Pure Polybenzoxazine Research Articles

Enhancing comprehensive performances of polybenzoxazine through integration of soft core–soft shell cellulose‐based nanoparticles

AbstractTo further increasing the toughness performance of thermoset resins without sacrificing their other properties is still a challenge task. In this study, the soft core–soft shell nanoparticles based on polydopamine‐modified cellulose nanocrystals (P‐CNC) were synthesized and seamlessly integrated with Bisphenol A‐aniline benzoxazine (BA‐a). Notably, the results underscore the remarkable impact of a mere 0.2 wt% of P‐CNC on BA‐a, boosting the impact strength of the modified system to 19.5 kJ/m2. This achievement represents a substantial 140.7% increase compared with pure polybenzoxazine. Moreover, the flexural strength reaches 133.4 MPa, surpassing pure polybenzoxazine by 16.2%. And the modified system exhibits a 10% weight loss temperature (Td10) at 321.7°C, accompanied by a char yield of 27.6%. This holistic approach results in a notable enhancement of the toughness performance while concurrently maintaining the flexural strength and the thermal stability of the modified system. Consequently, the integration of soft core–soft shell nanoparticles emerges as a promising strategy for enhancing thermoset resin properties without undermining their existing exceptional attributes.Highlights The core–shell nanoparticles were made by dopamine and cellulose nanocrystals. The core–shell nanoparticles can enhance the toughness of polybenzoxazine. Nanoparticle‐matrix interactions and deformation led to improved properties.

Benzoxazine/amine-based polymer networks featuring stress-relaxation and reprocessability

Amines as additives in benzoxazines are known to beneficially affect the polymerization temperature and furthermore to allow for partially reversible reaction steps yielding however a non-dynamic polybenzoxazine network. This contribution proves that the polymerization behavior of a two-component polymer of the polyetheramine Jeffamine® ED-600 and a bisphenol-A-based benzoxazine features stress-relaxation and reprocessability usually known from vitrimers. With the aim to gain a deeper understanding of the material properties of this system and the corresponding polymer structure, the reaction mechanism of a monofunctional benzoxazine and monoamine model system was studied revealing at first primary, and then secondary amine induced opening of oxazine rings, leading at first to linear polymer chains and then to covalently crosslinked networks. Both consist of repeated phenolic benzoxazine/amine motifs with permanently incorporated polyetheramine chains that do not impact the mechanical properties, compared to pure polybenzoxazine. Thermal, spectroscopic, and extraction analyses show that the addition of Jeffamine® reduces the polymerization temperature and introduces material properties such as reprocessability at the same time. Stress-relaxation measurements support the assumption that the reprocessability point to vitrimer-like molecular processes. The material shows rapid stress-relaxation of up to 11 s, a corresponding bond-exchange activation energy of 146 kJ/mol, and a topology freezing temperature of 97°C.

High electromagnetic interference shielding effectiveness achieved by multiple internal reflection and absorption in polybenzoxazine/graphene foams

AbstractElectromagnetic interference (EMI) is an increasingly severe issue in modern life and high‐performance EMI shielding materials are in desperate need. To achieve high EMI shielding effectiveness (EMI SE), a series of polybenzoxazine/graphene composites foams are developed using a simple sol–gel method. When the graphene loading increases from 1 to 20 wt%, the density of the composites foams drops from 0.4143 g/cm3 to 0.1654 g/cm3. Meanwhile, an electrically conductive path is formed at around 7 wt% of graphene. Below the percolation threshold, the dielectric constant increases with graphene content and composite foam with 5 wt% graphene shows dielectric constant of 10.8 (1 MHz). At the highest graphene content of 20 wt%, the electric conductivity reaches 0.02 S/cm, 10 orders of magnitude higher than pure polybenzoxazine foam. Benefiting from the high electrical conductivity and lightweight porous structure, the composite foam PF/20G delivers an EMI SE of 85 dB and a specific SE of 513.9 dB·cm3/g. Importantly, the EMI shielding is dominated by absorption attenuation, with PF/20G shows absorption ratio higher than 98% in the range of 8.4–11.0 GHz, which is believed to be caused by multiple internal reflection and absorption inside the conductive foam.

