Bio-based Benzoxazine Research Articles

Synthesis and characterization of novel bio-based benzoxazines from gallic acid with latent catalytic characteristics

A novel bio-based main chain benzoxazine with two oxazine rings and one phenolic hydroxyl group in the same aromatic ring was synthesized and characterized. The method includes the synthesis of polymeric benzoxazine precursors from simple chemicals such as gallic acid, gallic amide, 4,7,10-trioxa-1,13-tridecanediamine and formaldehyde by using traditional main chain synthesis methodology. The precursors were successfully characterized by the spectral and thermal investigations using 1H NMR, FTIR, GPC, DSC and TGA. The results demonstrated that phenolic hydroxyl groups in the benzene ring which are adjacent to the two oxazine rings have a great effect to reduce ROP temperature of benzoxazines. The clear reduction in ROP temperature was demonstrated by tracking exotherm in DSC analysis with an onset value at 126 °C. Moreover, thermal stability of the final products were investigated by TGA and high char yields observed.

Cardanol derived benzoxazine in combination with boron-doped graphene toward simultaneously improved toughening and flame retardant epoxy composites

A bio-based phosphorus-containing benzoxazine monomer (CBz) was successfully synthesized through the reaction between cardanol and DOPO-based diamine. In order to simultaneously improve the toughness and flame retardancy of epoxy resin (EP), various contents of CBz in combination with boron-doped graphene (BG) nanosheets were incorporated into EP to obtain boron-doped graphene/cardanol derived benzoxazine-epoxy composites (EP/CBz/BG). By comparison, cardanol derived benzoxazine-epoxy co-polymers (EP/CBz) were also fabricated. Results show that the addition of the as-prepared CBz into EP not only endowed EP with excellent flame retardancy, but also improved the glass transition temperature and impact strength. Specifically, the peak heat release rate of EP composite with 13 wt% CBz and 2 wt% BG decreased by 48% compared to that of neat EP, accompanying with an increase of impact strength by 22%. These favorable features of EP/CBz/BG composites are attributed to the unique structure of CBz and high resistance to thermal decomposition of BG.

Sustainability and antimicrobial assessments of bio based polybenzoxazine film

Renewable materials are abundantly available in nature and have the capability to degrade within a short period of time. In the present study, a novel class of chitosan-based polybenzoxazine has been synthesized for the first time. Water, an edible solvent was used for the benzoxazine synthesis, adopting moderate reaction temperature. This bio-based benzoxazine monomer was crosslinked by thermal treatment via ring-opening polymerization to form free-standing polymer films [poly(E-Ch)] without the evolution of volatiles. Hydrogen bonding interactions were found to exist between chitosan and polybenzoxazine. This type of interactions significantly enhance the thermal and mechanical properties with T10 of about 260 °C; ε′ of about 3.6 GPa; and Tg of about 135 °C showing unusual levels of synergism. Interestingly, both the bio-films-poly(E-Ch) and CH do not affect the cell growth. In particular, poly(E-Ch) is effective in preventing bio-film associted infections.

Making Benzoxazines Greener: Design, Synthesis, and Polymerization of a Biobased Benzoxazine Fulfilling Two Principles of Green Chemistry

Sesamol and furfurylamine are used to synthesize a novel benzoxazine monomer as part of the quest to develop greener benzoxazine monomers simultaneously fulfilling two Principles of Green Chemistry, the use of renewable feedstocks and safer solvents and auxiliaries. Respecting principle 5, the so-called preferred solvents (ethanol and ethyl acetate) are used in both the syntheses and purification processes. The chemical structure of the synthesized monomer is verified by proton and carbon nuclear magnetic resonance spectroscopy (1H and 13C NMR), 2D 1H–13C heteronuclear single quantum correlation (HSQC) spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The polymerization behavior of the monomer and the thermal stability of fully polymerized polybenzoxazine are studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A thermally stable polymer has been obtained as shown by the 5% and 10% weight reduction temperature (Td5 and Td10) values of 374 and 419 °C, re...

Biobased Benzoxazine Derived from Daidzein and Furfurylamine: Microwave-Assisted Synthesis and Thermal Properties Investigation.

