Property enhancement of polybenzoxazine modified with dianhydride

Flexible Composite Hydrogels Based on Polybenzoxazine for Supercapacitor Applications

Polybenzoxazines (Pbzs) are advanced forms of phenolic resins that possess many attractive properties, including thermal-induced self-curing polymerization, void-free polymeric products and absence of by-product formation. They also possess high Tg (glass transition temperature) and thermal stability. But the produced materials are brittle in nature. In this paper, we present our attempt to decrease the brittleness of Pbz by blending it with polyvinylalcohol (PVA). Benzoxazine monomer (Eu-Ed-Bzo) was synthesized by following a simple Mannich condensation reaction. The formation of a benzoxazine ring was confirmed by FT-IR and NMR spectroscopic analyses. The synthesized benzoxazine monomer was blended with PVA in order to produce composite films, PVA/Pbz, by varying the amount of benzoxazine monomer (1, 3 and 5 wt. % of PVA). The property of the composite films was studied using various characterization techniques, including DSC, TGA, water contact angle analysis (WCA) and SEM. WCA analysis proved that the hydrophobic nature of Pbz (value) was transformed to hydrophilic (WCA of PVA/Pbz5 is 35.5°). These composite films could play the same role as flexible electrolytes in supercapacitor applications. For this purpose, the composite films were immersed in a 1 M KOH solution for 12 h in order to analyze their swelling properties. Moreover, by using this swelled gel, a symmetric supercapacitor, AC//PVA/Pbz5//AC, was constructed, exhibiting a specific capacitance of 170 F g-1.

Accurate predictions of thermoset resin glass transition temperatures from all-atom molecular dynamics simulation

To enable the design and development of the next generation of high-performance composite materials, there is a need to establish improved computational simulation protocols for accurate and efficient prediction of physical, mechanical, and thermal properties of thermoset resins. This is especially true for the prediction of glass transition temperature (T_g), as there are many discrepancies in the literature regarding simulation protocols and the use of cooling rate correction factors for predicting values using molecular dynamics (MD) simulation. The objectives of this study are to demonstrate accurate prediction the T_g with MD without the use of cooling rate correction factors and to establish the influence of simulated conformational state and heating/cooling cycles on physical, mechanical, and thermal properties predicted with MD. The experimentally-validated MD results indicate that accurate predictions of T_g, elastic modulus, strength, and coefficient of thermal expansion are highly reliant upon establishing MD models with mass densities that match experiment within 2%. The results also indicate the cooling rate correction factors, model building within different conformational states, and the choice of heating/cooling simulation runs do not provide statistically significant differences in the accurate prediction of T_g values, given the typical scatter observed in MD predictions of amorphous polymer properties.

Graphene Oxide-Based Membranes Intercalated with an Aromatic Crosslinker for Low-Pressure Nanofiltration

Graphene oxide (GO), a carbonaceous 2D nanomaterial, has received significant interest as a next-generation membrane building block. To fabricate high-performance membranes, an effective strategy involves stacking GO nanosheets in laminated structures, thereby creating unique nanochannel galleries. One outstanding merit of laminar GO membranes is that their permselectivity is readily tunable by tailoring the size of the nanochannels. Here, a high-performance GO-based nanofiltration membrane was developed by intercalating an aromatic crosslinker, α,α/-dichloro-p-xylene (DCX), between the layers in laminated GO nanosheets. Owing to the formation of strong covalent bonds between the crosslinker and the GO, the resulting GO laminate membrane exhibited outstanding structural stability. Furthermore, due to the precisely controlled and enlarged interlayer spacing distance of the developed DCX-intercalated GO membrane, it achieved an over two-fold enhancement in water permeability (11 ± 2 LMH bar^-1) without sacrificing the rejection performance for divalent ions, contrary to the case with a pristine GO membrane.

Impact Response of Aramid Fabric-Reinforced Polybenzoxazine/Urethane Composites Containing Multiwalled Carbon Nanotubes Used as Support Panel in Hard Armor

The aim of this research project is to analyze support panels that are based on aramid fabrics which are reinforced with polybenzoxazine/urethane (poly(BA-a/PU)) composites and contain multiwalled carbon nanotubes (MWCNTs). Through the measurement of mechanical properties and a series of ballistic-impact tests that used 7.62 × 51 mm² projectiles (National Institute of Justice (NIJ), level III), the incorporated MWCNTs were found to enhance the energy-absorption (E_Abs) property of the composites, improve ballistic performance, and reduce damage. The perforation process and the ballistic limit (V₅₀) of the composite were also studied via numerical simulation, and the calculated damage patterns were correlated with the experimental results. The result indicated hard armor based on polybenzoxazine nanocomposites could completely protect the perforation of a 7.62 × 51 mm² projectile at impact velocity range of 847 ± 9.1 m/s. The results revealed the potential for using the poly(BA-a/PU) nanocomposites as energy-absorption panels for hard armor.

