18171341
Physicochemical Characterization of Functional Lignin–Silica Hybrid Fillers for Potential Application in Abrasive Tools
Functional lignin–SiO2 hybrid fillers were prepared for potential application in binders for phenolic resins, and their chemical structure was characterized. The properties of these fillers and of composites obtained from them with phenolic resin were compared with those of systems with lignin or silica alone. The chemical structure of the materials was investigated by Fourier transform infrared spectroscopy (FT-IR) and carbon-13 nuclear magnetic resonance spectroscopy (13C CP MAS NMR). The thermal stability of the new functional fillers was examined by thermogravimetric analysis–mass spectrometry (TG-MS). Thermo-mechanical properties of the lignin–silica hybrids and resin systems were investigated by dynamic mechanical thermal analysis (DMTA). The DMTA results showed that abrasive composites with lignin–SiO2 fillers have better thermo-mechanical properties than systems with silica alone. Thus, fillers based on lignin might provide new, promising properties for the abrasive industry, combining the good properties of lignin as a plasticizer and of silica as a filler improving mechanical properties.
137158784
Synthesis, characterization and reinforcing properties of novel, reactive clay/poly(glycidyl methacrylate) nanocomposites
Abstract Clay/polymer nanocomposites, of the type montmorillonite/poly(glycidyl methacrylate) [MMT/PGMA], were synthesized via atom transfer radical polymerization (ATRP). An ATRP initiator, consisting of quaternary ammonium salt bearing a 2-bromo-2-methyl propionate moiety was intercalated into the interlayer spacings of the layered silicate. The ammonium salt-modified montmorillonite (MMT–Br) served as macroinitiator for the in situ ATRP of glycidyl methacrylate resulting in highly exfoliated MMT/PGMA nanocomposites, as judged by XRD measurements. However, TEM shows the existence of intercalated clay regions, but at a very low extent. TGA and XPS analyses indicate that the nanocomposites have PGMA-rich bulk and surface. Indeed, the mass loading of PGMA reached 61 wt.% whilst XPS spectra, particularly the high resolution C1s region, resemble those of pure PGMA. The MMT/PGMA nanocomposites were found to be soluble in chloroform with a transparent solution, fully compatible with epoxy resin without any sign of phase separation. The primary MMT/PGMA nanocomposites were mixed with DGEBA and DETA in chloroform in order to prepare moulded, ternary MMT/PGMA–epoxy–DETA nanocomposites by solvent evaporation. The dried ternary systems exhibited superior viscoelastic properties (storage modulus and tan  δ ) compared to the neat crosslinked epoxy–DETA adhesive prepared in the absence of any clay nanocomposite.
28841948
Poly(acrylic acid) grafted montmorillonite as novel fillers for dental adhesives: synthesis, characterization and properties of the adhesive.
OBJECTIVE
This work investigates the graft polymerization of acrylic acid onto nanoclay platelets to be utilized as reinforcing fillers in an experimental dental adhesive. Physical and mechanical properties of the adhesive and its shear bond strength to dentin are studied. The effect of the modification on the stability of the nanoparticle dispersion in the dilute adhesive is also investigated.


MATERIALS AND METHODS
Poly(acrylic acid) (PAA) was grafted onto the pristine Na-MMT nanoclay (Cloisite(®) Na(+)) through the free radical polymerization of acylic acid in an aqueous media. The resulting PAA-g-nanoclay was characterized using FTIR, TGA and X-ray diffraction (XRD). The modified nanoclays were added to an experimental dental adhesive in different concentrations and the morphology of the nanoclay layers in the photocured adhesive matrix was studied using TEM and XRD. Shear bond strength of the adhesives containing different filler contents was tested on the human premolar teeth. The stability of nanoclay dispersion in the dilute adhesive was also studied using a separation analyzer. The results were then statistically analyzed and compared.


RESULTS
The results confirmed the grafting reaction and revealed a partially exfoliated structure for the PAA-g-nanoclay. Incorporation of 0.2 wt.% of the modified nanoclay into the experimental adhesive provided higher shear bond strength. The dispersion stability of the modified nanoparticles in the dilute adhesive was also enhanced more than 25 times.


SIGNIFICANCE
Incorporation of the modified particles as reinforcing fillers into the adhesive resulted in higher mechanical properties. The nanofiller containing bonding agent also showed higher shear bond strength due to the probable interaction of the carboxylic acid functional groups on the surface of the modified particles with hydroxyapatite of dentin.
