Eucalyptus bark lignin substituted phenol formaldehyde adhesives: A study on optimization of reaction parameters and characterization

The major adhesive resin worldwide used in the manufacture of plywood is phenol formaldehyde resole (PF) resin. The raw material for this kind of adhesive is derived from petroleum oil. Because of rising prices of crude oil and the scarcity of petroleum products, their replacement by natural resource–based raw material has become a necessity. In the present work, the possibility of replacing phenol in PF resin with lignin was explored. The parameters for preparation of bark lignin substituted PF (LPF) adhesive, such as lignin concentration, formaldehyde to phenol molar ratio, catalyst concentration, reaction time, and reaction temperature, were optimized. It was found that up to 50 wt % of phenol can be substituted by lignin to give an LPF adhesive with better bonding strength compared to that of control PF resin. Prepared resins were characterized using IR, DSC, and TGA. IR spectra of LPF adhesive showed structural similarity with that of PF adhesives. Thermal stability of LPF adhesive was found to be lower compared to that of control PF (CPF) adhesive. DSC studies revealed a lower curing temperature for LPF resin than that for CPF resin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3514–3523, 2004     

Properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde resin

The aim of this research was to investigate the physical and mechanical properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde (LPF) resin. For this purpose, soda bagasse lignin was modified by 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid, and then, various contents of modified lignins (10, 15, and 20 wt%) were added as a substitute of phenol in phenol–formaldehyde (PF) resin synthesis. The properties of the synthesized resin were compared with those of a control PF resin. The changes in curing behavior of the resins prepared were analyzed by differential scanning calorimetry (DSC). The physical properties of the resins prepared, as well as the water absorption, thickness swelling, shear strength, and formaldehyde emission of the plywood panels bonded with these adhesives, were measured according to standard methods. DSC analysis indicated that in comparison with PF resins, curing of the LPF resin occurred at lower temperatures. The physical properties of the synthesized resins indicated that viscosity and solid content increased, while gel time and density decreased by addition of treated lignin to the PF resin. Although the panels containing resins with modified lignin yielded low formaldehyde emission, their dimensional stability was worse than those bonded with a commercial PF adhesive. The plywood prepared using IL-treated lignin PF resins has shear strength, which satisfy the requirements of the relevant standards specifications and significantly better than that of panels prepared with the control PF resin. The mechanical properties of the panels could be significantly enhanced with increased percentage of treated lignin content from 0 to 20 wt%.     

Development and characterization of a wood adhesive using bagasse lignin

Bagasse is spent fiber left after extraction of sugar. It is mainly used as a fuel to concentrate sugarcane juice. In the present work, the possibility of preparing wood adhesives from bagasse has been explored. The parameters for the preparation of a lignin phenol formaldehyde (LPF) adhesive, (lignin concentration, formaldehyde to phenol molar ratio, catalyst concentration, reaction time and reaction temperature) have been optimized. It was found that up to 50% of phenol can be substituted by bagasse lignin to give LPF wood adhesive having better bonding strength in comparison to a control phenol formaldehyde (CPF) wood adhesive. Prepared resins were characterized using IR, DSC and TGA. IR spectra of LPF resin showed structural similarity with CPF resin. Thermal stability of LPF resin was found to be lower as compared to CPF resin. DSC studies reveal a lower curing temperature for LPF adhesive in comparison to CPF adhesive. A shelf-life study reveals that LPF exhibits consistent behavior as compared to CPF in respect to adhesive strength.     

Use of organosolv lignin in phenol–formaldehyde resins for particleboard production: I. Organosolv lignin modified resins

This paper describes the work considering the potential for partially replacing phenol with organosolv lignin in phenol–formaldehyde resin used as an adhesive in the production of particleboard. Lignin-based resins were synthesised with organosolv lignin using various percentages of lignin replacement for phenol. The lignin was introduced to the resin in two different ways. The first method was the replacement of a certain percentage of phenol (5–40%) with lignin (as supplied) directly into resins. In the second method, lignin was modified by phenolation prior to resin manufacture. Different degrees of phenol substitution (20–30%) were investigated for the production of lignin-based resins. The physical properties of the formulated resins were measured and compared to commercial PF resin.     

