Benzoxazine Research Articles

Post-polymerization modification of polybenzoxazines with boronic acids supported by B–N interactions

Polybenzoxazines (PBZs) were modified using the reactivity of their inherent bis(2-hydroxybenzyl)amine (BHBA) units toward boronic acids, RB(OH)2.

The molecular design of photo-curable and high-strength benzoxazine for 3D printing.

Low viscosity photo-curable benzoxazines (BZs) are designed and synthesized for use in stereolithography 3D printing. An initial investigation shows that the thermally polymerized polybenzoxazines (PBZs) have remarkably high Tg (264 °C) and flexural modulus (4.91 GPa) values. Subsequently, the formulated photoprintable resins are employed for use in high-resolution projection micro-stereolithography (PμSL) printing. Complex PBZ 3D structures can be achieved from the as-printed objects after they are thermally treated. These findings advance the design of BZ monomers for photopolymerization-based 3D printing and offer a method for the efficient fabrication of high-performance thermosets for various demanding engineering applications.

Heat-resistant and robust biobased benzoxazine resins developed with a green synthesis strategy

Two high-performance biobased benzoxazine resins from mono-phenols are developed with a green synthesis strategy.

Thermal properties of a series of tetra-functional quinoxaline-based benzoxazine/monofunctional benzoxazine blends

: In this article, a series of tetra-functional quinoxaline-based benzoxazine/ monofunctional benzoxazine (P-a) blending resins were prepared. Differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA) were utilized to study the curing behavior of blends and heat resistance and thermal stability of the corresponding resins. The obtained blends show lower onset and peak exothermic temperatures than that of a phenol/phenylamine-based benzoxazine. Additionally, the cured blends possess much better heat resistance, higher char yields, and better thermal stability than monofunctional benzoxazine resins.

Synthesis, Polymerization Kinetics and Thermal Properties of Benzoxazine Resin Containing ortho-Maleimide Functionality

A benzoxazine monomer with ortho-maleimide functionality has been synthesized using ortho-maleimide functional phenol, aniline and paraformaldehyde as starting materials. The chemical structure of this benzoxazine monomer is verified by 1H and 13C nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopies, elemental analysis as well as high-resolution mass spectrometry. The polymerization behavior of benzoxazine has been studied by differential scanning calorimetry (DSC) and in situ FT-IR. Besides, the kinetic parameters have been calculated by non-isothermal DSC with different heating rates. The apparent activation energy value of the ortho-maleimide functional benzoxazine is calculated to be 72.43 kJ/mol based on the Starink method. In addition, our predicted thermograms based on the developed model fit well with the curves obtained from experimental DSC results. Moreover, DSC and thermogravimetric analyses (TGA) are used to determine the thermal properties of the cross-linked thermoset. The resulting polybenzoxazine derived from ortho-maleimide functional shows excellent thermal stability (Tg of 247 °C; Td5 of 333 °C), evidencing its great potential application in high-performance fields.

A modus operandi toward interfacial enhancement of ethylene propylene diene monomer rubber/ polybenzoxazine blends using EPDM‐grafted‐vinyltrimethoxysilane copolymer

AbstractCompatibilization of polymer blends is performed to obtain synergistic effects in physical and mechanical properties. The present work demonstrates the ability of vinyltrimethoxysilane‐grafted‐ethylene propylene diene monomer rubber (VTMS‐g‐EPDM) to improve the compatibility between EPDM and polybenzoxazine (PB). EPDM reacted with 5 phr of VTMS showed the highest grafting efficiency as well as a relatively low gel content, and was added to EPDM/PB blends. The addition of 8 phr of compatibilizer to 70/30 (w/w) EPDM/PB reduced the dispersed PB droplet size from 3.1 μm to 800 nm. Effects of various blend compositions at constant dosage of compatibilizer (8 phr) on the swelling behavior and tensile properties of the samples were also studied. The tensile strength increased from 12 to 14.5 MPa upon adding the compatibilizer at 50/50 blend ratio of EPDM/PB; however, the increase in the PB content had no significant impact on the tensile strength in both compatibilized and non‐compatibilized samples.