98011359
Renewable benzoxazine monomers from “lignin‐like” naturally occurring phenolic derivatives
The benzoxazines of three naturally occurring phenylpropanoid phenols: ferulic, coumaric, and phloretic acids, and their esters are described. Benzoxazines with conjugated unsaturated chains exhibit unusual poor thermal stability and degrade partially at the polymerization temperature making necessary the use of a catalyst (BF3.Et2O) to low the polymerization temperature and prevent degradation. Polybenzoxazines are prepared thermally and characterized by DSC and TGA techniques. The resulting materials have superior Tgs when compared with those prepared from an unsubstituted monofuctional benzoxazine due to the additional crosslinking through the ester and carboxylic moieties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4894–4903
26932855
Brittleness and toughness of polymers and other materials
Materials are often characterized in terms of their toughness, though more than one definition of toughness exists. Likely the most widely recognized means of defining material toughness, denoted here as τ, is by the area under the stress strain curve from a tensile test. Another important feature describing the nature of materials is that property known as brittleness, which has for a long time been much less quantitatively understood. Using a quantitative definition of brittleness provided in 2006, we demonstrate the existence of a quantitative relationship between τ and brittleness B, valid for polymers with a very wide range of chemical structures and properties, for some polymer-based composites, and also for steel and aluminum. We provide an equation relating toughness to brittleness, while for polymers we mark the determining influence of chemical structures on the properties B and τ.
23065961
High-transparency polymer nanocomposites enabled by polymer-graft modification of particle fillers.
The role of polymeric ligands on the optical transparency of polymer-matrix composites is analyzed by evaluating the effect of surface modification on the scattering cross-section of particle fillers in uniform particle dispersions. For the particular case of poly(styrene-r-acrylonitrile)-grafted silica particles embedded in poly(methyl methacrylate), it is shown that the tethering of polymeric chains with appropriate optical properties (such as to match the effective refractive index of the brush particle to the embedding matrix) facilitates the reduction of the particle scattering cross-section by several orders of magnitude as compared to pristine particle analogues. The conditions for minimizing the scattering cross-section of particle fillers by polymer-graft modification are established on the basis of effective medium as well as core-shell Mie theory and validated against experimental data on uniform liquid and solid particle dispersions. Effective medium theory is demonstrated to provide robust estimates of the "optimum polymer-graft composition" to minimize the scattering cross-section of particle fillers even in the limit of large particle dimensions (comparable to the wavelength of light). The application of polymer-graft modification to the design of large (500 nm diameter) silica particle composites with reduced scattering cross-section is demonstrated.
138829358
Recycled HDPE reinforced with sol–gel silica modified wood sawdust
Abstract The goal of the work was improvement of mechanical and tribological properties of high density polyethylene (HDPE) while finding use for wood sawdust (wood flour). Two chemical modification methods have been used for wood sawdust treatment to improve compatibility between the HDPE matrix and wood sawdust. Traditional silane coupling was used as a first approach to modify the sawdust by 3-methacryloxypropyl-trimethoxysilane (3MPS) and thereby forming C O Si bonds. As a second method, we decided to combine sol–gel process with 3MPS treatment to form Si O Si and C O Si linkages. Silica nanoparticles are filling wood fiber cells and silica rods formation is seen; as a result, thermal expansivity decreases. As expected, the enthalpy of fusion and the degree of crystallinity go down with increasing filler concentration. Tensile modulus goes up as result of filler loading while the tensile strain at break goes down. As the result, brittleness B goes up somewhat, but overall the values of B are quite low. With one exception, residual depth in scratch resistance testing decreases as a consequence of introduction of the fillers. Addition of unmodified wood results in increasing dynamic friction, chemical modification of wood particles results in lowering friction. Combination of focused ion beam milling with scanning electron microscopy shows clearly positive effects of modification on adhesion between the phases.
55730683
Influence of Processing Conditions on the Thermal Stability and Mechanical Properties of PP/Silica-Lignin Composites
Functional silica-lignin dual fillers were obtained via mechanical grinding of the components (Syloid 244 silica and kraft lignin). Of particular importance here is the fact that lignin is a natural polymer and particularly that it is a waste by-product of paper production, whose recycling is highly desirable. The product underwent comprehensive dispersive-morphological and thermal analysis. SiO2-lignin hybrid fillers were also used in polypropylene-based composites, extruded via corotating a twin screw machine with different screw speeds. The thermogravimetric data obtained for the extrudates confirmed that the application of the lignin into PP produces a significant char residue. Addition of silica to lignin via this new hybrid formulation has a positive effect on the thermal stability of PP/silica-lignin composites, which can be seen even when observing the temperature for the maximum rate of weight reduction. Tensile test results show that the addition of silica by means of dual filler incorporation improves the mechanical parameters in comparison with pure PP and PP/lignin composite.
39762406
Application of inverse gas chromatography in physicochemical characterization of phenolic resin adhesives.
One of the most important stages during production of abrasive tools is their hardening. The degree of hardening is very important and influence toughness of the final product. During hardening process the cross-linking of the phenolic resins, used as a binder, occurs. Nowadays, there is no standard, accurate and simple method for the estimation of the hardening degree of abrasive tools. The procedure of the determination of hardening degree of the binder (phenolic resins) by means of inverse gas chromatography (IGC) was presented in this paper. Results obtained by use of IGC derived method was verified by Soxhlet extraction and by FTIR method. Good agreement was found for results from IGC and Soxhlet extraction whereas those from FTIR were much lower. FTIR method supplies data concerning bulk properties not the surface as in case of IGC and Soxhlet methods. These results indicate that resins are more cross-linked on the surface than inside the material.
