linking are the two phenomena in association with ultrasound to produce lignin microcapsule. It was observed lignin cross linking capability was induced at water/oil interface and enhanced by addition of cross linking agent. Mechanism involve in this process comprise two steps : the first process depends on the collapse intensity of the cavitation bubbles (responsible for the shear forces). The oil-in-water emulsion was obtained applying an acoustic power of 160 Wcm−2 for 40 s. The amphiphilic lignin chains are thought to diffuse toward the oil microdroplets so as to stabilize the water/oil interface. In the second

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step, lignin chains is induced for cross linking by the hydroxyl (•OH) and superoxide (HO2

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−•) radicals generated during the acoustic cavitation process (Tortora et al, 2014). Nypelo et

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al, (2015) prepared spherical particles using a water-in-oil microemulsion and thereby mixing

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of lignin solution with a blend of surfactants, for instance, Span 80, Tween 80 and pentanol pre-dissolved in octane. This led to the formation of hydrophilic–lipophilic balance with ca.

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7. In the another study performed by Chen et al, (2016), lignin nanocapsules having pH-

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responsive features has been synthesized through interfacial miniemulsion polymerization followed by crosslinking. In the first step, the ultrasonication process was performed to

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obtain an oil-in-water miniemulsion by mixing vigorously butyl acetate, hexadecane (costabilizer), azobisisobutyronitrile (AIBN, oil soluble initiator) and the cross-linker, trimethylolpropane tris(3-mercaptopropionate) and further mixed with water phase bound lignosulfonate [with and without sodium dodecyl sulfate (SDS)]. After this process, a crosslinking agent was made to undergo reaction with lignin at miniemulsion droplet interface so as to produce the nanocapsules. The prepared lignin nanocapsule possesses pH responsive properties due to presence of acid-labile b-thiopropionate cross-linkages in the capsule shell. Xiao et al, (2019) developed a Lignin-Based Nano-Trap (LBNT) using a simple inverseemulsion copolymerization method. Initially lignin was dissolved in the distilled water using amine and a cross-linker (CH2O), it was then emulsified in liquid paraffin using a surfactant

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Journal Pre-proof (Span80) followed by heating. This was then cooled down to 30°C to which CS 2 was added so that it undergoes esterification. The solution was then centrifuged, washed and freezedried so as to finally obtain the LGNT. The following features are expected in LGNT reduced sized of the particles so that the diffusion and contacting frequency can be increased; further it should possess heavy metal-binding groups on its surface that can afford various heavy metal ions with good adsorption capability and finally the surface-dispersed binding sites should be controlling the heavy metal ions thus helping in various applications.

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2.7. Antisolvent precipitation

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Over the last two decades, the ―compressed/supercritical fluid‖ based technology used in the

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production of polymeric nanoparticles has gained considerable attention. Its capability to

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control the size and size distribution as well as morphology are its unique features which are critical in the development of pharmaceutical and drug delivery applications. CO2 gained

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special attention since it possesses excellent and critically-important features (TC = 304.3 K

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and PC = 7.4 MPa) because of its physicochemical properties can be fine-tuned and its cheap, non-toxic, non-flammable with abundant quantities. In addition to the above, it remains a

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poor solvent in case of macromolecules, namely polymers, due to which it is often cited as the best antisolvent for precipitation processes in which the precipitates can be influenced through the control of temperature and pressure (Beisl et al, 2017). Lu et al, (2012) made use of 80.5% pure poplar OS in a supercritical CO2 (SC-CO2) process. In this method, precipitation chamber was filled with SC-CO2 at 30 MPa under 35°C temperature with pure acetone. After reaching stable conditions, 0.5 g/L lignin/acetone solution was used to replacing the acetone and precipitated nano-scale particles were removed out of the stainless steel-made frit in precipitation chamber. Result shows upon conversion into nano scale lignin solublility were significantly enhanced in the water. Myint et al, (2016) produced LNPs using compressed fluid anti-solvent method in which nanoparticles were quasi-spherical and

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Journal Pre-proof identical in nature. In this method, firstly KL was dissolved in DMF after which it was sprayed onto the precipitator with the help of compressed liquid CO2 (clCO2) as an antisolvent. This led to the formation of identical and quasi-spherical LNPs which shows enhanced solubility and stability in water in comparison to raw lignin. 2.8. Biological method Lignocellulose, the most abundant renewable biomass on earth, chiefly consists of cellulose, hemicelluloses, lignin and pectin as the major constituents with resins, waxes, proteins and

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extractives as minor constituents. Recently, there is an increased potential tapped in the

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enzymatic methods followed in biomass degradation processes by combining saccharification

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and fermentation processes. When the lignin is converted into nanolignin through enzymatic

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hydrolytic process, especially, with the help of lignocellulosic materials, there is an improvement observed in the properties of the materials. For the first time, Rangan et al,

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(2017) prepared lignin-rich cubodial nanoparticles from lignocellulosic fibers generated from

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Indian ridge gourd (Luffa cylindrica) through the breakdown of lignin-cellulose complex using specific enzymes. After this Juikar and Vigneshwaran (2017) generated LNPs using

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coconut fibres as sources with the help of Aspergillus sp, a fungal isolate that is capable of producing high amount of lignin peroxidase enzyme. The bulk lignin size was between 2– 150 μm with the peak value being 55 μm. On comparison between the microbial processes and homogenization & ultrasonication processes, the yield of nanolignin in the former was 58.4% whereas it was 81.4% and 64.3% in the latter respectively. Following this study, Tian et al, (2017a) produced LNPs from celluloytic enzyme treated lignin (CEL), obtained from steam-pretreated, agriculture reside corn stover, hardwood poplar, and softwood lodge pole following the prevalent dialysis method. In this method, the LNPs produced were in the range of 81.8%, 90.9% and 41.0% with their relevant average particle sizes being 218, 131, and 104 nm, respectively. The high-quality LNPs thus obtained were spherical in shape with abundant

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Journal Pre-proof functional groups and high stability in the pH range of 4-10, which showed tremendous promise for the applications in the emerging nanomaterial fields (Fig. 2). 2.9. Freeze-drying and thermal stabilization Gonugunta et al, (2012) synthesized LNPs through combination of freeze-drying process, thermal stabilization as well as carbonization processes using lignin as a renewable source. The researchers investigated the effect of adding different amounts of KOH to lignin solution in terms of its solubility, freeze-drying process and thermal stabilization of the freeze-dried

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lignin.. The SEM analyses confirmed lignin was influenced to form porous microstructure

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due to freeze-drying process. Furthermore, TEM analysis showed that the thermal

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stabilization of freeze-dried lignin has stopped the generation of agglomerated carbon

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nanoparticles at the time of carbonization. The carbon nanoparticles had the least size range of 25 nm when prepared using lignin precursor and 15% KOH.

