Resin transfer molding (RTM) has the potential to manufacture high quality, geometrically complex composite parts. Benzoxazine is a new kind of high performance composite matrix. It can be polymerized with a ring-opening reaction without releasing volatiles. In this article, a novel RTM resin made from aromatic diamine, phenol and formaldehyde is reported. The viscosity and curing behavior of the RTM resin as well as the properties of the cured neat resin and fiber reinforced composite were investigated. The resin has a viscosity lower than 0.5 Pa ⅐ s after 4 hr at 100°C, and can be cured at 180°C. The tensile strength, modulus, and elongation of the cast resin are 94 MPa, 4.6 GPa, and 2.2%, respectively. The flexural strength and modulus of the cast resin are 160 MPa and 4.9 GPa. The flexural strength and modulus of its glass fiber laminate are 662 MPa and 30 GPa. It is very easy to control the viscosity and curing rate of the RTM resin through the addition of reactive dilute agents and catalysts according to the requirement of RTM processing. POLYM. COMPOS., 26:563-571, 2005.
A ternary blend (BEM) of benzoxazine (BA-a), epoxy resin (E44), and imidazole (M) was prepared to study the effect of different curing cycles on curing reactions and properties of cured resins. Reactivity of two binary blends, E44 and BA-a, with the catalyst M, was first investigated based on the curing kinetics. Results suggest that E44/M has lower reaction activation energy than BAa/M meaning the reaction of E44/M easily proceeds. To further figure out the sequences of the curing reactions of E44, BA-a, and M in BEM, the curing behaviors of three BEM gels at 80, 140, and 180 C (defined as BEM-80g, BEM-140g, and BEM-180g) were studied by DSC and FTIR techniques. For BEM-80g, E44/M cured before BA-a/M. For BEM-180g, both curing reactions occurred simultaneously and the copolymerization of BA-a and E44 was promoted. The crosslinked structures of cured BEM with different initial curing temperatures were strongly influenced by the reaction sequences. The T g s, flexural properties and thermal stability of the copolymers with different curing cycles were compared. Good performance of this ternary system can be obtained by choosing suitable curing cycles.
ABSTRACT:The matrix polymer of reactive hot-melt adhesive (RHMA) is an isocyanate-terminated urethane prepolymer based on oligoester or oligoether diols and diisocyanates. In this study, we explored wet cure kinetics with both isothermal and nonisothermal differential scanning calorimetry methods. Second-order autocatalytic models were successfully used to evaluate the cure process of both oligoester-and oligoether-based RHMAs. The autocatalyzation effect did not to depend on the structure of diols but on the reaction nature of the end isocyanates. The apparent energy of the overall cure reaction was 86.54 and 84.46 kJ/mol, respectively, which was based on nonisothermal DSC results.
Thermoresponsive
membranes with nanoscale pores were successfully
fabricated. The membranes were composed of a poly(ethylene glycol
methyl ether methacrylate)-b-polystyrene-b-poly(ethylene glycol methyl ether methacrylate) (PMENMA-b-PS-b-PMENMA) mesoporous size-selective layer attached to a polyvinylidene
fluoride (PVDF) macroporous supporting layer. Mesopores were introduced
into the hydrophilic PMENMA domains by controlled
selective swelling with methanol and supercritical CO2.
Because selective swelling with methanol occurs only in the hydrophilic
PMENMA block domains, the mesopore interiors are
covered with PMENMA brushes. PMENMA has a lower critical solution temperature (LCSTs) in water that
depends on the number of ethylene glycol units in the oligo(ethylene
glycol) side chain (N), thus providing a means of
tuning the thermoresponsivity. Water permeability experiments showed
that a higher flux of water passes through the membranes at temperatures
greater than the LCST, suggesting that the pore sizes are temperature
controllable. Also, with increasing N, the response
temperature increased. The thermo-dependent size selectivity of the
membranes was also investigated, and the results show that the membranes
have very small pore sizes, about 5 nm, and a strong size-discriminating
property. The temperature dependent changes of water flux and particles
permeation all demonstrate the thermoresponsivity of the membranes;
however, the open-close transition of the pores was not sudden at
the LCSTs but instead occurred gradually over a broad temperature
range.
To improve the processability and toughness of bisbenzoxazine, a series of cardanol-based aromatic diamine benzoxazine (BZ-Xc) monomers were synthesized from cardanol, formaldehyde aqueous solution and aromatic diamines with different bridging groups such as -CH 2 -, -O-and -SO 2 -. The curing behavior, viscosity, thermal and mechanical properties of 4,4′-diaminodiphenylmethane (DDM)-based bisbenzoxazine (BM) and BZ-Xc copolymers were studied systematically. The results demonstrate that the plasticizing effect and flexibility of the alkyl side chain on BZ-Xc significantly reduced the melting viscosity of BM/BZ-Xc blends and improved the toughness of the copolymers. At the same time, the heat-resistant and mechanical properties of the copolymers were retained, because of the bifunctional structure of BZ-Xc. Moreover, the melting viscosity, glass transition temperature and curing temperature of the corresponding copolymers were increased as the result of rigidity and electron-withdrawing effects of the -SO 2 -bridging group compared to others.
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