Dispersion Of Lignin Research Articles

Siloxane–PMMA hybrid anti-corrosion coatings reinforced by lignin

Novel organic–inorganic hybrid coatings prepared using siloxane-poly(methyl methacrylate) (PMMA) were synthesized using the sol–gel process, with incorporation of lignin to improve mechanical strength, thermal stability and hydrophobicity, while maintaining the high anti-corrosive protection of siloxane–PMMA coatings. Dispersion of lignin in the siloxane–PMMA hybrid was analyzed by optical microscopy. Structural, morphological and wettability analysis of the about 2.5 μm thick coatings, deposited on carbon steel by dip-coating, was performed by X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. Thermal stability was investigated by thermogravimetry and the mechanical properties were studied by microhardness and microscratch measurements. Electrochemical impedance spectroscopy was used to evaluate corrosion resistance in saline aqueous environments. All coatings showed good dispersion of lignin in the hybrid matrix and low surface roughness between 0.3 and 0.4nm. Incorporation of lignin increased hydrophobicity, microhardness and scratch resistance, in addition to shifting thermal degradation events to higher temperatures. The electrochemical tests showed that the hybrids act as efficient diffusion barriers, with corrosion resistance in the range of 108Ωcm2 after exposure to 3.5% NaCl aqueous solution. The hybrid containing a intermediate lignin content of 0.10wt.% presented the best result, exhibiting the most hydrophobic surface (87.9° water drop contact angle), the highest hardness value (31.5 HV), high scratch resistance (up to 80.7mN) and elevated impedance modulus (108Ωcm2) after 50days exposure.

Sustainable Green Hybrids of Polyolefins and Lignin Yield Major Improvements in Mechanical Properties When Prepared via Solid-State Shear Pulverization

Lignin, a byproduct of paper and pulp industries, is a sustainable, inexpensive biomaterial with potential as composite filler. Past research on polyolefin/lignin composites made by melt processing has led to modest increases in Young’s modulus and drastic reductions in tensile strength and elongation at break relative to neat polymer. Here, green hybrids of low density polyethylene (LDPE) and polypropylene (PP) with 5–30 wt % lignin are made by solid-state shear pulverization (SSSP). Microscopy shows that SSSP leads to superior lignin dispersion and suppressed degradation when compared to melt-mixed composites reported in the literature. Composites made by SSSP exhibit major improvements in Young’s modulus (81% and 62% increases for 30 wt % lignin in LDPE and PP, respectively, relative to neat polymer), tensile strength equal to or better than that of neat LDPE and near that of neat PP, and much better strain at break than reported in the literature for polyolefin/lignin composites. The SSSP-produced hybrids exhibit major increases in hardness, with 70/30 wt % PP/lignin hybrids reaching values near that of polycarbonate. Well-dispersed lignin improves LDPE and PP thermo-oxidative stability as shown by thermogravimetric analysis (∼35 °C increase in 20% mass loss temperature in air with 20 wt % lignin addition) and isothermal shear flow rheology. Lastly, SSSP-processed composites exhibit slightly improved crystallizability and melt viscosities at moderate to high shear rates that differ relatively little from those of neat LDPE and PP.

In situ dispersion and compatibilization of lignin/epoxidized natural rubber composites: reactivity, morphology and property

ABSTRACTLignin, a naturally occurring polymer, was viewed as a potential substitute of carbon black for reinforcing rubber materials. However, it shows no reinforcing effect if directly mixed with rubber. In this study, lignin was in situ dispersed at submicrometer size and highly compatible with epoxidized natural rubber (ENR) by using a high‐temperature dynamic heat treatment (HTDHT). Rheology analysis indicated that the ring opening reaction between lignin and ENR occurred at 160°C or above, which was further confirmed by infrared spectroscopy. Due to the consumption of acidic groups of lignin by ENR, the retardant vulcanization effect of lignin was weakened. Morphology observation and dynamic mechanical analysis demonstrated the perfect lignin dispersion and the strong interactions between lignin and ENR. The mechanical properties of the lignin/ENR composites were significantly improved by using HTDHT. Compared to the directly mixed rubber composites, the tensile strength and tear strength of the heat treated rubber composites filled with 40 phr lignin were increased by 114% and 23%, respectively. Especially, the 300% modulus of the heat treated rubber composite was increased by ca. 400%. X‐ray diffraction results indicated that the reinforcement of the composites originated from the presence of lignin rather than the strain‐induced crystallization of ENR. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42044.