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2.10. Homogenization

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Nair et al, (2014) prepared nanolignin with the help of a simple high shear homogenizer. The kraft lignin particles with a broad distribution ranging from large micron- to nano-sized

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articles were completely homogenized to nanolignin particles with sizes less than 100 nm after 4 h of mechanical shearing. Based on the results obtained from

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C nuclear magnetic

resonance (NMR) and 31P NMR analyses, it was found that there was no significant chemical composition changes occurred in kraft lignin particles in comparison with mechanicallytreated nanolignin particles. There was no notable change observed among the nanolignin particles in terms of molecular weight distribution and polydispersity in comparison with pure lignin particles. 2.11. Alkaline precipitation Gutiérrez-Hernández et al, (2016) generated LNP via alkaline precipitation method using lignin obtained from Agave tequilana Weber bagasse by soda and organosolv. In brief, lignin

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Journal Pre-proof slurry 17 wt% was stirred for 1 h followed by the addition of NaOH (exact amount can be calculated on the basis of lignin content). After 2 h, ammonium hydroxide was added and then high intensity mixing was performed using Ultra-turrax (IKA, T10) at 24,000 rpm for 5 min. Then active formaldehyde was added and increased the temperature upto 85°C for 2 h. Finally, suspension was kept under magnetic stirring at 600 rpm for the crosslinking and the formation of nanoparticles. Total six types of lignin NPs were prepared, three for each type of lignin source, using 18 and 27 wt% of active formaldehyde (CH2O) and the lignin samples in

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absence of formaldehyde as blanks. L1 (without formaldehyde or blank), L2 (18 wt% CH2O)

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and L3 (27 wt% CH2O) are the labels for every type of lignin source i.e. organosolv or soda.

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3. Application of lignin nanoparticles

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LNPs have attracted a great deal of attention in the last decade because of their biotechnological potential in various industrial processes. The following section will discuss

Antibacterial agent

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3.1.

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some of the most promising and newly explored applications of LNPs.

As research in current medical and biological fields advances, an increasing interest in the

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possibility of lignin to act as an antimicrobial agent has been garnered. The phenolic components present in the lignin plays the vital role behind the antimicrobial characteristic of the lignin, more especially the side-chain structure as well as its functional groups. In general, presence of double bond in α and β positions of the side chain with a methyl group in γ position in phenolic fragment shows the highest efficacy against microbes. Gregorova et al, (2011) conducted detailed investigations about the application of lignin as an antimicrobial agent through agar diffusion tests for Gram +ve and Gram -ve bacteria. The antibacterial effectiveness of Bjorkman lignin that was produced by beechwood was compared with standard additives, for instance, silver nitrate, chlorhexidine, benzalkonium chloride and bronopol. Result showed that there were similarities in the diameter of the growth inhibition

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Journal Pre-proof for Bjorkman lignin and that of bronopol and chlorhexidine with both bacterial strains. So, it has been reported that the lignin’s antibacterial property is in par with the existing antimicrobial agents. Further, this study also investigated the possibilities of lignin being used as a commercial antimicrobial agent by incorporating Bjorkman lignin in polyethylene films, and mechanical testing was performed which shows that there was no drastic drop in the mechanical properties. Thus, it confirms that the Bjorkman lignin can potentially be used in polyethylene films while preserving the antibacterial properties of silver. Another study

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conducted with the same objective which shows lignin at a nano scale seems to be useful in

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the treatment of dangerous microbes after introducing it into silver nanoparticles. In spite of

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the fact that AgNPs are applied against a range of microbes, such as, but not limited to,

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Escherichia coli and Pseudomonas aeruginosa, they still are loaded with demerits. In their activated form, the unused silver nanoparticles remain in the environment and could

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adversely affect the ecosystems. Richer et al, (2015) suggested that lignin as the best choice

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to replace silver core since the former is abundantly available with environment-friendly characteristics. They tested the capability of environmentally-benign LNPs against a range of

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bacterial strains so that its antimicrobial efficiency can be evaluated. In this study bacteria were exposed to LNPs and then controlled the same for a specific time period before culturing

on

Luria-Bertani

agar

plates.

The

used

controls

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polydiallyldimethylammonium chloride polyelectrolyte solution, silver nitrate (AgNO3) solution, positively charged branched polyethyleneimine-coated silver nanoparticles, lignin nanoparticles without silver ions and centrifuged supernatant solution from the sample. Surprisingly outstanding performance of LNPs was recorded over controls, AgNO3, and traditional AgNP which had more than 12-times and 20-times excess silver ions respectively. Further, it was also found that the capability against microbes got lost after the silver ions got exhausted. But there is still absence of data on minimum concentration of lignin needed to get

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Journal Pre-proof rid of bacteria and its kinetics in targeting the bacteria. It is crucial to explore the life span of lignin and its degradation rate so that the amount of substance required to inhibit the growth of microbes can be found which eventually results in the elimination of bacteria (Fig. 3). Interestingly, Yang et al, (2016a) produced ternary polymeric films on the basis of content of LNPs (1 wt% and 3 wt%) with dispersing cellulose nanocrystals (CNC) in neat poly (lactic acid) in as well as in glycidyl methacrylate (GMA) grafted PLA (g-PLA) respectively which shows excellent antibacterial activity in order to reduce the expansion of Pseudomonas

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syringae pv. tomato (Pst), a bacterial plant pathogen. Furthermore, binary and ternary

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polymeric films produced on the basis of polyvinyl alcohol (PVA), chitosan (CH) and lignin

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nanoparticles (LNP) using solvent casting method. The capabilities to prevent the growth of

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Gram negative bacteria, Erwinia carotovorasub sp. carotovora and Xanthomonas arboricola pv. pruni over the time was revealed through antimicrobial assays (Yang et al, 2016b). The

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Polyvinyl alcohol/chitosan (PVA/Ch) hydrogels consist of 1 wt% as well as 3 wt% of LNPs

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were also prepared by the same group via freezing-thaw procedure. The results shows LNPs are effective against Gram -ve bacteria (E. coli) in comparison with Gram +ve

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(Staphylococcus aureus and S. epidermidis) strains when tested using antimicrobial tests. These results pointed out how this green functionality is able to develop novel strategies to save from harmful pathogens and how far it is helpful in food packaging sector (Yang et al, 2018b).

3.2. Antioxidant agent As mentioned earlier, due to complex chemical structure and presence of functional groups in lignin, the oxidation propagation reaction can be stopped through hydrogen donation. Lu et al, (2012) developed highly concentrated solution of nanolignin (12. 4 times higher than the raw lignin) which possesses higher antioxidant as well as free radical scavenging activities, resulting in improved hydrogenating power. Ge et al, (2014) conducted an investigation of

17

Journal Pre-proof nanolignin prepared by alkaline solution precipitation method for Free Radical Scavenging (FRS) activity and it was observed that nanolignin shows 3.3 fold higher activity compared to control because of small size, higher surface area and bioavailiability. The results achieved from the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) antioxidant assay inferred that the high amount of antioxidant activity is present in nanolignin. The IC50 value of nanoscale lignin was 2.70 ± 0.17 mg ml-1 indicating that it possesses high amount of antioxidant activity whereas in case of microscale lignin, the value as merely 32.21 ± 0.1 mg ml-1. Yearla and

of

Padmasree, (2016) performed study in which the dioxane LNPs were fabricated and higher

ro

antioxidant properties were observed than the bulk lignin based on the data recorded for E.

