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A recent increase in the use of biofibers as low-cost and renewable reinforcement for the polymer biocomposites has been seen globally. Biofibers are classified into: lignocellulosic fibers (i.e., cellulose, wood and natural fibers), nanocellulose (i.e., cellulose nanocrystals and cellulose nanofibrils), and bacterial cellulose, while polymer matrix materials can be petroleum based or bio-based. Green biocomposites can be produced using both biobased fibers and polymers. Incompatibility between the hydrophilic biofibers and hydrophobic polymer matrix can cause performance failure of resulting biocomposites. Diverse efforts have focused on the modification of biofibers in order to improve the performances of biocomposites. "Grafting" copolymerization strategy can render the advantages of biofiber and impart polymer properties onto it and the performance of biocomposites can be tuned through changing grafting parameters. This review presents a short overview of various "grafting" methods which can be directly or potentially employed to enhance the interaction between biofibers and a polymer matrix for biocomposites. Major grafting techniques, including ring opening polymerization, grafting via coupling agent and free radical induced grafting, have been discussed. Improved properties such as mechanical, thermal, and water resistance have provided grafted biocomposites with new opportunities for applications in specific industries. [ABSTRACT FROM AUTHOR]

ABSTRACT Lignin-based thermal responsive dual shape memory copolymeric elastomers were prepared with a highly branched prepolymer (HBP, A2B3 type) via a simple one-pot bulk polycondensation reaction. The effect of fractionated lignin type (with good miscibility in the HBP) on copolymer properties was investigated. The thermal and mechanical properties of the copolymers were characterized by DMA, DSC, and TGA. Tensile properties were dominated by HBP <45% lignin content while lignin dominated >45% content. The copolymers glass transition temperature ( Tg) increased with lignin content and lignin type did not play a significant role. Thermally stimulated dual shape memory effects (SME) of the copolymers were quantified by cyclic thermomechanical tests. All copolymers had shape fixity rate >95% and >90% shape recovery for all compositions. The copolymer shape memory transition temperature ( Ttrans) increased with lignin content and Ttrans was 20°C higher than Tg. Lignin, a renewable resource, can be used as a netpoint segment in polymer systems with SME behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41389. [ABSTRACT FROM AUTHOR]

Three industrial lignins (Indulin AT Kraft softwood, Protobind 1000, and corn stover) were fractionated in methanol to obtain soluble and insoluble fractions. The original lignin and obtained lignin fractions were characterized chemically by a combination of FTIR spectroscopy, pyrolysis-gas chromatography–mass spectrum (py-GC–MS), and derivatization followed by reductive cleavage (DFRC). The methanol soluble lignin fractions contained fewer condensed structures than the original lignin and methanol insoluble fractions. The thermal (e.g. glass transition temperature ( T g ) and thermal stability) and rheological properties of the lignins were characterized by a combination of DSC, TMA, TGA and parallel plate rheology. TMA and modulated temperature DSC (MTDSC) proved to be sensitive techniques in determining T g . The methanol soluble lignin fractions had the lowest T g values relative to the original lignin and methanol insoluble fractions. The original lignin and methanol insoluble fractions had a higher thermal degradation temperature relative to the methanol soluble lignin. Solvent partitioning offers a practical approach to fractionate lignin into low M w and T g fractions which show promise as starting materials for making lignin-copolymers. [ABSTRACT FROM AUTHOR]

ABSTRACT Lignin based thermal-responsive elastomers were produced by a melt polycondensation reaction with a long alkyl chain hyperbranched poly(ester-amine-amide) (B3-A2-CB31). The effect of lignin content on elastomers properties was investigated. The thermal and mechanical properties of the copolymers were characterized by DMA, DSC, and TGA. The morphology of the copolymer was examined by SEM. Tensile properties were dominated by HBP <25% lignin content while lignin dominated >25% content. The copolymers glass transition temperature ( Tg) increased with lignin content. The elastomer with 30% lignin content demonstrated optimal mechanical properties (tensile strength 5.3 MPa, Young's modulus 8.9 MPa, strain at break 301%, and toughness 1.03 GPa). Thermally stimulated dual shape memory effects (SME) of the copolymers were quantified by cyclic thermomechanical tests. The transition temperature ( Ttrans) of the polymer was able to be controlled (room to body temperature) by varying the amount of lignin added which broadens the range to medical applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41103. [ABSTRACT FROM AUTHOR]