136893711
Influence of different fillers on phenolic resin abrasive composites. Comparison of inverse gas chromatographic and dynamic mechanical–thermal analysis characteristics
Abstract The resin resol with selected zeolites fillers and abrasive grain (fused alumina) in a form of cuboid were studied as model material of investigated composites. Inverse gas chromatography (IGC) was used to determine the degree of hardening of studied resol and resol in the filler–resol composites. Dynamic mechanical thermal analysis (DMTA) was used for assessment of the influence of different inorganic fillers on the thermo-mechanical properties of phenolic resin, applied as a binder in manufacturing of abrasive articles. The application of IGC method supported by DMTA analyses makes possible to assess filler/resin interactions and hardening of resin matrix. These results can be applied in industry of abrasive articles. Moreover, presented measurements are cost-effective – there is no need to produce trial product. It was evidenced that fillers reveal significant impact on the thermo-mechanical behaviour of model semi-product used for production of abrasive articles.
206706218
Estimation of polyurethane-carbon black interactions by means of inverse gas chromatography.
The properties of composites depend mainly on the interfacial interactions between filler and matrix that can be related to the adhesion between filler and polymer matrix. In this study the work of cohesion between the carbon black particles - Wcoh - and the thermodynamic work of adhesion - Wa - between four carbon blacks of different specific surface area and surface chemistry (nature and content of carbon-oxygen functional groups) and thermoplastic polyurethane were calculated by means of inverse gas chromatography (IGC) at infinite dilution. IGC derived data indicated that the work of adhesion increased by increasing the surface area of the carbon black, but the opposite trend was found in Wa/Wcoh and work of cohesion. According to the Wa/Wcoh values the filler particles should be well dispersed into the polyurethane matrix giving homogenous composites. The carbon black-thermoplastic polyurethane interactions determined by plate-plate rheology showed the same trend than that for the Wa/Wcoh values. However, the thermodynamic work of adhesion values derived from IGC were not in agreement with the carbon black-polyurethane interfacial interactions, likely due to the dominant effect of the carbon black in reducing the crystallinity and increasing the degree of phase separation of the thermoplastic polyurethane.
17569919
Nanopharmaceuticals (part 1): products on the market
In 2000, the National Institute of Health launched the National Nanotechnology Initiative to support, coordinate, and advance research and development of nanoscale projects. The impact of this new program on health-science related research and development became quickly visible. Broad governmental financial support advanced the start of new, and the deepening of already existing, interdisciplinary research. The anticipated merger of nanoscience with medicine quickly instigated the conceptualization of nanomedicine. The adoption of nanoscience terminology by pharmaceutical scientists resulted in the advent of nanopharmaceuticals. The term “nano” became tantamount to “cutting-edge” and was quickly embraced by the pharmaceutical science community. Colloidal drug delivery systems reemerged as nanodrug delivery systems; colloidal gold became a suspension of nano gold particles. In this review, we first review nanoscience related definitions applied to pharmaceuticals, we then discuss all 43 currently approved drug formulations which are publicized as nanopharmaceuticals, and finally we analyze clinical aspects of selected drug formulations.
136818107
Synthesis and functionalization of nanoengineered materials using click chemistry
Abstract The synthesis of nanoengineered materials with precise control over material composition, architecture and functionality is integral to advances in diverse fields, including biomedicine. Over the last 10 years, click chemistry has emerged as a prominent and versatile approach to engineer materials with specific properties. Herein, we highlight the application of click chemistry for the synthesis of nanoengineered materials, ranging from ultrathin films to delivery systems such as polymersomes, dendrimers and capsules. In addition, we discuss the use of click chemistry for functionalizing such materials, focusing on modifications aimed at biomedical applications.
97575404
Lignins for Phenol Replacement in Novolac-Type Phenolic Formulations, Part I: Lignophenolic Resins Synthesis and Characterization
Several lignin (L)-based novolac-type phenolic prepolymers with two phenol (P) substitution degrees have been synthesized using three L from different origin (kraft pine L, soda/anthraquinone (AQ) flax L, and sulfonated kraft softwood L). These lignophenolic (LPF) resins have been characterized by means of free P and formaldehyde (F) analysis, viscosity, chemical structure (FTIR), and thermal behavior (DSC). Temperature at which curing reaction begins (DSC), hardening time at several curing temperatures (rheology) and volumetric changes (PVT) have also been determined for the curing process with 10 wt % hexamethylenetetraamine (HMTA). All the results have been compared to those obtained for a commercial novolac. Depending on the L type employed a homogeneous material with lower curing onset temperature and gelation time than reference PF can be obtained even at high P substitution level (45 wt %). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
96999988
Tannin/furanic foams without blowing agents and formaldehyde
Abstract Prorobinetinidin/profisetinidin type tannins have been used to prepare self-blowing tannin/furfuryl alcohol foams that do not need either formaldehyde or volatile organic blowing agents to prepare rigid foams. The 98% renewable materials foams so produced were even more environment-friendly, they presented equal thermal insulation and fire resistance and presented better stress–strain characteristics than tannin/furanic foams containing formaldehyde and organic blowing agents. Comparison of curves describing the simultaneously-measured foams expansion, hardening, temperature and pressure variation as a function of time allowed to show the differences in process and foaming parameters engendered by the differences in formulation of the experimental and control foams and optimisation of the foaming and hardening parameters involved. Tomography of the foams and foam controls produced supported the different characteristics observed for these foams obtained by stress–strain curves in compression.