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coli survival rate. Domenek et al, (2013) investigated the antioxidation effect in material

re

applications with the suggestion that lignin can replace synthetic antioxidants especially in food protection i.e., integration of active packaging materials with natural antioxidants.

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Pouteau et al, (2003) evaluated the polypropylene (PP)/lignin blends’ antioxidant activities on

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the basis of oxidation Induction Time (OIT) with the help of TGA. Results shows in the absence of lignin OIT of PP was 30 min but upon addition to 1 wt% lignin, the OIT of

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PP/lignin blends ranging from 70 to 670 min. Furthermore, when the phenolic content and OIT are compared (in the ratio of aliphatic hydroxyl groups to phenolic organosolv lignin groups), the OIT got increased with the diminishing values of phenolic content. This denotes the fact that when there is low phenolic content present, it would increase the compatibility between lignin and PP and accordingly the antioxidant activity too. Morandim-Giannetti et al, (2012) also performed similar study of lignin in PP/coir fibre (PP/CF) composite showing significant increase in OIT was observed upon addition of lignin and it vary from content of lignin. Tian et al, (2017b) introduced LNP into conventional polymeric matrix such as poly(vinyl alchol) to form transparent films which exhibit excellent antioxidant functionalities (reached ~160 μm mol Trolox g-1 with 4 wt% of LNPs). Simultaneously, high

18

Journal Pre-proof number of phenolic hydroxyl groups present in the shell region of the LNPs enabled an excellent interfacial adhersion with PVA matrix via the formation of hydrogen bonding network which further improved the mechanical and thermal performances of the fabricated LNPs/PVA nanocomposite films. The antioxidant properties and high dissolubility were found in nanolignin. In spite of the fact that highly-concentrated lignin can exhibit strong anti-oxidant properties but still there are some serious impacts caused by it. So, there must be an optimization of lignin concentration in biomaterials to equalize the cytotoxicity as well as

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antioxidant activity (Fig. 4).

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3.3. UV absorbents

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Lignin has tremendous potential in sun block due to its excellent non-oxidizability capability.

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Various lignin-based sunscreens were prepared through the amalgamation of LNPs and pure cream. It was observed that that the SPF value of pure cream was 1.03 whereas creams

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contained different concentration of LNPs has a SPF in the range of 1.26 to 2.23. There was

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an enhancement in SPF value to 2.23 with 5% increase in LNP content. The performance of the sunscreen cream having NAcL-2 was better with 2.23 SPF value i.e., 115% increase in

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comparison with pure cream. This phenomenon has a direct relation with LNP size i.e., smaller the size of LNPs, higher the performance of the sunscreens. The probable reason for the considerable higher performance of the sunscreen with LNPs might be attributed to the conjugated system in lignin which might have been produced at the preparation process of the nanoparticles. Furthermore, this system is supported by easy UV-absorbing functional groups namely methoxyl groups and S- and G-type lignin in a significant manner. The presence of π−π stacking between the sunscreen cream and aromatic rings in LNPs also benefit the performance of the sunscreen creams (Wang et al, 2019b). Tian et al, (2017b) incorporated the nanoparticles in conventional polymeric matrix namely poly(vinyl alcohol) and resultant transparent nanocomposite film have an added UV-shielding efficacy (reached ~80% at 400

19

Journal Pre-proof nm with 4 wt% of LNPs). Gutiérrez-Hernández et al, (2016) evaluate the photoprotection characteristics of LNPs produced from Agave tequilana lignin in association with ZnO nanoparticles (primary active ingredients for sunscreens). The SPF value was in the range of 4-13 achieved from the mixture of all the component in the presence of different concentration of LNPs. It was observed that presence of LNPs were able to absorb both UVB as well as UV-C regions which improve the SPF value of sunscreens in comparison to without LNPs. Xing et al, (2019) prepared the poly(butylene adipate-coterephthalate) (PBAT)

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films in combination with LNPs, lignin−melanin core−shell nanoparticles (LMNP) and

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melanin core - shell nanoparticles (MNP). All the films showed improved tensile properties,

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concentration ranging between 0.5-5.0 wt%.

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thermal stability with noteworthy UV-blocking ability (> 80% UV-B) in the presence of NPs

Yang et al, (2015c) also developed a thin film of poly (lacticacid) (PLA)/ LNP films by

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premixing 1%wt of LNP into PLA or glycidyl methacrylate(GMA) grafted PLA (g-PLA)

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with the help of novel master batch procedure and investigated for accelerated UV weathering (upto 480 h). Results retrieved from UV–vis characterization showed the better

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behaviour of the LNPs as a UV light barrier in grafted PLA and it has been also proved that GMA grafting onto PLA matrix promoted the dispersion of LNP in matrix. Pucciariello et al, (2008) blended the biodegradable poly(ε‐caprolactone) (PCL) and steam-explosion lignin by high-energy ball milling process. The lignin addition strongly enhanced the UV stabilization of PCL constituents, since the lignin has phenolic groups which acted as a radical scavenger, thereby reduces or promotes the rate of radical degradation process. Qian et al, (2015b) assessed the lignin in the upgradation of high-performing broad-spectrums sunscreens. The addition of 2 wt% and 10 wt% lignin leads to increment of SPF to 30 and 50 respectively from 15. Interestingly, sunscreen performance improves with UV-radiation time. After 2 h of UV radiation, the UV absorbance of the 10 wt% lignin SPF 15 lotion increases dramatically. . This

20

Journal Pre-proof might be due to the antioxidant property of lignin as well as specific synergistic effects that present between lignin and other such components in the lotions. The lignin is considered as a green option that can replace the synthetically prepared sunscreen actives. Yu et al, (2015) developed

lignin-grafted

co-polymers,

namely

lignin‐graft‐poly(methyl

methacrylate‐co‐butyl acrylate) (lignin‐g‐P(MMA‐co‐BA) through the process of grafting from Atom Transfer Radical Polymerization (ATRP) with help from lignin‐based macroinitiators and determined as Sustainable Thermoplastic Elastomers (TPEs). Based on

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the results, the TPEs lignin‐g‐P(MMA‐co‐BA) copolymers’ mechanical properties were

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improved in a significant manner compared with linear P(MMA‐co‐BA) copolymer

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counterparts with 70% elastic strain recovery. High amount of absorption was exhibited by

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lignin‐g‐P(MMA‐co‐BA) copolymers in UV spectrum which might allow the applications in

3.4. Hybrid nanocomposites

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UV‐blocking coatings.