Engineering Plastics from Lignin. IX. Phenolic Resin Synthesis and Characterization

The performance of phenol-formaldehyde (PF) resins, formulated with lignin derivatives previously synthesized as phenolic resin prepolymers, was evaluated by thermal analysis of the curing process, and by a hard maple shear block test. At 54 and 60% phenol replacement levels, respectively, kraft (KL) and steam explosion lignin (SEL)-based resoles exhibited cure behavior very similar to a standard PF resin. Acid hydrolysis lignin gelled prematurely, and was found to be incompatible with the normal synthesis procedure. Differential scanning calorimetry (DSC) was used to compare kinetic parameters for the curing process of neat and lignin derived phenolic resins. Activation energies and cure rates determined by DSC showed no difference between adhesives. High lignin contents had no inhibitory effect on resin cure. Shear strength properties were evaluated in a compression test, and results illustrate that both lignin-based resins have acceptable strength properties, both in a dry and accelerated aging test. Of the lignins tested, kraft lignin consistently demonstrated superior performance as a pre-polymer in phenolic adhesives. This was attributed to differences in the chemical structure of the two lignins, which had been found to vary in terms of their reactivity with formaldehyde and phenol. KL had been noted to be more amenable to derivatization with formaldehyde and phenol, hence its ability to crosslink with a phenol-formaldehyde fraction during resin synthesis was increased. Positive structural features in KL are a high phenolic guaiacyl (3-methoxy, 4-hydroxy phenyl) content, low carbon-to-carbon bonding between aromatic rings, high solubility in alkali, and a higher number average molecular weight than SEL.     

Lignin–phenol–formaldehyde resin adhesives prepared with biorefinery technical lignins

In this study, four biorefinery technical lignins were used to synthesize lignin–phenol–formaldehyde (LPF) resin adhesives with a proposed formulation that was designed based on accurate analysis of the active sites in lignin with ³¹P nuclear magnetic resonance (NMR). The properties of the LPF resin adhesives and the plywoods prepared with them were tested. The structural features and curing behavior of the LPF resin adhesives were thoroughly investigated by solution‐ and solid‐state ¹³C NMR. Results indicated that the proposed formulation exhibited favorable adaptability for all four of these technical lignins for synthesis of LPF resin adhesives. High‐performance plywood with low emissions of formaldehyde could be successfully prepared with the synthesized LPF resin adhesives. All the LPF resin adhesives exhibited similar structure and curing behavior with the commercial phenol–formaldehyde (CPF) resin adhesive. However, the LPF resin adhesives showed relatively higher curing temperatures as compared with the CPF resin adhesive. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42493.     

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.     

Properties of phenol‐formaldehyde resins prepared from phenol‐liquefied lignin

In this study, alkaline lignin (AL), dealkaline lignin (DAL), and lignin sulfonate (SL) were liquefied in phenol with sulfuric acid (H₂SO₄) or hydrochloric acid (HCl) as the catalyst. The phenol‐liquefied lignins were used as raw materials to prepare resol‐type phenol‐formaldehyde resins (PF) by reacting with formalin under alkaline conditions. The results show that phenol‐liquefied lignin‐based PF resins had shorter gel time at 135°C and had lower exothermic peak temperature during DSC heat‐scanning than that of normal PF resin. The thermo‐degradation of cured phenol‐liquefied lignin‐based PF resins was divided into four temperature regions, similar to the normal PF resin. When phenol‐liquefied lignin‐based PF resins were used for manufacturing plywood, most of them had the dry, warm water soaked, and repetitive boiling water soaked bonding strength fitting in the request of CNS 1349 standard for Type 1 plywood. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