30618478
Physicochemical and electrokinetic properties of silica/lignin biocomposites.
A new method of synthesis of novel composites obtained from silica and Kraft lignin has been proposed. Silica used in the study was obtained by three methods (hydrolysis and condensation of tetraethoxysilane, precipitation in a nonpolar and polar medium with the use of sodium silicate). To extend the possible range of applications, the silica was preliminary modified with N-2-(aminoethyl)-3-aminopropyltrimethoxsysilane, and finally it was modified with Kraft lignin earlier oxidised with sodium periodate (lignin bonded to SiO2 by covalent interactions). The products physicochemical and electrokinetic properties were thoroughly analysed. The dispersive properties and surface morphology were evaluated on the basis of particle size distributions and SEM images. The stability of dispersion in inorganic-organic systems were characterised on the basis of the zeta potential, whose value also permitted concluding on the interactions between colloidal molecules dispersed in water solutions. The products were subjected to elemental analysis to get percentage contents of N, C, H, S elements and were also characterised by XPS and FT-IR spectroscopy. Results of the study are of practical importance in prospective applications of SiO2/lignin biocomposites.
136666166
A novel functional silica/lignin hybrid material as a potential bio‐based polypropylene filler
A functional silica/lignin hybrid filler was obtained using a process of mechanical grinding of precursors (Syloid®244 silica and kraft lignin). The product underwent comprehensive physicochemical and dispersive–morphological analysis. The silica/lignin hybrid has good homogeneity and a surface area of 164 m2/g. The effectiveness of combination was confirmed by Fourier transform infrared spectroscopy and elemental analysis. The high electrokinetic stability (over almost the whole of the analyzed pH range) and above all the thermal stability of the resulting material (mass loss equal to 12%) indicate its potential use as a polypropylene (PP) filler. Experiments showed that the incorporation of a small amount of silica/lignin hybrid filler into PP may substantially influence its elongation at break and notched impact strength. Especially at low concentrations of silica/lignin filler (below 5 wt%) an exceptional set of mechanical properties was obtained. The addition of larger amounts of the filler was found not to bring any further improvement. POLYM. COMPOS., 36:913–922, 2015. © 2014 Society of Plastics Engineers
138377091
Supermolecular structure and nucleation ability of polylactide-based composites with silica/lignin hybrid fillers
In this paper, amorphous silica Syloid 244 and kraft lignin were mechanically coupled. Four hybrid materials containing silica and lignin in ratios 1:1, 2:1, 5:1 and 20:1 were prepared. As reference samples for hybrid fillers pristine silica and lignin were used. Particle size determination and microscopic observations were applied to determine dispersive and morphological properties of hybrid fillers. Fourier transform infrared spectroscopy confirmed the effective preparation of silica/lignin hybrid materials. The parameters of porous structure of examined hybrid filler were determined using the multipoint Brunauer–Emmett–Teller method and Barrett–Joyner–Halenda algorithm. Composite samples of polylactide (PLA) containing 2.5 % (w/w) of hybrid filler were extruded. Optical microscopy, wide-angle X-ray scattering and differential scanning calorimetry were applied to specify the supermolecular structure of functional PLA/hybrid composites and analyze the crystallization parameters as well as the phase transformation in PLA matrix. Silica/lignin hybrid material was found to be a filler capable of an effective crystal nucleation. The nucleating ability of silica/lignin hybrid filler in PLA matrix is related to porous properties of filler and its composition.
97652367
Synthesis and characterization by FTIR spectroscopy of silica aerogels prepared using several Si(OR)4 and R′′Si(OR′)3 precursors
Abstract We report the synthesis and Fourier Transform Infrared spectroscopy characterization results dealing with the surface modification of silica aerogels obtained via a two-step sol–gel process where various silicon precursors and co-precursors were used. The hydrolysis and poly-condensation steps were followed by carbon dioxide supercritical drying ( T c  = 31.1 °C; P c  = 73.7 bar). The silicon precursors contain four identical hydrolysable alkoxy groups (methoxy or ethoxy), while in the co-precursors, one of the alkoxy groups is substituted by a non-hydrolysable alkyl group (methyl, ethyl, n -propyl, iso -butyl, n -octyl, vinyl or phenyl). Identically, surface-functionalized silica aerogels were obtained from various silicon precursor/co-precursor combinations and their chemical structures were compared. The infrared spectroscopy revealed the existence of chemically comparable solid networks with some differences due to the nature of the silicon precursors.
