High performance wood composites from highly filled polybenzoxazine

Highly filled systems prepared by compression molding of Hevea brasiliensis woodflour filled polybenzoxazine composites with high mechanical properties and reduced water uptake has been developed. The effects of percent filler content and particle size of woodflour on the obtained composite's properties were examined. The low melt viscosity of BA‐a type polybenzoxazine allows substantial amount of woodflour to be easily incorporated into the composites. The results showed that mechanical properties from dynamic mechanical analysis and flexural test at filler content below the optimum filler packing show approximately linear relationship with filler loading. The outstanding compatibility between the woodflour and the polybenzoxazine matrix is evidently seen from the large improvement in the composite's T_g and char yield. Scanning electron micrographs of the composite also reveals substantially strong interface between the woodflour filler and the polybenzoxazine matrix. Water absorption of the composites is greatly reduced with increasing the amount of polybenzoxazine due to the inherent low water absorption of the matrix. The polybenzoxazine is; therefore, a highly attractive candidate as high performance lignocellulosic binder or adhesive and other related applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1240–1253, 2006     

Organic Heat Stabilizers for Polyvinyl Chloride (PVC): A Synergistic Behavior of Eugenol and Uracil Derivative

Recycling ability, mechanical, and thermal properties of PVC stabilized with organic heat stabilizers, i.e., uracil (DAU) and eugenol were investigated to substitute PVCs stabilized with commercial lead, Ca/Zn, and organic-based stabilizer for PVC pipe production. PVC stabilized with the DAU and the eugenol can be processable at 30 °C lower than that of the PVC stabilized with commercial heat stabilizers. The most remarkable short-term thermal stability belonged to the PVC stabilized with the DAU, and its original color can be maintained at least up to 3 processing cycles. Synergistic behavior in thermal stability of the PVC mixed with DAU and eugenol at mass ratios of 1.5:1.5 was observed. Mechanical properties of DAU- and eugenol-stabilized PVC were higher than the samples with other heat stabilizers. Glass transition temperature of the PVC stabilized with all heat stabilizers was determined to be 99 °C with the exception of the value of 89 °C for eugenol-stabilized PVC. Therefore, the DAU and the eugenol showed high potential to be used as an organic heat stabilizer for PVC because of their non-toxic and good heat resistance properties.     

Effect of triphenyl phosphate flame retardant on properties of arylamine‐based polybenzoxazines

Three types of arylamine‐based benzoxazine resins modified with both condensed‐phase and gas‐phase action flame retardant, i.e. triphenyl phosphate (TPP) at various weight ratios were investigated. From rheological study, it was found that the viscosity of benzoxazines/TPP mixtures were significantly lower than that of the neat benzoxazine monomers suggesting flow property enhancement. Furthermore, differential scanning calorimetry results revealed that the onset and the maximum temperatures of the exothermic peak, due to the ring opening polymerization of benzoxazine resins, shifted to lower temperatures with increasing TPP. In addition, all polybenzoxazines possessed relatively high char yield, which increased as the TPP content increased thus enhancing their flame retardancy. The limiting oxygen index values of the flame retarded polybenzoxazines also increased with TPP addition. The maximum flame retardancy of UL94 V‐0 class was obtained with an addition of only few percents of TPP in the polybenzoxazines. Flexural strength, flexural modulus, and glass transition temperature of those polybenzoxazines tended to decrease with an addition of TPP mainly due to its plasticizing effect. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1074‐1083, 2013     

Polybenzoxazine alloys and blends: Some unique properties and applications

Polybenzoxazine (PBZ), a novel class of high performance thermosetting phenolic resin, has been developed in order to overcome many shortcomings of conventional phenolic materials from either novolac or resole type resins. The paper first provides the overview of this high temperature material including main types, chemical structure of each type, and properties of the polymer, especially the synergistic behavior in thermal properties. It then describes the manufacturing technique to produce the monomeric resin as well as some applications of the polymer.     

Dielectric and thermal behaviors of fluorine‐containing dianhydride‐modified polybenzoxazine: A molecular design flexibility

Fluorine‐containing copolybenzoxazines were successfully prepared by reacting bisphenol‐AF/aniline‐based benzoxazine resin (BAF‐a) with 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) in N,N‐dimethylacetamide solvent. The dielectric and thermal properties as well as flexibility of the resulting copolymer films were investigated. The incorporation of fluorine groups into polybenzoxazine was found to substantially decrease the dielectric constant of the resulting copolybenzoxazine to as low as 2.6. The formation of ester linkages between the hydroxyl groups in the poly(BAF‐a) and the carbonyl groups in the 6FDA resulted in substantially enhanced flexibility of the copolybenzoxazines. Moreover, the copolymers showed superior degradation temperature and significant improvement in char yield, up to 464 °C and 56%, respectively. The glass‐transition temperature of the copolybenzoxazines was increased with increasing dianhydride content and exhibited a maximum value of 290 °C at 2.5/1 mole ratio of poly(BAF‐a) to 6FDA. Therefore, the fluorine‐containing dianhydride‐modified polybenzoxazines are appropriate for applications as polymeric films for coatings and as a good electrical insulation material with high thermal resistance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45204.     