Modification of traditional benzoxazine by blending with polyfunctional benzoxazines containing aromatic group and fluorene group

A series of polyfunctional benzoxazine monomers containing aromatic and fluorene group (AMFB) were used as modified agents to improve the performance of typical bifunctional bisphenol-A-aniline-based (BA-a) benzoxazine resins. The polymerization behaviors of BA-a/AMFB blends were investigated by using the differential scanning calorimetry (DSC), while the dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were used to analyze the thermomechanical and thermal properties of BA-a/AMFB copolymers [poly(BA-a/AMFB)]. Moreover, the cross-section morphologies of poly(BA-a/AMFB) were observed by scanning electron microscope (SEM). The experimental results showed that BA-a monomer has good catalytic activity for AMFB monomers during the curing process. Compared with BA-a polymer [poly(BA-a)], due to the introduction of heat-resistant fluorene ring and the increase of the crosslinking degree of copolymers, the copolymers showed higher glass transition temperature and better thermal properties. For poly(BA-a/AMFB), the T5, T10, and Yc were higher than those of poly(BA-a). With the increase of the alkyl chain length of AMFB monomers, the cross-section creases gradually changed from linear to dendritic, and the number of creases increased significantly, which indicated that the toughness of the copolymers was significantly improved.

Development and Mechanism of High-Performance Fully Biobased Shape Memory Benzoxazine Resins with a Green Strategy

Developing high-performance fully biobased shape memory thermosets with a green strategy is a challenging topic of great interest. Herein, two unique fully biobased benzoxazine resins with excellen...

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.

In situ co‐polymerization of high‐performance polybenzoxazine/silica aerogels for flame‐retardancy and thermal insulation

AbstractMaterials with high‐performance thermal insulation and excellent flame‐resistance are incredibly desirable for energy conservation and fire safety. In this study, a novel hybrid nanostructure network polybenzoxazine/silica (PBO/SiO2) aerogels were fabricated through facile in situ co‐polymerization sol‐gel methods with ambient pressure drying using benzoxazine (BO) monomers and SiO2 sol as reaction source, N, N‐dimethylformamide (DMF) as the solvent and hydrochloric acid (HCl) as the catalyst. The hybrid nanostructure network was retained by polymerization–induced nanoscale phase separation of PBO and SiO2. The resulting PBO/SiO2 aerogels exhibited finer microstructure, lower density (0.18 g/cm3), thermal conductivity (0.031 W/m·K), and better flame‐resistance in comparison with PBO aerogels. They demonstrated an excellent compressive strength of 0.81 to 1.12 MPa at 10% deformation. The remarkable improvement in thermal insulation and flame‐resistance of PBO/SiO2 aerogels could be attributed to the combined effects of finer microstructure and formation of SiO2 that was “in‐situ” interpenetrated and interacted with silanols (Si‐OH) in the PBO network during the combustion process. The successful synthesis of PBO/SiO2 aerogels highlights the possibility of fabricating a novel high‐performance thermal insulation and excellent flame‐resistance used for energy‐efficient buildings.

Design of High-Performance Polybenzoxazines with Tunable Extended Networks Based on Resveratrol and Allyl Functional Benzoxazine.

A novel resveratrol-based bio-benzoxazine monomer (RES-al) containing an allyl group has been synthesized using resveratrol, allylamine, and paraformaldehyde via Mannich condensation reaction, and its chemical structures have been characterized by FT-IR spectroscopy and NMR techniques. The polymerization behavior of this benzoxazine resin has been investigated using in situ FT-IR and differential scanning calorimeter (DSC) measurements, and the thermal-mechanical properties of its corresponding polybenzoxazines are evaluated by DMA and TGA. We show that by controlling the curing process of the oxazine ring, the C=C bond in resveratrol, and the allyl group in RES-al, the cross-linking network of the polybenzoxazine can be manipulated, giving rise to tunable performance of thermosets. As all curable functionalities in RES-al are polymerized, the resulted polybenzoxazine exhibits a good thermal stability with a Tg temperature of 313 °C, a Td5 value of 352 °C, and char yield of 53% at 800 °C under N2.

