Novel phosphorus-modified polysulfone as a combined flame retardant and toughness modifier for epoxy resins

This study demonstrated that fluorine functionalized carbon nanotubes (f-CNTs) can be used to reinforce in the midplane of a fiber reinforced epoxy composite laminate for increasing the interlaminar shear fracture toughness. A spraying methodology was used to deposit the f-CNTs on the midplane carbon fabric to produce this through-thickness interlaminar reinforcement. The four-point end notch flexure (4ENF) specimen was used in the experiments to calculate the critical strain energy release rate, GIIc, to quantify a value for fracture toughness. Compared to the neat case (0.0 wt% CNTs) there was a 23% increase in the average initiation and 27% increase in the average propagation GIIc with only 0.5 wt% f-CNTs dispersed on the fabric and in the resin of the midplane region. High resolution microscopic examinations of the specimen fracture surfaces suggest that the functionalized carbon nanotubes are covalent bonding nanoscale tethers between the fibers and the epoxy resin, resulting in toughened fiber–matrix interfacial strengths to achieve these improved through-thickness mechanical properties for this nanocomposite laminate system. This nanotube technology could displace the need for using cross-fabric stitching or pinning, or using thickening interleaf layers at the midplane region of laminates in order to improve the interlaminar shear fracture toughness.

An experimental study of interlaminar shear fracture toughness of a nanotube reinforced composite

Soybean oil-based composites are prepared by the solid freeforming fabrication (SFF) method. Epoxidized soybean oil is solidified with a gelling agent, and composites are formed by fiber reinforcement. Glass, carbon, and mineral fibers are used in the formulations. The type of fiber and degree of fiber alignments affect the properties of the composites. In addition, the effects of curing agents, curing temperature, fiber combination, and fiber loading on mechanical properties of composites and dynamic analysis are studied and reported.

https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=4343&content=PDF

Development of soybean oil‐based composites by solid freeform fabrication method: Epoxidized soybean oil with bis or polyalkyleneamine curing agents system

Nonisothermal reaction, thermal stability and dynamic mechanical properties of epoxy system with novel nonlinear multifunctional polyamine hardener

Extrusion freeform fabrication has been used to make bars of fiber-reinforced epoxidized soybean oil (ESO)/epoxy resin. Freeform fabrication methods build materials by the repetitive addition of thin layers. The mixture of epoxidized soybean oil (ESO) and epoxy resin are modified with a gelling agent to solidify the materials until curing occurs. The high strength and stiffness composites are formed through fiber reinforcement. Glass, carbon and mineral fibers are used in the formulations. It is shown that the fiber orientation follows the direction of motion of the write head that deposits the resins and has a large influence on the properties of the composite. In addition, the effects of curing agents, curing temperature, epoxy/ESO ratio, and fiber loading on mechanical properties of composites are studied and reported.

Solid freeform fabrication of epoxidized soybean oil/epoxy composite with bis or polyalkyleneamine curing agents

The curing of triglycidyl para-aminophenol (TGPAP) epoxy resin with three aromatic amine hardeners, diaminodiphenye sulphone (DDS), pyridinediamine (PDA), and toluenediamine (TDA), has been investigated. A series of isothermal cures was conducted and analyzed by Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC). The chemical reactions occurring during cure were monitored at different temperatures by qualitative and quantitative estimation of different groups in the IR spectra, and the ratio of rate constants (k2/k1) were evaluated. Dynamic DSC analysis of TGPAP/TDA resulted in two exothermal peaks, indicating cure kinetics different from those of TGPAP/DDS and TGPAP/PDA systems, which gave a single exothermal peak. Various kinetic parameters such as total heat of reaction ?H?, activation energy Ea, Frequency factor z, and order of reaction n were evaluated for all the three systems. From the initial kick-off temperatures and activation energy values it was concluded that the rate of curing followed the order TDA amp;gt; PDA amp;gt; DDS. The reaction conversions during cure, evaluated from IR analysis, were exactly the same as those obtained from DSC Borchardt-Daniels kinetics. Using this model, the plots of time vs. temperature for different conversions were constructed for all the three systems; on the basis of these, the cure cycles can be fixed.

/pdf/cure-characterization-of-triglycidyl-epoxy-aromatic-amine-4cwre2ouch.pdf

Cure characterization of triglycidyl epoxy/aromatic amine systems

Three multifunctional epoxy resins novolac epoxy (EPN), triglycidyl paraaminophenol (TGPAP), and tetraglycidyl diaminodiphenylmethane (TGDDM) were modified with a carboxy-terminated acrylate-based liquid elastomer (PnBA). The effect of prereaction of the epoxy groups in the resin and carboxyl group in the elastomer on curing parameters, such as the cure reaction conversions; processing parameters, such as gel times and verification times; initial cure temperatures, and activation energy values were evaluated. Fourier transform infrared spectrometry (FTIR), dynamic mechanical spectrometry (DMS), and differential scanning calorimetry (DSC) were used for the study. The results indicated that while the cure reactions were slightly retarded in the presence of elastomer, they were slightly accelerated when certain prereaction catalysts were used. The gel times and vitrification times decreased due to the prereaction. The physical properties such as fracture toughness and modulus of neat resin castings and flexural strength properties of carbon cloth-reinforced laminates were evaluated. Results indicated that the toughness property increased and the modulus decreased with elastomer addition.

A. Padma

Papers

Cure characterization of triglycidyl epoxy/aromatic amine systems

Effect of prereaction on curing of elastomer‐modified epoxy resins