Chitosan/biological benzoxazine composites: Effect of benzoxazine structure on the properties of composites

In this study, two bio-based benzoxazines, PH-f and SA-f, were synthesized and used to prepare benzoxazine/chitosan (CS) composites of PH-f/CS and SA-f/CS and their corresponding curing products poly(PH-f)/CS and poly(SA-f)/CS. Differential scanning calorimeter (DSC) and Fourier-transform infrared spectroscopy (FTIR) spectra show that, compared with poly(PH-f)/CS, the formation of imine-linkages (C=N) between SA-f and CS accelerates the benzoxazine ring-opening reaction and lowers the curing temperature of SA-f/CS. Although poly(PH-f)/CS and poly(SA-f)/CS have lower thermal stability than corresponding pure polybenzoxazine, it is still high and their LOI values are >35, indicative of good flame retardancy. Due to the formation of CN bonds between SA-f and CS, the poly(SA-f)/CS composite has more regular surfaces and a more uniform pore distribution than poly(PH-f)/CS, with a specific area of 1.135 m2/g and porosity of 97.5%. The unique pore structure of the poly(SA-f)/CS composite gives it high adsorption capacity (reaching 95% for rhodamine B within 48 h), suggesting that it is a promising adsorption material.

Thermal properties of polybenzoxazine exhibiting improved toughness: Blending with cyclodextrin and its derivatives

Polybenzoxazines are emerging as a class of high-performance thermoset polymers that can find their applications in various fields. However, its practical application is limited by its low toughness. The cyclic β-cyclodextrin and a newly synthesized derivative (β-cyclodextrin-MAH) were separately blended with benzoxazine to improve the toughness of polybenzoxazine. The results revealed that the maximum impact strength of the blend was 12.24 kJ·m−2 and 14.29 kJ·m−2 when 1 wt.% of β-Cyclodextrin and β-Cyclodextrin-MAH, respectively, were used. The strengths were 53% and 86% higher than that of pure polybenzoxazine. The curing reaction, possible chemical structures, and fractured surface were examined using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques to understand the mechanism of generation of toughness. The results revealed that the sea-island structure and the presence of hydrogen bonds between polybenzoxazine and β-cyclodextrin and β-cyclodextrin-MAH resulted in the generation of toughness. Furthermore, the curves generated during thermogravimetric analysis did not significantly change, revealing the good thermal properties of the system. The phase-separated structure and the hydrogen bonds present in the system can be exploited to prepare synergistically tough polybenzoxazine exhibiting excellent thermal properties. This can be a potential way of modifying the thermoset resins.

Curing mechanism, thermal and ablative properties of hexa-(4-amino-phenoxy) cyclotriphosphazene/benzoxazine blends

The demand for ablative material with high performance is eager in the aerospace industry. In this paper, hexa-(4-amino-phenoxy)-cyclotriphosphazene (CPA) was synthesized and then blended with bisphenol-A aniline benzoxazine (BA-a) firstly. The curing mechanism, thermal and ablative properties of cured blends were studied. The addition of CPA not only can decrease the curing temperature but can also increase the crosslink density of polybenzoxazine which is further beneficial for the improvement of thermal properties of cured blends. When the content of CPA is 5%, the Tg of the cured blend increases by 20 °C, and the char yield at 800 °C increases from 25.2% for pure polybenzoxazine to 49.2%. The oxyacetylene ablation tests showed that the ablation rate of cured blends could reach 0.047 mm s−1 while that of polybenzoxazine is 0.128 mm s−1. Further discussion based on SEM, XRD, Raman spectra showed that the CPA can effectively improve the graphitization degree of ablated samples and improve the integrity of graphite layer crystals. Moreover, the density functional theory (DFT) calculations and bond order analysis predict the bonding breakage sequence which is the C–N bonds between BA-a and CPA (N3–C55) > P–O bonds (P2–O12) > phosphazene ring, which means the phosphazene ring shows an effect after benzoxazine partly decomposed. The preparation method by adding CPA to benzoxazine to improve the ablative performance is facial and easy, which provides a new way of making novel ablative materials.

Sawdust reinforced polybenzoxazine composites: Thermal and structural properties

In this study, Mangifera Indica tree sawdust reinforced bisphenol-A aniline based benzoxazine composites were prepared by varying the sawdust from 20 wt% to 45 wt%. Thermogravimetric analysis of composites revealed excellent compatibility between polybenzoxazine and sawdust from the remarkable growth in char yield from 22% (neat resin) to 36% (for highly filled) and glass transition temperature from 151 to 165°C. Ultimate weight loss of the composites evaluated from the Derivatives of TG plots. Limiting oxygen index values of the composites reported considerable growth i.e., from 28 to 32 along with the increase in filler content. Differential scanning calorimetry results showed that sawdust particles have an insignificant effect on curing temperature (219°C) for the raise in sawdust content. Structure of the sawdust, benzoxazine monomer, polybenzoxazine and composites were studied using Fourier transformation infrared spectroscopy. Overall, polybenzoxazine composites with sawdust as filler showed improved thermal properties when compared with pure polybenzoxazine.

