A new softening agent for melt spinning of softwood kraft lignin

Kraft lignin obtained from the pulping of wood is an interesting new precursor material for carbon fiber production because of its high carbon content and ready availability. However, continuous spinning of softwood kraft lignin (SKL) has been impossible because of its insufficient softening characteristics and neat hardwood kraft lignin (HKL) has required extensive pretreatments to enable fiber formation. Softwood kraft lignin permeate (SKLP) and hardwood kraft lignin permeate (HKLP), fractionated by membrane filtration, were continuously melt spun into fibers. To improve the spinnability of SKL and HKL, HKLP was added as a softening agent. SKL‐ and HKL‐based fibers were obtained by adding 3–98 wt % HKLP. A suitable temperature range for spinning was 20–85°C above the T_g of the lignin samples, and this range gave a flawless appearance according to the SEM analysis. Smooth, homogeneous fibers of SKLP, HKLP, and SKL with HKLP were successfully processed into solid carbon fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of carbon fibers from polyacrylonitrile precursors

The present work deals with the preparation of carbon fibers from polyacrylonitrile (PAN) fibers. The chemical composition and physical properties of the starting fibers were determined. The PAN fibers were stabilized in air at the temperatures (230, 270, and 300°C) with the heating time from 40 to 420 min. The effects of both final stabilization temperature and heating rate on the chemical and physical properties of the prepared stabilized fibers were studied. The chosen stabilized fibers samples were carbonized in argon atmosphere at the temperatures (1000, 1200, and 1400°C) with different heating rates 5, 10, 15, and 20°C min^?1. The effects of both carbonizing temperature and heating rate on the weight loss, density, elemental composition, and IR absorption spectra of carbonized fibers were also studied. The fiber sample, which was carbonized at 1400°C, contains 97.55% carbon, 1.75% nitrogen, and 1.4% hydrogen. This means that carbonizing the stabilized fibers at 1400°C in argon atmosphere is suitable to get oxygen‐free carbon fibers. Therefore, the used carbonizing temperature in the present work (1400°C) is suitable to produce moderate heat‐treated carbon fibers with the heating rate of 15°C min^?1. The modulus of the prepared carbon fibers was compared to that of industrially produced fibers using the results of X‐ray analysis. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of temperature and holding time on preoxidation for aligned electrospun polyacrylonitrile nanofibers

In this article, aligned electrospun polyacrylonitrile nanofiber bundles were prepared as the precursor fibers to prepare preoxidized nanofibers through washing, drying densification, damp‐heat drafting, and preoxidation process. Effects of preoxidation temperature and holding time on appearance and microstructure of the preoxidized fibers were studied. Fiber density is increased from 1.159 to 1.193 g cm^?3 after drying densification. Crystallinity is increased from 22.66 to 45.90% after fourfold drafting. The aligned preoxidized nanofibers were prepared at the optimum preoxidation temperature of 283°C, heating speed of 1°C min^?1, and holding time of 1 h show a sufficient reaction degree of cyclization and crosslinking. Moreover, there is no occurrence of adhesion between fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1158‐1163, 2013     

Kraft lignin/poly(ethylene oxide) blends: Effect of lignin structure on miscibility and hydrogen bonding

Blends of poly(ethylene oxide) (PEO) with softwood kraft lignin (SKL) were prepared by thermal blending. The miscibility behavior and hydrogen bonding of the blends were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The experimental results indicate that PEO was miscible with SKL, as shown by the existence of a single glass‐transition temperature over the entire composition range by DSC. In addition, a negative polymer–polymer interaction energy density was calculated on the basis of the melting point depression of PEO. The formation of strong intermolecular hydrogen bonding was detected by FTIR analysis. A comparison of the results obtained for the SKL/PEO blend system with those previously observed for a hardwood kraft lignin/PEO system revealed the existence of stronger hydrogen bonding within the SKL/PEO blends but weaker overall intermolecular interactions between components; this suggested that more than just hydrogen bonding was involved in the determination of the blend behavior in the kraft lignin/PEO blends. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1437–1444, 2005     