Abstract: The preparation of hyperbranched polymers from a unique combination of commercially available A2, B3 and CB1 3-type monomers is presented. Direct melt condensation of aliphatic dicarboxylic acid (A2) to compounds having trihydroxy groups ((B3), triethanolamine) and trihydroxy-monoamino groups ((CB1 3), tris(hydroxymethyl)aminomethane) led to a series of hyperbranched polyesters with amine cores and amide linkages. Because of the monomers availability and simplicity of the synthetic process, hyperbranched poly(ester-amine-amide) (HBPEAA) materials can be readily scaled up. This approach was used to synthesize series of prepolymers with varying degree of branching (DB) and distance between branching points. Taking the advantage of reactivity differences of COOH with the NH2 and OH groups, the hyperbranched polymer with different arrangement of amide linkage along the network was synthesized. The influence of reaction conditions such as monomer compositions, temperature and mode of mixing on the polymerization was examined. The DB of the HBPEAA (0.46–0.63) was dependant on the synthetic route. The HBPEAA exhibited moderate molecular weights as determined by NMR and ESI-MS. Thermogravimetric analysis revealed that the prepolymers exhibit reasonable thermal stability. The synthesized prepolymer was successfully utilized to copolymerize with 40% lignin to form toughened elastomeric materials with tensile strength of 12 MPa, Young''s modulus of 33 MPa and 149% elongation. [Copyright &y& Elsevier]

Abstract: Combined characteristics of hydrogen bonded/cross-linked polymer networks based on lignin motifs have been developed. This new type of polymeric material was prepared from an industrial lignin and a highly branched poly(ester-amine) (HBPEA) obtained by melt polycondensation of 1,1,1-triethanolamine (TEA) and adipic acid (AA). The lignin-HBPEA polymers were shown to be insoluble in common organic solvents and were characterized by FTIR and NMR spectroscopies. Thermo-mechanical measurements showed that melt mixing HBPEA with 40% lignin results in a flexible and tough material (T g; 7.7 °C and E′ 3.5 GPa). The hydrogen bonding recognition was based on various hydroxyl groups in lignin and aliphatic ester groups from HBPEA. The extent of interactions could be controlled by varying the amount of lignin added. These networks were thermally reversible and have highly tunable mechanical properties that were controlled by the extent of interactions. High level of mechanical properties could be achieved through the addition of lignin-poly(ester-amine) covalent cross-links. This study shows that the poly(ester-amine) structure plays an important role in the thermo-mechanical properties. By varying the spacer length between lignin and tertiary amine unit, materials with various thermo-mechanical properties were also obtained from the same parent polymer backbone. [ABSTRACT FROM AUTHOR]

More than 23 million tonnes of lignin are produced annually in the US from wood pulping and 98% of this lignin is burnt. Therefore, creating products from lignin, such as plastics, offers an approach for obtaining sustainable materials in a circular economy. Lignin-based copolymers were synthesized using a single pot, solvent free, melt condensation reaction. The synthesis occurred in two stages. In the first stage, a biobased prepolymer consisting of butanediol (BD, 0.8–1 molar content) and a diacid (succinic (SA), adipic (AA) and suberic acids (SuA), with varying amounts of diaminobutane (DAB, 0–0.2 molar content) was heated under vacuum and monitored by Fourier transform infra-red (FTIR) spectroscopy and electrospray ionization-mass spectrometry (ESI-MS). In the second stage, prepolymer was mixed with a softwood kraft lignin (0–50 wt.%) and further reacted under vacuum at elevated temperature. Progression of the polymerization reaction was monitored using FTIR spectroscopy. The lignin-copolyester/amide properties were characterized using tensile testing, X-ray diffraction (XRD), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. Lignin co-polymer tensile (strength 0.1–2.1 MPa and modulus 2 to 338 MPa) properties were found to be influenced by the diacid chain length, lignin, and DAB contents. The lignin-copolymers were shown to be semi-crystalline polymer and have thermoplastic behavior. The SA based copolyesters/amides were relatively stiff and brittle materials while the AA based copolyesters/amides were flexible and the SuA based copolyesters/amides fell in-between. Additionally, > 30 wt.% lignin the lignin- copolyesters/amides did not exhibit melt behavior. Lignin-co-polyester/amides can be generated using green synthesis methods from biobased building blocks. The lignin- copolyesters/amides properties could be tuned based on the lignin content, DAB content and diacid chain length. This approach shows that undervalued lignin can be used in as a macromonomer in producing thermoplastic materials. [ABSTRACT FROM AUTHOR]