Characterization of novel composites from polybenzoxazine and granite powder

The potential of using granite dust as reinforcement into polybenzoxazine matrix was investigated. In this article, novel granite powder waste-reinforced bisphenol-A aniline-based benzoxazine composites were prepared using solution blending technique by varying the content of granite powder from 10 to 40 wt%. The effect of the granite powder content on the thermal, structural, dimensional, and morphological properties of granite powder/polybenzoxazine composites have been investigated. Thermogravimetric analysis (TGA) was performed on the composite samples. Char yield of the composites increased from 44.55 to 67.70% for increasing filler content from 10 to 40wt%, whereas 22% for pure polybenzoxazine. The maximum weight loss temperatures of the composites were analyzed from derivative of thermogravimetric analysis (DTG). Limiting oxygen index (LOI) values also increased as granite powder content increased. Structural properties of benzoxazine, polybenzoxazine, and composites were observed with Fourier-transform infrared spectroscopy (FTIR). Dimensional stability of the composites was investigated through the water absorption test up to 30 days. The composites exhibited zero percent water absorption. Micro-hardness of the composites increased from 17.45 to 78.66% for increasing filler content from 10–40 wt% when compared with pristine polybenzoxazine. The morphological analysis using scanning electron microscopy (SEM) showed the distribution of filler, aggregate formation, compatibility between polybenzoxazine and granite powder. Overall, the importance of using granite powder waste as reinforcement in polybenzoxazine composites revealed from results of the structural, dimensional, and morphological analysis along with the improvement in thermal properties and micro-hardness.

Ablation behavior of inorganic particle-filled polybenzoxazine composite coating irradiated by high-intensity continuous laser

Abstract Further utilization of aircraft structural materials is threatened by the fact that high-intensity continuous lasers are widely used in the field of military defense. To protect the aircraft structure from laser damage, ammonium polyphosphate filled polybenzoxazine composite coatings were prepared on the substrate. The anti-laser ablation characteristics of the coatings were investigated. Results showed that the addition of the inorganic filler improved the anti-laser ablation performance of polybenzoxazine. The back-surface temperature of substrates covered with the composite coatings was more 50% lower than that in the case of a pure polybenzoxazine coating after laser ablation. Further, the residue of the composite coating could be vertically divided into three distinct regions, with the dense surface char layer and the porous pyrolysis layer acting as shielding layers for the laser beam and preventing any heat-related transformations from occurring. The addition of the inorganic particles improved the surface reflectivity of the coatings resulting in much more laser energy dissipation. The decreased pyrolysis rate ensured that the pneumatic cooling effect of pyrolysis gas was more lasting and stable, owing to which the composite coatings could act as effective thermal protection layer for longer. These results confirmed that the inorganic filler modified polybenzoxazine coating exhibits excellent anti-laser properties and are suitable for protecting structural materials from laser-related damage.

DEVELOPMENT OF POLY(D,L-LACTIC ACID) WITH POLYBENZOXAZINE VIA SOLUTION BLENDING

Polybenzoxazine was synthesized by using bisphenol A, formaldehyde and diamine as precursor via condensation reaction. Triethylenetetramine was used as diamine precursor. Polybenzoxazine was characterized by FTIR technique in order to confirm the obtained polybenzoxazine. The ratio of poly(D,Llactic acid)/polybenzoxazine (Mw = 10,000 and 20,000 g/mol) was 0:100, 1:99, 3:97 and 5:95, respectively. The poly(D,L-lactic acid)/polybenzoxazine films were characterized by using Scanning Electron Microscope (SEM). The results showed homogenous and smooth films. Thermal stability of poly(D,L-lacticacid)/polybenzoxazine films was better than pure polybenzoxazine film. Moreover, 3:97 ratio of polybenzoxazine mixed with poly(D,L-lactic acid) (Mw = 20,000 g/mol) film showed good tensile strength,because the stress at break was 24.06 ± 7.99 when determined by Universal Tenting Machine. It was concluded that poly(D,L-lactic acid) improved the property of the polybenzoxazine film.