Chemical Modification of Methanol-Insoluble Kraft Lignin Using Oxypropylation Under Mild Conditions for the Preparation of Bio-Polyester

Methanol-insoluble high-molecular weight (M_w = 26,610 g mol^?1) soft wood kraft lignin was oxypropylated under the mild condition of 40°C and 1 atm for 12 h in the presence of NaOH catalyst for the production of bio-polyester. Fourier transform infrared spectra showed that polyether chains were extended due to the oxypropylation reaction. The M_w and M_n of the oxypropylated lignin were 46,330 and 17,110 g mol^?1, respectively. The high-molecular weight oxypropylated lignin was reacted with sebacic acid or polybutadiene (dicarboxy terminated) for bio-polyester synthesis. While the decomposition temperatures of the oxypropylated lignin were 217°C and 367°C, those of the bio-polyesters prepared with sebacic acid and polybutadiene (dicarboxy terminated) were 380°C and 453°C, respectively, indicating that the bio-polyesters possessed enhanced thermal properties. The oxypropylation of methanol-insoluble high-molecular weight lignin under mild conditions is one of the promising approaches for preparing bio-plastics with an enhanced thermal property.     

Effect of lignin on mechanical,biodegradability, morphology,and thermal properties of polypropylene/polylactic acid/lignin biocomposite

ABSTRACT

The effects of lignin on mechanical, biodegradability, morphology, and thermal properties of PP/PLA/lignin were investigated. PP/PLA/lignin film were manufactured by adding PP, PLA, lignin and compatibilizer into rheomix at 200°C, at 70?rev?min^?1 for 30?minthen pressed using Hydraulic Hot Press at 200°C–210°C, at 6 bar for 20?min. The functional groups of PP/PLA/lignin were analyzed using FTIR. The surface morphology, mechanical properties and thermal stability was measured by SEM, tensile strenght and TGA respectively. TThe FTIR intensity of vibration peak of –CH₃?cm^-1 from PP/lignin and PP/PLA/lignin at 997–993, 1458–1451 and 2966–2904?cm^-1 was lower than neat PP. The addition of lignin into PP/lignin, PLA/lignin and PP/PLA/lignin can reduce tensile strength and elongation at break. The thermal stability PP/PLA/lignin was lower than the PP/lignin but higher compared to PP/PLA biocomposites. The biodegradability of PP/PLA/lignin biocomposites was two times higher than that of PP/lignin.     

Optimal sintering parameters for Al2O3 optoceramics with high transparency by spark plasma sintering

Transparent Polycrystalline Alumina (PCA) optical ceramics were fabricated at a high heating rate and low temperature by spark plasma sintering (SPS). Maximum pressure (100?MPa) at dwell time keeps the grain size small irrespective of the dwell time. A heating and cooling rate of 100°C?min^?1 at the sintering temperature of 1150°C for a dwell time of 1?h at 100?MPa yielded highly densified samples with the good transparency of 63 and 83% in visible and infra-red region, respectively. Optoceramics yielded a mechanical hardness of (3000 Hv)/ 29.42?GPa and a thermal conductivity of 21?Wm^?1?K^?1.     

Electrically conductive kraft lignin-based carbon filler for polymers

Commercial kraft lignin was thermostabilised by heating up to 250 °C at a rate of 0.01 °C min⁻¹ in ambient atmosphere. Subsequent carbonisation at 2000 °C in argon atmosphere yielded carbon microparticles containing ordered graphitic domains. Micromechanical characterisation by nanoindentation yielded average values of 1.39 GPa for hardness and 8.2 GPa for the indentation modulus of carbon particles. Composite films of polycaprolactone with different carbon content were prepared by means of solvent evaporation casting. Tensile testing revealed an increase in composite stiffness while strength and elongation at break decreased with the loaded amount of carbon microparticles. Electrical conductivity of the composites was exemplarily observed for a carbon microparticle loading of 15% (w/w). Using a composite film as strain sensor in three-point bending, high sensitivity of electrical conductivity towards the applied strain was observed.     