A strategy of enhancing the reactivity of lignin molecule towards thermally initiated free radical polymerization was examined. Technical lignin samples were reacted with selected esterification agents (butyric and crotonic anhydrides) leading to extensive conversion of the available hydroxyl groups. The esterified lignins were then subjected to thermal processing in the presence or absence of dicumyl peroxide (DCP). The rheological and viscoelasticity behavior during this process were examined by in-situ rheology and dynamic mechanical analysis (DMA). The functionality and glass transition temperature (T g ) of samples before and after modification were assessed for evaluating the validity of modification. After crotonylation, the lignin derivatives were susceptible to thermally initiated free radical polymerization, especially in the presence of DCP. Upon heating, the lignin crotonate showed a significant increase in storage modulus (E′) from around 200 °C to 260 °C. The T g of lignin crotonate increased by about 20 °C after thermal treatment in the presence of DCP. Fourier transform infrared spectroscopy (FTIR) analysis of samples that were collected from rheological test confirmed the reaction of C C took place. Vanillyl alcohol as a lignin model compound was subjected to the same modification procedure with lignin to uncover the mechanism by FTIR and nuclear magnetic resonance (NMR) analysis, indicating there are three potential reaction sites: C C, C O and CH 2 -, among which C C is likely to form a cross-linked network. The conclusions from this study may provide the foundations for a rational design of technical lignin-based polymeric materials, by providing the double bonds to anchor the lignin molecules in the resin or copolymers. [ABSTRACT FROM AUTHOR]

Copolymers containing as high levels of bio-derived components were obtained mainly from two industrial byproducts, glycerol and lignin. A series of hyper branched prepolymers (HyBP) were prepared from in the first step by melt condensation of glycerol (Gly, B 2 B 3 2 ) and adipic acid (AA, A 2 ) and the prepolymer structure was also modified by the addition of commercially available diisopropanolamine (DIPA, DB 4 2 ) and tris(hydroxymethyl) aminomethane (THAM, CB 3 1 ) units. The HyBP were reacted with lignin to form thermally-stimulated shape memory copolymeric elastomers in the second step in the same pot by melt polycondensation. The prepolymers were characterized chemically by FTIR, NMR, and ESI-MS. Thermal and rheological behaviors were analyzed by DSC, DMA, TGA and dynamic rheometry. The higher branching crosslinkers, DIPA and THAM, were shown to influence the chemical and thermal properties of the prepolymers. The hyperbranched biobased lignin-copolymers demonstrated good shape memory and elastic properties. The shape transition temperature ( T trans ) could be tuned by variations of Gly, DIPA and THAM proportions for applications under different temperature circumstances. This study demonstrates that renewable Gly and AA based prepolymers could be incorporated into lignin based copolymeric systems with high biobased contents acting as soft segment to perform shape memory effect behavior. [ABSTRACT FROM AUTHOR]

Efficient conversion of all components in lignocellulosic biomass is essential to realizing economic feasibility of biorefineries. However, lignin cannot be fermented using biochemical routes. Furthermore, high lignin and high ash residues from simultaneous saccharification and fermentation (SSF) is difficult to thermochemically process due to feed line plugging and bed agglomeration. In this study a corn stover SSF digester residue was thermally pretreated at 300 °C for 22.5 min and gasified in a fluidized bed gasifier to study the effect of thermal pretreatment on its processing behavior. Untreated, pelletized SSF residue was gasified at the same conditions to establish the baseline processing behavior. Results indicate the thermal pretreatment process removes a substantial portion of the polar and non-polar extractives, with a resultant increase in the concentration of lignin, cellulose, and ash. Feed line plugging was not observed, although bed agglomeration occurred at similar rates for both feedstocks, suggesting that overall ash content is the most important factor affecting bed agglomeration. Benzene, phenol, and polyaromatic hydrocarbons in the tar were present at higher concentrations in the treated material, with higher tar loading in the product gas. Total product gas generation is lower for the treated material, although overall gas composition does not change. [ABSTRACT FROM AUTHOR]

Torrefaction enhances physical properties of lignocellulosic biomass and improves its grindability. Energy densification, via fuel pellets production, is one of the most promising uses of torrefaction. Lignin contributes to self-bonding of wood particles during pelletization. In biomass thermal pretreatment, part of lignin (in the form of lignin liquid intermediates – LLI) migrates from the cell wall and middle lamella and deposits on the fibers’ surfaces and/or inner surface of the secondary cell wall. This material can play an important role on bonding particles during wood pelletization as well as production of wood composites. The objective of this paper was to investigate the influence of torrefaction conditions on amount, composition, molecular weight, and pattern of deposition of LLI on wood cells. Torrefaction of extracted ponderosa pine in the range of temperatures 225–350 °C was conducted in a tube furnace reactor and the torrefied wood was extracted with dichloromethane (DCM) to isolate the lignin-rich soluble material. A maximum yield of DCM-soluble material was observed in wood torrefied at approximately 300 °C for 30 min. ESI/MS revealed that the molecular weight of the removed material is less than 1200 g mol −1 and decreases as torrefaction temperature augments. Semiquantitative Py-GC/MS of the DCM-soluble material suggests that this lignin-rich material migrates and deposits on cells’ surfaces in amounts that depend on the torrefaction conditions. Py-GC/MS of the solid fraction after the DCM process showed a progressive reduction of products of the pyrolysis of lignin and levoglucosan as torrefaction temperature increased, revealing that lignin content in the solid decreased due in part to migration. SEM of torrefied particles helped to show the apparent formation of LLI during torrefaction. Results suggest that it is possible to control the thermal pretreatment conditions to increase or reduce the amount of lignin-rich material on fiber surfaces as required for downstream processes (e.g., fuel pellets or wood composites manufacture). [ABSTRACT FROM AUTHOR]