A biobased benzoxazine resin (Dz-f) demonstrating excellent thermal properties was synthesized from daidzein and furfurylamine by using a microwave heating method. The chemical structure of synthesized benzoxazine monomer was identified by FTIR and NMR (1 H and 13 C NMR) before it was cured and its thermal properties evaluated by differential scanning calorimetry (DSC), TGA, and dynamic mechanical analysis (DMA). The cured resin p(Dz-f) exhibited a glass transition temperature (Tg ) of 391 °C, a very high char yield of 68.7 %, and outstanding thermal stability; the Tg value obtained was the highest thermal stability value ever reported for polybenzoxazine with a high biobased content. Moreover, Dz-f demonstrated a satisfying processability, which was rare for the high-performance thermosetting resins. This work provided us with a new strategy for the preparation of high biocontent resins with excellent thermal properties. In addition, the combination of biobased feedstocks with a microwave-assisted heating method as well as the potential application of this approach in high-end fields might perpetuate remarkable progress towards the sustainable development of the polymeric industry.

High-performance bio-based benzoxazines derived from phosphinated biphenols and furfurylamine

The purpose of this work is to achieve high-performance benzoxazine thermosets from renewable biomass such as furfurylamine and vanillin-derived biphenol. The benzoxazine (DVP-fu) derived from a vanillin-derived biphenol and furfurylamine shows promising properties after thermal curing. To understand the structure-property relationship, two other structurally-similar benzoxazines (DHP-fu and DVG-fu) derived from biphenols (DHP and DVG) were prepared. Thermal analyses (DMA, TMA, and TGA) show that the thermosets of DHP-fu and DVP-fu are high-performance materials, demonstrating that the sustainability and high performance could be achieved simultaneously. This study found that their properties are strongly related to the number of free ortho to the oxygen of oxazine.

Synthesis of Eugenol-Based Silicon-Containing Benzoxazines and Their Applications as Bio-Based Organic Coatings

In this work, several bio-based main-chain type benzoxazine oligomers (MCBO) were synthesized from eugenol derivatives via polycondensation reaction with paraformaldehyde and different diamine. Afterwards, their chemical structures were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance Spectroscopy (1H-NMR). The curing reaction was monitored by Differential Scanning Calorimetry (DSC) and FT-IR. The polybenzoxazine films were prepared via thermal ring-opening reaction of benzoxazine groups without solvent, and their thermodynamic properties, thermal stability, and coating properties were investigated in detail. Results indicated that the cured films exhibited good thermal stability and mechanical properties, showing 10% thermal weight loss (Td10%) temperature as high as 408 °C and modulus at a room temperature of 2100 MPa as well as the glass transition temperature of 123 °C. In addition, the related coatings exhibited high hardness, excellent adhesion, good flexibility, low moisture absorption, and outstanding solvent resistance.

Synthesis of Biobased Benzoxazines Suitable for Vacuum-Assisted Resin Transfer Molding Process via Introduction of Soft Silicon Segment

A series of biobased benzoxazine oligomers suitable for vacuum-assisted resin transfer molding (RTM) were prepared from eugenol derivatives, furfurylamine, diamine, and paraformaldehyde. After the structures of these oligomers were identified by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR), their curing behaviors and processability were evaluated by differential scanning calorimetry, FT-IR, and rheological tests. Results showed that the oligomers had stable viscosity lower than 1 Pa·s in the temperature range from 60 to 190 °C, and their processing window was found to be wider than 160 °C. The cured resins exhibited excellent thermal properties (10% thermal weight loss at 406 °C and glass transition temperature greater than 110 °C), good hydrophobic performance, and low moisture absorption. The benzoxazine oligomers reported here demonstrated great potential in the fabrication of composites, especially the green composites via more effici...

Enhancing the processibility of high temperature polymerizing cardanol derived benzoxazines using eco-friendly curing accelerators

The advent of bio-based benzoxazine in the field of polybenzoxazines is a major breakthrough towards their sustainable development. Cardanol derived benzoxazine offers solvent less synthesis and processing benefits over the petro based resin, however these mandate high curing temperatures. The polymerization temperature can be alleviated through structural modifications or physical blending with curing accelerators; the latter approach being preferred in view of its economic viability. Most of the curing accelerators are moisture sensitive, which adversely affect the end performance of the polymer. In this paper, the potential of eco-friendly stearates based on transition metals as curing accelerators for the polymerization of cardanol based benzoxazine resin has been demonstrated. Metal stearates were formulated with bio-based monomer which leads to significant lowering of the curing profiles, the extent of which was proportional to the amount of accelerator. The hydrophobicity associated with the long alkyl chain in stearate bestows it hydrolytic stability, which allows its use under ambient conditions without special caution. Zinc(II) stearate exhibit highest activity towards acceleration and its inclusion does not alter the viscosity of the formulation offering a processing advantage. Kinetic parameters associated with polymerization of the resin were established using Kissinger Akahira Sunose method.