101084909
Functional lignin-SiO2 hybrids as potential fillers for phenolic binders
Abstract Functional lignin-SiO2 hybrid fillers were synthesized and characterized with a view to their potential application in binders for phenolic resins. The properties of these fillers and of composites obtained from them with phenolic resin were compared with those of systems with lignin or silica alone. The chemical structure of the materials was investigated by Fourier transform infrared spectroscopy. Surface properties of lignin-SiO2 fillers were tested using inverse gas chromatography (IGC). IGC was used for determination of surface energy and surface heterogeneity of the studied fillers. IGC made it possible to assess the adhesion between the tested fillers and phenolic resins. Interactions of functional fillers with phenolic resins were also evaluated by IGC. The results indicated that lignin-SiO2 interacted strongly with the phenolic resin, more strongly than pure lignin. This was proved by SEM observations: thanks to the stronger interactions of lignin-SiO2 hybrid with phenolic resins, a more homogeneous composite was obtained. Thermo-mechanical properties of lignin–silica and resin systems were investigated by DMTA. DMTA results showed that phenolic binders with lignin-SiO2 fillers have better thermo-mechanical properties than systems with lignin or silica alone: higher glass transition temperature and a smaller decrease in storage modulus. Lignin fillers can thus provide new, promising properties for a phenolic binder combining the good properties of lignin as a plasticizer and of silica as a filler improving mechanical properties.
14718403
Recent Advances in Characterization of Lignin Polymer by Solution-State Nuclear Magnetic Resonance (NMR) Methodology
The demand for efficient utilization of biomass induces a detailed analysis of the fundamental chemical structures of biomass, especially the complex structures of lignin polymers, which have long been recognized for their negative impact on biorefinery. Traditionally, it has been attempted to reveal the complicated and heterogeneous structure of lignin by a series of chemical analyses, such as thioacidolysis (TA), nitrobenzene oxidation (NBO), and derivatization followed by reductive cleavage (DFRC). Recent advances in nuclear magnetic resonance (NMR) technology undoubtedly have made solution-state NMR become the most widely used technique in structural characterization of lignin due to its versatility in illustrating structural features and structural transformations of lignin polymers. As one of the most promising diagnostic tools, NMR provides unambiguous evidence for specific structures as well as quantitative structural information. The recent advances in two-dimensional solution-state NMR techniques for structural analysis of lignin in isolated and whole cell wall states (in situ), as well as their applications are reviewed.
7388346
Modification of Chitin with Kraft Lignin and Development of New Biosorbents for Removal of Cadmium(II) and Nickel(II) Ions
Novel, functional materials based on chitin of marine origin and lignin were prepared. The synthesized materials were subjected to physicochemical, dispersive-morphological and electrokinetic analysis. The results confirm the effectiveness of the proposed method of synthesis of functional chitin/lignin materials. Mechanism of chitin modification by lignin is based on formation of hydrogen bonds between chitin and lignin. Additionally, the chitin/lignin materials were studied from the perspective of waste water treatment. The synthetic method presented in this work shows an attractive and facile route for producing low-cost chitin/lignin biosorbents with high efficiency of nickel and cadmium adsorption (88.0% and 98.4%, respectively). The discovery of this facile method of synthesis of functional chitin/lignin materials will also have a significant impact on the problematic issue of the utilization of chitinous waste from the seafood industry, as well as lignin by-products from the pulp and paper industry.
95851422
Silica synthesis by the sol-gel method and its use in the preparation of multifunctional biocomposites
AbstractThis study focuses on the optimization process of silica synthesis using the sol-gel method while applying a statistical design of experiments which was based on a multilevel mathematical model. The product obtained in the process of optimized synthesis, characterized by the best dispersive and morphological parameters, was used for the preparation of organic/inorganic composites. The organic precursor was Kraft lignin, a high-molecular natural polymer. Synthesis of silica/lignin biocomposites was carried out by three proposed methods. The physicochemical properties and dispersive-morphological properties of each product were determined using the following available methods: Scanning Electron Microscopy — SEM, Non-Invasive Back-Scattering — NIBS, Fourier Transform Infrared Spectroscopy — FT-IR, Thermogravimetric analysis — TG and others. The electrokinetic and thermal properties of the biocomposites sufficed to be applied for example, as a cheap and biodegradable polymer filler. Further areas of application of these composites were sought, especially in electrochemistry as the advanced electrode materials.

35343290
Thermal conversion of alkaline lignin and its structured derivatives to porous carbonized materials.
Alkaline lignin was thermally converted to microporous carbon in ca. 50% yield by heating up from room temperature to 900°C without activation process under flowing of an argon gas. The carbonized material prepared by heating up conditions of 1°C min(-1) showed 530 m(2)/g of the Brunauer-Emmett-Teller (BET) specific surface area, which increased to 740 m(2)/g after washing with water. Furthermore, alkaline lignin derivatives were structured as micron scale particles by micelle formation and polymer gelation techniques. Carbonization of the structured lignins could afford high porous materials having BET surface areas above 1000 m(2)/g without surface activation processes.