麦草碱木素酚化改性及其制备LPF胶粘剂工艺研究

利用碱性条件下酚化改性的麦草碱木素代替部分苯酚制备了高木质素/苯酚比例和胶粘强度高的木质素酚醛树脂(LPF)胶粘剂.利用傅立叶红外光谱(FT-IR)和凝胶色谱(GPC)研究了麦草碱木素在碱性条件下酚化改性前后的结构变化.FT-IR分析表明,麦草碱木素发生了酚化反应,伴随着酯基的断裂和甲氧基的脱落;GPC结果显示,木质素平均分子量降低,分子量分布范围变宽.接着,研究了木质素/苯酚比例、氢氧化钠浓度、甲醛/木质素比例、酚化温度、酚化时间、缩聚温度、缩聚时间等反应工艺参数对LPF胶粘剂性能的影响,优化了麦草碱木素酚化改性制备LPF胶粘剂的反应工艺参数.最后,比较了反应工艺参数优化的LPF胶粘剂与传统PF胶粘剂的各项性能,结果显示,麦草碱木素酚化改性后代替70 % 的苯酚制备得到的LPF胶粘剂的胶粘强度与传统PF胶粘剂相近.     

Use of organosolv lignin in phenol-formaldehyde resins for particleboard production: II. Particleboard production and properties

The objective of this work was to demonstrate the utility of lignin-based resins designed for application as an adhesive in the production of particleboard. Bond qualities of lignin-phenol-formaldehyde resins, phenolated-lignin-formaldehyde resins and commercial phenol-formaldehyde (PF-com) resin were assessed by using an automatic bonding evaluation system, prior to production of particleboards. In order to evaluate the quality of lignin-based resins, particleboards were produced and physical and mechanical properties were investigated. These physical properties included internal bond, modules of rupture and modulus of elasticity. Thickness swell and water absorption properties of particleboards bonded with lignin-based resins were also determined. The lignin-based resins have been reported previously in Part I of this study. The results showed that particleboards bonded with phenolated-lignin formaldehyde resins (up to 30% lignin content) exhibited similar physical and mechanical properties when compared to particleboards bonded with PF-com. The work has indicated that phenolated-lignin formaldehyde resins (up to 30% substitution level) can be used successfully as a wood adhesive for constructing particleboard. The performance of these panels is comparable to those of boards made using PF-com resin.     

Engineering biomass into formaldehyde‐free phenolic resin for composite materials

The use of formaldehyde to prepare phenol‐formaldehyde (PF) resins is one of the primary challenges for the world‐wide PF industry with respect to both sustainability and human health. This study reports a novel one‐pot synthesis process for phenol‐5‐hydroxymethylfurfural (PHMF) resin as a formaldehyde‐free phenolic resin using phenol and glucose, and the curing of the phenolic resin with a green curing agent organosolv lignin (OL) or Kraft lignin (KL). Evidenced by ¹³C NMR, the curing mechanism involves alkylation reaction between the hydoxyalkyl groups of lignin and the ortho‐ and para‐carbon of PHMF phenolic hydroxyl group. The curing kinetics was studied using differential scanning calorimetry and the kinetic parameters were obtained. The OL/KL cured PHMF resins were tested in terms of thermal stability, and mechanical properties for their applications in fiberglass reinforced composite materials. The results obtained demonstrated that OL/KL can be promising curing agents for the PHMF resins. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1275–1283, 2015     

Properties of compression‐molded plates made from wood powders impregnated with liquefied wood‐based novolak‐type phenol‐formaldehyde resins

Novolak‐type phenol‐formaldehyde (PF) resins with solution form were prepared by reacting phenol‐liquefied Cryptomeria japonica (Japanese cedar) wood with formalin in the presence of methanol. Wood powders of Albizzia falcate (Malacca albizzia) impregnated with these resins were air dried followed by an oven‐dried at 60°C. DSC analysis showed the PF resin existing in wood powders could be melted, and could be cured if hexamine was mixed and heated at high temperature. Compression‐molded plates made with PF resin impregnated woods had a high degree of curing reaction. However, compression‐molded plates hot‐pressed at 180°C for 8 min or 200°C for 5 min had better internal bonding strength and dimensional stability than others. Premixing hexamine with PF resin and impregnating into wood powders simultaneously could enhance the reactivity of PF resin, but it was not useful for improving the properties of compression‐molded plates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Use of a methylolated softwood ammonium lignosulfonate as partial substitute of phenol in resol resins manufacture