Poly(benzoxazine-co-urea): A Solventless Approach Towards The Introduction of Alternating Urea Linkages In Polybenzoxazine

In this paper, an alternative approach towards synthesis of phenolic/urea copolymers has been explored via benzoxazine chemistry. Biobased poly(benzoxazine-co-urea) has been prepared through ring opening polymerisation of a benzoxazine monomer containing urea linkages. The amine co-reactant for the benzoxazine synthesis was derived by the additive rearrangement of 4,4′-methylenebis(phenyl isocyanate) (MDI) with ethylene diamine, which underwent Mannich like condensation with cardanol and paraformaldehyde to yield biobased benzoxazine monomer containing urea linkages. The structure of the amine and the benzoxazine has been characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1H-NMR). Benzoxazine monomer undergoes thermally accelerated ring opening polymerization to form cross-linked networks, which has been demonstrated using rheometry and non-isothermal differential scanning calorimetry (DSC). The presence of alternating urea linkages in the benzoxazine network is expected to improve the adhesive properties of the resin, which was quantified in terms of Lap shear strength. Thermal degradation of the crosslinked copolymer has also been studied by thermogravimetric analysis (TGA).

Synthesis and characterization of bio-based benzoxazine oligomer from cardanol for corrosion resistance application

The Mannich-like condensation of a cardanol, paraformaldehyde, and N,N′-bis(2-aminoethyl)ethane-1,2-diamine were carried out to synthesize the amine functional benzoxazine (Bnz) resin. The amine functionality of Bnz resin was evaluated by physiochemical methods, and the structure was characterized using Fourier transform infrared and 1H-nuclear magnetic resonance spectroscopy. The added functionality into the Bnz resin backbone was utilized to modify the Bnz resin structure by glycidoxypropyltrimethoxysilane (GPTMS) in various proportions. The results revealed that the silane-modified Bnz coatings have improved mechanical, chemical, and solvent resistance properties as compared to the neat Bnz coating. The gel and water absorption of polyamide-cured coatings also has been evaluated. Furthermore, the cured films have been evaluated for glass transition temperature (T g) and thermal resistance by differential scanning calorimetry and thermogravimetric analysis, respectively. The corrosion resistance properties were studied by salt spray and electrochemical analysis. It was observed that the highly crosslinked structure of the GPTMS-modified Bnz coatings enhanced the barrier protection to corrosive species.

Thermal and mechanical analyses of biocomposites from cardanol-based polybenzoxazine and bamboo fibers

The aim of this work was to evaluate the thermal and mechanical properties of new biocomposites, using bamboo fibers as reinforcements in a cardanol-based polybenzoxazine matrix, using diethylenetriamine (DETA) as catalyst. The natural bamboo fibers underwent an alkaline treatment for a better compatibility with the polymer matrix and increase the crystallinity degree. The untreated and treated fibers were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction, while the bio-based benzoxazine was characterized by nuclear magnetic resonance (1H-NMR) spectroscopy and FT-IR. The thermal polymerization behavior of the benzoxazine with and without the presence of DETA was analyzed by differential scanning calorimetry, and it was observed that with the presence of the catalyst (5%), the initial temperature of polymerization (Te) was reduced by 47 °C. The polymer and the biocomposites were also analyzed by FT-IR, observing the main polymer structure and confirming the presence of the bamboo fibers. The obtained biocomposites were characterized by dynamic mechanical analysis and thermogravimetric analysis (TG). It was noticed the addition of the bamboo fibers increased the storage modulus (E′) and glass transition temperature of the material, but the thermal stability was affected negatively with the addition of reinforcements.

Enhancement of anti-corrosive performances of cardanol based amine functional benzoxazine resin by copolymerizing with epoxy resins