102036841
PYROLYSIS OF LIGNIN - A POTENTIAL METHOD FOR OBTAINING CHEMICALS AND/OR FUELS
The paper shows some results on thermal degradation of aspen lignin, lignosulfonate and cellolignin, obtained from TG-FTIR/MSD analysis and from pyrolysis, followed by GC-MSD analysis of the liquid products. The thermal behaviour (temperature range and decomposition stages) depends on the lignin type. Degradation of aspen lignin starts above 200 °C, with the formation of acetic acid, methanol and methylacetate, at a maximum rate around 340 °C, and of phenol derivatives, at 250-450 °C. Ammonia and sulfur dioxide are formed around 250 °C from lignosulfonate, followed by derivatives of the structural compounds in lignin. Some nitrogenand sulfur-containing compounds were found in the light fraction of pyrolysis oils from the lignosulfonate. Cellolignin, a solid fraction resulting from the vegetable materials during furfural manufacturing, decomposes at a fast rate within a narrow temperature range, the formation of particular compounds being difficult to distinguish. However, furfural and its derivatives were found in degradation products of cellolignin, but not in the other lignins studied.
102077372
THERMAL DEGRADATION OF LIGNIN - A REVIEW
INTRODUCTION Lignin, a valuable resource for chemicals and energy, is a main component of wood, together with cellulose and hemicellulose. It is the second large source of organic raw material, constituting about 4-35 wt% of most biomass, 16-25 wt% of hardwoods and 23-35 wt% of softwoods. As the most abundant natural aromatic polymer, lignin has a highly branched three-dimensional phenolic structure including three main phenylpropane units, namely p-coumaril, coniferyl and sinapyl (Fig. 1). Softwood lignin contains relatively fewer sinapyl units and consists mainly of guaiacyl structures, while hardwood lignin contains guaiacylsyringyl structures. As a by-product of the paper industry, lignin is most often used by paper mills as a fuel for the recovery of its energy content. However, due to the very large generated quantities, lignin is increasingly considered as a potential source of chemicals, and studies on its thermal degradation receive much interest. “Pyrolytic lignin”, the organic phase obtained from the pyrolysis of wood or of other biomass resources, consists of a brown tar containing high molecular weight compounds derived from lignin, while the water-soluble fraction, accounting for 60-70 wt% of the whole oil, contains lower molecular weight substances.
96160969
Thermal degradation of various lignins by TG-MS/FTIR and Py-GC-MS
Abstract Thermal degradation was comparatively studied by TG-MS/FTIR and Py-GC-MS for four lignins of different raw materials and manufacturing processes. Acid hydrolysis by the Klason method was applied to wheat straw and oak, organosolv process based on acetic acid/phosphinic acid cooking to white birch and kraft cooking to Scandinavian mixed softwood, followed by the Lignoboost® process to recover lignin from the black liquor. The temperature domains of degradation were determined and indications on the main compounds produced during each stage were obtained. The composition of pyrolysis oils was determined. Similarities and differences in thermal behaviour and composition of degradation products among studied lignins were observed and discussed. Klason wheat straw and Lignoboost® softwood lignins showed a similar thermal behaviour but different composition of pyrolysis oils while the lignin obtained by acid hydrolysis from oak (Klason quercus) and Organosolv birch had similar composition of pyrolysis oils.
138420791
Dynamic mechanical thermal analysis (DMTA) of cellulose nanofibril/nanoclay/pMDI nanocomposites
Abstract Cellulose nanofibrils and montmorillonite nanoclay were used to reinforce polymethylene diphenyl diisocyanate (pMDI) resin at loading levels ranging from 1 to 5%. Laminate sandwich samples were prepared using nano-reinforced resin and wood strands. The laminate samples were analyzed for viscoelastic properties using dynamic mechanical thermal analysis (DMTA). Results obtained in this study showed that storage modulus, final cure temperature, and storage modulus at final cure of the pMDI resin were affected by nanoparticle reinforcement. The highest storage modulus was obtained for the 1% cellulose nanofibril reinforced pMDI-wood laminate sample. It was found that the neat pMDI resin had a slightly higher (max %3.82) final cure temperature compared with the pMDI resin reinforced with cellulose nanofibril or nanoclay at different loading levels.
135702844
Glass transitions of hygrothermal aged pultruded glass fibre reinforced polymer rebar by dynamic mechanical thermal analysis
Abstract The changes that can occur in glass fibre reinforced polymer (GFRP) composites with ageing can affect its application, performance and lifetime. Hygrothermal ageing (i.e. accelerated ageing by moisture absorption and temperature change) is a very useful technique to evaluate durability as well as development of GFRP composites in a reasonable timeframe. Dynamic mechanical thermal analysis (DMTA) is essentially able to detect all changes in the state of molecular motion in polymer composites as temperature is scanned. In this work, pultruded GFRP rebars were accelerated aged in an alkaline aqueous environment at 60 °C for 1, 2, 3, 4 and 6 months to evaluate the changes in glass transition of viscoelastic GFRP rebars by DMTA. Five different glass transitions in an average temperate range from 110 to 165 °C were observed at storage modulus, loss modulus and damping factor traces of DMTA. It was also found that glass transition temperature ( T g ) of the aged samples changed up to maximum 6 °C compared with that of controlled sample. This change in T g with ageing time was believed to be due to moisture absorption by rebars.
