Curing of an epoxy resin modified with poly(methylmethacrylate) monitored by simultaneous dielectric/near infrared spectroscopies

Usability of dielectric properties for evaluation and research of deconsolidation of endless fiber-reinforced thermoplastics

Understanding the deconsolidation behavior of endless fiber-reinforced thermoplastics is essential for reliable predictions of parts behavior and advancements in the corresponding processing technologies. Deconsolidation is usually described by an increasing void ratio of the part volume arising due to fiber relaxation effects, which can strongly affect the mechanical performance. Most methods for measuring the degree of deconsolidation are destructive and require long testing or preparation times. As the dielectric permittivity of a material is usually proportional to its porosity, often reported in foam-related research, dielectric measurements are evaluated as a nondestructive alternative to identify the degree of deconsolidation of endless fiber-reinforced thermoplastics. Polypropylene and glass-woven–based organo-sheets are deconsolidated and density measurements are compared with dielectric measurements for their effect strength and measurement deviations. A relative permittivity in the range of 5–20 MHz was found to allow for a proper differentiation of different degrees of deconsolidation with a ratio of measurement deviation to sample deviation of 26.31% for a single-layer composite (42.96% for a four-layer composite). Additional research is required to identify all relevant influences and to further qualify the method for the research of the deconsolidation behavior or quality control.

A synergistic effect of a ferrocenium salt on the diaryliodonium salt-induced visible-light curing of bisphenol-A epoxy resin

Diaryliodonium and ferrocenium salts undergo photo-electron transfer (PET) to initiate photopolymerizations under a halogen lamp.

Sensitivity of Dielectric Properties to Wear Process on Carbon Nanofiber/High-Density Polyethylene Composites

We examined the correlation of wear effects with dielectric properties of carbon nanofibers (CNFs; untreated and organosilane-treated)-reinforced high-density polyethylene (HDPE) composites. Wear testing for the nanocomposites over up to 120 h was carried out, and then, dielectric permittivity and dielectric loss factor of the polymer composites with the increased wear time were studied. Scanning electron microscope and optical microscope observations were made to analyze the microstructure features of the nanocomposites. The results reveal that there exist approximate linear relationships of permittivity with wear coefficient for the nanocomposites. Composites containing silanized CNFs with the sufficiently thick coating exhibited high wear resistance. The change in permittivity was more sensitive to the increased wear coefficient for the nanocomposites with lower wear resistance. This work provides potential for further research on the application of dielectric signals to detect the effects of wear process on lifetime of polymeric materials.

Study of the infrared spectral features of an epoxy curing mechanism

In this work, the isothermal curing process of diglycidyl ether of bisphenol A (DGEBA) cured with 4,4'-diaminodiphenylmethane (DDM) was monitored in situ by mid-infrared (MIR) and near-infrared (NIR) spectroscopy. With the help of generalized two-dimensional (2D) correlation analysis, the results obtained showed that, during curing, the change of amine and epoxy groups was simultaneous, taking place prior to the change of hydroxyl groups, followed by the change of CH(2)/CH groups, resulting from the ring-opening reaction of epoxy groups. In addition, 2D MIRxNIR hetero-spectral correlation analysis and second-derivative analysis were also employed, by means of which direct evidence of the curing mechanism could be obtained and obscure NIR band assignments in the overlapped CH combination region could be made.