Experimental and numerical study of composite sandwich panels for lightweight structural design

Composite sandwich panels are commonly considered as lightweight materials for structural design in many applications including automotive, aerospace and defence systems. These panels must be developed and validated for its mechanical strength characteristics under different loading conditions before deploying them for the practical application. Hence, the present paper deals with the experimental and numerical studies on composite sandwich panels subjected to quasi-static edgewise and flatwise compression loads. The composite face sheet was developed using 2 × 2 bi-directional 200GSM twill carbon fibre with hot cure benzoxazine resin. Sandwich panels were made using the developed composite face sheets with aluminium honeycomb core. The developed composite face sheets were tested for tensile and flexural conditions and the sandwich panels for edgewise and flatwise compression loads. Three samples for each of these tests were conducted in Shimadzu UTM with 50 kN capacity machine. A consistent load-displacement profile and the failure pattern were observed for all the samples tested in each test category. It is noted from these tests that the composite face sheets exhibited an ultimate tensile strength of 444 MPa and a flexural strength of 842 MPa which is pretty to close to the epoxy based composites used in the aerospace applications; sandwich panels showed an edgewise compressive strength of 610 MPa and flatwise compressive strength of 3.5 MPa. Tensile test coupons initially had undergone certain delamination before failure and failed close to the specimen holding end. Flexural test specimens were shown delamination of only one layer at the loading face. However, the specimen was well intact together even after failure. Bending mode of failure was noted during edgewise compression test of the sandwich; severe delamination was seen in the tension side of the sandwich whereas a line-folding crack with failure was exhibited at the mid-plane of the specimen. In case of flatwise compression, no evident of damage was observed in the sandwich structure. The second part of the paper describes the numerical simulations of these test cases including tensile, flexural, edgewise compression and flatwise compression using an explicit finite element solver viz. LS-DYNA. Material type 22 and 26 was selected to define the material behaviour of composites and honeycomb respectively. The delamination was modelled using *CONTACT_AUTOMATIC_SURFACE_SURFACE_TIEBREAK card with option 9 that works under B-K linear fracture mechanics law to define the normal and shear failure of cracks. The numerical results were found to match well with experimental observations for the individual coupons as well as the sandwich samples. Therefore, it is concluded from this study that the developed LS-DYNA simulation methodology can be used as a tool for composite sandwich panels based lightweight structural design.

Effect of thermo‐oxidative aging on surface characteristics of benzoxazine and epoxy copolymer

AbstractThe copolymer of bisphenol A‐based benzoxazine and cycloaliphatic epoxy resin possesses greater processability and glass‐transition temperature compared to that of benzoxazine homopolymer, making it suitable for high‐temperature aerospace applications. The aim of this work is to investigate the behavior of the copolymers under thermos‐oxidative aging conditions using the surface characterization techniques. The benzoxazine homopolymer and copolymer samples were thermally aged in an air‐circulating oven under controlled temperatures of 180 and 200°C for various periods of time up to 24 weeks. The thermo‐oxidative‐induced weight change and surface cracking were monitored for samples during the aging period. As an alternative method to characterize thermal aging, static contact angle, and contact angle hysteresis of samples were measured over time. Moreover, droplet impact tests using deionized water were performed on stationary and moving samples to investigate the effects of aging time and temperature on impact dynamics of droplets. In addition, FTIR analysis was performed to evaluate the chemical changes on the surface of samples. The results indicated the extent of degradation of aged samples increased with increasing the aging time and temperature. In addition, the copolymer of cycloaliphatic epoxy and benzoxazine showed a greater amount of thermos‐oxidative degradation than the one for benzoxazine homopolymer. More importantly, the results obtained from the surface analysis measurements (e.g., contact angle) followed a similar trend to the one obtained from the traditional aging experiments (e.g., weight change). This showed the former nondestructive and simple method can be used to monitor thermal aging of materials in service.