Tribological Performance and Thermal Stability of Nanorubber-Modified Polybenzoxazine Composites for Non-Asbestos Friction Materials

Asbestos-free friction composite based on ultrafine full-vulcanized acrylonitrile butadiene rubber particles (UFNBRPs)-modified polybenzoxazine was successfully developed. The UFNBRPs-modified polybenzoxazine friction composite was characterized for chemical, tribological, and mechanical properties as well as thermal stability. The UFNBRPs not only act as a filler to reduce noise in the friction composites due to their suitable viscoelastic behaviors but also play a key role in friction modifiers to enhance friction coefficient and wear resistance in the polybenzoxazine composites. The chemical bonding formation between UFNBRPs and polybenzoxazine can significantly improve friction, mechanical, and thermal properties of the friction composite. The outstanding tribological performance of the friction composite under 100–350 °C, i.e., friction coefficients and wear rates in a range of 0.36–0.43 and 0.13 × 10⁻⁴–0.29 × 10⁻⁴ mm³/Nm, respectively, was achieved. The high flexural strength and modulus of the friction composite, i.e., 61 MPa and 6.4 GPa, respectively, were obtained. The friction composite also showed high thermal stability, such as 410 °C for degradation temperature and 215 °C for glass transition temperature. The results indicated that the obtained UFNBRPs-modified polybenzoxazine friction composite meets the industrial standard of brake linings and pads for automobiles; therefore, the UFNBRPs-modified polybenzoxazine friction composite can effectively be used as a replacement for asbestos-based friction materials.

Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers

Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.

Design of low dielectric constant polybenzoxazine nanocomposite using mesoporous mullite

In this present work, porous mullites (PM0–5) were synthesized through a template-assisted method using various weight percentages of pluronic (P-123). PM5 obtained using 10 wt% of P-123 was found to show maximum porosity (3.8 Å) and low dielectric constant value (2.4). PM5 was functionalized using glycidyl-terminated silane and denoted as FPM and various weight percentages of FPM were reinforced with polybenzoxazine (PBZ) matrix in order to develop FPM/PBZ nanocomposites. The thermal studies indicate that 1.5 wt% of FPM/PBZ nanocomposite showed improved thermal stability with 34% char yield at 800°C and 162°C as glass transition temperature. It also exhibits low dielectric constant (2.6) than that of the neat PBZ matrix and other FPM/PBZ nanocomposites. The microscopic analysis confirms the homogenous dispersion of FPM into the PBZ polymer that has a porous morphology. The results suggest that the as-synthesized mesoporous mullite with low dielectric constant ( k), synthesized via template-assisted method can be used as a reinforcement to decrease the dielectric constant of polymeric material, which is of industrial significance.

Enhanced thermal stability and flame retardancy of polyurethane foam composites with polybenzoxazine modified ammonium polyphosphates

The influence of polybenzoxazine modified ammonium polyphosphate (BMAPP) on the thermal behavior and flame retardancy of a rigid polyurethane foam (PU) are investigated using various techniques.

Studies on graphene oxide–reinforced polybenzoxazine nanocomposites

In the present work, different weight percentages (1, 3, and 5 wt%) of benzoxazine-functionalized graphene oxide (FGO) were reinforced with polybenzoxazine (PBZ) matrix by means of ring-opening polymerization. The resulting nanocomposites were characterized for their thermal, mechanical, dielectric, and optical properties using different analytical techniques. From the results of these studies, it was observed that the 5 wt% FGO-reinforced PBZ composite shows an improved glass transition temperature, thermal stability, and dielectric constant to the extent of 18%, 39%, and 197%, respectively, when compared with those of neat PBZ matrix. Furthermore, 5 wt% FGO-reinforced PBZ composite also exhibits an enhanced ultraviolet shielding efficiency (88%), with improved tensile strength (52%) compared with those of neat PBZ matrix. The enhanced properties may be due to homogeneous and uniform distribution of FGO into the PBZ matrix, which was confirmed from scanning electron microscopic and high-resolution transmission electron microscopic images. Data obtained from these studies indicate that the developed nanocomposites with high dielectric constant can be used in the form of coatings, sealants, and encapsulates for high-performance dielectric as well as antistatic applications.