The synthesis of lignin‐phenol‐formaldehyde (LPF) was studied to determine its optimum operating conditions. The lignin proposed as phenol substitute has been the softwood ammonium lignosulfonate. The resin synthesis was optimized by varying the methylolated lignosulfonate content, 18–52%; the sodium hydroxide to phenol‐modified lignosulfonate molar ratio, 0.3–0.94; and the formaldehyde to phenol‐modified lignosulfonate molar ratio, 1.1–3.5. The parameters employed in the characterization of LPF resins were free phenol, free formaldehyde, gel time, alkaline number, viscosity, pH, solid content, and chemical structure changes. The properties of LPF resin comply with the requirements for its utilization in plywood manufacture. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 643–650, 2004     

Renewably sourced phenolic resins from lignin bio‐oil

Traditional lignin pyrolysis generates a bio‐oil with a complex mixture of alkyl‐functionalized guaiacol and syringol monomers that have limited utility to completely replace phenol in resins. In this work, formate assisted fast pyrolysis (FAsP) of lignin yielded a bio‐oil consisting of alkylated phenol compounds, due to deoxyhydrogenation, that was used to synthesize phenol/formaldehyde resins. A solvent extraction method was developed to concentrate the phenolics in the extract to yield a phenol rich monomer mixture. Phenolic resins were synthesized using phenol (phenol resin), FAsP bio‐oil (oil resin), and an extract mimic (mimic resin) that was prepared to resemble the extract after further purification. All three phenolic sources could synthesize novolac resins with reactive sites remaining for subsequent resin curing. Differential scanning calorimetry and thermogravimetric analysis of the three resins revealed similar thermal and decomposition behavior of phenol and the mimic resins, while the oil resin was less stable. Resins were cured with hexamethylenetetramine and the mimic resin demonstrated improved curing energies compared to the oil resin. The adhesive strength of the mimic resin was found to be superior to that of the oil resins. These results confirmed that extracting a mixture of substituted aromatics from FAsP bio‐oil could synthesize resins with properties similar to those from phenol and improved over the parent bio‐oil. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44827.     

木质素酚醛树脂胶粘剂黏度的研究

木质素胶粘剂高黏度的特征阻碍了其工业化应用,该文考察了木质素酚醛树脂(LPF)胶粘剂的pH、质量分数、氯化钠与尿素的加入、贮存时间等因素对其黏度的影响,作为对比,同时测试了这些因素对酚醛树脂胶粘剂和麦草碱木素(WSSL)碱性溶液黏度的影响。结果表明,LPF胶粘剂的黏度随着尿素的加入降低,而随着其质量分数的增加、pH的降低、氯化钠的加入急剧升高,并分别在w(LPF)=30.0%、pH=10.2、w(NaCl)=8.3%处有一个转折点;LPF胶粘剂的黏度曲线与WSSL碱性溶液相似,而与酚醛树脂胶粘剂相差较大;要制得高含量的LPF胶粘剂,其pH应大于10.2,w(NaCl)<8.3%,并且w(尿素)=2%～3%。     

Replacing 100% of phenol in phenolic adhesive formulations with lignin

Lignin, produced as a byproduct of pulp and paper and bioethanol industries, is a polyphenolic compound that has excellent potential to be used as phenol replacement in phenolic adhesive formulation. In this study, the phenol portion of phenol formaldehyde (PF) resin has been replaced by an agricultural‐based lignin, which was produced as a byproduct of a cellulosic bioethanol process through dilute‐acid pretreatment and enzymatic hydrolysis from corn stover. The PF resol resin was formulated using isolated lignin under alkaline condition. Chemical, physical, and thermal properties of the isolated lignin, PF resin and adhesive were measured using advanced analytical techniques such as Fourier transformed infrared spectroscopy (FTIR), size exclusion chromatography (SEC), phosphorous nuclear magnetic resonance spectroscopy (³¹P NMR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The developed 100% lignin‐based adhesive and a commercially formulated phenol resorcinol formaldehyde (PRF, as reference) were used to prepare single‐lap‐joint samples for mechanical testing. The plywood samples were pressed under exactly the same conditions (time, temperature, and pressure) as what recommended for the commercial PRF formulation. According to two‐way ANOVA results, statistically there was no significant difference between the shear strengths of plywood samples made with 100% lignin‐based adhesive and those made with the commercial PRF resin. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45124.     

