The thermal degradation of phenol–formaldehyde resins (PFR) was studied using thermogravimetry analysis (TG) technique. The structural changes of thermal degradation of synthetical and commercial PFR ...were investigated by Fourier-transform infrared rays (FTIR) and solid-state
13C nuclear magnetic resonance (
13C NMR) spectroscopy. The experimental results show that the degradation of PFR can be divided into three stages. Additional cross-links are formed and small exposed groups of the cured resin are removed in the first stage. In the second stage, methylene bridges decompose into methyl groups then both phenol and cresol homolog appear. The degradation of phenol group occurs in the third stage. According to these results, a novel degradation mechanism of phenol–formaldehyde type resins is proposed: the mainly degradation process of PFR is the decomposition reaction of methylene bridges in this mechanism instead of auto-oxidation of the methylene bridges in the prevenient mechanism.
Enzymatic hydrolysis lignin (EHL) derived from bio-ethanol production is attracting increased attention for use as a substitute for petroleum-based phenol in phenolic resins. In this work, EHL was ...successfully liquefied into small phenolic compounds catalyzed by oxalic acid in the presence of phenol. Experiments were designed to determine the effects of different replacement percentages of phenol by EHL on the residue content (RC) and the combined phenol (CP). Up to a 55% weight of phenol was substituted by liquefied EHL to formulate a novolac bio-based phenolic resin (EHL–PF). The differences between EHL and liquefied EHL, PF and EHL–PF were studied by Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC), 1H NMR spectroscopy, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). RC was found to increase with the increasing replacement percentage, while CP was found to increase at a lower replacement percentage and decrease at a higher replacement percentage. EHL–PF possessed comparable properties to those of commercial products.
•Liquefaction is proposed to improve the activity of EHL.•Residue rate of liquefaction strikingly decreased to 11.9%.•The replacement percentage of phenol by liquefied EHL was up to 55%.•55%-LPF has comparable properties versus counterparts.
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•Microbial O-demethylase offers a promising modification in lignin, xenobiotic and drugs.•Fungal mediated lignin demethylation produces methanol and pyrocatecholic structures.•Cytochrome ...P450O-demethylase catalyzes aryl-O-demethylation of guaiacol into catechol.•Bacterial O-demethylase requires cofactors: NADH, H2O2 or O2 for lignin demethylation.•Catechol 1,2-dioxygenases and catechol 2,3-dioxygenase are cleaved intradiol or extradiol position of catechol derivatives.
Lignin is an abundant natural plant aromatic biopolymer containing various functional groups that can be exploited for activating lignin for potential commercial applications. Applications are hindered due to the presence of a high content of methyl/methoxyl groups that affects reactiveness. Various chemical and enzymatic approaches have been investigated to increase the functionality in transforming lignin. Among these is demethylation/demethoxylation, which increases the potential numbers of vicinal hydroxyl groups for applications as phenol-formaldehyde resins. Although the chemical route to lignin demethylation is well-studied, the biological route is still poorly explored. Bacteria and fungi have the ability to demethylate lignin and lignin-related compounds. Considering that appropriate microorganisms possess the biochemical machinery to demethylate lignin by cleaving O-methyl groups liberating methanol, and modify lignin by increasing the vicinal diol content that allows lignin to substitute for phenol in organic polymer syntheses. Certain bacteria through the actions of specific O-demethylases can modify various lignin-related compounds generating vicinal diols and liberating methanol or formaldehyde as end-products. The enzymes include: cytochrome P450-aryl-O-demethylase, monooxygenase, veratrate 3-O-demethylase, DDVA O-demethylase (LigX; lignin-related biphenyl 5,5′-dehydrodivanillate (DDVA)), vanillate O-demethylase, syringate O-demethylase, and tetrahydrofolate-dependent-O-demethylase. Although, the fungal counterparts have not been investigated in depth as in bacteria, O-demethylases, nevertheless, have been reported in demethylating various lignin substrates providing evidence of a fungal enzyme system. Few fungi appear to have the ability to secrete O-demethylases. The fungi can mediate lignin demethylation enzymatically (laccase, lignin peroxidase, manganese peroxidase, O-demethylase), or non-enzymatically in brown-rot fungi through the Fenton reaction. This review discusses details on the aspects of microbial (bacterial and fungal) demethylation of lignins and lignin-model compounds and provides evidence of enzymes identified as specific O-demethylases involved in demethylation.
This paper considers problems of developing a technology for producing low-toxicity formaldehyde resins used in the woodworking industry. It is shown that application 5% fusel alcohol as a modifier ...at the stage of SFZh-3014 resin synthesis reduces the content of free phenol, formaldehyde, and alkali in the resin and shortens its curing time, as well as increases the strength and water resistance of adhesive joints in woodworking products.
A new strategy for the preparation of a lignin phenol formaldehyde (LPF) resin has been developed. Nanolignin with high specific surface area and porous structure with an average particle size of ...about 300 nm was prepared, used as the raw material to substitute phenol partially, and combined with formaldehyde to produce a wood adhesive. The results show that the artificial board prepared with a nanolignin phenol formaldehyde (NLPF) resin with nanolignin substitution degree of 40% wt for phenol could give a dry bond strength of 1.30 ± 0.08 MPa, which is 1.85 times that of the Chinese national grade 1 plywood standard (0.7 MPa) and whose formaldehyde emission of 0.40 mg L
−1
meets the standard of GB/T 14732-2006 (
E
0
, 0.5 mg L
−1
). TG and DSC analyses show that the replacement of phenol by nanolignin could improve the thermal stability and decrease the curing temperature of the prepared lignin-based resin, with the residual ratio of 40% NLPF being 45% wt at 800 °C and the curing exothermic peak being 145.4 °C, which are much better than that of the 40% LPF resin with the residual ratio being 40% wt and the exothermic peak being 186 °C, respectively. The present study provides a new thought for preparation of LPF resins.