Copolymers of vinyl-containing benzoxazine with vinyl monomers as precursors for high performance thermosets

A benzoxazine containing a vinyl group (P-4va) was prepared by the reaction of phenol, 4-vinylaniline, and paraformaldehyde. A differential scanning calorimetry (DSC) study revealed that ring-opening polymerization of the benzoxazine and chain polymerization of the vinyl group occurred in the same temperature range. When 2,2'-azobisisobutyronitrile was added as a radical initiator to P-4va, however, only the vinyl groups were polymerized at lower temperature, giving oligo(P-4va) that contains pendent benzoxazine units. Radical copolymerization of P-4va with various vinyl monomers such as styrene, methyl methacrylate (MMA), and n-butyl acrylate (BuA) was examined. The chemical structure of the copolymers was confirmed by FT-IR and ¹H-NMR to be one of polyolefins bearing benzoxazine units as the pendant groups. The weight-average molecular weights of the copolymers determined by size exclusion chromatography were to be in the range of 1900–51,500 depending on the comonomers. DSC of the copolymers showed that the maxima of the exothermic peaks corresponding to the ring-opening polymerization of the pendent benzoxazine units were observed in the temperature range of 229–250 °C. Thermal cure up to 240 °C of the copolymer films afforded homogenous transparent films with improved thermal properties. Tough cured film was obtained by the copolymerization with MMA, while a tough and flexible film was obtained by the copolymerization with BuA.

Copolymers based on telechelic benzoxazine with a reactive main-chain and anhydride: monomer and polymer synthesis, and thermal and mechanical properties of carbon fiber composites

Enhanced thermomechanical properties of polybenzoxazine based on allylamine-terminated oligomeric benzoxazine (Allyl-oligomer) are obtained by copolymerizing the oligomer with maleic anhydride (MA) in the presence of a free radical initiator.

Polymer alloys of high-molecular-weight benzoxazine and epoxy resin

Novel polymer alloys were prepared by curing the mixture of a high-molecular-weight benzoxazine (B-oda) that was synthesized from 4,4′-oxydianiline (oda), bisphenol-A, and formaldehyde and a typical epoxy resin prepolymer, epoxy-terminated copolymer of bisphenol-A and epichlorohydrin, up to 240°C. It was confirmed by differential scanning calorimetric and infrared (IR) investigations that the novel alloys had ether linkages that was formed by the reaction between the phenolic hydroxyl groups formed from the thermal ring-opening polymerization of B-oda and the epoxy groups of the epoxy resin. The properties of the alloy films were compared with polybenzoxazine (PB-oda), the pristine polybenzoxazine obtained by curing B-oda without the epoxy resin. The alloy films were more flexible and were found to have higher glass transition temperatures ( Tgs) from the dynamic mechanical analyses. From the IR analyses of the films, the polymer alloys were found to have higher amount of intermolecular hydrogen bonding compared with the pristine PB-oda. It was suggested that this increase of the hydrogen bonding was the cause of the higher Tgs of the polymer alloys.

Preparation and properties of polymer alloys consisting of high-molecular-weight benzoxazine and bismaleimide

Novel polymer alloys were prepared by blending a high-molecular-weight benzoxazine (HMWB) and a typical bismaleimide (4,4′-bismaleimidodiphenyl methane (BMI)) followed by thermal treatment up to 240°C. It was confirmed by the infrared and differential scanning calorimetric analyses that the phenolic hydroxyl group formed by the ring-opening polymerization of HMWB reacted with the double bond of BMI, in addition to the chain polymerization of the double bond of BMI and the ring-opening polymerization of HMWB. This further cross-linking through the formation of ether linkage made the polymer alloy films much more tough and flexible than each homopolymer film. Moreover, viscoelastic analyses and thermogravimetric analyses of the polymer alloy films showed that glass transition temperature and thermal stability also increased by alloying.

Studies on Thermal and Mechanical Properties of Polybenzoxazine Modified with Succinic Acid

Polybenzoxazine (PBA-a), a novel type of phenolic resin, possesses many outstanding properties, i.e. good mechanical strength, electrical insulation, dimensional stability, resistance against many types of solvents, flame retardation, and low smoke emission from burning. However, shortcoming of this material is from its brittleness. In this study, the rigidity of polybenzoxazine was improved by adding succinic acid (SA) as plasticizer. The content of SA was varied from 0 to 50 phr. The thermal properties were determined by Differential Scanning Calorimeter (DSC) and Thermogravimetric Analyzer (TGA), while the mechanical properties were analysed by Universal Testing Machine (UTM) and Microhardness tester. In addition, the results that the glass transition temperature (Tg) of PBA-a was decreased with increasing the amount of SA, i.e. decreasing from 168°C (0 phr) to 121°C (50 phr). Furthermore, the degradation temperature at 5 % weight loss (Td5%) was decreased from 328°C (0 phr) to 240°C (50 phr). It could be noticed that the char yield of the polymer at 800°C had no significant change (in the range of 30-33%) when SA was added. The polybenzoxazine exhibited softening decreased of hardness from 39.8 MPa (at 0 phr) to 9.62 MPA (at 50 phr).