The formation of liquid intermediates and the distribution of products were studied under slow and fast pyrolysis conditions. Results indicate that monomers are formed from lignin oligomeric products during secondary reactions, rather than directly from the native lignin. Lignin from Douglas-fir (Pseudotsuga menziesii) wood was extracted using the milled wood enzyme lignin isolation method. Slow pyrolysis using a microscope with hot-stage captured the liquid formation (>150 °C), shrinking, swelling (foaming), and evaporation behavior of lignin intermediates. The activation energy (E a) for 5–80% conversions was 213 kJ mol−1, and the pre-exponential factor (log A) was 24.34. Fast pyrolysis tests in a wire mesh reactor were conducted (300–650 °C). The formation of the liquid intermediate was visualized with a fast speed camera (250 Hz), showing the existence of three well defined steps: formation of lignin liquid intermediates, foaming and liquid intermediate swelling, and evaporation and droplet shrinking. GC/MS and UV-Fluorescence of the mesh reactor condensate revealed lignin oligomer formation but no mono-phenols were seen. An increase in pyrolytic lignin yield was observed as temperature increased. The molar mass determined by ESI-MS was not affected by pyrolysis temperature. SEM of the char showed a smooth surface with holes, evidence of a liquid intermediate with foaming; bursting from these foams could be responsible for the removal of lignin oligomers. Py-GC/MS studies showed the highest yield of guaiacol compounds at 450–550 °C. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pyrolysis of beech wood particles (0.3 and 14mm). [•] The yield of pyrolytic lignin decreased as particle size increased. [•] Two different pyrolysis regimes were confirmed between 0.3 and 14mm. [•] Secondary reactions and mass transfer limitations lead to more char. [Copyright &y& Elsevier]

Inthis work we report on the preparation, characterization, andproperties of a thermally treated lignin-derived, phenolic-rich fraction(PRF) of wood pyrolysis bio-oil obtained by ethyl acetate extraction.The PRF was characterized for viscoelastic and rheological behaviorusing dynamic mechanical analysis (DMA) and cone and plate rheology.A unique thermoplastic behavior was evidenced. Heat-treated PRFs acquirehigh modulus but show low temperatures of thermal flow which can besystematically manipulated through the thermal pretreatment. Lossof volatiles, changes in molecular weight, and glass transition temperature(Tg) were investigated using thermogravimetricanalysis (TGA), mass spectrometry (MS), and differential scanningcalorimetry (DSC), respectively. Underlying mechanisms for the thermaland rheological behavior are discussed with regard to interactionsbetween pyrolytic lignin nanoparticles present in the system and therole of volatile materials on determining the properties of the materialresembling in several aspects to colloidal suspension systems. Lowthermal flow temperatures and reversible thermal effects can be attributedto association of pyrolytic lignin particles due to intermolecularinteractions that are easily ruptured at higher temperatures. Thethermoplastic behavior of PRF and its low Tgis of particular interest, as it gives opportunities for applicationof this fraction in several melt processing and adhesive technologies. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the effect of sulfuric acid (H2SO4) concentration, as an additive to enhance the production of anhydrosugars via pyrolysis of Douglas-fir, on the yield and composition of the lignin derived oligomers. Pyrolysis tests at 500°C were conducted in auger and fluidized bed reactors. For both reactors the yield of lignin derived oligomers decreased as H2SO4 was added. Several analytical techniques (UV-fluorescence, TGA, ESI-MS, FTIR, solid state 13C NMR and Pyrolysis-GC/MS) were used to characterize the lignin derived oligomers collected. Four peaks were observed in the UV-fluorescence spectra. The addition of H2SO4 reduces the yield of all the peaks. DTG curves also show the presence of several peaks. The addition of H2SO4 decreased the yield of all the peaks but its effect was more pronounced on peaks at 320 and 400°C. Electrospray ionization-mass spectrometry studies did not show any major change on the molecular weight of the lignin oligomers ionized products obtained as a function of H2SO4 concentration. Solid state NMR results indicate that the methoxyl groups decreased and the carbonyl increased gradually as sulfuric acid concentration increases. The Py-GC/MS confirmed the phenolic compounds with methoxyl substitutions were substantially reduced as the acid concentration increased. The experimental results obtained suggest the presence of H2SO4 enhances the polycondensation of methoxyl substituted aromatic rings. [Copyright &y& Elsevier]