木质素酚醛树脂的固化动力学及机理研究

通过差示扫描量热法（Dsc）和红外光谱（IR）分别研究了木质素酚醛树脂（LPF）的固化动力学及机理。DSC分析表明,LPF的固化反应起始温度比酚醛树脂高,终止温度及活化能比酚醛树脂低,因此,LPF凝胶点比酚醛树脂高,贮存稳定性比酚醛树脂好,固化速度比酚醛树脂快;IR分析表明,LPF的固化机理与酚醛树脂相似,都是羟基之间及羟基与芳环上的氢之间的缩合反应。不同的是LPF固化后仍有部分醚键结构。     

木素基酚醛树脂胶粘剂的应用性能研究

采用热化学酚化技术活化木素得到木素酚化产物,以酚化产物代替苯酚制备低成本的木素酚化液基酚醛树脂(LPF)胶粘剂。采用红外光谱(FT-IR)对LPF和传统PF的结构进行了表征,通过对比试验分析了LPF的应用性能,并对LPF胶粘剂应用性能产生的机理作了一定的探讨。结果表明:酚化后的木素参与了LPF胶粘剂的合成,并具有新的不同取代基的苯环结构;LPF胶粘剂与传统酚醛树脂(PF)胶粘剂具有相似的应用性能,前者比后者具有更低的游离酚(醛)含量(游离酚<0.12%,游离醛<0.08%)、更快的干燥速率和更低的施胶量(固含量29%时施胶量为297g/m2);另外,LPF胶粘剂具有优异的胶合性能(达到了Ⅰ类胶合板的标准要求)和储存稳定性,完全满足高性能环保型胶粘剂的使用要求。     

The Present Status and Potential of Kraft Lignin-Phenol-Formaldehyde Wood Adhesives

Kraft lignin (KL), a phenolic polymer formed during the kraft pulping process, is presently burned as a low value fuel. For decades, researchers have attempted to use KL as an inexpensive substitute for phenol in phenol-formaldehyde (PF) resins, but no one has produced a commercially satisfactory KL-PF resin. This paper reviews the literature on the present status of KL-PF adhesives and makes recommendations on needed research.

Kraft lignin solutions are complex mixtures which have broad molecular weight distributions, high viscosities, relatively low reactivities, and low solubilities. Attempts to overcome these inherent problems include methylolation of lignin to improve reactivity, the use of co-solvents to improve solubility, and ultrafiltration to yield more homogeneous molecular weight fractions. Future research efforts need to focus on understanding the fundamental chemical and physical properties of kraft lignin and its resins. The search for an economic lignin-based wood adhesive should continue.     

Rheology Study of Sugar Cane Bagasse Lignin-Added Phenol–Formaldehyde Adhesives

The rheological properties of sugar cane bagasse lignin–phenol formaldehyde (PF) (30% lignin – PF) resins were studied using oscillation tests. The bagasse lignin was introduced in the classic adhesive formulation in order to supply a part of PF. Rheological qualities of optimal lignin–PF (30% lignin – PF) resins and commercial PF resin were assessed by using a rotary rheometer (ARES). Dynamic rheological measurements, performed at low strain in the linear range, are useful to characterize the network properties of resins.

The results obtained showed that the time sweep indicates excellent structural stability of optimal lignin–PF (30% lignin–PF) resins and commercial PF resin. The elastic modulus is greater than the viscous one showing a remarkable elastic character of the resins, and the performed frequency sweeps show a typical spectrum of a “weak gels” structure. The time dependence at 125°C shows that the optimum cure time is 7.5 min.