The resultant

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LNPs have also been exploited as reinforcing agents in polymer matrix and nanocomposites. copolymers

possess

excellent

mechanical,

thermal

properties and

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biocompatibility compared to original polymers (Feldman, 2016; Figueiredo et al, 2018; Yang et al, 2019). Gupta et al, (2015) made use of LNPs as reinforcing agent to biopoly(trimethylene terephthalate) (bio-PPT) hybrid nanocomposites which had 1.5 % weight of LNPs and 7.0 % weight of vapor-grown carbon fibers (VGCF). Results established that there was an enhancement in the mechanical features of nanocomposites, for instance, impact strength in the thermal properties, tensile strength, tensile modulus and biodegradation characteristics compared to bio-PTT. LNPs were also utilized as reinforcing agent for those materials which contain porous structures as shown by Del Saz-Orozco et al, (2012). In this study LNP’s in their different weight fraction were added into phenolic foams and results were analyzed using analysis of 21

Journal Pre-proof variance approach (ANOVA). The results showed that low density and smaller cell sizes were obtained, due to the surfactant effect of lignin in the formulation mixture.. In addition, there was a 28% increment in compressive modulus and 74% increase in compressive strength experienced was observed in comparison with non-reinforced foams. Qian et al, (2015a) developed lignin reverse micelles (LRM) films using cyclohexane, alkali lignin (AL)/dioxane solution into high density polyethylene (HDPE). It was observed that water contact angle of the LRM films was more than 80° while it was only 52° in AL film control

of

sample this leds to an improvement in the miscibility LRM films because of hydrophobic

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1066 to 2104 MPa when 5 wt% LRM was loaded.

ro

nature. .There was also an increase in mechanical strength as well as young’s modules from

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Yang et al, (2015a) incorporated 0, 1 and 3 %wt of LNPs into Wheat Gluten (WG) bionanocomposites in order to efficient absorbance of the UV spectrum and enhancement of the

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water sensitivity. Further, in spite of the fact that when LNPs are added, it reduces the

na

transparency at two varied weight contents, but it still improved the thermal stability, glass transition as well as the mechanical behaviour of the WG-based bio-nanocomposites. In

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addition to the above, Yang et al, (2015b) prepared LNPs/polylactic (acid) (PLA) bionanocomposites through the processes of melt extrusion (E-PLA) and solvent casting (CPLA) with an aim to increase the content of lignin. The nucleation effect was proved to be effectively improved at the time of accomplishing homogenous dispersion of LNPs in PLA matrix at 1 wt% in melt-extruded samples but on further addition of LNPs, there was no favourable crystallization behaviour observed. Silmore et al, (2016) developed polymergrafted lignin nanoparticles (PGLNs) with the help of reversible addition–fragmentation chain transfer (RAFT) chemistry in order to tune the aggregation strength while at the same time it also retain the interfacial activities in generating the pickering emulsions. The results observed, notified a fact that there is a significant impact of salt concentration on zeta

22

Journal Pre-proof potential, aggregation, as well as interfacial tension. These factors are responsible for the alterations in solubility of both kraft lignin as well as polyacrylamide grafts. Sun et al, (2015) prepared PLA-lignin composites by mixing lignin-g-rubber-g-poly (Dlactide) copolymer particles and commercial poly (L-lactide) (PLLA) in chloroform. Although this method observed as an efficient for the dispersion of lignin in PLA matrix but it is challenging and cost-consuming. In addition to the above, the lignin was modified by Chung et al, (2013) through graft copolymerization reaction using lactide and in the presence

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of triazabicyclodecene (TBD) as a catalyst. By changing the lignin/lactide ratio and pre-

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acylation treatment, one can easily control the PLA’s chain length in lignin-g-poly (lactic

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acid) copolymer. It was observed that there is a notable increase in the tensile strength as well

re

as strain upto 16% and 9% respectively upon addition of lignin-g-PLA copolymers without losing tensile modulus.

lP

Jiang et al, (2014) suggested the dual role of lignin as a cross-linker to cure epoxidized

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natural rubber (ENR) as well as reinforcing filler to enhance the mechanical properties of the lignin/ENR composites. It was hypothesized that presence of hydroxyl and carboxyl groups

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of lignin could react with ENR’s epoxy sites through ring opening reaction under a hightemperature dynamic heat treatment (180°C) leads to an even dispersion of lignin along the matrix of ENR and provides excellent compatibility to rubber materials. Liu et al, (2015) developed composite fibres with lignin/PAN/carbon nanotubes (CNT) following the gelspinning technology. The PAN, PAN/lignin and PAN/lignin/CNT were transformed into carbon filters under carbonization (1100°C) and identical stabilization conditions. Yang et al, (2014) prepared lignin-based xerogel having excellent self-cleaning properties and super hydrophobicity with the use of lignin, modified diisocyanate (MMDI) and polyurethane. The produced xerogel capable to absorb high amount of oil from the oil/water mixture which open the new route in removal of spilled oil. Few years after Mahmood et al,

23

Journal Pre-proof (2016) prepared polyurethane based lignin foam showing enhanced mechanical properties, thermal stability, curing rates, and also the flame resistance in comparison to without lignin based polyurethane foam, which suggest that presence of lignin is advantageous in foam and rubber materials (Hatakeyama et al, 2005). Peng et al, (2011) developed pH-sensitive hydrogels by the chemical crosslinking of acetic acid lignin with isocyanate group-terminated polyurethane monomers, in which the swelling ratios enhanced with the increase of the pH. Moreover, thermal stabilities of the generated hydrogels were improved and the release

of

profiles of ammonium sulfate suggested that prepared hydrogels could be used as coating

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materials to control the release of fertilizer for different agricultural and horticultural

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applications (Peng et al, 2011). Yang et al, (2018a) developed LNPs reinforced Poly(methyl

re

methacrylate) (PMMA) nanocomposites through a combination of hot-press methods, solvent-free radical polymerization and micro extrusion following the masterbatch approach.

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Result shows there was significant improvement was observed in various parameters,

na

specifically, excellent thermal, scratch, UV resistance and hardness in case of PMMA/LNP nanocomposites and it also paves the way for these systems to be used in other sectors such

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as lenses, acrylic glasses, flooring and automotive industry. 3.5. Drug delivery system

Lignin has the potential to produce nanoparticles for encapsulation of different compounds for different pharmaceutical applications such as anticancer therapy (Figueiredo et al, 2017a;b). For the first time Frangville et al, (2012) explored the use of nontoxic LNPs for encapsulation of hydrophilic compounds i.e. Rhodamine 6G with high loading capacity. Thereafter Tortora et al, (2014) prepared hydrophobic compound namely Coumarin-6 loaded lignin microcapsule (LMC) and showed products had low cytotoxicity and could be effectively internalized into Chinese hamster ovary cells. The coumarin-6 release in the presence of SDS solution 5% w/v showed that almost 100% of entrapped Coumarin-6 was

24

Journal Pre-proof released in 60 min. There may be two concomitant reasons associated with the release of entrapped Coumarin-6 in the presence of SDS such as deterioration on lignin hydrophobic interactions and the high affinity of the molecule for the new dispersion fluid. The SDS molecule interfere with the lignin’s stabilizing characteristics at the core−shell boundaries which induce the release of Coumarin-6 because of the high solubility of the hydrophobic molecule in SDS solution. From these results, it can be understood that lignin micro/nanocapsules can be used as the topical applications since the pool of antioxidants and

of

essential oils may get released if they contact with lipid tissue or dermatological diseases.

ro

One step further Chen et al, (2016) developed pH sensitive nanocapsule loaded with

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hydrophobic coumarin-6, in which release of coumarin-6 can be controlled by altering the pH

re

of outer solution because of the presence of acid-labile β-thiopropionate cross-linkages in capsule shell.