Organosolv lignin as natural grafting additive to improve the water resistance of films using cellulose nanocrystals

Within the framework of research on the valorization of by-products from 2nd generation biorefineries, we designed novel nanocomposite materials composed of lignin and cellulose nanocrystals. These nano-composites were in the form of thin films which could be self-supported or supported on glass or quartz slides. These materials were prepared by coating or casting the polymer mixtures at ambient conditions. The lignins used included synthetic lignin oligomers as standards and organosolv lignin fractions from maize stalks and spruce wood. The Fenton’s reagent was incorporated into the polymeric mixture to improve the dispersion of lignin and to facilitate its grafting onto the surface of cellulose nanocrystals. This grafting process improved the anti-UV property, water resistance, water retention of the thickener films and micromechanical properties of cellulose/lignin films. On the nanocomposite market, the combination of these physico-chemical properties with known antibacterial property of lignin on one hand and oxygen barrier property of cellulose nanocrystal films on the other hand, would make relevant the use of these films in food and non-food (medical, packaging, surface coverings) application fields.

Study of lignin dispersion in low-density polyethylene

A maximum of 20% (w/w) lignin was used as a filler in low-density polyethylene (LDPE), together with 3–6% maleic anhydride-grafted LDPE as compatibilizer and 3–10% copper(II) sulphate pentahydrate (CuSO4·5H2O) as lignin’s dispersing agent. The resulting composites were investigated for both their mechanical properties and their melting point following the ASTM standards as well as their behaviour was compared with neat LDPE. The results reveal that addition of compatibilizer significantly improved the mechanical properties of lignin, yielding closer values to those of neat LDPE. In fact, the addition of 3% maleated polyethylene induced a 37% increase of the Young’s modulus, whilst 3% CuSO4·5H2O provides a good lignin dispersion. The above observations are further supported by the scanning electron micrographs of the blend specimens. Finally, the differential scanning calorimetry analysis revealed that the melting temperature and the crystallinity of LDPE slightly increase with the addition of 3% CuSO4·5H2O.

Enhanced dispersion of lignin in epoxy composites through hydration and mannich functionalization

ABSTRACTLignin was used as a biobased fill material to create epoxy composites. Lignin was incorporated into diglycidyl ether of bisphenol A–based epoxy using hydration and Mannich functionalization. The effects of chemical functionalization on the interfacial chemistry of lignin are examined, and the corresponding changes in materials properties are examined. Several types of lignin–epoxy composites were formed through dissolution of lignin in aliphatic amine. Lignin–amine solutions were modified through hydration and the Mannich reaction and were used to cure the epoxy. The resulting composites exhibited two‐phase microstructures containing lignin‐rich agglomerates. Thermomechanical properties were examined using dynamic mechanical analysis, differential scanning calorimetry, and fracture testing. Morphological and chemical changes were examined using scanning electron microscopy and Fourier transform infrared spectroscopy. The hydrated lignin samples showed similar glass transitions and mechanical properties to the neat epoxy samples. Interactions between water and the Mannich functionalized lignin decreased the glass transition temperature and mechanical properties of the highly hydrated Mannich reacted lignin samples because of a plasticization effect. Fracture testing was conducted on the samples and showed that the yield strength and elastic modulus were similar to the neat epoxy, but the fracture toughness decreased in the lignin‐containing specimen. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41263.

Effect of irradiation on aqueous dispersions of humic acids and lignin

The influence of electron-beam irradiation on the optical absorption of dilute aqueous solutions of lignin and humic acids has been studied. It has been shown that when the thickness of the irradiated layer of the solution is less than the electron range, preferential enlargement and precipitation of polyphenolic impurities observed. The most profound effect is achieved at doses of 5–15 kGy. When the irradiated-layer thickness is less than the electron range, the radiation-induced coagulation of impurities weakens. This effect can be due to the buildup of uncompensated charge of thermalizing electrons affecting the negatively charged micelles of polyphenolic impurities.