Facile preparation of the novel castor oil-based benzoxazine–urethane copolymer with improved high-frequency dielectric properties

The novel star shaped benzoxazine-co-urethane prepolymers are first synthesized from the natural resource castor oil, hydroxyl terminated benzoxazine and diisocyanate through the facile one-pot formulation method. Then the cured benzoxazine copolymers can be obtained by the ring-opening polymerization of oxazine groups of the prepared prepolymers. Both hexamethylene diisocyanate and 4,4′-methylenediphenyl diisocyanate are employed as aliphatic and aromatic diisocyanate, respectively, to clarify their effects on the chemical structure and high-frequency dielectric properties of copolymers. In comparison with the pure polybenzoxazine, the copolymer films occupy the improved high-frequency dielectric properties owing to the introduction of three branching aliphatic castor oil, leading to the reduction of molecular polarity and the improvement of free volume. It should be noted that the aliphatic diisocyanate not only decreases the polarity of the copolymer, but also enhances the intermolecular interaction and intermolecular entanglement between castor oil and benzoxazine for the copolymers. Accordingly, the aliphatic diisocyanate based poly(benzoxazine-co-urethane) occupies the minimum high-frequency dielectric constants (2.94, 5 GHz; 2.96, 10 GHz) and relatively high glass transition temperature (220 °C). Therefore, this work not only provides a simple path for improving high-frequency dielectric properties of benzoxazine, but also gives some insight into the effects of diisocyanates on the formation and high-frequency dielectric properties of poly(benzoxazine-co-urethane)s.

Synthesis and characterization of thermally curable guaiacol based poly(benzoxazine-urethane) coating for corrosion protection on mild steel

Biobased hydroxyl functional benzoxazine monomer was synthesized from Guaiacol (lignin derivative) by Mannich condensation reaction using solvent less method. The structure of hydroxyl functional benzoxazine monomer was elucidated from FTIR, 1H NMR, 13C NMR spectroscopy and mass spectrometry. The ring opening polymerization conversion with respect to time was estimated by 1H NMR. Thermal curing behaviour of benzoxazine monomer was studied by DSC. The hydroxyl functional benzoxazine monomer was cured with isocyanate hardener in varying concentrations based on equivalent weight to prepared the poly(benzoxazine-urethane) (BZPU) coatings. After thermal curing, BZ and BZPU coatings were examined by FTIR analysis. The effect of varying concentrations of isocyanate hardener with benzoxazine monomer on mechanical, chemical, solvent, thermal and anticorrosive properties of coatings was investigated. The study revealed that, an increased concentration of urethane moieties in BZPU coatings improved the mechanical, chemical and thermal properties, compared to pure polybenzoxazine (BZ) coating. The effect of urethane content on corrosion resistance of BZPU coatings were investigated by salt spray and electrochemical impedance spectroscopy (EIS) technique. The results shown that corrosion resistance of BZPU coating enhanced with increasing urethane content in polymer backbone. The protection efficiency values for BZPU coatings were found more than 97%.

Effects of Gamma Radiation on Thermal Properties of Benzoxazine Filled with Carbon Black

In this study, the mixtures between benzoxazine monomer and electrically conductive carbon black (CB) were radiated with gamma ray at different doses, i.e. 0, 25, 50, 75, and 100 kGy before polymerization. The contents of carbon black filler were varied i.e. 0, 5, and 30wt%. The thermal properties such as curing temperatures and glass transition temperatures were determined using differential scanning calorimeter (DSC), while the decomposition temperature and char yields were analyzed using thermogravimetric analyzer (TGA).The results reveal that the radiation could decrease the curing temperature of pure polybenzoxazine. In addition, the decomposition temperature and char yield were increased with the increase of CB content. At the same CB content, the radiation dose could decrease the decomposition temperature and char yield.

Morphology and thermal properties of copolymer based on p-aminobenzonitrile type benzoxazine and diglycidyl ether of bisphenol-A

A copolymer of p-aminobenzonitrile type benzoxazine (BA-pabn) and diglycidyl ether of bisphenol-A (DGEBA) was prepared. With rising DGEBA content, the peak temperature of the differential scanning calorimetry curve for polymerization of BA-pabn/DGEBA blend shifts to higher value, and the roughness of the fracture surface of the BA-pabn/DGEBA copolymer increases. In the glassy state, the storage modulus of the copolymer initially tends to increase with rising DGEBA content over pure polybenzoxazine (PBA-pabn), but decreases when DGEBA content reaches to 50wt%. The copolymer exhibits a single glass transition temperature lower than that of PBA-pabn. The onset weight loss temperature of the copolymer is higher than that of PBA-pabn, but the char yield at 800°C is lower.