lP

Figueiredo et al, (2017a) synthesized three different type of LNPs namely : pLNPs, Fe-LNPs

na

and Fe3O4-LNPs having limited cytotoxicity with different tested cell lines and only 12% haemolytic rate was observed even after 12 h. In addition, prepared LNPs showing the

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production of H2O2 and interaction with cells in time-bound manner. With regards to drug loading, pLNPs were able to showed their abilities for efficient loading of poorly watersoluble drugs and other cytotoxic agents, e.g. sorafenib and benzazulene (BZL) and at the same time, increase its release profiles in the pH range of 5.5 and 7.4 with sustainable manner therby enhanced antiproliferation effect. The same researchers developed carboxylate kraft lignin in order to make the carboxylated lignin nanoparticles (CLNPs) with a block copolymer made of PEG, poly(histidine), cell-penetrating peptide and showed its anticancer effect in tumor cells. On the whole, the LNPs seem to be promising candidates that can be used to deliver the drug and its superparamagnetic behaviour of Fe3O4-LNPs makes it very

25

Journal Pre-proof powerful and challenging player in anti-cancer therapy as well as its diagnosis, for instance, MRI, magnetic targeting etc. (Figueiredo et al, 2017b). Li et al, (2017) proposed an easy and practical method for the preparation of pH-sensitive lignin-based complex spherical micelles in green solvents using pure AL for the encapsulation of Ibuprofen (IBU) with the help of hydrophobic interaction. The in vitro release behaviour of IBU was pH-dependent and exhibited controlled release properties. It is possible to preserve 75% of IBU in simulated gastric fluid whereas in simulated intestinal

of

fluid, 90% could release smoothly. This work offer a unique technique for the formulation

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and fabrication of oral drug delivery carrier and it possess significant importance in the value-

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added use of lignin. Dai et al, (2017) showed that AL undergoes self-assembly with bioactive

re

molecule resveratrol (RSV) and Fe3O4 magnetic nanoparticles, it results in the creation of stable nanodrug carrier. In cytological as well as animal tests, excellent anti-cancer effects are

lP

produced by the magnetic RSV-loaded lignin nanoparticles (AL/RSV/Fe3O4 NPs) which

tumour reduction (Fig. 5).

na

further improved the in vitro release and stability of RSV, drug accumulation, and better

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Yiamsawas et al, (2014) generated lignin based polyurethane hollow nanocapsule at the interface of water–cyclohexane which possess 2,4-toluene diisocyanate (TDI) and a surfactant. The encapsulating capacity of the capsules was calculated with the help of hydrophilic fluorescent dye sulfo-rhodamine and long-time stability was observed over several months in both aqueous and organic phases. The release of the dye could be obtained by an enzymatic degradation of the lignin shell. Interestingly Chen et al, (2018) developed LNP through self-assembly process using renewable and non-toxic aqueous sodium ptoluenesulfonate (pTsONa) solution. Number of water-soluble or even water-insoluble drugs can be dissolved in pTsONa and undergoes 90% encapsulation and possess sustained drugreleasing capability. In addition to the above, it is easy to recycle the non-loaded drugs as

26

Journal Pre-proof well as free pTsONa for multiple times to achieve environmental sustainability. This synthesis approach with broad processing window could realize the industrial scale-up production of LNPs and have wide potential applications. 3.6. As support for enzyme immobilization Gong et al, (2017) checked the feasibility of a-amylase immobilization supported by lignin of bamboo shoot shells (BSS). It was interesting to know that BBS work as a α-amylase activator as well as improve the α-amylase activity twice in the concentration of 5 mg/ml..

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Even after reused for 14 times, the residual activity remained competent enough at 53.2%.

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Further, Sipponen et al, (2018) prepared cationic colloidal lignin nanospheres (c-CLP) as

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activating anchors for hydrolases, which is helpful for aqueous ester production through the

re

creation of spatially-limited biocatalysts in the event of self-assembly and drying-driven aggregation in calcium alginate hydrogel. The microbial cutinase and lipase which were

lP

spatially-confined had 97% and 70% synthetic activities when the volume ratio of water to

na

hexane increased from 1:1 to 9:1 in the reaction medium. Overall above findings work out for the fabrication of novel, dynamic and renewable biocatalysts to be used in various

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applications and can provide insight into segmentation of different heterogenous catalysts. 3.7. As an adsorbent to remove dyes Azimvand et al, (2018a) prepared lignin nanoparticle-g-polyacrylic acid adsorbent using copolymerization reactions between lignin nanoparticle and polyacrylic acid in the presence of radical initiator namely potassium persulfate. The results inferred that the lignin nanoparticle had adsorption capacity of 99 mg g-1 whereas it was 138.88 mg g-1 in case of lignin nanoparticle-g-polyacrylic acid adsorbent. They further assessed the adsorption capacity of AL and LNPs for the removal of Basic Red 2 (BR2) from aqueous solutions.. The Langmuir Isotherm was accepted by both the absorbents AL and LNPs with values such as 55.2 mg/gr and 81.9 mg/gr respectively (Azimvand et al, 2018c).

27

Journal Pre-proof 3.8. As a super capacitor Yu et al, (2018) developed lignin-based microsphere activated and lignin precursor activated sample (LAC-M and LAC-P) and exploited their testing it as super capacitors in 6M KOH solution. The Cyclic voltammetry (CV) curves of LACs at 50 mV s-1 exhibited approximately a clean capacitive behaviour of LACs and excellent rate performance as the specific current from 0.05 to 100 A g-1. 3.9. As a nano trap

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Yin et al, (2018) create LNPs-gelatin complex by the combination of Gelatin and LNP for

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their use as a flocculant. Result shows that complex shows better flocculation property than

-p

LNPs however efficiency of flocculation isgreatly influenced by pH and dosage against Gram

re

+ve (Staphylococcus aureus) and Gram -ve (Escherichia colii) strains. Approximately 95% of the flocculation efficiency was attained within 30 min at pH 4.5 whereas it took 1 h for the

lP

flocculation efficiency to reach 90% at pH 5. The LNPs-gelatin complex showed promising

na

results so that it is a better option to be applied in the flocculation of bacteria in wastewater treatment, identification of microbes and enrichment of wastewater.

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Recently Xiao et al, (2019) developed lignin-based nano-trap (LBNT) by lignin functionalization for the removal of various heavy metal ions. The results showed that there was excellent (>99%) removal efficiency achieved by LGNT in case of soft Hg(II), Cd(II)) as well as borderline (Pb(II), Cu(II), Zn(II)) ions.. Furthermore, high amount of bactericidal rate and antimicrobial rate was showed by LGNT with Ag (Ag@LBNT) towards E. coli (99.68%) and Staphylococcus aureus (99.76%). Above work gives clear idea for producing more efficient cheap biomass-based and application-based nanomaterials as antimicrobial agents in near future. 4. Conclusion

28

Journal Pre-proof The field of lignin-based materials has seen significant growth in the last decade, however, development and usage of lignin for broader application still faces some challenges, because of its variable chemical structure and polydispersity. LNPs are one of the lucrative form of the lignin which shows tremendous opportunity for value added applications. Unfortunately, most of LNPs preparation methods use hazardous solvents, therefore it is desirable to replace them with green solvents namely water and room temperature ionic liquids (RTILs). In near future, we need to create eco-friendly methods for LNPs synthesis and their properties should

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be optimum for specific applications.