Application of Sulphur-Free Lignins as a Filler for Elastomers: Effect of Hexamethylenetetramine Treatment

Lignins from a steam explosion process in crude and purified forms and modified sulphur-free commercial lignin (Protobind 3000®) were characterised to establish their chemical compositions. Then, the lignins were tested again after treatment with hexamethylenetetramine (HMT). The resulting products were used to make rubber composites, and their mechanical properties were compared to rubber composites made with carbon black to test the possibility of using HMT-treated lignins as a partial replacement for carbon black in the production of rubber composites. In the crude lignin, a significant amount of impurities were detected, such as ash and residual polysaccharides, and these substances interfered in filler-elastomer interactions. The purified lignin maintained a high content of strongly polarised hydroxyl groups that interfered with the interaction of the filler and elastomer, resulting in low performance. Improvements in the mechanical properties were observed using Protobind 3000® lignin or purified lignin with HMT added during mixing with the rubber. Finally, the mixing of HMT-treated lignin with elastomers resulted in composites with higher reinforcement abilities compared to previously described rubber composites. However, in all samples, a poor and unsatisfactory dispersion of lignin in the polymeric matrix was observed. This is likely due to the incompatibility of lignin with the hydrophobic rubber, resulting in lower performances compared to the carbon black.

Morphology, Tensile Strength and Oil Resistance of Gum Rubber Sheets Prepared from Lignin Modified Natural Rubber

The paper describes the preparation of lignin filled natural rubber latex composite and its subsequent use to obtain lignin modified rubber. Two types of lignin i.e.: rubber wood and commercial alkali lignin were used as rubber filler. Gum rubber sheets were prepared from the lignin modified rubber and their properties were compared to Standard Malaysian Rubber (SMR 20) and a type of rubber obtained from the coagulation of high ammonia latex. Rubber morphology was investigated using Scanning Electron Microscope on the cross-sectional area of cryo-fractured samples. Oil resistance of the rubber sheets was determined by measuring the mass change before and after ASTM IRM 903 oil immersion, while the tensile strengths were determined according to ASTM D412 standard. Low values of tensile strength obtained for the commercial alkali lignin modified rubber sheet relative to the rest of the rubber samples was attributed to poor lignin dispersion. This occurrence was substantiated by the SEM analysis of cryo- fractured samples where crazes and inhomogeneity was observed. Nonetheless, both lignin modified rubbers exhibited higher level of oil resistance compared to SMR 20. This is due to the nature of lignin as a hydrophilic component and its presence in the rubber matrix complicates the oil diffusion process into rubber.

Thermomechanical Properties of Lignin-Based Electrospun Nanofibers and Films Reinforced with Cellulose Nanocrystals: A Dynamic Mechanical and Nanoindentation Study

We produced defect-free electrospun fibers from aqueous dispersions of lignin, poly(vinyl alcohol) (PVA), and cellulose nanocrystals (CNCs), which were used as reinforcing nanoparticles. The thermomechanical performance of the lignin-based electrospun fibers and the spin-coated thin films was improved when they were embedded with CNCs. Isochronal dynamic mechanical analysis (DMA) was used to assess the viscoelastic properties of the lignin:PVA electrospun fiber mats loaded with CNCs. DMA revealed that α relaxation processes became less prominent with an increased lignin content, an effect that correlated with the loss tangent (tan δ = E″/E') and α peak (Tg) that shifted to higher temperatures. This can be ascribed to the restraint of the segmental motion of PVA in the amorphous regions caused by strong intermolecular interactions. The reinforcing effect and high humidity stability attained by addition of CNCs (5, 10, or 15 wt %) in the multicomponent fiber mats were revealed. Nanoindentation was performed to assess the elastic modulus and hardness of as-prepared and cross-section surfaces of spin-coated lignin:PVA (75:25) films loaded with CNC. The properties of the two surfaces differed, and only the trend in cross-section elastic modulus correlated with DMA results. After addition of 5 wt % CNCs, both the DMA and nanoindentation elastic modulus remained constant, while after addition of 15 wt % CNCs, both increased substantially. An indentation size effect was observed in the nanoindentation hardness, and the results provided insight into the effect of addition of CNCs on the microphysical processes controlling the yield behavior in the composites.

The effect of electron irradiation on aqueous dispersions of humic acids and lignin

The effect of irradiation by accelerated electrons on optical absorption of diluted aqueous solutions of lignin and humic acids was studied under two different irradiation conditions: when thickness of irradiated solution layer was less than the electrons range in the solution (mode I) and vice versa (mode II). Dominating agglomeration and sedimentation of the compounds has been demonstrated to take place under irradiation in mode I, maximal effect being achieved at absorbed dose 5–15kGy. Under irradiation in mode II, i.e. when all the incident electrons were being absorbed, the radiation-induced coagulation was depressed. The dependence of radiation effect on irradiation conditions may be caused by stabilizing action of accumulating excess charge of absorbed electrons on negatively charged micelles of lignin and humic acids.