Abstract The bio-based amine functional benzoxazine (Bnz) resin was synthesized from cardanol, N , N' -Bis(2-aminoethyl)ethane-1,2-diamine and paraformaldehyde by the Mannich condensation reaction. The additional amine functionality in Bnz resin was introduced by using multi functional amine ( N , N' -Bis(2-aminoethyl)ethane-1,2-diamine) to react with monofunctional cardanol. The synthesized amine functional Bnz resin was chemically analyzed for amine value by volumetric titration method. The Fourier Transform Infrared spectroscopy (FTIR) and 1 H-Nuclear Magnetic Resonance ( 1 H NMR) spectroscopy used to illustrate the structure of amine functional Bnz resin. The synthesized Bnz resin was copolymerized with conventional epoxy resins to prepare Poly(Benzoxazine-co-Epoxy) coatings for anti-corrosive application. The network formation of Bnz and epoxy resins was monitor by FTIR analysis. The Poly(Benzoxazine-co-Epoxy) coatings have shown good mechanical, chemical, and solvent resistance properties as compared to the crosslinked Polybenzoxazine coating. Further, gel content and water absorption of Poly(Benzoxazine-co-Epoxy) and Polybenzoxazine coatings were also studied. The cured coatings were evaluated for thermal behavior by thermogravimetric analysis (TGA). The corrosion resistance properties of coatings were investigated by salt spray and electrochemical analysis.

Metal‐Organic Frameworks as curing accelerators for benzoxazines

AbstractBenzoxazine resins, although exhibiting attractive properties; particularly high thermal stability and near zero‐ shrinkage, suffer from a major drawback associated with its high curing temperature. In view of the Lewis acidity associated with the Zn4O nodes in a zinc based metal organic framework [Zn4O(BDC)3, MOF5], we considered it of interest to explore its potential as a curing accelerator for a representative biobased benzoxazine resin. MOF 5 was solvothermally synthesized and characterized using different techniques including powder X‐ray diffraction (PXRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Fourier transform infrared spectroscopy (FT‐IR) and Nitrogen physisorption measurements. Bio‐based benzoxazine resin was synthesized by mannich type condensation of cardanol and aniline with formaldehyde under solventless conditions, the structure of which was confirmed using FT‐IR and 1H‐NMR. The curing behavior of the synthesized resin was systematically investigated using non‐isothermal Differential Scanning Calorimetry (DSC). Introduction of MOF 5 led to a shift in the curing profile to lower temperature, the extent of which was proportional to the amount of MOF 5 in the formulation. DSC studies were performed at different heating rates to establish the kinetic parameters associated with the curing of the resin. Activation energy, as calculated using Kissinger Akahira Sunose method, was found to concomitantly decrease from 98 kJ/mol to 58 kJ/mol upon addition of MOF 5 (5 % w/w).

Smart, Sustainable, and Ecofriendly Chemical Design of Fully Bio‐Based Thermally Stable Thermosets Based on Benzoxazine Chemistry

A smart synthetic chemical design incorporating furfurylamine, a natural renewable amine, into a partially bio-based coumarin-containing benzoxazine is presented. The versatility of the synthetic approach is shown to be flexible and robust enough to be successful under more ecofriendly reaction conditions by replacing toluene with ethanol as the reaction solvent and even under solventless conditions. The chemical structure of this coumarin-furfurylamine-containing benzoxazine is characterized by FTIR, (1) H NMR spectroscopy and two-dimensional (1) H-(1) H nuclear Overhauser effect spectroscopy (2D (1) H-(1) H NOESY). The thermal properties of the resin toward polymerization are characterized by differential scanning calorimetry (DSC) and the thermal stability of the resulting polymers by thermogravimetric analysis (TGA). The results reveal that the furanic moiety induces a co-operative activating effect, thus lowering the polymerization temperature and also contributes to a better thermal stability of the resulting polymers. These results, in addition to those of natural renewable benzoxazine resins reviewed herein, highlight the positive and beneficial implication of designing novel bio-based polybenzoxazine and possibly other thermosets with desirable and competitive properties.

Chavicol benzoxazine: Ultrahigh Tg biobased thermoset with tunable extended network

A novel biobased benzoxazine monomer containing additional allyl functionality was synthesized using a solventless approach from the reaction of a natural occuring phenol: chavicol, para-phenylene diamine and formaldehyde. The chemical structure of this functionalized benzoxazine monomer was confirmed by 1H NMR and FTIR. Its polymerization was investigated and monitored by DSC showing two well defined exotherms allowing the selective ring-opening polymerization of benzoxazine functions and the preservation of the allyl functionality. The network crosslink density could be further increased via the controlled polymerization of allyl functionalities with a post-cure in order to adjust the thermo-mechanical properties. When both networks were polymerized, the thermoset presented an excellent thermo-mechanical stability with a Tα higher than 350°C as measured by DMTA. This exceptional behavior for a potentially biobased benzoxazine resin will allow the preparation of sustainable high performance biocomposite materials.