Flammability of polyacrylonitrile and its copolymers II. Thermal behaviour and mechanism of degradation

Homopolymeric polyacrylonitrile and fibre-forming copolymers containing either vinyl acetate or methyl acrylate comonomer have been studied by thermal analysis (DSC, TGA and DTG) at various heating rates (10–100 K min^?1) and under air and nitrogen. Three well-defined pyrolysis stages have been observed which occur over the temperature ranges 250–350°C, 350–550°C and above 550°C. Each stage involves a competition between volatilisation and cyclisation or char-forming reactions which depends on heating rate and the presence or absence of oxygen. The well-established dominance of cyclisation in the 250–350°C temperature range obtained during carbon fibre production from acrylic precursors occurs only at low heating rates. At high heating rates, volatilisation dominates and this explains why acrylic polymers have high flammabilities when heating rapidly. The full pyrolysis mechanism has been semi-quantitatively analysed and the role that comonomers play discussed. This has enabled a fuller understanding of the potential burning behaviour of these polymers to be developed.     

Development of lignin carbon fibers: Evaluation of the carbonization process

The use of lignin as a renewable resource for the production of less‐expensive carbon fibers has in recent years attracted great interest. In order to develop the strength properties, the stabilization and carbonization processes have to be optimized. For this reason, the process parameters during carbonization have here been studied on stabilized lignin fibers in the temperature interval from 300 to 1300 °C. The effects of temperature, heating rate, and straining of fibers during carbonization on the strength properties of carbon fibers were investigated. The heating rate, in the range from 1 to 40 °C/min, was shown to have no effect on the property development of the fibers. During carbonization with no load applied to the fibers, a shrinkage of 20% was noted. Counteracting the shrinkage by imposing a load on the fibers during the carbonization resulted in fibers with a greater stiffness. The tensile strength was not, however, affected by this loading. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43965.     

Improvement of Mechanical Properties of Softwood Lignin-Based Carbon Fibers

PEG-lignin fibers obtained by a solvolysis pulping of Japanese cedar with polyethylene glycol (PEG) 400 were successfully converted into defective-free, infusible fibers as a precursor for carbon fibers (CFs) by chemical curing followed by oxidative thermostabilization. The curing was performed by immersing PEG-lignin fibers in an aqueous mixed solution of hexamethylenetetramine (60 g/L) and hydrochloric acid (3 M) at 85°C for 1 h, resulting in the formation of crosslinkages between lignin molecules through methylene groups. These cured fibers were completely thermostabilized upon heating up to 250°C at a heating rate of 2°C/min under an air atmosphere. Finally, the thermostabilized fibers were carbonized to yield CFs, which showed about 1.5 times the tensile strength of our CFs previously prepared.     

Preparation and properties of polyimide solvent‐resistant nanofiltration membrane obtained by a two‐step method

This study investigated the preparation of polyimide solvent‐resistant nanofiltration membranes by a two‐step method (casting the membrane first and then crosslinking by the thermal imidization method). The influences of polymer concentration, thickness of membranes, temperature of the imidization, phase inversion time and thermal imidization procedure were studied. The membranes with the highest rejection rate of Fast Green FCF (molecular weight 808.86 g mol^?1) were prepared in the following conditions: polymer concentration 13 wt%, phase inversion time 1 h, membrane thickness 150 µm and thermal imidization procedure 200 °C for 2.5 h, 250 °C for 2 h and 300 °C for 2 h in a vacuum environment; the heating rate was 5 °C min^?1. The membrane was stable in most of the solvents tested and the fluxes of some common solvents were equal to or higher than a number of commercial solvent‐resistant nanofiltration membranes. A much higher rejection of dyes in water than in methanol was observed in the filtration experiments and a new way to explain it was developed. Copyright © 2011 Society of Chemical Industry     