Innovative Hyperbranched Polybenzoxazine-Based Graphene Oxide-Poly(amidoamines) Nanomaterials.

The covalent functionalization of graphene oxide (GO) surface with hyperbranched benzoxazine (BZ) structures has been achieved using poly(amidoamine) dendrimers (PAMAM) of different generations. By increasing the PAMAM generation, multiple benzoxazine rings were synthesized decorating the GO layers. The polymerization process and the exfoliation behavior were investigated. The novel BZ-functionalized GO hybrid materials were characterized by a combination of techniques such as FT-IR, XPS, and 1H-NMR for the confirmation of benzoxazine formation onto the GO layer surfaces. Raman and XRD investigation showed that the GO stacking layers are highly disintegrated upon functionalization with hyperbranched benzoxazine monomers, the exfoliation being more probably to occur when lower PAMAM generation (G) is involved for the synthesis of hybrid GO-BZ nanocomposites. The polymerization of BZ rings may occur either between the BZ units from the same dendrimer molecule or between BZ units from different dendrimer molecules, thus influencing the intercalation/exfoliation of GO. DSC data showed that the polymerization temperature strongly depends on the PAMAM generation and a significant decrease of this value occurred for PAMAM of higher generation, the polymerization temperature being reduced with ~10 °C in case of GO-PAMAM(G2)-BZ. Moreover, the nanoindentation measurements showed significant mechanical properties improvement in case of GO-PAMAM(G2)-BZ comparing to GO-PAMAM(G0)-BZ in terms of Young modulus (from 0.536 GPa to 1.418 GPa) and stiffness (from 3617 N/m to 9621 N/m).

Room Temperature Oxalic Acid‐Catalyzed, Ambient Pressure Dried, and Cost‐Effective Synthesis of Polybenzoxazine Aerogels for Thermal Insulation

The quest for ambient pressure dried, cost‐effective, and environmentally friendly synthesis technology has been continuously pursued throughout the aerogel research process. Herein, oxalic acid catalyst is used to synthesize a series of polybenzoxazine (PBZ) aerogels through room temperature ring‐opening polymerization and ambient pressure drying technique based on phenol‐4,4′‐diaminodiphenylmethane benzoxazine (PH–mda) monomer. The resultant PBZ aerogels with a microstructure of 3D nanoporous network exhibit a low density of 0.13–0.36 g cm−3 and relatively low thermal conductivities of 0.0323 (105 Pa) and 0.0119 W m−1 K−1 (10 Pa), respectively. Remarkably, PBZ aerogels possess excellent compressibility (the maximum strain can be more than 80%), high compressive modulus, and specific modulus because of their rough skeleton structure. Taking advantage of the simple synthetic route, easily scaled‐up, lightweight, low thermal conductivity, and excellent mechanical property, such PBZ aerogels may have great potential to serve as a new material for energy‐efficient buildings and the other thermal insulating field.

Achieving a 3D Thermally Conductive while Electrically Insulating Network in Polybenzoxazine with a Novel Hybrid Filler Composed of Boron Nitride and Carbon Nanotubes.

To solve the problem of excessive heat accumulation in the electronic packaging field, a novel series of hybrid filler (BN@CNT) with a hierarchical “line-plane” structure was assembled via a condensation reaction between functional boron nitride(f-BN) and acid treated carbon nanotubes (a-CNTs). The reactions with different mass ratios of BN and CNTs and the effect of the obtained hybrid filler on the composites’ thermal conductivity were studied. According to the results, BN@15CNT exhibited better effects on promoting thermal conductivity of polybenzoxazine(PBz) composites which were prepared via ball milling and hot compression. The thermally conductive coefficient value of PBz composites, which were loaded with 25 wt% of BN@15CNT hybrid fillers, reached 0.794 W· m−1· K−1. The coefficient value was improved to 0.865 W· m−1· K−1 with 15 wt% of BN@15CNT and 10 wt% of BN. Although CNTs were adopted, the PBz composites maintained insulation. Dielectric properties and thermal stability of the composites were also studied. In addition, different thermal conduction models were used to manifest the mechanism of BN@CNT hybrid fillers in enhancing thermal conductivity of PBz composites.