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Acknowledgment

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This research did not receive any specific grant from funding agencies in the public,

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commercial, or not-for-profit sectors. Conflict of interest

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References

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The author declares that he has no conflict of interest.

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Journal Pre-proof Table 1 Summary of different methods used in the preparation of lignin nanoparticles and their potential applications. Morphology

Raw materi al

Diam eter

Shape

Preparation method

Brief description of method

Applica tion

Refere nce

HX-40DHP-G-

Nanoparticle

HX with ferulate

12.4 36.8 nm

Polymerizati on

Nanoparticle

Baraka t et al, 2007; Baraka t et al, 2008

HX-90DHP-G

Nanoparticle

HX dissolved in buffer; coniferyl /sinapyl alcohol dissolve in dioxane; mixed in presence of peroxidase.

NR

HX-40DHPGS

Compl ex pattern s Compl ex pattern s Spheri cal

HX-90DHPGS LNP

Nanoparticle

Nanoparticle

IAT

Nanoparticle

IAT

Encapsu lation of hydroph obic compou nds for drug delivery .

Frangv ille et al, 2012

LNP

3

CLNP

Nanoparticle

Protobi nd 2400 lignin

NR

Gonug unta et al, 2012

4

NR

Nanoparticle

As a antioxid ant and free radical scaveng er.

Lu et al, 2012

5

LRPFs

Nanoparticlereinforced

IAT dissolved in EG and then HCl added. IAT dissolved in high pH solution and then rapidly HNO3 added. Lignin dissolved in KOH solution followed by freeze drying, thermal stabilization and carbonized in a furnace. Organosolv lignin dissolved in acetone, carried away by super critical CO2. NR

As a reinforc

Del Saz-

50150 nm

ro

-p

Spheri cal Lignin cluster s

Acid precipitation

re

21.8 39.8 nm 16.8 47.2 nm 100 1200 nm

lP

HX without ferulate

Lignin cluster s

Acid precipitation

25 150 nm

Porous micros tructur e

Freezedrying and stabilization

Organo solv lignin

140 147 nm

Sphere

Anti-solvent precipitation

Calciu m

1600 nm

NR

NR

na

2

2.2 35 nm

of

Abbrev ation

Jo ur

S . N o . 1

41

Journal Pre-proof foams

softwo od lignosu lfonate

LNP

Nanoparticle

Protobi nd 2400 lignin

154 762 nm

Lignin cluster

Acid precipitation

7

LMC

Nanocapsules

Kraft lignin

300 1400 nm

Sphere

Interfacial crosslinking

8

LigningDEAE MA

Nanoparticle

Alkali lignin

20 50 µm

Spheri cal

9

NR

Colloidal spheres

Alkali lignin

1 1

NLP

Nanoparticle

Kraft lignin

1 2

LNP

Nanoparticle

Sarkan da grass lignin

Lignin dissolved in EG and than HCl was added. Lignin cross linking at the interface of oil droplets using highintensity ultrasonic technology. PDEAEMA -grafted lignin nanoparticle s prepared via ATPR. Acetylated lignin was dissolved in THF and water was gradually added to the solution. Lignin (kraft) dissolved in water, treated using a high shear homogenize r for 4 h. Lignin dissolved in water followed by heating and increase the pH by NaOH; After adding formaldehy de solution pH was decrease by

-p

ro

of

6

lP

re

Polymerizati on

Sphere s

Solvent exchange

10 30 nm

Irregul ar shape

Mechanical shearing

0.081 - 0.27 nm

NR

Acid precipitation

Jo ur

na

104 110 nm

ing agent or filler in phenoli c composi tes. NR

Orozco et al, 2012

Encapsu lation of hydroph obic compou nds

Tortor a et al, 2014

Surfacta nt for Pickerin g emulsio ns Drug delivery systems or encapsu lation of pesticid es NR

Qian et al, 2014a

NR

Gilca et al, 2014

Gupta et al, 2014

Qian et al, 2014b

Nair et al, 2014

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Journal Pre-proof

EbNPs

Nanoparticle

Indulin alkali lignin

30 175 nm

Nonspheri cal

Acid precipitation

1 4

LRM

Micelles

Alkali lignin

100 120 nm

Sphere s

Selfassembly

1 7

bioPTT/LN P/VGC F

Nanoparticle

Lignin protobi nd1000

5.79 117 nm

Cluste rformin g aggreg ate

Acid precipitation

1 8

LNP

Nanoparticle

Pristine lignin,

32.5 65.1 nm

Spheri cal

Acid precipitation

1 9

LNP

Nanoparticles

Kraft lignin

150 15200 nm

Spheri cal

Microemulsi on; Interfacial crosslinking

2 0

ALNP, DLNP

Nanoparticle

Hardw ood dioxan e lignin, alkali lignin

44 164, 53 107 nm

Spheri cal

Solvent exchange; Nanoprecipit ation

HCl. IAT dissolved in EG and precipitated by HNO3.

Lignin dissolved in dioxane, aggregation induced by adding cyclohexan e. Lignin (protobind1000) dissolved in EG, precipitated by HCl Lignin dissolved in EG and than HCl was added.

Jo ur

na

lP

re

-p

ro

of

1 3

Lignin solution added to the octane containing a mixture of Span 80, Tween 80 and 1pentanol, and crosslinking by adding epichlorohy drin. Lignin (dioxane, alkali) dissolved in acetone/ water mixture (9 :

Antibac terial effects; drug delivery vehicles and as a absorbe nts for heavy metal Lignin/ highdensity polyeth ylene blends

Richter et al, 2015

Hybrid nanoco mposite s

Gupta et al, 2015

As a nanofill er in biobased matrices , food packagi ng applicat ions. Surfacta nt for Pickerin g emulsio ns; Loading of silver nanopar ticles

Yang et al, 2015a, 2015b, 2015c

As an antioxid ants and UV protecta nts

Yearla and Padma sree, 2016

Qian et al, 2015a

Nypelo et al, 2015

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LNP

Nanoparticle

Acetic acid lignin

10 900 nm

Spheri cal and aggreg ate like cluster

Solvent exchange; Nanoprecipit ation

2 2

LNP

Nanoparticle

10 – 10000 nm

Spheri cal

Ultrasonicati on

2 3

NR

Nanocapsules

Wheat straw and Sarkan da grass lignin Allylfunctio nalized lignin

100 400 nm

Spheri cal

Miniemulsio n; Interfacial crosslinking

2 4

NR

Nanocapsules

Kraft lignin

200 300 nm

Hollo w spheri cal

Solvent exchange

2 6

PKL

Nanoparticle

Kraft lignin

19 28 nm

Quasispheri cal nanop article s

Anti-solvent precipitation

Jo ur

na

lP

re

-p

ro

of

2 1

1, v/v), precipitated in water. Acetylated lignin was dissolved in THF and water was gradually added to the solution. Sonication for 60 min at 20 KHz frequency, 600W power. Lignin was grafted with allyl groups via etherificatio n and dispersed in an oil-inwater miniemulsi on by ultrasonicati on, and then reacted with a thiolbased crosslinking agent at the interface of miniemulsi on droplets. A solution of lignin in ethanol was prepared and the ultra-pure water was dropped into this solution (90%). Lignin was dissolved in DMF, and the solution was sprayed into the precipitator using compressed liquid CO2.