Grafting of methyl methacrylate (MMA) onto Antheraea assama silk fiber

Graft copolymerization of methyl methacrylate (MMA) onto nonmulberry silk fiber Antheraea assama was investigated in aqueous medium using the KMnO₄–oxalic acid redox system. Grafting (%) was determined as a function of the reaction time, temperature, and monomer and initiator concentrations. The rate of grafting increased progressively with increase of the reaction time up to 4 h and then decreased. The extent of grafting was maximum at 55°C. The extent was also dependent upon monomer and initiator concentrations up to 75.5 × 10^?2 and 6 × 10^?3 M, respectively. The grafted products were evaluated by infrared spectroscopy and their thermal decompositions were studied by TG and DTG techniques in static air at 20°C min^?1 and 30°C min^?1 in the range 30–800°C. The kinetic parameters for ungrafted and grafted fibers were evaluated using the Coats and Redfern method. The grafted products were found to be thermally more stable than were those of the ungrafted fibers. The surface characteristics of the ungrafted and grafted fibers were evaluated by scanning electron microscopy. The water‐retention values (WRVs) of the grafted fibers were in decreasing order with increase in the grafting (%). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2633–2641, 2001     

Mathematical modelling of lignin pyrolysis

Seven lignins from different sources were pyrolysed (i) isothermally in vacuum over the temperature range 300–1300 °C and (ii) at a constant heating rate of 30 °C min^?1 and a pressure of 0.1 MPa over the temperature range 150–900 °C. The mass fraction of each product—char, tar and gas species—and the elemental composition of the char and the tar were determined for the flash pyrolysis experiments. The evolution rates of the gas species and the tar versus the dynamic temperature of pyrolysis were determined for the constant heating rate pyrolysis experiments. Although the amount of each product species varied from lignin to lignin, the evolution rates were insensitive to the lignin source and the extraction process. To model the data, modifications were made to a recently developed model of coal pyrolysis. The model proved to be successful in simulating both the data from vacuum flash pyrolysis and constant heating rate pyrolysis of Iotech lignin.     

Kraft lignin in phenol formaldehyde resin. Part 1. Partial replacement of phenol by kraft lignin in phenol formaldehyde adhesives for plywood

The objective of this study was to investigate the potential for partially replacing phenol with kraft lignin in the phenol formaldehyde (PF) resin designed for application as an adhesive in the production of plywood. The kraft lignin, considered to be an environmentally friendly alternative to phenol, was precipitated from black liquor recovered from kraft pulping of softwood. Kraft lignin phenol formaldehyde (KLPF) resin was prepared in a one-step preparation with different additions of lignin. Replacing 50 wt% of the phenol with kraft lignin (50KLPF) was, under the conditions used, considered to be optimal with respect to resin viscosity, storage stability, and bonding ability. The resin consists of an integrated kraft lignin-phenol network. The hot-pressing time in the plywood manufacturing had to be increased by approximately 30% at 150°C for the 50KLPF resin compared with that normally used for PF resin, in order to comply with plywood standard demands. The mechanical properties of test samples made from KLPF resins were equal to or better than those of test samples made from PF resin only.     

The fast pyrotechnic reaction of silicon with lead oxides: Differential scanning calorimetry and hot-stage microscopy studies

Differential scanning calorimetry has been applied in the study of the fast pyrotechnic reaction of silicon with (a) PbO; and (b) Pb₃O₄ in powder form. Samples were heated up to 725 °C at heating rates from 0.3 to 160 °C min^?1 under a nitrogen atmosphere. Hot-stage microscopy was used to observe phase changes up to 1000 °C at heating rates of 0.1–100 °C min^?1, and X-ray analysis to identify products. The DSC studies of both compositions indicate two exothermic peaks at 548–667 °C and 667–726 °C, corresponding to surface and bulk reaction. The use of PbO with a smaller particle size results in a larger first and smaller second peak indicating enhanced surface activity. For Pb₃O₄/Si compositions, reaction is principally between Si and PbO, resulting from the decomposition of PbO. At a heating rate of 100 °C min ^?1 both compositions ignite above 700 °C. Hot-stage microscopy correlates phase and colour changes with temperature of occurrence of peaks in the DSC studies.     