Synthesis, characterization, and properties of flexible magnetic nanocomposites of cobalt ferrite–polybenzoxazine–linear low‐density polyethylene

AbstractA simple method for the preparation of magnetic nanocomposites consisting of cobalt ferrite (CF; CoFe2O4) nanoparticles, polybenzoxazine (PB), linear low‐density polyethylene (LLDPE), and linear low‐density polyethylene‐g‐maleic anhydride (LgM) is described. The composites were prepared by the formation of benzoxazine (BA)–CF nanopowders followed by melt blending with LLDPE and the thermal curing of BA. The composites were characterized by X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, universal testing machine measurement, and vibrating sample magnetometry. The composites consisting of LLDPE, PB, and LgM (47.5L–47.5PB–5LgM) exhibited a higher tensile strength (23.82 MPa) than pure LLDPE and a greater elongation at break (6.11%) than pure PB. The tensile strength of the composites decreased from 19.92 to 18.55 MPa with increasing CF loading (from 14.25 to 33.25 wt %). The saturation magnetization of the composites containing 33.25 wt % CF was 18.28 emu/g, and it decreased with decreasing amount of CF in the composite. The composite films exhibited mechanical flexibility and magnetic properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation and characterization of flexible polybenzoxazine–LLDPE composites

Polybenzoxazine-based flexible composites have been prepared by blending benzoxazine with linear low density polyethylene (LLDPE) in presence of a compatibilizer (maleic anhydride grafted linear low density polyethylene [LLDPE-g-MA]) using a melt blending method. It has been observed that the thermal stability of the composites increased with increasing amount of polybenzoxazine in the composition. Mechanical properties of the composites have been investigated by using tensile and flexural tests. Presence of 5 wt% compatibilizer in the composition showed very good mechanical properties. Pure polybenzoxazine possessed high tensile strength and less elongation at break whereas LLDPE showed low tensile strength and significantly more elongation at break. Composites consist of LLDPE and polybenzoxazine with additional LLDPE-g-MA, exhibited higher tensile strength than pure LLDPE and more elongation at break than pure polybenzoxazine. Prepared composites possess very good mechanical flexibility, which makes them good candidates to prepare of complex structures and coating.

Rheological and Thermomechanical Characterizations of Fumed Silica-Filled Polybenzoxazine Nanocomposites

The composites of fumed silica-filled polybenzoxazine at various nanofiller contents ranging from 0 to 10 wt% were fabricated. In this study, the rheological and thermomechanical analysis of neat polybenzoxazine and its nanocomposites were performed. The rheograms show the shear thinning behaviours of the melted nanocomposite compound. In addition, the complex viscosity of the nanocomposites revealed that the liquefying temperature of these molding compounds increased with increasing the amount of fumed silica, while the gel-point temperature was not changed even though the amount of nanofiller was increased. The DSC thermograms confirmed that fumed silica loading had neither retarding nor accelerating effect on the thermal curing reaction of the benzoxazine monomer. Furthermore, the flexural modulus and microhardness of the nanocomposites were increased with an increase of the nanofiller. DMA thermograms also revealed that the glass transition temperatures (Tg) of pure polybenzoxazine were shifted from 157 o C to higher values from the presence of the fumed silica.

Syntheses, thermal properties, and phase morphologies of novel benzoxazines functionalized with polyhedral oligomeric silsesquioxane (POSS) nanocomposites

We have successfully synthesized a novel benzoxazine ring-containing polyhedral oligomeric silsesquioxane (BZ-POSS) monomer by two routes: (1) hydrosilylation of a vinyl-terminated benzoxazine using the hydro-silane functional group of a polyhedral oligomeric silsesquioxane (H-POSS) and (2) reaction of a primary amine-containng POSS (Amine-POSS) with phenol and formaldehyde. The benzoxazine-containing POSS (BZ-POSS) monomer can be copolymerized with other benzoxazine monomers through ring-opening polymerization under conditions similar to that used for polymerizing pure benzoxazines. Thermal properties of these POSS-containing organic/inorganic polybenzoxazine nanocomposites have been improved over the pure polybenzoxazine analyzed by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The BZ-POSS monomer is poorly miscible with the benzoxazine monomer and tends to aggregate and forms its own domains, both before and after polymerization. At a higher BZ-POSS content, gross aggregation occurs and results in a lower than expected improvement in the thermal properties.

Synergism observed in polybenzoxazine and poly(ε-caprolactone) blends by dynamic mechanical and thermogravimetric analysis

Benzoxazine resins and poly(ε-caprolactone) (PCL) are melt blended and the properties of the blends in the range of 0–15wt.% of PCL are studied by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The Tgs of the benzoxazine blends in the presence of PCL are found to be slightly lower than that of neat polybenzoxazine resin. The blends show improved mechanical properties, including higher crosslink densities, rubbery plateau moduli, and flexural strengths compared to pure polybenzoxazine. Moreover, the thermal stabilities at middle temperature range in the presence of PCL modifiers are also enhanced, which is evident from the delayed onset decomposition temperature and the disappearance of the first degradation event.