A new strategy for the preparation of a lignin phenol formaldehyde (LPF) resin.
The advent of organic molecules as inhibitors in the field of corrosion monitoring has been exponentially expanding in the past few years which enhanced the scope for innovation in polymers as ...potential corrosion inhibitors. The current research focused on the development of azomethine functionalised benzothiazole moiety containing four phenol-formaldehyde resins designated as PF1, PF2, PF3, and PF4; with the aim to combat impending degradations due to corrosion of low carbon containing steel in corrosive acid medium. The present work comprises empirical gravimetric and electrochemical techniques for analysing corrosion inhibition behavior of the developed resins, followed by subsequent surface characterization employing different analytical procedures. The synthesized polymeric resins performed as efficient corrosion inhibiting additives. Its anti-corrosion performance was found in the order: PF4 > PF2 > PF1 > PF3, established from all the experimental findings. It is revealed that the substitution in the benzene unit of benzothiazole moiety played crucial role in corrosion inhibiting mechanism. The activation energy steadily increased after addition of resins into the corrosive medium suggested that this elevated barrier is required to be crossed for the occurrence of corrosion phenomenon, which leads towards declining of corrosion rate. The application of phenol-formaldehyde resins in acid media substantially prevented carbon steel from deterioration due to corrosion. This is attributed to the corrosion inhibiting nature of the adsorbed resin, whereas, the adsorption of resins was confirmed by surface analysing techniques like SEM-EDX, AFM and XPS. Furthermore, these wet-chemical experimental outcomes are well complemented from results analysed from ab initio DFT study and MD simulation. Additionally, MD simulation outcomes helped in visualization of the adsorbed configuration of the modeled resins in presence of different corrosive components.
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•XPS confirmed the elemental composition of film deposited on MS surface.•Charge transfer process controlled the corrosion inhibition.•Adsorption of inhibitors followed Langmuir isotherm.•The surface roughness reduced considerably by the presence of inhibitors.
Gluing hardwood with standard adhesives often appears problematic; therefore, their broader use in practice is limited. On the other hand, using hardwood in laminated beams would undoubtedly benefit ...because mechanical properties would reduce construction dimensions compared to commonly used materials. The hardwood surfaces are highly heterogeneous and porous structure, and the high tannin content in heartwood restrict the use of standard structural PUR adhesives. Using modified adhesives is one of the possibilities to overcome these problems. This work deals with PUR adhesive based on polymeric methylene diphenyl diisocyanate (C15H10N2O2). For this specific PUR adhesive, three different application methods were used (pure polyurethane adhesive as a reference, the adhesive system with application of deep penetration, and the adhesive system with application of deep penetration with an admixture of thermoset particles (C7H6O) and polyurethane adhesive). Such a combination of a particular adhesive with a thermoset increases adhesive parameters, especially for hardwood. Above glass transitions point Tg of the thermoset resin, a 3D network between the thermoset and PUR is formed as a novel species which appears highly resistant to moisture. This protocol has been verified on glued surfaces of several difficult-to-glue types of wood, such as oak (Quercus robur), beech (Fagus sylvatica), and black locust (Robinia pseudoacacia). A lap joint shear strength test using a joint test according to EN 302-1 1 was used to determine the mechanical properties of the adhesives. The results of lap joint shear strength tests are determined based on the classification standard EN 15425 2. Based on the collected results, it is possible to confirm the positive effect of adhesives modified by thermosets on the overall strength of the glued joints in the longitudinal direction of the laminates.
Aromatic amines was produced from PF resins with 14.2 C% yield and 58% selectivity.
Co-pyrolysis effectively enhanced aromatic amines yield by 32.2% to 11.8 C%.
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•Aromatic amines were ...produced from PF resins via catalytic pyrolysis with NH3.•Commercial HZSM-5-3 (Si/Al of 80) zeolites performed high actively.•Acidity of catalyst played a key role for the animation of polymers with NH3.•Co-pyrolysis effectively enhanced aromatic amines yield by 32.2%.•Synergy between PF resins and lignin increased simple phenols production.
Aromatic amines could be produced from organic wastes via catalytic pyrolysis with ammonia that served not only as a carrier gas but also as a reactant. Aromatic amines of 14.2 C% with selectivity of 57.6% were obtained from phenol-formaldehyde resins via pyrolysis over commercial HZSM-5-3 zeolite (Si/Al ratio of 80) catalyst at 650 °C. Significant synergetic effects have been observed when lignin was added, which improved aromatic amines yield by 32.2% to 11.8 C% at the mixing weight ratio of lignin to PF resins of 1:1. HZSM-5-3 was slightly deactivated after 3 cycles with acid sites loss. Catalytic co-pyrolysis of plastics and biomass wastes is a fast and effective method to produce aromatic amines.
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