Sulfonic acid-containing benzoxazine surfactant and its waterborne benzoxaizne resins

A sulfonic acid-containing benzoxazine surfactant, sodium 3-dodecyl-3,4-dihydro- 2H-1,3-benzoxazine-6-sulfonate (SBZ), was synthesized via Mannich reaction using sodium 4-hydroxybenzenesulfonate and n-dodecylamine as raw materials. The chemical structure of SBZ was characterized by 1H NMR and FT-IR. Using SBZ as the surfactant, a series of waterborne benzoxazine resin (WBR) emulsions were prepared. The effects of SBZ concentration and oil–water ratio on the behavior of WBR emulsions were studied. Furthermore, polybenzoxazine film was prepared via curing a WBR emulsion with 50 vol% oil phase. The results showed that SBZ had a strong emulsifying ability. Only using low SBZ concentration of 2.0%, the high solid contents of 50–80 vol% and stable WBR emulsions were obtained. After polymerizing the WBR emulsion, a transparent and flexible polybenzoxazine film was fabricated. The SBZ surfactant was incorporated into the cross-linked polybenzoxazine network after polymerization. The film had a moderate mechanical property and a high glass transition temperature of 288 °C. This work provides a new strategy for the development of high heat-resistant and environmentally friendly waterborne benzoxazine coatings.

Structure and Performance of Benzoxazine Composites for Space Radiation Shielding.

Innovative multifunctional materials that combine structural functionality with other spacecraft subsystem functions have been identified as a key enabling technology for future deep space missions. In this work, we report the structure and performance of multifunctional polymer matrix composites developed for aerospace applications that require both structural functionality and space radiation shielding. Composites comprised of ultra-high molecular weight polyethylene (UHMWPE) fiber reinforcement and a hydrogen-rich polybenzoxazine matrix are prepared using a low-pressure vacuum bagging process. The polybenzoxazine matrix is derived from a novel benzoxazine resin that possesses a unique combination of attributes: high hydrogen concentration for shielding against galactic cosmic rays (GCR), low polymerization temperature to prevent damage to UHMWPE fibers during composite fabrication, long shelf-life, and low viscosity to improve flow during molding. Dynamic mechanical analysis (DMA) is used to study rheological and thermomechanical properties. Composite mechanical properties, obtained using several standardized tests, are reported. Improvement in composite stiffness, through the addition of carbon fiber skin layers, is investigated. Radiation shielding performance is evaluated using computer-based simulations. The composites demonstrate clear advantages over benchmark materials in terms of combined structural and radiation shielding performance.

Improvement of thermal conductivity and mechanical properties for polybenzoxazine composites via incorporation of epoxy resin and segregated structure

Developing tendency of increasing integration in electronic components filed led to the demand for thermally conductive polymer materials. Forming a segregated structure with thermally conductive fillers in the matrix has been proven to be a promising technique. However, the mechanical properties of the material prepared via this technique are commonly sacrificed because the interaction between fillers and matrix are weak. We present a simple method to improve the mechanical properties while maintaining the segregated structure via the collaboration of epoxy and polybenzoxazine(PBz). The fillers, epoxy resin, and benzoxazine(BOZ) were mixed and then hot pressed under 12 MPa of pressure with a certain heating strategy. The thermal conductivity, density, mechanical properties, morphology, and thermal stability of the composites were investigated. With 25 wt% filler, the value of thermal conductivity coefficient of EP/PBz composites reached 0.811 W mK−1, while that of PBz composites was 0.762 W mK−1. The tensile strength of the matrix improved from 58.3 MPa to 99.7 MPa.

Flammability of Benzoxazine Resin Based Carbon Fibre Composite Samples

Flammability of Benzoxazine Resin Based Carbon Fibre Composite Samples