Nanostructure and bimodal structure of Si3N4 ceramics developed by spark plasma sintering method

Abstract

The densification of high energy ball milled Si₃N₄ nanopowders through spark plasma sintering was investigated. Nanoceramics of Si₃N₄, with fine microstructure, comprising of grains with a diameter of ～70 nm, were produced after sintering at 1600°C for 5 min in N₂ atmosphere with a fast heating rate of 300 K min^?1. The size and the aspect ratio of Si₃N₄ grains increased with decreasing heating rate and increasing holding time and temperature. Post-annealing of sintered ceramics at 1850°C for 3 h favoured development of a self-reinforced bimodal microstructure containing large elongated grains.     

Formation and Reaction of Coniferyl Alcohol During Alkaline Pulping

The formation and subsequent disappearance of coniferyl alcohol during kraft and soda-AQ (anthraquinone) pulping of western hemlock wood meal have been studied under isothermal condition. At 140°C, the amount of coniferyl alcohol generated increases to a sharp maximum (0.4% of total lignin in kraft and 1.9% in soda-AQ pulping) and then declines rapidly to low values. It was found that the disappearance of coniferyl alcohol was mainly due to condensation with other components of dissolved lignin. Nearly identical activation energies, 125 kJ mole^?1 for kraft and 128 kJ mole^?1 for soda-AQ pulping, were derived from the initial rates of coniferyl alcohol formation, conforming closely with the value 121 kJ mole^?1 for the cleavage of phenolic β-ether model compounds in the kraft process.     

Molecular Mass Distribution of Lignin from the Alkaline Pulping of Hardwood,Softwood, and Wheat Straw

Abstract

The behavior of lignin during kraft (hardwood, softwood, and wheat straw) and soda-AQ (wheat straw) pulping was studied, mainly in terms of delignification degree and molecular mass distribution (MMD). In the initial delignification phase (at 140°C for 15–60 min), a prominent part of the dissolved softwood kraft lignin (18–25 g/L, MM mostly > 3,000 Da) was found in the liquid phase of chip cavities, rather than in the external bulk black liquor (5–7 g/L, MM mostly < 3,000 Da). The maximum weight average MM values ( _w) of the soluble lignin under conventional cooking conditions were detected for the kraft softwood (4,100 Da), and kraft birch (3,400 Da) when the degree of delignification was 65–75%, corresponding to a residual lignin content of 5–10%. The maximum _w of the dissolved wheat straw kraft (5,050 Da) and soda-AQ (5,900 Da) lignins was clearly higher than that of wood-based kraft lignins (2,950–4, 100 Da).     

Preparation of ultra-thin PAN-based activated carbon fibers with physical activation

This study elucidates the stabilization and activation in forming activated carbon fibers (ACFs) from ultra-thin polyacrylonitrile (PAN) fibers. The effect of stabilization time on the properties and structure of resultant stabilized fibers was investigated by thermal analysis, X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy (SEM). Stabilization was optimized by the pyrolysis of ultra-thin PAN fibers in air atmosphere at 280°C for 15 min, and subsequent activation in steam at 1000°C for 0.75 to 15 min. Resultant ACFs were characterized by N₂ adsorption at 77 K to evaluate pore parameters, XRD to evaluate structure parameters, and field emission scanning electron microscopy (FESEM) to elucidate surface morphology. The produced ACFs had surface areas of 668–1408 m²/g and a micropore volume to total pore volume ratio from 78 to 88%. Experimental results demonstrate the surface area and micropore volume of 1408 m²/g and 0.687 cm³/g, respectively, following activation at 1000°C for 10 min. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008