NR

Kai et al, 2015

NR

Gilca et al, 2015

Drug delivery and controll ed release of hydroph obic compou nds

Chen et al, 2016

Potentia l applicat ions in various fields

Li et al, 2016

Applica tions in cosmeti cs, drug delivery systems , and nanoco mposite s

Myint et al, 2016

44

Journal Pre-proof

IATNP, HPLNP

Nanoparticle

Kraft lignin and Organo solv

45 250 nm

Spheri cal

Acid precipitation; Solvent exchange

2 8

PLA – LNP/C NC; PVA/C H/LNP

Binary and Ternary polymeric films

Pristine lignin

NR

Film

Acid precipitation

2 9

LPAM1 00; LPAM7 00

Nanoparticle

Kraft lignin

3 0

NR

Nanoparticle

IAT lignin dissolved in EG and than HCl was added; HPL dissolve in acetone and than H2O was added. Lignin dissolved in EG and than HCl was added and grafted with glycidyl methacrylat e and poly (lactic acid).

lP

re

-p

ro

of

2 7

Spheri cal

NR

Spheri cal

Solvent exchange

Jo ur

na

5 - 12 nm

LignoB oostTM

200 500 nm

By reacting lignin with potassium xanthate, 2bromopropi onic acid, and thionyl chloride in dry THF under nitrogen at 70°C overnight. Kraft lignin was dissolved in THF and water was subsequentl y introduced into the system via dialysis.

material s Potentia l applicat ion at extreme pH conditio ns

Richter et al, 2016

UV light blockin g capabili ty, helpful towards harmful pathoge ns, helpful in the food packagi ng sector Applica tion ranging from lubricati on to improve d composi te material s.

Yang et al, 2016a, 2016b

Potentia l applicat ion in composi tes, Pickerin g emulsio ns and antimicr obial material s. Drug delivery carrier

Lievon en et al, 2016

Silmor e et al, 2016

45

Journal Pre-proof

LNP

Nanoparticle

Agave tequila na lignin

1200 – 3800 nm (Orga nosolv ), 400 – 1400 nm (Soda)

Spheri cal

Alkaline precipitation

Lignin slurry was stirrer and followed by NaOH, NH4OH, formaldehy de solution was added and heating to 85°C.

3 2

pLNP; FeLNPs; Fe3O4LNPs

Nanoparticle

LignoB oost™ softwo od kraft lignin

200 220; 139 181; 449 479 nm

Spheri cal

Solvent exchange

3 3

CLNPs

Nanoparticle

LignoB oost™ softwo od kraft lignin

3 4

QAL/S DBS

Micelles

Alkali lignin

3 6

NR

Nanoparticle

Lignin from bambo o shoot shells

A mixture containing 50:50 w/w of lignin solution and oleic acid coated Fe3O4 NPs in THF was prepared and dialyzed against Milli-Q water. Lignin was dissolved in THF and water was subsequentl y introduced into the system via dialysis Lignin was reacted with CHMAC to prepare QAL and dialysis in water; QAL mixed with SDBS, heat and precipitate dissolve in ethanol. Lignin suspensions were prepared by suspending the lignin in the buffer

lP

re

-p

ro

of

3 1

218 – 262 nm

Solvent exchange

45 110 nm

Spheri cal

Self assembly

NR

Spheri cal

Adsorption

Jo ur

na

Spheri cal

for cancer therapy As a skin protecto r

Gutiérr ezHernán dez et al, 2016

Promisi ng for cancer therapy and diagnosi s

Figueir edo et al, 2017a

Targete d and pHresponsi ve delivery of anticanc er drugs

Figueir edo et al, 2017b

Controll ed and pH responsi ve delivery of hydroph obic oral drugs

Li et al, 2017

Support for enzyme immobil ization

Gong et al, 2017

46

Journal Pre-proof

NR

Nanoparticle

Lignoc ellulosi c fibers

20 100 nm

Cubod ial

Solvent exchange; Enzyme mediated

3 8

LNP

Nanoparticle

Steam treated poplar, pine, corn stover

500 1000 nm

Spheri cal

Solvent exchange; Enzyme mediated

3 9

NR

Nanoparticle/ Nanolignin

Cocou nt fibre

4 0

DLNPs/ PVA; OLNPs/ PVA

LNP films

Poplar biomas s

4 1

AL/RS V/Fe3O 4 NPs

Nanoparticle

Alkali lignin

lP

re

-p

ro

of

3 7

Steam pretreatment of lignocellulo se, enzyme treated residue extracted with DMSO and dialysis with tap water. Bulk lignin degraded by fungi under shaking condition followed by centrifugati on.

Spheri cal

Microbial hydrolysis

195 nm; 197 nm

Spheri cal

Solvent exchange

Lignin were dissolved in DMSO and subjected to micellizatio n using dialysis; blend with PVA.

131.2 nm

Spheri cal

Self assembly

Alkali lignin was dissolved in Methanol, Ethanol,

Jo ur

na

2 -150 µm

and varying the final concentratio n. Cryo crushing of dried fruit; Organo solvent extraction of powdered fruit, Enzymatic hydrolysis in acidic pH.

Applica tions across fields includin g automo bile, pharma ceutical and polymer industri es Helpful in integrat ed lignocel lulose biorefin ery process

Ranga n et al, 2017

Useful in textile, biomedi cal and environ mental applicat ions Nanoco mposite s having high UVshieldin g efficacy , antioxid ant activity, and in advance d packagi ng field. Efficien t delivery of hydroph

Juikar and Vignes hwaran , 2017

Tian et al, 2017a

Tian et al, 2017b

Dai et al, 2017

47

Journal Pre-proof

LNPs

Nanoparticle

Wileymilled poplar NE222

108.6 – 238.9 nm (AL conc. 0.5 mg/ml )

Spheri cal and Non Spheri cal

4 3

NL

Nanoparticle

Kraft lignin

10 50 nm

Irregul ar

4 4

LNP

Nanoparticle

Steam explod ed Rice straw lignin

15 20 nm

4 5

LN-gPAA

Nanoparticle

Alkali lignin

4 6

CLPs

Nanoparticle

LignoB oost™

Self assembly

obic drug

Helpful in bioreme diation

Chen et al, 2017

Gonzal ez et al, 2017

SERSL dissolve in EG or castor oil and HCl was added dropwise to the reaction mixture in a nitrogen atmosphere. AL dissolved in polyethylen e glycol and HCl was added dropwise to the reaction mixture until pH 4.0.