135908445
Synthesis, characterization, thermal properties and flame retardance of novel phenolic resin/silica nanocomposites
Novel phenolic/silica hybrid ceramers were synthesized by the sol-gel process. FTIRand 29 Si NMRwere used to characterize the structure of the hybrids. The results revealed that Q 4 ,Q 3 andT 3 are the major microstructures. That is, network structures were formed. SEM, TEM and Si mapping revealed that the hybrids were nanocomposites. The thermal properties were investigated by thermogravimetric analysis (TGA). The char yields of the hybrids increased with TEOS content. Td5 (the degradation temperature at 5% weight loss) of the hybrid that contained 20 wt.% TEOS was 290 � C. The Td5 of the hybrid rose to 312 � C as the TEOS content was increased to 80 wt.%. TEOS inorganic components enhance the thermal stability of the hybrids. The limiting oxygen index (L.O.I.) and the UL-94 test revealed that the hybrid ceramer possesses excellent flame retardance. # 2003 Elsevier Ltd. All rights reserved.
4497511
Physico-chemical characterization of lignins from different sources for use in phenol-formaldehyde resin synthesis.
During the last decades lignin has been investigated as a promising natural alternative to petrochemicals in phenol-formaldehyde (PF) resin production, due to their structural similarity. Physico-chemical characterization of three types of lignin, namely kraft pine lignin (L1), soda-anthraquinone flax lignin (L2), and ethanol-water wild tamarind lignin (L3) has been evaluated to determine which one is the most suitable chemical structure for above purpose. Characterization has been performed using Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectrometry ((1)H NMR) to analyse the chemical structure, gel permeation chromatography (GPC) for determining molecular weight (MW) and molecular weight distribution (MWD), differential scanning calorimetry (DSC) to measure the glass transition temperature and thermogravimetric analysis (TGA) to follow the thermal degradation. Both structural and thermal characteristics suggest that kraft pine lignin (L1) would be a better phenol (P) substitute in the synthesis of lignin-phenol-formaldehyde (LPF) resins, as it presents higher amounts of activated free ring positions, higher MW and higher thermal decomposition temperature.
97967524
Functionalized green tea tannins as phenolic prepolymers for bio-based epoxy resins
Abstract Phenolic extract from the green tea leaves was used for the production of thermoset epoxy resins. The commercial green tea extract (GTE) was functionalized by the reaction with epichlorohydrin in the presence of phase transfer catalyst. The glycidyl ether derivative of the green tea extract (GEGTE) obtained with a good yield was cured in epoxy polymer with isophorone diamine (IPD) and the resulting network was compared to catechin-IPD and diglycidyl ether of bisphenol A (DGEBA-IPD) systems. The thermal and mechanical analyses of this bio-based epoxy polymer showed its high reactivity associated with a high crosslinking density ( T g : 140–190 °C), a high thermal resistance and interesting mechanical properties.
93164946
Thermokinetic behavior of powdered phenol-formaldehyde (PPF) resins
Abstract This study was conducted to investigate thermokinetic behavior of powdered phenol-formaldehyde (PPF) resins used for the production of wood-based panel products. Both fusion diameter and stroke cure time of the PPF resins were measured to characterize flow properties and reactivity of PPF resins. In addition, differential scanning calorimetry (DSC) was also used to obtain apparent glass transition temperature ( T g ) and activation energy ( E a ) of the PPF resins. The results showed that the stroke cure time of PPF resins was positively related with fusion diameter of the PPF resins. The T g of PPF resins depended on the heating rate with a linear relationship established between heating rate and the T g . The E a of PPF resins depended on types of PPF resin and spray-drying temperatures.
137632369
Relaxation behaviour of the amorphous components of wood
The viscoelastic properties of mod were investigated using dynamic mechanical thermal analysis and differential scanning calorimetry. Under a limited set of conditions, two separate glass transitions (Tg) could be identified with both techniques. These two transitions were identified as arising from the amorphous lignin and hernicellulose matrix in the wood cell wall. Moisture dramatically affected the temperature at which the two dispersions occurred and, consequently, the ability to resolve their independent responses. The relationship betweenTg and moisture for both components could be modelled with the Kwei equation, which accounts for the presence of secondary interactions. Annealing and specific interactions of a series of organic diluents were wed in an attempt to enhance the resolution of the two components values ofTg. Time-temperature superposition was shown to be applicable to wood plasticized with ethyl formamide, following Williams-Landel-Ferry behaviour over the temperature rangeTg toTg + 85° C. These observations allow certain conclusions to be drawn concerning the applicability of existing models of the wood cell wall's supermolecular morphology. Most notably, models of thein situ morphology of the three wood components can be limited to those which consider the amorphous matrix of lignin and hemicellulose to be immiscible.