Potential of Lignins as Antioxidant Additive in Active Biodegradable Packaging Materials

Due to their polyphenolic structure lignins bear a number of interesting functional properties, such as antioxidant activity. Natural antioxidants are very much looked for in the aim of protection of light or oxygen sensitive goods and are being used in active packaging. Poly(lactide) (PLA)-lignin films were prepared by twin screw extrusion followed by thermo-compression using two different commercial sources of alkali lignins obtained from gramineous plants. A good dispersion of lignin in the matrix was observed. Mechanical properties of the compounded material were merely diminished and oxygen barrier properties slightly enhanced. The chromatographic study of the lignins revealed that the low molecular weight fraction of both lignins increased during the polymer processing. The migration of low molecular weight compounds in an ethanol/water solution simulating fatty foodstuff was performed and the antioxidant activity of the extract was analysed. It was found that the activity increases with increasing severity of the heat treatment because of the generation of free phenolic monomers during processing. These results open an interesting way for application of lignins as an active compound in packaging materials. Lignins do not impair the mechanical and barrier performance of the polymer and the plastics processing even allows for the generation of active substances.

Interfacial Properties of Lignin-Based Electrospun Nanofibers and Films Reinforced with Cellulose Nanocrystals

Sub-100 nm resolution local thermal analysis, X-ray photoelectron spectroscopy (XPS), and water contact angle (WCA) measurements were used to relate surface polymer distribution with the composition of electrospun fiber mats and spin coated films obtained from aqueous dispersions of lignin, polyvinyl alcohol (PVA), and cellulose nanocrystal (CNC). Defect-free lignin/PVA fibers were produced with radii which were observed to increase with lignin concentration and with the addition of CNCs. XPS and WCA results indicate a nonlinear relationship between the surface and the bulk compositions. A threshold around 50 wt % bulk composition was identified in which extensive partitioning of PVA and lignin components occurred on the surface below and above this value. In 75:25 wt % lignin/PVA solvent cast films, phase separated domains were observed. Using nanoscale thermal analyses, the continuous phase was determined to be lignin-rich and the discontinuous phase had a lignin/PVA dispersion. Importantly, the size of the phase separated domains was reduced by the addition of CNCs. When electrospun fiber surfaces were lignin-rich, the addition of CNCs affected their surfaces. In contrast, no surface effects were observed with the addition of CNCs in PVA-rich fibers. Overall, we highlight the importance of molecular interactions and phase separation on the surface properties of fibers from lignin as an abundant raw material for the fabrication of new functional materials.

Lignin-Based Electrospun Nanofibers Reinforced with Cellulose Nanocrystals

Lignin-based fibers were produced by electrospinning aqueous dispersions of lignin, poly(vinyl alcohol) (PVA), and cellulose nanocrystals (CNCs). Defect-free nanofibers with up to 90 wt % lignin and 15% CNCs were achieved. The properties of the aqueous dispersions, including viscosity, electrical conductivity, and surface tension, were examined and correlated to the electrospinnability and resulting morphology of the composite fibers. A ternary lignin-PVA-water phase diagram was constructed as a tool to rationalize the effect of mixing ratios on the dispersion electrospinability and morphology of the resulting fibers. The influence of reinforcing CNCs on the thermal properties of the multicomponent fibers was investigated by using thermal gravimetric analysis and differential scanning calorimetry. The thermal stability of the system was observed to increase owing to a strong interaction of the lignin-PVA matrix with the dispersed CNCs, mainly via hydrogen bonding, as observed in Fourier transform infrared spectroscopy experiments.

Influence of AlCl3 on aggregation stability of aqueous dispersions of kraft lignin according to filtration through track membranes

The influence of AlCl3 (0–10−3 M) and pH (9.5–2.0) on the aggregation of dilute (10 mg/l) aqueous dispersions of kraft lignin is studied by filtration through several track membranes with pore diameters of 50–2500 nm. AlCl3 is shown to have markedly higher coagulating ability than NaCl and CaCl2. In a pH range of 4.1–7.0, which corresponds to the significant hydrolysis of AlCl3, the concentration inversion of AlCl3 coagulating ability is observed when passing from 10−4 to 10−3 M, which is caused by the charge reversal of negatively charged kraft lignin particles under the action of AlCl3 hydrolysis products.