Epoxy emulsions stabilized with reactive bio-benzoxazine surfactant from epoxidized cardanol for coatings

Epoxidized cardanol was used as a starting material for the development of a novel bio-based benzoxazine surfactant (BOX). The designed surfactant was used as a stabilizer for epoxy aqueous emulsions. As dispersed phase two epoxy resins were used; synthetic bisphenol A diglycidy ether type epoxy resin (EP) and bio-renewable epoxidized soybean oil (ESO). Formation and stability of aqueous emulsions were studied by investigating particle size and distribution and rheological behavior. Copolymer films (coatings), produced by drying the emulsions, were cured at elevated temperature. To ensure a highly crosslinked structure of thermosetting films amine curing agent (AM) was used. Benzoxazine surfactant showed excellent compatibility with both epoxy resins and effectively copolymerized with both of them. The introduction of polybenzoxazine into the epoxy network improved the thermomechanical properties (higher value of storage modulus and higher crosslink density) of neat epoxy resins. The glass transition temperature was reduced only slightly.

Synthesis of an intrinsically flame retardant bio-based benzoxazine resin

Abstract An intrinsically flame retardant bio-based benzoxazine (diphenolic acid pentaerythritol caged phosphate benzoxazine, DPA-PEPA-Boz) monomer was synthesized from bio-based diphenolic acid (DPA) using a four-step process. The monomer of DPA-PEPA-Boz was characterized by FT-IR, 1H NMR and 13C NMR. The curing behavior of DPA-PEPA-boz was studied and compared with those of DPA based benzoxazine (DPA-Boz) and DPA ester derivative (MDP) based benzoxazine (MDP-Boz) without PEPA by means of non-isothermal differential scanning calorimetry. The results indicated that DPA-PEPA-Boz system showed a two-stage curing, assigned to the exothermic opening reactions of oxazine rings and P–O–C ring in PEPA respectively, while the DPA-Boz and MDP-Boz showed a one-stage curing. In addition, the effect of the introduction of PEPA on thermal and inflammable properties of the resin was evaluated. The residual char of the cured DPA-PEPA-Boz (P-DPA-PEPA-Boz) after 400 °C was much higher than those of cured DPA-Boz (P-DPA-Boz) and cured MDP-Boz (P-MDP-Boz) under nitrogen and air atmospheres. Meanwhile, total heat release (THR), peak heat release rate (PHRR) and heat release capacity (HRC) of P-DPA-PEPA-Boz were about half of those of P-DPA-Boz and P-MDP-Boz. P-DPA-PEPA-Boz had a limiting oxygen index (LOI) of 33.5% and achieved V0 rating in UL94 test. P-DPA-PEPA-Boz behaved as a very good intrinsic thermal and flame retardant bio-based benoxazine resin.

Kinetic investigation of a complex curing of the guaiacol bio-based benzoxazine system

AbstractCuring kinetics of guaiacol based benzoxazine synthesized from guaiacol, furfurylamine and formaldehyde forming bio-based polybenzoxazine was investigated. The curing process showed complex polymerization behavior, as the exothermal signal consisted of several overlapped peaks. Differentiation and fitting of overlapped peaks was performed by Pearson VII distribution obtaining two separate exothermal signals further associated to stage 1 and stage 2. The apparent activation energies of both stages were determined to be 113.8 kJ mol-1and 117.5 kJ mol-1, respectively, according to Kissinger. The first could be explained by benzoxazine ring-opening and electrophilic substitution, whereas the second stage corresponds to the rearrangement and diffusion-controlled step. Kinetics of each stage was studied separately. As a result, the first stage was described by Šesták-Berggren autocatalytic model, whereas the second stage appeared to follownthorder kinetics proved by the Friedman method. Application of both kinetic models demonstrated that the predicted curves fit well with the non-isothermal DSC thermograms and as such sufficiently describes the complex curing behavior of guaiacol based benzoxazine.

High performance bio-based benzoxazine networks from resorcinol and hydroquinone

This work presents a scalable and solventless synthesis of two fully bio-based bis-benzoxazine resins derived from resorcinol, hydroquinone and furfurylamine. The structures of the two synthesized precursors have been studied by 1H NMR and FTIR spectroscopies and SEC. The polymerization and degradation of the precursors have been investigated and monitored by DSC and TGA. The properties of the resulting polybenzoxazine networks were found to be dependent on the precursor molecular structure. In both cases, an excellent thermomechanical behavior associated with high charring ability were obtained which highlights the great potential of these fully bio-based resins as new matrices for the preparation of structural composites following a sustainable approach.