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     

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     

Physico-mechanical properties and automotive fuel resistance of EPDM/ENR blends containing hybrid fillers

This research aimed to investigate the effect of blend ratios on cure characteristics, mechanical and dynamic properties, morphology and automotive fuel resistance of ethylene-propylene diene rubber (EPDM) and epoxidized natural rubber (ENR) blends containing carbon black and calcium carbonate hybrid filler. The composition of EPDM/ENR blends varied were 100/0, 70/30, 50/50, 30/70 and 0/100 %wt/wt. All ingredients used for preparing each blended compound, except for the curatives, were mixed in a kneader. Thereafter, the compound was further mixed with curatives on a two-roll mill and then were vulcanized together with shaped by compression molding before determining cure characteristics, mechanical properties, morphology and weight swelling ratio in three automotive fuels; gasohol-91, diesel and engine oils. The results indicated that Mooney viscosity and cure time of EPDM/ENR blends tended to decrease with increasing ENR content, while cure rate index and crosslink density increased. Tensile strength of all EPDM/ENR blends is lower than that of the individual EPDM and ENR. This is attributed to the incompatibility between nonpolar and polar nature of EPDM and ENR, respectively, supporting by the glass transition temperature form dynamic mechanical thermal analysis (DMTA) and scanning electron micrographs (SEM). Owing to the differences in polarity of automotive fuels and rubbers, weight swelling of EPDM/ENR vulcanizates decreased in diesel and engine oils, but increased in gasohol-91 with increasing in ENR content.     

Highly filled graphene‐benzoxazine composites as bipolar plates in fuel cell applications

This research emphasizes on the development of highly filled graphene‐polybenzoxazine composites and investigates thermal, electrical, and mechanical properties of the obtained composites for bipolar plate applications. The composition of graphene loading was achieved to be in the range of 10–60 wt%. The experimental results revealed that at the maximum graphene content of 60 wt% (44.8 vol%) in the polybenzoxazine, storage moduli at room temperature of the composites were considerably enhanced with the amount of the graphene, that is, from 5.9 GPa of the neat polybenzoxazine to about 25.1 GPa at 60 wt% of graphene. Glass transition temperatures (T_g) of the obtained composites were observed to be 174–188°C and the values substantially increased with increasing the filler contents. At 60 wt% of graphene content, thermal conductivity, as high as 8.0 W/mK, is achieved for the graphene‐filled polybenzoxazine. Furthermore, the flexural modulus and flexural strength of the composites were found to be as high as 18 GPa and 42 MPa, respectively. Water absorption of graphene filled‐composite is relatively low with the value of only about 0.06% at 24 h of water immersion. Additionally, electrical conductivity was measured to be 357 S/cm at maximum loading of the graphene. Therefore, the graphene‐filled composites based on polybenzoxazine are highly attractive as bipolar plates for polymer electrolyte membrane fuel cells applications. POLYM. COMPOS., 37:1715–1727, 2016. © 2014 Society of Plastics Engineers     

Mechanical,thermal, and water uptake characteristics of woodflour‐filled polyvinyl chloride/acrylonitrile butadiene styrene blends

Woodflour‐filled composites based on polymeric blends of polyvinyl chloride (PVC) and super high‐impact grade ABS were developed. Mechanical, thermal, and water uptake characteristics of the PVC/ABS matrix and their wood composites were evaluated. In the case of PVC/ABS matrix, the blend at a mass ratio of 50/50 rendered the impact strength with a very high value of up to 65 kJ/m², noticeably higher than those of the parent resins, that is, 6 kJ/m² of PVC and 35 kJ/m² of ABS. Dynamic mechanical analysis thermograms showed two distinct glass transition temperatures (T_gs) that shifted toward each other indicating partial miscibility of the blends. Water absorption of the blends after 24 h immersion was low, that is, within the range of 0.04–0.2 wt % and exhibits a behavior closed to pseudo‐Fickian type. The obtained PVC/ABS wood composites exhibited an increase of flexural modulus as well as T_gs with an increase of woodflour content. Finally, impact strength of the PVC/ABS composites was significantly higher than those of PVC composites or polyethylene composites comparing at the same woodflour content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Chemorheology and thermomechanical characteristics of benzoxazine‐urethane copolymers

In this research, processability and some important thermomechanical properties of polybenzoxazine (BA‐a) modified with a highly flexible urethane elastomer (PU) are discussed. This copolymer has been reported to show synergy in its glass transition temperature and some mechanical properties thus provides a fascinating group of high temperature polymers with enhanced flexibility. The results reveal that a processing window of the BA‐a/PU mixtures is widened with the increasing urethane prepolymer fraction, that is, the liquefying temperature is lowered and the gel point shifted to higher temperature with the amount of the PU. Synergism in glass transition temperature (T_g) of this copolymer was clearly confirmed, i.e., T_g's of the BA‐a/PU alloys were significantly greater than those of the parent resins, i.e., BA‐a (T_g = 166°C) and PU (T_g = ? 70°C). In addition, flexural modulus was found to systemically decrease from 5.4 GPa of the neat polybenzoxazine to 2.1 GPa at 40% by weight of the PU. Flexural strength of the alloys also shows a synergistic behavior at the BA‐a/PU ratio of 90/10. Coefficient of thermal expansion of the polymer alloys were also found to show a minimum value at BA‐a/PU = 90/10. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of SiC whisker on benzoxazine‐epoxy‐phenolic ternary systems: Microwave curing and thermomechanical characteristics

Microwave radiation at 2.45 GHz with variable power input was investigated as a tool to facilitate the curing reaction of benzoxazine‐epoxy‐phenolic molding compound i.e., BEP893. Dielectric filler for microwave coupling was silicon carbide whisker (SiC_w). Factors such as whisker loading and input irradiation power were found to have a profound effect on the microwave heating of the BEP893 particularly on the rate of temperature rise and maximum heating temperature. The SiC_w loading of 10% by weight with the microwave irradiation condition of 300 W for 10 min renders the ultimate curing of the molding compound. Significant reduction in processing time of the microwave cured sample compared with the conventional heat cured sample i.e., 150 min at 200°C using conventional heating is the key benefit of this technique. Mechanical properties of the microwave cured and conventional heat cured samples show similar characteristics with slightly lower T_g in the microwave cured samples. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and characterization of anatase photocatalyst powder from sodium titanate compounds

The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO₂:Na₂CO₃ at 850 °C. Then, the powder was dissolved in 5 M H₂SO₄ solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m²/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO₂:Na₂CO₃ and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation.     

Influence of talc particle size and content on crystallization behavior,mechanical properties and morphology of poly(lactic acid)

This research aimed to employ inorganic filler such as talc to promote crystallization in poly(lactic acid) (PLA). Three different talc particle sizes, namely 1, 5 and 30 µm, were used as nucleating agents; each was compounded with PLA at various contents from 0 to 10 wt%. The crystallization temperature (T _c) reduced most rapidly from 128 to 107 °C with the presence of 1 wt% talc. Beyond this concentration, the T _c still decreased but only minutely. Compared to other sizes, finer talc particles were found to promote a slightly higher degree of crystallinity. X-ray diffraction peaks indicated that the α-crystal was formed in all PLA/talc compositions. The heat distortion temperature values suggested that the modified PLA could resist the thermal deformation from 58 °C to a maximum value of 139 °C when 1 µm talc was added at 10 wt%. With the presence of talc, the composites were more brittle and both tensile elongation at break and impact strength were decreased.