136759102
Kinetic analysis of phenol–formaldehyde bonded wood joints with dynamical mechanical analysis
Abstract Cure development of phenol–formaldehyde (PF) resins has been extensively modeled based on chemical advancement. However, it is in situ mechanical development of wood–adhesive systems that is most relevant with process optimization such as hot-pressing of wood-based panels. The objective of this research is to examine the feasibility of applying common model-fitting kinetic analyses to describe cure development based on storage modulus development recorded with dynamic mechanical analysis (DMA). Dynamic three-point bending tests were conducted on a sandwich specimens composed of two wood adherends bonded with an adhesive layer. Two commercial PF resins of different molecular weights distributions (labeled as PF-high and PF-low, respectively) were used as adhesives. In addition, PF-high bonded wood joints were also wrapped by aluminum foil to investigate the effect of moisture loss. The specimen curing process was monitored using various isothermal and linear heating regimes. The results showed that the PF-low joints cured more slowly than the PF-high joints. The foil-wrapped PF-high joints displayed slower curing process than the unwrapped joints and rendered two peaks in the tan δ curves. These peaks were attributed to gelation and vitrification, respectively. Overall, model-fitting kinetic analyses were effective to describe the mechanical development of wood–adhesive systems.
137412323
Silica fiber–polybenzoxazine–syntactic foams; Processing and properties
Polybenzoxazine filled with chopped silica fibers and their syntactic foams of varying composition and densities were processed. The composition and density variations were achieved by regulating the relative concentrations of silica fiber and glass microballoons (MB). The variation of tensile, compressive, and flexural properties with change in composition was investigated. For the silica-fiber filled materials, the property attained a maximum at about 40% volume content of fiber, and thereafter, the properties showed a diminishing trend. The incorporation of microspheres significantly lowered the strength of silica filled materials. However, the decrease in the specific flexural strength was less pronounced and the strength was unaffected beyond a certain microsphere content. During processing and mechanical testing, a large quantity of fibers was fractured, which reduced the strength of silica filled systems. The diminution in material strength on embedding microspheres is attributed to the presence of stress concentrating loci as evidenced from SEM analysis. The various factors leading to the property variation with composition are discussed with microscopic analyses, like clustering of fibers, crack propagation, fiber pull out, and debonding of fibers from resin phase. Dynamic mechanical analysis revealed an improved damping property for the filled materials in contrast to the unfilled polymer. The Tg (deduced from tan δ maximum from DMTA) decreased in silica fiber containing materials and on incorporating the MB, the values reverted back to that of the neat polymer. Both silica and MB conferred better thermal and thermooxidative stabilities to the polybenzoxazine. However, the degradation mechanism is nonoxidative in nature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
137098416
Master curve and time-temperature-transformation cure diagram of lignin-phenolic and phenolic resol resins
The aim of this work is to generate both a master curve of resol resins based on the time–temperature superposition principle and their TTT cure diagrams. The samples used for this purpose were lignin–phenolic and phenol–formaldehyde resol resins. A TMA technique was employed to study the gelation of resol resins. In addition, a DSC technique was employed to determine the kinetic parameters through the Ozawa method, which allowed us to obtain isoconversional curves from the data fit to the Arrhenius expression. Establishing the relationship between the glass-transition temperature and curing degree allowed the determination of the vitrification lines of the resol resins. Thus, using the experimental data obtained by TMA and DSC, we generated a TTT cure diagram for each of resins studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3362–3369, 2007
96989399
Catalytic activity of graphite-based nanofillers on cure reaction of epoxy resins
Abstract The strong influence of graphite oxide (GO) nanofiller on the glass transition temperature ( T g ) of epoxy resins, generally attributed to restricted molecular mobility of the epoxy matrix by the nanofiller or to the crosslinking of GO layers via the epoxy chains, is investigated. The study confirms that large increases of the glass transition temperature of the nanocomposite can be observed in presence of GO. However, similar T g increases are observed, when the filler is a high-surface-area graphite (HSAG), lacking oxidized groups. Moreover, these T g differences tend to disappear as a consequence of aging or thermal annealing. These results suggest that the observed T g increases are mainly due to a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine), rather than to reaction of the epoxide groups with functional groups of GO. This hypothesis is supported by investigating the catalytic activity of graphite-based materials on reactions between analogous monofunctional epoxide and amine compounds.
92826637
X-ray photoelectron spectroscopy of reduced graphene oxide prepared by a novel green method
Abstract This work is focused on the surface characterization of reduced graphene oxide (rGO) obtained through reduction of graphite oxide. The reduction was performed using a green method (based on UV irradiation under N2) with low environmental impact, free of additional functionalization reagents, simple and low-cost. X-ray photoelectron spectroscopy (XPS) was applied for chemical characterization of surface C species showing a significant reduction of oxygen-containing functional groups from the surface of rGO.