Highly processable ternary systems based on benzoxazine,epoxy, and phenolic resins for carbon fiber composite processing

Effects of resin compositions in ternary systems of benzoxazine, epoxy, and phenolic novolac resins on processability, and thermomechanical properties of their carbon fiber‐reinforced composites are investigated. At suitable range of resin mass ratios, the ternary mixtures can provide a relatively wide processing window ranging from 50 to 200°C by maintaining their low A‐stage viscosity for a relatively long time which is crucial in the fiber preimpregnating process. Furthermore, relatively long shelf‐life of the ternary mixtures stored at room temperature (～ 30°C) up to 270 days is obtained with minimal effect on their processability. The optimum mass ratio of B : E : P was determined to be 3 : 6 : 2, i.e., BEP362 resin. Finally, the carbon fiber composite based on BEP362 was found to exhibit substantial enhancement in its mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of novel benzoxazine reactive diluent on processability and thermomechanical characteristics of bi‐functional polybenzoxazine

Effects of a monofunctional benzoxazine diluent (Ph‐a) on properties of a bifunctional benzoxazine resin (BA‐a) have been investigated. The BA‐a/Ph‐a mixtures are miscible in nature rendering the properties highly dependent on their compositions. The viscosity of the BA‐a resin can be reduced to one third using only about 10% by weight the Ph‐a diluent. The addition of the Ph‐a resin into the BA‐a resin can also lower the liquefying temperature of the resin mixtures whereas the gel point is marginally decreased. The gel point, which depends on the BA‐a/Ph‐a mixtures and the cure temperature, was determined by the frequency independence of loss tangent in the vicinity of the sol‐gel transition. The relaxation exponent values of the copolymer were found to be 0.24–0.55, which is dependent on the cure temperature. Gel time of the BA‐a/Ph‐a systems decreases with increasing temperature according to an Arrhenius relation with activation energy of 60.6 ± 1.5 kJ/mol. Flexural moduli of the BA‐a/Ph‐a polymers also increase with the Ph‐a mass fraction, however, with the sacrifice of their flexural strength and glass‐transition temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Flammability and thermomechanical properties of dianhydride‐modified polybenzoxazine composites reinforced with carbon fiber

Composites based on carbon fiber (CF) and benzoxazine (BA‐a) modified with PMDA were investigated. The flammability of the carbon fiber composites was examined by limiting oxygen index (LOI) and UL‐94 vertical tests. The LOI values increased from 26.0 for the CF/poly(BA‐a) composite to 49.5 for the CF‐reinforced BA‐a/PMDA composites as thin as 1.0 mm and the CF‐reinforced BA‐a/PMDA composites were also achieved the maximum V‐0 fire resistant classification. Moreover, the incorporation of the PMDA into poly(BA‐a) matrix significantly enhanced the T_g and the storage modulus (E') values of the CF‐reinforced BA‐a/PMDA composites rather than those of the CF/poly(BA‐a). The T_g values and storage moduli of the obtained CF‐reinforced BA‐a/PMDA composites were found to have relatively high value up to 237°C and 46 GPa, respectively. The CF‐reinforced BA‐a/PMDA composites exhibited relatively high degradation temperature up to 498°C and substantial enhancement in char yield with a value of up to 82%, which are somewhat higher compared to those of the CF/poly(BA‐a) composite, i.e., 405°C and 75.7%, respectively. Therefore, due to the improvement in flame retardant, mechanical and thermal properties, the obtained CF‐reinforced BA‐a/PMDA composites exhibited high potential applications in advanced composite materials that required mechanical integrity and self‐extinguishing property. POLYM. COMPOS., 34:2067–2075, 2013. © 2013 Society of Plastics Engineers     

Thermal and mechanical properties enhancement obtained in highly filled alumina‐polybenzoxazine composites

Highly filled polymer composites based on bisphenol‐A/aniline based polybenzoxazine (PBA‐a) and alumina particles were investigated. A very low A‐stage viscosity of benzoxazine monomer gives it excellent processability exhibiting maximum alumina content as high as 83% by weight (60% by volume) which is one of the highest maximum packing values with negligible void contents. The storage modulus (E′) at room temperature was increased from 5.93 GPa of the polybenzoxazine to 45.27 GPa of the composites. The significant high microhardness of the composites up to 1124 MPa was obtained and the behavior can be well predicted by the Halpin‐Tsai model. Moreover, the modulus dependence of the composites on the alumina contents is well fitted by Lewis‐Nielsen equation. Glass transition temperatures, degradation temperature, and solid residue of the composites also significantly increased with increasing the alumina contents. Finally, the scanning electron microscope of the composite fracture surface indicated a good distribution of the alumina particles in the PBA‐a matrix. The resulting PBA‐a/alumina composites are a highly attractive for an application that requires high modulus and hardness as well as high thermal stability. POLYM. COMPOS., 35:2269–2279, 2014. © 2014 Society of Plastics Engineers     

Thermomechanical characteristics of benzoxazine–urethane copolymers and their carbon fiber‐reinforced composites

Copolymers of polybenzoxazine (BA‐a) and urethane elastomer (PU) with three different structures of isocyanates [i.e., toluene diisocyanate (TDI), diphenylmethane diisocyanate, and isophorone diisocyanate], were examined. The experimental results reveal that the enhancement in glass transition temperature (T_g) of BA‐a/PU copolymers was clearly observed [i.e., T_g of the BA‐a/PU copolymers in 60 : 40 BA‐a : PU system for all isocyanate types (T_g beyond 230°C) was higher than those of the parent resins (165°C for BA‐a and ?70°C for PU)]. It was reported that the degradation temperature increased from 321°C to about 330°C with increasing urethane content. Furthermore, the flexural strength synergism was found at the BA‐a : PU ratio of 90 : 10 for all types of isocyanates. The effect of urethane prepolymer based on TDI rendered the highest T_g, flexural modulus, and flexural strength of the copolymers among the three isocyanates used. The preferable isocyanate of the binary systems for making high processable carbon fiber composites was based on TDI. The flexural strength of the carbon fiber‐reinforced BA‐a : PU based on TDI at 80 wt % of the fiber in cross‐ply orientation provided relatively high values of about 490 MPa. The flexural modulus slightly decreased from 51 GPa for polybenzoxazine to 48 GPa in the 60 : 40 BA‐a : PU system. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009