Influence of NaOH, HCl, NaCl, and CaCl2 electrolytes on aggregation stability of aqueous craft lignin dispersion according to data of filtration through track membranes

The method of filtration through track membranes with different capillary diameters (50–2500 nm) is used to study the aggregation stability of dilute (10 mg/l) aqueous dispersions of craft lignin in NaCl and CaCl2 solutions (0–10−1 mol/l) at pH 9.5–2.0. It is shown that, in the absence of salts, the isolation of craft lignin on filters increases at decreasing pH, i.e., upon approaching the isoelectric point of craft lignin (pH 2.0). The addition of the salts enhances the efficiency of craft lignin rejection, which is higher in the case of CaCl2. The sizes of craft lignin aggregates in solutions of different compositions are determined from the obtained data.

EFFECTS OF COMPATIBILIZERS ON THE MECHANICAL PROPERTIES OF LOW DENSITY POLYETHYLENE/LIGNIN BLENDS

Low density polyethylene (LDPE)/lignin blends were prepared using melt blending. Two kinds of compatibilizers, ethylene-vinylacetate (EVA) which is softer than LDPE and polyethylene grafted with maleic anhydride (PE-g-MA) which is harder than LDPE were used to improve the interfacial adhesion. Scanning electron microscope (SEM) was used to investigate the dispersion of lignin in LDPE matrix. The results showed that both of the compatibilizers could improve the interaction between the low density polyethylene and lignin. However, the effects of the two compatibilizers on the mechanical properties of LDPE/lignin blends were different. The elongation at break of the blends was obviously increased by adding EVA, while significant improvement of tensile strength was observed by adding PE-g-MA. Several theoretical models have been used to further analyze the experimental data, combined with the morphological observation of tensile fractured surfaces by SEM.

Prevulcanized Natural Rubber Latex/Modified Lignin Dispersion for Water Vapour Barrier Coatings on Paperboard Packaging

Modified natural rubber latex can be used as paperboard barrier coating in order to replace unrecyclable wax coating material. Natural rubber latex (NRL) was prevucanized in different time interval and the efficiency of crosslinking were determined by swelling ratio test. Prevulcanized natural rubber latex (Pre-VNRL) was blended with modified lignin dispersion to decrease sticking tendency of the coatings. Particle size of lignin dispersion was reduced by Mannish reaction using octylamine which can increase hydrophobility in lignin. Compared with Pre-VNRL coating, a reduction of water vapour transition rate (WVTR) was observed in blendingcoated paper. Such moisture-barrier behaviour is attributable to a good compatibility of the nanosized modified lignin particles with rubber. The blocking (sticking) tendency decreased with the content increase of lignin due to stiffness of lignin.

Study of the dependences of particle sizes in aqueous dispersions of sulfate lignin on pH by the filtration through track-etched membranes

Aggregation stability of low concentrations (10 mg/l) of aqueous dispersions of sulfate lignin is studied in a wide pH range (9.40–2.15) by filtration through track-etched membranes with pore sizes of 30–200 nm. It is shown that at all of the studied pH values, the solution of sulfate lignin is a polydisperse system. As pH decreases, the size of sulfate lignin particles increases, whereas the polydispersity of a system in the studied range of particles sizes (30–200 nm) decreases.

Spectrophotometric and flow ultramicroscopic study of the aggregation and sedimentation stability of aqueous dispersions of sulfate lignin in a pH range of 12.0–2.3

The aggregation and sedimentation stability of low-concentrated (10 mg/l) aqueous dispersions of sulfate lignin are studied by the spectrophotometry and flow ultramicroscopy methods in a wide pH range (12.0–2.3). Initial solution of sulfate lignin (pH 12.0) is shown to be a polydisperse system stable with respect to aggregation and sedimentation. As pH decreases up to 3.2, the sedimentation stability is retained, whereas a loss of aggregation stability resulting in an enlargement of initial fine particles invisible with a flow ultramicroscope and their transition into the visible size range are observed even at pH 11.0. In the course of time, the formed visible particles aggregate with a concomitant decrease in their total concentration. This process is even more pronounced at pH 10.0. At pH 2.3, the system loses its sedimentation and aggregation stability, and the visible particle concentration increases by tens of times compared to pH 12.0 then, the particles aggregate that results in a decrease in the total particle concentration. At any pH value, the systems studied are polydisperse that is most pronounced at pH 2.3.