Bioderi ved fillers for advance d nanoco mposite applicat ions Acted as a anticorr osive nanofill ers for the protecti on of carbon steel Used as a adsorbe nt to remove Safranin -O dye and Basic Red 2 dye

Lignin dissolved in THF and

To prepare bionano

Mattin en et al,

-p

ro

of

4 2

THF and water was subsequentl y introduced into the system via dropwise. Fractionate of poplar wood and spent acid liquor stream containing mainly dissolved lignin that converting into nanoparticle upon dilution with water. Lignin dissolved in water and ultrasonicati on for 2,4 and 6 h.

na

lP

re

Ultrasonicati on

Acid precipitation

40 – 60 nm

Unifor m and flat

Acid precipitation

300 nm

Spheri cal

Self assembly

Jo ur

Spheri cal

Rahma n et al, 2018

Azimv and et al, 2018a; 2018b; 2018c

48

Journal Pre-proof

80 1000 nm

NR

Microsphere

Comm ercial lignin

6.85 43.90 µm

4 8

L-NPs; L-NPsgelatin

Nanoparticle

Switch grass lignin

80 – 800 nm; 500 – 2000 nm

4 9

CLPs; Enzyme coated c-CLPs

Nanoparticle

Pine kraft lignin

5 0

LNP; PMMA-

Nanoparticle/ Nanocomposi

Pristine lignin

Spheri cal

Reverse phase polymerizati on

re

-p

ro

of

4 7

dialysis system with water. Lignin was dissolved in NaOH under stirring and than HCl was added. Lignin dissolve in ammonia, Hexamethyl enetetramin e and water thereafter formaldehy de was added. Heated at 94°C for 2 h in oil phase and cooled down to get microsphere . Lignin was dissolve in water, NaOH and sonication for 60 min at 600W. Gelatin is attached through direct mixing in different ratio. KL was dissolved in THF and water was subsequentl y introduced into the system via dialysis. Hydrolase/ Lipase is attached through adsorption on surface. Lignin dissolved in

Ultrasonicati on

175 179 nm

Spheri cal

Solvent exchange

32.5 65.1

Spheri cal

Acid precipitation;

Jo ur

na

lP

Spheri cal

material s for advance d applicat ions

2018a; 2018b

Potentia l applicat ions on adsorpti on or superca pacitor

Yu et al, 2018

Applica tion as a floccula nt in wastew ater treatme nt and detectio n of microor ganism, etc. Applica tion in aqueous ester synthesi s

Yin et al, 2018

Applica tion in

Yang et al,

Sippon en et al, 2017;S ippone n et al, 2018

49

Journal Pre-proof te

5 1

PVA/C h/LNP

Nanoparticle/ Nanocomposi te

5 2

LNPs

Nanoparticle

Alkalin e lignin

80 230 nm

Spheri cal

Solvent exchange

5 3

LBNT

Nanoparticle

Alkalin e lignin

154.4 165.6 nm

Mostly spheri cal

Inverseemulsion copolymeriza tion

40 60 nm

Spheri cal

Acid precipitation; Freezingthawing

Jo ur

na

lP

re

-p

Pristine lignin

Solvent-free radical polymerizati on, Micro extrusion

ro

nm

EG and than HCl was added. For PMMA-gLNP, MMA monomer and LNP mixed, ultrasound for 30 min followed by benzoyl peroxide was added, cooled down and heated. Lignin dissolved in EG and than HCl was added; For PVA/Ch/L NP, PVA dissolve in water and than add LNP. Chitosan dissolved in 1% acetic acid and mix with above solution, final mixture freeze thaw upto 5 cycles. AL dissolved in APS solution and dilute with water upto below MHC to obtain LNP precipitate. Lignin dissolved in distilled water, with an amine, and formaldehy de

of

g-LNP

automot ive, flooring , acrylic glasses and lenses

2018a

Applica tion in drug delivery , food packagi ng, wound dressing

Yang et al, 2018b

Drug delivery vehicle for hydroph obic compou nds

Chen et al, 2018

Applica tion in bioreme diation and antimicr obial.

Xiao et al, 2019

50

Journal Pre-proof

Alkali lignin

200 800 nm (size can be contro lled)

5 5

LNPs

Nanoparticle

Soda lignin

50 300 nm

5 6

LNPs

Nanoparticle

Iroko saw dust and Norwa y spruce

5 7

LNPs

Nanoparticle

Corn stover

Spheri cal

Solvent exchange; Ultrasonicati on

of

Nanoparticle

ro

LnPAcL

re

-p

5 4

Solvent exchange/Na noprecipitati on

NR

NR

Solvent exchange

132 1099 nm

Spheri cal and unifor m

Acid precipitation; Solvent exchange

na

lP

Aggre gated particl es

Jo ur

emulsified in liquid paraffin by a surfactant. Heated and cooled down to 30°C after adding CS2 for esterificatio n and freeze drying to obtain LBNT. Acetylated lignin dissolves in THF and ultrasonicati on to different intensity. Precipitates were dialyzed with DDW. Soda lignin dissolved in acetone and water, filtered and filtrate added rapidly in deionized water. Acetone removed and centrifuged to get LNP. Lignin dissolved in DMSO and dialysis with excess water.

Fractionate d lignin from each SOFA was precipitated in HCl, than centrifuged, washed with distilled

Applica tion in UV absorba nce in sunscre en creams.

Wang et al, 2019b

UVblockin g films for potentia l applicat ions in agricult ural or food packagi ng material s. Woodprotecti on applicat ions against weather ing Applica tion in biorefin eries.

Xing et al, 2019

Zikeli et al, 2019

Liu et al, 2019

51

Journal Pre-proof

NR

Nanoparticle

Kraft lignin

30 152 nm

NR

Acid precipitation

NR

Yang et al, 2019

of

5 8

water and freeze dried. The lignin was dissolved in THF, sonicate it and dialysis with water. Lignin (protobind1000) dissolved in EG, precipitated by HCl.

poly(2-(diethylamino) ethyl

ro

NR = Not reported. HX: Heteroxylan. IAT: Indulin AT. PDEAEMA:

-p

methacrylate). THF: Tetrahydrofuran. EG: Ethylene glycol. CO 2: Carbon dioide. HCL: Hydrochloric acid. HNO3: Nitiric acid. DMF: Dimethylformamide. NaOH: Sodium hydroxide. NH4OH: Ammonium hydroxide.

MMA:

Methyl

methacrylate.

Ch:

Chitosan.

CHMAC:

3-chloro-2-hydroxypropyltri

lP

methacrylate).

re

QAL: quaternized alkali lignin. DMSO: Dimethyl sulfoxide. PVA: Polyvinyl alchol. PMMA: Poly(methyl

Jo ur

na

methylammonium chloride. SDBS: Sodium dodecyl benzenesulfonate.

52

Journal Pre-proof Highlights Conversion of raw lignin into nanolignin leds to improvement in properties.



LNPs are biocompatible with tuneable surface functional groups.



LNPs can be synthesized by variety of Physico-chemical-biological methods.



LNPs has excellent antibacterial, antioxidant and UV-shielding efficacy.

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na

lP

re

-p

ro

of



53

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5